Nano-Engineered Cementitious Composites: Principles and Practices [1st ed.] 978-981-13-7077-9;978-981-13-7078-6

Table of contents :
Front Matter ....Pages i-xxiv
Basic Principles of Nano-Engineered Cementitious Composites (Baoguo Han, Siqi Ding, Jialiang Wang, Jinping Ou)....Pages 1-96
Current Progress of Nano-Engineered Cementitious Composites (Baoguo Han, Siqi Ding, Jialiang Wang, Jinping Ou)....Pages 97-398
Carbon Nanotubes-Engineered Cementitious Composites (Baoguo Han, Siqi Ding, Jialiang Wang, Jinping Ou)....Pages 399-458
Graphene-Engineered Cementitious Composites (Baoguo Han, Siqi Ding, Jialiang Wang, Jinping Ou)....Pages 459-518
Nano-SiO2-Engineered Cementitious Composites (Baoguo Han, Siqi Ding, Jialiang Wang, Jinping Ou)....Pages 519-560
Nano-TiO2-Engineered Cementitious Composites (Baoguo Han, Siqi Ding, Jialiang Wang, Jinping Ou)....Pages 561-599
Nano-ZrO2-Engineered Cementitious Composites (Baoguo Han, Siqi Ding, Jialiang Wang, Jinping Ou)....Pages 601-637
Nano-BN-Engineered Cementitious Composites (Baoguo Han, Siqi Ding, Jialiang Wang, Jinping Ou)....Pages 639-664
Electrostatic Self-Assembled Carbon Nanotube/Nano-Carbon Black Fillers-Engineered Cementitious Composites (Baoguo Han, Siqi Ding, Jialiang Wang, Jinping Ou)....Pages 665-707
Future Developments and Challenges of Nano-Engineered Cementitious Composites (Baoguo Han, Siqi Ding, Jialiang Wang, Jinping Ou)....Pages 709-731

Citation preview

Baoguo Han · Siqi Ding · Jialiang Wang · Jinping Ou

NanoEngineered Cementitious Composites Principles and Practices

Nano-Engineered Cementitious Composites

Baoguo Han Siqi Ding Jialiang Wang Jinping Ou •

•

•

Nano-Engineered Cementitious Composites Principles and Practices

123

Baoguo Han School of Civil Engineering Dalian University of Technology Dalian, Liaoning, China Jialiang Wang School of Civil Engineering Dalian University of Technology Dalian, Liaoning, China

Siqi Ding Department of Civil and Environmental Engineering The Hong Kong Polytechnic University Hung Hom, Kowloon, Hong Kong Jinping Ou School of Civil Engineering Dalian University of Technology Dalian, Liaoning, China

ISBN 978-981-13-7077-9 ISBN 978-981-13-7078-6 https://doi.org/10.1007/978-981-13-7078-6

(eBook)

Library of Congress Control Number: 2019933712 © Springer Nature Singapore Pte Ltd. 2019 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

To the families! Baoguo Han, Siqi Ding, Jialiang Wang, Jinping Ou

Preface

Cement has been used for millennia. However, no one knows for sure who first came up with the idea to use a cement substance to make civil engineering materials. In general terms, the word cement refers to any binder that sets, hardens, and tightly holds other materials together. Most used cement is inorganic and hydraulic including Portland cement and other cements (e.g., calcium aluminate cement, supersulfated cement, calcium sulfoaluminate cements, and geopolymer cement). Cement is seldom used solely but is used with sand to produce mortar, or with sand and gravel to produce concrete. Therefore, cementitious composites (also called cement-based composites) refer to all materials made of cement in a generalized concept. They include concrete (containing coarse and fine aggregates), mortar (containing fine aggregates), and binder only (containing no aggregate, whether coarse or fine). In this book, cementitious composites refer in particular to Portland cement-based composites unless otherwise stated, because of previous research and application of nano-engineered cementitious composites focused mainly on cementitious composites fabricated with Portland cement. Thanks to their excellent mechanical strength, resistant to water, easily formed into various shapes and sizes, and cheap and readily available everywhere, cementitious composites are the most widely used civil engineering materials and serve as the primary materials in constructing the infrastructures necessary to provide society with basic safety and living requirements. It was reported that China had used more cementitious composites between 2011 and 2013 (3 years) that has been used by the USA in the entire twentieth century, indicating that Chinese economic growth is especially reliant on infrastructure development and more precisely on the usage of cementitious composites. This is not only evident in China as the pattern can be observed across the whole world with many countries demonstrating unprecedented growth in the cementitious composite industry. The usage of cementitious composites has been increasing with the result that cementitious composites have become the second-most used resources in the world after water. Twice as much cementitious composites are used in infrastructures around the world as the total of all other building materials, including wood, steel, plastic, and aluminum. Production and application of cementitious composites have a vii

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significant impact on resources, energy, and environment. Although the cement production needs intensive energy, cementitious composites have more excellent ecological profile than other construction materials such as metal, glass and polymers. Compared with other construction materials, the production of cementitious composites consumes the least amount of materials and energy, produces the least amount of harmful by-products, and causes the least amount of damage to environment. Cementitious composites are a responsible choice for sustainable development of society. As human populations continue to grow and urbanize, cementitious composites will continue to play an important role in infrastructure construction. However, the development of cementitious composites is encountering enormous problems and challenges. (1) Cement manufacturing has a direct and visible negative impact on the world’s resources, energy consumption and environment. For example, making 1 ton of cement requires about 2 tons of raw material (limestone and shale), consumes about 4 GJ of energy in electricity, process heat, and transport (energy equivalent to 131 cubic meters of natural gas), produces approximately 1 ton of CO2, about 3 kg of NOX (an air contaminant that contributes to ground-level smog), and about 0.4 kg of PM10 (an airborne particulate matter harmful to respiratory tract when inhaled). (2) The properties/performances (e.g., mechanical properties/performances, dimensional stability, durability, workability and functional/smart properties/performances) of cementitious composites should be further improved or modified to maintain sustainable development of cementitious composites and infrastructures. In general, cementitious composites have a relatively high compressive strength, but are significantly more brittle and exhibit a poor tensile strength. They carry flaws and micro-cracks both in the material and at the interfaces even before an external load is applied. These defects and micro-cracks emanate from excess water, bleeding, plastic settlement, thermal and shrinkage strains, and stress concentrations imposed by external restraints, etc. Under an applied load, distributed micro-cracks propagate, coalesce, and align themselves to produce macro-cracks. When loads are further increased, conditions of critical crack growth are attained at the tip of the macro-cracks, and unstable and catastrophic failure is precipitated. Under fatigue loads, cementitious composites crack easily, and cracks create easy access routes for deleterious agents. This will lead to early saturation, freeze-thaw damage and scaling, discoloration, and so on. Additionally, the durability of concrete has become increasingly important as there has been a push to extend the life expectancy of existing and planned infrastructures. Due to the degeneration of cementitious composites, complex interaction between cementitious composites and their service environment, absence of advanced design and condition assessment tools and timely maintenance, many infrastructures fabricated with cementitious composites are in a state of utter disrepair. For example, more than 50% of Europe’s annual construction budget is devoted to repair and maintenance of existing infrastructures. For example, the cost of maintenance of bridges and buildings in Europe exceeds €1 and €20 billion per year, respectively; with a significant part of this being spent on repair of infrastructures made of cementitious composites. What’s more, cementitious composites belong to primary and complex materials in

Preface

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nature. Their behaviors during the life cycle should be able to be controlled through mass, energy or information exchange with external environment. Multifunctional and smart cementitious composites are required since traditional cementitious composites just serving as structural materials cannot meet the upgrading requirement in terms of safety, longevity, and function of advanced engineering infrastructures. (3) Cementitious composites are multi-component, multi-phase, and multi-scale materials in nature. Its compositions mainly include cement, water, aggregates, chemical admixtures, and mineral admixtures. The proportion of these components can vary within a flexible and wide range. Hardened cementitious composites contain solid, liquid, and gas phases. Their structure covers over ten orders of magnitude in size, ranging from nanometers (e.g., hydration product) to micrometers (e.g., binder), and then from millimeters (e.g., mortar and concrete) to tens of meters (final structures). In addition, the cementitious composites feature time variant characteristic because cement hydration is a long-term evolutionary progress and hydration products are thermodynamic instability. The complex compositions and structures of cementitious composites have not been completely understood yet, which limits the utility and predictability of cementitious composites in critical applications but offers opportunities for the formulation of additional control. The properties/performances of cementitious composites closely depend on their compositions, fabrication/processing, and structures. The compositions and structures of cementitious composites exist in multiple length scales (nano to micro to macro) where the properties/performances of each scale derive from those of the next smaller scale. Big changes in micro-macroscale behaviors of cementitious composites are predicted form the nanoscale impact. Even with small changes in the nanoscale where properties/performances differ significantly from those at a larger scale, need-driven innovative design and production of materials and infrastructures could lead to large accumulated benefits, such as lower use of raw materials, improved properties, and higher construction efficiency that make infrastructures stronger, more durable, multifunctional/smart, resource and energy-efficient, and environment-friendly throughout their life cycle. Therefore, nano science and technology opens up new visionary opportunities that may build up a fundamental for comprehensively understanding the genomic code of cementitious composites in nature, featuring the blueprint to describe, predict, and control properties of cementitious composites from the bottom-up (i.e., from nanoscale to micro– macro-scale) approach, and providing guide for design, fabrication, and applications of cementitious composites. Since cementitious composites are nanostructure in nature and feature obvious nano-behaviour, nanoscience and nanotechnology has the great potential to engineer cementitious composites with superior mechanical performance, durability, and sustainability. For example, the size of the calcium silicate hydrate, the primary hydration products responsible for such properties as mechanical properties, dimensional stability, and durability in cementitious systems, lies in the few nanometers range. In addition, there inevitably exist nanoscale particles in cement or mineral admixtures (in the case of using mineral admixtures, especially

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submicron-scale silicon fume). However, these nanoscale phenomena or behaviors in cementitious composites do not receive enough attention. In the early 2000s, the nano science and technology in cementitious composites garnered increased scientific and commercial attention because the nano science and technology has created great excitement and expectations in other fields. The basic principle of nano-engineered cementitious composites is based on multiscale and multicomponent composition. The nano-engineered cementitious composites are achieved through material composition design, special processing, and modification of microstructure. The initial approach for developing nano-engineered cementitious composites is nano-modification by adding nanomaterials such as nano-ZrO2, nano-SiO2, and nano-TiO2. Since then, some novel approaches (e.g., adding nano-seed, using nano-cement or mineral admixtures, and using cement, mineral admixtures, or aggregates with nanomaterial modification) are continuously developed. In the past nearly two decades, much work has been done on the development and deployment of nano-engineered cementitious composites. This book provides a summary report on current researches in the field of nano-engineered cementitious composites to help people working on this particular aspect to their job better. This book covers theory, techniques, and applications of nano-engineered cementitious composites containing their design, fabrication/processing, test/characterization and simulation, properties/performances and their control methods, mechanisms and models, applications, and future development. This book is organized as shown below. The first part provides a general introduction to the basic principles of nano-engineered cementitious composites (Chap. 1) and current progress of nano-engineered cementitious composites (Chap. 2). The second part presents the authors’ research results in this area involving carbon nanotubes-engineered cementitious composites (Chap. 3), graphene-engineered cementitious composites (Chap. 4), nano-SiO2-engineered cementitious composites (Chap. 5), nano-TiO2-engineered cementitious composites (Chap. 6), nano-ZrO2-engineered cementitious composites (Chap. 7), nano-BN-engineered cementitious composites (Chap. 8), and electrostatic self-assembled carbon nanotube/nano-carbon black composite fillers-engineered cementitious composites (Chap. 9). Finally, the third part discusses the future developments and challenges of nano-engineered cementitious composites (Chap. 10). Dalian, China Hong Kong, China Dalian, China Dalian, China

Baoguo Han Siqi Ding Jialiang Wang Jinping Ou

Acknowledgements

Many professional colleagues and friends have contributed directly or indirectly to this book: Xun Yu, Wei Zhang, Danna Wang, Liqing Zhang, Yanfeng Ruan, Zhen Li, Xia Cui, Shan Jiang, Qiaofeng Zheng, Shengwei Sun, Yunyang Wang, Chenyu Zhang, Zhu Wang, Linyang Han, Shuzhu Zeng, Sufen Dong, and Xinyue Wang. The authors thank all of them most sincerely. This book is funded by the National Science Foundation of China (grant nos. 51578110, 51428801, 51178148, and 50808055), Program for New Century Excellent Talents in University of China (grant no. NCET-11-0798), the Ministry of Science and Technology of China (grant no. 2011BAK02B01), and the Fundamental Research Funds for the Central Universities in China (grant no. DUT18GJ203). We also thank Springer for his enthusiastic and hard work to make the publication of possible.

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Contents

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2

Basic Principles of Nano-Engineered Cementitious Composites 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Fundamental of Cementitious Composites . . . . . . . . . . . . . 1.2.1 General Introduction of Compositions of Cementitious Composites . . . . . . . . . . . . . . . . . 1.2.2 General Introduction of Structures of Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.3 Hierarchy of Science and Technology of Cementitious Composites . . . . . . . . . . . . . . . . . 1.3 Fundamental of Nano-Engineered Cementitious Composites 1.3.1 Significance of Nanoscience and Nanotechnology of Cementitious Composites . . . . . . . . . . . . . . . . . 1.3.2 Thermodynamic and Kinetic Principles of Nano-Engineered Cementitious Composites . . . . 1.3.3 Nano-core Effect in Nano-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-Engineered Cementitious Composites 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 General Overview of Current Progress of Nano-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Nano-Engineered Composition Materials of Cementitious Composites . . . . . . . . . . . . . . . . . 2.2.2 Fabrication/Processing of Nano-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . 2.3 Current Progress of Specific Type of Nano-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Current Progress of Nano-Cement-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . .

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2.3.2 2.3.3 2.3.4 2.3.5 2.3.6 2.3.7 2.3.8 2.3.9 2.3.10 2.3.11 2.3.12 2.3.13 2.3.14 2.3.15 2.3.16 2.3.17 2.3.18 2.3.19 2.3.20 2.3.21 2.3.22 2.3.23

Current Progress of Nano-Silica Fume-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-Fly Ash-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-Carbon Black-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Carbon Nanotube-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Carbon Nanofiber-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Graphene-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-SiO2-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-TiO2-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-ZrO2-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-Al2O3-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-MgO-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-ZnO-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-ZnO2-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-CuO-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-Fe2O3-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-Fe3O4-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-Cr2O3-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-SiC-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-Ti3C2-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-BN-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-CaCO3-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . Current Progress of Nano-BaSO4-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . .

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Contents

2.3.24 Current Progress of Al2SiO5 Nanotube-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . 2.3.25 Current Progress of Nano-Ferrite-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . 2.3.26 Current Progress of Nano C–S–H Seed-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . 2.3.27 Current Progress of Nano-Clay-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . 2.3.28 Current Progress of Nano-Perovskite-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . 2.3.29 Current Progress of Nanocellulose-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . 2.3.30 Current Progress of Nano-Carbonized Bagasse Fiber-Engineered Cementitious Composites . . . . . . . 2.3.31 Current Progress of Hybrid Nanomaterial-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . 2.3.32 Current Progress of In-Situ Growing Carbon Nanotubes/Carbon Nanofiber-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . 2.3.33 Current Progress of Carbon Nanotube-Latex Thin Film Coating Aggregate-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Carbon Nanotubes-Engineered Cementitious Composites . . . . . . 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Rheology of Carbon Nanotubes-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1 Preparation of Fresh Cement Pastes with Carbon Nanotubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2 Effect of Carbon Nanotube Dosage on Rheology . . . 3.2.3 Effect of Water to Cement Ratio on Rheology . . . . . 3.2.4 Effect of Superplasticizer Dosage on Rheology . . . . 3.3 Mechanical Properties/Performances of Carbon NanotubesEngineered Cementitious Composites . . . . . . . . . . . . . . . . . . 3.3.1 Fabrication of Cement Pastes with Carbon Nanotubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.2 Effect of Size of Untreated Carbon Nanotubes on Mechanical Properties/Performances . . . . . . . . . . 3.3.3 Effect of Surface Functionalization of Carbon Nanotubes on Mechanical Properties/Performances . . 3.3.4 Effect of Special Structure and Surface Modification of Carbon Nanotubes on Mechanical Properties/Performances . . . . . . . . . . . . . . . . . . . . .

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3.4

Transport Properties of Carbon Nanotubes-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.1 Fabrication of Cement Mortars with Carbon Nanotubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.2 Water Sorptivity . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.3 Water Permeability . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.4 Gas Permeability . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 Electrical Properties/Performances of Carbon Nanotubes-Engineered Cementitious Composites . . . . . . . . . 3.5.1 Effect of Carbon Nanotube Size on Electrical Properties/Performances . . . . . . . . . . . . . . . . . . . . . 3.5.2 Effect of Surface Functionalization of Carbon Nanotubes on Electrical Properties/Performances . . . 3.5.3 Effect of Surface Modification and Special Structure of Carbon Nanotubes on Electrical Properties/Performances . . . . . . . . . . . . . . . . . . . . . 3.6 Self-sensing Properties/Performances of Carbon Nanotubes-Engineered Cementitious Composites . . . . . . . . . 3.6.1 Self-sensing Properties/Performances of Cement Pastes with Carbon Nanotubes . . . . . . . . . . . . . . . . 3.6.2 Self-sensing Properties/Performances of Cement Mortars with Carbon Nanotubes . . . . . . . . . . . . . . . 3.6.3 Mechanisms of Self-sensing Properties/Performances . . . . . . . . . . . . . . . . . . . . . 3.7 Case Study of Applications of Carbon Nanotubes-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . 3.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

Graphene-Engineered Cementitious Composites . . . . . . . . . . . . . 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Preparation of Graphene-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Rheology of Graphene-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Mechanical Properties/Performances of Graphene-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.1 Compressive Properties/Performances . . . . . . . . . . . 4.4.2 Flexural Properties/Performances . . . . . . . . . . . . . . . 4.4.3 Nano-Hardness . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.4 Reinforcement Mechanisms . . . . . . . . . . . . . . . . . . .

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Durability of Graphene-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.1 Wear Resistance . . . . . . . . . . . . . . . . . . . . . . . . 4.5.2 Chloride Penetration Resistance . . . . . . . . . . . . . 4.6 Functional/Smart Properties/Performances of Graphene-Engineered Cementitious Composites . . . . . 4.6.1 Damping Properties/Performances . . . . . . . . . . . 4.6.2 Electrically Conductive Properties/Performances . 4.6.3 Thermal Properties/Performances . . . . . . . . . . . . 4.6.4 Electromagnetic Properties/Performances . . . . . . 4.6.5 Smart Properties/Performances of GrapheneEngineered Cementitious Composites . . . . . . . . 4.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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482 482 484 493 495

. . . . . 506 . . . . . 515 . . . . . 516

Nano-SiO2-Engineered Cementitious Composites . . . . . . . . . . . . 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Rheology of Nano-SiO2-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.1 Preparation of Fresh Cement Paste with Nano-SiO2 . 5.2.2 Effect of Nano-SiO2 Dosage on Rheology . . . . . . . . 5.2.3 Effect of Water-to-Cement Ratio on Rheology . . . . . 5.2.4 Effect of Superplasticizer Dosage on Rheology . . . . 5.2.5 Effect of Ultrasonic Time on Rheology . . . . . . . . . . 5.2.6 Effect of Mixing Rate on Rheology . . . . . . . . . . . . . 5.3 Mechanical Properties/Performances of Nano-SiO2Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . 5.3.1 Fabrication of Cement Mortars/Powder Reactive Concrete with Nano-SiO2 . . . . . . . . . . . . . . . . . . . . 5.3.2 Compressive and Flexural Properties/Performances of Cement Mortars with Nano-SiO2 and Reinforcement Mechanisms . . . . . . . . . . . . . . . . . . . 5.3.3 Impact Properties/Performances of Reactive Powder Concrete with Nano-SiO2 and Reinforcement Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Durability of Nano-SiO2-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.1 Wear Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.2 Chloride Penetration Resistance . . . . . . . . . . . . . . . . 5.4.3 Modification Mechanisms . . . . . . . . . . . . . . . . . . . . 5.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . 519 . . 519 . . . . . . .

. . . . . . .

520 520 520 522 524 525 526

. . 527 . . 527

. . 527

. . 542 . . . . . .

. . . . . .

551 551 552 553 557 559

xviii

6

7

Contents

Nano-TiO2-Engineered Cementitious Composites . . . . . . . . . . . . 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Rheological Properties/Performances of NanoTiO2-Engineered Cementitious Composites . . . . . . . . . . . . . . 6.3 Mechanical Properties/Performances of NanoTiO2-Engineered Cementitious Composites . . . . . . . . . . . . . . 6.3.1 Preparation of Nano-TiO2-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.2 Mechanical Properties/Performances of Anatase Phase Nano-TiO2-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.3 Mechanical Properties/Performances of Rutile Phase Nano-TiO2-Engineered Cementitious Composites . . . 6.3.4 Mechanical Properties/Performances of NanoSiO2@TiO2-Engineered Cementitious Composites . . 6.4 Durability of Nano-TiO2-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.1 Wear Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.2 Chloride Penetration Resistance . . . . . . . . . . . . . . . . 6.5 Electrical Properties of Nano-TiO2-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nano-ZrO2-Engineered Cementitious Composites . . . . . . . . . . . 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Preparation of Nano-ZrO2-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Mechanical Properties/Performances of Nano-ZrO2Engineered Cementitious Composites with Standard Curing 7.3.1 Flexural Strength . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.2 Compressive Strength . . . . . . . . . . . . . . . . . . . . . . 7.3.3 Splitting Strength . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.4 Impact Properties/Performances . . . . . . . . . . . . . . . 7.3.5 Reinforcement Mechanisms . . . . . . . . . . . . . . . . . . 7.4 Mechanical Properties/Performances of Nano-ZrO2Engineered Cementitious Composites Under Heat Curing . . 7.4.1 Comparison of Strength of Nano-ZrO2-Engineered Cementitious Composites with Different Curing Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.2 Stress–Strain Relationship Under Uniaxial Compression . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.3 Load–Deflection Relationship Under Four-Point Bending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . 561 . . 561 . . 562 . . 565 . . 565

. . 565 . . 577 . . 581 . . 594 . . 594 . . 594 . . 595 . . 596 . . 598

. . . 601 . . . 601 . . . 602 . . . . . .

. . . . . .

. . . . . .

603 603 605 607 608 613

. . . 618

. . . 618 . . . 622 . . . 625

Contents

xix

7.4.4

Fracture Properties/Performances Under Three-Point Bending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.5 Fracture Properties/Performances Under Four-Point Shear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5 Electrical Properties/Performances of Nano-ZrO2-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6 Durability of Nano-ZrO2-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6.1 Wear Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6.2 Chloride Penetration Resistance . . . . . . . . . . . . . . . . 7.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

9

Nano-BN-Engineered Cementitious Composites . . . . . . . . . . . . . 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Preparation of Nano-BN-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3 Mechanical Properties/Performances of Nano-BN-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.1 Effect of Nano-BN Particle Size on Mechanical Properties/Performances . . . . . . . . . . . . . . . . . . . . . 8.3.2 Effect of Nano-BN Content on Mechanical Properties/Performances . . . . . . . . . . . . . . . . . . . . . 8.3.3 Effect of Curing Method on Mechanical Properties/Performances . . . . . . . . . . . . . . . . . . . . . 8.3.4 Reinforcement Mechanisms of Nano-BN to Cementitious Composites Under Standard Curing . . . 8.3.5 Reinforcement Mechanisms of Nano-BN to Cementitious Composites Under Heat Curing . . . . . . 8.4 Durability of Nano-BN-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.1 Abrasion Resistance and Modification Mechanisms . 8.4.2 Chloride Penetration Resistance and Modification Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . 626 . . 629 . . 632 . . . . .

. . . . .

633 633 634 635 636

. . 639 . . 639 . . 640 . . 642 . . 642 . . 645 . . 647 . . 649 . . 658 . . 659 . . 659 . . 661 . . 662 . . 663

Electrostatic Self-Assembled Carbon Nanotube/Nano-Carbon Black Fillers-Engineered Cementitious Composites . . . . . . . . . . . . . 665 9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 665 9.2 Preparation of Electrostatic Self-Assembled Carbon Nanotube/Nano-Carbon Black Fillers-Engineered Cementitious Composites/Sensors . . . . . . . . . . . . . . . . . . . . . . 666

xx

Contents

9.3

Properties/Performances of Electrostatic Self-Assembled Carbon Nanotube/Nano-Carbon Black Fillers-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3.1 Mechanical Properties/Performances . . . . . . . . . . . . 9.3.2 Electrically Conductive Properties/Performances . . . . 9.3.3 Self-sensing Properties/Performances . . . . . . . . . . . . 9.4 Case Study of Applications of Electrostatic Self-Assembled Carbon Nanotube/Nano-Carbon Black Fillers-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4.1 Sensors Fabricated with Electrostatic Self-Assembled Carbon Nanotube/Nano-Carbon Black FillersEngineered Cementitious Composites . . . . . . . . . . . 9.4.2 Smart Concrete Columns Embedded with Sensors . . 9.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10 Future Developments and Challenges of Nano-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.2 Design of Nano-Engineered Cementitious Composites . . . . 10.3 Fabrication/Processing of Nano-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4 Test/Characterization and Simulation of Nano-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . 10.5 Properties/Performances of Nano-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.6 Mechanisms and Models of Nano-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.7 Applications of Nano-Engineered Cementitious Composites 10.8 Potential Risks About Nano-Engineered Cementitious Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.9 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . .

. . . .

669 669 673 675

. . 695

. . . .

. . . .

695 698 705 706

. . . 709 . . . 709 . . . 712 . . . 713 . . . 715 . . . 717 . . . 723 . . . 724 . . . 727 . . . 728 . . . 729

About the Authors

Baoguo Han received his Ph.D. degree in the field of smart materials and structures from the Harbin Institute of Technology, China, in 2005. He is currently a professor of civil engineering in the Dalian University of Technology, China. His main research interests include cement and concrete materials, nanotechnology, smart materials and structures, multifunctional composites, structural health monitoring, and traffic detection. He is a member of the editorial board of five international journals and has published two books, 12 chapters, and more than 130 technical papers. He was invited to the University of Minnesota and has worked as a visiting research scholar there for 3 years. He was also awarded the New Century Excellent Talents in University and the First Prize of Natural Science by the Ministry of Education of China. e-mail: [email protected]; [email protected] Siqi Ding received his M.S. degree in material science from the Dalian University of Technology, China, in 2015. He is currently pursuing his Ph.D. degree at The Hong Kong Polytechnic University, majored in structural engineering. His main research interests include cement and concrete materials, nanotechnology, smart materials and structures, and structural health monitoring. He has published five chapters and 14 journal papers. He and Jialiang Wang contributed equally, and they are alphabetically ordered. e-mail: [email protected] Jialiang Wang received his M.S. degree in material engineering from the Lanzhou University of Technology, China, in 2015. He is currently pursuing his Ph.D. degree at Dalian University of Technology, China. His current research interests include cement and concrete composites, smart materials and structures, and nanotechnology. He has published one chapter and five journal papers. He and Siqi Ding contributed equally, and they are alphabetically ordered. e-mail: [email protected]

xxi

xxii

About the Authors

Jinping Ou received his Ph.D. degree from the Harbin Institute of Technology, China, in 1987. He is a professor at both Harbin Institute of Technology and Dalian University of Technology, China. His main research interests include structural damage, reliability and health monitoring, structural vibration and control, smart materials and structures. He has published more than 300 technical papers/reports and six books. He has been awarded the second-level National Awards of Science and Technology Progress twice and the first-level provincial and ministerial Awards of Science and Technology Progress five times. He has been an academician of Chinese Academy of Engineering since 2003 and was the president of the Chinese Society for Vibration Engineering, the vice-president of the Architectural Society of China, an executive board member at the International Association for Structural Control and Monitoring, as well as the vice-president and fellow of the International Society for Structural Health Monitoring of Intelligent Infrastructure. e-mail: [email protected]; [email protected]

Abbreviations

AC AFM AFm AFt ANT B C CF CH CL CNC CNF CNF* CNM CNT C-S-H DC DSC DTG EDS EIS FA G GGBFS GO HD ITZ MCL MIP MLG

Alternating current Atomic force microscope Monosulfate Ettringite Aluminosilicate nanotube Binder Cement Carbon fiber Calcium hydroxide Crushed limestone Cellulose nanocrystals Carbon nanofiber Cellulose nanofibrils Calcined nano-montmorillonite Carbon nanotube Calcium silicate hydrate Direct current Differential scanning calorimetry Derivative TG Energy-dispersive spectrometer Electrochemical impedance spectroscopy Fly ash Gravel Ground granulated blast furnace slag Graphite oxide Hydration degree Interfacial transition zone Mean chain length Mercury intrusion porosimetry Multi-layer graphene

xxiii

xxiv

MWCNT NaDDBS NCB NCBF NFC NK NM NMK NMR PD PVA RH RHA S SDS SEM SF SHM SP SWCNT TEM TG W W/B W/C XRD

Abbreviations

Multi-walled CNT Sodium dodecylbenzene sulfonate Nano-carbon black Nano-carbonized bagasse fiber Nanofibrillated cellulose Nano-kaolinite Nano-montmorillonite Nano-metakaolin Nuclear magnetic resonance Polymerization degree Polyvinyl alcohol Relative humidity Rice husk ash Sand Sodium dodecyl sulfate Scanning electron microscope Silica fume Structural health monitoring Superplasticizer Single-walled CNT Transmission electron microscope Thermogravimetry Water Water-to-binder ratio Water-to-cement ratio X-ray diffraction

Chapter 1

Basic Principles of Nano-Engineered Cementitious Composites

Abstract The cementitious composites are multi-component and multi-phase materials; thus they feature complex thermodynamics and kinetics as well as multi-scale and multi-equal characteristics according to the fundamental and the hierarchy of cementitious composites. The properties/performances of cementitious composites closely depend on their compositions and fabrication/processing as well as structures. Because the properties/performances of each scale derive from those of the next smaller scale, the nano science and technology provides a bottom-up approach for understanding and controlling the cementitious composites. The principles of nano-engineered cementitious composites can be attributed to the nano-core effect. The behaviors of the nano-engineered cementitious composites are governed by nano-core effect zone, i.e., nano-core-shell element.










Keywords Cementitious composites Nano-engineered Principles Hierarchy Nano-core effect

1.1




Introduction

Cementitious composites are materials composed of aggregates bonded together with Portland cement or other hydraulic cements such as high alumina cement, supersulfated cement, and geopolymer cement. Because previous research and application mainly focused on cementitious composites fabricated with Portland cement, cementitious composites refer to Portland cement-based materials unless otherwise stated in this book. In addition, it should be noted that cementitious composites here are generalized concept for which they can be concrete (containing coarse and fine aggregates), cement mortar (containing fine aggregates), or cement paste (containing no aggregate, whether coarse or fine) [1–5]. As shown in Fig. 1.1, cementitious composites are multi-component, multi-phase, and multi-scale materials in nature. Their main components include cement, water, aggregates, chemical additives, and mineral additives. The proportion of these components can vary within a flexible and wide range. Hardened cementitious © Springer Nature Singapore Pte Ltd. 2019 B. Han et al., Nano-Engineered Cementitious Composites, https://doi.org/10.1007/978-981-13-7078-6_1

1

2

1 Basic Principles of Nano-engineered Cementitious Composites

Fig. 1.1 Multi-component, multi-phase and multi-scale nature of cementitious composites

composites contain solid, liquid, and gas phases. Their structure covers over ten orders of magnitude in size, ranging from nanometers (e.g., hydration product) to micrometers (e.g., binder), and then from millimeters (e.g., mortar and concrete) to tens of meters (final structures). In addition, the cementitious composites feature time-dependent characteristic because cement hydration is a long-term evolutionary progress and hydration products are thermodynamic instability [6–10]. The central theme of material science and engineering is that the relationships between the compositions, fabrication/processing, structures, properties/performances

1.1 Introduction

3 Properties Environmental effect (atmosphere, temp. stress)

Composition

Structures

Theory, design, test/characterization, simulation, mechanisms and models Fabrication/processing Performances

Fig. 1.2 Central theme of material science and engineering

of materials are crucial to their functions, as shown in Fig. 1.2. Although the complex compositions and structures of cementitious composites have not been completely understood yet, and the structure–property/performance relationships in cementitious composites have not yet been fully developed, the progress in the field of materials has resulted primarily from recognition of the principle that their properties/performances depend on structures and compositions, which in turn are the results of the history of the materials (i.e., its fabrication/processing). Thus, the properties/performances of cementitious composites can be modified by making suitable changes in their compositions, fabrication/processing, and structures. As a new engine to promote science and technology development, nano science and technology opens up new visionary opportunities that may build up a fundamental for comprehensively understanding and controlling cementitious composites from the bottom up (i.e., from nanoscale to micro–macro-scale) approach [2, 3, 11]. Therefore, this chapter will firstly give an overall introduction to the fundamental of cementitious composites, and then the hierarchy of science and technology of cementitious composites is also briefly summarized. Finally, the fundamental of nano-engineered cementitious composites is discussed in detail.

1.2 1.2.1

Fundamental of Cementitious Composites General Introduction of Compositions of Cementitious Composites

(1) Cement 1. Manufacture, compositions, and fineness ASTM C 150 defines cement as hydraulic cement produced by pulverizing clinkers consisting essentially of hydraulic calcium silicates, and a small amount of one or

4

1 Basic Principles of Nano-engineered Cementitious Composites

more forms of calcium sulfate as an interground addition. Clinkers are 5- to 25-mm diameter nodules of a sintered material that is produced when a raw mixture of predetermined composition is heated to high temperatures. Since calcium silicates are the primary constituents of cement, the raw material for the production of cement must provide calcium and silica in suitable forms and proportions. Naturally occurring calcium carbonate materials (e.g., limestone, chalk, marl, and sea-shells) are the common industrial sources of calcium, but clay or dolomite (CaCO3
MgCO3) are usually presented as impurities. Clays and shales, rather than quartz, are the preferred sources of additional silica in the raw mix for making calcium silicates because quartzitic silica does not react easily with lime. Clay minerals contain alumina (Al2O3), iron oxide (Fe2O3), and alkalies. The presence of aluminum, iron and magnesium ions, and alkalies in the raw mix has a mineralizing effect on the formation of calcium silicates; i.e., they facilitate the formation of the calcium silicate at considerably lower temperatures than would otherwise be possible. Therefore, when sufficient amounts of iron and alumina minerals are not present in the primary raw materials, these are purposely incorporated into the raw mix through the addition of secondary materials such as bauxite and iron ore. As a result, besides the calcium silicate compounds, the cement clinker also contains aluminates and alumino ferrites of calcium. To facilitate the formation of the desired compounds in cement clinker, it is necessary to homogenize the raw mix before heat treatment. That is why the materials are subjected to a series of crushing, grinding, and blending operations [2]. Although cement consists essentially of various compounds of calcium, the results of a routine chemical analysis are reported in terms of oxides of the elements present. Actually, the properties of cement are closely related to the compound composition, so it is a common practice in the cement industry to use the compound composition of cement from the oxide analysis. Cement consists of four major compound compositions (as shown in Fig. 1.3), all of which can react with water to produce different types of hydration products. Chemical composition and compound composition of typical cement are listed in Table 1.1 [12].

Fig. 1.3 Cement consists of four major compound compositions

1.2 Fundamental of Cementitious Composites

5

Table 1.1 Composition ranges of cement Chemical composition (%)

Compound composition (%)

CaO

SiO2

Al2O3

Fe2O3

MgO

3CaO
SiO2

2CaO
SiO2

3CaO
Al2O3

4CaO
Al2O3
Fe2O3

62–68

20–24

4–7

2.5–6.5

95

–

83 350

Collins et al. [60] Azhari and Banthia [61]

>95 –

40–300 –

Li et al. [59]

0.5–2

0.1–10

180

>95

Mohsen et al. [58]

10–30

10–20

Cwirzen et al. [57]

95 –

1333

–

10 10–30

10

10–20

Ibarra et al. [54]

Al-Rub et al. [56]

>90 >90

250–300 –

1.5 1–50

9.5

Ibarra et al. [54]

Makar et al. [55]

Ibarra et al. [54]

References

10–20

–

– >95

>90

– >500

Purity/%

Specific surface area/(m2/g)

10–30

1.97

–

Baeza et al. [103], Galao et al. [104]

100

50–200

44

–

–

Yazdani and Mohanam [105]

100

50–200

45

1.95

>90

Meng and Khayat [106]

100

50–200

230

–

–

Jiang et al. [31, 107]

The mix proportion and main fabrication progress of CNFs-engineered cementitious composites are listed in Tables 2.45 and 2.46, respectively. (2) Structures Meng and Khayat investigated the pore size distribution and porosity of CNFs-filled cementitious composites (as listed in Table 2.47). They observed the incorporated CNFs can improve the pore structure of cement mortars at the curing age of 28 d. When the CNF content is up to 0.3%, the porosity of capillary pores is reduced by 76%, while the porosity of gel pores is increased by 68%. That is indicative of a refinement of the pore structure existed in the cement mortars [106]. (3) Properties/performances 1. Rheology Jiang et al. investigated the rheology of cement pastes with different CNF dosages. They found that both yield stress and plastic viscosity of cement pastes increase with the increasing CNF dosage (as listed in Table 2.48). 2. Hydration (i) Hydration heat Meng and Khayat studied the hydration heat of ultrahigh-performance concrete with CNFs through the isothermal calorimetry test [106]. The experimental results indicated that the addition of CNFs (from 0 to 3%) increases the cumulative heat of concrete, i.e., enhancing the hydration degree of cement. (ii) Setting time The effect of CNFs on the setting time of cementitious composites is listed in Table 2.49. It can be seen that adding CNFs in the cement mortars shortens the setting time about 22 min/7.4% [105]. The researchers suggested that CNFs accelerate the hydration process of cement, resulting in faster setting time.

0.1, 0.3, 0.4, 0.8 (wt% of C)

–

Portland cement (type I) 1.0, 1.5, 2.0, 2.5 (vol.% of B)

0.02, 0.2 (wt% of C)

–

Portland cement (type I)

Crushed limestone, natural river sand

0.1, 0.5 and 1.0 (wt% of C)

–

Ordinary Portland cement (42.5R)

Portland cement (type I/ II)

1, 2, 5 (wt% of C)

–

Ordinary Portland cement (type I 52.5 R)

SP (2–7 wt% of C)

–

SF (0, 10 wt% of C), SP (1 wt% of C)

SP (0.75 wt% of C)

–

SP (0.15, 0.3, 0.55 wt% of C)

Admixturetype and content

B:W:S:G = 1:0.4:2.09:1.87

B:W = 1:0.3

B:W = 1:0.33

C:W = 1:0.20

B:W = 1:(0.4, 0.5, 1)

B:W = 1:(0.5, 1)

Proportion of C (B), W, S, and G

Gao et al. [110]

Gdoutos-Gdoutos and Aza [109]

Gay and Sanchez [108]

Jiang et al. [31], Jiang et al. [107]

Galao et al. [104]

Baeza et al. [103]

References

Note C (B), W, S, and G represent cement (binder), water, sand, and gravel, respectively. SP represents superplasticizer, and SF represents silica fume

Self-compacting concrete

0.5, 1, 2, 5 (wt% of C)

–

Ordinary Portland cement (type I 52.5 R)

Cement paste

CNF content

Aggregate type and size

Cement type

Matrix type

Table 2.45 Mix proportion of CNFs-engineered cementitious composites

142 2 Current Progress of Nano-Engineered Cementitious Composites

Fabrication progress

Mix (100r/ min) Mix (1000r/ min)

Cement

–

Stir

CNFs + C + G Sonicate (400 W, 20– 25 kHz)

Mix

C+G

CNFs + W+SP

Stir Stir

Mix

C + SF

CNFs + W + SP

Sonicate

CNFs + W + SP

CNFs + C + S + SF

Mix

SP + C

3 min

–

5 min

Several minutes

3 min

3 min

6 min

3 min

30 min

5 min

10 + 5 min

Vibration (60 s)

Vibration

Vibration

Vibration

Method

Time

Method Stir + sonicate

Molding/mm

Technology

CNFs + W

Feeding order

W (20 °C)

W

60  60  200 (compressive and flexural test)

40  40  40 (compressive test)

W (room temperature, 100% RH)

U 50  101.6 (split tensile testing)

Condition Saturated limewater

Size 20  20  80, 200  7  80, 25  100  10 (four-point bending and electrical resistance test)

Curing Time

28 d

28 d

7d

28 d

Jiang et al. [107]

Gao et al. [110]

Gay and Sanchez [7]

Baeza et al. [103]

References

Note C (B), W, S, and G represent cement (binder), water, sand, and gravel, respectively. SP represents superplasticizer, SF represents silica fume, and RH represents relative humidity

Ultrasonication + non-covalent surface modification by SP

Shear mixing

Dispersion method of CNFs

Table 2.46 Main fabrication process of CNFs-engineered cementitious composites

2.3 Current Progress of Specific Type of Nano-Engineered … 143

144

2 Current Progress of Nano-Engineered Cementitious Composites

Table 2.47 Effect of CNFs on the pore structure of cementitious composites Matrix type

Cement mortar

Increase/decrease of porosity/% Gel micropore

CNF content/%

Reference

32.8

0.15

35.82

0.3

Meng and Khayat [106]

Macro-pore

Capillary pore

Total

Abs.

Rel.

Abs.

Rel.

Abs.

Rel.

Abs.

Rel.

−0.8

−44.4

−6.3

−80.8

2.2

84.6

4.4

−0.8

−44.4

−7.0

−89.8

2.2

92.3

4.80

Note Abs. and Rel. represent the absolute and relative values, respectively

Table 2.48 Rheological parameters of cement pastes with different CNF dosages Cement pastes

Yield stress/Pa

Plastic viscosity/(Pa s)

Reference

Control (i.e., without CNFs) With 0.1% of CNFs With 0.5% of CNFs With 1.0 of CNFs

6.01 18.39 292.93 Over range

1.20 3.96 7.55 Over range

Jiang et al. [31]

Table 2.49 Effect of CNFs on the setting time of cementitious composites Matrix type

Decrease of setting time Abs./min Rel./%

CNF content/%

Reference

Cement mortar 22 7.4 0.1 Yazdani and Mohanam [105] Note Abs. and Rel. represent the absolute and relative values, respectively

3. Mechanical properties/performances (i) Strength The effect of CNFs on the strength of cementitious composites is summarized in Table 2.50. Most researchers observed that the incorporation of CNFs can improve the strength of the cementitious composites, but the improvement only occurs at a certain content of CNFs. Beyond this content, the addition of CNFs is not conducive to the development of strength. Metaxa et al. suggested that CNFs are mainly existed in the form of highly entwined clumps, which result in the creation of pockets or cavities in the cement pastes. The physical cross-linking and bridging of the pockets by the CNFs network offset the stress concentration at the pocket sites. When the composites are subjected to loads, the network created by the entangled CNFs may have limited the propagation of cracks, allowing the composites to retain some mechanical resistance [112]. Additionally, CNFs slow down the hydration rate, which may form the C–S–H gels with better crystallinity, contributing to enhance the strength of cementitious composites [113]. However, Jiang et al. observed that CNFs show

Strength

Increase/decrease 7d Abs./MPa Rel./%

Cement paste

Compressive

– – – – – – 0.9 2.3 0.3 0.7 −0.8 −2.1 Split tensile −0.14/−0.16 −4/−6 0.73/0.72 22/26 Self-compacting concrete Compressive – – – – – – – – Note Abs. and Rel. represent the absolute and relative values, respectively

Matrix type

Table 2.50 Effect of CNFs on the strength of cementitious composites

−2.3 −1.4 −37.2 2.4 −0.7 −1.6 – – 1.4 0.8 −0.25 −0.17

28 d Abs./MPa −1.8 −1.1 −28.7 5.1 −1.5 −3.4 – – 21.4 12.4 −3.6 −2.6

Rel./% 0.1 0.5 1 0.5 1 2 0.02 (without/with SF) 0.2 (without/with SF) 10 15 20 25

CNF content/%

Gao et al. [110]

Gay and Sanchez [108]

Galao et al. [111]

Jiang et al. [107]

References

2.3 Current Progress of Specific Type of Nano-Engineered … 145

146

2 Current Progress of Nano-Engineered Cementitious Composites

negative effect on the compressive strength of cement pastes. The compressive strength of cement pastes continually decreases with the increasing CNF content [107]. (ii) Shrinkage Meng and Khayat found that the autogenous shrinkage of ultrahigh-performance concrete increases by adding CNFs [106]. They suggested that CNFs refine the pore size and increase the mesopore volume within the concrete, which can cause higher self-desiccation and then promote greater autogenous shrinkage. (iii) Fracture Gdoutos et al. reported that the incorporation of CNFs significantly improves the fracture resistance of cement mortars. The fracture parameters of cement mortars including fracture toughness, critical strain energy release rate, and critical crack tip opening displacement can be increased by 128.6%, 154.9%, and 39%, respectively, due to the addition of 0.1% of CNFs [114]. 4. Durability Brown and Sanchez studied the sulfate attack resistance of cement pastes with CNFs. They observed the cement pastes with CNFs after exposing 550 d experience less changes in flexural strength than the control cement pastes [115]. Galao et al. also confirmed that CNFs-engineered cementitious composites have advantages in the aggressive environments, such as high levels of carbonation and chloride ions [116]. 5. Functional/smart properties/performances (i) Electrical properties/performances The effect of CNFs on the electrical resistivity of cementitious composites is summarized in Table 2.31. It can be seen that the resistivity of cementitious composites decreases with increasing CNF content. Jiang et al. observed that the resistivity of composites with CNFs drops sharply in the dosage range from 0.1 to 1%, which illustrates that the threshold zone of composites with CNFs is in the Table 2.51 Effect of CNFs on the electrical resistivity of cementitious composites Matrix type

Cement paste

Decrease of resistivity (28 d) Abs./(kX cm) Rel./%

CNF content/%

References

3.3 45 0.1 Jiang et al. [107] 7.0 97 0.5 7.2 99 1.0 1500 79 0.048 Konsta-Gdoutos and Aza [109] 1300 68 0.1 Note Abs. and Rel. represent the absolute and relative values, respectively

2.3 Current Progress of Specific Type of Nano-Engineered …

147

range from 0 to 0.5%. When the content of CNFs reaches 0.5%, the resistivity of the composites is 0.24 kX
cm, which decreases to 1/30 of the composites without CNFs. Although CNFs do not have much effect on the compressive strength, it can effectively reduce the electrical resistivity of cementitious materials [107]. (ii) Self-sensing properties/performances Gao et al. studied the relationship between electrical resistance variation and strain of self-compacting concrete with CNFs. They found the concrete with 1.0% of CNFs exhibits the highest electrical sensitivity with roughly 4% of reduction in electrical resistance [9]. Galao et al. observed the strain-sensing function is emerged in CNF-modified cement pastes at the curing age of 28 d. An addition of 2% of CNFs can sensitively represent the structural damage of cement pastes [10]. Additionally, Ślosarczyk et al. investigated that the CNF-modified cement mortars present the correspondence between the electrical resistance and the relative dynamic elasticity modulus loss [117]. (4) Applications Baeza et al. applied the CNFs-filled cementitious composites as sensors to monitor the strain and damage of reinforced concrete beam. The sensors are embedded and bonded into different service locations of reinforced beam. They observed that the sensors have high strain sensitivity. The smaller thickness of the sensors makes higher self-sensing capacity. The sensors can achieve elastic strain sensing of compression and tension region of beam and are capable of measuring strains on the surface of a structural element. However, there is no change in initial resistance for sensors during damage-sensing test. This means that CNF-modified cement pastes can act as a strain sensor attached to reinforced concrete beam, but they are not applicable as damage sensors due to the low strains that concrete admits [103].

2.3.7

Current Progress of Graphene-Engineered Cementitious Composites

(1) Fabrication/processing Graphene used to fabricate cementitious materials includes multi-layer graphene (MLG) and graphene dioxide (GO). GO is a type of graphene with single-layer structure that has been oxidized to intersperse the carbon layers with oxygen molecules. MLG as another type of graphene structure can be formed from graphite or GO. The existence of functional groups along the edges and over the surface of GO sheets will fracture the conjugated bonds between carbon atoms, thereby compromising its natural conducting property. The properties of graphene used to fabricate cementitious composites are summarized in Table 2.52. The mix proportion and main fabrication progress of graphene-engineered cementitious composites are listed in Tables 2.53 and 2.54, respectively.

–

–

8–10

About 32

23–42

–

23–42

–

1000

2.6

2.6

0.8–1.2

–

–

–

99% attenuation) [157]. Chen et al. found the shielding effectiveness of cementitious composites changes from 26 dB to 34 dB (31% increase) as 0.4% of GO is added [160]. (iv) Solar reflectivity D’Alessandro et al. studied the spectral solar reflectance of cementitious composites with different nano-carbon materials (including CNTs, CNFs, NCB, and MLGs). They found that the composite with MLG has the lowest solar reflectance and shows a singular behavior under all wavelengths [128]. (v) Self-sensing properties/performances Du et al. investigated the pressure–strain relationships of cementitious composites with graphene and observed that the resistivity decreases with the strain. They suggested that the decreased resistivity results from the better electrical contact between adjacent or overlaying graphene sheets as well as the contact between graphene and surrounding cement mortars. At the same time, the shortened distance between graphene sheets under compressive strain also possibly contributes to decreasing the resistivity [161]. Pang et al. reported that when the concentration of graphene exceeds 2.4%, a linear pressure-sensitive behavior of cementitious composite under a considerable compression strain range is appeared [162]. (4) Applications Peyvandi et al. added MLG into the concrete pipes used to resist aggressive sanitary sewer environment. They observed the mechanical behavior and durability including the moisture sorptivity and acid resistance are significantly improved due to the addition of MLG [163]. Saafi et al. mixed MLG into geopolymeric cement to fabricate superionic conductor (sensor) for structural health monitoring. The sensor is able to measure tensile strains up to 1300 le with extremely high gauge factor, thus making it suitable for measuring very small tensile strain [164]. Singh et al. prepared GO–ferrofluid–cement composites for electromagnetic interference shielding application and attained a prominent shielding effectiveness (>99% attenuation) [160]. In addition, Zhang applied the MLG to cementitious materials to remove the heavy metal ions and purify the sewage [165].

2.3 Current Progress of Specific Type of Nano-Engineered …

2.3.8

159

Current Progress of Nano-SiO2-Engineered Cementitious Composites

(1) Fabrication/processing The properties of nano-SiO2 used to fabricate cementitious composites are summarized in Table 2.62. The raw materials and mix proportion of nano-SiO2-engineered cementitious composites are listed in Table 2.63. The main fabrication progress of nano-SiO2engineered cementitious composites is summarized in Table 2.64. Table 2.62 Properties of nano-SiO2 Nano-SiO2 form

Particle size/nm

Powder

7

7–40

Specific surface area/(m2/g)

Purity/ %

Nano-SiO2 concentration/%

References

380

99.8

–

Khaloo et al. [166]

380

–

–

Kim et al. [167]

321.6

99.8

–

Zhang et al. [168]

300

>99.8

–

Liu et al. [119] Cai et al. [170]

296

99.8

–

10

670

99.9

–

Lin et al. [171, 172]

10 ± 5

640 ± 50

 09.9

–

Li [173], Zhang [174]

12

200

99.8

–

Khaloo et al. [165], Haruehansapong et al. [175]

200.1

99.8

–

Zhang et al. [168], Zhang and Islam [176]

13

200 (Blaine value)

99.8

–

Oltulu and Şahin [177, 178]

200

 99.8

–

Jiang et al. [107], Ouyang et al. [179]

200

–

–

15

15 ± 1

15 ± 5

Du et al. [180] Gaitero et al. [181]

20

–

–

Senff et al. [182]

200

>99.9

–

Babu [183]

640

99.5

–

Collodetti et al. [184], Farzadnia et al. [185]

–

–

–

Mei et al. [186]

160

>99.9

–

Givi et al. [187]

165 ± 65

>99.9

–

Nazari and Riahi [188]

640

>99.9

–

Najigivi et al. [189]

160 ± 20

>99.9

–

Xiao [190] , Ji [191] , Beigi et al. [192]

16

158

99.9

–

Wang et al. [193]

20

90

99.8

–

Khaloo et al. [174], Haruehansapong et al. [175]

220

99.9

–

Behfarnia and Salemi [194]

25

109

99.9

–

Zapata et al. [195]

30

80

–

–

40 80 ± 5

Zhang et al. [196] Jo et al. [197]

50

99.8

–

Haruehansapong et al. [175]

–

>99.9

–

Givi et al. [186]

(continued)

160

2 Current Progress of Nano-Engineered Cementitious Composites

Table 2.62 (continued) Nano-SiO2 form

Particle size/nm

Specific surface area/(m2/g)

Purity/ %

Nano-SiO2 concentration/%

References

Colloid

5

500

–

15

Björnström et al. [198], Aly et al. [199]

–

5

Rupasinghe et al. [200, 201]

8–20

–

–

39

Mukharjee and Barai [202]

–

–

30.3

Kong et al. [203]

9 10

300

99.4

30

Senff et al. [204, 205]

99.9

30

Ltifi et al. [206]

345

–

30

Berra et al. [207]

–

–

30

Hou et al. [208]

250

–

30

Bahadori and Hosseini [209]

99.9

15 ± 3

155 ± 12

>99.9

20

–

–

74 10–25

– –

– –

30–50

40–45

99.9

Nazari et al. [307] Soleymani [308, 309] Nazari and Riahi [310] Nazari and Riahi [311] Nazari and Riahi [312] Rafeipour et al. [313] Nazari and Riahi [314] Negahdary and Habibi [315] Silva et al. [316] Jaishankar and Mohan [317] Umarajyadav and Vahini [318]

results appeared in the study of Nazari and Riahi [310, 311] and Li et al. [319]. It is of note that Li et al. observed that the AFt crystal size within composites with ZrO2 is far smaller than that of crystals in the control cement pastes [319]. In addition, Li et al. studied the effect of nano-ZrO2 on hydration products with Si NMR [321], Gogtas detected the XRD intensity peaks of hydration products [320], and Silva et al. measured the release of calcium ion [316]. All the results indicated nano-ZrO2 does not involve more in the hydration reaction leading to the existence of new hydration phase. 2. Pore structure Researchers performed MIP experiment on nano-ZrO2-engineered cementitious composites. Their exponential results are summarized in Table 2.94. With the increasing nano-ZrO2 content, the porosity, average diameter, and total specific pore volume of nano-ZrO2-filled cementitious composites significantly decrease, and the most probable pore diameters shift to smaller pores and then fall in the range of few-harm pore. This indicates that the incorporation of nano-ZrO2 refines the pore structure of concrete, but the improvement effect on the concrete pore structure is weakened [314, 319]. The same results are also found in the study of Soleymani [308, 309], Rafieipour et al. [313], and Nazari and Riahi [312, 314]. (3) Properties/performances 1. Workability Nazari and Riahi investigated the workability of cementitious composites with nano-ZrO2 under different curing conditions. Results showed the composites with nano-ZrO2 have low slump values and non-acceptable workability. It is of note that

Crushed limestone, sand

1, 2, 3, 4, 5 (wt % of C and nano-ZrO2)

1, 2, 3, 4 (wt% of C and nano-ZrO2)

0.2, 0.4, 0.6, 0.8, 1.0, 1.2 (wt % of B)

1.5 (wt% of C and nano-ZrO2)

0.5, 1.0, 1.5, 2.0 (wt% of C and nano-ZrO2)

B:W = 1:0.4

B:W = 1:0.4

SP (1.0 wt% of W)

C:W = 1:0.25

SP (1.5 wt% of B)

SP (1.0 wt% of W), GGBFS (15, 30, 45, 60 wt% of C)

B:W = 1:0.4, S: G = 3:7

–

B:S: G = 1:1.52:2.62

B:W = 1:0.4, S: G = 3:7

–

SP (1 wt% of C)

B:W = 1:0.33

C:W = 1:0.3

–

–

Proportion of C (B), W, S, and G

Admixture type and content

Nazari and Riahi [310]

Nazari and Riahi [311]

Umarajyadav and Vahini [318]

Jaishankar and Mohan [317]

Nazari and Riahi [307], Nazari and Riahi [312], Nazari and Riahi [314], Soleymani [308, 309], Rafeipour et al. [313]

Negahdary and Habibi [315]

Silva et al. [316]

Li et al. [319]

References

Note C (B), W, S, and G denote cement (binder), water, sand, and gravel, respectively. SP denotes superplasticizer, and GGBFS denotes ground granulated blast furnace slag

Ordinary Portland cement

Coarse aggregate, sand

Ordinary Portland cement (43 grade)

High-performance concrete

Coarse aggregate (10–12 mm), nature river sand (99.8 >99.8 – –

30−50 60

– –

99.5 99

–

>202

–

10−15 50 5−8 3−8

 120 – – 130−270

 99.9 20 – >99

Li et al. [324] He and Shi [222] Arefi et al. [325] Oltulu and Sahin [176, 326] Barbhuiya et al. [327] Gurumurthy et al. [328] Miyandehi et al. [329] Murugan and Santhanam [330] Nazari et al. (2010a) [331] Nazari and Riahi [224, 332, 333] Shekari and Razzaghi [246] Agarkar and Joshi [334] Behfarnia and Salemi [194] Salemi et al. [248] Sanju et al. [335] Karthikeya and Kumar [336] Rahim and Nair [244] Sheikhaleslamzadeh and Raofi [337] Jaishankar and Karthikeyan [338] Jiang [243] Campillo et al. [339] Hase and Rathi [340] Sharbaf et al. [341]

Colloidal Flaky

products existed are mainly in the form of reticulated C–S–H gels, CH plate crystals, and needle-shaped crystals of AFt. Similar results are observed in the study of He et al. by SEM observation [336]. 2. Pore structure The effect of nano on the pore structure of cementitious composites is summarized in Table 2.105. It can be seen that with the addition of nano-Al2O3, the total porosity and most probable pore diameter/volume of cementitious composites are decreased [332, 333, 339]. The most probable pore shifts to smaller pores and falls in the range of few-harm pore, which indicates adding nano-Al2O3 refines the pore structure of cementitious composites.

0.5, 1.25, 2.5 (wt% of B) 2, 4 (wt% of C) 1 (wt% of C)

0.2 (wt% of C

Sand (  2 mm)

–

–

–

Normalized sand

Sulfate resisting cement (type I 42.5 R)

–

Ordinary Portland cement (43 Grade)

Ordinary Portland cement (53 Grade)

Belite cement 1, 3, 5 (wt% of C)

3, 9 (wt% of C)

0.5, 1.25, 2.5 (wt% of B)

Sand (  2 mm)

Sulfate resisting cement (type I 42.5 R)

Natural river sand

1, 3, 5 (wt% of C and nano-Al2O3)

Crushed silica sand (  4.75 mm)

Portland cement (type II)

Portland cement (type II)

1 (wt% of C)

River sand (  2 mm)

Portland cement (type I)

Self− compacting cement mortar

3, 5,7 (wt% of C)

Standard sand

Portland cement (325)

Nano-Al2O3 content

Ordinary cement mortar

Aggregate type and size

Cement type

Matrix type

B:W = 1:0.4

C:W:S = 1:0.8:3

– FA (25 wt% of C), SP

C:W = 1:0.32

C:W = 1:0.4

B:W = 1:0.4

B:W = 1:0.4, C: S = 1:3

SP (0.05 wt% of C)

–

–

FA (15 wt% of C), Defoamer(1 wt% of B), SP (0.75 wt% of B)

B:W = 1:0.4, C: S = 1:3

C:W:S = 1:0.42:5

SP

SF (5 wt% of C), Defoamer, SP (1 and 0.75 wt% of B)

C:W:S = 1:0.5:1

C:W:S = 1:0.4:1

– –

Proportion of C(B), W, S and G

Admixture type and content

Table 2.103 Mix proportion of nano-Al2O3−engineered cementitious composites

(continued)

Miyandehi et al. [329]

Campillo et al. [339]

Murugan and Santhanam [330]

Gurumurthy et al. [328]

Barbhuiya et al. [327]

Oltulu and Şahin [176]

Oltulu and Şahin [326]

Arefi et al. [325]

He and Shi [222]

Li et al. [324]

References

218 2 Current Progress of Nano-Engineered Cementitious Composites

Natural river sand, crushed stone (5 −12 mm)

Fine aggregate (  4.75 mm), coarse aggregate(  20 mm)

Fine river sand (  4.75 mm), coarse aggregate(  20 mm)

River sand (  4.75 mm), coarse aggregate (12.5−16 mm)

Ordinary Portland cement

Ordinary Portland cement (53 Grade)

Portland pozzolanic cement

Ordinary Portland cement (53 Grade)

Sand, crushed limestone

Natural river sand (  4.74 mm), crushed stone (  12 mm)

Ordinary Portland cement

Ordinary Portland cement

0.5, 1.0, 1.5 (wt % of C and metakaolin)

Natural sand (  0.5 mm), crushed basalt

Ordinary Portland cement (53 Grade)

Self− compacting concrete

2 (wt% of C)

Natural sand (  0.5 mm), crushed basalt(  15 mm)

Ordinary Portland cement

1, 2, 3, 4 (wt% of C)

0.5, 0.75, 1.0 (vol.% of C)

0.5, 1.0, 1.5, 2.0 (vol.% of C)

1, 2, 3 (wt% of C)

0.5, 1.0, 1.5, 2.0 (wt% of C)

0.5, 1.0, 1.5, 2.0 (wt% of C)

0.5, 1.0, 1.5, 2.0 (wt% of C)

Natural sand (  0.5 mm), crushed basalt (  15 mm)

Ordinary Portland cement

Nano-Al2O3 content

Ordinary oncrete

Aggregate type and size

Cement type

Matrix type

Table 2.103 (continued)

B:W:S: G = 1:0.4:0.89:2.09 –

–

–

GGBFS (45 wt% of C), SP (1 wt % of W)

SP

GGBFS (50 wt% of C)

Metakaolin (15 wt% of C and metakaolin), SP (1 wt% of C and metakaolin)

SP (0.5 wt% of C)

B:W = 1:0.4:

C:W = 1:0.33

B:W:S: G = 1:0.5:1.71:2.85

B:W:S: G = 1:0.38:1.87:3.20

B:W:S: G = 1:0.48:2.74:2.63

B:W:S: G = 1:0.48:2.74:2.63

B:W:S: G = 1:0.4:0.89:2.09

–

SP (0.5 wt% of C)

Proportion of C(B), W, S and G

Admixture type and content

(continued)

Nazari and Riahi [333]

Jaishankar and Karthikeyan [338]

Karthikeya and Kumar [336]

Sanju et al. [33]

Salemi et al. [248]

Behfarnia and Salemi [194]

Agarkar and Joshi [334]

Nazari and Riahi [224]

Nazari et al. [331]

References

2.3 Current Progress of Specific Type of Nano-Engineered … 219

Fine aggregate, coarse aggregate (  12.5 mm)

Sand, gravel (  12.5 mm)

Quartz sand (0.12– 0.83 mm)

Ordinary Portland cement (53 Grade)

–

Ordinary Portland cement (42.5R)

Fiber− reinforced concrete

Reactive powder concrete

0.5, 1, 1.5 (wt% of C)

1, 2, 4 (wt% of C)

2, 3, 4, 5, 6 (wt % of C)

1, 2, 3, 4 (wt% of C)

0.5, 1, 2, 4, 8 (wt% of C)

1.5 (wt% of C and metakaolin)

Nano-Al2O3 content

SP (0.7 wt% of C), FA (15 wt% of C), SF (31 wt% of C)

Polypropylene fiber(0.2 wt% of C), super lubricants (1.5 wt% of C)

GGBFS (40 wt% of C), SP

SP (1 wt% of C)

SP (1.2 wt% of B)

Metakaolin(15 wt% of C and metakaolin), SP (1.5 wt% of C and metakaolin)

Admixture type and content

C:W: S = 1:0.375:1.375

Jiang [243]

Sheikhaleslamzadeh and Raofi [337]

Rahim and Nair [244]

–

C:W = 1:0.45

Hase and Rathi [340]

Sharbaf et al. [341]

Shekari and Razaghi [246]

References

C:W = 1:0.26

C:W:S: G = 1:0.35:2.6:2.24

B:W = 1:0.25

Proportion of C(B), W, S and G

Note C (B), W, S and G represent cement (binder), water, sand and gravel, respectively. SP represents superplasticizer, SF represents silica fume, FA represents fly ash, and GGBFS represents ground granulated blast furnace slag

Crushed sand, coarse aggregate

Ordinary Portland cement (53 Grade)

River sand,crushed coarse aggregates (  19 mm)

Portland cement (type I 42.5)

High strength concrete

Fine aggregate (  4.75 mm), coarse aggregate(  19 mm)

Ordinary Portland cement

High performance concrete

Aggregate type and size

Cement type

Matrix type

Table 2.103 (continued)

220 2 Current Progress of Nano-Engineered Cementitious Composites

Shear mixing

SP + C S

FA + 30%W + nanoAl2O3 – 70%W + SP W + nano-Al2O3 Rest Mix Stir (250 −300 rpm) Mix Mix

Stir (80 rpm) Mix

G + C + nano-Al2O3 W

S+C

Mix Stir

W C + nano-Al2O3

Shear mixing

Shear mixing + sieving Shear mixing

S + nano-Al2O3

Shear mixing

30S –

1.5 min 1 min 6−10 h

1 min

1 min

2 min 3 min

10 min –

5 min

Technology Method Time Stir (high speed) Stir Mix

Fabrication progress Feeding order

Dispersion method of nano-Al2O3 –

–

75  25  25 (tensile test), 50  50  50 (compressive test), 40  40  160 (flexural test)

50  50  50

–

–

W/ saturated limewater (20 °C)

U150  300 (split tensile test), 200  50  50 (flexural test)

Vibration

W

W

W

W (20 °C)

Curing Condition

50  50  50

Vibration

Size/mm

Molding Method

Table 2.104 Main fabrication process of nano-Al2O3−engineered cementitious composites

7d

3, 7, 28, 90 d

1, 3, 7d 7, 28, 90 d

7, 28 d

Time

(continued)

Arefi et al. [325]

Barbhuiya et al. [327] Nazari et al. [331], Nazari and Riahi [224, 332] Miyandehi et al. [329]

Li et al. [324]

References

2.3 Current Progress of Specific Type of Nano-Engineered … 221

C + SF/FA

Shear mixing

G+S+C

Shear mixing

W + SP + nano-Al2O3 (in sequence) –

W + nano-Al2O3 C

Ultrasonication

1/5 W

– 1/5 W + SP

3/ 5 W + defoamer + nanoAl2O3 (in sequence) –

S

Fabrication progress Feeding order

Dispersion method of nano-Al2O3

Table 2.104 (continued)

5 min 2 min

Mix

2 min

– –

1 min

5 min 1 min

1 min

15 min

1 min

1 min

Stir (140 rpm) Rest Stir (140 rpm) Stir (140 rpm) Sonicate Manual mixing Mix (low speed) Stir

Stir (140 rpm) Stir (140 rpm) Stir (1000 rpm)

Technology Method Time

Vibration

–

Vibration (10 s)

Molding Method

W

Moist room

70  70  70

Saturated limewater (20 ± 2 ° C)

20  20  20 (compressive test), 20  20  80 (flexural test)

50  50  50

Size/mm

Curing Condition

7, 28, 120 d

28 d

3, 7, 28, 56, 180 d

Time

(continued)

Behfarnia and Salemi [194]

Gurumurthy et al. [328]

Oltulu and Şahin [177, 327]

References

222 2 Current Progress of Nano-Engineered Cementitious Composites

Fabrication progress Feeding order Technology Method Time

Molding Method Size/mm

Curing Condition Time

References

Shear mixing

C+S+G W + SP + nano-Al2O3 (in sequence) – C + S + metakaolin 30% W + SP + nano-Al2O3 70%W W + SP + nano-Al2O3

Mix 1 min – 70  70  70 (compressive W 7, Sharbaf et al. test), 10  10  10 (sorptivity (20 ± 1 ° 28, [341] Stir 5 min and water absorption tests) C) 90 d (120 rpm) Mix 10 min Shear mixing Mix 2 min – 100  100  100(compressive W 28 d Sanju et al. test, water absorption and rapid [335] Stir 5 min chloride permeability tests), (350 rpm) U100  200 (split tensile test) Mix 3 min Mix (low 20 s Vibration 40  40  160 (Strength test) Standard 3, 28 Jiang [243] Shear mixing speed) (60 s) curing d + Non-covalent surface SF Mix (low 60 s modification by speed) SP C + FA Mix (low 2 min speed) Mix(high 2 min speed) S Mix (low 1 min speed) Mix(high 4 min speed) Note C, S, W and G represent cement, sand, water and gravel, respectively. SP represents superplasticizer, SF represents silica fume, and FA represents fly ash

Dispersion method of nano-Al2O3

Table 2.104 (continued)

2.3 Current Progress of Specific Type of Nano-Engineered … 223

7d Abs./%

Rel./%

Decrease Total porosity

90 d Abs./%

Ordinary cement mortar

0.9 1.19 0.08 0.26 –

6.80 8.99 0.60 1.96 –

– – – – Ordinary concrete 0.425/ 1.428 – – 0.855/ 1.617 – – 0.687/ 1.764 – – 0.152/ 1.943 Self-compacting – – 0.89 concrete – – 1.04 – – 1.12 – – 1.08 Note Abs. and Rel. represent the absolute and relative

Matrix type

– – – – – – – – 4.25/ 6.3/10.5 14.08 8.56/ 11.5/15.7 15.94 6.88/ 9.4/17.8 17.39 1.52/ 3.1/21 19.15 13.28 – 15.52 – 16.72 – 16.12 – value, respectively

Rel./%

– – –

– – – 2.3 3.2 3.2 2.3

27.38/ 37.38 22.38/ 42.38 7.38/50 – – – –

19.17 26.67 26.67 19.17

– – – – –

– – – – –

Most probable pore diameter 90 d Abs./nm Rel./%

– – – – 15/7.38

Most probable pore volume 90 d Abs./ Rel./% (mL/g)

Table 2.105 Effect of nano-Al2O3 on the pore structure of cementitious composites

0.6 (colloidal) 1.8 (colloidal) 3 (powder) 9 (powder) 0.5 (water/ limewater) 1.0 (water/ limewater) 1.5 (water/ limewater) 2.0 (water/ limewater) 1 2 3 4

Nano-Al2O3 comtent/%

Nazari and Riahi [333]

Nazari and Riahi [332]

Campillo et al. [339]

References

224 2 Current Progress of Nano-Engineered Cementitious Composites

2.3 Current Progress of Specific Type of Nano-Engineered …

225

In addition, He and Shi analyzed the structure of cement mortars after 28 d of curing through the electrochemical impedance spectroscopy test. They observed that adding nano-Al2O3 into cement pastes increases the ionic transport resistance but decreases its electric capacitance. This confirmed that the incorporated nano-Al2O3 leads to denser microstructure of cementitious composites [222]. (3) Properties/performances 1. Workability Nazari and Riahi investigated the workability of nano-Al2O3-modified concrete through standard slump tests. They discovered concrete containing nano-Al2O3 has low slump values and non-acceptable workability [332]. Agarkar and Joshi observed 2% of nano-Al2O3 leads to a reduction in the concrete workability of 75% [334]. The influence mechanism of nano-Al2O3 particles to the workability of concrete can be interpreted as follows. Nano-Al2O3 with ultrahigh specific surface area has stronger attraction to water than that of cement particle. As a result, the amount of lubricating water available in the fresh concrete is decreased. However, Miyandehi et al. performed the standard slump test to self-compacting cement mortars with different nano-Al2O3 contents. They observed that the addition of nano-Al2O3 increases the slump flow diameter of fresh cement mortars but shortens the flow time (as listed in Table 2.106) [329]. 2. Hydration (i) Hydration process Nazari and Riahi measured the weight loss of concrete with nano-Al2O3 by the TG analysis [332, 333]. Results showed the incorporation of nano-Al2O3 significantly increases the weight loss of concrete, but the increment is decreased with increasing nanoparticle content. They suggested that more C–S–H gels are formed during the hydration due to the presence of nano-Al2O3. (ii) Hydration heat Nazari and Riahi investigated the hydration heat of concrete through conduction calorimetry test [224, 332]. They found that decreasing the percentage of nano-Al2O3 particles in the cement pastes retards peak times and raises heat release rate. What’s more, the nano-Al2O3-modified concrete cured in saturated limewater shows a shorter peak time and lower heat release rate with respect to the concrete cured in water. This is indicative of a delay in initial cement hydration for the concrete cured in water.

226

2 Current Progress of Nano-Engineered Cementitious Composites

Table 2.106 Effect of nano-Al2O3 on the workability of cementitious composites Matrix type

Increase/decrease Slump flow diameter Abs./mm Rel./%

V-funnel flow time Abs./s Rel./%

Nano-Al2O3 content/ %

3 1.2 −0.4 −3.6 1 3 2.0 −1 −9.1 3 5 2.0 −1 −9.1 5 Note Abs. and Rel. represent the absolute and relative value, respectively Self-compacting cement mortar

Reference

Miyandehi et al. [329]

(iii) Setting time Nazari et al. studied the initial and final setting times of cement mortars with nano-Al2O3. They found that the provision of nano-Al2O3 significantly shortens the setting time of the cement mortars [331]. Furthermore, Nazari and Riahi further observed the reduction in setting time of cement mortars with nano-Al2O3 cured in saturated limewater is more evident than that of cement mortars with nano-Al2O3 cured in water [332]. In brief, nano-Al2O3 with its unique surface effects, smaller particle sizes, and higher surface energy remarkably accelerates the cement hydration in the nano-Al2O3-modified cement mortars. 3. Mechanical properties/performances (i) Strength Most researchers investigated the effects of nano-Al2O3 on the strength of cementitious composites and found that the incorporated nano-Al2O3 significantly improves the compressive, flexural, tensile, and split tensile strengths of cementitious composites [18, 19, 21, 22, 24, 243, 244, 246, 248, 328, 331–334, 340]. Some researchers observed that excessive nanoparticles lead to a defect in the matrix, which is not conducive to the development of strength [177, 325, 326, 341]. Compared with the concrete with nano-Al2O3 cured in water, concrete with nano-Al2O3 cured in limewater has higher compressive strength [332]. The experimental results are summarized in Tables 2.107 and 2.108. For cement mortars with nano-Al2O3, the maximum growth ratio of compressive strength, flexural strength, and split tensile strengths reaches 119%, 24.3%, and 55.55% at 28 d compared with control cement mortars, respectively. For concrete with nano-Al2O3, the maximum growth rate of those strengths is 56.98%, 44.93%, and 52.38% at 28 d, respectively. The influence mechanisms of nano-Al2O3 on the strength of cementitious composites are proposed as follows. Firstly, nano-Al2O3 particles work as filler and lead to a denser and less permeable microstructure of cementitious composites. Secondly, nano-Al2O3 particles act as a nucleus to guide the formation and growth of cement hydration products. Moreover, the nanoparticles located in cement pastes as kernel can further promote cement hydration due to their high activity. This

Split tensile

Tensile

Flexural

Compressive

Belite cement pastes

Ordinary cement mortar

Strength

Matrix type

– – – – –

–

–

–

–

–

–

–

– –

–

–

–

–

–

–

– –

–

–

– –

–

–

–

–

−5.1

2.7

0.97 –

0.5

0.18

−1.85

−6

−2.5

–

11

4.9

−1.06

–

– –

–

–

1

–

–

–

–

–

0.4

7.58

–

–

Abs./MPa

–

0.3

0.9

1.1

0.7

−0.11

1.23

1.01

0.2

0.8

1.1

–

−0.16

1.54

1.05

0.4

–

−0.79

1.67

0.5

−2.2

7.3

1.1

5.29

3.7

3.9

3.4

2.3

Rel./% –

Abs./MPa

7d

3d

Increase/decrease Rel./%

20

60

73.33

46.67

−7.3

81.46

66.89

4.76

19.05

26.19

–

−7.27

70

47.73

9.52

–

−1.8

3.9

1.2

−4

13

2

−8.86

63.38

44.23

142

96

84

56

0.1

0.7

1.0

0.5

–

–

–

0.4

0.6

0.8

1.096

–

–

–

0.7

6.88

−0.83

1.95

0.73

3.4

11.5

3.3

–

–

–

10.0

7.2

9.5

7.5

Abs./MPa

28 d Rel./%

5.56

38.89

55.55

27.78

–

–

–

9.09

13.64

18.18

24.3

–

–

–

15.91

24.11

−1.8

4.3

1.6

6

20

6

–

–

–

119

85

113

89

2

1.5

1

0.5

5

3

1

2

1.5

1

1

5

3

1

0.5

1

2.5

1.25

0.5

2.5

1.25

0.5

5

3

1

9 (powder)

3 (powder)

1.8 (colloidal)

0.6 (colloidal)

Nano-Al2O3 content/%

Table 2.107 Effect of nano-Al2O3 on the strength of cementitious composites at curing age from 3 d to 28 d

Nazari et al. [331]

Arefi et al. [325]

Nazari et al. [331]

(continued)

Gurumurthy et al. [328]

Arefi et al. [325]

Gurumurthy et al. [328]

Oltulu and Sahin [176]

Oltulu and Sahin [326]

Arefi et al. [325]

Campillo et al. [339]

References

2.3 Current Progress of Specific Type of Nano-Engineered … 227

Self-compacting concrete

Compressive

Ordinary concrete

Split tensile

Flexural

Compressive

Split tensile

Strength

Matrix type

Table 2.107 (continued)

– – – – – – – – – – – – – – –

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

Rel./%

80

100

0.8

70

1.0

50

64.29

73

53.57

39.29

81.88

96.88

67.50

51.25

–

–

–

–

–

–

8.0

0. 7

16.85

16.12

11.36

0.73/44.8

16.85/35.9

16.12/23.3

11.36/15.2

0.7

0.5

1.8

2.1

1.5

1.1

13.1

15.5

10.8

8.2

–

–

–

–

–

–

2.2

0.2

4.6

4.4

3.1

0.2/12.1

4.6/9.7

4.4/6.3

3.1/4.1

Abs./MPa

Rel./% –

Abs./MPa

7d

Increase/decrease

3d

0.9

1.1

0.9

0.6

1.1

1.7

1.0

0.5

20.7

24.9

19.8

13.7

0.83

0.66

0.42

–

–

11.44

6.34

1.64

5.3

1.1

6.0

5.5

4.3

0.9/15.6

6.0/12.7

5.5/10.8

4.3/8.1

Abs./MPa

28 d Rel./%

42.86

52.37

42.86

28.57

20.37

31.5

18.52

9.26

47.37

56.98

45.31

31.35

27.12

21.57

13.73

35.9

27.1

43.61

24.17

6.25

12.6

3.51

16.30

14.95

11.68

2.45/44.1

16.30/35.9

14.95/30.5

11.68/22.8

4

3

2

1

4

3

2

1

4

3

2

1

1

0.75

0.5

1

1

1

0.75

0.5

2

2

1.5

1

0.5

2.0 (water/limewater)

1.5 (water/Limewater)

1.0 (water/limewater)

0.5 (water/limewater)

Nano-Al2O3 content/%

(continued)

Nazari and Riahi [333]

Jaishankar and Karthikeyan [338]

Sanju et al. [335]

Jaishankar et al. [338]

Salemi et al. [248]

Agarkar and Joshi [334]

Nazari and Riahi [332]

References

228 2 Current Progress of Nano-Engineered Cementitious Composites

Compressive

High performance concrete

Flexural

Strength

Matrix type

Table 2.107 (continued)

– – – – – – – – –

–

–

–

–

–

–

–

–

–

–

– – – – – – – –

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

Rel./%

−5.7

–

–

–

1.83

2.66

1.5

0.83

−8.1

−9.3

–

–

–

68.54

99.63

56.18

31.09

−20.5

−23. 5

−14.4

−15.7

9.0

3.6 −6.2

–

–

–

–

2.97

5.94

–

–

–

–

1.4

2.8

6.58

10.4

3.1

3.61

4.9

14.68

26.94

18.48

15.34

–

1.7

2.9

5.32

3.65

3.03

–

Abs./MPa

Rel./% –

Abs./MPa

7d

Increase/decrease

3d

1

1.13

0.5

1.5

2.17

1.43

0.84

−6.2

−7.1

−10

−9.3

3.2

11.70

14.3

9.20

6.40

5.79

7.59

8.39

11.04

6.69

3.53

5.57

4.68

3.14

50.8

Abs./MPa

28 d Rel./%

11.11

12.56

5.56

31.06

44.93

27.74

17.39

−13.5

−15.6

−21.9

−20.3

7.1

16.93

20.7

13.31

9.26

8.95

11.73

12.97

17.06

10.34

11.67

18.42

15.48

10.39

55.0

4

3

2

2

1.5

1

0.5

8

4

2

1

0.5

4

3

2

1

6

5

4

3

2

2

1.5

1

0.5

1.5

Nano-Al2O3 content/%

(continued)

Rahim and Nair [244]

Karthikeya and Kumar [336]

Sharbaf et al. [341]

Hase and Rathi [340]

Rahim and Nair [244]

Karthikeya and Kumar [336]

Shekari and Razzaghi [246]

References

2.3 Current Progress of Specific Type of Nano-Engineered … 229

Flexural

Compressive

Split tensile

Strength

– – – – – – – – – – – −3 −7.2 −10.2

–

–

–

–

–

–

–

–

–

–

–

–

−1.96

−4.73

−6.68 1.9

–

–

15.7

–

–

0.14

–

–

1.2

–

–

24

–

–

0.18

–

–

Rel./%

– – – –

– – –

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

24.87

38.58

0.76 0.49

21.83

14.21

–

–

–

–

–

–

0.43

0.28

–

–

–

–

–

–

Abs./MPa

Rel./% –

Abs./MPa

7d

Increase/decrease

3d

Note Abs. and Rel. represent the absolute and relative value, respectively

Reactive powder concrete

Matrix type

Table 2.107 (continued)

−0.99

−2.17

0.3

−3.32

−7.74

4.46

1.4

2.0

1.4

1.0

0.1

0.25

0.3

0.48

0.12

0.37

0.9

0.57

0.4

1.9

2.5

2.1

1.6

0.5

0.75

Abs./MPa

28 d Rel./%

−5.8

−12.9

1.8

−3.7

−8.6

5

22.58

32.25

22.58

16.12

2.86

7.14

8.57

13.71

3.43

13.41

32.61

20.65

14.49

28.35

37.31

31.34

23.80

5.56

8.33

1.5

1

0.5

1.5

1

0.5

4

3

2

1

6

5

4

3

2

2

1.5

1

0.5

4

3

2

1

6

5

Nano-Al2O3 content/%

Jiang [243]

Hase and Rathi [340]

Rahim and Nair. [244]

Karthikeya and Nair [336]

Hase and Rathi [340]

References

230 2 Current Progress of Nano-Engineered Cementitious Composites

Compressive

Ordinary cement mortar

Compressive

Compressive

Ordinary concrete

Self-compacting concrete

Split tensile

Flexural

Strength

Matrix type

– – – –

–

–

–

–

– –

–

–

– –

–

–

– –

–

–

– –

–

–

–

–

5.6

2.85 0.4

2.7

1.39

–

7

4.5

0.2

22

13.9

–

7

Rel./%

– – – –

– – – –

16.6

12.2

0.3/11.3

3/9.2

3.8/6.9

1.8/4.2

0

0.5

0.8

0.3

0.1

0.6

2.7

27.1

19.9

0.7/28.5

7.09/23.1

9.0/17.3

4.3/10.6

0

21.7

34.8

13.0

2.1

12.8

57.5

21.3

–

–

1

Rel./% –

Abs./MPa –

Abs./MPa

4.4

90 d

56 d

Increase/decrease

–

–

–

–

–

–

–

–

–

–

–

–

–

–

−0.25

2.94

0.87

5.7

13.9

4.9

Abs./MPa

180 d

Table 2.108 Effect of nano-Al2O3 on the long-term strength of cementitious composites

Rel./%

–

–

–

–

–

–

–

–

–

–

–

–

–

–

−0.4

5.0

1.5

9

21

8

2

1

2.0 (water/limewater)

1.5 (water/limewater)

1.0 (water/limewater)

0.5(water/limewater)

2.0

1.5

1.0

0.5

2.0

1.5

1.0

0.5

2.5

1.25

0.5

2.5

1.25

0.5

Nano-Al2O3 content/%

(continued)

Nazari and Riahi [333]

Nazari and Riahi [332]

Nazari et al. [331]

Nazari et al. [331]

Oltulu and Sahin [176]

Oltulu and Sahin [326]

References

2.3 Current Progress of Specific Type of Nano-Engineered … 231

Compressive

Split tensile

Flexural

Strength

– – –

–

–

–

– –

–

–

– –

–

–

– –

–

–

– –

–

–

– –

–

–

–

–

–

Rel./%

−14.4 −12. 5

−6.1

−19.8

−19.3

9.9

51.7

58.6

44.8

20.7

13.7

19.2

11.0

−4.1

33.3

38.1

−7.1

−9.7

−9.4

4.8

1.5

1.7

1.3

0.6

1.0

1.4

0.8

−0.3

20.4

23.3

Abs./MPa

Rel./% –

Abs./MPa

90 d

Increase/decrease

56 d

Note Abs. and Rel. represent the absolute and relative value, respectively

High performance concrete

Matrix type

Table 2.108 (continued)

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

Abs./MPa

180 d Rel./%

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

8

4

2

1

0.5

4

3

2

1

4

3

2

1

4

3

Nano-Al2O3 content/%

Sharbaf et al. [341]

References

232 2 Current Progress of Nano-Engineered Cementitious Composites

2.3 Current Progress of Specific Type of Nano-Engineered …

233

Table 2.109 Effect of nano-Al2O3 on the hardness and toughness of cementitious composites Matrix type

Increase of toughness (dimensionless)

Ordinary cement mortar

Abs./

Rel./%

0.53

53

Nano-Al2O3 content/%

Reference

1

Gurumurthy et al. [328]

Note Abs. and Rel. represent the absolute and relative value, respectively

makes the matrix become more homogeneous and compact. Thirdly, the nanoparticles may promote the formation of high-density C–S–H structures via parallel packing [222, 324]. (ii) Hardness and toughness Gurumurthy et al. measured the toughness of cementitious composites with nano-Al2O3, respectively [328]. The results as listed in Table 2.109 indicated that the values of the two indexes are increased as the nano-Al2O3 is incorporated. (iii) Deformation Li et al. studied the deformation behavior of cementitious composites with nano-Al2O3 at different curing ages [324]. As seen from Table 2.110, the incorporated nano-Al2O3 significantly enhances the elastic modulus of cement mortars. The largest increase for the elastic modulus is occurred for 5% of nano-Al2O3-filled cement mortars at the curing age of 28 d, and this increased value can be up to 243%. 4. Durability (i) Water absorption and capillary absorption Researchers studied the water absorption and capillary absorption of cementitious composites with nano-Al2O3. In their studies, the parameters including percentage of capillary absorption [177, 326], water absorption [329, 333, 194], and the initial water absorption [340] are measured. It can be seen from Table 2.111 that the water absorption and capillary absorption of cementitious composites decrease significantly as nano-Al2O3 is incorporated.

Table 2.110 Effect of nano-Al2O3 on the elastic modulus of cementitious composites Matrix type

Increase in elastic modulus Abs./GPa

Rel./%

Abs./GPa

Rel./%

Abs./GPa

Rel./%

Ordinary cement mortar

–

135

–

133

–

–

154

–

241

–

–

–

209

3d

7d

Nano-Al2O3 content/%

Reference

139

3

–

243

5

Li et al. [324]

–

208

7

28 d

Note Abs. and Rel. represent the absolute and relative value, respectively

234

2 Current Progress of Nano-Engineered Cementitious Composites

Table 2.111 Effect of nano-Al2O3 on the water absorption of cementitious composites Matrix type

Parameter

Increase/decrease Abs. Rel. %

Nano-Al2O3 content/%

References

Cement mortar

Capillary absorption (28 d)/%

– – – – – – – – −1.34 −1.43 −1.58 −1.50 −0.96 −1.16 −1.40 –

0.5 1.25 2.5 0.5 1.25 2.5 1 3 1 2 3 4 1 2 3 1.5

Oltulu and Sahin [326]

Water absorption (28 d)/% Self-compacting concrete

Water absorption (28 d)/%

Ordinary concrete

−12 −29 −15 3 4 10 −4.2 −1.6 −39.30 −41.94 −46.33 −43.99 −15.56 −18.80 −22.69 −30.6

0.32 24.2 0.5 0.12 9.1 1 0.22 16.7 2 0.44 33.3 4 0.59 −44.7 8 Note Abs. and Rel. represent the absolute and relative value, respectively High performance concrete

Initial water absorption/((1 h)/ (kg/m2))

Oltulu and Sahin [177] Miyandehi et al. [329] Nazari and Riahi [333]

Behfarnia and Salemi [194] Sanju and Kumar [336] Sharbaf et al. [341]

(ii) Freeze-thaw resistance Behfarnia and Salemi [194] and Salemi et al. [248] investigated the effect of nano-Al2O3 on the freeze-thaw resistance of cementitious composites. As listed in Table 2.112, the loss of mass, change in length, water absorption, and compressive strength loss of concrete are all declined due to the addition of nano-Al2O3, which means the nano-Al2O3 improves the freeze-thaw resistance of cementitious composites. (iii) Wear resistance Nazari and Riahi observed the depth of wear of concrete is significantly decreased with the addition of nano-Al2O3, regardless of whether the concrete is cured in water or saturated limewater. Compared with the water curing, the limewater curing is more conducive to decrease the depth of wear of concrete with nano-Al2O3 [224]. The experimental results are listed in Table 2.113.

Abs./g

Rel./%

76.16

78.69

81.81

76.9

Abs./MPa

–

–

–

–

–

–

–

–

Mass loss

Decrease (300 cycles)

Strength loss

–

86.26

83.14

79.30

Rel./%

–

–

–

–

Abs./mm

Length

Note Abs. and Rel. represent the absolute and relative value, respectively

Ordinary concrete

Matrix type

–

86.44

83.02

79.29

Rel./%

85.07

87.47

77.35

66.89

Abs./%

72.60

74.65

66.01

57.08

Rel./%

Water absorption

Table 2.112 Effect of nano-Al2O3 on the freeze-thaw resistance of cementitious composites

2

3

2

1

Nano-Al2O3 content/%

Salemi et al. [248]

Behfarnia and Salemi [194]

References

2.3 Current Progress of Specific Type of Nano-Engineered … 235

Decrease in depth of wear 7d 28 d Abs./mm Rel./% Abs./mm Rel./%

1/1.5 20.4/28.9 1.6/2.6 43.2/59.1 1.6/2.2 32.7/42.3 2.2/2.1 59.5/70.4 1.7/2.4 34.7/46.2 2.3/3.6 62.2/77.3 1.9/2.5 38.8/48.1 2.4/3.1 64.9/81.8 Note Abs. and Rel. represent the absolute and relative value, respectively

Ordinary concrete

Matrix type

11.6 1.6/2.5 2/2.9 2.2/3

90 d Abs./mm

Table 2.113 Effect of nano-Al2O3 on the abrasion resistance of cementitious composites

35.7/45.7 57.1/71.4 71.4/82.9 78.6/85.7

Rel./% 1 2 3 4

(water/limewater) (water/limewater) (water/limewater) (water/limewater)

Nano-Al2O3 content/%

Nazari and Riahi [224]

Reference

236 2 Current Progress of Nano-Engineered Cementitious Composites

Increase/decrease in condition of accelerated corrosion Weight loss Corrosion rate Abs./gms Rel./% Abs./mpy Rel./% −27.42/ −37.42 15.65/14.00

104.33/ 60.87

Increase/decrease in condition of non-destructive corrosion Potential Resistivity Abs./mV Rel./% Abs./kX.cm Rel./%

Ordinary −5.66/ −60.66/ −190.42/ −60.66/ −151.75/ concrete −1.00 −37.45 −33.65 −37.46 −1115.25 Note Abs. and Rel. represent the absolute and relative value, respectively

Matrix type

Table 2.114 Effect of nano-Al2O3 on the chemical attack resistance of cementitious composites

3 (5% NaCl/5% H2SO4 solution)

Nano-Al2O3 content/%

Rahimand Rair [244]

Reference

2.3 Current Progress of Specific Type of Nano-Engineered … 237

238

2 Current Progress of Nano-Engineered Cementitious Composites

(iv) Chemical attack Rahim and Nair studied the anti-ion erosion of nano-Al2O3-filled concrete. In their study, different saltine solutions and corrosion conditions are considered (as listed in Table 2.114). The results proved the significant improvement of nano-Al2O3 on the resistance to harmful ion erosion of concrete [244]. Miyandehi et al. conducted the rapid chloride penetration test and resistivity test on the cement mortars with nano-Al2O3. They confirmed using nano-Al2O3 can improve the resistance of cement mortars to chloride permeability dramatically. The electrical resistivity of cement mortars can be enhanced by 10–20 kX cm as the nano-Al2O3 content increases from 1 to 5% [329].

2.3.12 Current Progress of Nano-MgO-Engineered Cementitious Composites (1) Fabrication/processing The properties of nano-MgO powder used to fabricate cementitious composites are listed in Table 2.115. The mix proportion and main fabrication progress of nano-MgO-engineered cementitious composites are summarized in Tables 2.116 and 2.117, respectively. (2) Structures Ye et al. observed the XRD patterns of cement pastes containing 6% of nano-MgO cured in water at different times and conditions. When the composites are cured in 20 °C water, regardless of the curing ages of 28 d, 180 d, or 365 d, the crystal phases including CH, Mg(OH)2, and AFt appeared in the hydration products. Additionally, the a-quartz and nano-MgO are also observed in the composites [343]. (3) Properties/performances 1. Workability Ahmed and Kumari found most of the modified expanded polystyrene concrete display good workability, while the incorporation of nano-MgO particles significantly decreases its workability [344]. This can be attributed to the high surface area Table 2.115 Properties of nano-MgO Nano-MgO form

Particle size/nm

Surface volume ratio/(m2/g)

References

Powder

100 50 30−80 40−50

– – –  30

Polat et al. [342] Ye et al. [343] Ahmed and Kumari [344] Jiang [243]

Quartz sand (0.12–0.83 mm)

0.5, 1, 1.5 (wt % of C)

SP(0.7 wt% of C), FA(15 wt % of C), SF (31 wt% of C)

C:W: S = 1:0.375:1.375

B:W = 1:0.32, S: G = 0.74:1

B:W:S = 1:0.5:3

–

SP(1.4 wt% of B), FA(30 wt % of B), SF (8 wt% of B), GGBS (14 wt% of B)

B:W: S = 1:0.3:2.75

B:W = 1:0.28

Proportion of C (B), W, S and G

SP (1.5 wt% of B)

–

Admixture type and content

Jiang [243]

Ahmed and Kumari [344]

Ye et al. [343]

Polat et al. [342]

Ye et al. [343]

References

Note C (B), W, S and G represent the cement (binder), water, sand and gravel, respectively; SP denotes superplasticizer, FA denotes fly ash, SF stands for silica fume, and GGBS represents ground granulated blast slag

Ordinary Portland cement (42.5R)

Reactive powder concrete

1, 2, 3, 4, 5 (wt% of C and nano-MgO)

Modified expanded polystyrene fine aggregate (4.75−20 mm), modified expanded polystyrene coarse aggregate (99.99 >99 99 >99.5

50−60 20−30

17  15

99  99.9

Rezaand Saeed [348] Behfarnia et al. [259] Albashir et al. [349] Nivethitha and Dharmar [350] Singh and Tiwari [351] Jiang [243]

0.2, 0.4, 0.6, 0.8, 1.0 (wt% of C) 1, 3, 5 (wt% of B)

0.05,0.1,0.2,0.5,1.0 (wt% of B)

–

Nature river sand

Crushed basalt, fine sand

Crushed basalt (99

Miyandehi et al. [369]

262

2 Current Progress of Nano-Engineered Cementitious Composites

Table 2.137 Mix proportion of nano-CuO-engineered cementitious composites Matrix type

Cement type

Aggregate type and size

Nano-CuO content

Admixture type and content

Proportion of C (B), W, S and G

References

Self− compacting concrete

Ordinary Portland cement

Crushed limestone, sand

1, 2, 3, 4, 5 (wt% of C)

SP (1 wt% of C)

B: W = 1:0.4

Nazari and Riahi (2011 l) [365]

Ordinary Portland cement

Crushed limestone, sand

1, 2, 3, 4 (wt% of C)

GGBFS (15, 30, 45, 60 wt % of C) SP (1 wt% of W)

B: W = 1:0.4

Nazari et al. [366]

Portland cement (type II)

River sand

1, 2, 3, 4, 5 (wt% of B)

FA (25 wt% of C) SP

B: W = 1:0.4, C:S = 1:2.3

Madandoust et al. [367]

Portland cement (type II)

Natural river sand (2.25 fineness modulus)

1, 2, 3, 4 (wt% of B)

FA (20, 25, 30 wt% of B) SP

B: W = 1:0.4

Khotbehsara et al. [368]

Ordinary cement mortar

Ordinary Portland cement (type I)

Natural river sand

0, 1, 2, 3 (wt% of B)

RHA (20, 25, 30 wt% of B), SP (0.6, 0.7, 0.85, 1 wt% of B)

B: W = 1:0.4

Miyandehi et al. [369]

Ordinary concrete

Ordinary Portland cement

Crushed basalt, natural sand (2.25 fineness modulus)

0.5, 1.0, 1.5, 2.0 (wt % of C)

–

B: W = 1:0.4

Riahi and Nazari [370]

Self− compacting cement mortar

Note C (B), W, S and G represent cement (binder), water, sand and gravel, respectively. GGBFS represents ground granulated blast furnace slag, FA represents fly ash, RHA represents rice husk ash, and SP represents superplasticizer

3. Crack Nazari and Riahi observed that the incorporation of nano-CuO leads to cracks in the ITZ (especially in the aggregate–cement paste transition zone) in the self-compacting concrete. They suggested that the C–S–H gels formed around the cement particles can maintain its coherency with nano-CuO because both C–S–H gels and nanoparticle have nanoscale dimensions. However, the size of aggregate particles in the concrete is too large, which makes the C–S–H gels formed around the aggregate has a completely incoherent interface with aggregate. As a result, more voids are formed in ITZ of cementitious composites, thus causing more defects in ITZ [365].

S+C SP + W + 75% nano-CuO G SP + W + 25% nano-CuO – S+C W + 75% nanoCuO FA –

Shear mixing

– 1 min

5 min 1 min –

– 3 min

1 min 3 min

Time

W (21 ± 2 °C)

W (20 °C)

100  100  100 (compressive test)

50  50  50 (compressive, flexural and durability test)

Curing Condition

Molding Size/mm

2, 7, 28 d

2, 7, 28 d

Time

– 90 s SP + W + 25% 2 min nano-CuO Note C, W, S, and G represents cement, water, sand and gravel, respectively. FA denotes fly ash, and SP denotes superplasticizer

– Mix (120 rpm) stop Mix

Homogenize Stir (high speed) – Stir (high speed) Mix Mix –

Fabrication progress Feeding order Technology Method

Dispersion method of nano-CuO

Table 2.138 Main fabrication process of nano-CuO-engineered cementitious composites

Madandoust et al. [367]

Nazari and Riahi [365]

References

2.3 Current Progress of Specific Type of Nano-Engineered … 263

264

2 Current Progress of Nano-Engineered Cementitious Composites

Table 2.139 Effect of nano-CuO on the flow ability of cementitious composites Matrix type

Increase/decrease Slump flow diameter Abs./mm Rel./%

Self-compacting cement mortar

V-funnel flow time Abs./s Rel./%

Nano-CuO content/%

0 0 0.4 4.4 1 0 0 0.6 6.6 2 −5 −2.0 0.9 9.9 3 −5 −2.0 1.0 11.0 4 Note Abs. and Rel. represent the absolute and relative value, respectively

Reference

Khotbehsara et al. [368]

(3) Properties/performances 1. Workability Khotbehsara et al. assessed the flowability of the self-compacting cement mortars by measuring the slump flow diameter and V-funnel flow time. As shown in Table 2.139, the incorporation of nano-CuO decreases the flow diameter and leads to a longer V-funnel time. This is because that an increase of nano-CuO content improves the packing of particles and reduces the free water. The larger internal friction between the particles in the cement mortars leads to a decrease in the flowability [368]. 2. Hydration (i) Hydration process Zhang and Massazza investigated the hydration process in the cementitious composites with nano-CuO. They observed that the nano-CuO contributes to generate C–S–H gels through reaction with CH, which promotes the cement hydration [174, 371]. In the study of Nazari and Riahi [365] and Khotbehsara et al. [368], nano-CuO also accelerates the cement hydration in the self-compacting concrete and cement mortars, especially at early ages. The CH crystals quickly form, and then more C–S–H gels are generated in the nano-CuO-filled cementitious composites. Nazari and Riahi measured the weight loss of concrete containing nano-CuO according to TG analysis [372]. The results showed that the weight loss of the concrete after 28 d of curing is increased with increasing nano-CuO content to 4%. This is because more hydrated products are rapidly formed due to the presence of nano-CuO, which is confirmed by XRD analysis. (ii) Hydration heat Nazari and Riahi investigated the hydration heat of self-compacting concrete through conduction calorimetry test. The experimental results are listed in Table 2.140. It can be seen that the addition of nano-CuO, especially at the content of 4%, significantly accelerates peak time and drops heat release rate.

Rate Abs./(w/kg) Rel./%

16.7 0.11 15.5 29.2 0.14 19.8 41.7 0.17 23.9 51.5 0.22 31.0 45.8 0.20 28.2 the absolute and relative value,

Decrease First peak Time Abs./h Rel./%

0.4 0.7 1.0 1.3 1.1 Note Abs. and Rel. represent

Self-compacting concrete

Matrix type

4.3 20.9 5.4 26.2 7.0 33.9 8.6 41.7 7.7 37.4 respectively

Second peak Time Abs./h Rel./% 0.75 1.06 1.33 1.53 1.40

Rate Abs./(w/kg)

Table 2.140 Effect of nano-CuO on the hydration heat release of cementitious composites

22.0 31.1 39.0 44.9 41.1

Rel./% 67.1 93.3 107.7 127.7 113.8

Abs./(kJ/kg)

Total heat

18.1 25.1 29.0 34.4 30.1

Rel./% 1 2 3 4 5

Nano-CuO content/%

Nazari and Riahi [365]

Reference

2.3 Current Progress of Specific Type of Nano-Engineered … 265

266

2 Current Progress of Nano-Engineered Cementitious Composites

3. Mechanical properties (i) Strength The effect of nano-CuO on strength of cementitious composites is summarized in Table 2.141. It can be seen that the addition of nano-CuO significantly increases the strength of cementitious composites, especially for the early stages. Nazari and Riahi investigated the effect of nano-CuO on the compressive, flexural, and split tensile strengths of self-compacting concrete at the curing ages of 7, 28, and 90 d. They found that nano-CuO is conducive to increase these types of strength, and the largest increase in strength occurs for the composites with 3–4% of nano-CuO [365]. Madandoust et al. suggested that the optimum content of nano-CuO for the compressive strength is 3%. The increases in the 7 d and 28 d strength of the self-compacting cement mortars are 18.4% and 16.4%, respectively [367]. Similar results also appeared in the study of Riahi and Nazari [370]. They observed that the compressive strength of concrete cured in water increases with increasing nano-CuO content (up to 1%). As the nano-CuO content continues to increase (from 1 to 2%), the strength of concrete tends to decline. The influence mechanism of nano-CuO to the strength of cementitious composites is expressed as follows: (i) Nano-CuO recovers the particle packing of the matrix and reduces volume of larger pores in the cementitious composites. (ii) Nano-CuO with high reactivity leads to the rapid consumption of CH crystals and therefore generates large amounts of C–S–H gels [365, 372]. (iii) Excessive nanoparticles lead to excess silica leaching out and causing a deficiency in strength. Furthermore, the aggregation of nanoparticles also decreases the compactness of the matrix structure, so the strength of composites tends to decrease. (ii) Shrinkage and creep Nazari and Riahi investigated the effect of nano-CuO on the time-dependent deformation of cementitious composites. They found that the shrinkage and creep of the cement matrix increase with increasing nano-CuO content (up to 4%). They suggested that the distance between nanoparticles decreases with increasing nano-CuO content. The CH crystals cannot grow enough due to the limited space, and the crystal quantity is decreased, which leads to the ratio of this crystal to C-S-H gels being low, and therefore the shrinkage and creep of the cement matrix are increased [365]. 4. Durability (i) Water absorption Researchers performed the water absorption test to the cementitious composites with nano-CuO and found that the water absorption of composites reduces with the increase of nano-CuO content (from 1 to 4%) (as listed in Table 2.142) [367–369].

Compressive

Self-compacting concrete

Split tensile

Flexural

Strength

Matrix type

1.9 6.4 9.8 14.6 12.5 6.8 9.1 13.5 11.3 1.1 1.5 2.1 1.8 0.5 0.7 1.0 0.8

−0.1 1.1 2.6 3.7 5.0 – – – – – – – – – – – –

−0.7 7.9 18.6 26.4 35.7 – – – – – – – – – – – –

7d Abs./MPa

Increase/decrease 2d Abs./MPa Rel./% 9.2 31.1 47.6 70.9 60.7 42.5 56.9 84.4 70.6 39.3 53.6 75 64.3 50 70 100 80

Rel./%

Table 2.141 Effect of nano-CuO on the strength of cementitious composites

1.3 4.2 10.0 15.3 14.0 10.1 15.9 20.7 16.8 0.4 0.9 1.6 1.0 0.6 0.9 1.1 0.9

28 d Abs./MPa 4.1 13.3 31.6 48.4 44.3 23.1 36.4 47.4 38.4 7.4 16.7 29.6 18.5 28.6 42.9 52.4 42.9

Rel./% – – – – – 7.7 11.7 18.1 15.3 0.3 0.7 1.3 0.9 0.6 1.3 1.7 1.5

90 d Abs./MPa – – – – – 12.6 19.1 29.6 25.0 4.1 9.6 17.8 12.3 20.7 44.8 58.6 51.7

Rel./% 1 2 3 4 5 1 2 3 4 1 2 3 4 1 2 3 4

Nano-CuO content/%

(continued)

Nazari et al. [366]

Nazari et al. [366]

Nazari et al. [366]

Nazari and Riahi [365]

References

2.3 Current Progress of Specific Type of Nano-Engineered … 267

Compressive

Self-compacting cement mortar

Increase/decrease 2d Abs./MPa Rel./% 7d Abs./MPa Rel./%

6.0 50 2 8.3 6.0 50 3 12.7 7.0 58.3 4.5 18.4 5.0 41.7 1 4.1 3.0 25 3 12.5 Ordinary concrete Split tensile 0.3 75 0 0 0.8 200 0.2 16.7 1.1 275 0.6 50 1.4 350 1 83.3 1.1 275 0.8 66.7 Note Abs. and Rel. represent the absolute and relative value, respectively

Strength

Matrix type

Table 2.141 (continued)

0.5 2 6 2 0 −0.4 0 0.5 0.9 0.6

28 d Abs./MPa 1.7 5.2 15.7 5.6 0 −22.2 0 27.8 50.0 33.3

Rel./% 2 7 9 7 6 – – – – –

90 d Abs./MPa 4.2 14.6 18.8 14.6 12.5 – – – – –

Rel./% 1 2 3 4 5 1 2 3 4 5

Nano-CuO content/%

Nazari and Riahi [372]

Madandoust et al. [367]

References

268 2 Current Progress of Nano-Engineered Cementitious Composites

2.3 Current Progress of Specific Type of Nano-Engineered …

269

Table 2.142 Effect of nano-CuO on the water absorption of cementitious composites Matrix type

Decrease in water absorption/%

Nano-CuO content/%

References

Self-compacting concrete

21.7 49.3 53.4 51.0 5.7 6.7 8.9 2.0 1.0 4.9 9.8 15.7 17.6 4.3 9.8 13

1 2 3 4 1 2 3 4 5 1 2 3 4 1 2 3

Nazari et al. [366]

Self-compacting cement mortar

Ordinary cement mortar

Madandoust et al. [367]

Khotbehsara et al. [368]

Miyandehi et al. [369]

In addition, Khotbehsara et al. studied the statistical correlation between water absorption and compressive strength. The results showed that the water absorption of cement mortars with nano-CuO tends to decrease linearly with the increase of compressive strength. They suggested the hydration product with more compact structure has lower porosity, which increases the compressive strength and decreases the water absorption [368]. (ii) Corrosion resistance Khotbehsara et al. performed the electrical resistivity test on the self-compacting cement mortars and reported that the resistivity increases with increasing nano-CuO content. They suggested that the provision of nano-CuO gives rise to a lower porosity and hence a lower pore water solution in the self-compacting cement mortars. The reduction in the pore water solution (as an electrolyte for the current) makes the resistivity higher [368]. Miyandehi et al. studied the chloride penetration resistance of concrete with nano-CuO by conducting rapid chloride permeability test. The tested results are listed in Table 2.143. It is clear that the incorporated nano-CuO improves the chloride penetration resistance of the concrete [369]. (iii) Wear resistance Riahi and Nazari investigated the wear resistance of concrete with nano-CuO after 7, 28, and 90 d of curing in water and saturated limewater. They observed that the wear resistance of concrete containing nano-CuO is remarkably improved at all the

270

2 Current Progress of Nano-Engineered Cementitious Composites

Table 2.143 Effect of nano-CuO on the chloride penetration resistance of cementitious composites Matrix type

Durability

Increase/decrease

Nano-CuO content/%

References

Rel./%

−550

−19.6

1

−1020

−36.4

2

Madandoust et al. [367]

−1020

−36.4

3

−1150

−41.1

4

−900

−32.1

5

2.2

29.3

1

6.7

89.3

2

Abs. Self-compacting cement mortar

Passing charge/C

Electrical resistivity/ (kX•cm)

Ordinary cement mortar

Passing charge/C

16.5

220

3

20

266.7

4

10

133.3

5

3

30

1

4

40

2

8

80

3

13

130

4

−296

−9.7

1

−544

−17.9

2

−1087

−35.7

3

2.19

19.9

1

4.79

43.5

2

10.29

93.5

3

Electrical resistivity/(kX•cm)

Madandoust et al. [367]

Khotbehsara et al. [368]

Miyandehi et al. [369]

Note Abs. and Rel. represent the absolute and relative value, respectively

Table 2.144 Effect of nano-CuO on the abrasion resistance of cementitious composites Matrix type

Decrease in depth of wear of concrete in the curing condition of water/ lime water 7d

Ordinary concrete

28 d

Nano-CuO content/%

Reference

Riahi and Nazari [370]

90 d

Abs./mm

Rel./%

Abs./mm

Rel./%

Abs./mm

Rel./%

1.5/1.1

25.4/21.1

1.1/2.3

30.6/52.2

0.7/1.3

25/37.1

0.5

2/1.6

33.9/30.7

1.9/2.9

52.8/65.9

1.4/2.4

50/68.6

1.0

2.1/2

35.6/38.5

2/3.3

55.6/75

1.9/2.9

67.9/82.9

1.5

2.4/2.2

40.7/42.2

2.1/3.4

58.3/77.3

2.2/3

78.6/85.7

2.0

Note Abs. and Rel. represent the absolute and relative value, respectively

2.3 Current Progress of Specific Type of Nano-Engineered …

271

curing ages, and this improvement is more evident in the curing condition of limewater [370]. The detailed experimental results are listed in Table 2.144.

2.3.16 Current Progress of Nano-Fe2O3-Engineered Cementitious Composites (1) Fabrication/processing The properties of nano-Fe2O3 used to fabricate cementitious composites are summarized in Table 2.145. The mix proportion and main fabrication process of nano-Fe2O3-engineered cementitious composite are listed in Tables 2.146 and Table 2.147, respectively. (2) Structures Xiao observed the morphology of hydration products of cement mortars by SEM. They found that in the control cement mortars, C–S–H gels mostly exist in the form of “independent” agglomeration, which is linked by the needle rod AFt and type I hydration products that inserted in the middle of C–S–H gels. A lot of CH crystals are also distributed in the C–S–H gels. However, when the nano-Fe2O3 is added, the hydration products become more compact and denser, and no obvious CH crystals are observed [373]. In addition, Sanju et al. observed that most of the voids of concrete are filled up by the rapid formation of C–S–H gels due to the presence of nano-Fe2O3 [335]. (3) Properties/performances 1. Workability Nazari et al. investigated the workability of concrete with nano-Fe2O3 through the standard slump test. They observed that the workability of concrete decreases with increasing nano-Fe2O3 content [374]. They suggested the increasing surface area of powder after adding nano-Fe2O3 requires more water to wet the cement particles.

Table 2.145 Properties of nano-Fe2O3 Nano-Fe2O3 form

Particle size/nm

Specific surface area/(m2/g)

Purity/%

References

Powder

30 15 ± 3 10.0 90–100 60

– – 200−220 150 –

– >99.9 >99.8 – 99

Xiao [373] Nazari et al. [354, 374] Salemiet al. [248] Sanju et al. [335] Sheikhaleslamzadeh and Raofi [375]

Natural river sand, crushed stone (5–12 mm)

Fine aggregate (200 – 100–200 – 1–10 – – >30 – ID, and SSA represent outer diameter, inner diameter, and specific surface area, respectively

(a)

(b)

20 nm

200 nm

(c)

(d)

(e)

200 nm

20 nm

200 nm

(f)

(g)

(h)

Fig. 3.4 Microscopic morphologies of a M5, b M1, c SM5, d SM1, e NiM5, f GM5, g LIM, and h HIM

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3 Carbon Nanotubes-Engineered Cementitious Composites

Table 3.8 Mix proportion of CNTs-filled cement pastes Cement type

CNT contents

SP type

Proportion of C, W and SP

P
O 42.5R 0.1, 0.5 and 0.8 (wt% of C) Polycarboxylate C:W:SP = 1:0.20: 0.75% Note C represents cement, W represents water, and SP represents superplasticizer

Table 3.9 Main fabrication process of CNTs-filled cement pastes Dispersion method of CNTs

Fabrication process Feeding order

Technology Method

Time

Method

Size/mm

Condition

Time

Ultrasonication + Non-covalent surface modification by SP

CNTs +W+SP

Ultrasonication (400 W, 20–25 kHz)

5 min

Vibration

W (20 °C)

28d

C

Shear mixing (1000r/min)

–

20  20  40 (Compressive test), 20  20  80 (Flexural test)

–

Shear mixing (2000r/min)

60 s

Standard curing

180 d

Molding

Curing

Note C, W, and SP represent cement, water, and superplasticizer, respectively

3.3.2

Effect of Size of Untreated Carbon Nanotubes on Mechanical Properties/Performances

(1) Compressive strength Figure 3.5 shows the compressive strength of four different sizes of CNTs (including diameter and length)-filled cement pastes. Relative and absolute increases in compressive strength of cement pastes compared with control cement pastes are listed in Table 3.10. As seen from Fig. 3.5 and Table 3.10, the compressive strength of cement pastes with short- and large-diameter CNTs (SM5) at a concentration of 0.8% is the largest, which is increased by 47.1%/44.2 MPa compared with the control cement pastes without CNTs. Besides, the compressive strength of M1- and M5-filled 180

Compressive strength / MPa

Fig. 3.5 Compressive strength of cement pastes with different content of untreated CNTs

150

0 0.5%

0.1% 0.8%

M1

SM1

120 90 60 30 0

M5

SM5

Types of CNTs

3.3 Mechanical Properties/Performances of Carbon Nanotubes-Engineered …

407

Table 3.10 Relative/absolute increase in compressive strength of cement pastes with untreated CNTs CNT content

SM1 Rel./%

Abs./MPa

M1 Rel./%

Abs./MPa

0.10% 7.8 7.3 23.7 22.3 0.50% 24.5 23 14.6 13.7 0.80% −21.0 −19.8 20.5 19.3 Note Abs. and Rel. denote the absolute and relative value,

SM5 Rel./%

Abs./MPa

37.6 35.3 45.3 42.5 47.1 44.2 respectively

M5 Rel./%

Abs./MPa

32.7 18.1 30.0

30.7 17.0 28.2

cement pastes reaches the maximum at a CNTs concentration of 0.1%, both increasing greatly as compared to the control cement pastes. It is obvious that M5 produces a slightly higher compressive strength than that of M1. Compressive strength of SM1-filled cement pastes reaches the maximum at 0.5% SM1 dosage, which increases greatly as compared to the control cement pastes. However, compressive strength of cement pastes with 0.8% of SM1 is decreased by 21%/ 19.8 MPa compared with the control cement pastes. This is principally because a large amount of SM1 is not easily dispersed; the local agglomeration and winding in the hydration products of cement are formed. Thus, void and pore in the cement matrix increase and interface compatibility of CNTs is poor. Certainly, mechanical properties are compromised. However, too few CNTs will have no obvious influence on the mechanical properties of cement pastes. In order to improve the mechanical properties of CNTs cement pastes, the volume ratio of nanotubes must be greater than the critical value. Reference [4] proposed the critical volume fraction (Vfcrit ) based on the composite model of fiber-reinforced cementitious composites. It can be expressed as: Vfcrit ¼

rum
 gl g0 ruf  Ef eum þ rum

ð3:1Þ

where gl is coefficient of length of CNTs, determined by the ratio of actual length of CNTs and critical pull-out length of CNTs, g0 is orientating coefficient of CNTs and is equal to 0.20 when fibers are 3D-distributed in matrix, ruf is the tensile strength of CNTs and is about 30GPa [5], Ef is the elastic modulus of CNTs and is about 600 GPa [5], eum is ultimate tensile strain and is about 0.00015, and rum is the tensile strength of cementitious composites. There is a relationship between compressive strength and tensile strength of fiber-reinforced cementitious composites, as shown in Eq. 3.2. rum ¼ rcm =20

ð3:2Þ

where rcm is the compressive strength of cement pastes obtained by test and shown in Fig. 3.5. Therefore, critical volume fraction of CNTs can be calculated according to Eqs. (3.1) and (3.2). The minimum value of Vfcrit is about 0.08% when gl reaches

408

3 Carbon Nanotubes-Engineered Cementitious Composites

Table 3.11 Volume fraction of CNTs Weight fraction of CNTs

Volume of the composites/V (cm3)

Mass of CNTs/M (g)

Density of CNTs/q (g/cm3)

Volume fraction of CNTs (Vf = m/q/V)

0.1 wt% 0.5 wt% 0.8 wt%

144 144 144

0.32 1.6 2.56

2.1 2.1 2.1

0.104 vol.% 0.528 vol.% 0.847 vol.%

the maximum, i.e., 1. In this study, the volume fractions (Vf) of CNTs are listed in Table 3.11 and are all larger than critical volume fraction, which guarantees effective enhancement of CNTs on the strength of cement pastes. Through the above analysis, the conclusion can be drawn that compressive strength of cement pastes with large-diameter CNTs is higher than that of cement pastes with small-diameter CNTs. (2) Flexural strength Figure 3.6 displays the flexural strength of four different sizes of CNTs (including diameter and length)-filled cement pastes. Relative and absolute increases in flexural strength of composites compared with the control cement pastes are listed in Table 3.12.

Flexural strength / MPa

Fig. 3.6 Flexural strength of cement pastes with different contents of untreated CNTs

0.1% 0.8%

0 0.5%

16 12 8 4 0

M5

SM5

SM1

M1

Types of CNT

Table 3.12 Relative/absolute increase in flexural strength of cement pastes with untreated CNTs CNT content 0.1% 0.5% 0.8% Note Abs. and

SM1 Rel./%

Abs./MPa

M1 Rel./%

Abs./MPa

4.6 0.4 48.3 4.2 21.8 1.9 36.8 3.2 3.4 0.3 42.5 3.7 Rel. denote the absolute and relative value,

SM5 Rel./%

Abs./MPa

55.2 4.8 27.5 2.4 36.8 3.2 respectively

M5 Rel./%

Abs./MPa

44.8 37.9 44.8

4.8 2.4 3.2

3.3 Mechanical Properties/Performances of Carbon Nanotubes-Engineered …

409

As seen from Fig. 3.6 and Table 3.12, the flexural strength of cement pastes with short- and large-diameter CNTs (SM5) reaches the maximum, which presents a 55.2%/4.8 MPa increase at a CNT concentration of 0.1% compared with the control cement pastes. However, flexural strength of cement pastes with short- and small-diameter CNTs (SM1) is smallest in all cases. Flexural strength of the SM1 cement pastes reaches the maximum at 0.5% of CNTs dosage, which is increased by 21.8%/1.9 MPa compared with the control cement pastes. Like compressive strength, variation in flexural strength between M1 and M5 cement pastes is similar to the changing contents of CNTs. However, the gain in flexural strength of M1 and M5 cement pastes is higher than that in compressive strength. Judging from the test results, the long CNTs are better for improving flexural strength in most cases against short CNTs. In terms of compressive and flexural strengths, the effect of CNT size on cement pastes is summarized as follows. It can be concluded that cement pastes with large-diameter CNTs present relatively higher compressive strength, since the compressive strength of SM5- and M5-filled cement pastes is higher than that of SM1- and M1-filled cement pastes. Theoretically, surface energy of small-diameter CNTs is bigger than that of large-diameter CNTs. Thus, compared with large-diameter CNTs, small-diameter CNTs is easily agglomerated. Therefore, the large-diameter CNTs should achieve relatively better dispersion. Moreover, the orientation index of CH indicates that large-diameter CNTs are conducive to obtain better mechanical property compare with small–large CNTs. Compared with short CNTs, the reinforcement effects of long CNTs (M1 and M5) on flexural strength of cement pastes are enhanced. It is therefore concluded that long CNTs have a better reinforcement effect on flexural strength compared with short CNTs. (3) Reinforcement mechanisms 1. X-ray diffraction analysis Figure 3.7 shows XRD patterns of cement pastes with four different sizes of CNTs. In order to avoid the interference of concentration, cement pastes containing 5% of

Fig. 3.7 XRD patterns of cement pastes with untreated CNTs (Note C3S represents 3CaO
SiO2.)

AFt (001)

CH

C3S

♦

(101)

♦CaCO3 M5 M1 SM5 SM1

Control

8

16

24

32

40

2θ/°

48

56

64

410

3 Carbon Nanotubes-Engineered Cementitious Composites

Table 3.13 Diffraction intensity and orientation of CH in cement pastes with untreated CNTs Cement pastes

Control

With SM1

With SM5

With M5

With M1

(001)CH (101)CH CH orientation

1794 898 2.70

1462 868 2.27

1458 952 2.07

1319 881 2.02

1442 853 2.28

CNTs are selected in microscopic analysis. As seen from Fig. 3.7, hydration products such as Ca(OH)2 (i.e., CH), ettringite (i.e., AFt), unreacted C3S and CaCO3 from carbonization of CH all can be detected by XRD. Moreover, no special diffraction peak in CNTs cement pastes different from control cement pastes occurs, which indicates that the addition of CNTs cannot produce new materials. The calculation results of the CH orientation are listed in Table 3.13. It can be seen from Table 3.13 that the CH orientation degree is reduced as CNTs are added into cement. This is due to the fact that CNTs can accelerate calcium silicate hydrate (i.e., C–S–H) gels formation by means of increasing CH amount at the early age, prevent the CH and AFt crystal from forming large size, and modify the orientation index of CH crystal [6]. It is also found that the sizes of CNTs have an influence on the CH orientation. By comparative analyses, CNTs with large diameter are helpful in reducing the CH orientation of cement pastes as compared to small-diameter CNTs. The large-diameter CNTs have larger tube thickness compared with the small-diameter CNTs. As a result, they are more effective to restrain the directional growth of CH. The small CH orientation is beneficial to increase the strength of cement pastes. This is also consistent with the results of the strength of composites. Meanwhile, the length of CNTs is not the obvious factor affecting the CH orientation compared with the diameter of CNTs because the total length of CNTs is the same at the same concentration level of CNTs. 2. Thermogravimetry analysis TG and derivative TG (i.e., DTG) diagrams of cement pastes with untreated CNTs are shown in Fig. 3.8. The hydration degree of cement pastes can be calculated [7–9], and the results are listed in Table 3.14. As shown in Table 3.14, cement hydration degree decreases when CNTs are added into cement pastes. This indicates that CNTs have a certain inhibiting effect on the cement hydration. This behavior is justified taking into account of adsorption effect of CNTs and small water–cement ratio in this study. Reference [10] pointed out that surface-treated CNTs are so hydrophilic as to absorb most of the water contained in cement paste, hence hampering the proper hydration of cement paste. Due to large specific surface area and great surface energy, CNTs can serve as adsorption nucleus of hydration products, water and ions [6]. Furthermore, low water–cement ratio results in an incomplete hydration. Therefore, hydration of CNTs cement pastes is retrained. However, it is beneficial to reduce hydration heat and primary cracks. As a result, the strength of CNTs cement pastes increases even if CNTs inhabit cement hydration. On the other hand, it is found that cement hydration degree shows a

3.3 Mechanical Properties/Performances of Carbon Nanotubes-Engineered …

411

(a)

Mass / %

100

Control SM1 SM5 M1 M5

95 90 85 80 200

400

600

800

1000

Temperature / °C

1st derivative of mass / %

(b) 0.0000 -0.0002 -0.0004 Control

-0.0006

SM1 SM5

-0.0008

M1 M5

-0.0010

0

200

400

600

800

1000

Temperature / °C Fig. 3.8 TG diagram (a) and DTG diagram (b) for cement pastes with untreated CNTs

Table 3.14 Hydration degree of cement pastes with untreated CNTs Cement pastes

Control

With M5

With SM5

With M1

With SM1

Hydration degree/%

69.5

62.7

62.6

61.9

62.8

negligible difference when CNTs with different size are added into cement pastes. It is indicated that the size of CNT has unobvious influence on cement hydration degree. 3.

29

Si nuclear magnetic resonance analysis

29

The Si NMR spectra of cement pastes are shown in Fig. 3.9. Table 3.15 lists the calculation results of deconvolution of the 29Si NMR of cement pastes. Figure 3.9 shows that 29Si resonance signals mainly appear in the ranges of −68 * −76 ppm, 76 * −82 ppm, and −82 * −88 ppm, which belong to Q0, Q1, and Q2, respectively, according to reference [11]. Q0 represents the uncondensed silicate (monomer), Q1 is disilicate/dimer (chain end group), and Q2 represents disilicate/dimer short chain (chain middle group). It can be seen from Fig. 3.9 that the peak of Q0 is dominant, while the peaks of Q1 and Q2 are relatively weak, indicating that the hydration degree (PD) of cement pastes is relatively low. Moreover, the 29Si resonance signals of

412

3 Carbon Nanotubes-Engineered Cementitious Composites

(a)

(b)

Q0

Q0

Q1

Q1

Q2

-60

-70

-80

-90

Q2

-100 -110 -120

-60

Chemical shift / ppm Fig. 3.9 Deconvolved

-70

-80

-90

-100 -110 -120

Chemical shift / ppm

29

Si NMR spectra of cement pastes a without CNTs and b with SM5

Table 3.15 Deconvolution results of 29Si NMR for cement pastes with and without SM5

Cement pastes

Q0/%

Q1/%

Q2/%

PD

MCL

Control With SM5

49.79 45.30

29.68 35.64

20.52 19.06

0.69 0.534

3.38 3.07

SM5-filled cement pastes is the same as that of cement pastes without CNTs, which indicates that the silicon-oxygen tetrahedron in C–S–H gels is also in the form of dimer short chain. As shown in Table 3.15, the incorporation of SM5 decreases the PD of C–S–H gels compared with that of cement pastes without CNTs, but the maximum PD does not exceed 0.7. This manifests that the structure of silicon–oxygen tetrahedron has no essential change, and it is still dominated by dimer structure with a low degree of polymerization. Additionally, the mean chain length (MCL) of C–S–H gels of cement pastes with SM5 is also reduced, but the reduction is only 9% compared with cement pastes without CNTs. Therefore, the inclusion of CNTs brings no significant change to the PD and MCL of cement pastes. Figure 3.10 shows the SEM micrographs of SM5 and M5 distributed in cement matrix. As can be seen, SM5 forms extensive spatial distribution inside cement paste and M5 can distribute within cement hydration and lap each other in space. Assuming CNTs are in ideal geometrical shape and exist in single particle, the number of CNTs

(a)

(b)

SM5

2μm

M5

5μm

Fig. 3.10 SEM images of a 0.8% of SM5 and b 0.8% of M5 distributed in cement paste matrix

3.3 Mechanical Properties/Performances of Carbon Nanotubes-Engineered …

413

Table 3.16 Numbers of untreated CNTs per 1 cm3 in cement pastes CNT type

Out diameter (2R)/nm

Inner diameter (2r)/nm

Length (L)/l m

Volume of single CNT (Vc = p(R2-r2)L)/nm3

SM1 M1 SM5 M5

6–8 6–8 20–30 20–30

2–5 2–5 5–10 5–10

0.5–2 10–30 0.5–2 10–30

4.3 8.8 1.2 3

   

103–9.5 104–1.4 105–1.4 105–2.1

   

104 106 106 107

Number of CNTs per 1 cm3 1.1 7.4 7.4 5

   

1013–2.4 1011–1.2 1011–8.7 1010–3.5

   

1014 1013 1012 1012

per cm3 in the composites can be calculated. As shown in Table 3.16, the number of CNTs per cm3 can reach 5  1010 to 2.4  1014 when the CNTs content is only 0.1 wt%. This means that numerous of CNTs exist in cement pastes even at low filler concentration levels. The extensive distribution of CNTs in cement pastes is closely related to the number of CNTs per unit volume, but also an average center distance between two CNTs in cement pastes. Reference [12] suggested that the average center-to-center spacing of fibers and the cracking resistance has an inverse relationship and found that when the fibers are disorderly 3D-distributed in the matrix, the average center-to-center spacing S can be expressed as: S ¼ 13:8df

qffiffiffiffiffiffiffiffiffiffi 1=Vf

ð3:3Þ

Equation (3.3) indicates that the average center-to-center spacing of CNTs in cement pastes is only related to the diameter and contents of CNTs. The average center distance between adjacent CNTs in matrix is shown in Table 3.17. It indicated that as the CNTs content increases, average center distance between adjacent CNTs decreases gradually and CNTs per unit volume can carry high loading.

3.3.3

Effect of Surface Functionalization of Carbon Nanotubes on Mechanical Properties/Performances

(1) Compressive strength The relationships between compressive strength of cement pastes and content of two sizes of functionalized CNTs are presented in Fig. 3.11a and b, respectively. Table 3.17 Average center distance (S) between adjacent CNTs in cement pastes Volume fraction

M5 (lm)

SM5 (lm)

M1 (lm)

SM1 (lm)

0.1% 0.5% 0.8%

8.56–12.84 3.8–5.7 3–4.5

8.56–12.84 3.8–5.7 3–4.5

2.57–3.42 1.14–1.52 0.9–1.2

2.57–3.42 1.14–1.52 0.9–1.2

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3 Carbon Nanotubes-Engineered Cementitious Composites

Fig. 3.11 Compressive strength of cement pastes with different content of functionalized a M1 and b SM1

Compressive strength / MPa

(a) 0 0.5%

180

0.1% 0.8%

150 120 90 60 30 0

M1

MH1

MC1

Types of CNTs

Compressive strength / MPa

(b) 0.1% 0.8%

0 0.5%

180 150 120 90 60 30 0

SM1

SMH1

SMC1

Types of CNTs

For comparison, compressive strength of cement pastes with untreated CNT of the same size is also shown in Fig. 3.11. The corresponding relative and absolute increases in compressive strength compared with the control cement pastes are listed in Table 3.18. As shown in Fig. 3.11 and Table 3.18, compressive strength of cement pastes with carboxyl-functionalized and hydroxyl-functionalized CNTs enhances greatly as compared to untreated CNTs of the same size. Compressive strength of cement pastes with carboxyl-functionalized M1 (i.e., MC1) at a concentration of 0.5% is increased by 52%/49 MPa compared to the control cement pastes, producing an Table 3.18 Relative/absolute increase in compressive strength of cement pastes with functionalized CNTs CNT content

M1 Rel./ %

MC1 Abs./ MPa

Rel./ %

MH1 Abs./ MPa

Rel./ %

SM1 Abs./ MPa

Rel./ %

SMC1 Abs./ MPa

Rel./ %

SMH1 Abs./ MPa

Rel./ %

Abs./ MPa −3.1

0.1%

23.7

22.3

37.5

35.2

30.5

28.7

7.8

7.3

0.6

0.6

−3.0

0.5%

14.6

13.7

52.0

48.9

64.6

60.5

24.5

23.0

43.5

40.9

61.9

58.2

0.8%

20.5

19.3

50.6

47.6

28.2

26.5

−21.1

−19.8

−11.7

−11.0

−0.7

−0.7

Note Abs. and Rel. denote the absolute and relative value, respectively

3.3 Mechanical Properties/Performances of Carbon Nanotubes-Engineered …

415

improvement of approximately 38% compared with untreated M1 of the same size. Cement pastes containing 0.5% of hydroxyl-functionalized M1 (i.e., MH1) present a 64.6%/60.5 MPa higher compressive strength compared with the control cement pastes, which is increased by 50% as compared to M1. In another group having short size of CNTs, compressive strength of cement pastes filled with hydroxyl-functionalized SM1 (i.e., SMH1) and carboxyl-functionalized SM1 (i.e., SMC1) at a concentration of 0.5% are increased by 62%/58.2 MPa and 43.5%/ 41 MPa compared with control cement pastes, respectively. Compared with untreated SM1 of the same size, 0.5% addition of SMH1 and SMC1 leads to 34.7% and 19% of increase in compressive strength, respectively. According to the above analytical results, 0.5% of CNTs with hydroxyl groups produce higher compressive strength of cement pastes than those with carboxyl groups. (2) Flexural strength The relationships between flexural strength of cement pastes and contents of two sizes of functionalized CNTs are shown in Fig. 3.12a and b, respectively. For comparison, the flexural strength of cement pastes with untreated CNTs of the same size is also shown in Fig. 3.12. The corresponding relative and absolute increases in flexural strength compared with control cement pastes are listed in Table 3.19.

Flexural strength / MPa

(a)

16

0 0.5%

0.1% 0.8%

12 8 4 0

M1

MH1

MC1

Types of CNTs

(b) Flexural strength / MPa

Fig. 3.12 Flexural strength of cement pastes with different content of functionalized a M1 and b SM1

16

0 0.5%

0.1% 0.8%

12 8 4 0

SM1

SMH1

Types of CNTs

SMC1

416

3 Carbon Nanotubes-Engineered Cementitious Composites

Table 3.19 Relative/absolute increase in flexural strength of cement pastes with functionalized CNTs CNT content

M1 Rel./ %

Abs./ MPa

Rel./ %

MC1 Abs./ MPa

MH1

0.1%

48.3

4.2

49.4

4.3

4.6

0.4

0.5%

36.8

3.2

34.5

3.0

24.1

2.1

0.8%

42.5

3.7

54

4.7

26.4

2.3

3.4

Rel./ %

SM1 Abs./ MPa

Rel./ %

SMC1

SMH1

Abs./ MPa

Rel./ %

Abs./ MPa

Rel./ %

Abs./ MPa

4.6

0.4

18.4

1.6

26.4

21.8

1.9

54

4.7

75.9

6.6

0.3

11.5

1.0

−10.3

−0.9

2.3

Note Abs. and Rel. denote the absolute and relative value, respectively

As shown in Fig. 3.12 and Table 3.19, flexural strength of cement pastes with carboxyl-functionalized and hydroxyl-functionalized CNTs enhances greatly, compared with untreated CNTs of the same size in most cases. MH1 is an exception which produces a negative effect on flexural strength of cement pastes compared to M1. Compared with control cement pastes, the flexural strength of cement pastes with 0.8% of MC1 and SMC1 is increased by 54%/4.7 MPa and 11.5%, respectively. In another group, the variation in flexural strength of SMH1 and SMC1 cement pastes is the same as that of SM1, both achieving the maximum at 0.5% of CNTs concentration. In addition, reinforcement effect of SMH1 on strength of cement pastes is more remarkable than that of SMC1 at less than 0.8% dosage level. Flexural strength of cement pastes reaches the maximum (15.3 MPa) at a SMH1 content of 0.5%. It is increased by 76%/6.6 MPa compared with that of control cement pastes and presents a 54%/4.7 MPa increase than that of SM1-filled cement pastes. The addition of functionalized CNTs results in higher strength of cement pastes than that of untreated CNTs in most cases. It is known that the functionalized CNTs own hydrophilic groups like hydroxyl or carboxyl groups on their surface, which promote the dispersion of CNTs in water and enhance the bond effect by their interfacial interaction with hydrations (e.g., C–S–H or CH) of cement. The interaction leads to a stronger covalent force on the interface between CNTs and matrix in the composites and therefore improves the load-transfer efficiency from matrix to CNTs with respect to untreated CNTs [2, 13, 14]. Moreover, it is found that the highest strength is obtained by hydroxyl-functionalized CNTs cement pastes in majority of case. Compared with carboxyl groups, hydroxyl groups can more effectively enhance wettability of CNTs, thus leading to an improvement in hydrophility of CNTs [15, 16]. As a result, hydroxyl-functionalized CNTs can achieve better dispersion in matrix against carboxyl-functionalized CNTs. This may be the reason why hydroxyl-functionalized CNTs produce better reinforcing effect to matrix than carboxyl-functionalized CNTs. (3) Reinforcement mechanisms 1. X-ray diffraction analysis XRD patterns of two sizes of functionalized CNTs cement pastes are presented in Fig. 3.13. For comparison, XRD patterns of cement pastes with untreated CNTs of

3.3 Mechanical Properties/Performances of Carbon Nanotubes-Engineered …

(a) AFt

Ca(OH)2 (001)

♦

C3S

417

♦CaCO3

(101)

M1 MC1

MH1

Control

8

16

24

32

40

48

56

64

2θ/°

(b) AFt (001)

Ca(OH) 2

♦

C3S

♦CaCO3

(101)

SMC1

SMH1 SM1

Control

8

16

24

32

40

48

56

64

2θ/° Fig. 3.13 XRD patterns of cement pastes with functionalized a M1 and b SM1 (Note C3S represents 3CaO
SiO2.)

the same size are also shown in Fig. 3.13. CH orientation of two sets of cement pastes is listed in Table 3.20. It is obvious that the CH orientation is reduced as functionalized CNTs are added into cement pastes as compared to control cement pastes. Compared with CNTs of the same size, CNTs with hydroxyl groups have an increasing effect on CH orientation, while that with carboxyl groups decrease CH orientation. The functionalized CNTs, especially carboxyl-functionalized CNTs, Table 3.20 Diffraction intensity and orientation of CH in cement pastes with functionalized CNTs Cement pastes

Control

With M1

With MH1

With MC1

With SM1

With SMH1

With SMC1

(001)CH (101)CH CH orientation

1794 898 2.70

1442 853 2.28

1388 794 2.36

1211 951 1.72

1462 868 2.27

1518 970 2.11

1312 889 1.99

418

3 Carbon Nanotubes-Engineered Cementitious Composites

(a) 100

Mass / %

Fig. 3.14 TG diagram (a) and DTG diagram (b) for cement pastes with functionalized CNTs

Control M1 MH1 MC1

95 90 85 80 200

400

600

800

1000

Temperature / °C 1st derivative of mass / %

(b) 0.0000 -0.0002 -0.0004 -0.0006

Control M1 MH1 MC1

-0.0008 -0.0010

0

200

400

600

800

1000

Temperature / °C

will react with CH in composites and consume CH, thus restraining the growth of CH crystal. CH orientation in MH1 cement pastes is higher than that in M1 cement pastes, which is one of the reasons for that MH1 reduces flexural strength compared with M1. 2. Thermogravimetry analysis TG and DTG diagrams of two sizes of functionalized CNTs cement pastes are shown in Figs. 3.14 and 3.15, respectively. Cement hydration degrees of two groups of cement pastes are shown in Table 3.21, respectively. As seen from Table 3.21, cement hydration degree of functionalized CNTs-filled cement pastes is lower than that of control cement pastes, but higher than that of untreated CNTs cement pastes. It indicates that CNTs with hydroxyl or carboxyl groups have a positive effect on cement hydration. MH1 obtained highest hydration degree of cement among functionalized CNTs, which may be a minus point for mechanical property of cement pastes due to the increase of primary cracks caused by temperature stress. 3.

29

Si nuclear magnetic resonance analysis

Figure 3.16 is the 29Si NMR spectra of cement pastes with functionalized CNTs, and their calculation results of deconvolution are listed in Table 3.22. In the 29Si NMR spectra of cement pastes with functionalized CNTs, the peak intensity of Q0

3.3 Mechanical Properties/Performances of Carbon Nanotubes-Engineered …

419

(a)

Mass / %

100

Control SM1 SMH1 SMC1

95 90 85 80 200

(b) 1st derivative of mass / %

400

600

800

1000

Temperature / °C 0.0000

-0.0002 -0.0004 -0.0006

Control SM1

-0.0008

SMH1 SMC1

-0.0010

0

200

400

600

800

1000

Temperature / °C Fig. 3.15 TG diagram (a) and DTG diagram (b) for cement pastes with functionalized and short CNTs

Table 3.21 Hydration degree of cement pastes with functionalized CNTs Cement pastes

Control

With M1

With MH1

With MC1

With SM1

With SMH1

With SMC1

Hydration degree/%

69.5

61.9

68

64.1

62.8

63.9

65.5

is strongest while the peaks intensity of Q1 and Q2 are weaker. This manifests that gel structure inside cement pastes with functionalized CNTs is dimer short chain, which is the same as that inside cement pastes incorporating untreated CNTs. As shown in Table 3.22, the PD of C–S–H gels in all cement pastes is less than 1, indicating that the gel structure is dominated by dimer or high polymers linear end structure. Besides, the MCL varies between 3.1 and 3.4. Therefore, the functionalization of CNTs has no significant effect on the gel structure of CNTs-modified cement pastes. As shown in Fig. 3.17, crack bridging and fiber pull-out effect are observed in functionalized CNTs-filled cement pastes. When the cracks in the matrix encounter well-distributed CNTs, the efficient crack bridging can inhibit the crack growth at

420

3 Carbon Nanotubes-Engineered Cementitious Composites

Q0

SM5 SMC1 SMH1 Control

Q1

Q2

-60

-70

-80

-90

-100

-110

-120

Chemical shift / ppm Fig. 3.16

29

Si NMR spectra of cement pastes with functionalized CNTs

Table 3.22 Deconvolution results of 29Si NMR for cement pastes with functionalized CNTs and untreated CNTs Cement pastes

Q0/%

Q1/%

Q2/%

PD

MCL

With SM5 With SMH1 With SMC1

45.30 43.9 44.20

35.64 34.8 32.76

19.06 21.3 23.03

0.53 0.61 0.70

3.07 3.22 3.41

(b)

(a)

MC1

SMH1 1μm

2μm

Fig. 3.17 SEM images in cement paste matrix: a pull-out of SMH1; b crack bridging of MC1

the very preliminary stage of crack propagation within composites [17]. The enhancement mechanisms are different when the length or content of CNTs are changing. The applied load will be transferred to the CNTs, and CNTs are pulled out or snapped. According to the reference [4], if the CNT length (Lf, lm) is larger than critical length (Lcrit f , lm), the damage state of CNTs will be mainly dominated by tensile failure. On the contrary, the damage state of CNTs will be based on pull-out. The critical length of CNTs can be calculated as follows.

3.3 Mechanical Properties/Performances of Carbon Nanotubes-Engineered … Table 3.23 Critical length of CNTs at different dosage levels

421

CNT contents

0.1%

0.5%

0.8%

M1/lm MC1/lm MH1/lm SM1/lm SMC1/lm SMH1/lm

6.07–18.2 6.03–18.1 7.63–22.9 0.38–1.53 0.35–1.41 0.34–1.35

15.48–46.44 15.61–46.83 16.25–48.74 0.82–3.28 0.73–2.92 0.68–2.73

19.21–57.62 18.48–55.43 20.39–61.17 1.13–4.51 1.09–4.34 1.21–4.84

Lcrit ¼ Lf f Lcrit ¼ f

qffiffiffiffiffiffiffiffiffiffiffiffiffiffi qffiffiffiffiffiffiffiffi rlf g0 Vf = 2rlfc 2g0 Vf ruf Lf 2rufc þ g0 Vf ruf

Lf  Lcrit f

Lf [ Lcrit f

ð3:4Þ ð3:5Þ

where Lf is the length of CNTs and is shown in Table 3.7, rlf , g0 and Vf have been known, rlfc is tensile strength of the composites and its relationship with flexural strength is shown in Eq. (3.6) [18]. rufc ¼ 1:8rbfc

ð3:6Þ

where rbfc is flexural strength of composites and is shown in Fig. 3.12. Thus, the critical length of CNTs can be calculated using Eqs. (3.4)–(3.6). As listed in Table 3.23, the critical length of CNTs increases as the CNT content increases. When CNT content is 0.1%, the actual length is all larger than the critical length, and the CNTs will be broken when the CNTs cement pastes are damaged. On the contrary, with the increase of CNT content, the actual length is all shorter than the critical length, and the CNTs will be pulled out when the CNTs cement pastes are damaged. During the pulling-out or snapping process, CNTs owning excellent stiffness can absorb energy in order to overcome the friction force of the interface between CNTs and matrix, which can increase the demand of failure energy of CNTs-filled cement pastes. The calculation method for the pull-out energy of CNTs-filled cement pastes is shown as Eqs. (3.7) and (3.8), based on Pigott’s theory [19]. The average pull-out energy of one single CNT can be expressed as: WP ¼

pl2f df2 ruf 1 pdf sl2f ¼ 24 48Lcrit f

ð3:7Þ

The pull-out energy of CNTs in the composites can be given by Eq. (3.8). WP ¼ N
WP

ð3:8Þ

422

3 Carbon Nanotubes-Engineered Cementitious Composites

Table 3.24 Fracture energy increments of CNTs-filled cement pastes CNT type

WP  10−12/J Vf = 0.5% Vf = 0.8%

N  1012/cm2

Wp/(J/cm2)

Vf = 0.5%

Vf = 0.8%

Vf = 0.5%

Vf = 0.8%

M1 MH1 MC1 SM1 SMH1 SMC1

0.45–2.43 0.43–2.3 0.45–2.4 0.02–0.15 0.02–0.17 0.03–0.18

21–6 21–6 21–6 419–86 419–86 419–86

34–9 34–9 34–9 672–138 672–138 672–138

9.58–14.6 9.13–13.9 9.5–14.5 9.02–13.2 10.2–14.8 10.8–15.8

12.5–17.7 11.8–16.6 13.0–18.4 10.5–15.4 10.9–16.0 9.8–14.3

0.37–1.96 0.35–1.85 0.38–2.0 0.02–0.11 0.02–0.12 0.01–0.1

where N is the number of CNTs per 1 cm2 in the composites and df represents the diameter of CNTs. Table 3.24 shows the pull-out energy of the composites when damage state of CNTs is based on pull-out. Compared with untreated CNTs, functionalized CNTs consume more pull-out energy.

3.3.4

Effect of Special Structure and Surface Modification of Carbon Nanotubes on Mechanical Properties/ Performances

(1) Compressive strength

Fig. 3.18 Compressive strength of cement pastes with special types of CNTs

Compressive strength / MPa

Figure 3.18 shows compressive strength of cement pastes with four special types of CNTs. For comparison, compressive strength of cement pastes with untreated M5 is plotted in Fig. 3.18. The corresponding relative and absolute increases in compressive strength compared with control cement pastes are listed in Table 3.25. As shown in Fig. 3.18 and Table 3.25, compressive strength of cement pastes with special types of CNTs improves greatly as compared to control cement pastes. Addition of 0.5% nickel-coated CNT (NiM5) produces the maximum compressive

0 0.5%

180

0.1% 0.8%

150 120 90 60 30 0

NiM5

GM5

LIM

HIM

Types of CNTs

M5

3.3 Mechanical Properties/Performances of Carbon Nanotubes-Engineered …

423

Table 3.25 Relative/absolute increase in compressive strength of cement pastes with special types of CNTs CNT content

M5 Rel./ %

0.1% 32.6 0.5% 18.1 0.8% 30.0 Note Abs. and Rel.

Abs./ MPa

GM5 Rel./ Abs./ % MPa

NiM5 Rel./ Abs./ % MPa

30.7 0.2 0.2 64.7 17.0 44.8 42.1 78.8 28.2 56.0 52.6 54.0 denote the absolute and relative

HIM Rel./ %

Abs./ MPa

60.7 5.7 5.3 74.0 65.3 61.3 50.7 50.0 47.1 value, respectively

LIM Rel./ %

Abs./ MPa

4.3 20.4 46.0

4.0 19.2 43.2

strength (168 MPa) in this study, which is about 79%/74 MPa and 61%/57 MPa higher than that of control cement pastes and M5-filled cement pastes, respectively. For surface-modified CNTs, compressive strength of cement pastes with NiM5 and GM5 enhances greatly as compared to untreated M5 of the same size. However, reinforcement effect of nickel-coated treatment on compressive strength is better than that of graphitized treatment. As for CNTs with special structure, the highest compressive strength is achieved by helical CNT (HIM) cement pastes at content of 0.5%, which is about 65%/61 MPa higher than control cement pastes. Compared with HIM, compressive strength of large-inner thin-walled CNT (LIM) cement pastes is relatively small. (2) Flexural strength

Fig. 3.19 Flexural strength of cement pastes with special types of CNTs

Flexural strength / MPa

Figure 3.19 shows flexural strength of cement pastes with four special types of CNTs. For comparison, flexural strength of cement pastes with untreated M5 is also plotted in Fig. 3.19. The corresponding relative and absolute increases in flexural strength compared with control cement pastes are listed in Table 3.26, respectively. It can be seen from Fig. 3.19 that the addition of these special CNTs improves flexural strength of cement pastes. The maximum flexural strength (14.3 MPa) is obtained from 0.5% of NiM5-filled cement pastes, which is increased by 64.4%/ 5.6 MPa compared with control cement pastes. Furthermore, compared with M5-filled cement pastes, the flexural strength of NiM5-filled cement pastes

0 0.5%

16

0.1% 0.8%

12 8 4 0

NiM5

GM5

LIM

HIM

Types of CNTs

M5

424

3 Carbon Nanotubes-Engineered Cementitious Composites

Table 3.26 Relative/absolute increase in flexural strength of cement pastes with special types of CNTs CNT content

M5 Rel./ %

0.1% 44.8 0.5% 37.9 0.8% 44.8 Note Abs. and Rel.

Abs./ MPa

GM5 Rel./ Abs./ % MPa

NiM5 Rel./ Abs./ % MPa

3.9 5.6 0.5 57.1 3.3 28.7 2.5 64.4 3.9 39.1 3.4 34.5 denote the absolute and relative

HIM Rel./ %

Abs./ MPa

4.8 21.8 1.9 5.6 28.7 2.5 3.0 56.3 4.9 value, respectively

LIM Rel./ %

Abs./ MPa

4.6 43.7 17.2

0.4 3.8 1.5

increases, while that of GM5 cement pastes reduces. As for CNTs with special structure, the highest flexural strength is achieved by HIM-filled cement pastes at a content of 0.8%, which is about 56%/5 MPa higher than control cement pastes. Flexural strength of LIM filled cement pastes at large concentration enhances greatly as compared to control cement pastes. It should be noted that reinforcement effect of CNTs with the special structure on flexural strength is relatively smaller than that on compressive strength. Through comprehensive analysis, it is observed that these four types of special CNTs have good enhancement effects on compressive and flexural strengths of cement pastes compared with control cement pastes in most cases. Moreover, strength enhancement on cement pastes with special kinds of CNTs at large amount is sometimes higher than pristine CNTs. The maximum enhancements in compressive (78.8%/74 MPa) and flexural strength (64.6%/5.6 MPa) are both achieved by incorporating nickel-coated CNTs at content of 0.5% into cement pastes. Moreover, comparing the result in this study with the results obtained by present studies [20–22], it is observed that, despite the lower CNT concentration used, strength increase for NiM5-filled cement pastes are higher. The thermal conductivity of nickel is better than that of carbon materials, which can greatly reduce primary cracks. Moreover, nickel plating on surface can improve hardness of CNTs. In addition, graphitized treatment is a purification method of CNTs, which is helpful to decrease structural defects of CNTs and enhance the degree of crystallization. The distinctive structure of helical CNTs is just like the ribbed bars, which increases bonding strength between CNTs and matrix. Moreover, the average bonding strength can be expressed as: s¼

df ruf 2Lcrit f

ð3:9Þ

It can be calculated through combining with Eqs. (3.4)–(3.6). Table 3.27 lists the average bonding strength of helical and graphitized CNTs at 0.5 wt% level. It is obvious that bonding strength of HIM is higher than that of NiM5. The tube wall of LIM is very thin and about 5 nm. As listed in Table 3.28, LIM’s number per cm3 can reach in the range from 1.5  1014 to 3.1  1015 as the CNTs content is only

3.3 Mechanical Properties/Performances of Carbon Nanotubes-Engineered …

425

Table 3.27 Average bonding strength of CNTs at 0.5wt% level CNT type

Diameter/nm

Length/lm

Critical length/lm

Average bonding strength/MPa

NiM5 HIM

20–30 100–200

10–30 1–10

16.44–49.32 1.86–18.58

18.25–9.12 807.47–161.49

Table 3.28 Number of LIM per 1 cm3 in the composites Diameter (d)/nm

Length (l)/lm

Thickness of wall(h)/nm

Volume (V = pdlh)/nm3

Numbers of LIM per 1 cm3 in the composites

30–60

1–10

5

3.2  104–6.4  105

1.5  1014–3.1  1015

0.1 vol.%. The numerous LIM can form an extensive distribution network and guarantee full enhancement effect. (3) Reinforcement mechanisms 1. X-ray diffraction analysis Figure 3.20 shows XRD patterns of four special types of CNTs cement pastes. For comparison, XRD pattern of cement pastes with untreated M5 is also shown in Fig. 3.20. Diffraction intensity and orientation of CH are listed in Table 3.29. It can be observed that CH orientation of cement pastes containing HIM and LIM is larger than that of untreated CNT, even more than that of control cement pastes. Moreover, the main diffraction intensity of CH (I(001) = 2039 and I(101) = 1007) in cement pastes with LIM at content of 0.8% is also higher than that of control cement pastes. Because the helical CNTs have large out diameter and are curly, their effect on the CH orientation is weak. LIM also have no obvious effect on restraining the directional growth of CH because of their small tube thickness. However, CH orientation of cement pastes containing GM5 and NiM5 has

Fig. 3.20 XRD patterns of cement pastes with special types of CNTs (Note C3S represents 3CaO
SiO2.)

AFt

Ca(OH)2

(001)

♦

C3S

♦CaCO3

(101)

LIM HIM GM5 NiM5 Control

8

16

24

32

40

2θ/°

48

56

64

426

3 Carbon Nanotubes-Engineered Cementitious Composites

Table 3.29 Diffraction intensity and orientation of CH in cement pastes with special types of CNTs Cement pastes

Control

With M5

With GM5

With NiM5

With HIM

With LIM

(001)CH (101)CH CH orientation

1794 898 2.70

1319 881 2.02

1542 964 2.16

1512 980 2.08

2147 1102 2.63

2046 963 2.87

relatively small changes compared with untreated M5. It is concluded that structure variety of CNTs has significant influence on the CH orientation. By contrast, the effect of nickel plating and graphitization of CNTs on CH orientation is ignorable. 2. Thermogravimetry analysis TG and DTG diagrams for cement pastes with four special types of CNTs are shown in Fig. 3.21. For comparison, TG and DTG diagrams for cement pastes with untreated M5 are also shown in Fig. 3.21. Cement hydration degree of cement pastes with special kinds of CNTs is shown in Table 3.30. As shown in Table 3.30, cement hydration degree decreases as the CNTs are added into cement pastes. Compared with untreated CNTs, cement hydration degree for cement pastes having GM5, LIM, and HIM increase slightly. It is indicated that surface modification and special structure of CNTs have little influence on cement hydration degree.

(a) Mass / %

100

Control GM5 NiM5 LIM HIM

95 90 85 80 200

400

600

800

1000

Temperature / °C

(b) 1st derivative of mass / %

Fig. 3.21 TG diagram (a) and DTG diagram (b) for cement pastes with special types of CNTs

0.0000 -0.0002 -0.0004 -0.0006

Control GM5 NiM5 LIM HIM

-0.0008 -0.0010 0

200

400

600

800

Temperature / °C

1000

3.3 Mechanical Properties/Performances of Carbon Nanotubes-Engineered …

427

Table 3.30 Hydration degree of cement pastes with special types of CNTs Type of cement pastes

Control

With M5

With GM5

With NiM5

With LIM

With HIM

Hydration degree/%

69.5

62.7

63.2

61.5

63.2

64.8

Fig. 3.22 29Si NMR spectra of cement pastes with NiM5 and HIM

Q0

SM5 HIM NiM5 Cotrol

Q1 Q2

-60

-70

-80

-90

-100

-110

-120

Chemical shift / ppm Table 3.31 Deconvolution results of 29Si NMR for cement pastes with NiM5 and HIM

3.

29

Cement pastes

Q0/%

Q1/%

Q2/%

PD

MCL

Control With NiM5 With HIM

49.79 43.25 48.8

29.68 29.63 31.5

20.52 27.11 19.6

0.69 0.91 0.62

3.38 3.83 3.24

Si nuclear magnetic resonance analysis

Figure 3.22 shows the 29Si NMR spectra of cement pastes with NiM5 and HIM, and their calculation results of devolution are summarized in Table 3.31. It can be seen from Fig. 3.22 that uncondensed silicate monomers (Q0), disilicate/dimer (Q1), and middle group of disilicate/dimer short chain (Q2) exist in CNTs-filled cement pastes, indicating that the structure of C–S–H gels does not change. As listed in Table 3.31, the PD and MCL of NiM5-filled cement pastes are enhanced by 32% and 13% compared with control cement pastes, respectively, which is conductive to improve the mechanical strength of cement pastes. Whereas, the inclusion of HIM leads to slight reduction in the PD and MCL of cement pastes, which is negligible. This indicates that HIM has no significant effect on the structure of C–S–H gels. 4. Microstructure observation The size and surface morphology of CH crystals in cement pastes without and with CNTs are shown in Fig. 3.23. It can be observed that the size of CH in cement pastes decreases due to the addition of CNTs. XRD analyses also manifest the NiM5 at content of 0.5% decreases the orientation index of CH crystals in matrix. Thus, it can be concluded that CNTs enhance strength of cement pastes by means of

428

3 Carbon Nanotubes-Engineered Cementitious Composites

(b)

(a)

CH 20μm

10μm

CH

Fig. 3.23 SEM images of CH in cement pastes a without and b with 0.5% of NiM5

(a)

HIM

1μm

4μm

(b)

GM5

2μm

500nm

Fig. 3.24 SEM images of 0.8% of a HIM and b GM5 in cement pastes

lowering the size and orientation of CH. Figure 3.24 shows SEM micrographs of HIM and GM5 at content of 0.8% in cement pastes. It can be observed that helical CNTs and graphitized CNTs bundles are anchored well inside the hydration products. The CNTs and matrix tightly bond with each other.

3.4 Transport Properties of Carbon Nanotubes-Engineered …

3.4 3.4.1

429

Transport Properties of Carbon Nanotubes-Engineered Cementitious Composites Fabrication of Cement Mortars with Carbon Nanotubes

The type of CNTs used to fabricate CNTs-filled cement mortars is MC1 mentioned in Sect. 3.3.1. The mix proportion and main fabrication progress of CNTs-filled cement mortars are shown in Tables 3.32 and 3.33, respectively.

3.4.2

Water Sorptivity

Figure 3.25 depicts the variations of absorbed water with water absorbing time for three types of cement mortars. Figure 3.25a shows that the water absorbing amounts of three types of cement mortars firstly increase and then stabilize with the increase of water absorbing time. Both CNTs-filled cement mortars demonstrate lower amounts of absorbed water than that of control cement mortars. Figure 3.25b shows the linear range of the experimental data. The sorptivity coefficients ks of three types of cement mortars are listed in Table 3.34. It can be seen from Table 3.34 that the sorptivity coefficient of control cement mortars is twice of that of CNT-filled cement mortars. The above results indicate that the use of CNTs decreases the water sorptivity of cement mortars. The improvement of CNTs to water sorptivity of cement mortars is mainly due to: (1) the modification of hydration products; (2) refined pore size distribution and reduction of the porosity; (3) the reduction of autogenous shrinkage [6, 23–25]. Therefore, the CNTs-filled cement mortars become much more compacted and exhibit lower water sorptivity relative to control cement mortars.

3.4.3

Water Permeability

Figure 3.26 shows the temporal evolution of cumulative water flow penetrating the cement mortars. As shown in Fig. 3.26a, the cumulative water flow increases with Table 3.32 Mix proportion of CNTs-filled cement mortars Cement type

CNT content

Sand type

Surfactants Dispersion agent Type Concentration (mol/L) 8.1  10−3 1.4  10−2

Defoamer agent

C:W: S = 1:0.46: 1.5 Note NaDDBS, SDS, C, W, and S represent sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, cement, water, and sand respectively ASTM Type I Portland cement

0.2 wt % of C

Fine sand

NaDDBS SDS

0.25 vol. %

Proportion of C, W and S

Fabrication process Feeding order Technology Method Time

Molding Method Size/mm

Curing Condition

Ultrasonication + Carboxyl surface modification + Non-covalent surface modification by NaDDBS or SDS

W+NaDDBS or SDS CNTs

Magnetic 3 min Vibration 50.8  50.8  50.8 20 °C and 100% mixing relative humidity Ultrasonication 2 h (40 Hz) C+S Shear mixing 3 min Defoamer Shear mixing 3 min Note NaDDBS, SDS, C, W, and S represent sodium dodecylbenzene sulfonate, sodium dodecyl sulfate, cement, water, and sand, respectively

Dispersion method of CNTs

Table 3.33 Main fabrication process of CNTs-filled cement mortars

Time 28 d

430 3 Carbon Nanotubes-Engineered Cementitious Composites

3.4 Transport Properties of Carbon Nanotubes-Engineered …

431

(a) (Q/A) / (g/cm 2 )

0.12 #0 #1 #2

0.08 0.04 0.00

0

200

400

600

800

½ ½ t /s

(b)

y=0.0022x R2 =0.9730

y=0.0011x R2 =0.9096

2

(Q/A) / (g/cm )

0.12 0.08

y=0.0009x R2 =0.9718

#0 #1 #2 Linear fit of #0 Linear fit of #1 Linear fit of #2

0.04 0.00

0

40

80

t

120

½ ½ /s

Fig. 3.25 Relationships between water absorbing amounts and water absorbing time of cement mortars with and without CNTs: a overall; b linear range (Note #0, #1, and #2 represent cement mortars without CNTs, with 0.2% CNTs combined with NaDDBS and 0.2% CNTs combined with SDS, respectively; Q is the amount of water absorbed, A is the cross-sectional area of the specimen that was in contact with water, and t is the time.) Table 3.34 Water sorptivity coefficients of three types of cement mortars Cement mortars types

#0 (Without CNTs)

#1 (With 0.2% CNTs +NaDDBS)

#2 (With 0.2% CNTs +SDS)

ks /(g/cm2 s1/2)

2.2  10−3

1.1  10−3

9.0  10−4

time and the cumulative water flows of both CNTs-filled cement mortars are lower than that of control cement mortars. As shown in Fig. 3.26a and b, the time intervals exhibit a straight line in the permeation cures after 14 days. The permeability coefficients kf of three types of cement mortars are calculated between 16 and 26 days and are listed in Table 3.35. It can be seen from Table 3.35 that the permeability coefficients of CNTs-filled cement mortars are obviously lower than that of control cement mortars. This can also be attributed to the modification in hydration products and microstructures of the cement mortars caused by CNTs [6, 23–25].

432

3 Carbon Nanotubes-Engineered Cementitious Composites

Cumulative flow / mL

(a) #0 #1 #2

6 4 2 0

0

6

12

18

24

Time / d

Cumulative flow / mL

(b) 6

y=0.2095x+1.6736 R2 =0.9995

4

y=0.1179x+1.0829 R2 =0.9987

2

y=0.0718x+1.6814 R2 =0.9988

0

15

18

#0 #1 #2 Linear fit of #0 Linear fit of #2 Linear fit of #3

21

24

27

Time / d Fig. 3.26 Relationships between the cumulative water flow and time for cement mortars with and without CNTs: a overall; b linear range (Note #0, #1, and #2 represent cement mortars without CNTs, with 0.2% CNTs combined with NaDDBS and 0.2% CNTs combined with SDS, respectively.)

Table 3.35 Water permeability coefficients of three types of cement mortars Cement mortars types

#0 (Without CNTs)

#1 (With 0.2% CNTs +NaDDBS)

#2 (With 0.2% CNTs +SDS)

kf /(cm/s)

9.02  10−10

3.14  10−10

5.16  10−10

3.4.4

Gas Permeability

The variations in the loss of methanol with time are illustrated in Fig. 3.28. As shown in Fig. 3.27a, all three types of cement mortars have the same temporal trends; i.e., the loss of methanol increases with time. Figure 3.27b shows that there is a linear relationship between the loss of methanol and time after 100 min. The rate of mass loss m0 and the intrinsic permeability coefficient k of three types of

3.4 Transport Properties of Carbon Nanotubes-Engineered …

Loss of methanol / g

(a)

0.9

433

#0 #1 #2

0.6

0.3

0.0

0

60

120

180

240

Time / min

(b) Loss of methanol / g

0.9

0.6

y=0.0045x-0.2522 R2 =0.9786

y=0.0038x-0.1696 R2 =0.9616

#0 #1 #2 Linear fit of #1 Linear fit of #2 Linear fit of #3

0.3 y=0.0036x-0.1992 R2 =0.9651

0.0

100

150

200

250

Time / min Fig. 3.27 Relationships between loss of methanol and time for cementitious composites with and without CNTs: a overall; b linear range (Note #0, #1, and #2 represent cement mortars without CNTs, with 0.2% CNTs combined with NaDDBS and 0.2% CNTs combined with SDS, respectively.)

Table 3.36 Gas permeability coefficients of three types of cementitious composites Cementitious composites 0

m /(g/s) kf /(cm/s)

#0 (Without CNTs)

#1 (With 0.2% CNTs +NaDDBS)

#2 (With 0.2% CNTs +SDS)

0.0045

0.0038

0.0036

4.00  10−17

3.38  10−17

3.20  10−17

cement mortars can be calculated and are listed in Table 3.36. The data indicate that the intrinsic permeability coefficients of CNTs-filled cement mortars are lower than that of control cement mortars. This further proves that the addition of CNTs is beneficial for improving transport properties of the cement mortars, thus reducing the permeability of the composites.

434

3.5

3 Carbon Nanotubes-Engineered Cementitious Composites

Electrical Properties/Performances of Carbon Nanotubes-Engineered Cementitious Composites

The CNTs-filled cement pastes and their mix proportion and main fabrication progress are the same as that in Sect. 3.3.1.

3.5.1

Effect of Carbon Nanotube Size on Electrical Properties/Performances

(1) Alternating current electrical resistivity Figure 3.28 shows the alternating current (AC) electrical resistivity of cement pastes with different sizes of untreated CNTs. It can be seen from Fig. 3.28 that compared with control cement pastes, the introduction of various sizes of untreated CNTs at different content all decrease the electrical resistivity of cementitious composites, which indicates the incorporation of CNTs into matrix, is beneficial to improve the electrical conductivity of cement pastes. The maximal decrease rate of 56.6% in electrical resistivity can be achieved by adding 0.8% M5. The maximal reduction in electrical resistivity achieved by CNTs with long length and large diameter at high content may be attributed to three aspects. First, CNTs with a higher content can form a more widely distributed filler network in matrix, which is beneficial for the formation of conductive paths. However, the dispersion of CNTs in cement pastes is a pivotal issue, and excess CNTs will form agglomeration inside cementitious composites, thus hindering the formation of conductive paths, as shown in Fig. 3.29a and b. Therefore, the optimal content of CNTs with different sizes to reduce electrical resistivity of cementitious composites is not always 0.8%. The electrical resistivity of cementitious composites can be decreased by 21.1%, Control

Fig. 3.28 Electrical resistivity of cement pastes with untreated CNTs with different sizes

210 180 150

SM1

M5

120 90 60

0.1% 0.5% 0.8%

M

1

5

SM

Electrical resistivity / Ω·m

3.5 Electrical Properties/Performances of Carbon Nanotubes-Engineered …

435

Fig. 3.29 Distribution of CNTs in matrix: a excessive content; b suitable content; c long tube length; d short tube length

36.8%, and 31.4% with the introduction of 0.1% SM1, 0.5% SM5, and 0.5% M1, respectively. Second, CNTs with long length can better contact and overlap with adjacent CNTs than CNTs with short length. In other words, assuming the CNTs are well dispersed in matrix, and short CNTs are not easy to contact with each other, as shown in Fig. 3.29c and d. In the case of adding the same content of CNTs, the decrease rate in electrical resistivity of cement pastes with M1 is always greater than that with SM1. Third, larger diameter means larger cross-sectional area; the space inside matrix occupied by CNTs with large diameter is greater than that with small diameter, which is conducive to electrical conductivity of cement pastes. In most instances, the decrease rate in electrical resistivity of cement pastes with SM5 is larger than that of cement pastes with SM1. It can be inferred that in majority of cases, the electrical conductivity of long CNTs-filled cement pastes is better than that of short CNTs-filled cement pastes, and the electrical conductivity of large-diameter CNTs-filled cement pastes is superior to that of small-diameter CNTs-filled cement pastes. (2) Electrochemical impedance spectroscopy The electrochemical impedance spectroscopy (i.e., EIS) (drawn in Nyquist plot) of cement pastes without CNTs is shown in Fig. 3.30. The frequency in each plot decreases from left to right. For control cement pastes without CNTs, the pore solution resistance, matrix, and electrodes all will generate influences on EIS. In EIS, the intersection point of the arc starting point and horizontal axis corresponds to Rs in the equivalent circuit model. Rs represents the electrical resistance value of pore solution; thus, it can characterize the total porosity of matrix. The higher the Rs value, the lower the total porosity of matrix. The arc section in the high-frequency region represents the charge transfer resistance Rst, including

436

3 Carbon Nanotubes-Engineered Cementitious Composites 60

-jZ'' / kΩ

45 30 15 0

0

7

14

21

28

35

Z'/ kΩ Fig. 3.30 EIS of cement pastes without CNTs

the charge transfer resistance (Rst2) by the hydration electrons in C–S–H gels and the charge transfer resistance (Rst1) between electrode and matrix. Moreover, the arc section also includes the resistance caused by the C–S–H gels surface capacitance (Cs2) and the electrode–matrix interface double-layer capacitance (Cs1). The part of the curve from horizontal axis intersection point indicates that when the voltage is applied, the adsorption and desorption of ions have appeared on the surface of C–S–H gels; this part is represented by L in the equivalent circuit diagram. The straight part in the low-frequency region indicates that the real and imaginary parts of the impedance are linearly related. This part of the electrochemical process is mainly controlled by diffusion, and the corresponding impedance is called Warburg impedance (Zw). Zw includes two parts: impedance in matrix (Zw2) and impedance between electrode and matrix (Zw1). Therefore, the corresponding equivalent circuit model is diagramed in Fig. 3.31a, i.e., RsL(Q1(R1W1))(Q2(R2W2)). In order to verify the accuracy of equivalent circuit model, measured values and calculated values (using ZsimpWin electrochemical simulation software) are drawn in Nyquist plot together in Fig. 3.32. The chi-squared is 3.93  10−4, which indicates the calculated values can well match the measured values of EIS. Therefore, the established equivalent circuit model can well describe the EIS of cement pastes without CNTs. It can be seen from Figs. 3.33, 3.34, 3.35, and 3.36 that the EIS of cement pastes with different sizes of untreated CNTs all qualify quasi-Randles situation. The circular arc section in the figure is mainly determined by the cement paste matrix and CNTs. The corresponding equivalent circuit section is represented by a series connection circuit consisting of Rs and Rcnt. The two parameters represent the pore solution resistance and CNTs resistance, respectively. The complete equivalent circuit model of CNTs-filled cement pastes is diagramed in Fig. 3.31b, i.e., Rs(Q1(R1W1))(Q2(R2W2))(Q3R3). Calculated values acquired by ZsimpWin software can well match the measured values of EIS in Figs. 3.37, 3.38, 3.39, and 3.40. These values indicate the established equivalent circuit model is accurate and credible. In addition, as mentioned in Sect. 3.6.1, among four types of untreated CNTs with different sizes, the electrical resistivity of cement paste with 0.8% M5 is

3.5 Electrical Properties/Performances of Carbon Nanotubes-Engineered …

437

Fig. 3.31 Equivalent circuit models of cement pastes: a without CNTs; b with CNTs (Note Rs, L, Cs2, Rst2, Zw2, Cs1, Rst1, Zw1, Rcnt, Ccnt represent pore solution resistance, inductance, C–S–H gels surface capacitance, charge transfer resistance in matrix, Warburg impedance in matrix, electrode– matrix interface double-layer capacitance, charge transfer resistance between electrode and matrix, Warburg impedance between electrode and matrix, CNTs resistance, and CNTs–matrix interface capacitance, respectively)

60

Fig. 3.32 Simulated and measured EIS curves of cement pastes without CNTs

-jZ'' / kΩ

50 chi-squared: 3.93×10-4

40 30 20

Measured value

10 0

Calculated value

0

5

10

15

20

25

30

Z' / kΩ

60

Fig. 3.33 EIS of cement pastes with M1

2.0

-jZ'' / kΩ

-jZ'' / kΩ

50 40

1.5 1.0 0.5 0.0 2

30

4

Z' / kΩ

6

8

20 0.1% 0.5% 0.8%

10 0 0

5

10

15

Z' / kΩ

20

25

30

3 Carbon Nanotubes-Engineered Cementitious Composites

Fig. 3.34 EIS of cement pastes with different content of M5

8

60

0.1% 0.5%

-jZ'' / kΩ

50

6

40 4

30 20

-jZ'' / kΩ

438

2

10

0.8%

0

0 0

5

10

15

20

25

30

Z' / kΩ

50

Fig. 3.35 EIS of cement pastes with SM1

0.1% 0.8%

-jZ'' / kΩ

40 30 20 10 0 0

5

10

15

20

25

Z' / kΩ

50

Fig. 3.36 EIS of cement pastes with SM5

0.1% 0.5%

40

20

3

-jZ'' / kΩ

-jZ'' / kΩ

0.8%

30

10

2 1 0

0

2

4

6

8

10

Z' / kΩ

0

5

10

15

20

25

30

35

Z' / kΩ

the lowest. As shown in Fig. 3.34, the impedance value of cement pastes with 0.8% M5 is obviously reduced. Moreover, the straight-line section controlled by charge diffusion in the low-frequency region is replaced by circular arc, and the EIS consists of double arc, which indicates the CNTs at this content play an important role in conductive paths.

3.5 Electrical Properties/Performances of Carbon Nanotubes-Engineered …

(c)

(b) 50

40

40 chi-squared: 2.91×10 -4

30 20

Measured value

10

60 50

chi-squared: 2.99×10 -4

30

Measured value Calculated value

20

40

-jZ'' / kΩ

50

-jZ'' / kΩ

-jZ'' / kΩ

(a)

0

5

10

20

10

10

0

0

15

20

25

30

0

5

Z' / kΩ

10

15

chi-squared: 2.58×10 -4

30

Calculated value

0

439

20

Measured value Calculated value

0

5

10

15

20

25

30

Z' / kΩ

Z' / kΩ

Fig. 3.37 Simulated and measured EIS curves of cement pastes with M1: a 0.1%; b 0.5%; c 0.8%

(b)

(c)

60

50

50

40 chi-squared: 3.63×10-4

30 20 Calculated value

0

5

10

15

20

25

chi-squared: 3.93×10

30 Measured value

20

Calculated value

0

30

4 Measured value

2

10

Measured value

10

6

-4

-jZ'' / kΩ

40

0

8 chi-squared: 1.77×10-4

-jZ'' / kΩ

-jZ'' / kΩ

(a)

Calculated value

0

5

10

15

0

20

0

7

14

Z' / kΩ

Z' / kΩ

21

28

35

Z' / kΩ

Fig. 3.38 Simulated and measured EIS curves of cement pastes with M5: a 0.1%; b 0.5%; c 0.8%

(b)

(a) 40

30 chi-squared: 3.93×10 -4

-jZ'' / kΩ

-jZ'' / kΩ

30

40

20 10

chi-squared: 3.93×10 -4

20

Measured value Calculated value

10

Measured value Calculated value

0

0

5

10

15

20

25

30

Z' / kΩ

0

0

5

10

15

20

25

30

Z' / kΩ

Fig. 3.39 Simulated and measured EIS curves of cement pastes with SM1: a 0.1%; b 0.8%

3.5.2

Effect of Surface Functionalization of Carbon Nanotubes on Electrical Properties/Performances

(1) Alternating current electrical resistivity As shown in Fig. 3.41, except for adding MH1 at a content of 0.1%, the introduction of four types of surface functionalized CNTs all can decrease the electrical

440

3 Carbon Nanotubes-Engineered Cementitious Composites

(a)

50

10

5

10

15

20

Z' / kΩ

20 10

Measured value Calculated value

0

chi-squared: 3.20×10-4

30

-jZ'' / kΩ

-jZ'' / kΩ

chi-squared: 2.35×10-4

20

0

40

40

30

-jZ'' / kΩ

(c)

(b)

40

25

0

5

10

15

20

20 10

Measured value Calculated value

0

chi-squared: 2.75×10-4

30

25

Measured value Calculated value

0

0

Z' / kΩ

5

10 15 20 25 30 35 40

Z' / kΩ

Fig. 3.40 Simulated and measured EIS curves of cement pastes with SM5: a 0.1%; b 0.5%; c 0.8%

Control 210

C1

180

M

1

150

SM

Fig. 3.41 Electrical resistivity of cement pastes with surface functionalized CNTs

120 60

MH1

C1 SM Electrical resistivity / Ω·m M1

SMH1

90

0.1% 0.5%

0.8%

resistivity of cement pastes. Compared to the cement pastes with the same size of untreated M1, the cement pastes with MC1 and MH1 at contents of 0.5% and 0.8% both can achieve lower electrical resistivity, whereas the decrease rate in electrical resistivity achieved by incorporating 0.1% MH1 is smaller than that achieved by adding 0.1% M1. The incorporation of SMH1 to cement pastes can acquire lower electrical resistivity than SM1 at the same content. This may be attributed to the different dispersion situations of these two conductive fillers in cement paste. The absolute value of zeta electrical potential of SMH1 (28.8 mV) is larger than that of SM1 (20.0 mV), which indicates that the dispersion of SMH1 is superior to that of SM1. Among four types of surface functionalized CNTs (MC1, MH1, SMC1, and SMH1), a maximum decrease rate of 54.9% in electrical resistivity can be observed with the introduction of 0.8% MC1 into cement pastes. In addition, other three types of surface functionalized CNTs at content of 0.5% can minimize the electrical resistivity of cement pastes; the corresponding decrease rates of SMH1-, SMC1-, and MH1-filled cement pastes are 52.9%, 43.1%, and 38.2%, respectively.

3.5 Electrical Properties/Performances of Carbon Nanotubes-Engineered …

441

(2) Electrochemical impedance spectroscopy EIS of various types of surface functionalized CNTs-filled cement pastes were tested, as shown in Figs. 3.42, 3.43, 3.44, 3.45. The EIS of these types of CNTs-filled cement pastes are similar to that of M1- and SM1-filled cement pastes, as shown in Figs. 3.33 and 3.35. They all have similar topological structures composed of two parts: arc section in the high-frequency region and straight-line Fig. 3.42 EIS of cement pastes with MC1

4

-jZ'' / kΩ

60

-jZ'' / kΩ

45

3 2 1 0

2

4

6

8

10

Z' / kΩ

30 15

0.1% 0.5%

0

0.8%

0

5

10

15

20

25

30

Z' / kΩ 60

Fig. 3.43 EIS of cement pastes with MH1

3

-jZ'' / kΩ

-jZ'' / kΩ

50 40

2 1 0

30

2

4

6

8

10

Z' / kΩ

20

0.1% 0.5%

10

0.8%

0 0

5

10

15

20

25

30

20

25

30

Z' / kΩ 60

Fig. 3.44 EIS of cement pastes with SMC1

0.1% 0.5% 0.8%

-jZ'' / kΩ

50 40 30 20 10 0 0

5

10

15

Z' / kΩ

442

3 Carbon Nanotubes-Engineered Cementitious Composites

-jZ'' / kΩ

60 50

0.1% 0.5%

40

0.8%

30 20 10 0 0

5

10

15

20

25

30

Z' / kΩ Fig. 3.45 EIS of cement pastes with SMH1

section in the low-frequency region. Therefore, similar to untreated CNTs, the incorporation of functionalized CNTs also cannot change the EIS characteristic of cement pastes, of which Nyquist plot figure meets quasi-Randles situation. In order to verify the equivalent circuit model diagramed in Fig. 3.34b, simulated impedance values acquired by ZsimpWin electrochemical simulation software were drawn together with measured impedance values in Nyquist plot, as shown in Figs. 3.46, 3.47, 3.48, and 3.49. The chi-squared in these figures is less than or

(a)

(c)

(b)

40

50

70 60

20 10

30 20

Measured value

0

5

10

15

20

25

chi-squared: 3.38×10-4

40

0

30

20

5

10

15

20

25

Measured value

10

Calculated value

Calculated value

0

chi-squared: 3.05×10-4

30

Measured value

10

Calculated value

0

40

50

-jZ'' / kΩ

chi-squared: 2.17×10-4

-jZ'' / kΩ

-jZ'' / kΩ

30

0

30

0

5

10

Z' / kΩ

Z' / kΩ

15

20

25

Z' / kΩ

Fig. 3.46 Simulated and measured EIS curves of cement pastes with MC1: a 0.1%; b 0.5%; c 0.8%

(c)

(b) 50

50

40

40

chi-squared: 3.29×10-4

30 20

0

Calculated value

0

5

10

15 20 Z' / kΩ

25

50 chi-squared: 3.64×10-4

30 20 Measured value

10

Measured value

10

60

30

-jZ'' / kΩ

60

-jZ'' / kΩ

-jZ'' / kΩ

(a)

0

Calculated value

0

5

10

15

Z' / kΩ

20

25

30

40

chi-squared: 3.08×10-4

30 20 Measured value

10 0

Calculated value

0

5

10

15

20

25

30

Z' / kΩ

Fig. 3.47 Simulated and measured AC-EIS curves of cement pastes with MH1: a 0.1%; b 0.5%; c 0.8%

3.5 Electrical Properties/Performances of Carbon Nanotubes-Engineered …

(b)

(c)

50

50

40

40

chi-squared: 3.93×10-4

30 20

0

Calculated value

0

5

10

15

20

25

30 20

0

30

Measured value

50 chi-squared: 3.97×10-4

10

Measured value

10

60

-jZ'' / kΩ

60

-jZ'' / kΩ

-jZ'' / kΩ

(a)

443

Measured value

5

10

15

chi-squared: 3.93×10-4

30 20 10

Calculated value

0

Calculated value

40

0

20

0

5

10

15

20

25

30

Z' / kΩ

Z' / kΩ

Z' / kΩ

Fig. 3.48 Simulated and measured EIS curves of cement pastes with SMC1: a 0.1%; b 0.5%; c 0.8%

(b)

(a)

50

Measured value

40

Calculated value

-jZ'' / kΩ

40 chi-squared: 3.28×10-4

30 20

20

10

10

0

0

0

5

10

15

Z' / kΩ

20

25

30

40 chi-squared: 3.07×10-4

30

-jZ'' / kΩ

50

-jZ'' / kΩ

(c)

50

60

Calculated value

5

10

15

Z' / kΩ

20

20 10

Measured value

0

chi-squared: 2.91×10-4

30

25

0

Measured value Calculated value

0

5

10

15

20

25

30

Z' / kΩ

Fig. 3.49 Simulated and measured EIS curves of cement pastes with SMH1: a 0.1%; b 0.5%; c 0.8%

equal to 3.97  10−4, which indicates the calculated values can well match the measured values of EIS. Therefore, the equivalent circuit model of cement pastes with untreated CNTs established in Sect. 3.6.1 can be adopted for cement pastes with surface functionalized CNTs.

3.5.3

Effect of Surface Modification and Special Structure of Carbon Nanotubes on Electrical Properties/ Performances

(1) Alternating current electrical resistivity Figure 3.50 shows except for incorporating LIM at the content of 0.1%, the introduction of surface modification and special structure of CNTs (GM5, NiM5, HIM, and LIM) all can decrease the electrical resistivity of cement pastes. The cement pastes with GM5 at contents of 0.5, 0.8%, or NiM5 at contents of 0.1, 0.5% both can achieve lower electrical resistivity, compared to the cement pastes with the same size of untreated M5 at same contents. The electrical resistivity of cement

444

3 Carbon Nanotubes-Engineered Cementitious Composites

Control

Fig. 3.50 Electrical resistivity of cement pastes with special types of CNTs

210 180 150 120

HIM

GM5

90 60

0.1% 0.5% 0.8%

LIM NiM5 Electrical resistivity / Ω·m

pastes with NiM5 at different contents is basically the same, which is about 30% lower than that of control cement pastes. Moreover, GM5 and NiM5 are two types of surface modification CNTs based on M5. The absolute value of zeta electrical potential of GM5 (22.3 mV) is greater than that of NiM5 (19.6 mV), which reflects that the dispersion of GM5 is better than that of NiM5. Therefore, the electrical resistivity of cement pastes with GM5 is lower than that of cement pastes with NiM5 at contents of 0.5 and 0.8%. In addition, among these four types of CNTs, the incorporation of 0.8% GM5 maximally decreases the electrical resistivity of cement pastes, and the decrease rate is 63.8%. Moreover, the optimal contents of NiM5, LIM, and HIM are 0.5%, 0.8%, and 0.8%, and the corresponding decrease rates in electrical resistivity of cement pastes are 34.1%, 42.8%, and 34.2%, respectively. (2) Electrochemical impedance spectroscopy As exhibited in Figs. 3.51, 3.52, 3.53, and 3.54, the AC-EIS of cement pastes with GM5, NiM5, HIM, and LIM at different contents all consists of two parts including arc section and straight-line section. The introduction of CNTs with surface modification and special structure cannot change the topological structures of cement

50

Fig. 3.51 EIS of cement pastes with GM5

0.1% 0.5%

-jZ'' / kΩ

40

0.8%

30 20 10 0 0

5

10

15

20

Z' / kΩ

25

30

35

3.5 Electrical Properties/Performances of Carbon Nanotubes-Engineered …

445

60

Fig. 3.52 EIS of cement pastes with NiM5

3

-jZ'' / kΩ

-jZ'' / kΩ

50 40

2 1 0

30

3

4

5

6

7

8

Z' / kΩ

20 0.1% 0.5%

10

0.8%

0 0

5

10

15

20

25

Z' / kΩ

60

Fig. 3.53 EIS of cement pastes with HIM

3

-jZ''/ kΩ

50

-jZ''/ kΩ

40

2 1 0

30

4

6

8

Z' / kΩ

20

0.1% 0.5%

10

0.8%

0 0

5

10

15

20

25

30

Z' / kΩ

50

Fig. 3.54 EIS of cement pastes with LIM

0.1% 0.5%

0.8%

30 20

3

-jZ'' / kΩ

-jZ'' / kΩ

40

10

2 1 0

0

2

4

6

8

Z' / kΩ

0

5

10

15

20

25

30

Z' / kΩ

pastes. Surface modification can certainly affect the electrical properties of cement pastes because the materials (i.e., nickel and graphite) adopted to modify the surface of CNTs are electrically conductive. However, the topology of cement pastes depends on various factors. The content of conductive fillers will play a vital role in the topology rather than the surface modification of CNTs. As shown in Figs. 3.55,

446

3 Carbon Nanotubes-Engineered Cementitious Composites

(b)

(c)

60

50

50

40

chi-squared: 2.40×10-4

30 20 Measured value

10 0

5

10

15

20

25

30

50

40

chi-squared: 2.89×10-4

30 20 Measured value

10

Calculated value

0

60

35

-jZ'' / kΩ

60

-jZ'' / kΩ

-jZ'' / kΩ

(a)

0

40

5

10

15

20

25

30

30 20 Measured value

10

Calculated value

0

40 chi-squared: 3.55×10-4

0

35

Calculated value

0

5

10

Z' / kΩ

Z' / kΩ

15

20

25

30

Z' / kΩ

Fig. 3.55 Simulated and measured EIS curves of cement pastes with GM5: a 0.1%; b 0.5%; c 0.8%

(c)

(b) 60

50

50

40

chi-squared: 2.47×10-4

30 20 Measured value

10 0

5

10

15

20

40

40

chi-squared: 3.08×10-4

30 20

0

25

20

Calculated value

0

5

10

Z' / kΩ

15

20

chi-squared: 3.08×10-4

30

10

Measured value

10

Calculated value

0

50

-jZ'' / kΩ

60

-jZ'' / kΩ

-jZ'' / kΩ

(a)

0

25

Measured value Calculated value

0

5

10

Z' / kΩ

15

20

25

Z' / kΩ

Fig. 3.56 Simulated and measured EIS curves of cement pastes with NiM5: a 0.1%; b 0.5%; c 0.8%

(b)

(c)

60

50

50

40

chi-squared: 4.95×10-4

30 20 Measured value

10 0

5

10

15

Z' / kΩ

20

25

50

40

chi-squared: 3.30×10-4

30 20 Measured value

10

Calculated value

0

60

30

-jZ'' / kΩ

60

-jZ'' / kΩ

-jZ'' / kΩ

(a)

0

5

10

15

Z' / kΩ

20

25

30 20 Measured value

10

Calculated value

0

chi-squared: 3.93×10-4

40

30

0

Calculated value

0

5

10

15

20

25

30

Z' / kΩ

Fig. 3.57 Simulated and measured EIS curves of cement pastes with HIM: a 0.1%; b 0.5%; c 0.8%

3.56, 3.57, and 3.58, the calculated values acquired by ZsimpWin electrochemical simulation based on equivalent circuit model diagramed in Fig. 3.31b can well conform to the measured values of EIS. It can be concluded that this equivalent circuit model can also be used for cement pastes containing CNTs with surface modification and special structure, further proving that this model is universal in CNTs-filled cement pastes.

3.6 Self-Sensing Properties/Performances of Carbon Nanotubes-Engineered …

(b)

(c)

60

50

50

40

chi-squared: 2.92×10-4

30 20 Measured value

10 0

5

10

15

20

25

40 chi-squared: 3.52×10-4

40 30 20

30

Z' / kΩ

0

Calculated value

0

5

10

15

20

25

chi-squared: 2.93×10-4

30 20 10

Measured value

10

Calculated value

0

50

-jZ'' / kΩ

60

-jZ'' / kΩ

-jZ'' / kΩ

(a)

447

30

0

Measured value Calculated value

0

5

Z' / kΩ

10

15

20

25

Z' / kΩ

Fig. 3.58 Simulated and measured EIS curves of cement pastes with LIM: a 0.1%; b 0.5%; c 0.8%

3.6 3.6.1

Self-sensing Properties/Performances of Carbon Nanotubes-Engineered Cementitious Composites Self-sensing Properties/Performances of Cement Pastes with Carbon Nanotubes

The type of CNTs used to fabricate self-sensing CNTs-filled cement pastes is MC1 in Sect. 3.3.1. The mix proportion and main fabrication progress of CNTs-filled cement pastes are as shown in Tables 3.37 and 3.38, respectively. Figure 3.59 shows the sensing properties of CNTs-filled cement pastes under repeated compressive loading with different stress amplitudes. As shown in Fig. 3.59a–c, the electrical resistance (R) of the CNTs concrete decreases reversibly upon loading and increases reversibly upon unloading in every cycle under compressive loading. The higher compressive stress (r) level yields bigger change in electrical resistance (DR, i.e. R  R0 , where R0 is the baseline electrical resistance of CNTs-filled cement pastes and is defined as the maximum electrical resistance of the first loading and uploading cycle here). However, Fig. 3.59c shows that DR appears irreversible change when the compressive stress amplitude increases to 12 MPa; i.e., the initial value of DR in each loading and uploading cycle slightly increases with the cycle number. Table 3.37 Mix proportion of CNTs-filled cement pastes Cement type

CNT content

Sand type

Surfactants Dispersion agent Type Concentration (mol/L)

Defoamer agent

Proportion of C and W

0.25 vol. C:W = 1:0.6 ASTM Type I 0.1wt Fine NaDDBS 1.4  10−2 % Portland cement % of C sand Note NaDDBS, C, and W represent sodium dodecylbenzene sulfonate, cement, and water, respectively

W+NaDDBS

Ultrasonication + carboxyl surface modification + non-covalent surface modification by NaDDBS

Time

Molding Method

Magnetic 3 min Vibration mixing CNTs Ultrasonication 2 h (40 Hz) C Shear mixing 3 min Defoamer Shear mixing 3 min Note NaDDBS, C, and W represent sodium dodecylbenzene sulfonate, cement, and water, respectively

Fabrication process Feeding Technology order Method

Dispersion method of CNTs

Table 3.38 Main fabrication process of CNTs-filled cement pastes

50.8  50.8  50.8

Size/mm

20 °C and 100% relative humidity

Curing Condition

Time 28 d

448 3 Carbon Nanotubes-Engineered Cementitious Composites

3.6 Self-Sensing Properties/Performances of Carbon Nanotubes-Engineered …

σ / MPa

(a)

0 -4 -8

-12 0 -3 -6 -9

ΔR / kΩ

Fig. 3.59 Sensing properties of self-sensing CNTs cement pastes under compressive loading: a with different amplitudes; b with amplitude of 10 MPa; c with amplitude of 12 MPa (Note DR and r represent the change in electrical resistance and stress.)

449

0

200

400

600

Time / s

σ / MPa

(b)

0 -4 -8

-12

ΔR / kΩ

0 -3 -6 -9

0

150

300 450 Time / s

600

σ / MPa

0 -4 -8 -12

ΔR / kΩ

(c)

0 -3 -6 -9

0

300

600

900

Time / s

3.6.2

Self-sensing Properties/Performances of Cement Mortars with Carbon Nanotubes

The CNTs-filled cement mortars and their mix proportion and main fabrication progress are the basically same as that in Sect. 3.4.1. Only the content level of CNTs is 1.0%, and the surfactant is NaDDBS. The variation in electrical resistance of cement mortar with CNTs under repeated compressive loading and impulsive loading is illustrated in Fig. 3.60. As shown in Fig. 3.60a, the relationships between the change in electrical resistance of the composite and the compressive stress are similar to that of CNTs-filled cement

3 Carbon Nanotubes-Engineered Cementitious Composites

(a) σ / MPa

Fig. 3.60 Self-sensing properties of cement mortars with NaDDBS and 1% of CNTs: a under repeated compressive loading with amplitude of 10 MPa; b under impulsive loading (Note Dq and r represent the change in electrical resistivity and stress.)

ΔR / Ω

450

0 -3 -6 -9

0 -200 -400 -600 -800

0

200

400

600

800

Time / s

σ / MPa

(b)

0 -3 -6

Δρ / Ω

-9 0 -200 -400 -600 -800

0

100

200

300

400

Time / s

pastes. The change in electrical resistance decreases about 700X as the compressive stress is 10 MPa respectively. In addition, Fig. 3.60b shows that there is a good correlated relationship between the electrical resistance and the impulsive loading.

3.6.3

Mechanisms of Self-sensing Properties/Performances

The electrical resistance of self-sensing CNTs-filled cementitious composites comes from two sources: the intrinsic resistance of nanotubes and the contact resistance at nanotube junctions (i.e., the resistance of the matrix connecting the crossing nanotubes and through which electrical tunneling occurs) as shown in Fig. 3.61a and b. Thus, the electrical conductivity of the CNTs-filled cementitious composites strongly depends on the morphology of nanotube network and the number of contact points. The electric conductivity of individual CNT is in the order of 104*107 s/m. But the contact resistance is rather complicated and depends on nanotube diameter, tunneling gap at contact points, and matrix material filling the tunneling gap. The electrical resistance of self-sensing CNTs-filled cementitious composites can be changed when they are deformed under applied loading. Several factors may contribute to the electrical resistance change. First, when self-sensing CNTs-filled cementitious composites are deformed under external loading, the

3.6 Self-Sensing Properties/Performances of Carbon Nanotubes-Engineered …

451

(b) (a) Matrix

Tunneling

Nanotube resistance

(c)

Damage

Tunneling reduced

Fig. 3.61 A schematic diagram of conductive network in CNTs-filled cementitious composites

nanotube length and diameter will alter, resulting in the change of nanotube intrinsic resistance, and hence the electrical resistance of the nanotube network. However, this resistance change is expected to be negligible because of the extremely small elastic deformation in nanotubes. The second and more important factor contributing to the resistance change of the CNTs-filled cementitious composites is the contact resistance. Under the applied load, the thickness of the insulating matrix between adjacent nanotubes may be changed considerably. The compressive loading gives rise to the decrease of the gap at the contact area where electrical tunneling takes place and thus decreases the contact resistance [26–29]. Therefore, the self-sensing property of CNTs-filled cementitious composites results from the variation in the contact resistance among CNTs and between CNTs and matrix under compressive loading, which is caused by the deformation of CNTs-filled cementitious composites. It should be noted that the compressive strength of CNTs-filled cement pastes is higher than 40 MPa, so the CNTs-filled cement pastes are still within an elastic regime when the stress amplitude is lower than 10 MPa. Since elastic deformation is recoverable, the sensing property of the CNTs-filled cement pastes in the elastic regime is stable and reversible. However, when the compressive loading amplitude reaches 12 MPa, the deformation of CNTs-filled cement pastes possibly has gone beyond the elastic regime. Some minor damages appear inside the CNTs-filled cement pastes. Figure 3.61c illustrates the effect of damage on the change in contact resistance. The damage spot assumes the form of a nanoscopic void and its formation give rise to the increase of the opening gap at the contact area where electrical tunneling takes place and thus increases the contact resistance. As a result, the sensing property of CNTs-filled cement pastes under compression with compressive stress amplitude of 12 MPa is irreversible. Therefore, the self-sensing CNTs-filled cementitious composites can be used to achieve not only stress/strain monitoring by measuring the reversible resistance change, but also damage monitoring by measuring the irreversible resistance change.

452

3.7

3 Carbon Nanotubes-Engineered Cementitious Composites

Case Study of Applications of Carbon Nanotubes-Engineered Cementitious Composites

The mix proportion and main fabrication progress of self-sensing CNTs-filled cement mortars are as same as that in Sect. 3.4.1. The fabricated self-sensing CNTs-filled cementitious composites are embedded in concrete pavement, and vehicles are driven passing over the pavement to investigate the feasibility of traffic detection. The variation in electrical resistance of self-sensing CNTs-filled cementitious composites under vehicular loading is illustrated in Fig. 3.62, where Fig. 3.62 shows the changes of resistance when two mid-size passenger vehicles and a mini-van vehicle pass over the self-sensing CNTs-filled cementitious composites. As can be seen in Fig. 3.62, vehicular loads can lead to remarkable change in electrical resistance of the self-sensing CNTs-filled cementitious composites. It can also be seen from Fig. 3.62 that the change amplitude in electrical resistance of mini-van passing over is larger than that of passenger vehicles, which is due to the heavier axis weight of the mini-van (i.e., larger mechanical stress). These findings indicate that self-sensing CNTs-filled cementitious composites can detect traffic flow and even possible to identify different vehicular loadings (weight-in-motion detection). The weight of vehicles such as heavy trucks is needed to avoid damage to highways due to overweight. It is currently conducted in weighing stations off the highway while the vehicle is stationary. The monitoring of the weight of vehicles can be more convenient and effective if the weighing is performed on the highway while the vehicle is moving normally. In this way, traffic is not affected and time is saved. The self-sensing CNTs-filled cementitious composite pavements with intensive road tests have been performed. The self-sensing CNTs-filled cementitious composites were integrated into a controlled pavement test section at the Minnesota Road Research Facility of USA to build a self-sensing concrete pavement system for traffic detection. Road test results show that the proposed self-sensing pavement system can accurately detect the passing of different vehicles under different vehicular speeds and test environments. As shown in Fig. 3.63, abrupt changes occurred in the voltage signal curves when the truck passes over the self-sensing

100 0

ΔR / Ω

Fig. 3.62 Variation in electrical resistance of self-sensing CNTs-filled cementitious composites under different vehicular loadings (Note DR represents the change in electrical resistance.)

-100 -200 -300 0

30

60

90

Time / s

120

3.7 Case Study of Applications of Carbon Nanotubes-Engineered …

453

Fig. 3.63 Variation in voltage of self-sensing CNTs-filled cementitious composites under different vehicular loadings

CNTs-filled cementitious composites. Each peak indicates a passing wheel, which is well corresponding to the structure of the truck. Therefore, the developed self-sensing CNTs-filled cementitious composite pavement system can achieve real-time vehicle flow detection with a high detection rate and a low false-alarm rate [30]. In addition, the changes in electrical resistivity signal (i.e., voltage signal) caused by the polarization the environmental factors (including temperature and humidity) are continuous and gradual, while those caused by vehicular loading are transient and abrupt. As a result, the former can be filtered out in the post-processing of measured voltage signals, and they will not influence the detection accuracy. Therefore, the self-sensing CNTs-filled cementitious composite pavements feature excellent robustness to polarization inside the composites and changes in external environment [31]. Vehicle detection is one of the critical elements in traffic management and operations. Currently, various detection systems are being used to collect and process traffic data. These traffic data are mainly obtained from vehicle sensors buried under the pavement or installed along the roadway. However, when conventional vehicle detection sensors such as inductive loop, piezoelectric, and optical fiber detectors are buried under the pavement, the pavement life would inevitably be decreased due to the unfavorable compatibility of sensors with pavement and/or the short life span of the sensors [32–34]. The self-sensing CNTs-filled cementitious composites provide a new way for developing vehicle detection sensors. The vehicle detection sensor fabricated with the self-sensing CNTs-filled cementitious composites has several advantages over the conventional detectors, such as easy

454

3 Carbon Nanotubes-Engineered Cementitious Composites

Detection parameters: traffic flow, vehicle speed, traffic density and weighing in motion

Self-sensing CNTs-engineered cecmentitious composites

Fig. 3.64 Schematic diagram of self-sensing CNTs-engineered cementitious composite pavement

installation and maintenance, wide detection area, low cost, high anti-jamming ability, long service life, and good compatibility with pavement structures, since they are made of cementitious materials. The pavements or bridge sections fabricated/embedded with the self-sensing CNTs-filled cementitious composites, as shown in Fig. 3.64, can detect a lot of important traffic data such as traffic flow rates, vehicular speed, and traffic density, even achieve weighing in motion. They not only can detect vehicles on the roads, but also could be applied in the parking automation system. Moreover, these self-sensing pavements or bridge sections can also provide data support for structural health monitoring and condition assessment of the traffic infrastructures such as highway and bridge.

3.8

Summary

The fresh cementitious composites with CNTs were fabricated, and their typical flow curves were tested. Two rheological parameters, i.e., yield stress and plastic viscosity, are obtained from fitting with modified Bingham model. The rheological characteristics of fresh cementitious composites with different CNT content levels, W/C and superplasticizer dosages were analyzed through comparing two rheological parameters. The mechanical properties of cementitious composites with different types of CNTs were studied at levels of 0, 0.1, 0.5, and 0.8%. The results obtained from strength, XRD, TG, NMR, SEM, and theory calculation had been summarized and analyzed to identify the reinforcement effect of different types of

3.8 Summary

455

CNTs on behavior of CNTs-engineered cementitious composites. The general transport properties including water sorptivity, water permeability, and gas permeability of CNTs-engineered cementitious composites were investigated to analyze the effect of CNTs on the durability of cementitious composites. The effects of CNT type and content on the electrical conductivity and electrochemical impedance spectroscopy of cementitious composites were studied, and the equivalent circuit model of cementitious composites with different types of CNTs was established. Finally, a self-sensing CNTs-engineered cementitious composite pavement system for traffic detection is proposed and built up. This system was also tested in the road under vehicular loading to investigate the feasibility of using it for traffic monitoring. The conclusions can be summarized as below. (1) The rheological properties of fresh CNTs-engineered cementitious composites coincided to the modified Bingham model, and rheological parameters can be calculated accurately with this model. Both yield stress and plastic viscosity of fresh CNTs-engineered cementitious composites are increased with increasing dosage of CNTs. Rheological parameters are significantly affected by the variation of W/C and superplasticizer concentration. (2) The incorporation of well-dispersed CNTs has significant enhancement on the mechanical properties of cementitious composites, while reinforcement effect of different types of CNTs on cementitious composites is different from each other. The compressive strength of cementitious composites with large-diameter CNTs is higher than that of composites with small-diameter CNTs. Long CNTs are better for improving the flexural strength than short CNTs. Functionalized CNTs result in better strength of cementitious composites than untreated CNTs. The reinforcement effect can be attributed to extensive distributing meshwork in cement matrix, crack bridging, fiber pull-out effect, lowering orientation index of CH crystal in hydration products and decreasing cement hydration degree. The orientation index of CH crystal in cementitious composites is decreased due to the addition of CNTs. CNTs have certain inhibiting effect on the cement hydration due to adsorption effect of CNTs. Decrease of hydration degree is helpful to lower hydration heat, thus reducing primary cracks. In addition, crack bridging and fiber pull-out have also contribution to the strength of cementitious composites. (3) Thanks to the modification of CNTs to hydration products and microstructures of cementitious composites, even at a very small dosage of CNTs can help decrease water sorptivity coefficient, water permeability coefficient, and gas permeability coefficient of cementitious composites, thus improving the durability of cementitious composites. (4) The introduction of different types of CNTs all can decrease the electrical resistivity of cementitious composites due to the CNT distribution network inside composites. The untreated CNTs with long length and large diameter can better decrease the electrical resistivity of cementitious composites. Only the introduction of 0.8% of untreated CNTs with long length and large diameter into cementitious composites can change the topological structure of EIS. The

456

3 Carbon Nanotubes-Engineered Cementitious Composites

established equivalent circuit models are accurate for describing the EIS characteristics of CNTs-filled cementitious composites. (5) The integrated self-sensing CNTs-engineered cementitious composite pavement system presents sensitive and stable responses to vehicular loadings, so it can accurately detect the passing of different vehicles under different vehicular speeds and test environments. This smart pavement system has the advantages of high detection precision, high anti-jamming ability, easy installation and maintenance, long service life, and good structural properties. It has great potential in detecting many kinds of important traffic data such as traffic flow rates, vehicular speed, and traffic density. This would be beneficial for the traffic management and control as well as the health monitoring and condition assessment of infrastructures.

References 1. B.G. Han, S.Q. Ding, S.W. Sun, L.Q. Zhang, J.P. Ou, Chapter 33: Chemical modification of carbon nanotubes/nanofibers for application in cement and concrete field, in Book: Chemical Functionalization of Carbon Nanomaterials: Chemistry and Applications, ed. by V.K. Thakur (Taylor & Francis CRC, 2015), pp. 748–773 2. B.G. Han, S.W. Sun, S.Q. Ding, L.Q. Zhang, S.F. Dong, X. Yu, Chapter 8: Nano carbon materials filled cementitious composites: fabrication, properties and application, in Book: Innovative Developments of Advanced Multifunctional Nanocomposites in Civil and Structural Engineering, ed. by K.J. Loh, S. Nagarajaiah (Elsevier, 2016), pp. 153–181 3. S. Jiang, B.H. Shan, J. Ouyang, W. Zhang, X. Yu, P.G. Li, B.G. Han, Rheological properties of cementitious composites with nano/fiber fillers. Constr. Build. Mater. 158, 786–800 (2018) 4. R.X. Shen, Q. Cui, Q.H. Li, New Type Fiber Reinforced Cement-Based Composites (China Building Material Industry Publishing House, Beijing, 2004) 5. M.F. Yu, O. Lourie, M.J. Dyer, K. Moloni, T.F. Kelly, R.S. Ruoff, Strength and breaking mechanism of multiwalled carbon nanotubes under tensile load. Science 637–640 (2000) 6. B.G. Han, L.Q. Zhang, S.Z. Zeng, S.F. Dong, X. Yu, R.W. Yang, J.P. Ou, Nano-core effect in nano-engineered cementitious composites. Compos. A Appl. Sci. Manuf. 95, 100–109 (2017) 7. A. Peschard, A. Govin, P. Grosseau, B. Guilhot, R. Guyonnet, Effect of polysaccharides on the hydration of cement paste at early ages. Cem. Concr. Res. 34, 2153–2158 (2004) 8. R. Yu, P. Spiesz, H.J.H. Brouwers, Effect of nano-silica on the hydration and microstructure development of ultra-high performance concrete (UHPC) with a low binder amount. Constr. Build. Mater. 65(9), 140–150 (2014) 9. H. Madani, A. Bagheri, T. Parhizkar, The pozzolanic reactivity of monodispersed nanosilica hydrosols and their influence on the hydration characteristics of Portland cement. Cem. Concr. Res. 42(12), 1563–1570 (2012) 10. S. Musso, J.M. Tulliani, G. Ferro, A. Tagliaferro, Influence of carbon nanotubes structure on the mechanical behavior of cement composites. Compos. Sci. Technol. 69(11), 1985–1990 (2009) 11. E. Lippmaa, M. Mägi, A. Samoson, G. Engelhardt, A.R. Grimmer, Structural studies of silicates by solid-state high-resolution 29Si NMR. J. Am. Chem. Soc. 102(15), 4889–4893 (1980)

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32. B.G. Han, K. Zhang, T. Burnham, E. Kwon, X. Yu, Integration and road tests of a self-sensing CNT concrete pavement system for traffic detection. Smart Mater. Struct. 22, 015020 (2013) 33. B.G. Han, S.Q. Ding, Y. Yu, X. Yu, S.F. Dong, J.P. Ou, Design and implementation of a multiple traffic parameter detection sensor developed with quantum tunneling composites. IEEE Sens. J. 15(9), 4845–4852 (2015) 34. B.G. Han, Y.Y. Wang, S.F. Dong, L.Q. Zhang, S.Q. Ding, X. Yu, J.P. Ou, Smart concrete and structures: a review. J. Intell. Mater. Syst. Struct. 26(1), 1303–1345 (2015)

Chapter 4

Graphene-Engineered Cementitious Composites

Abstract Multi-layer graphenes with two-dimensional structure are added into cementitious composites to develop multifunctional/smart materials. The effects of graphene content on the rheology, mechanical properties/performances, durability, and functional/smart properties/performances of fresh and hardened cementitious composites are investigated. The underlying reinforcement/modification mechanisms are also analyzed through X-ray diffraction, nuclear magnetic resonance, thermogravimetry and scanning electron microscope, and electromagnetic parameter tests as well as theoretical calculation. Experimental results show that the incorporation of multi-layer graphenes makes obvious changes in the properties/ performances of fresh and hardened cementitious composites due to their layer structure in combination with the essential characteristics of nano-carbon materials.




Keywords Graphene Multi-layer performances Mechanisms




4.1


Cementitious composites
Properties/

Introduction

Multi-layer graphenes, as 2D nano-carbon materials, are stacking from monolayer carbon atom flat structure graphene. Their extreme case is single-layer graphene, of which the lattice is a hexagon formed by six carbon atoms. The carbon atoms are connected by r-bonds, and their combination modes are sp2 hybridization. These r-bonds endow multi-layer graphenes extremely excellent mechanical property and structural rigidity. It should be noted here that multi-layer graphenes are different from graphene nano-platelet which also stacks from graphene. The differences lie in their layer number and properties. The layer number of graphene nano-platelet is larger than 10 with a thickness between 5 and 100 nm. The layer number of multi-layer graphenes is between 3 and 10 with a thickness less than 5 nm, so the properties of multi-layer graphenes are more like those of single-layer graphene. The stiffness of multi-layer graphenes is 100 times higher than that of the best steels ever known, even higher than that of diamonds. The strength of multi-layer graphenes is dozens of times stronger than that of steels. The coefficient of thermal conductivity of © Springer Nature Singapore Pte Ltd. 2019 B. Han et al., Nano-Engineered Cementitious Composites, https://doi.org/10.1007/978-981-13-7078-6_4

459

460

4 Graphene-Engineered Cementitious Composites

multi-layer graphenes is as high as 5300 W/(m K), which is higher than that of carbon nanotubes and diamond [1–6]. Owing to the remarkable physical properties, significant nano-size effects, low density, and excellent chemical and thermal stability, multi-layer graphenes offer the possibility to develop a new generation of strong, durable, and multifunctional/smart cementitious composites [7–9]. In this chapter, the cementitious composites with different content levels of multi-layer graphenes and different water-to-cement ratios (W/C) were fabricated. The rheology, mechanical properties/performances, durability and functional/smart properties/performances of the fresh and hardened graphene-engineered cementitious composites were investigated. The reinforcement/modification mechanisms of graphene to the properties/performances of cementitious composites were also discussed through theoretical calculation, thermogravimetry (TG) analysis, X-ray powder diffraction (XRD) analysis, scanning electron microscope (SEM) observation, and 29Si nuclear magnetic resonance (NMR) analysis, and electromagnetic parameter analysis.

4.2

Preparation of Graphene-Engineered Cementitious Composites

The properties of multi-layer graphenes used to fabricate graphene-filled cementitious composites are listed in Table 4.1. Figure 4.1 shows the images of multi-layer graphenes. Table 4.1 Physical properties of multi-layer graphenes Diameter/ lm

Thickness/ nm

Specific surface area/(m2/g)

Electrical conductivity/ (s/cm)

Thermal conductivity/ (W/m K)

Oxygen content/ wt%

Nitrogen content/ wt%

107

>3000

6

2

100 nm

Fig. 4.1 Images of multi-layer graphene

4.2 Preparation of Graphene-Engineered …

461

Table 4.2 Mix proportion of cementitious composites with graphene Matrix type

Cement type

Graphene content

W/C

SP Type

Cement pastes

P
O 42.5R

1.0, 2.0, 3.0, 4.0, and 5.0 vol. % 4.0%, 5.0, 6.0, 8.0, 9.0, and 10.0 vol. % 1.0, 5.0, 10.0, and 15.0 vol. %

0.3

Polycarboxylate

Content 1.0 vol. %

0.4

Cement 0.6 mortars Note C, W, and SP represent cement, water, and superplasticizer, respectively

The mix proportion and main fabrication progress of graphene-filled cementitious composites are shown in Tables 4.2 and 4.3, respectively.

4.3

Rheology of Graphene-Engineered Cementitious Composites

Figures 4.2 and 4.3 illustrate the rheological curves of fresh cement pastes with different graphene dosages and W/C. Table 4.4 lists the calculated values of zero tangent apparent viscosity, yield stress, and rheological behavior index (n). Among them, the zero tangent apparent viscosity refers to the ratio of the corresponding shear stress to the shear rate when the shear rate is very small. It can be observed from Figs. 4.2, 4.3 and Table 4.4 that the zero tangent apparent viscosity of graphene-filled cement pastes increases slowly first and then rapidly with the increase of graphene content. This is because graphene itself has lubricating properties, which can reduce the consistency of cement pastes with a low amount of graphene, so that the zero tangent apparent viscosity of graphene-filled cement pastes increases slightly. This influence is particularly pronounced when graphene content is 2.0%, suggesting that the effect on the consistency of cement pastes with around 2.0% of graphene reaches a critical value. As the amount of graphene continues to increase (more than 2.0%), it plays a much less lubrication role than it does in making cement pastes thicker. As a result, the increase of zero tangent apparent viscosity value becomes larger. However, when W/C is 0.3, the zero tangent apparent viscosity and the yield stress of cement pastes without graphene are low, while when W/C is 0.4, those of the cement pastes without graphene and with 4.0/5.0% of graphene are all small. It is noteworthy that the yield stress of graphene-filled cement pastes increases with increasing graphene content, which indicates that the addition of graphene makes the plasticity critical value of cement pastes larger. It is attributed to the irregular shape and the adsorption effect of graphene, which make particles in cement pastes easier to bond to each other and form a more stable network structure. As the concentration of graphene increases, this stable network structure can

Ultrasonication + non-covalent surface modification by SP

Ultrasonication + non-covalent surface modification by SP

Cement pastes

Cement mortars

Shear mixing Ultrasonication (40 Hz) Shear mixing (at low speed) Shear mixing (at high speed) Shear mixing (at low speed) Shear mixing (at high speed)

C

–

S

–

Shear mixing (at high speed)

–

W + SP

Shear mixing (at low speed)

C

Graphene

Ultrasonication (40 Hz)

Graphene

30

60

30

60

1h

–

–

–

1h

Vibration

Vibration

–

Shear mixing

Method

Method

W + SP

Molding Time

Technology

Fabrication process

Feeding order

Note C represents cement; W represents water; S represents sand; and SP represents superplasticizer

Dispersion method of graphene

Matrix type

Table 4.3 Main fabrication process of graphene-filled cementitious composites

40  40  160 (flexural test), 90  90  10 (thermal conductivity test), 150  150  150 (wear resistance test), 260  20  20 (damping test), 200  200  10 (wave absorbing test)

20  20  40 (compressive and sensing test)

Size/mm

20 °C and 100% relative humidity

20 °C and 100% relative humidity

Condition

Curing Time

28 d

3, 28, 90 d

462 4 Graphene-Engineered Cementitious Composites

4.3 Rheology of Graphene…

463

(b)

(a) 1.0% Fitting curve

30

20

10

30

40

50

2.0% Fitting curve

40

Shear stress / Pa

Shear stress / Pa

40

30 20 10 10

60

20

Shear rate / s-1

40

50

60

(d)

(c) 60

100

3.0% Fitting curve

45

Shear stress / Pa

Shear stress / Pa

30

Shear rate / s-1

30 15

4.0% Fitting curve

75 50 25 0

0 0

15

30

45

60

0

15

30

45

60

Shear rate / s-1

Shear rate / s-1

(e) Shear stress / Pa

225

5.0% Fitting curve

180 135 90

0

15

30

45

60

Shear rate / s-1

Fig. 4.2 Rheological curves of fresh cement pastes a with 1.0% of graphene, b with 2.0% of graphene, c with 3.0% of graphene, d with 4.0% of graphene, and e with 5.0% of graphene (W/C = 0.3)

fill the entire space in cement pastes. Therefore, the shear stress required to break the continuous structure is larger, and the yield stress increases. It can be demonstrated from the calculation results of the rheological behavior index regression coefficient that the fluid properties/performances of graphene-filled cement pastes is closer to that of plastic expansion fluid. Nonetheless, the cement pastes with 5.0/ 10.0% of graphene exhibit rheological properties of the pseudoplastic fluid.

464

4 Graphene-Engineered Cementitious Composites

(b) 60

6.0% Fitting curve

30

Shear stress / Pa

Shear stress / Pa

(a)

20 10

8.0% Fitting curve

55 50 45 40

0

30

40

50

60

0

15

(c)

45

60

(d)

140

100

9.0% Fitting curve

Shear stress / Pa

Shear curve / Pa

30

Shear rate / s-1

Shear rate /s-1

90 80 70 0

15

30

45

60

10.0% Fitting curve

120

100

80

0

-1

Shear rate / s

15

30

45

60

Shear rate / s-1

Fig. 4.3 Rheological curves of fresh cement pastes a with 6.0% of graphene, b with 8.0% of graphene, c with 9.0% of graphene, and d with 10.0% of graphene (W/C = 0.4)

4.4 4.4.1

Mechanical Properties/Performances of Graphene-Engineered Cementitious Composites Compressive Properties/Performances

(1) Graphene-filled cement pastes Compressive stress of cement pastes with different graphene dosage is illustrated in Fig. 4.4. It can be observed that with the increase of graphene dosage from 0 to 10.0%, compressive stress of cement pastes fluctuates significantly. Compressive stress of the control cement pastes is 55 MPa and then increases rapidly with the addition of graphene. Compressive stress of cement pastes with 2.0% of graphene reaches its maximum and is 154% of that of control cement pastes. Figure 4.5 shows the relationship between compressive stress and compressive strain of cement pastes without graphene and with 2.0% of graphene under monotonic loading to failure. It can be seen from Fig. 4.5 that compressive stress approximately linearly increases with the compressive strain. However, continued increase of graphene leads to a severe drop in the compressive strength. Compressive stress of cement pastes with 6.0% of graphene is even smaller with respect to the control cement pastes. A similar trend is observed

106.92 – – –

0.702

1.083

1.732

3.743

– –

–

0.344

1.001

1.673

2.616

0.3

0.3

0.3

0.3

0.4 0.4

0.4

0.4

0.4

0.4

0.4

78.059

70.044

39.976

13.183

26.752

9.645

9.329

– 7.985

– 0.562

0.3 0.3

Control 1 With 1.0% of graphene With 2.0% of graphene With 3.0% of graphene With 4.0% of graphene With 5.0% of graphene Control 2 With 4.0% of graphene With 5.0% of graphene With 6.0% of graphene With 8.0% of graphene With 9.0% of graphene With 10.0% of graphene

Yield stress/ Pa

Zero tangent apparent viscosity/Pa t

Water/ cement

Cementitious composites

Table 4.4 Rheological parameters of fresh cement pastes with graphene

0.993 0.996 0.999

s = 9.645 + 0.1571.398 s = 26.752 + 0.771.108 s = 106.92 + 2.280.951

– 0.519 0.927 0.973 0.991

– s = 13.183 + 0.1792.281 s = 39.976 + 0.731.77 s = 70.044 + 0.3651.055 s = 78.059 + 2.960.714

– –

0.988

s = 9.329 + 0.0181.797

– –

– 0.98

R2

– s = 7.985 + 0.011.962

Fitting formula (ahear stress–shear rate)

0.714

1.055

1.771

2.281

–

– –

0.951

1.108

1.398

1.797

– 1.962

n

1.378

1.361

1.325

1.237

–

– –

1.222

1.7555

1.123

1.012

– 1.083

Standard error

4.4 Mechanical Properties… 465

Fig. 4.4 Compressive strength of cement pastes with different contents of graphene

4 Graphene-Engineered Cementitious Composites

Compressive strength / MPa

466

0.3 of W/C 0.4 of W/C

80 47.7%

60 40 20 0

0

1

2

3

4

5

6

8

9 10

Graphene content / %

80

Compressive stress / MPa

Fig. 4.5 Stress and strain curves of cement pastes (0.3 of W/C) without graphene and with 2.0% of graphene under compression

54%

60 40 20

0 2.0%

0

0

-1000

-2000

-3000

Compressive strain / με

25

0.3 of W/C 0.4 of W/C

24.5%

Elastic modulus / GPa

Fig. 4.6 Elastic modulus of cement pastes filled with different contents of graphene

20 15 10 5 0

0

1

2

3

4

5

6

8

9

10

Graphene content / %

for elastic modulus of cement pastes as shown in Fig. 4.6. It is interesting to note that an increase in graphene content to 6.0% and above has no clear positive or negative influence, producing a composite with mechanical properties slightly worse than those of control cement pastes.

4.4 Mechanical Properties…

467 0.30

Fig. 4.7 Poisson ratio of cement pastes filled with different contents of graphene

0.3 of W/C 0.4 of W/C

Possion ratio

0.24

28%

0.18 0.12 0.06 0.00

0

1

2

3

4

5

6

8

9 10

Graphene content / % 60

Compressive strength / MPa

Fig. 4.8 Compressive strength of cement mortars filled with different contents of graphene

13.6%

55

50

45

0

1

5

10

15

Graphene content / %

As shown in Fig. 4.7, the relationship between graphene content and Poisson ratio of cement pastes has an opposite trend with that of elastic modulus. Cement pastes without graphene have the highest Poisson ratio, peaking at about 0.25. On the other hand, all the cement pastes with graphene have relative low Poisson ratio with respect to the control cement pastes. Cement pastes with 2.0% of graphene show a maximum reduction of approximately 28%. This further confirms that graphene can enhance/modify the mechanical properties of cement pastes. (2) Graphene-filled cement mortars According to Fig. 4.8, the compressive strength of graphene-filled cement mortars also increases first and then decreases with increasing content of graphene. The maximal relative increasing rate of 13.6% in compressive strength can be achieved by adding 1.0% of graphene to cement mortars. It is worth noting that when the dosage of graphene exceeds 5.0%, the enhancement effect of graphene on the compressive strength of cement mortars is weakened.

4 Graphene-Engineered Cementitious Composites

Fig. 4.9 Flexural strength of cement mortars with different contents of graphene

6

Flexural strength / MPa

468

5 20.45% 4 3 2 1 0

0

1

5

10

15

Graphene content / %

4.4.2

Flexural Properties/Performances

As can be seen from Fig. 4.9, the flexural strength of cement mortars with graphene increases at the beginning and then reduces with increasing the graphene content. The flexural strength of 1.0% graphene-filled cement mortars maximally increased by 20.45% compared with the cement mortars without graphene. As the content of graphene continues to increase, the enhancement of graphene on the flexural strength diminishes. Moreover, the flexural strength of cement mortars with 15.0% of graphene is decreased instead with respect to the control cement mortars. Figure 4.10 gives the relationships between load and deflection of cement mortars without graphene and with 1.0% of graphene under flexure. According to the ultimate load in Fig. 4.10, the flexural strength of cement mortars without graphene and with 1.0% of graphene can be calculated, and they are 4.39 MPa and 5.30 MPa, respectively, which means that the ultimate load of cement mortars with graphene is 21% higher compared with that of cement mortars without graphene. Moreover, Fig. 4.10 also shows that the displacement of the cement mortars with graphene is 7% larger than that of cement mortars without graphene. The above research results revealed that graphene can obviously strengthen the cementitious materials.

4.4.3

Nano-Hardness

The hardness cloud images of cement mortars at 0, 1.0 and 5.0% of graphene are shown in Fig. 4.11a–c. The average hardness of cement mortars at different graphene contents can be calculated and illustrated in Fig. 4.12. It can be seen from Fig. 4.12 that the hardness of cement mortars shows an increasing trend with the increasing graphene content. Furthermore, the hardness firstly increases and then remains stable with increasing penetration depth. The hardness of control cement

4.4 Mechanical Properties…

469

2.5 21%

Load / kN

2.0 1.5 1.0 0.5

0 1.0%

0.0 0.00

0.04

0.08

0.12

0.16

Displacement / mm Fig. 4.10 Load and displacement curves of cement mortars (0.6 of W/C) without graphene and with 1.0% of graphene under flexure

(a)

15

5.280 5.514 5.747 5.981 6.215 6.449 6.682 6.916 7.150

9

6

3 0

160

is ax

y

0

(c)

0

m

0

80

/m m

40

160 120

is

m m s/

ax i

/m

m

/m

16

0

s

is ax

12 0

0

i ax

80

80

120

3

x

x

0

40

y

0 40

0

160

ax

3

6

y

6

9

16 0

9

10.35 10.62 10.89 11.16 11.43 11.69 11.96 12.23 12.50

12

12 0

12

15

80

8.100 8.525 8.950 9.375 9.800 10.23 10.65 11.08 11.50

40

15

Hardness / GPa

(b) Hardness / GPa

16

m

/m

12

0

is

ax

80

x

40

0

120

m

80

40

0

/m

Hardness / GPa

12

Fig. 4.11 Nano-indentation hardness cloud images of cementitious composites a without graphene, b with 1.0% of graphene, c with 5.0% of graphene

470

4 Graphene-Engineered Cementitious Composites

(a)

Hardness / GPa

6

0 4.79 ± 0.16GPa

4

Stable stage

2

0

500

0

1000

1500

Displacement into surface / mm

(b)

(c) 1.0%

8

8.41± 0.17GPa

6 4 Stable stage

2 00

500

5.0%

12

Hardness / GPa

Hardness / GPa

10

1000

1500

2000

11.87± 0.13GPa

9 6 Stable stage

3 0

0

Displacement into surface / nm

300

600

900 1200 1500 1800

Displacement into surface / nm

Fig. 4.12 Hardness of cementitious composites a without graphene, b with 1.0% of graphene, and c with 5.0% of graphene

mortars is about 4.79 GPa. The hardness of cement mortars with 1.0% of graphene increases by 75.57% compared with control cement mortars. The hardness of cement mortars with 5.0% of graphene represents a 1.5-fold increase over control cement mortars.

4.4.4

Reinforcement Mechanisms

(1) Extensive distribution strengthening network The graphene thickness is in the range from 1 to 5 nm. Assuming the graphene diameter is 2 lm, the graphene number per cm3 in the composites can be calculated by Eq. (4.1). Results are shown in Fig. 4.13, where the graphene number per cm3 can reach in the range from 6.4  1011 to 3.2  1012 as the graphene content is 1.0% and 1.3  1012 to 6.4  1012 as the content is 2.0%. Therefore, graphene forms an extensive spatial distribution inside the composites. Besides, the surface

4.4 Mechanical Properties…

471

Number of graphene / cm-3

Fig. 4.13 Numbers of graphene in 1 cm3 volume of cementitious composites with graphene

6.0×10

12

Graphene in thickness of 5nm Graphene in thickness of 1nm

4.0×1012 2.0×1012

6.4×1012

3.2×1012

1.6×1012

1.3×1012 6.4×1011

3.2×1011

0.0 0.0

0.5

1.0

1.5

2.0

Graphene content / %

area of graphene in unit volume composites can also be calculated using the specific surface area of graphene (500 m2/g), density of graphene (2–2.25 g/cm3), and volume fraction. Results show that the surface area per cm3 is 10–11.25 m2/cm3 for 1.0% of graphene and 20–22.5 m2/cm3 for 2.0% of graphene. With this extensive distribution and surface area, graphene can form extensive networks in the composites and guarantee to fully achieve enhancement effect to the matrix. p ¼ npD2 t=4

ð4:1Þ

where p is volume fraction of graphene in composites, n is graphene number, D is graphene diameter, and t is graphene thickness. (2) Lowering W/C and self-curing Specific surface area of graphene used in this study is 500 m2/g, which results in high surface energy of graphene. In addition, it can be seen from Table 4.1 that there exist oxygen and nitrogen elements in graphene, which makes the surface of graphene hydrophilic. As shown in Fig. 4.14, the graphene has strong water absorption capacity.

300

Water absorption / (cm3/g)

Fig. 4.14 Water adsorption of graphene along with pressure under room temperature

250 200 150 100 50 0 0.0

0.5

1.0

1.5

Pressure / kPa

2.0

2.5

4 Graphene-Engineered Cementitious Composites

(b)

(a) 3.0 2.5

120

0.3 of W/C 0.4 of W/C

Yield stress / Pa

Consistency coefficient / Pa·s n

472

2.0 1.5 1.0 0.5 0.0

0.3 of W/C 0.4 of W/C

100 80 60 40 20

0 1 2 3

4

5

6

8

9 10

Graphene content / %

0

0 1

2

3

4

5

6

8

9 10

Graphene content / %

Fig. 4.15 Rheology parameters of cement pastes filled with different contents of graphene and different W/C: a consistency coefficient; b yield stress

Therefore, as shown in Fig. 1.30, the water adsorption of numerous and extensively distributed graphene lowers the local W/C in the cementitious composites inside the micro-zone surrounding each graphene and uniformly reduces W/C inside total cementitious composites during early hydration. Figure 4.15 gives the rheological parameters of cementitious composites without and with different contents of graphene. It can be seen from Fig. 4.15 that the rheological properties of the cementitious composites with 9.0% of graphene (W/C is 0.4) are consistent with 5.0% of graphene-filled cementitious composites (W/C is 0.3). Therefore, when the content of graphene is increased, the amount of water required for graphene-filled cement pastes to achieve the same rheological properties will increase. This indicates that the graphene addition lowers the flowability of fresh cement pastes by changing the actual W/C of the composites. The decrease of W/C is beneficial for the strength of the composites. The adsorbed water will be released from the graphene into the cementitious composites during the later hydration stage to achieve a self-curing effect. The self-curing effect is also beneficial for the strength and the hardness of the composites. The increase in nano-hardness suggests that the hardness of the cementitious composites increases from microscale to macroscale. This proves that the strengthening effect results from lowering W/C caused by water adsorption of graphene and self-curing effect by water released from graphene. (3) Reducing primary cracks Figure 4.16 gives the images of cementitious composites without and with 2.0% of graphene. As shown in Fig. 4.16, the graphene inhibits the crack development and endows cementitious matrix “crack free” property essentially. Cementitious composite hydration generates plenty of heat, especially during the early stage of hydration. This leads to a temperature gradient inside the composites, thus causing temperature stress. Furthermore, the strength of the composites during the early stage of hydration is not as high as the temperature stress. Therefore, there are primary cracks in the cementitious composites. Graphene has much higher thermal

4.4 Mechanical Properties…

473

(a)

(b)

(c)

(d)

Fig. 4.16 SEM images of cement pastes a without graphene (5000), b without graphene (40000), c with 1.0% of graphene (5000), and d with 1.0% of graphene (40000)

conductivity against the cementitious matrix. The presence of graphene can increase the thermal conductivity and decrease the specific heat of the cementitious composites (this can be referred to as Sect. 4.6.3). In addition, it should be noted from Fig. 1.30 that graphene with extensive distribution functions as numerous hydathodes. The water adsorbed by graphene will release from graphene during later hydration of cementitious composites. This is beneficial for the curing of cementitious composites, thus reducing the autogenous shrinkage [10]. The difference of nano-hardness of cementitious composites without and with graphene shown in Fig. 4.12 can also prove this effect. Based on the above analysis, the addition of graphene can improve the thermal stability and reduce original manufacturing defects, thus reducing primary cracks inside the composites. (4) Bonding effect between graphene and matrix As shown in Fig. 4.17, graphenes are anchored well inside the hydration products. The graphene and matrix features tightly bond with each other. When the cracks in

474

4 Graphene-Engineered Cementitious Composites

Fig. 4.17 Graphene anchored inside cementitious matrix of composites with 2.0% of graphene

the matrix encounter well-distributed graphenes, the pinning effect and the efficient crack bridging can inhibit the crack growth at the very preliminary stage of crack propagation within composites. In addition, the debonding and breaking of graphene can also consume energy as the composites are subjected to external force, and the composites are strengthened in this way [9]. (5) Lowering orientation index of calcium hydroxide Thermogravimetric analysis was conducted as shown in Fig. 4.18. The cement hydration degrees at different curing ages can be calculated, and the result is listed in Table 4.5. It is shown that cement hydration degrees of cementitious composites at 3 d and 28 d of curing age were improved as graphene dosage increased, which is usually attributed to the nucleation effect of graphene. However, at 90 d of curing age, cement hydration degrees of cementitious composites with 1.0% of graphene were almost the same as the one without, and the degree of the one with 2.0% of graphene was just slightly higher. The result indicates that graphene has little improvement in cement hydration degree at 90 d of curing age, and consequently, the strengthening of graphene to cementitious composites cannot be concluded as the nucleation effect at early stage. XRD analysis helps for a further understanding of strengthening mechanism of graphene-filled cementitious composites. It is shown in Fig. 4.19 that the addition of graphene neither brought in nor eliminated any kind of hydration product, but indeed lowered the orientation index of calcium hydroxide (CH) crystals and promoted 3 d and 28 d hydration degree of the composites without decreasing its 90 d hydration degree. Hence, it is safe to conclude that graphene is enhancing the mechanical properties of the cementitious composites by means of lowering the orientation index of CH crystals (Table 4.6).

475

(a) Mass loss / %

100

0 1.0% 2.0%

95 90 85 80 75

200

400

600

800

1000

First derivative of mass loss

4.4 Mechanical Properties…

(b) 0.0000 -0.0002 -0.0004 0 1.0% 2.0%

-0.0006 -0.0008

0

200

Mass loss / %

0 1.0% 2.0%

95 90 85 80 75 200

400

600

800

First derivative of mass loss

(c) 100

-0.003 -0.006 0 1.0% 2.0%

-0.009 0

85 80 75 400

600

800 1000 1200

Temperature / °C

First derivative of mass loss

Mass loss / %

0 1.0% 2.0%

200

1000

200

400

600

800

1000

Temperature / °C

90

70

800

0.000

1000

(e) 95

600

(d)

Temperature / °C 100

400

Temperature / °C

Temperature / °C

(f) 0.000 -0.004 -0.008 -0.012

0 1.0% 2.0%

-0.016 0

200

400

600

800 1000 1200

Temperature / °C

Fig. 4.18 TG analysis of graphene-filled cementitious composites: a TG curve cured for 3 d; b derivative TG (i.e., DTG) curve cured for 3 d; c TG curve cured for 28 d; d DTG curve cured for 28 d; e TG curve cured for 90 d; and f DTG curve cured for 90 d

Table 4.5 Cement hydration degree at 3 d, 28 d, and 90 d of curing age Curing age

Cement hydration degree of cementitious composites Control (%) With 1.0% of graphene (%) With 2.0% of graphene (%)

3d 28 d 90 d

48.49 71.04 81.61

49.58 76.78 81.43

52.01 78.11 83.08

476

Intensity

0

400

♦

600 400 200 0 600 400 200 0

Intensity

800

Intensity

(a)

• (001) •

0

♥

•

♦

•

•

♣

••

••

• (101) •

16

♥ C3S ♣ C-S-H

•(101)

♥ ♥

♦

8

♥

• (001)

2.0%

0

• CH

♣

•(001)

1.0% ♦

♦ AFt ♥ ♥ • (101)

24

•

♣

32

40

48

•• 56

64

2θ / °

Intensity

Intensity

Intensity

(b) ♦

300

♦

0

8

•

♦

• CH

• (001)

•

♣

16

• •

• •

•(101) ♥ ♥

•

♦

♥ C3S ♣ C-S-H

• (101) ♥ • ♥

♦

•

♣

• (001)

2.0% ♦

♦ AFt

• (101) ♥ ♥

1.0%

900 600 300 600 400 200 0

• (001)

0

600

24

•

♣

32

40

48

• •

56

64

2θ / °

Intensity

Intensity

(c)

Intensity

Fig. 4.19 XRD analysis of cementitious composites filled with 0–2% of graphene: a curing for 3 d; b curing for 28 d; c curing for 90 d (Note C3S represents 3CaO
SiO2.)

4 Graphene-Engineered Cementitious Composites

1600 1200 800 400

♦

♦

0

8

• CH

• (001)

•(101) ♣

•

♥ C3 S ♣ C-S-H

• •

• (101) ♥ ♥

•

♦

♣

•

• •

• (001)

2.0% ♦

♦ AFt ♥ • ♥

♦

1.0%

900 600 300 900 600 300 0

• (001)

0

♥

• ♥

♦

16

• (101)

24

32

2θ / °

♣

40

•

•

48

56

64

4.4 Mechanical Properties…

477

Table 4.6 Orientation index of CH crystals Curing age

Cementitious composites Control With 1.0% of graphene

With 2.0% of graphene

3d 28 d 90 d

2.1 1.7 3.05

1.5 1.4 1.88

(a)

-60

Q0

-70

Q1

-80

1.6 1.6 1.88

Q2

0 2.0%

-90

-100

-110

-120

(b)

-60

Q0

-70

2.0%

Q2

-80

-90

-100

-110

-120

Chemical shift / ppm

Chemical shift / ppm Fig. 4.20 a

Q1

29

Si NMR spectra and b the deconvoluted graph of cement paste with graphene

(6) Changing structure of calcium silicate hydrate gels Figure 4.20 shows the 29Si NMR spectra and the deconvolution of hardened cement pastes containing graphene with respected to control cement pastes. Results and characterization parameters from deconvolution are demonstrated in Table 4.7 and Fig. 4.21. As shown in Fig. 4.20, there are three resonance absorption peaks (Q0, Q1, and 2 Q ) in the spectra of the composites, regardless of whether or not adding graphene. The integral intensity of Q2 peak of the composites with graphene is significantly enhanced compared with control composites. Besides, it can be seen from Fig. 4.21 that all the parameter values are significantly increased by 166.5%, 786.2%, and 27.4% after adding graphene to composites, respectively. On one hand, graphene as a two-dimensional stacked flake structure is easy to be embedded in the cement matrix and contact with them. Furthermore, the high Table 4.7 Results from the deconvolution of cementitious composites with graphene

Cementitious composites

Distribution of Si/% Q1 Q2 Q0

Q3

Q4

Control With 2.0% of graphene

41.37 25.62

– –

– –

45.79 21.98

12.35 52.39

478

4 Graphene-Engineered Cementitious Composites

Fig. 4.21 Characterization parameters of 29Si NMR from deconvolution for hardened cement pastes with graphene (Note MCL, PD, and HD represent the mean chain length, polymerization degree, and hydration degree, respectively)

specific surface area will help graphene to attract more hydration products and significantly enhances the nucleation effect, which promotes hydration. On the other hand, graphene reduces the proton water in calcium silicate hydrate (i.e., C–S–H) gels structure due to water absorption, which shortens the distance between Ca, O, and Si groups. As a result, the strength of chemical bond is enhanced, and then the polymerization degree is increased. In addition, the functional groups on the surface of graphene, such as carboxyl groups reacting with CH, decreases the CaO/SiO2 and increases the polymerization degree and mean chain length of C–S–H gels. Taken together, the incorporation of graphene is generally beneficial for improving the mechanical properties/performances of cementitious composites. However, it should be noted that the enhancement extent of compressive/flexural strength of cement mortars reduces with the increase of graphene content (greater than 5.0%). It can be interpreted by the fact that the excessive incorporation of graphene leads to an increase in the internal pores of cement mortars, which decreases the strength of composites. In addition, due to the nano-filling effect of graphene, the density of cementitious composite is improved with the increasing graphene content. Therefore, the hardness of cementitious composite also increases as the content of graphene increases.

4.5 4.5.1

Durability of Graphene-Engineered Cementitious Composites Wear Resistance

Figure 4.22 shows the relationship between the graphene content and the abrasive loss per unit area of cement mortars. The abrasive loss per unit area of graphene-filled cement mortars shows obviously decreasing trend with the

4.5 Durability of Graphene-Engineered Cementitious Composites 30

Abrasion loss / (kg/m2)

Fig. 4.22 Abrasive loss per unit area of graphene-filled cement mortars

479

25

19.5%

20 70.88%

15 10 5

0

1

5

Graphene content / %

increasing graphene content The abrasive loss per unit area of cement mortars with 5.0% of graphene represents a 70.88% decrease over control cement mortars. Therefore, graphene plays a distinct role in improving the abrasion resistance performance of cementitious composites. Figure 4.23 displays the relationship between the graphene content and the abrasion depth of cement mortars. The abrasion depth of cement mortars declines sharply as the graphene content increases. The abrasion depth of cement mortars with 5.0% of graphene is only 3 mm and decreases by 70.96% compared with control cement mortars. It illustrates further that the graphene can improve the wear resistance performance of cementitious composites. The addition of graphene can improve the wear resistance property of cementitious composites, which can be attributed to the self-lubricating property and high hardness of graphene. As we know, the graphite is a typical lamellar compound. Figure 4.24 shows the overview microstructures of graphene. It can be seen that graphene is quite well dispersed and cement matrix becomes denser with increasing graphene content. The graphene can enhance the friction-bearing capacity of the composites through modifying the hardness of the composites. In other word, the high hardness can endow better resist abrasion. The clear laminated structure of

10

Abrasion depth / mm

Fig. 4.23 Abrasion depth of graphene-filled cement mortars

19.36%

8 70.96%

6 4 2

0

1

Graphene content / %

5

480

4 Graphene-Engineered Cementitious Composites

(a)

(b)

Interfaces

Graphene

(c)

Graphene

Fig. 4.24 SEM images of cement mortars: a without graphene; b with 1.0% of graphene; c with 5.0% of graphene

graphene can be seen in SEM images. Sliding relatively between the multi-layer structures of carbon–carbon hexagonal plane endows the graphite with lubricating function. As for lubricant mechanism of cementitious composites filled with graphene, there are two main reasons. On one hand, it is not a chemical bond between the fillers and cementitious composites. Therefore, lubricant molecules and polymer molecules are separated from each other under the influence of frictional heat. Then nanoparticles of graphene are pushed to the frictional surface. At the same time, it is just filled with the pits of frictional surface, which is equivalent to the surface-repairing function. On the other hand, graphene, which acts as the lubricant, will give priority to transfer into the grinding surface in the process of friction and form a lubricating film on the frictional surface. This behavior gives rise to a decreasing trend in abrasion between friction pair and the cementitious composites filled with graphene. On the basis of the above analysis and discussion, it is found that the filling effect of nanoparticles becomes better and the area of the lubricating film in the frictional surface becomes grouter with the increasing content of

4.5 Durability of Graphene-Engineered Cementitious Composites

481

Table 4.8 Test results of density and chloride migration coefficient of graphene-filled cement pastes Graphene contents / %

0

1.0

5.0

Density / (g/cm3) 2.37 2.41 2.43 33.84 33.38 3.11 DRCM / (0.110−12m2/s) DRCM Chloride migration coefficient from non-steady-state migration experiments

graphene in cementitious composites in a certain dosage range. In other word, the abrasion loss of the cementitious composites will reduce.

4.5.2

Chloride Penetration Resistance

Since graphene has excellent conductivity, it will definitely improve the electric flux in cement mortars, which is a favorable factor for chloride ions. However, tests result from non-steady-state chloride migration experiments (as listed in Table 4.8) shows an evident deduction in chloride ingress that cement mortars with 5.0% of graphene has a DRCM value less than 10% of one of the control cement mortars, meaning the positive effects of graphene have countered the negative effects. The positive effects mainly come from two aspects. On one hand, graphene has compacted the cement composites. As exhibited in Table 4.8, when graphene content rises from 0 to 5.0%, the density of graphene-filled cement mortars increases slightly yet shows a clear tendency, which makes it harder for chloride ions to penetrate in. On the other hand, graphene has extremely large specific surface area, so the graphene inside matrix will absorb chloride ions and act like “filters” (as illustrated in Fig. 4.25), and in this way, these harmful chemicals will be blocked out in the surface area of composites [1].

Fig. 4.25 Graphene acting like “filters” for chloride ions

482

4 Graphene-Engineered Cementitious Composites

4.6

Functional/Smart Properties/Performances of Graphene-Engineered Cementitious Composites

4.6.1

Damping Properties/Performances

Figure 4.26 expresses the free vibration time–history decay curves of the cement mortars with different graphene contents. As shown in Fig. 4.26, the acceleration amplitude attenuates roughly between 0 and 0.04 s after incentive action. Through analysis and comparison, it can be seen that the bigger graphene dosage is, the greater attenuation rate of acceleration is. Figure 4.27 shows the damping ratio of

0.30

0

i = 10

0.15 0.00 -0.15 -0.30 0.00

0.02

0.04

0.06

i =10

Acceleration / (m/s2)

Acceleration / (m/s 2)

(a)

0.15 0.00 -0.15 -0.30 0.000 0.004 0.008 0.012 0.016 0.020

0.08

Time / s

Time / s

i =10

1.0%

0.01 0.00 -0.01 0.00

0.02

0.04

0.06

Acceleration / (m/s2)

Acceleration / (m/s 2)

(b) 0.02

0.08

0.02

-0.01 0.000 0.004 0.008 0.012 0.016 0.020

Time / s

Acceleration / (m/s 2)

Acceleration / (m/s2)

0.05 0.00 -0.05 -0.10 0.02

0.15

5.0%

0.10

-0.15 0.00

0.04

0.06

Time / s

1.0%

0.00

(c) i =10

i =10

0.01

Time / s 0.15

0

0.30

0.08

i =10

5.0%

0.10 0.05 0.00 -0.05 -0.10 -0.15 0.000 0.004 0.008 0.012 0.016 0.020

Time / s

Fig. 4.26 Free vibration response time–history decay curve and local amplification of cementitious composites with graphene

4.6 Functional/Smart Properties

483 0.013

Fig. 4.27 Damping ratio of cementitious composites with graphene

20%

Damping ratio

0.012

0.011

4.7%

0.010

0.009

0

1

5

Graphene content / %

cement mortars with graphene at different concentrations. It can be seen from Fig. 4.27 that the damping ratio of cement mortars is directly proportional to the amount of graphene. When the graphene is not added, the damping ratio of control cement mortars is 0.01. However, the damping ratio of cement mortars increases by 4.7% when the graphene content is 1.0%. The damping ratio of cement mortars increases by 20% as the graphene content is 5.0%. This also indirectly proves that graphene has a potential to improve the damping property of cementitious composite. The improvement of damping is beneficial to vibration attenuation. In general, introducing the material damping can make vibrational energy of structure convert irreversibly into other formal energy, which reaches the purpose of dissipating vibrational energy through an internal system of material. The reasons for fillers can improve the damping property of the cementitious composites which can be divided into two types. Firstly, the addition of fillers makes the cementitious composites create inevitably some defects, such as dislocations, phase boundaries, grain boundaries, and weak interface. These defects can dissipate vibrational energy. Secondly, the viscoelastic admixtures can provide damping and dissipate vibrational energy. The dissipating energy of graphene mainly has three kinds. (1) The dislocation slip in graphene own layer consumes vibrational energy. The lamellar structure of graphite is hexagonal plane lattice unit connected by covalent bond. The interlayer relies on the connection between delocalized p bonds that is similar to metal bond and van der Waals forces. Because of the small interlayer binding force and large gaps between the layers, it is easy to create relative slip for graphene, which can dissipate vibrational energy and cause high internal friction. (2) Viscous friction between graphene and cementitious composites consumes vibrational energy. The cementitious composites appear diversity phase boundaries and crystal interfaces when graphene is combined with the cement mortars. In addition, a large number of diversity interfaces increase frictional energy of cementitious composites. Under the action of shear stress, deformation between the two interfaces is short of coordination, which leads to interface friction. Furthermore, these interfaces also make a contribution to dislocation damping. (3) Contact friction between the hydration productions inside the matrix and graphene consumes vibrational energy [11–13].

484

4.6.2

4 Graphene-Engineered Cementitious Composites

Electrically Conductive Properties/Performances

(1) Direct current electrical conductivity Figure 4.28 shows the variation of resistivity of cement pastes with different content levels of graphene along with test time. It can be seen from Fig. 4.28 that the electrical resistivity increases rapidly at the beginning of the test and then grows slowly. This indicates that there exists polarization effect in these cement pastes under direct current (i.e., DC) voltage. This phenomenon is similar to the charge of the capacitor, which produces an opposite charging current inside the composites during the electrical resistance test. This leads to the decrease of the current and the increase of the measured electrical resistivity along with test time [14]. It can also be seen from Fig. 4.28g that the electrical resistivity of graphene-filled cement pastes decreases with the increase in graphene dosage. When the graphene content reaches 2.0%, the electrical resistivity of the composites decreases to 1/4 of that of the cement pastes without graphene. It reveals that the percolation threshold of electrical resistivity of cement pastes with graphene is nearly 2.0%. The electrical resistivity of cement pastes with 9.0% of graphene decreases to 1/40 of that of the cement pastes without graphene. This indicates that there appears a secondary percolation phenomenon as the graphene content reaches 8.0%. When the addition of graphene reaches 10.0%, the electrical resistivity of graphene-filled cement pastes is 20 KX cm, which decreases to 1/120 of 2400 KX cm of the cement pastes without graphene. (2) Alternating current electrical conductivity Figure 4.29 shows the electrical resistivity of cement pastes as a function of graphene volume fraction measured by using alternating current (i.e., AC) method with frequency of 100 kHz. The experimental result for AC method is in agreement with the expectations. At the same percolation threshold (2.0%), the establishment of percolation path produces a dramatic decrease of the resistivity values, from 55 KX cm to 1 KX cm, which indicates that the percolation phenomenon is not subject to AC and DC voltage. In fact, the AC method exhibits a considerably lower value of electrical resistivity and a more distinct percolation zone and conduction zone. These features agree with the fact that, since there exists polarization effect in these cement pastes under DC voltage, it is able to cause the charging of the capacitor formed in C–S–H gels surface and the interface between graphene and cement matrix, which produces an opposite charging current inside the composites when DC voltage imposed. The graphenes behave as if they are insulating at DC or low AC frequencies. As a consequence, a larger value of the electrical resistivity is obtained. By contrast, at high AC frequencies, due to the characteristics of sinusoidal variation, there will not produce polarization voltage [15, 16].

0

2.4 2.2 2.0 1.8 0

10

20

30

50

60

70

80

Time/ S 2.0%

480 400 320 240 160 80 0

0

10

20

30

40

50

60

70

80

Time / S

(e) 320

8.0%

280 240 200 160 120 80 40

0

10

20

30

40

(b) 1.0%

800

700

600

500

0

10

20

30

50 60

70 80

50

60

70

80

60

70 80

60

70

400 5.0%

360 320 280 240 200 160 0

10 20

30

40

50

Time / S

(f) 21 10.0%

20 19 18 17 16

0

10

20

Time / S

30

40

50

80

Time / S

(g) 2.5 2.0 1.5 1.0

Electrical resistivity (M Ω·cm)

Electrical resistivity / MΩ·cm

40

Time / S

(d)

560

Electrical resistance / KΩ ·cm

Electrical resistance / K Ω·cm

40

Electrical resistance / KΩ·cm

(a)

(c)

Electrical resistance / KΩ·cm

485

Electrical resistance / KΩ·cm

Electrical resistance / MΩ·cm

4.6 Functional/Smart Properties

4.0 3.0 2.0

1.0 0.0 6

7 8 9 Graphene contents / %

10

0.5 0.0 -1 0 1 2 3 4 5 6 7 8 9 10 11

Graphene content / % Fig. 4.28 Electrical resistivity of representative cement pastes a without graphene, b with 1.0% of graphene, c with 2.0% of graphene, d with 5.0% of graphene, e with 8.0% of graphene, f with 10.0% of graphene, g relationship between electrical resistivity and graphene content

Fig. 4.29 Electrical resistivity of cement pastes with 0–10.0% graphene, measured by using AC method

4 Graphene-Engineered Cementitious Composites

Electrical resistivity / kΩ·cm

486

60 50 Percolation threshold

40 30 20 10 0 -1 0

1

2

3

4

5

6

7

8

9 10 11

Graphene content / %

(3) Mechanisms of electrical conductivity The graphenes have pi electrons that participate in interlayer p bonding. This makes graphene good electrical conducting characteristic. Besides, the carbonation process with temperature up to 1050 °C during fabrication of graphene produces a large excess of holes in the valence band. These characteristics of graphene contribute to the electrical conductivity and piezoresistivity of cementitious composites filled with graphene through the following paths: (1) Electronic conduction through graphene by tunneling effect; (2) electronic conduction and hole conduction through contacting conduction of graphene. When the graphene content is within percolation zones, graphenes filled in the cementitious composites form conductive networks through the above two paths, which leads to the obvious decrease of electrical resistivity as shown in Fig. 4.30c–f. However, when the graphene content is lower than percolation threshold, the separation between graphenes is too far. The graphenes in the cementitious composites cannot form conductive networks. As shown in Fig. 4.30a, b, the electrical resistivity of cementitious composites without and with 1.0% of graphene is much higher than that of cementitious composites filled with graphene whose content levels are within percolation zones. (4) Capacitance As shown in Fig. 4.31, capacitance under 100 Hz frequency of the cement pastes increases with the increase of graphene content. When graphene content reaches 10.0%, the capacitance is nearly 15.5 lF. It is about 30 times of that of cement pastes without graphene. Moreover, capacitance of the cement pastes with 2.0 and 9.0% of graphene change greatly as presented in Fig. 4.31. It indicates that percolation threshold of the cement pastes with graphene exists next to 2.0%. There exists a second percolation phenomenon when graphene content is nearly 9.0%. It verifies the percolation phenomenon of the electrical resistivity of the cement pastes with graphene.

4.6 Functional/Smart Properties

(a)

487

(b) Graphene

(c)

(d)

(e)

(f)

Fig. 4.30 Cement pastes a without graphene; b with 1.0% of graphene; c with 2.0% of graphene: 30000 and 100000 (on the top left); d with 5.0% of graphene: 30000 and 70000 (on the top right); e with 8.0% of graphene: 30000 and 100000 (on the top right); and f with 10.0% of graphene: 20000 and 100000 (on the top left)

Fig. 4.31 Relationship between electrical capacitance and graphene content

4 Graphene-Engineered Cementitious Composites 18 16

Electrical capacity / μF

488

100Hz Secondary percolation threshold

14 12

Percolation threshold

10 8 6 4 2 0 -1 0

1

2

3

4

5

6

7

8

9 10 11

Graphene content / %

(5) Impedance Electrochemical impedance spectroscopy (EIS) and equivalent circuit were used to analyze the conductive mechanism of the cement pastes with graphene. A wide range of frequency (from 106 Hz to 5  10−2 Hz) and a low-amplitude AC excitation of 50mv were used for EIS test in this study. Each frequency generates a single current response datum, which has both real and imaginary component. EIS experimental results of the cement pastes with different graphene content can be drawn in Nyquist plot, as shown in Figs. 4.32 and 4.33. The test frequency in each plot decreases from 106 Hz to 5  10−2 Hz as horizontal axis values increases from 0 to the maximum. Figure 4.32 shows that typical EIS of cement pastes without graphene consists of three parts, and the equivalent circuit of the cement pastes without graphene is shown in Fig. 4.34a. The beginning of the EIS is marked as D on Fig. 4.32, and it corresponds to Rs in equivalent circuit. The value of Rs is an inverse function of porosity and pore solution concentration. The arc diameter (“DC” section) in high-frequency region mainly represents the value of charge transfer electrical resistance (Rst), which is closely related to the cement hydration product, water

Fig. 4.32 Typical electrochemical impedance spectroscopy of cementitious composites

4.6 Functional/Smart Properties

489

(b)

(a) 2.0%-1 2.0%-2 2.0%-3

60

5.0%-1 5.0%-2 5.0%-3

8

A

3.5 2.0%-1 2.0%-2 2.0%-3

3.0

A 20

2.5 2.0

4

1.5 1.0

2

1.5

C

1.0

0

0.5

B

C 0

5

0.0

10

15

20

25

30

35

40

0.5

C

0.0

B

0

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Zr / kΩ

5.0%-1 5.0%-2 5.0%-3

2.0

Zim / k Ω

40

Zim / k Ω

6

Zim / kΩ

Zim / kΩ

80

0

0.5

5

1.0

1.5 2.0 Zr / kΩ

10

Zr / k Ω

2.5

15

20

Zr / kΩ

(c) 1.8 10.0%-1 10.0%-2 10.0%-3

1.5

Zim / k Ω

A 1.2 0.8 10.0%-1 0.7 10.0%-2 0.6 10.0%-3 0.5 0.4 0.3 0.2 0.1 0.0 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Zr / k Ω

0.9

Zim / kΩ

0.6 0.3 C

B

0.0 0

1

2

3

4

5

6

Zr / k Ω

Fig. 4.33 AC impedance spectroscopy curve of representative cementitious composites a with 2.0% of graphene, b with 5.0% of graphene, and c with 10.0% of graphene

content, and ion concentration. Meanwhile, the “DC” section also involves the resistance caused by C–S–H gels surface capacitance, which is represented by Cs in Fig. 4.34a. The “CB” section represents that ion adsorption, and desorption has been occurred in C–S–H gels surface in the process of voltage application, which is expressed as Rc in equivalent circuit. The “BA” section in low-frequency region shows that the real part and imaginary part are linear dependence, and the slope is closely related to the inner connected pore structure of the cementitious composites filled with graphene. The electrochemical process is controlled by diffusion, and the corresponding impedance is called Warburg impedance Zw [17, 18]. Figure 4.33a shows that EIS of cement pastes with 2.0% of graphene consists of two parts and the equivalent circuit of that is shown in Fig. 4.34b. EIS of the cement pastes with 2.0–4.0% of graphene is a classic Randles curve. The “CB” section of the curve is determined by cement matrix and graphene together. Therefore, the corresponding equivalent circuit is expressed as the parallel connection of Rs and RN, which represent the pore solution resistance and graphene resistance, respectively, as shown in Fig. 4.34b. This is based on that a large part of matrix may be bypassed by current flow due to graphene incorporation. “CB” section of the cement pastes with

490

4 Graphene-Engineered Cementitious Composites

Fig. 4.34 Equivalent circuits of cementitious composites filled with graphene: Rs—pore solution resistance; Rst—charge transfer resistance; Rc—inductance; Cs—C–S–H gels surface capacitance; Zw—Warburg impedance; RN—graphene resistance; CN—graphene–matrix interface capacitance: a–c three kinds of equivalent circuits of cementitious composites filled with graphene

2.0% of graphene is smaller than that of composites without graphene. This means that the pore solution transfer electrical resistance is lowered due to the increase of graphene content. “CB” section in Fig. 4.33a is controlled by the charge transfer and C–S–H gels surface capacitance together, which correspond to Rst and Cd in equivalent circuit. The “BA” section in Fig. 4.33a represents the process of charge diffusion, which is irrelevant to graphene. This can be attributed to that the electric double layer forms at graphene surface, and it makes graphene insulate under the excitation of low AC frequency [19]. The linear part of EIS controlled by charge diffusion gradually disappears with the increase of graphene content. This means that graphenes have become a leading element in the conductive pathway of the cementitious composites filled with graphene. This result illustrates that the percolation network has been formed when the content of graphene is nearly 2.0%, in accordance with the test results of electrical resistivity.

4.6 Functional/Smart Properties

491

Figure 4.33b, c show that EIS of the cement pastes with 5.0 and 10.0% of graphene has similar topological structure, and it is composed of two semicircles. The graphenes and pore solution behave conducting in series–parallel way at high frequency. Corresponding equivalent circuit consists of RN, Rs, and CN, as shown in Fig. 4.34d, where CN represents the double layer capacitance at graphene–matrix interface. Double layer capacitance of C–S–H gels surface and the charge transfer govern conducting at low frequency, which can be represented by Cs and Rst, respectively. Figure 4.34d shows that the equivalent circuit has been dominated by graphene. Based on the above analysis, conductive pathway of the cement pastes with graphene can be divided into three categories, as shown in Fig. 4.34. When graphene content is below percolation threshold, the electrical transport behavior of the cementitious composites is dominated by cement matrix. The graphenes are scattered in matrix and cannot contact with each other, so the electric conduction of the composite is limited. The graphenes and cement matrix constitute a conductive pathway together with the increase of graphene content. Meanwhile, the double layer capacitance at graphene–matrix interface and C–S–H gels surface also plays a certain role in electrical conduction. When conductive network of graphene has been formed in composites, the electrical transport behavior of cementitious composites is dominated by graphene. The three categories show that conductive mechanism of the cement pastes with graphene mainly depends on the connection of graphene, which verifies the above-mentioned electrical conductive mechanisms [20]. Based on the conductive path model established above, the component parameters are analyzed by Zsim fitting, and the distribution of specific conductive factors inside the test piece is analyzed according to the obtained component parameters. The selected models for fitting are RsRc(Q1R1), RsRNRc(Q1R1)(Q2(R2W)), and Rs(Q1R1)(Q2(R2W)), respectively. The chi-squared value in Fig. 4.35 represents the fit degree of fitting curve, i.e. iteration error, and the smaller the value, the higher the fit repeatability. As can be seen from Fig. 4.35, the repeatability of the fitted curve is relatively high, which indicates that the established conductive model is also relatively accurate. Table 4.9 lists the pore solution resistance of cementitious composites with graphene in the equivalent circuit models, in which Rs represents the resistance of the pore solution. As can be seen from Table 4.9, the pore solution resistance of graphene-filled cementitious composites gradually decreases with the increase of graphene content, which indicates that the compactness of graphene-filled cementitious composites gradually increases. According to the above analysis, the resistance value of cementitious composites can be calculated by substituting the matrix resistance value into Eq. (4.2), and verified with the measured resistance value of cementitious composites, where r and rm represent the conductivity of cementitious composites and matrix; Rm and R represent the resistivity of cementitious composites and matrix; Ф and rf represent the content and conductivity of conductive fillers, respectively. [r] is a function of △, which is suitable for materials with good conductivity when D tends to infinity and is suitable for insulating materials when D tends to zero. According

492

(b)

8

80

2.0%-Measured value 2.0%-Calculated value

-Zi / kΩ

60

6

10-3

-Zi / kΩ

(a)

4 Graphene-Engineered Cementitious Composites

40

4 ×10-5

2

20

5.0%-Measured value 5.0%-Calculated value

0

0 0

5

10

15

20

25

30

35

0

2

4

6

8

Zr / kΩ

10 12 14 16 18 20

Zr / kΩ

(c) 0.8

-Zi / kΩ

0.6 0.4 ×10-5

0.2

10.0%-Measured value 10.0%-Calculated value

0.0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Zr / kΩ Fig. 4.35 ZSim simulating AC impedance spectroscopy curve of representative cementitious composites a with 2.0% of graphene, b with 5.0% of graphene, and c with 10.0% of graphene

Table 4.9 Pore solution resistance in the equivalent circuit models Graphene content/%

2.0

3.0

4.0

5.0

9.0

10.0

Rs/X

4500

2647.5

1282

848.5

420.6

292.3

to the conductivity of graphene and cement matrix, △ in this study tends to infinity. [r] can be calculated with reference to the Fixman formula as listed in Eq. (4.3). Then, the resistivity of cementitious composites filled with graphene can be calculated according to Eq. (4.2). The comparison of calculated and measured intrinsic resistivity of graphene-filled cementitious composites is listed in Table 4.10. As it Table 4.10 Calculated and experimental intrinsic resistivity of cementitious composites filled with graphene Graphene content/%

2.0

3.0

4.0

5.0

9.0

10.0

Measured value Rm/kX cm Calculated value Rm/kX cm

3.06 5.9

2.26 3.9

1.76 2.1

1.66 1.5

0.7 1.03

0.6 0.76

4.6 Functional/Smart Properties

493

shows, the calculated resistivity value is a little larger than the measured value, but the variation is the same as that of the measured resistivity value. This indicates that the relationship between the content of graphene and the resistivity of composites can be calculated by substituting the specific surface area of graphene according to the equation: r Rm rf ¼ 1 þ ½rD UðD ¼ Þ ¼ rm R rm ! 1 2ðARÞ2 ½r1 ¼ þ4 3 ½3ln½4ðARÞ  7

4.6.3

ð4:2Þ ð4:3Þ

Thermal Properties/Performances

Fig. 4.36 Thermal conductivity of cementitious composites with graphene

Thermal conductivity / (W/(m⋅k))

A plot of the thermal conductivity of cement mortars with graphene is presented in Fig. 4.36. The specific heat is chosen to represent the thermal conductivity performance of cement mortars with graphene in Fig. 4.37. The thermal conductivity of cement mortars with graphene grows with increasing graphene content. The thermal conductivity of cement mortars with 1.0% of graphene reaches 1.22 W/ Microsoft K, which represents an 11% increase over control cement mortars. It is amazing that the thermal conductivity of cement mortars is twice as much as that of control cement mortars when the graphene content is 5.0%. The specific heat of cement mortars is negatively correlated to the graphene dosage. The specific heat of cement mortars with 1.0% of graphene decreases by 5.88%, compared with cement mortars without graphene. The specific heat of cement mortars with 5.0% of graphene is 17.7% smaller than that of control cement mortars. The small specific heat indicates the large temperature rise rate, which implies further the better thermal conductivity property. In contrast, the large thermal conductivity indicates the good thermal conductivity property. Thus, it is inferred that graphene can enhance the

77.3%

2.0 11.2%

1.5 1.0 0.5 0.0

0

1

Graphene content / %

2

Fig. 4.37 Specific heat of cementitious composites filled with graphene

4 Graphene-Engineered Cementitious Composites 1400

Specific heat / (J/(kg⋅K))

494

1300

5.88% 17.7%

1200

1100

1000

0

1

2

Graphene content / %

thermal conductivity performance of the cementitious composites. The increasing thermal conductivity is beneficial for transmitting and releasing heat of hydration and maintaining the uniformity of the temperature and decreasing the thermal stress inside the composites. Thermal conductivity is a concept based on phonons, and both filler and matrix contribute to the heat flow. It attributes the outstanding thermal conductivity property of this material to a favorable combination of the high aspect ratio, stable crystal structure, ordered carbon atom layer, and low thermal interface resistance of the graphenes. In the process of thermal vibration, the effective transmission of phonons reflects the good thermal conductivity of crystals. Hence, the high thermal conductivity of graphene can be explained from the following four aspects. (1) The carbon bond of graphene has good flexibility [21], and its energy is very high [22]. When an external force is applied to the graphene, the surface of carbon atoms may be bent and deformed. In other word, the carbon atoms do not need to rearrange to adapt to the changes in the outside world, which maintains the stability of the structure. At room temperature, when the carriers motion in the crystal, they are mainly suffered from scattering of phonon. However, the stable lattice structure can reduce the scattering in the phonon transmission. (2) The ordered carbon atom layer within the graphenes provides a highly efficient channel of heat transfer, which promotes the phonon transmission between the graphenes and the cement mortars [23]. (3) Compared with other fillers, such as spherical or cylindrical shape, the sheet thermal-conductive fillers have more advantages. Because the close contact is formed between the adjacent sheet fillers and the contact area of the sheet filler is larger, the interfacial thermal resistance can be reduced and the phonon transmission can be improved [24]. (4) Compared with the cementitious composites, the nanoparticles can substantially improve the thermal conductivity of the composites. It is because that the nanoparticles provide heat-transfer carrier, so as to enhance the electron mobility [13].

4.6 Functional/Smart Properties

4.6.4

495

Electromagnetic Properties/Performances

(1) Electromagnetic wave shielding properties/performances 1. Graphene-filled cement pastes Shielding effectiveness of cement pastes with graphene presents an upward trend with the increase of graphene content, as shown in Fig. 4.38. When the graphene content is 10.0%, the shielding effectiveness of cement pastes with graphene can reach 10.4 dB. The shielding effectiveness of cement pastes with 10.0% of graphene is 1.6 times of that of cement pastes without graphene. The shielding effectiveness of cement pastes with 5.0% of graphene is nearly 1.4 times of that of cement pastes without graphene, which increases obviously compared with the cement pastes with 1.0–2.0% of graphene. It indicates that 5.0% dosage of graphene has been diffusely distributed to cover most areas in the cementitious composites. Therefore, when the graphene content continues increasing, the shielding effectiveness does not improve as much as the cement pastes with graphene do. As presented in Fig. 4.38, in the frequency range of 2–18 GHz, the shielding effectiveness of the cement pastes with graphene is the highest when the frequency is about 14 GHz. 2. Graphene-filled cement mortars It can be observed from Fig. 4.39 that the electromagnetic wave shielding effectiveness of graphene-filled cement mortars also shows a trend of increasing with the increase of graphene content, which is consistent with the variation of that of the cement pastes mentioned above. The shielding effectiveness of cement mortars with 5.0% of graphene reaches 4.7 dB, which is 42.4% higher than that of control cement mortars. The incorporation of 15.0% of graphene maximally increases the shielding effectiveness of cement mortars by 95%. It verifies that the introduction of sand does not affect the enhancement law of graphene content on the shielding effectiveness of cementitious composites. However, it should be noted that the shielding effectiveness of graphene-filled cement mortars is less than that of 12

Shielding effectiveness / dB

Fig. 4.38 Shielding effectiveness of cement pastes with different contents of graphene in the frequency of 2 and 18 GHz

10 8 6 0 1.0% 2.0% 5.0% 9.0% 10.0%

4 2 0

0

2

4

6

8

10 12 14 16 18 20

Frequency / GHz

Fig. 4.39 Shielding effectiveness of cement mortars with different graphene contents between 2 and 18 GHz

4 Graphene-Engineered Cementitious Composites

Electromagnetic shielding effectiveness/ dB

496

0 1.0%

6

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2

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Frequency / GHz

graphene-filled cement pastes under the same graphene content, which indicates that the introduction of fine aggregates affects the electromagnetic shielding effectiveness values of graphene-filled cementitious composites. (2) Electromagnetic wave absorbing properties/performances 1. Calculated reflectivity of graphene-filled cement pastes The calculated reflectivity of the electromagnetic wave of the 10-mm-thick and 20-mm-thick graphene-filled cement pastes is given in Figs. 4.40 and 4.41. It can be observed from Figs. 4.40 and 4.41 that the electromagnetic wave absorbing properties of graphene-filled cement pastes are influenced by the graphene content, the thickness of cement pastes, and the frequency of the electromagnetic wave. Under the same electromagnetic wave frequency, the electromagnetic wave absorbing properties of 10-mm-thick graphene-filled cement pastes is increased with the increasing graphene content. When the electromagnetic wave frequency is about 8 GHz, the absolute value of the reflectivity of cement pastes with 10.0% of graphene reaches up to 33 dB, which is three times higher than that of the cement pastes without graphene. In the high-frequency range, the best absorbing properties of graphene-filled cement pastes can be achieved by incorporating 5.0% of graphene, but as the graphene content continues to increase, the absorbing properties

0

Reflectivity / dB

Fig. 4.40 Reflectivity of the 10-mm-thick cement pastes filled with different contents of graphene between 2 and 18 GHz

-7 -14 -21

0 1.0% 2.0% 5.0% 9.0% 10.0%

-28 -35

0

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20

4.6 Functional/Smart Properties 0

Reflectivity / dB

Fig. 4.41 Reflectivity of the 20-mm-thick cement pastes filled with different content of graphene between 2 and 18 GHz

497

-5 -10 -15 0 1.0% 2.0% 5.0% 9.0% 10.0%

-20 -25 0

4

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Frequency / GHz

are reduced instead. It results from that the penetration ability of electromagnetic wave in the low frequency is not well, and thus, the more the addition of graphene with enhanced absorbing properties, the stronger the absorbing properties of cement pastes. While the penetration ability of electromagnetic wave in high frequency is relatively strong, and when the content of graphene is excessively high, the cracks in the cement matrix become larger and part of electromagnetic wave will pass through. As a result, the reflectivity of electromagnetic wave even increases when the content of graphene exceeds 5.0%. In addition, with increasing content of graphene, the electromagnetic wave absorbing properties of 20-mm-thick cement pastes filled with graphene still show an increasing trend and that of cement pastes with 5.0% of graphene have been optimized. As shown in Figs. 4.40 and 4.41, when the same content of graphene is added, the electromagnetic wave reflectivity of cement pastes at different frequencies is different. In the frequency bands of 8 and 14 GHz, the absorbing properties of 10-mm-thick cement pastes with graphene are the best, and its bandwidth is around 2 GHz, while the absorbing properties of the 20-mm-thick graphene-filled cement pastes are mainly better for the frequency bands of 4, 6, 10, 14, and 18 GHz, and its bandwidth is smaller than that of 10-mm-thick cement pastes incorporated with graphene. 2. Calculated reflectivity of graphene-filled cement mortars The calculated reflectivity of electromagnetic wave of the 10-mm-thick and 20-mm-thick graphene-filled cement mortars is demonstrated in Figs. 4.42 and 4.43, respectively. It is evident from Figs. 4.42 and 4.43 that the electromagnetic wave absorbing properties of graphene-filled cement mortars are also influenced by the content of graphene, the thickness of cement mortars, and the frequency of the electromagnetic wave, but it is slightly different from cement pastes with graphene. Under the same electromagnetic wave frequency, the electromagnetic wave absorbing properties of 10-mm-thick cement mortars with filled graphene rises as the graphene content increases. The absolute value of the reflectivity of cement mortars with 15.0% of graphene reaches a maximum of 18 dB, which is nine times higher than that of the control cement mortars. Besides, with increasing content of

Fig. 4.42 Reflectivity of the 10-mm-thick cement mortars filled with different contents of graphene between 2 and 18 GHz

4 Graphene-Engineered Cementitious Composites 0

Reflectivity / dB

498

-3 -6 -9 -12

0 1.0% 5.0% 10.0% 15.0%

-15 -18 0

4

8

12

16

20

Frequency / GHz

graphene, the electromagnetic wave absorbing properties of 20-mm-thick graphene-filled cement mortars also show an increasing trend. It can be observed that the absorbing properties of 20-mm-thick cement mortars with 5.0% graphene have been best at the frequency of around 15 GHz. Similar to graphene-filled cement pastes, the electromagnetic wave reflectivity of cement mortars with the same content of graphene at different frequencies is also different. The electromagnetic wave absorbing properties of 10-mm-thick graphene-filled cement mortars are mainly better for the frequency bands around 10 and 16 GHz, while the width of bands with better absorption properties is about 2 GHz. In the frequency bands of 5, 8, 11, 16, and 18 GHz, the absorbing properties of 20-mm-thick cement mortars with graphene are the best, but the bandwidth is smaller compared with that of 10-mm-thick graphene-filled cement mortars and is only about 1 GHz. 3. Measured reflectivity of graphene-filled cementitious composites From Figs. 4.38, 4.39, 4.40, 4.41, 4.42, 4.43, it can be seen that the electromagnetic wave shielding and absorbing properties of 5.0% of graphene-filled cementitious composites have been obviously increased with respect to the control cementitious composites. Therefore, the 10-mm-thick cement mortar slabs without graphene and with 1.0 and 5.0% of graphene were fabricated to measure its electromagnetic wave reflectivity by the bow method directly, which were used to compare with the calculated reflectivity. The results are exhibited in Fig. 4.44. According to Fig. 4.44, the measured values of the electromagnetic wave reflectivity of cementitious composites filled with graphene are close to the calculated values, but slightly larger than the calculated values. This also verifies the accuracy and feasibility of the previously calculated results of the electromagnetic shielding and absorbing properties of graphene-filled cementitious composites, which are obtained by testing the electromagnetic parameters. As shown in Fig. 4.44, it is easy to find that the trend of the reflectivity of cementitious composites in three groups is basically similar. The only difference lies in the amplitude of the change. The electromagnetic wave absorbing properties of cementitious composite reach the best of the entire frequency band (1–18 GHz)

4.6 Functional/Smart Properties 0

Reflectivity / dB

Fig. 4.43 Reflectivity of the 20-mm-thick cement mortars filled with different contents of graphene between 2 and 18 GHz

499

-6 -12 -18

0 1.0% 5.0% 10.0% 15.0%

-24 -30

0

4

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0

Reflectivity / dB

Fig. 4.44 Reflectivity of cementitious composites filled with graphene

-1 -2 -3 0 1.0% 5.0%

-4 -5

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18

Frequency / GHz

in the vicinity of 8 GHz. At the same frequency, the reflectivity of the cementitious composites decreases with the increasing content of graphene. Compared with the control cementitious composites, the reflectivity of cementitious composites with 1.0% of graphene is 3.96 GHz and reduces by 12%. The reflectivity of cementitious composites with 5.0% of graphene reduces by 38% (reach 4.87 GHz). At the high-frequency band (8–18 GHz), the trend of reflectivity is similar to that of the composites at the low-frequency band. In the 14–18 GHz band, the electromagnetic wave absorbing curve is basically in the platform. However, unlike the reflectivity of composites at low-frequency band, the reflectivity of the composites even increases with the increasing content of graphene at high-frequency band. In other word, the electromagnetic wave absorbing property of the composites decreases with the increasing content of graphene, which is due to the reduction of electrical resistance [25]. If cementitious composite is expected to have good electromagnetic wave absorbing property, first of all, it should have good electromagnetic wave impedance matching. On one hand, it should reduce reflection of electromagnetic wave and enhance incidence of electromagnetic wave. On the other hand, it should enhance electromagnetic wave absorbing in the absorbing layer. Secondly, cementitious composites should meet the attenuation characteristics. Composites

500

4 Graphene-Engineered Cementitious Composites

with high electromagnetic loss can absorb and attenuate the electromagnetic wave. Only in this way, it can improve the electromagnetic wave absorbing effect of the cementitious composites layer. (3) Modification mechanisms The effect mechanisms of graphene on the electromagnetic wave shielding and absorbing properties of cementitious composites were analyzed by calculating the single reflection loss, multiple reflection loss, absorption loss, dielectric constant, and permeability of cementitious composites with graphene. It can be seen from Fig. 4.45 that there is nearly no single reflection and absorption loss in the low-frequency electromagnetic wave band. The electromagnetic wave shielding effectiveness of cementitious composites without graphene is mainly due to multiple reflections of cementitious composites. With the increase of graphene content, the electromagnetic shielding effectiveness of graphene-filled cementitious composites is a combination of single reflection loss, multiple reflection loss, and absorption loss, which indicates that the addition of graphene can increase the single reflection loss and absorption loss of cementitious composites. In the high-frequency electromagnetic wave band, the shielding effectiveness of cementitious composites without graphene is mainly derived from multiple reflection and single reflection of cementitious composites, among which multiple reflection accounts for a large proportion, and there is nearly no absorption loss. As the graphene content increases, the electromagnetic shielding effectiveness of cementitious composites with graphene is a combination of single reflection loss, multiple reflection loss, and absorption loss, among which single reflection accounts for a large proportion, and graphene also makes cementitious composites capable of absorbing electromagnetic waves. It demonstrates that cementitious composites filled with graphene are more capable of single-reflecting high-frequency electromagnetic waves than single-reflecting low-frequency electromagnetic waves. It can be observed from Fig. 4.46 that the proportion variations of single reflection loss, multiple reflection loss, and absorption loss in the electromagnetic shielding effectiveness of cementitious mortars with graphene as a function of graphene content are similar with that of cement pastes with graphene. Due to the large particle size of the sand, the effect of graphene in the cement mortars is less than that in the cement pastes when the same amount of graphene is added. Figure 4.47 shows the electromagnetic parameters of the cementitious composites with graphene, in which e′ represents the real part of the complex dielectric constant er, indicating the degree of polarization of the material medium under the electric field; e″ is the imaginary part of the complex dielectric constant, representing a measure of the loss caused by the rearrangement of the electric dipole moment of the material medium under the electric field. l′ represents the real part of the complex magnetic permeability lr, indicating the degree of polarization of the material medium under the magnetic field; lʺ is the imaginary part of the complex magnetic permeability, indicating a measure of the loss caused by the rearrangement of the magnetic dipole moment of the material medium under the magnetic

501

(a) 100

R-0 T-0 A-0

80 60 40 20 00

4

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Shielding effectiveness ratio / %

Shielding effectiveness ratio / %

4.6 Functional/Smart Properties

(b) 100 R-1.0% T-1.0% A-1.0%

80 60 40 20 0

0

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(c) 100

R-9.0% T-9.0% A-9.0%

40 20 0

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R-5.0% T-5.0% A-5.0%

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(e)

60

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(d)

Frequency / GHz

80

8

Frequency / GHz

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Shielding effectiveness ratio / %

Shielding effectiveness ratio / %

Frequency / GHz

(f) R-10.0% T-10.0% A-10.0%

80 60 40 20 0 0

4

8

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20

Frequency / GHz

Fig. 4.45 Shielding effectiveness ratio of cementitious pastes a without graphene, b with 1.0% of graphene, c with 2.0% of graphene, d with 5.0% of graphene, e with 9.0% of graphene, and f with 10.0% of graphene between 2 and 18 GHz (Note R, T, and A represent the single reflection, multiple reflection loss, and absorption loss)

field. The electromagnetic parameters er and lr are the two most important parameters for characterizing the interaction between electromagnetic wave and material medium, and since the frequency range of microwaves is very wide, both dielectric constant and magnetic permeability are complex vectors. It can also be seen from the above analysis that the imaginary part e″ of the complex dielectric

4 Graphene-Engineered Cementitious Composites

(a) 100 80

R-0 T-0 A-0

60 40 20 0 0

4

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Shielding effectiveness ratio / %

Shielding effectiveness ratio / %

502

(b) 100 80

R-1.0% T-1.0% A-1.0%

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4

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(c) 100

60

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8

Frequency / GHz

Frequency / GHz

8

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Frequency / GHz

(e) 100 R-15.0% T-15.0% A-15.0%

80 60 40 20 0

0

4

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Frequency / GHz Fig. 4.46 Shielding effectiveness ratio of cementitious mortars a without graphene, b with 1.0% of graphene, c with 5.0% of graphene, d with 10.0% of graphene, and e with 15.0% of graphene between 2 and 18 GHz (Note R, T, and A represent the single reflection, multiple reflection loss, and absorption loss)

constant and the imaginary part l″ of the complex magnetic permeability can reflect the ability of the material medium to reduce electromagnetic waves. The larger the two electromagnetic parameters mean the higher loss of electromagnetic waves by the material medium. Dielectric loss tangent e′/e″ and magnetic loss tangent l′/l″

4.6 Functional/Smart Properties

503

(b)

9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0

0 1.0% 2.0% 5.0% 9.0% 10.0%

0

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1.3

μ'-real part of the magnetic permeability

ε'-real part of the dielectric constant

(a)

0 1.0% 2.0% 5.0% 9.0% 10.0%

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4

8

μ''-imaginary part of the magnetic permeability

ε"-imaginary of the dielectric constant

2.8

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Frequency / GHz

(f)

(e) 0.30

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Electromagnetic loss angle of tangent

Dielectric loss angle of tangent

16

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Frequency / GHz

Frequency / GHz

0.04 0.00 -0.04

0 1.0% 2.0% 5.0% 9.0% 10.0%

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Fig. 4.47 Electromagnetic parameters of the cement pastes filled with different contents of graphene: a eʹ—real part of the dielectric constant; b lʹ—real part of the magnetic permeability; c eʺ—imaginary part of the dielectric constant; d lʺ—imaginary part of the magnetic permeability; e dielectric loss angle of tangent, and f electromagnetic loss angle of tangent

reflect the dielectric loss and magnetic loss of the dielectric medium to electromagnetic waves, respectively. Therefore, the larger dielectric loss tangent and magnetic loss tangent mean the greater ability of the material to reduce electromagnetic waves. It can be seen from Fig. 4.47 that the real part of the dielectric constant of the cementitious composites without graphene is about 5.5. With the increase in the amount of graphene, the real part of the dielectric constant of the graphene-filled cementitious composites increases. This indicates that the degree of dielectric polarization of electromagnetic wave on the cementitious composites with

504

4 Graphene-Engineered Cementitious Composites

graphene increases. In addition, the imaginary part of the dielectric constant of cementitious composites with graphene increases with the increase amount of graphene, indicating that the dielectric loss and the dielectric loss tangent of electromagnetic wave both increase with the increase of graphene content. Therefore, it can be concluded that as the amount of graphene increases, the dielectric loss of cementitious composites with graphene to electromagnetic waves increases. When the dosage of graphene reaches 5.0%, it can be seen that the imaginary part of the dielectric constant of cementitious composites with graphene has increased by about 50%, which indicates that the dielectric loss of electromagnetic waves has been relatively large when the amount of graphene is 5.0%. At the same time, the accuracy of the above electromagnetic wave shielding and absorbing properties calculation can be verified. When the electromagnetic wave frequency is in high-frequency range, the imaginary part of the dielectric constant of the cementitious composites with 5.0% of graphene is larger than the imaginary part of the dielectric constant of the cementitious composites with 9.0 and 10.0% of graphene. When the content of graphene exceeds 9.0%, the graphene-filled cementitious composites are relatively viscous, and there are many pores inside after molding. As the penetration of high-frequency electromagnetic waves is relatively strong, the imaginary part of the dielectric constant of the cementitious composites will be smaller than the imaginary part of the dielectric constant of the cementitious composite with 5.0% of graphene in the high-frequency range. However, the imaginary part of the magnetic permeability and the magnetic loss tangent of the cementitious composites with graphene are almost zero, indicating that graphene has no capability of magnetic loss. The electromagnetic parameters of the graphene-filled cement mortars are shown in Fig. 4.48. It can be seen that with the increase of graphene content, the real, imaginary, and dielectric loss tangent of the dielectric constant of graphene-filled cement mortars increase. This shows the dielectric loss performance of graphene on electromagnetic waves. In addition, it indicates that the dielectric loss of graphene-filled cement mortars increases with the increase of graphene content. However, the electromagnetic parameter value of the cement mortars with graphene is smaller than that of cement pastes with graphene. This is due to the large particle size of sand blocking the effect of graphene on electromagnetic waves. This also verifies that the calculation results of the electromagnetic absorbing performance of the cement pastes greater than that of the cement mortars are correct. The magnetic loss tangent, the real part, and the imaginary part of the magnetic permeability of cement mortars with graphene are still close to zero, which also verifies that the graphene has no capability of magnetic loss. This is consistent with the above test results of the cementitious composites with graphene, thus verifying the accuracy of the electromagnetic parameter of the cementitious composites with graphene. It can be concluded from the above research results that the shielding and absorbing properties of the cementitious composites with graphene mainly include the following aspects: (1) Graphene has excellent electromagnetic wave shielding

4.6 Functional/Smart Properties

505

(b)

ε'-real part of the dielectric constant

6 5 4 0 1.0% 5.0% 10.0% 15.0%

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(a)

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Electromagnetic loss angle of tangent

ε''-imaginary part of the dielectric constant Dielectric loss angle of tangent

0 1.0% 5.0% 9.0% 10.0%

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Fig. 4.48 Electromagnetic parameters of the cement mortars filled with different contents of graphene: aeʹ—real part of the dielectric constant; b lʹ—real part of the magnetic permeability; c e′ —imaginary part of the dielectric constant; d lʺ—imaginary part of the magnetic permeability; e dielectric loss angle of tangent, and f electromagnetic loss angle of tangent

and absorbing properties so that the addition of graphene into cementitious composites can improve the electromagnetic wave shielding and absorbing properties of cementitious composites. (2) Graphene has a uniquely tiny, two-dimensional layer structure, which enlarges the reflection area of electromagnetic waves of graphene. In addition, the distribution of graphene in the cement matrix increases, thus enhancing the single reflection loss of electromagnetic waves. (3) Graphene has excellent conductivity, which makes graphene capable of dielectric absorption loss

506

4 Graphene-Engineered Cementitious Composites

for electromagnetic waves. In this case, with the amount of graphene increases, the absorption loss of graphene-filled cementitious composites increases as well as the absorbing properties [26, 27].

4.6.5

Smart Properties/Performances of Graphene-Engineered Cementitious Composites

(1) Pressure-sensitive properties/performances 1. Effect of graphene content on pressure-sensitive properties/performances Figure 4.49 shows the fractional change in electrical resistivity of cement pastes with 0 to 10.0% of graphene under cyclic compressive loading. As presented in Fig. 4.49a, b, there is no change in electrical resistivity for the composites with low graphene doping levels (

>

(b)

(c)

CH CH

CH

Fig. 5.14 SEM micrographs of CH in cementitious composites at curing age of 28 d: a without nano-SiO2; b with 0.5% of nano-SiO2; c with 1.0% of nano-SiO2

539

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40 20 0.0

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Electrical resistivity / KΩ.cm

5.3 Mechanical Properties/Performances of Nano

0

Content of nano SiO2 / %

Fig. 5.15 Electrical resistivity and compressive strength of cementitious composites with nano-SiO2 at 3 d and 28 d of curing age

micrographs are not taken in ITZ. Thus, nano-SiO2 can not only reduce the size of CH in ITZ, but also CH in matrix. 4. Electrical resistivity analysis Figure 5.15 shows the relationship between compressive strength, electrical resistance, and content of nano-SiO2. It can be seen that the electrical resistivity of cementitious composites at curing ages of 3 d and 28 d increases as nano-SiO2 content increases. The enhancements of electrical resistivity of 2.0% nano-SiO2filled cementitious composites at curing ages of 3 and 28 d are 19.4% and 47.0%, respectively (as shown in Table 5.22). In addition, the electrical resistivity of cementitious composites at 28 d of curing age is higher than that at 3 d of curing age. Interestingly, the change trends of compressive and flexural strengths with the increasing content of nano-SiO2 and curing age are similar to those of electrical resistivity (as shown in Figs. 5.15 and 5.16). It can be seen in Fig. 5.17 that the compressive strengths at 3 d and 28 d exponentially and linearly increase with the increasing electrical resistivity, respectively. However, as shown in Fig. 5.18, the flexural strengths and electrical resistivity at 3 and 28 d of curing age are close to quadratic polynomial relation. Table 5.22 Increase rate of electrical resistivity of cementitious composites with different contents of nano-SiO2 Curing age

Cementitious composites With 1.0% of With 0.5% of nano-SiO2 (%) nano-SiO2 (%)

With 1.5% of nano-SiO2 (%)

With 2.0% of nano-SiO2 (%)

3d 28 d

6.7 11.9

17.5 33.0

19.4 47.0

15.9 21.1

5 Nano-SiO2-Engineered Cementitious Composites

540 120

10 9

100

Flexural strength / MPa

Electrical resistivity / KΩ.cm

Fig. 5.16 Electrical resistivity and flexural strength of cementitious composites with nano-SiO2

8 80

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40 20 0.0

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(a) Compressive strength / MPa

40 38 36 34 32

compressive strength Exponential Fit R2=0.740 y=y0+ A1*exp(x/t1) Parameter Value Error y0 26.54 2.60 A1 8.53E-11 1.69E-9 t1 1.17 0.904

30 28 26 25

26

27

28

29

30

Electrical resistivity / KΩ·cm

(b) 65 Compressive strength / MPa

Fig. 5.17 Relationship between electrical resistivity and compressive strengths of cementitious composites at: a 3d of curing age; b 28 d of curing age

60 55 Compressive strength Linear Fit R2=0.916 y=a+ bx Parameter Value Error a 0.63 7.78 b 0.78 0.12

50 45 40 50

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85

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5.3 Mechanical Properties/Performances of Nano

(a) 8.5

Flexural strength / MPa

Fig. 5.18 Relationship between electrical resistivity and flexural strengths of cementitious composites at: a 3d of curing age; b 28 d of curing age

541

8.0 7.5 Flexural strength Polynomial Fit R2= 0.997 y=c+ b1x+b2x2 Parameter Value Error c -118.81 9.39 b1 8.65 0.68 b2 -0.15 0.0012

7.0 6.5 6.0 5.5 25

26

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(b)

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8.6 8.4 8.2

Flexural strength Polynomial Fit R 2= 0.859 y=c+ b1x+b2x2 Parameter Value Error c -3.66 5.01 b1 0.32 0.15 b2 -0.0021 0.0012

8.0 7.8 7.6 7.4 50

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Electrical resistivity / KΩ·cm

Cementitious composite without conductive filler is a poor conductor of electricity. The main electrical conduction depends on the transfer of electrolyte ion. When cementitious composite matrix becomes dense, the pathway of electrolyte ion is longer and the movement of electrolyte ion becomes difficult. Therefore, the denser the matrix, the higher the electrical resistivity. Nano-SiO2 can enhance the compactness of cement matrix by the following reasons. Nano-SiO2 can react with CH; thus, more hydration products are produced compared with control cement mortar, which can be seen from Table 5.15. Nano-SiO2 and the hydration products can fill the pore in cementitious composites, which make cement matrix much denser (as shown in Fig. 5.13). In addition, nano-SiO2 particles or agglomerates are able to absorb part of the mixing water [1], thus reducing the effective W/C of the cementitious composite. Therefore, low W/C makes silica gel hydrates and cement

5 Nano-SiO2-Engineered Cementitious Composites

542

matrix much denser. Those contribute to increasing electrical resistivity, flexural, and compressive strength at the same time. Therefore, electrical resistivity may describe the change trend of compactness, flexural, and compressive strengths.

5.3.3

Impact Properties/Performances of Reactive Powder Concrete with Nano-SiO2 and Reinforcement Mechanisms

(1) Compression impact properties/performances under split Hopkinson pressure bar test 1. Dynamic compressive strength Figure 5.19 shows the dynamic compressive strength of cementitious composites with different contents of nano-SiO2 at curing age of 90 d, compared with control cementitious composites. The relationship between strength and strain rate is shown in Fig. 5.20. As shown in Fig. 5.19, whether or not incorporating nano-SiO2, the dynamic compressive strength of cementitious composites increases as the strain rate increases; i.e., there exists the strain rate effect of concrete. With the incorporation of nano-SiO2, the strength of cementitious composites does not increase significantly or even slightly decreases (cementitious composites with 3.0% nano-SiO2) at low strain rates (321/s–600/s). This phenomenon, however, is reversed at high strain rates. In the split Hopkinson pressure bar test of high strain rate, a large number of micro-cracks inside the concrete form in the initial stage of loading and retard the propagation time of these cracks to expand along the weak interface of concrete,

240

Dynamic compressive strength / MPa

Fig. 5.19 Dynamic compressive strength of cementitious composites with and without nano-SiO2 at 90 d of curing age

200

3.0%

160 120 240 200

1.0%

160 120 240 200

0

160 120 200

400

600 Strain rate / s-1

800

1000

5.3 Mechanical Properties/Performances of Nano

Dynamic compressive strength / MPa

(a) 270 240

Dynamic compressive strength

Fitting curve y=92.9977+0.13922x R2=0.67511

210 180 150 120 200

400

600

Strain rate / s-1

800

Dynamic compressive strength / MPa

(b) Dynamic compressive strength

270 240

Fitting curve y=130.99008+0.11748x R2=0.44695

210 180 150 120 200

400

Strain rate

600 / s-1

800

(c) Dynamic compressive strength / MPa

Fig. 5.20 Relationship between the dynamic compressive strength and the strain rate of cementitious composites with different content of nano-SiO2 at 90 d of curing age, compared with control cementitious composites: a without nano-SiO2; b with 1.0% of nano-SiO2; c with 3.0% of nano-SiO2

543

270 240

Dynamic compressive strength

Fitting curve y=65.07461+0.21038x R2=0.77878

210 180 150 120 200

400

600

Strain rate / s-1

800

544

5 Nano-SiO2-Engineered Cementitious Composites

thus increasing the failure stress [9]. The incorporated nano-SiO2 fills the cement matrix, which decreases the micro-crack size within the concrete [8]. Furthermore, the pozzolanic reaction between nano-SiO2 and CH can consume CH and contribute to the enhancement of the dynamic compressive strength of cementitious composites. What’s more, the nucleation effect of nano-SiO2 decreases the size of CH crystals and the crystal orientation, resulting in the increase of compressive strength [10]. However, the excessive nano-SiO2 may cause inhomogeneous dispersion and agglomeration and produce side effects on the development of strength. When the strain rate is relative high, more cracks form in the concrete and more nano-SiO2 particles are required to function, since then the effect of nano-SiO2 is fully reflected. As can be seen from Fig. 5.20, compared with the control cementitious composites at 90 d of curing age, the increased curves fitting linearity degree and the decreased slopes of cementitious composites with nano-SiO2 indicate that nano-SiO2 improves the rate-hardening effect of cementitious composites and decreases the strain rate sensitivity. This is because nano-SiO2 with small-size effect reduces the initial defects of cementitious composites, thereby preventing the formation of early micro-cracks within RPC. As the loading rate increases, more micro-cracks form inside cementitious composites. The newly formed cracks require more energy than the energy required for developing existing cracks [11]. Considering the decreased strain rate sensitivity of cementitious composites with nano-SiO2, the high water absorption of nano-SiO2 can display a critical role. The provision of nano-SiO2 reduces the free water content in mortar and therefore weakens the bonding effect and inertia effect of cementitious composites [12–14]. 2. Dynamic compressive deformation Figure 5.21a, b shows the dynamic peak strain and dynamic ultimate strain of cementitious composites with different contents of nano-SiO2 at 90 d of curing age, compared with control cementitious composites. It is seen from Fig. 5.21a that the incorporated nano-SiO2 significantly increases the dynamic peak strain of cementitious composites. The enhancement effect, however, as the strain rate increases, first increases and then decreases. As can be seen from Fig. 5.21b, when the strain rate is below 600/s, the dynamic ultimate strain of cementitious composites with nano-SiO2 is close to or even lower than that of the control cementitious composites. After that, cementitious composites with nano-SiO2 gradually show the higher strain value compared with control cementitious composites. In the crack formation stage, the concrete deformation resistance is mainly originated from the structure compactness. Nano-SiO2 with filling effect and nucleation effect increases the compactness of cementitious composites and reduces the initial defects within cementitious composites [15]. However, under the excessive high strain rates, a large number of cracks in the concrete rapidly increase and connect with each other, which weakens the nano-SiO2 role and then instantly breaks the cementitious composites.

5.3 Mechanical Properties/Performances of Nano

(a)

0 1.0% 3.0%

0.015

Dynamic peak strain / ε

Fig. 5.21 Dynamic peak strain a and dynamic ultimate strain b of cementitious composites with and without nano-SiO2 at 90 d of curing age

545

0.012

0.009

0.006

0.003

0.000

305

449

645

800

278

444

630

844

334

404

679

859

Strain rate /

(b)

s -1

0.20

Dynamic ultimate strain / ε

0

0.16

1.0% 3.0%

0.12

0.08

0.04 200

400

600

800

1000

Strain rate / s -1

In the crack propagation stage, the residual strain is mainly related to the concrete spatial structure. The incorporated nano-SiO2 builds a new three-dimensional network structure within the original cementitious composite network structure. The hydration product is firmly bonded to the transition zone, thus improving the performance of cementitious composite weak interface [16]. Additionally, the water absorption and nano-core effect of nano-SiO2 reduce the size of CH crystal and result in more interfaces, which enables cracks along the crystal fracture path to become more tortuous and therefore inhibits the cracks expansion [8].

546

5 Nano-SiO2-Engineered Cementitious Composites

3. Dynamic impact stress-strain curves Figure 5.22 exhibits the dynamic stress/strain curves of cementitious composites with different contents of nano-SiO2 at curing age of 90 d under different strain rates.

(a) B

240

340/s 449/s

Stress / MPa

569/s 804/s

160

80 C A

0 0.00

0.04

0.08

0.12

0.16

Strain /ε

(b) 278/s

240

444/s

Stress / MPa

630/s 825/s

160

80

0 0.00

0.04

0.08

0.12

0.16

Strain / ε

(c) 278/s

240

444/s 630/s

Stress / MPa

Fig. 5.22 Dynamic impact stress/strain curves of cementitious composites at 90 d of curing age: a without nano-SiO2; b with 1.0% of nano-SiO2; c with 3.0% of nano-SiO2

825/s

160

80

0 0.00

0.04

0.08

Strain /ε

0.12

0.16

5.3 Mechanical Properties/Performances of Nano

547

As shown in Fig. 5.22, whether or not incorporating nano-SiO2, the stress/strain curves of cementitious composites are thought to be divided into two stages: the approximately nonlinear ascent stage (AB) and the nonlinear descent stage (BC). These two stages are corresponding to the strain rate hardening and damage softening of cementitious composites. At a comparable strain rate range, the incorporation of nano-SiO2 at two contents increases the dynamic peak stress, dynamic peak strain, and dynamic ultimate strain of cementitious composites. 4. Dynamic compression toughness Figure 5.23 is the impact toughness of cementitious composites containing different types of nano-SiO2 and control cementitious composites at 90 d of curing age. The corresponding specific energy absorption of cementitious composites is shown in Fig. 5.25. As shown in Fig. 5.24, whether or not incorporating nano-SiO2, the impact toughness of RPC increases with the rise of strain rate. The incorporation of nano-SiO2 increases the impact toughness, especially at the high strain rates. When the content of nano-SiO2 is 1.0%, the toughness of cementitious composites is improved by 13.6% maximally at the strain rate of 280/s–580/s. The toughness development of cementitious composites containing 3.0% nano-SiO2 is similar to that of the cementitious composites with 1.0% nano-SiO2, and the maximum increased value of the cementitious composites with nano-SiO2 is 12.4%. It can be seen from Fig. 5.24 that the incorporation of nano-SiO2 evidently increases the specific energy absorption of cementitious composites. When the Fig. 5.23 Impact toughness of cementitious composites with and without nano-SiO2 at 90 d of curing age

0 1.0% 3.0%

100

Impact toughness / KJ/m 2

80

60

40

20

0

278

376

449

569

802

334

404

680

757

859

280

325

440

630

840

Strain rate / s-1

5 Nano-SiO2-Engineered Cementitious Composites

Fig. 5.24 Specific energy absorption of cementitious composites with and without nano-SiO2 at 90 d of curing age

Specific enegy absorption / KJ/m3

548

0

40000

1.0% 3.0%

30000 20000 10000 200

400

600

Strain rate / s -1

800

1000

strain rate ranges from 280/s to 645/s, 3.0% of nano-SiO2 maximally increases the specific energy absorption by 159.7%. When the strain rate is between 803/s and 845/s, the increased specific energy absorption values of 3.0% nano-SiO2-filled cementitious composites are up to 211.2%. In general, the addition of nano-SiO2 significantly improves the impact properties of cementitious composites. In fact, if the compactness of concrete is too high, i.e., the pore volume of cementitious composites is too small, the energy release path will be limited to some extent, resulting in brittle failure of the concrete. This is why high-strength concrete generally has poor fire resistance and heat resistance. The incorporation of nano-SiO2 not only increases the compactness of cementitious composites, but more important, it also improves its structural performance by controlling the morphology of hydration products from the nanometer scale, which in turn improves the impact properties of cementitious composites. (2) Impact toughness under pendulum test

Fig. 5.25 Impact toughness of cementitious composites with different content of nano-SiO2 at 90 d of curing age

Impact toughness / KJ/m2

Figure 5.25 displays the comparison between the impact toughness of cementitious composites containing different content of nano-SiO2 at 90 d of curing age, according to pendulum test.

28 24 39.9%

20

36.2%

16 12

0

1.0

Content of nano SiO2 / %

3.0

5.3 Mechanical Properties/Performances of Nano

549

As shown in Fig. 5.25, the incorporation of nano-SiO2 obviously enhances the impact toughness of cementitious composites, and the enhancement can be up to 39.9% and 36.2% at the content of 1.0% and 3.0% of nano-SiO2, respectively. It is noteworthy that the toughness value obtained by pendulum test is much smaller than that by split Hopkinson pressure bar experiment (even at the lowest strain rate of 268/s of split Hopkinson pressure bar test), which is mainly related to the difference in the strain rates. The higher strain rates in the split Hopkinson pressure bar test, due to its higher impact velocity, make concrete bear the more obvious three-dimensional confining pressure, thus enabling the materials to possess higher elastic modulus. (3) Reinforcement mechanisms The reinforcement mechanisms of enhanced compression impact properties/ performances and impact toughness of nano-SiO2-filled cementitious composites are the same as that mentioned in Sect. 5.3.2. According to the analysis of TG/ DTG, XRD, SEM, and electrical resistivity test results, the denser microstructure, and the decreased CH amount, CH size as well as orientation of CH crystal are all beneficial to improve the impact properties/performances of cementitious composites with nano-SiO2. In order to comprehensively analyze the reinforcement mechanisms of nano-SiO2 on the impact properties/performances of cementitious composites, 29Si NMR analysis test is also carried out. Figure 5.26a, b illustrates the original and the deconvoluted 29Si NMR spectra of cementitious composites with nano-SiO2. Results and characterization parameters from deconvolution are given in Table 5.23 and Fig. 5.27, respectively. As shown in Fig. 5.26, cementitious composites have a sharp absorption peak Q2 along with four weak peaks (Q0, Q1, Q3, and Q4) in the 29Si NMR spectrum,

(b)

(a)

Q0

-70

-80

3.0%

Q1 Q0

Q1

Q3

-60

Q2

0 3.0%

Q2

-90

-100

Chemical shift / ppm

Q4

-110

Q3

-120

-60

-70

-80

-90

Q4

-100 -110 -120

Chemical shift / ppm

Fig. 5.26 29Si NMR spectra a and the deconvoluted graph b of cementitious composites with nano-SiO2

550

5 Nano-SiO2-Engineered Cementitious Composites

Table 5.23 Deconvolution results of cementitious composites with and without nano-SiO2 Cementitious composites Without nano-SiO2 With nano-SiO2

Distribution of Si Q1 (%) Q0 (%)

Q2 (%)

Q3 (%)

Q4 (%)

17.7 15.3

41 48.2

13.7 13.4

11.7 8

15.9 14.9

Fig. 5.27 Characterization parameters of deconvoluted 29 Si NMR for cementitious composites with and without nano-SiO2

whether or not nano-SiO2 is incorporated. Compared with control cementitious composites, cementitious composites with nano-SiO2 have a lower but broader peak Q4, which indicates the incorporation of nano-SiO2 reduces the crystallinity of-SiO2 in mineral additives; i.e., the activity of additives is improved. It can be seen from Fig. 5.27 that compared with cementitious composites without nano-SiO2, composites with nano-SiO2 increase mean chain length (MCL) and polymerization degree (PD) by 18.5% and 26.7%, respectively. Combined with the increased number of Q2 and the decreased number of Q1 and Q4 that listed in Table 5.3, it can be found that the addition of nano-SiO2 reduces the residual amount of cement clinker. More tetrahedral network structures (SiO2) from mineral additives are decomposed, and more dimer short chains appear in the hydration products. Furthermore, the addition of nano-SiO2 breaks the Si–O–Si spacial structure of silicate tetrahedron in C–S–H gels and makes the tetrahedron hydroxylated. As a result, the newly formed Si–OH monomers mutually connect and condense into higher polymerization silicate tetrahedron. In this way, the PD and MCL of C–S–H gels are increased.

5.4 Durability of Nano-SiO2-Engineered Cementitious Composites

5.4

551

Durability of Nano-SiO2-Engineered Cementitious Composites

The mix proportion and main fabrication process of the nano-SiO2-modified cementitious composites for durability test are listed in Tables 5.10 and 5.11, respectively.

5.4.1

Wear Resistance

The abrasion loss per unit area of nano-SiO2-filled cementitious composites with standard curing for 28 d and heat curing for 3 d is diagramed in Fig. 5.28. As the nano-SiO2 content raises, the abrasion loss of RPC with standard curing decreases first and then increases. When the content of nano-SiO2 increases from 1.0 to 3.0%, the abrasion loss of the cementitious composites with standard curing increases from 0.38 to 0.50 kg/m2, and the absolute/relative decrease in abrasion loss decreases from 0.25 (kg/m2)/39.68 to 0.13 (kg/m2)/20.63%. Whereas, the abrasion loss of cementitious composites with heat curing continuous to decrease and obtains a maximal absolute/relative decrease of 0.22 (kg/m2)/45.85% when 3.0% of nano-SiO2 is added. As a result, the wear resistance of cementitious composites containing nano-SiO2 is remarkably improved, but the contribution of nano-SiO2 to the wear resistance of cementitious composites under standard curing decreases as its content increases. Besides, it is more effective to improve the wear resistance of cementitious composites with the addition of 1.0% rather than 3.0% of nano-SiO2. It can also be seen from Fig. 5.28 that all of the abrasion loss of nano-SiO2-filled cementitious composites with heat curing is less than that with standard curing. When the amount of nano-SiO2 is 3.0%, the abrasion loss of cementitious composites with heat curing maximally is decreased by 0.23 kg/m2 compared with that

0.8

Abrasion loss / kg/m2

Fig. 5.28 Abrasion loss per unit area of cementitious composites containing nano-SiO2 with two curing methods (Note S represents standard curing and H represents heat curing)

S H

0.6

29.63% 39.68%

0.4

37.72%

45.85%

0.2 0.0

0

1.0

2.0

Content of nano-SiO2 / %

5 Nano-SiO2-Engineered Cementitious Composites

552

of cementitious composites with standard curing. In summary, heat curing method is more effective than standard curing method to enhance the wear resistance of the cementitious composites containing nano-SiO2.

5.4.2

Chloride Penetration Resistance

Fig. 5.29 Chloride diffusion coefficient of cementitious composites containing nano-SiO2 with two curing methods (Note S represents standard curing and H represents heat curing)

Chloride transport coefficient / (1×10-14m2/s)

The chloride diffusion coefficient of cementitious composites containing nano-SiO2 with standard curing and heat curing is demonstrated in Fig. 5.29. The chloride diffusion coefficient of 1.0% of nano-SiO2-filled cementitious composites with standard curing is reduced by 60% compared with that of control cementitious composites; i.e., the chloride penetration resistance is enhanced. Conversely, the chloride diffusion coefficient of cementitious composites containing 3.0% of nano-SiO2 with standard curing is increased by 1.0  10−14 (m2/s)/78.57%; i.e., the chloride penetration resistance is reduced. This is because that the greater the amount of nanoparticles, the more the water demand of cementitious composites due to its ultrahigh specific surface area [17–20]. The cementitious composites will produce larger voids after hardening as water consumption raises, thereby reducing the chloride penetration resistance of cementitious composites. With heat curing, the chloride diffusion coefficient of cementitious composites continuously decreases and the introduction of 3.0% of nano-SiO2 endows it a drop from 1.9  10−14 m2/s to 0. Therefore, adding 1.0% of nano-SiO2 is more effective to improve the chloride penetration resistance of cementitious composites with standard curing, while 3.0% of nano-SiO2 is more effective for cementitious composites with heat curing. Figure 5.29 reveals that both the chloride penetration resistance of control cementitious composites and 1.0% of nano-SiO2-filled cementitious composites with heat curing are weaker than that with standard curing. Whereas, when 3.0% of nano-SiO2 is incorporated, the chloride penetration resistance of cementitious composites with heat curing is improved maximally but that of cementitious composites with standard curing is significantly weakened.

S H

3

78.57%

2 52.63%

1 60%

0 0

1.0

2.0

Content of nano-SiO2 / %

5.4 Durability of Nano-SiO2-Engineered Cementitious Composites

(a)

553

(b) Denser

Pores

(c) Denser

Fig. 5.30 SEM images of cementitious composites: a without nano-SiO2; b with 1.0% of nano-SiO2; and c with 3.0% of nano-SiO2

5.4.3

Modification Mechanisms

(1) Scanning electron microscope observation The SEM images as shown in Fig. 5.30 indicate that nano-SiO2-filled cementitious composites are denser than control cementitious composites. This helps to enhance the wear resistance and chloride penetration resistance of cementitious composites. In addition, hydrate products diffuse and envelop nano-particles as nucleus after hydration begins, which is called as “nucleation effect,” and they will further promote and accelerate cement hydration due to their high surface energy or activity. (2) Thermogravimetry analysis and theoretic calculation The TG and DTG tests (as shown in Figs. 5.31 and 5.32) of control RPC as well as nano-SiO2-filled cementitious composites with standard curing for 28 d are

5 Nano-SiO2-Engineered Cementitious Composites

554

(b)

(a) 0

1st derivative mass / %

Mass loss / %

100 95 90 85 80

0

200

400 600 Temperature /

800

0

0.0000 -0.0001 -0.0002 -0.0003

1000

0

200

400 600 Temperature /

800

1000

Fig. 5.31 TG (a) and DTG (b) curves of cementitious composites without nano-SiO2 under standard curing

Mass loss / %

100

1.0% 3.0%

95 90 85 80

0

200

400 600 Temperature /

800

1st derivative mass / %

(b)

(a)

1000

0.0000 -0.0001 -0.0002 1.0% 3.0%

-0.0003 0

200

400 600 Temperature /

800

1000

Fig. 5.32 TG (a) and DTG (b) curves of nano-SiO2-filled cementitious composites with standard curing

Table 5.24 Cement hydration degree with standard curing Cementitious composites

Without nano-SiO2 (%)

With 1.0% of nano-SiO2 (%)

With 3.0% of nano-SiO2 (%)

Hydration degree

0.63

0.66

0.66

conducted to calculate the cement hydration degree. The results are illustrated in Table 5.24. As it shows, the incorporation of nano-SiO2 can slightly improve the cement hydration degree. Obviously, the cement hydration degree obtained here is contrary to the results shown in Table 5.16, which may be the contribution of the added FA and SF. (3) X-ray diffraction analysis XRD patterns of cementitious composites with standard curing for 28 d are showed in Fig. 5.33, and the corresponding orientation of CH crystal are calculated in

5.4 Durability of Nano-SiO2-Engineered Cementitious Composites

(a)

0 AFt CH (001) SiO 2 CaCO 3 C 3S CH (101)

400

Intensity

555

200

0 10

20

30

40

50

60

70

80

2θ/°

Intensity

(b) 3.0%

400 200

AFt SiO2

CH (001) CaCO3

C 3S

CH (101)

Intensity

0 1.0%

400 200 0 10

20

30

40 50 2θ /°

60

70

80

Fig. 5.33 XRD patterns of cementitious composites with standard curing: a without nano-SiO2; b with nano-SiO2 (Note C3S represents 3CaO
SiO2.) Table 5.25 Diffraction intensity and orientation of CH in cementitious composites with standard curing Cementitious composites

CH (001)

CH (101)

Orientation of CH

Without nano-SiO2 With 1.0% of nano-SiO2 With 3.0% of nano-SiO2

315 257 173

284 275 193

1.49 1.26 1.21

Table 5.25. For cementitious composites containing 3.0% nano-SiO2, the indexes of CH is decreased by a maximum of 0.28 compared with that of control cementitious composites without nano-SiO2. It means the composite matrixes are more uniform and compact. The ITZ is also improved [17, 20]. Thus, the wear resistance and chloride penetration resistance of cementitious composites are evidently improved because of the addition of nano-SiO2. Nano-SiO2 has pozzolanic activity, and it can

5 Nano-SiO2-Engineered Cementitious Composites

556

generate high-strength, high-hardness C–S–H gels through reacting with CH. It reduces the amount of CH and the crystallographic orientation, which can significantly improve the compactness of the cementitious composites. It can be observed from Fig. 5.33 and Table 5.25 that incorporating nano-SiO2 into cementitious composites can maximally decrease the CH diffraction intensity, and the CH crystal orientation of 3.0% nano-SiO2-filled cementitious composites is the lowest. In summary, the reinforcement mechanisms of nano-SiO2 to the wear resistance and chloride penetration resistance of cementitious composites are mainly attributed to their nucleation effect which can lead to the reduction of CH size and orientation, the densification of microstructure, and the improvement of ITZ. (4)

29

Si nuclear magnetic resonance of cementitious composites under heat curing

Figure 5.34 is the 29Si NMR spectra of cementitious composites under heat curing. Results and characterization parameters of deconvolution are shown in Table 5.26 and Fig. 5.35. As shown in Fig. 5.34, under the heat curing, the spectral shape for composites with different types of nano-SiO2 does not change significantly. It is still dominated by sharp Q2 peaks in the spectra, but the integral intensity of Q4 peak is significantly increased. The increased values of Q3 and Q4 that listed in Table 5.26

0 3.0%

Q2 Q0

-60

-70

-80

-90

Q2

Q4

-100

-110

-120

Chemical shift / ppm Fig. 5.34

29

Si NMR spectra of cementitious composites under heat curing

Table 5.26 Deconvolution results of cementitious composites under heat curing Cementitious composites Without nano-SiO2 With nano-SiO2

Distribution of Si Q1 (%) Q0 (%)

Q2 (%)

Q3 (%)

Q4 (%)

10.64 7.62

37.45 45.02

23.3 24.74

5.15 14.37

23.45 8.25

5.4 Durability of Nano-SiO2-Engineered Cementitious Composites

557

Fig. 5.35 Characterization parameters of 29Si NMR from deconvolution for cementitious composites with heat curing

indicate higher condensation reactions occur in the hydration process, and the layered or even spatial network of silicate tetrahedron may appear in the C–S–H gels structure. It can be seen from Fig. 5.35 that composites with different nano-SiO2 under heat curing significantly increase the values of MCL and PD, but the improvement of HD is not obvious. Among these cementitious composites, composites with nano-SiO2 has the largest increase on these parameters, which can be up to 241.9%, 199.3%, and 2.5%, respectively. The increase of curing temperature is beneficial to enhance the surface activity of nano-SiO2 and cement particles. The dehydration effect of nano-SiO2 on C–S–H gels is enhanced, which enhances the chemical bond strength of groups between Ca, O, and Si atoms in the gel, and therefore helps to increase the PD and MCL. In addition, nano-SiO2 with enhanced activity will consume more hydration product CH, which further facilitates the hydration. However, the high polymerized silicate tetrahedron structure (the layered and spatial network structure) is not fully considered in the calculation formula of parameter values, which obstructs the increase of HD value.

5.5

Summary

The fresh cementitious composites with nano-SiO2 were fabricated, and their typical flow curves were tested. Two rheological parameters, i.e., yield stress and plastic viscosity, are obtained from fitting with modified Bingham model. The rheological characteristics of fresh cementitious composites with different nano-SiO2 content levels, W/C, superplasticizer dosages, ultrasonic time, and

558

5 Nano-SiO2-Engineered Cementitious Composites

mixing rates are analyzed through comparing two rheological parameters. The cementitious composites with nano-SiO2 at levels of 0.0, 0.5, 1.0, 1.5, and 2.0% were fabricated. Compressive and flexural strengths were tested at curing age of 3 d and 28 d. Theoretical calculation of consumed CH and TG, SEM, XRD, NMR and electrical resistivity tests were carried out to explore the reinforcing mechanisms. The impact properties and durability (including wear resistance and chloride penetration resistance) of cementitious composites with different dosages (1.0 and 3.0%) of nano-SiO2 are investigated. Three mechanical parameters (dynamic compressive strength, dynamic ultimate strain, and dynamic peak strain) and two toughness indicators (impact toughness and specific energy absorption) were used as the evaluation indexes of impact properties of nano-SiO2-engineered cementitious composites. The conclusions can be summarized as below. (1) The rheological properties of fresh nano-SiO2-engineered cementitious composites coincided to the modified Bingham model, and rheological parameters can be calculated accurately by this model. Both yield stress and plastic viscosity of fresh nano-SiO2-engineered cementitious composites are increased with the increasing dosage of nano-SiO2. The rheological parameters are significantly affected by the variation of W/C and superplasticizer concentration. In addition, the ultrasonic time and stirring speeds have an influence on the rheology of fresh nano-SiO2-engineered cementitious composites. (2) The compressive strengths of nano-SiO2-engineered cementitious composites at 3 d and 28 d of curing age increase as the nano-SiO2 content increases. The compressive strengths of cementitious composites with 2.0% of nano-SiO2 at 3d and 28 d of curing age reach the maximum of 39.4 MPa and 61.4 MPa, respectively. They are increased by 48.1% and 48.7% compared with control cementitious composites, respectively. The maximum flexural strengths of nano-SiO2-engineered cementitious composites at 3 d and 28 d of curing ages are 8.3 MPa and 8.7 MPa, which are enhanced by 45.6% and 16.0% relative to control cementitious composites, respectively. Theoretically, consumed CH increases linearly with increasing nano-SiO2, which shows that nano-SiO2 has huge potential to react with CH. Actual amount of consumed CH increases and agrees with theoretical calculation when the content of nano-SiO2 is less than 1.5%. However, the mass of consumed CH is stable when the content of nano-SiO2 exceeds 1.5%. Therefore, compressive strength of cementitious composites with 2.0% of nano-SiO2 is enhanced by 11.07% compared with that of cementitious composites with 1.5% of nano-SiO2 at 28 d of curing age, which attributes to filling effect of SiO2. The incorporation of nano-SiO2 significantly improves the dynamic impact properties of cementitious composites. The increase of dynamic compressive strength, peak strain, and ultimate strain indicates that nano-SiO2 enhances the cementitious composite deformation resistance during crack formation and propagation. (3) The microstructures of cementitious composites with SiO2 are much denser than that of control cementitious composites. Nano-SiO2 can not only significantly reduce the size of CH in ITZ, but also in cement mortar matrix except for

5.5 Summary

559

ITZ. Nano-SiO2 can also decrease tendency of CH crystal in cement matrix. The change trends of electrical resistivity of cementitious composites with increasing-SiO2 content and curing age are similar to those of flexural and compressive strengths. The denser the cementitious composite matrix, the higher the electrical resistivity, flexural, and compressive strength. The flexural strengths and electrical resistivity of cementitious composites at 3 and 28 d are both close to quadratic polynomial relation. However, compressive strengths of cementitious composites at 3 d and 28 d exponentially and linearly increase with increasing electrical resistivity, respectively. (4) The inclusion of nano-SiO2 significantly enhances the wear resistance and chloride penetration resistance of cementitious composites with standard curing and heat curing. The lowest abrasion loss is obtained in cementitious composites containing 3% of nano-SiO2 with heat curing, and its relative reduction is 39.68% compared with that of control cementitious composites with heat curing. The chloride diffusion coefficient of 1.0% nano-SiO2-engineered cementitious composites with standard curing is decreased by 60% compared with that of control cementitious composites. The enhancement mechanisms of nano-SiO2 on the durability of cementitious composites are similar to that on mechanical strength, which are due to the increased microstructure compactness and the decreased CH size and CH orientation.

References 1. L.Q. Zhang, S.Q. Ding, S.W. Sun, B.G. Han, X. Yu, J.P. Ou, Chapter 2: Nano-scale behavior and nano-modification of cement and concrete materials, in Book: Advanced Research on Nanotechnology for Civil Engineering Applications, ed. by A. Khitab, W. Anwar (Publisher: IGI Global, 2016), pp. 28–79 2. X. Wang, L. Xu, J. Ouyang, L.Q. Zhang, B.G. Han, Rheology and mechanical strength of cementitious composite with nano-particles. J. Mater. Appl. 5(2), 43–48 (2016) 3. A. Peschard, A. Govin, P. Grosseau, B. Guilhot, R. Guyonnet, Effect of polysaccharides on the hydration of cement paste at early ages. Cem. Concr. Res. 34, 2153–2158 (2004) 4. R. Yu, P. Spiesz, H.J.H. Brouwers, Effect of nano-silica on the hydration and microstructure development of Ultra-High Performance Concrete (UHPC) with a low binder amount. Constr. Build. Mater. 65, 140–150 (2014) 5. H. Madani, A. Bagheri, T. Parhizkar, The pozzolanic reactivity of monodispersed nanosilica hydrosols and their influence on the hydration characteristics of Portland cement. Cem. Concr. Res. 42, 1563–1570 (2012) 6. P.K. Mehta, R.M. Monteiro, Concrete: Structure, Properties and Materials, 3 edn. (Prentice Hall, USA, 2006) 7. Q. Ye, Z. Zhang, D. Kong, R. Chen, Influence of nano-SiO2 addition on properties of hardened cement paste as compared with silica fume. Constr. Build. Mater. 21, 539–545 (2007) 8. B. Han, L. Zhang, S. Zeng, S. Dong, X. Yu, R. Yang, J. Ou, Nano-core effect in nano-engineered cementitious composites. Compos. A Appl. Sci. Manuf. 95, 100–109 (2017)

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9. S.F. Dong, B.G. Han, X. Yu, J.P. Ou, Dynamic impact behaviors and constitutive model of super-fine stainless wire reinforced reactive powder concrete. Constr. Build. Mater. 184, 602– 616 (2018) 10. T. Ji, Preliminary study on the water permeability and micro-structure of concrete incorporating nano-SiO2. Cem. Concr. Res. 35(10), 1943–1947 (2005) 11. G.H. Li, B. Gao, Effect of level SiO2 and level CaCO3 on concrete performance. J. China Railway Soc. 28(2), 131–136 (2006) 12. W.G. Li, Z.Y. Luo, C. Long, L. Huang, Experimental study on the dynamic mechanical performance of nanomodified recycled aggregate concrete. J. Hunan Univ. (Nat. Sci). 44(9), 92–99 (2017) 13. D. Zheng, Q. Li, An explanation for rate effect of concrete strength based on fracture toughness including free water viscosity. Eng. Fract. Mech. 71(16–17), 2319–2327 (2004) 14. S.A. Kaplan, Factors affecting the relationship between rate of loading and measured compressive strength of concrete. Mag. Concr. Res. 32(111), 79–88 (2015) 15. S. Jiang, D. Zhou, L.Q. Zhang, J. Ouyang, X. Yu, X. Cui, B.G. Han, Comparison of compressive strength and electrical resistivity of cementitious composites with different nano-and micro-fillers. Arch. Civil Mech. Eng. 18(1), 60–68 (2018) 16. L.Q. Zhang, N. Ma, Y.Y. Wang, B.G. Han, X. Cui, X. Yu, J.P. Ou, Study on the reinforcing mechanisms of nano silica to cement-based materials with theoretical calculation and experimental evidence. J. Compos. Mater. 50(29), 4135–4146 (2016) 17. Z. Li, B.G. Han, X. Yu, S.F. Dong, L.Q. Zhang, X.F. Dong, J.P. Ou, Effect of nano-titanium dioxide on mechanical and electrical properties and microstructure of reactive powder concrete. Mater. Res. Expr. 4(9), 095008 (2017) 18. B.G. Han, Z. Li, L.Q. Zhang, S.Z. Zeng, X. Yu, B.G. Han, J.P. Ou, Reactive powder concrete reinforced with nano SiO2-coated TiO2. Constr. Build. Mater. 148, 104–112 (2017) 19. Z. Li, S.Q. Ding, X. Yu, B.G. Han, J.P. Ou, Multifunctional cementitious composites modified with nano titanium dioxide: A review. Compos. A Appl. Sci. Manuf. 111, 115–137 (2018) 20. P. Hosseini, A. Booshehrian, A. Madari, Developing concrete recycling strategies by utilization of nano-SiO2 particles. Waste Biomass Valorizat. 2(3), 347–355 (2011)

Chapter 6

Nano-TiO2-Engineered Cementitious Composites

Abstract Nano-TiO2 particles with high strength and hardness are incorporated into cementitious composites to reinforce/modify their properties/performances. The effects of type, content, and particle size as well as surface treatment of nano-TiO2 on the mechanical properties/performances of cementitious composites are investigated. The enhancement mechanisms are analyzed through zeta potential, water vapor adsorption, contact angle, thermogravimetry, X-ray diffraction, nuclear magnetic resonance, and scanning electron microscope tests. The effects and modification mechanisms of nano-TiO2 on the rheological, durability, and electrical properties/performances of cementitious composites are also studied. Experimental results indicate that all types of nano-TiO2 present an obvious impact on the properties/performances cementitious composites because of their excellent mechanical characteristics and dispersibility in combination with nucleation and filling effects.








Keywords Nano-TiO2 Types Cementitious composites Properties/performances Mechanisms

6.1




Introduction

Nano-titanium dioxide, also known as nano-titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO2. Nano-TiO2 is in the form of powder, sol, and slurry, and its particle is spherical or ellipsoidal. There are four main types of crystal structures of nano-TiO2 including rutile phase, anatase phase, brookite, and the phase mixed with rutile phase and anatase phase (hybrid phase). Nano-TiO2 features excellent physical and chemical behaviors including high strength and hardness, high dielectric constant, semiconductor performance, shielding ultraviolet radiation and weather ability as well as antimicrobial, superhydrophobic, self-cleaning, and photocatalytic effects [1–8]. Owing to these characteristics, the incorporation of nano-TiO2 can endow cementitious composites with high-performance and multifunctional/smart properties/performances. © Springer Nature Singapore Pte Ltd. 2019 B. Han et al., Nano-Engineered Cementitious Composites, https://doi.org/10.1007/978-981-13-7078-6_6

561

562

6

Nano-TiO2-Engineered Cementitious Composites

In this chapter, cementitious composites with different types, particle sizes, and content levels of nano-TiO2 were fabricated. The rheology, mechanical properties/ performances, durability, and electrical conductivity of nano-TiO2-engineered cementitious composites were investigated. The enhancement/modification mechanisms of nano-TiO2 on cementitious composites were also analyzed by zeta potential, water vapor adsorption, contact angle, thermogravimetry (TG), X-ray diffraction (XRD), 29Si nuclear magnetic resonance (NMR), and scanning electron microscope (SEM) tests.

6.2

Rheological Properties/Performances of NanoTiO2-Engineered Cementitious Composites

The properties of nano-TiO2 used to fabricate fresh cementitious composites with nano-TiO2 are listed in Table 6.1. As listed in Table 6.1, the contact angles between nano-TiO2 particles and water are all less than 90°, indicating that nano-TiO2 is hydrophilic [9]. The transmission electron microscope (TEM) image of nano-TiO2 is shown in Fig. 6.1. The water adsorption and desorption isotherms of nano-TiO2 along with pressure under room temperature are demonstrated in Fig. 6.2. The mix proportion and main fabrication progress of fresh cementitious composites with nano-TiO2 are as shown in Tables 6.2 and 6.3, respectively. The regression flow curves for cementitious composites with different nano-TiO2 contents are shown in Fig. 6.3. Rheological properties/performances of cementitious composites with nano-TiO2 are described with modified Bingham model. The regression equation, rheological parameters of yield stress, and plastic viscosity are summarized in Table 6.4. As shown in Table 6.4, the yield stress of cementitious composites increases with the increasing nano-TiO2 content, and the plastic viscosity values of cementitious composites with nano-TiO2 show a slightly decreased tendency with increasing nano-TiO2 content. Generally, the increasing effect of nano-TiO2 on the yield stress and the plastic viscosity is similar to that of

Table 6.1 Physical properties of nano-TiO2 Average particle size (nm)

Specific surface area/(m2/g)

Density/ m3

Pure/ %

Crystal form

Contact angle/°

Zeta potential/ mV

Adsorption capacity/ (mg/g)

10

 150

4.2

99.9

18.4

−10.1

159.5

15

 150

4.2

99.9

–

−19.2

246.9

25

–

4.2

99.9

12.0

−21.9

69.9

50

 20

4.2

99.9

Anatase phase Anatase phase Rutile phase Rutile phase

–

−16.7

17.1

6.2 Rheological Properties/Performances of Nano …

563 15nm (anatase phase)

10nm (anatase phase)

50nm (rutile phase)

25nm (SiO2 @ rutile phase TiO2)

Adsorption capacity / (mg/g)

Fig. 6.1 TEM images of nano-TiO2

240 200 160 120

10nm +adsorption 10nm + desorption 15nm + adsorption 15nm + desorption 25nm + adsorption 25nm + desorption 50nm + adsorption 50nm + desorption

80 40 0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Balanced partical pressure / (P/P0)

Fig. 6.2 Water adsorption and desorption isotherms of nano-TiO2 along with pressure under room temperature

Table 6.2 Mix proportion of fresh cementitious composites with nano-TiO2 Cement type P.O 42.5R

Nano-TiO2 type

Nano-TiO2 content

SP type

Proportion of C, W and SP

10 nm 0.1, 0.5 and 1.0 Polycarboxylate C:W:SP = 1: 0.20: (anatase (wt% of C) 0.75 wt% phase) Note C represents cement, W represents water, and SP represents superplasticizer

564

6

Nano-TiO2-Engineered Cementitious Composites

Table 6.3 Main fabrication process of fresh cementitious composites with nano-TiO2 Dispersion method of nano-TiO2

Fabrication process

Shear mixing + non-covalent surface modification by SP

Feeding order

Technology Method

Time

NanoTiO2+W+SP

Shear mixing

30 s

C

Shear mixing (100 r/min)

–

–

Shear mixing (500, 1000, 2000 or 3000 r/min)

3 min

Note C represents cement, W represents water, and SP represents superplasticizer

Shear stress / Pa

500

0 0.1% 0.5% 1.0%

400 300 200 100 0

0

10

20

30

40

50

60

Shear rate / s-1

Fig. 6.3 Regression flow curves for cementitious composites with different contents of nano-TiO2 Table 6.4 Rheological parameters of cementitious composites with different contents of nano-TiO2 Cementitious composites

Yield stress/ Pa

Plastic viscosity/ (Pa s)

Regression equation

R2

6.01

1.20

s = 6.01 + 1.20 c_ +0.046 c_ 2

0.999

With 0.1% of nano-TiO2

16.01

7.47

s = 16.01 + 7.47 c_ +0.007 c_ 2

0.995

With 0.5% of nano-TiO2

28.81

7.17

s = 28.81 + 7.17 c_ +0.009 c_ 2

0.996

With 1.0% of nano-TiO2

42.93

4.68

s = 42.93 + 4.68 c_ +0.038 c_ 2

0.998

Without nano-TiO2

nano-SiO2 in Sect. 5.2.2 of Chap. 5. Nano-TiO2-filled cementitious composites have lower yield stress and plastic viscosity compared with that of nano-SiO2-filled cementitious composites at the same content. It is mainly caused by their different surface characteristics and content. Nano-SiO2 is hydrophilic and has a larger specific surface area with respect to nano-TiO2. In addition, the content of nano-TiO2 is lower than that of nano-SiO2 because the density of nano-TiO2 is higher than that of nano-SiO2 as shown in Tables 5.1 and 6.1.

6.3 Mechanical Properties/Performances of Nano …

6.3

565

Mechanical Properties/Performances of NanoTiO2-Engineered Cementitious Composites

6.3.1

Preparation of Nano-TiO2-Engineered Cementitious Composites

The mix proportion and main fabrication progress of nano-TiO2-engineered cementitious composites (i.e., nano-TiO2-filled reactive powder concrete) are shown in Tables 6.5 and 6.6, respectively.

6.3.2

Mechanical Properties/Performances of Anatase Phase Nano-TiO2-Engineered Cementitious Composites

(1) Flexural strength Figure 6.4 illustrates the flexural strengths of cementitious composites without and with two sizes of anatase phase nano-TiO2 cured at 3 d and 28 d, respectively. The relative and absolute increase values of flexural strengths are listed in Table 6.7. As demonstrated in Fig. 6.4a and Table 6.7, the flexural strengths of cementitious composites cured at 3 d are significantly enhanced by adding anatase phase nano-TiO2. It has been found that 10 nm and 15 nm anatase phase TiO2 can improve the flexural strength of cementitious composites cured at 3 d up to 52.72%/ 2.81 MPa and 65.29%/3.48 MPa, respectively. Figure 6.4b and Table 6.7 indicate that the flexural strengths of 10 nm anatase TiO2-engineered cementitious composites are higher than that of 15 nm anatase TiO2-engineered cementitious composites cured at 28 d. The maximum flexural strength of cementitious composites with 10 nm TiO2 can be improved by 47.07%/3.62 MPa. However, the maximum flexural strength of cementitious composites with 15 nm TiO2 can only be improved by 10.53%/0.81 MPa. Table 6.5 Mix proportion of nano-TiO2-engineered cementitious composites Cement type

Nano-TiO2 type

P.O 42.5R

10 15 25 50

nm nm nm nm

(anatase phase), (anatase phase), (rutile phase), (rutile phase)

NanoTiO2 content

SP type

Proportion of C, W, S, FA, SF, and SP

0.78, Polycarboxylate C:W:S:FA:SF: 2.32 SP = 1:0.38:1.38:0.25:0.31: and (0.400 wt%, 0.468 wt%, 3.88 0.567 wt%, 0.629 wt%) vol. % of C Note C represents cement, W represents water, S represents sand, FA represents fly ash, SF represents silica fume, and SP represents superplasticizer

2 min

Shear mixing (low speed)

Shear mixing (low speed)

Shear mixing (high speed)

SF

C+FA

S

2 min

Shear mixing (low speed)

W+SP +nano-TiO2

1 min 4 min

Shear mixing (low speed)

Shear mixing (high speed)

60 s

20 s

Method Vibration (60 s)

Molding Method

Time

Technology

Feeding order

Fabrication process

Heat curing (90 °C of W)

Condition Standard curing

40  40  160 (strength tests), 150  150  150 (abrasion resistance test), U100  50 (chloride diffusion coefficient test), 15  15  60 (pendulum test), U30 15 (split Hopkinson pressure bar test)

Curing Size/mm

Time

48 h

3, 28d

6

Note C represents cement, W represents water, S represents sand, FA represents fly ash, SF represents silica fume, and SP represents superplasticizer

Shear mixing + non-covalent surface modification by SP

Dispersion method of nano-TiO2

Table 6.6 Main fabrication process of nano-TiO2-engineered cementitious composites

566 Nano-TiO2-Engineered Cementitious Composites

6.3 Mechanical Properties/Performances of Nano …

(b) 0 2.32%

0.78% 3.88%

Flexural strength / MPa

Flexural strength / MPa

(a) 10

567

8 6 4 2 0

0 2.32%

10

0.78% 3.88%

8 6 4 2 0

15 nm

10 nm

12

10 nm

15 nm

Fig. 6.4 Flexural strengths of two sizes of anatase phase nano-TiO2-engineered cementitious composites: a cured at 3 d; b cured at 28 d

Table 6.7 Relative and absolute increases of flexural strengths of nano-TiO2-engineered cementitious composites Cementitious composites With 0.78% of nano-TiO2 With 2.32% of nano-TiO2 With 3.88% of nano-TiO2 With 0.78% of nano-TiO2 With 2.32% of nano-TiO2 With 3.88% of nano-TiO2

3 d of curing age Absolute Relative Increase/MPa increase/%

28 d of curing age Absolute Relative Increase/MPa increase/%

10 nm

2.7

50.66

1.33

17.30

10 nm

2.81

52.72

3.62

47.07

10 nm

1.98

37.15

1.60

20.81

15 nm

3.10

58.16

0.81

10.53

15 nm

2.85

53.47

0.51

6.63

15 nm

3.48

65.29

–0.20

–2.60

(2) Compressive strength Figure 6.5 illustrates the compressive strength of two sizes of anatase phase nano-TiO2-engineered cementitious composites at 3 d and 28 d. The relative and absolute increases of compressive strengths with anatase phase nano-TiO2 compared to control cementitious composites are listed in Tables 6.8. As demonstrated in Fig. 6.5a, there are only small increases exist in compressive strength of cementitious composites with two sizes of nano-TiO2 cured at 3 d. Figure 6.5b shows that both two sizes of nano-TiO2 can improve the compressive strength of cementitious composites cured at 28 d. Moreover, the improvement degree of 10 nm anatase phase TiO2 is greater than that of 15 nm anatase phase

6

Compressive strength / MPa

(a) 80

0 2.32%

60 40 20 0

10 nm

15 nm

0.78% 3.88%

Nano-TiO2-Engineered Cementitious Composites

Compressive strength / MPa

568

(b)

0 2.32%

120

0.78% 3.88%

100 80 60 40 20

0

10 nm

15 nm

Fig. 6.5 Compressive strengths of two sizes of anatase phase nano-TiO2-engineered cementitious composites: a cured at 3 d; b cured at 28 d Table 6.8 Relative and absolute increases of compressive strengths of nano-TiO2-engineered cementitious composites Cementitious composites With 0.78% nano-TiO2 With 2.32% nano-TiO2 With 3.88% nano-TiO2 With 0.78% nano-TiO2 With 2.32% nano-TiO2 With 3.88% nano-TiO2

3 d of curing age Absolute Relative increase/MPa increase/%

28 d of curing age Absolute Relative increase/MPa increase/%

of 10 nm

3.76

5.95

8.25

8.29

of 10 nm

0.54

0.82

18.42

18.50

of 10 nm

3.17

4.79

16.16

16.23

of 15 nm

0.44

0.66

6.38

6.41

of 15 nm

1.65

2.49

5.61

5.64

of 15 nm

−0.99

−1.50

0.61

0.61

TiO2. The compressive strength of cementitious composites with 10 nm anatase phase TiO2 cured at 28 d increases to 18.50%/18.42 MPa compared with control cementitious composites. (3) Flexural strength to compressive strength ratio The flexural strength to compressive strength ratios of cementitious composites with two sizes of anatase phase nano-TiO2 are listed in Table 6.9. As illustrated in Table 6.9, both sizes of anatase nano-TiO2 can enhance the flexural strength to compressive strength ratios of cementitious composites cured at 3 d significantly. The flexural strength to compressive strength ratios of cementitious composites with 10 nm TiO2 and 15 nm TiO2 cured at 3 d increases to 51.55% and 67.83% compared with control cementitious composites, respectively. However, 15 nm TiO2 nearly has no impact on the flexural strength to compressive strength ratios of

6.3 Mechanical Properties/Performances of Nano …

569

Table 6.9 Flexural strength to compressive strength ratios of two sizes of anatase nano-TiO2engineered cementitious composites Cementitious composites

3 d of curing age Flex./ Comp./ Flex./ MPa MPa comp.

Relative increase/ %

28 d of curing age Flex./ Comp./ Flex./ MPa MPa comp.

5.33 66.20 0.0805 – 7.69 Without nano-TiO2 69.96 0.1148 42.61 9.02 With 0.78% of 8.03 10 nm nano-TiO2 With 2.32% of 8.14 66.74 0.1220 51.55 11.31 10 nm nano-TiO2 With 3.88% of 7.31 69.37 0.1054 30.93 9.29 10 nm nano-TiO2 With 0.78% of 8.43 66.64 0.1265 57.14 8.50 15 nm nano-TiO2 With 2.32% of 8.18 67.85 0.1206 49.81 8.20 15 nm nano-TiO2 With 3.88% of 8.81 65.21 0.1351 67.83 7.49 15 nm nano-TiO2 Note Flex. represents flexural, and comp. represents compressive

Relative increase/ %

99.55

0.0772

–

107.80

0.0837

8.42

117.97

0.0959

24.22

115.71

0.0803

4.02

105.93

0.0802

3.89

105.16

0.0780

1.04

100.16

0.0748

−3.11

cementitious composites at 28 d of curing age. For the cementitious composites with 10 nm TiO2 cured at 28 d, the flexural strength to compressive strength ratios can be obviously increased. It can be increased by 24.22% when the dosage of 10 nm TiO2 is 2.32%. The flexural strength to compressive strength ratios can be used to present the brittleness and fracture toughness of cementitious composites; i.e., they are inversely proportional to the brittleness and proportional to fracture toughness of cementitious composites [10]. Therefore, both sizes of anatase phase nano-TiO2 can enhance the fracture toughness of cementitious composites cured at 3 d. But at the curing age of 28 d, 10 nm TiO2 can obviously enhance the fracture toughness of cementitious composites, while 15 nm TiO2 has nearly no impact on the fracture toughness of cementitious composites. (4) Reinforcement mechanisms The 29Si NMR spectra of cementitious composites with and without anatase phase nano-TiO2 are shown in Fig. 6.6. The results of deconvolution of cementitious composites without and with anatase phase nano-TiO2 are listed in Table 6.10.

570

Nano-TiO2-Engineered Cementitious Composites

6

With 2.32% Q0 15nm TiO 2

Q1

Q2 Q4

Q3

With 2.32% 10nm TiO 2

Without nano TiO 2

-60

-70

-80

-90

-100

-110

-120

Chemical Shift (ppm)

Fig. 6.6

29

Si NMR spectra of cementitious composites without and with anatase nano-TiO2

Table 6.10 Results of deconvolution for cementitious composites without and with anatase nano-TiO2 Cementitious composites

Q0 (%)

Q1 (%)

Q2 (%)

Q3 (%)

Q4 (%)

Without nano-TiO2 With 2.32% of 10 nm nano-TiO2 With 2.32% of 15 nm nano-TiO2

18.40 16.45 11.72

13.43 14.23 12.31

23.99 29.54 23.88

12.54 12.28 16.91

31.62 27.56 35.71

1.8 1.5 1.2

8.62%

With 10nm TiO2 With -out nano TiO2

With 15nm TiO2

PD

10.41% 5.57%

With 10nm TiO2 With -out nano TiO2

With 15nm TiO2

MCL

6.5 6.0 5.5 5.0 4.5

Numerical value

16.24%

2.1

Numerical value

Fig. 6.7 Characterization parameters of 29Si NMR from deconvolution for cementitious composites

4.0 3.5

As illustrated in Fig. 6.7, the polymerization degree (PD) of [SiO4]4− in calcium silicate hydrate (i.e., C–S–H) of cementitious composites with 10 nm TiO2 and 15 nm TiO2 can be increased by 16.24% and 8.62% compared to control cementitious composites, respectively. The mean chain length (MCL) can be increased by 10.41% and 5.57%, respectively. The reason for the enhancements in PD and MCL caused by adding nano-TiO2 is mainly attributed to the high specific surface area of nano-TiO2, which can promote nucleation effect and adsorb hydration products [11]. However, the number of nucleation points will affect the nucleation effect of nano-TiO2 to a large extent [12, 13] and further affect the improvement degree on

6.3 Mechanical Properties/Performances of Nano …

571

Table 6.11 Numbers of two sizes of nano-TiO2 in 1 cm3 of cementitious composites Types of nano-TiO2

Diameter/ nm

Volume of single nano-TiO2/nm3

Concentration of nano-TiO2/%

Numbers of nano-TiO2 in 1 cm3 of composites

10 nm TiO2 15 nm TiO2

10

4.19  103

2.32

4.43  1013

15

1.41  104

2.32

1.31  1013

the mechanical properties of cementitious composites. The numbers of anatase phase nano-TiO2 in 1 cm3 cementitious composites can be calculated by assuming that anatase phase nano-TiO2 is existed in single particle and in ideal geometrical shape. As listed in Table 6.11, when the content of nano-TiO2 is 2.32%, the numbers of 10 nm TiO2 and 15 nm TiO2 existed in the 1 cm3 cementitious composites are 4.43  1013 and 1.31  1013, respectively. The particle numbers of 10 nm TiO2 outnumber that of 15 nm TiO2 by 3.12  1013. According to Ref. [14], I ¼ A
NT
expðDG =KT Þ

ð6:1Þ

where I is nucleation rate of nano-TiO2, A is a constant, NT is the number of nano-TiO2, DG is the critical free energy, T is the absolute temperature, and K is the Boltzmann’s constant. It can be seen from Eq. (6.1) that the number of nucleating points is direct proportion to the number of particles. Thus, 10 nm TiO2 can produce more nucleation points than 15 nm TiO2 in cementitious composites when they are at the same content. Therefore, 10 nm TiO2 can be assembled to a larger number of nucleation points than 15 nm TiO2, which forms larger binding force between nano-TiO2 and cement hydration products. Zeta potential can be used to characterize the attractive or repulsive force between particles. Its value is in connection with the stability of the colloidal dispersion. Therefore, the absolute value of zeta potential is in inverse proportion to the size of dispersed particle and in direct proportion to the stability degree of system [14]. The zeta potential of 15 nm TiO2 is greater than that of 10 nm TiO2 as listed in Table 6.1, which means that 15 nm TiO2 is more stable and needs more energy to be nucleated. Additionally, it can be explained through the free energy of nucleation [15]. DG ¼ V
DGv þ S
c

ð6:2Þ

where DG denotes the change in free energy, V denotes the volume of nano-TiO2, S denotes the surface area of nano-TiO2, T denotes interface free energy of nano-TiO2, and DGv denotes the unit volume energy of nano-TiO2, which is an invariant because 10 nm TiO2 and 15 nm TiO2 are of same substances. Equation (6.2) can be written as:

572

6

Nano-TiO2-Engineered Cementitious Composites



 DG ¼ 4=3
pr 3
ðDGv Þ þ 4pr 2
c

ð6:3Þ

It can be seen from Eq. (6.3) that the free energy increases with increasing diameter of nano-TiO2 [13]; i.e., the probability that 15 nm TiO2 is assembled as a nucleus is lower than that to assemble 10 nm TiO2 as a nucleus. This also explains the reason why the nucleation effect caused by 10 nm TiO2 is greater than that caused by 15 nm TiO2 in another way. Figure 6.8 shows the XRD curves of cementitious composites with two sizes of anatase phase nano-TiO2 at 28 d of curing age. The corresponding results of diffraction intensities and orientations of calcium hydroxide (i.e., CH) are listed in Table 6.12. It can be found that both two sizes of nano-TiO2 (especially for 10 nm

1 C3S 2 C2S 3 Zincite 4 CH 5 SiO2 6 Tobermorite With 3.88% of 15nm TiO 2 With 2.32% of 15nm TiO 2 With 0.78% of 15nm TiO 2 With 3.88% of 10nm TiO 2 With 2.32% of 10nm TiO 2 With 0.78% of 10nm TiO 2 Without nano TiO 2 5

10

15

20

25

30

35

40

45

50

55

60

2θ / ° Fig. 6.8 XRD curves of cementitious composites without and with two sizes of anatase phase nano-TiO2 cured at 28 d (Note C3S represents 3CaO
SiO2.)

Table 6.12 Diffraction intensities and orientations of CH in cementitious composites cured at 28 d Cementitious composites

28d of curing age Ið101Þ Ið001Þ

CH orientation

Without nano-TiO2 With 0.78% of 10 nm With 2.32% of 10 nm With 3.88% of 10 nm With 0.78% of 15 nm With 2.32% of 15 nm With 3.88% of 15 nm

548 430 326 430 450 524 564

1.84 1.56 1.29 1.34 1.70 1.72 1.72

nano-TiO2 nano-TiO2 nano-TiO2 nano-TiO2 nano-TiO2 nano-TiO2

298 275 253 320 265 304 328

6.3 Mechanical Properties/Performances of Nano …

573

TiO2) decrease the orientation of CH in cementitious composites, and the decreased value can be up to 29.89% and 7.61% compared to control composites, respectively. These results reveal that both of two sizes of anatase phase nano-TiO2 can decrease the orientation of CH crystals. Furthermore, the reinforcing effect of 10 nm TiO2 is better than that of 15 nm TiO2. Such behavior could be associated with the nucleation effect of nano-TiO2, which can make CH crystallize on the surface of nano-TiO2 and make the large size CH crystals with weak orientation become smaller size CH crystals with strong orientation [16]. As a result, the orientation of CH in nano-TiO2-engineered cementitious composites is smaller than that in control cementitious composites. Moreover, the number of nucleation points of 10 nm TiO2 is more than that of 15 nm TiO2, which can decrease the growth space of CH and make the orientation of CH change greater, thus generating a positive effect on the mechanical strength (as shown in Fig. 6.9).

Fig. 6.9 Schematic diagram of nucleation effect

574

6

(a)

Nano-TiO2-Engineered Cementitious Composites

(b)

Cracks

(c)

Cracks

Cracks

(d)

(f)

(e)

CH crystals CH crystals

CH crystals

Fig. 6.10 SEM images of cementitious composites at curing age of 28 d a–c 1200, d–f 10000: a cementitious composites without nano-TiO2; b 15 nm TiO2-engineered cementitious composites; c 10 nm TiO2-engineered cementitious composites; d cementitious composites without nano-TiO2; e 15 nm TiO2-engineered cementitious composites; f 10 nm TiO2-engineered cementitious composites

Figure 6.10a–c illustrates the microstructures of cementitious composites at curing age of 28 d. As shown in Fig. 6.10a–c, both two sizes of anatase nano-TiO2 can reduce the micro-cracks. This can be attributed to that both two sizes of nano-TiO2 have nano-core effect which can restrain the extension of cracks by making the cracks deviate the original expansion route or go through the crystal. Moreover, they have nucleation effect which can act as a nucleus to tightly bond with cement hydrate and promote cement hydration [17, 18]. The mechanical properties/performances of cementitious composites can be therefore improved. In addition, 10 nm TiO2 makes more contribution to cementitious composites because 10 nm TiO2 can compact the microstructure denser. This may be due to that 10 nm TiO2 can produce more nucleation points than 15 nm TiO2 in cementitious composites at the same nano-TiO2 content, thus playing a greater role in filling effect. Figure 6.10d–f shows that the crystals of CH in nano-TiO2-engineered cementitious composites are not only smaller but also less uniform in orientation than that in control cementitious composites. This is beneficial for the development of strength. The CH crystals size decreases because of the addition of two sizes of anatase phase nano-TiO2 [18, 19]. As a result, the size of CH in the nano-TiO2engineered cementitious composites is smaller than that in the control cementitious composites. Additionally, the number of nucleation points of 10 nm TiO2 is more than that of 15 nm TiO2. Hence, the separation between each two nucleation points in 10 nm TiO2-engineered cementitious composites is smaller than that in 15 nm

6.3 Mechanical Properties/Performances of Nano …

575

TiO2-engineered cementitious composites, so does the growing space for CH. Therefore, it can be found that the size of the CH crystals in 10 nm TiO2-engineered cementitious composites is smaller than that in 15 nm TiO2-engineered cementitious composites. The mechanical property/performance of nano-TiO2-engineered cementitious composites is closely related to the system compactness. According to composite theory, the particle accumulation per unit volume consists of n kinds of particle whose equivalent diameters are Ri , which can be ranged as R1 [ R2 [ n [ Rn1 [ Rn . The deformations of particles can be ignored. The Pthe n volume content is defined as Vi. Obviously, V i¼1 i ¼ q, where q denotes the compactness of particle accumulation. Assume that the rate of volume fraction of P the i kind of particle is Xi , Xi ¼ Vqi , and ni¼1 Xi ¼ 1. Based on particle accumui lation calculation model (the particle diameter ratios do not tend to 0) [20], there are relaxation effect function and wall effect function. When the particle diameters are homogeneous, there is the relaxation effect exists in the system. The compactness of particle accumulation can be expressed as: q1 ¼ a1 þ f ð1; 2ÞV2

ð6:4Þ

where a1 denotes the compactness in unit volume of large particles. When the large particles are packed closely, adding small particles into system can cause wall effect. The compactness of particle accumulation can be expressed as: q2 ¼ a2 þ ð1a2 Þgð2; 1ÞV1

ð6:5Þ

where a2 denotes the compactness in P unit volume of small particles. According to Eqs. (6.4), (6.5), and ni¼1 Vi ¼ q, the constrained relationship can be derived as follow: 

V1  a1  V2 ½1  f ð1; 2Þ V2  a2  V ½1  ð1  a2 Þgð2; 1Þ

ð6:6Þ

… 8 < V1  a1  V2 ½1  f ð1; 2Þ  V3 ½1  f ð1; 3Þ V  a2  V ½1  ð1  a2 Þgð2; 1Þ  V3 ½1  f ð2; 3Þ : 2 Vi  ai  V1 ½1  ð1  ai Þgði; 1Þ 


 Vi1 ½1  ð1  ai Þgði; i  1Þ  Vi þ 1 ½1  f ði; i þ 1Þ 


 Vn ½1  f ði; nÞ

ð6:7Þ Referred to the calculation method given in Ref. [21], the system compactness of particle accumulation can be calculated as follow: ai

q¼ 1  ð 1  ai Þ

iP 1 j¼1

gðj; iÞXj 

n P j¼i þ 1




f i; jÞXj

ð6:8Þ

576

6

Nano-TiO2-Engineered Cementitious Composites

It is assumed that the initial porosity of the uniform diameter particles is P0 (0.36–0.50 as usual). The value of P0 can be determined as 0.36 [22], and the functions of f , g can be expressed as follows: ( f ði; jÞ ¼

0:49qðrÞ ð1 þ 0:36qðrÞÞð0:36 þ r2 Þ ;

r ¼ dj =di  0:741 r ¼ dj =di [ 0:741

0; (

gði; jÞ ¼

1:36qðrÞ ð1 þ 0:36qðrÞÞð1r2 Þ ;

0;

ð6:9Þ

r ¼ dj =di  0:741 r ¼ dj =di [ 0:741

ð6:10Þ

qðr Þ ¼ 1  2:35r þ 1:35r 2

ð6:11Þ

The main distribution of the particle size and the equivalent grain of raw materials are listed in Table 6.13. Besides, it is reasonable to assume that the fly ash and silica fume particles are spherical, and the cement and sand particles are approximately spherical. Thereby, the compactness of nano-TiO2-engineered cementitious composites with different types and contents of nano-TiO2 can be calculated. Table 6.14 shows that the compactness of nano-TiO2-engineered cementitious composites increases with increasing content of nano-TiO2. The change trends of flexural and compressive strengths are similar to those of system compactness. This may be due to the improvement of particle gradation, increasing the compactness of Table 6.13 Particle size distribution of raw materials Materials

Sand

Cement

Fly ash

Silica fume

Nano-TiO2

Diameter/µm

830–380

380–212

212–120

60–40

20–10

25–5

0.15–0.05

0.015–0.005

0.02–0.01

Equivalent grain/µm

605

296

166

50

15

15

0.1

0.01

0.015

Volume fraction/%

31.4

32.5

31.6

42

47

89.5

89

95

95

Table 6.14 Compactness and porosity of cementitious composites with different types and contents of nano-TiO2 Cementitious composites

Compactness

Increase rate of compactness/ %

Porosity/ %

Without nano-TiO2 With 0.78% of 10 nm nano-TiO2 With 2.32% of 10 nm nano-TiO2 With 3.88% of 10 nm nano-TiO2 With 0.78% of 15 nm nano-TiO2 With 2.32% of 15 nm nano-TiO2 With 3.88% of 15 nm nano-TiO2

0.9096 0.9132 0.9205 0.9304 0.9132 0.9203 0.9275

0 0.40 1.20 2.29 0.40 1.18 1.97

9.04 8.68 7.95 6.96 8.68 7.97 7.25

6.3 Mechanical Properties/Performances of Nano …

577

the system, reducing the micro-cracks, increasing the fracture energy between the particles, thereby improving the flexural and compressive properties of cementitious composites. In addition, the results show that the particle size of the system is reasonable and the uniformity is improved. The improvement of flexural strength and compressive strength is related to the reasonable degree of the grain gradation. The compactness model demonstrates that nano-TiO2 can improve the compactness and reduce the porosity of cementitious composites, which is in accordance with the SEM observation.

6.3.3

Mechanical Properties/Performances of Rutile Phase Nano-TiO2-Engineered Cementitious Composites

(1) Flexural strength Figure 6.11 illustrates the flexural strengths of cementitious composites with rutile phase nano-TiO2 at 3 d and 28 d of curing age. The relative and absolute increases of flexural strengths of cementitious composites with rutile phase nano-TiO2 are listed in Table 6.15. As indicated in Fig. 6.11, the presence of rutile phase nano-TiO2 has an obvious impact on the flexural strength of cementitious composites no matter at 3 d or 28 d of curing age. The flexural strength of composites with rutile phase nano-TiO2 at 3 d and 28 d of curing age increases to 51.22%/2.73 MPa and 27.70%/2.13 MPa compared with control cementitious composites, respectively. (2) Compressive strength Figure 6.12 demonstrates the compressive strength of cementitious composites with rutile phase nano-TiO2 at 3 d and 28 d of curing age. The relative and absolute increases in compressive strengths of cementitious composites with rutile phase nano-TiO2 in comparison with control cementitious composites at 3 d and 28 d of curing age are listed in Tables 6.16. It is illustrated in Fig. 6.12 and Table 6.16 that there are no increases in compressive strengths of the composites with rutile phase nano-TiO2 at 3 d of curing age compared with control composites. In addition, there 12

Flexural strength / MPa

Fig. 6.11 Flexural strengths of cementitious composites with rutile phase nano-TiO2 at 3 d and 28 d of curing age

10

0 2.32%

0.78% 3.88%

8 6 4 2 0

3d

28 d

578

6

Nano-TiO2-Engineered Cementitious Composites

Table 6.15 Relative increase and absolute increase of flexural strengths of cementitious composites with rutile phase nano-TiO2 Cementitious composites

3 d of curing age Absolute increase/MPa

Relative increase/%

28 d of curing age Absolute Relative increase/MPa increase/%

With 0.78% of nano-TiO2 With 2.32% of nano-TiO2 With 3.88% of nano-TiO2

2.32

43.53

0.6

7.80

2.73

51.22

1.52

19.77

2.55

47.84

2.13

27.70

120

Compressive strength / MPa

Fig. 6.12 Compressive strengths of cementitious composites with rutile phase nano-TiO2 at 3 d and 28 d of curing age

0 2.32%

0.78% 3.88%

100 80 60 40 20 0

3d

28 d

are significant increases appear in the composites with rutile phase nano-TiO2 compared with control composites in compressive strengths at 28 d of curing age. When the content of rutile phase nano-TiO2 is 3.88%, the increase in compressive strengths of the composites at 28 d of curing age is 10.78%/10.73 MPa. (3) Flexural strength to compressive strength ratio The flexural strength to compressive strength ratios of cementitious composites with rutile phase nano-TiO2 are listed in Table 6.17. As illustrated in Table 6.17, rutile phase nano-TiO2 can improve the flexural strength to compressive strength ratios of cementitious composites significantly. The flexural strength to compressive strength ratios of cementitious composites with rutile phase nano-TiO2 at 3 d and 28 d of curing age can increase 64.87% and 15.34% compared with control cementitious composites, respectively. Therefore, rutile phase nano-TiO2 can improve the fracture toughness of cementitious composites. (4) Reinforcement mechanisms 1.

29

Si Nuclear magnetic resonance analysis

The 29Si NMR spectra of cementitious composites with and without rutile phase nano-TiO2 are shown in Fig. 6.13. The average degree of C–S–H connectivity nc,

6.3 Mechanical Properties/Performances of Nano …

579

Table 6.16 Relative increase and absolute increase of compressive strengths of cementitious composites with rutile phase nano-TiO2 Cementitious composites

3 d of curing age Absolute increase/MPa

Relative increase/%

28 d of curing age Absolute Relative increase/MPa increase/%

With 0.78% of nano-TiO2 With 2.32% of nano-TiO2 With 3.88% of nano-TiO2

−2.87

–4.34

9.26

9.30

−5.47

–8.26

9.55

9.59

−5.44

–8.22

10.73

10.78

Table 6.17 Flexural strength to compressive strength ratios of cementitious composites with rutile phase nano-TiO2 Cementitious composites

3 d of curing age Flex./ MPa

Comp./ MPa

Flex./ comp.

Relative increase/%

28 d of curing age Flex./ MPa

Comp./ MPa

Flex./ comp.

Relative increase/%

Without nano-TiO2

5.33

66.20

0.0805

–

7.69

99.55

0.0772

–

With 0.78% of nano-TiO2

7.65

63.33

0.1208

50.06

8.29

108.81

0.0762

−1.31

With 2.32% of nano-TiO2

8.06

60.73

0.1327

64.87

9.21

109.10

0.0844

9.35

With 3.88% of nano-TiO2

7.88

60.76

0.1297

61.11

9.82

110.28

0.0890

15.34

Note flex. represents flexural, and comp. represents compressive

Fig. 6.13 29Si NMR spectrum of cementitious composites with and without rutile phase nano-TiO2

Q2 0 With 2.32% Q

1

Q

nano TiO 2

Q4

Q3

Without nano TiO 2

-60

-70

-80

-90

-100

-110

-120

Chemical Shift (ppm)

PD, and MCL is presented in Table 6.18. It can be indicated in Table 6.18 that there is almost no effect of rutile phase nano-TiO2 on the average degree of C–S–H connectivity. However, adding rutile phase nano-TiO2 can enhance PD and increase MCL of C–S–H by 49.37%. The reason for the enhancement in PD caused by rutile

580

6

Table 6.18 Deconvolution results of without rutile phase nano-TiO2

Nano-TiO2-Engineered Cementitious Composites

29

Si NMR spectra of cementitious composites with and

Cementitious composites

Q0 (%)

Q1 (%)

Q2 (%)

Q3 (%)

Q4 (%)

nc

PD/ %

MCL

Without nano-TiO2 With 2.32% of nano-TiO2

18.40

13.43

23.99

12.54

31.62

1.98

1.786

5.57

14.79

13.25

41.88

12.69

17.39

1.99

3.161

8.32

Fig. 6.14 EDS analysis results of rutile phase nano-TiO2-engineered cementitious composites (50000)

phase nano-TiO2 is mainly because that rutile phase nano-TiO2 has a higher specific surface area which can promote nucleation effect and adsorb hydration products. 2. Scanning electron microscope observation Figure 6.14 presents the SEM images of rutile phase nano-TiO2-engineered cementitious composites. It can be seen from results of energy dispersive spectrometer (i.e., EDS) analysis that the chemical composition of C–S–H in rutile phase nano-TiO2-engineered cementitious composites featured a CaO2/SiO2 of 0.72:1. In general, the C–S–H has a mean ratio of CaO2/SiO2 = 1.5 [23]; it means that nano-TiO2 can modify the property of C–S–H by changing CaO2/SiO2, thereby enhancing the mechanical property of cementitious composites. In addition, Ti element can be observed in the EDS image in Fig. 6.14. This may be due to the fact that rutile phase nano-TiO2 can act as the nucleus of C–S–H. The SEM morphology of the fracture surfaces of cementitious composites without and with rutile phase nano-TiO2 is given in Fig. 6.16. As shown in Fig. 6.15a, the fracture surface morphology of control cementitious composites is quite loose and has some deep cracks. Figure 6.15b shows that rutile phase nano-TiO2 can improve the microstructure of cementitious composites by reducing and refining the cracks. However, as shown in Fig. 6.15c and d, the aggregations of

6.3 Mechanical Properties/Performances of Nano …

581

Fig. 6.15 SEM images of a control cementitious composites (1200); b rutile phase nano-TiO2engineered cementitious composites (1200); c, d the aggregations of rutile phase nano-TiO2 in cementitious composites (10000 and 50000)

rutile phase nano-TiO2 inside composites become obvious when the content of nano-TiO2 surpasses 2.32%. The agglomerations are like the defects inside cementitious composites, thus weakening the reinforcing effect of rutile phase nano-TiO2 on cementitious composites. This is an important reason for why the reinforcement effect of 3.88% of rutile phase nano-TiO2 is lower than that of 2.32% of rutile phase nano-TiO2.

6.3.4

Mechanical Properties/Performances of Nano-SiO2@TiO2-Engineered Cementitious Composites

(1) Flexural strength The flexural strengths of nano-SiO2@TiO2-engineered cementitious composites at curing age of 3 d and 28 d are demonstrated in Fig. 6.16. The relative increase rates in

582

6

83.80%

10

(b)18 73.73%

55.91%

8 6 4 2 0

0

0.78

2.32

3.88

Content of nano-SiO 2@TiO2 / %

Flexural strength / MPa

Flexural strength / MPa

(a)12

Nano-TiO2-Engineered Cementitious Composites

74.90%

15

87.00%

43.43%

12 9 6 3 0

0

0.78

2.32

3.88

Content of nano-SiO 2@TiO2 / %

Fig. 6.16 Flexural strengths of nano-SiO2@TiO2-engineered cementitious composites: a at 3 d of curing age; b at 28 d of curing age

flexural strength of nano-SiO2@TiO2-engineered cementitious composites with respect to control cementitious composites at curing age of 3 d and 28 d have been marked in Fig. 6.16. It can be indicated from Fig. 6.16 that the flexural strength of nano-SiO2@TiO2-engineered cementitious composites at 3d of curing age increases firstly and then decreases slightly as the content of nano-SiO2@TiO2 increases. When the content of nano-SiO2@TiO2 is 2.32%, flexural strength of nano-SiO2@TiO2engineered cementitious composites reaches its maximum 9.77 MPa and increases 83.3%/4.44 MPa with respect to that of cementitious composites without nano-SiO2@TiO2. When the nano-SiO2@TiO2 content is 3.88%, the flexural strength of nano-SiO2@TiO2-engineered cementitious composites is still much higher than that of control cementitious composites, even though it was a little bit lower than that with 2.32% of nano-SiO2@TiO2. The increase in flexural strength of cementitious composites with 3.88% of nano-SiO2@TiO2 at 3 d of curing age is less than that of cementitious composites with 2.32% of nano-SiO2@TiO2. It may be attributed to a reduction in hydration speed due to water absorption. The flexural strength of nano-SiO2@TiO2-engineered cementitious composites at 28 d of curing age increases with increasing content of nano-SiO2@TiO2. The flexural strength of cementitious composites with optimal content level of nano-SiO2@TiO2 (3.88%) is 14.38 MPa and improves 87%/6.69 MPa relatively to that of control cementitious composites at the curing age of 28 d. (2) Compressive strength The compressive strengths of nano-SiO2@TiO2-engineered cementitious composites at 3 d and 28 d of curing age are demonstrated in Fig. 6.17. The relative increase rates in compressive strength of nano-SiO2@TiO2-engineered cementitious composites with respect to control cementitious composites at curing age of 3 d and 28 d have been marked in Fig. 6.17. As indicated in Fig. 6.17, the presence of nano-SiO2@TiO2 has no obvious effect on the compressive strength of the composites at the curing age of 3d, but it has obvious impact on that at the curing age of

80

(a)

5.44% 1.78% 4.09%

60 40 20 0

0

0.78

2.32

3.88

Content of nano-SiO2@TiO2/ %

Compressivestrength / MPa

Compressivestrength / MPa

6.3 Mechanical Properties/Performances of Nano …

583

140

(b)

120

5.97% 12.26% 10.32%

100 80 60 40 20 0

0

0.78

3.88

2.32

Content of nano-SiO2@TiO2/ %

Fig. 6.17 Compressive strengths of nano-SiO2@TiO2-engineered cementitious composites: a at 3 d of curing age; b at 28 d of curing age

28d. For the nano-SiO2@TiO2-engineered cementitious composites at 28 d of curing age, the compressive strength reached its maximum 111.75 MPa and increased to 12.26%/12.2 MPa compared with the control cementitious composites. (3) Flexural strength to compressive strength ratio The flexural strength to compressive strength ratios of cementitious composites with nano-SiO2@TiO2 are listed in Table 6.19. As illustrated in Table 6.19, nano-SiO2@TiO2 can improve the flexural strength to compressive strength ratios of cementitious composites significantly. The flexural strength to compressive strength ratios of cementitious composites with nano-SiO2@TiO2 at 3 d and 28 d of curing age can increase 79.01% and 70.13% compared with control cementitious composites, respectively. Therefore, nano-SiO2@TiO2 can improve the fracture toughness of cementitious composites significantly. Table 6.19 Flexural strength to compressive strength ratios of cementitious composites with nano-SiO2@TiO2 Cementitious composites

3 d of curing age Flex./ Comp./ Flex./ MPa MPa comp.

Relative increase/ %

28 d of curing age Flex./ Comp./ Flex./ MPa MPa comp.

5.33 66.20 0.081 – 7.69 Without nano-SiO2@TiO2 8.31 69.80 0.119 46.91 11.03 With 0.78% of nano-SiO2@TiO2 9.77 67.38 0.145 79.01 13.45 With 2.32% of nano-SiO2@TiO2 With 3.88% of 9.26 68.91 0.134 65.43 14.38 nano-SiO2@TiO2 Note Flex. represents flexural and comp. represents compressive

Relative increase/ %

99.55

0.077

–

105.49

0.105

36.36

111.75

0.120

55.84

109.82

0.131

70.13

584

6

Nano-TiO2-Engineered Cementitious Composites

(4) Impact properties/performances 1. Compression impact properties/performances under split Hopkinson pressure bar test (i) Dynamic compressive strength Figure 6.18 shows the dynamic compressive strength of cementitious composites without and with nano-SiO2@TiO2. The relationship between the strength and the strain rate is demonstrated in Fig. 6.19. As seen from Fig. 6.18, the dynamic compressive strength of cementitious composites increases with increasing the strain rates. Compared with the low content (0.78%) of nano-SiO2@TiO2, the 2.32% nano-SiO2@TiO2 has an obvious reinforcing effect on the dynamic compressive strength, whose maximum increase value can reach 29.59%. (ii) Dynamic compressive deformation Figure 6.20a and b shows the dynamic peak strain and dynamic ultimate strain of cementitious composites with different contents of nano-SiO2@TiO2 compared to control composites. As shown in Fig. 6.20a, the incorporated nano-SiO2@TiO2 increases the cementitious composites dynamic peak strain, but the enhancement first increases and then decreases as the strain rate increases. As seen from Fig. 6.20b, whether or not incorporating nano-SiO2@TiO2, the dynamic ultimate strain increases as the strain rate increases. This corresponds to the strain rate effect of cementitious composites. When the strain rate is low (