Concrete Structures: New Trends and Old Pathologies (Building Pathology and Rehabilitation, 27) 3031388402, 9783031388408

Table of contents :
Preface
Contents
Application of Hazardous Waste Management Model for Sustainable Cities
1 Introduction
2 Project Profile
3 The Model
4 Storage Design
5 Design of Truss
6 The Model: Benefits
7 Conclusions
References
Moisture Transport Phenomenon in Block Masonry Ceramics with Interfaces of Cementitious Mortar
1 Introduction
1.1 Research Objectives
2 Literature Review
2.1 Moisture in Porous Materials
2.2 Interface—Hygric Resistance
3 Experimental Program
3.1 Preparation of the Test Bodies
3.2 Capillary Absorption
3.3 Physical and Hygroscopic Characteristics of the Materials
3.4 Hygric Resistance Measurement
4 Results and Discussions
4.1 Material Results
4.2 Hydraulic Interface
4.3 Perfect Contact
4.4 Comparison Between Hydraulic Interface and Perfect Contact
4.5 Resistance Values
5 Conclusions
References
Electrical Model of a Bulk Concrete and Analysis of Its Frequency-Dependent Electrical Resistivity
1 Introduction
2 Resistor–Capacitor Circuit
3 Electrical Model of a Two-Plate Configuration
3.1 DC Analysis
3.2 AC Analysis
4 Discussion
5 Conclusion
References
Studies on Rheological Properties of High-Flowable Concrete
1 Introduction
2 Rheology of Fluids
3 Rheology of Fresh Concrete
4 Measurement of Rheological Properties
4.1 Shear Box Test
5 Case Study on Shear Box Test Method
5.1 Materials
5.2 Mix Design
5.3 Test Methodology
6 Experimental Results and Discussion
7 Concluding Remarks
References
Sewage Sludge: Some Applications in Civil Engineering
1 Introduction
2 Literature Review
2.1 Sewage Water Classification
2.2 Sewage Systems
2.3 Evolution of the Sewage Systems
2.4 Sewage Sludge
2.5 Current Legislation
2.6 Treatment Process in the STP Mangueira and STP Curado
2.7 Applications of Sewage Sludge in the Civil Construction Industry
3 Materials and Methods
3.1 Experimental Program: Soil, Sludge and Soil-Sludge Mixture
3.2 Preparation of the Samples of Soil and Soil-Sludge Mixture
3.3 Methods
3.4 Use of Sewage Sludge as Fine Aggregate in Concrete
4 Results and Discussions
4.1 Physical Characterization of Soil, Sludge and Soil-Sludge Mixtures
4.2 Chemical Mobility Test of Soil and Soil-Sludge Mixtures—STP of Mangueira
4.3 Microstructural Analysis of Soil and Soil-Sludge Mixture—STP of Mangueira
4.4 Hydraulic Conductivity
4.5 Chemical Characterization of the Soil, Sludge and Soil-Sludge Mixture
4.6 Compressibility Analysis
5 Application of Sludge for the Substitution of Fine Aggregates for Concrete
5.1 Physical Characterization of Fine and Coarse Aggregate
5.2 Ultrasonic Velocity
5.3 Sclerometer Index
5.4 Compressive Strength
5.5 Absorption by Capillarity
6 Conclusions
References

Citation preview

Building Pathology and Rehabilitation

João M. P. Q. Delgado   Editor

Concrete Structures: New Trends and Old Pathologies

Building Pathology and Rehabilitation Volume 27

Series Editors Vasco Peixoto de Freitas, University of Porto, Porto, Portugal Aníbal Costa, Aveiro, Portugal João M. P. Q. Delgado , University of Porto, Porto, Portugal

This book series addresses the areas of building pathologies and rehabilitation of the constructed heritage, strategies, diagnostic and design methodologies, the appropriately of existing regulations for rehabilitation, energy efficiency, adaptive rehabilitation, rehabilitation technologies and analysis of case studies. The topics of Building Pathology and Rehabilitation include but are not limited to - hygrothermal behaviour - structural pathologies (e.g. stone, wood, mortar, concrete, etc…) - diagnostic techniques - costs of pathology - responsibilities, guarantees and insurance analysis of case studies - construction code - rehabilitation technologies - architecture and rehabilitation project - materials and their suitability - building performance simulation and energy efficiency - durability and service life.

João M. P. Q. Delgado Editor

Concrete Structures: New Trends and Old Pathologies

Editor João M. P. Q. Delgado CONSTRUCT-LFC, Department of Civil Engineering, Faculty of Engineering University of Porto Porto, Portugal

ISSN 2194-9832 ISSN 2194-9840 (electronic) Building Pathology and Rehabilitation ISBN 978-3-031-38840-8 ISBN 978-3-031-38841-5 (eBook) https://doi.org/10.1007/978-3-031-38841-5 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 This work is subject to copyright. All rights are solely and exclusively licensed 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, expressed 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 Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland Paper in this product is recyclable.

Preface

Building rehabilitation is a strategic area that is concerned not only with historic buildings but also with other buildings that have been in use for some time and need to be adapted to the demands of the present. The success of a good rehabilitation project depends on the specific plans for it, so the correct evaluation of the concrete structures plays a fundamental role in an adequate building rehabilitation. Concrete is a common building material that is used prolifically in the construction of many buildings and infrastructure projects. The strength, durability, and flexibility of this material have added to its popularity. The main purpose of this book, Concrete Structures: New Trends and Old Pathologies, is to provide a collection of recent research works related to new trends and pathologies associated with concrete structures, in order to contribute to the systematization and dissemination of knowledge related to moisture transport, durability, construction pathology, diagnostic techniques, and the most recent advances in this domain. The book is divided into five chapters that intend to be a resume of the current state of knowledge for benefit of professional colleagues, scientists, students, practitioners, lecturers, and other interested parties to network. At the same time, these topics will be going to the encounter of a variety of scientific and engineering disciplines, such as civil, mechanical, and materials engineering. Porto, Portugal

João M. P. Q. Delgado

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Contents

Application of Hazardous Waste Management Model for Sustainable Cities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prafulla Parlewar

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Moisture Transport Phenomenon in Block Masonry Ceramics with Interfaces of Cementitious Mortar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 L. M. Freitas, F. A. N. Silva, and A. C. Azevedo Electrical Model of a Bulk Concrete and Analysis of Its Frequency-Dependent Electrical Resistivity . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 C. E. T. Balestra, A. Y. Nakano, G. Savaris, F. W. D. Pfrimer, and R. Schneider Studies on Rheological Properties of High-Flowable Concrete . . . . . . . . . . 75 Nagaraj Ajay, S. Girish, Ashwin M. Joshi, and Namratha Bharadwaj Sewage Sludge: Some Applications in Civil Engineering . . . . . . . . . . . . . . . . 95 M. C. A. Feitosa, S. R. M. Ferreira, J. M. P. Q. Delgado, F. A. N. Silva, J. T. R. Oliveira, P. E. S. Oliveira, and A. C. Azevedo

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Application of Hazardous Waste Management Model for Sustainable Cities Prafulla Parlewar

Abstract Application of hazardous waste management model for cities look into planning a model for collection, storage and disposal of potentially hazardous waste for sustainable cities. The model particularly, illustrates an innovative design for industrial hazardous waste management in a petroleum corporation at Mumbai, India. It is significant that cities shall handle the hazardous waste effectively for sustainable environment conservation. Hazardous waste is potential danger for the citizens in event of disaster. So, what can be effective way to plan a hazardous waste management in cities? How we can develop an accurate model? Some of these research questions are discussed in this research. Finally, this research looks into the major methods for designing a model storage unit for industrial hazardous waste. Keywords Hazardous waste · Steel structure · Disaster management · Industrial waste management

1 Introduction The application of hazardous waste management model looks into a project developed for a petroleum corporation in Mumbai, India. The model focuses on the system of waste collection, storage and disposal. It particularly focuses on a project developed for the storage in a large industrial complex. A hazardous waste is waste with properties capable of harmful to health and environment. The hazardous waste may be solid, liquid and gases. Characterises of this waste is classified into ignitibility, corrosivity, reactivity and toxicity. One such waste which was developed in petroleum refinery is Sulphur. This is highly toxic waste and harmful to humans. The model here looks into developing a structure for long span storage of hazardous waste. This model looks into effective storage mechanism for storing large number of toxic wastes. Second aspect of design include effective vehicular circulation for storage and removal of toxic waste. Also, design looks into air movement around the hazardous P. Parlewar (B) School of Planning and Architecture, New Delhi, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 J. M. P. Q. Delgado (ed.), Concrete Structures: New Trends and Old Pathologies, Building Pathology and Rehabilitation 27, https://doi.org/10.1007/978-3-031-38841-5_1

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waste. Importantly, the design looks into structure which is cohesive to all type of the loading conditions such as wind, dead load, seismic load etc. The researches further identify how the industrial waster has to be handled for developing safer cities? What are design criteria for developing structure for storing hazardous waste? How industrial waste is potentially harmful to citizens? How do we make safer cities from industrial waste? Some of these questions are discussed in this chapter to investigate problems of hazardous waste management. In the United States, generators are required to submit biennial reports of the generation, management and final disposition of hazardous waste (LaGrega et al. 2010). The day to day generation of hazardous waste in many parts of the world poses tremendous threats to humans, animals, and the ecosystem at large. The increase in waste generation can be strictly linked to the rise in the global population, thus leading to a rapid boost in industrial activities (Olukanni and Oresanya 2018). Hazardous waste is the most difficult waste to be managed, since in the treatment process, heavy metal and dioxin among others are obtained. During the last decades, the Portuguese government has been doing a set of efforts to bet ter manage and handle the hazardous waste in Portugal. To accomplish these goals, the legislation framework was modified, network infrastructures such as the Integrated Centers of Recovery Valuation and Elimination of Hazardous Industrial Waste were created and new organization and management methods were developed. It is clear that Portugal has now a more efficient system to handle and mange hazardous wastes. However, more efficient and environmental friendly energy conversion methods are still needed (Couto et al. 2013). The developed countries such as USA, Japan and many European countries are the major hazardous wastes generators, while increasing quantity of hazardous wastes is being generated by the newly industrialized countries (NICs). To minimize hazardous waste disposal problems, certain technologies to reduce waste quantity are recommended. These technologies include; in-plant minimization, raw material alteration, equipment redesign, improved housekeeping and product substitution (ChongrakPolprasert and Liyanage 1996). The key driver of hazardous waste management is involvement of all the stakeholders including waste generation, regulations, decision makers, waster processor and informal and formal sectors. The stake holders have a crucial role in proving the system by ensuring the development and delivery of an effective and efficient hazardous waste management program (Hora 1996). In the Environment Quality Act, 1974 as amended, legislation on hazardous waste management has the main objective of controlling/regulating waste generation and improving waste management process and procedure in Malaysia. The legislation describes waste management process from generation, storage, handling, treatment, and final disposal (Aja et al. 2016). Wang has suggested that China should strengthen the management of hazardous waste sources, improve the technical abilities of sound utilization and disposal of hazardous waste, push forward the management of hazardous waste from nonindustrial sources, and strengthen the construction of hazardous waste supervision and technical supporting system (Wang et al. 2013). Manufacturing of many petrochemicals and other types of products results in most cases in the generation of

Application of Hazardous Waste Management Model for Sustainable Cities

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substantial quantities of hazardous/toxic materials. Much of the wastes are generated by the chemical and petrochemical industries, which produce different types of chemicals needed by any advanced society (Alidi 1996). The management of hazardous waste is a process which includes the collection, recycling, treatment, transportation, disposal, and monitoring of wastes disposal sites. In the current scenario of developing countries, hazardous wastes are often disposed directly into the environment posing health and environmental risk. On the other hand, governments and international agencies are taking steps for controlling the growing problem of hazardous substances in the environment which appears to be a difficult process because the wastes are from many sources. Toxic and hazardous substances from these sources contaminate the land, air, and water (Enger and Smith 2004). The major part of handling hazardous waste is design of storage. Generally, the design of storage has to be long span structure. The design of long span steel structure for hazardous waste storage needs accurate considerations for load design, vehicular circulation, ventilation, safety, storage system and aesthetic. In cities hazardous waste management is a major issue. To handle industrial waste, it is important to develop model which will remove the hazard near from human habitation. Cities are complex mechanism with dynamic patterns of growth and demography. Cities continuously evolve and decay. In this process, framing sustainable cities, it is important to identify accurate models for waste management in cities. This is an important intervention to make live-able and sustainable cities. Urban waste management include residential, commercial, and industrial waste. Residential and commercial waste are not potentially harmful for citizens. On contrary industrial waste is highly harmful to citizens due to existence of hazardous materials like Sulphur or radioactive substance. The research here particularly focuses on hazardous industrial waste containing sulphurous materials. Furthermore, research here illustrate a model for industrial hazardous waste management with a project in Mumbai India. Lastly, this chapter illustrates and discusses future directions and innovative methods and proposals for industrial waste management.

2 Project Profile The project is located in a petroleum corporation in Mumbai, India. The total production capacity of the plant is 9.5 Million Metric Tonnes Per Annum. The plant is spread across approximately 400 Acre of land. Perhaps, it is considered as one of the Asia largest petroleum product suppliers. As a largest producer, the hazardous waste generated is highest as compared to the other industries in the city. The industry is located in the city area. Hence, it leads to health threats to the citizens. This industrial waste if not collected, stored and disposed properly, it can lead to environmental disaster. This affect air quality, pollute water and further affect heath of humans in the city. City of Mumbai is particularly deteriorated for its environmental conditions. It has high level of environmental pollution. Due to the urbanization city is facing problems of high level of pollution for air and water. Petrochemical industrial

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waste affects significantly to health of citizens. How such hazardous waste need to be effectively managed to reduce health hazards? What is effective mechanism for management of hazardous waste? Cities like Mumbai have independent development authority for urban development. But large petroleum industries owned by federal government are independent entities for operation and maintenance of waste. In such a situation industrial hazardous waste management are task of industries. Hence, it is important to have a model which is responsible to urban environmental management without compromising public health. So, a model is needed based on sound mechanism for collection, storage, movement, management and disposal of waste. These can be achieved by

Fig. 1 Plan at ground level

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developing model effective and responsible to environment and provide accurate solution for collection, storage, maintenance and management of waste. This model was developed by construction of steel structure in Mumbai. The purpose of structure was to collect, store, maintain, and effectively manage the store waste. The size of the structure is 18.30 m .× 23.20 m with height 4.585 m. The structure is internally column free. It is located near a sulphur storage area. The structure is designed such that it has easy accessibility form various waste generation areas in the industrial complex. Six number of steel trusses with span of 6.10 m are place at 4.521 m centre to centre. Steel columns are rested on Reinforced Cement Concrete (R.C.C) columns at two metre height. High density concrete floors are placed for the circulation of forklifts. Building design is made such that a high level of ventilation is maintained for ventilation of hazardous waste. The surrounding landscape is integrated for easy circulation. Concrete foundation is made with seismic loading in the prevailing seismic zone. Aesthetic considerations are taken care to integrate the building in surrounding (Figs. 1, 2, 3, 4, 5 and 6).

Fig. 2 Section of storage

Fig. 3 Elevation of storage

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Fig. 4 View of storage

Fig. 5 View of storage

Fig. 6 View of storage

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Fig. 7 The model

3 The Model The model looks into an effective mechanism for collection, storage and management. Generally, collection of waste is the first step towards hazardous waste management. Collection of the waste is a process in which mechanical methods are involved to collect the waste and transport it to the storage. In the first stage, it is important to have a Waste Management Program which looks into a comprehensive program to develop a Master Plan for the waste management. This looks into a comprehensive policy for waste management. In India, National Waste Management policies are National Policy of Hazardous Waste. This looks after prevention and control of the pollution, The Hazardous Waste (Management and Handling) Rule 1989 controls the waste management in industries. Hence, it is essential to develop comprehensive policies towards waste management. The Hazardous Waste Management Plan includes identification of characteristic of waste, treatment, storage, transfer and disposal and also, remedial actions for the disposal. Significantly, in these management plans, emergency actions plan has to be developed for mitigation of any potential disaster. The hazardous waste management training has following components: (1) identification of nature of contamination, (2) environmental legislation for contamination, (3) contamination problems and waste management issue, (4) hazardous waste and its consequences on human health, and (5) learning current practices (Fig. 7). The hazardous audits look into correct violations and identify any undisclosed violations as per the rules and regulations. It prevents recurrence of any future violations which can lead to disaster. It is an important step to prevent environmental damage. Any conscious violations are liable to criminal liability of the companies. Hence, audits are an important part in stage one of the hazardous waste management model. These audits further lead to regulatory inspections which are statutory mandates. Second and most important part of model is storage of the hazardous waste materials. The design of the storage is discussed in detail in the next section. The design of storage is based on accurate location of storage inventory, circulation, ventilation and structural design. The structural design is developed as long span steel structure for easy circulation and movement. The location of the store building is strategic to

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Fig. 8 Waste management system

reduce environmental damages. Final part of the model is disposal of the waste. The disposal of waste is undertaken by the companies as per the regulatory guidelines (Fig. 8).

4 Storage Design The hazardous waste store is designed as long span structure. The structure is designed as hybrid structure with structure till plinth level in concrete and superstructure in steel. At 2.5 m concrete columns and beams are cast and above 2.5 m steel structure is erected for store, The concept of design is based on systematized inventory or arrangement of hazardous waste containers, environmental conducive site planning, design of internal and external vehicular movement pattern, natural ventilation for storage of waste, and sustainable steel structure (Fig. 9). The site is located near a Sulphur plant. But it is well located for collection of waste from various locations in the industrial campus. The site planning is designed such that the building has an access from main road and exit on other end of block. The site is derived into two parts: a) open storage area and b) covered storage area. In site planning, the open storage area is connected by vehicular circulation. So, the road pattern is designed such that it connects the site effectively for vehicular movement. The building is oriented as per the prevailing wind directions. Due to this, good ventilation is achieved in building. Because of this, obnoxious gases do not remain in side the building. The location has particular advantage of accessibility from all parts of industrial complex.

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Fig. 9 Design of storage

The building profile is 23.20 m .× 18.30 m. The span of 18.30 m is kept free for easy movement of forklift and vehicles. The 18.30 m span is divided into three parts of 5.675 m each. These 5.675 m bays are used for storage and vehicular circulation. The central bay of 5.675 m is kept for the movement of forklift and access is allowed from South of building. Main arterial road is located on West side of the building. An existing pipeline is located at East side of building (Fig. 10). The foundation is designed as box R. C. C. foundation with 1000 mm mm thick P. C. C. bed concrete. The size of foundation bottom reinforcement is 12 mm diameter torque steel bars at 150 mm center to center. Minimum clearance cover for footing is 50 mm. All R. C. C works area undertaken in M 20 concrete and FE - 500 steels. Plain Cement Concrete (PCC) is taken as M-15. The soil bearing capacity considered for design is 20 Mt/Sq. M. Following two sizes of foundations were constructed in the building: (1) F1 - 1.9 m .× 2.0 m and (b) F2 - 1.850 m .× 1.85 m. Both foundation slab reinforcement are torque steel in 12 mm diameter at 150 mm center to center. Two types of columns are proposed in the building: (a) C1 - 400 mm .× 500 mm and (b) C2 - 350 mm .× 350 mm. The main bars in columns are: (a) 4 mm .× 16 mm torque steel, (b) 10 mm .× 12 mm torque steel, and (c) 12 mm .× 12 mm torque. The links in columns near support are 8 mm diameter torque steel are 125 mm (4 legged) for C1 type columns. The R. C. C. layout of building for plinth include: (a) PB1 250 mm .× 500 mm with bottom reinforcement in 16 diameter (3 No. s) straight bars, PB2 as 230 mm .× 450 mm with top reinforcement 12 diameter (2 No. s) continuous bars and 16 diameter (2 No. s) extra top bars. The plinth beams are in rectangular layout with columns at equal distances. The R. C. C. slab at plinth level is 100 mm thick with 8 diameter bars at 200 center to center both ways.

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Fig. 10 Foundation layout

5 Design of Truss A truss includes system of triangulated members to carry loads. Fink truss are most common type of trusses found in design of steel structures. The roof truss is rested on the R. C. C. columns with base plate (350 mm .× 450 mm) having 10 mm thickness. The mild steel columns are designed in two ISMC - 150 with sizes: (a) 150 mm .× 300 mm and 150 mm .× 150 mm. The top cord (TC1) is designed in two mild steel angles ISA 65 mm .× 65 mm .× 8 mm. Bottom cord (BC1) is designed in two steel angles ISA 60 mm .× 65 mm .× 5 mm. Three are two types of verticals and diagonals. B1 consist of two mild steel section of 50 mm.× 50 mm.× 5 mm. Runners are deigned in ISA 65 mm .× 65 mm .× 5 mm. Purlins are designed in ISMC 100 (P1) at 1.37 m

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Fig. 11 Section of truss

center to center and ISMC 100 (P2) at 1.5 m center to center. The bracing is designed in two ISA 65 mm .× 62 mm .× 5 mm as wind bracing at bottom cord (Fig. 11).

6 The Model: Benefits The proposed model this provides efficient ways to collect, store and dispose waste. The storage design in particular has following benefits: (1) The storage as a long span structure is a cost-effective solution. Also, it has the benefit of faster construction. (2) The mild steel simply supported triangular truss has the advantage for optimum design of long span structure. The long span structure provides a larger operational area for the storage. (3) The use of a composite system of steel and concrete has wider suitability for the storage of waste. This suitability includes easy movement of heavy vehicles and mitigating effects of hazardous materials. (4) The high strength concrete in flooring and concrete columns provides easy and long-term suitability of waste storage for longer time. (5) The super structure is completely made from steel. This provides flexibility to erect or de-erect the structure. This also provides speed for erection of structure. (6) The design also provides ease with moment and vehicular circulation. Similarly, this model can allow handling large numbers of hazardous waste. The model can be adapted due to its benefits.

7 Conclusions The hazardous waste management model for cities is a significant necessity for sustainable cities. In process of urbanization, it is essential for urban planners to mitigate disaster. Hence, it is essential to identify industrial waste management models suitable for industries within the planning area of cities. The proposed model looks into effective management and design of structure for waste management. The model looks into design which responds to circulation, ventilation and steel structure design.

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The proposed model has various benefits. Some of the benefits are as follows: (a) collection and effective solution to site planning to reduce hazards, (b) the design of storage based on effective solution to store and manage waste, and (c) the design of an innovative long span structure provides solution for storage and management of industrial waste. Furthermore, such approaches can be used in various cities having industrial areas within the city limits. The cities across globe have difficulties in achieving sustainability due to waste generation. This directly affects the environmental pollution leading to disasters and poor living conditions. Sustainable cities look into reducing and managing the waste to conserve the natural resources. Thus, the hazardous waste management can provide effective solution to achieve sustainable goals of cities.

References LaGrega MD, Buckingham PL, Evans JC (2010) Hazardous waste management. Waveland Press Olukanni DO, Oresanya, (2018) O.O. progression in waste management processes in Lagos State, Nigeria. Int J Eng Res Afr 35:11–23 Couto N, Silva V, Monteiro E, Rouboa A (2013) Hazardous waste management in Portugal: an overview. Energy Procedia 36:607-611. ISSN 1876-6102 Hora SC (1996) Aleatory and epistemic uncertainty in probability elicitation with an example from hazardous waste management. Reliab Eng Syst Safety 54(2–3):217–223 Aja OC, Al-Kayiem HH, Zewge MG, Joo MS (2016) Overview of hazardous waste management status in Malaysia. Management of Hazardous wastes ChongrakPolprasert LRJ, Liyanage (1996) Hazardous waste generation and processing. Resour Conserv Recycling 16(1–4). ISSN 213–226:0921–3449 Wang Q, Hung QF, Yan, Li DH (2013) Current status and suggestions on hazardous waste management in China. J Environ Eng Technol 3(1):1–5 Alidi AS (1996) A multiobjective optimization model for the waste management of the petrochemical industry. Appl Math Model 20(12):925–933 Enger ED, Smith BF (2004) A study of interrelationships. Environmental Science. Edward E. Bartell, California, USA

Moisture Transport Phenomenon in Block Masonry Ceramics with Interfaces of Cementitious Mortar L. M. Freitas, F. A. N. Silva, and A. C. Azevedo

Abstract In Brazil, buildings use ceramic bricks and Portland cement mortar as constituent materials of the walls, which act as coatings and delimiting elements for internal areas. These materials are porous and highly susceptible to degradation due to the presence of moisture. Water penetrates structures through pores and compromises the useful life of buildings if not identified and treated early. The region between two layers of a wall is called the interface, and due to the presence of this region, the transport of moisture in multilayer elements diverges from those found in monolithic elements. The change in moisture transport behaviour is proportional to the change in the nature of the contact and the water properties of the interface, and it is called as interface resistance. This work sought to obtain information on the storage and transfer of moisture, throughout the useful life of the system formed by ceramic brick and Portland cement mortar. For this, the analysis of the performance of standardized samples was carried out, with different interface configurations, mortar traces, and base dimensions. Different performances were observed for samples of different traits, where some absorbed less water than others. When comparing the different areas of the specimen bases for each trace, in all cases the absorption (moisture content) of water increases as the area is increased. This work presents and discusses the current situation, original techniques, and strategies used in the development of structural reinforcement design of both towers of the Basilica of Penha Church. Repair techniques were, poorly, designed, and conducted in 1981, along with a lack of preventive maintenance, leaks and even the growth of bushes embedded in the masonry led to the instability of the towers of the Basilica of Penha Church. This paper, which combines integrated solutions in a historic monument reinforcement project, was initially challenging and became an important case study, possibly one of the first works using carbon fiber reinforcement in masonry. Another important contribution is the insertion of visitable galvanic protection that enables monitoring L. M. Freitas · F. A. N. Silva Civil and Engineering Department, Catholic University of Pernambuco, Pernambuco Recife, Brazil A. C. Azevedo (B) Instituto Federal de Ciencias de Educacao E Tecnologia de Pernambuco (IFPE), Pernambuco, Brazil e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 J. M. P. Q. Delgado (ed.), Concrete Structures: New Trends and Old Pathologies, Building Pathology and Rehabilitation 27, https://doi.org/10.1007/978-3-031-38841-5_2

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and possible replacement of sacrificial anodic inserts, keeping the protection active over time. Keywords Experimental campaign · Moisture transport · Ceramic block · Mortar · Masonry

1 Introduction In Brazil, it is common for buildings to use ceramic bricks and Portland cement mortar as the main constituent materials of the walls of buildings, which act as coatings and also as delimiting elements of internal areas. These materials are porous and therefore highly susceptible to degradation due to moisture. Water, being one of the most responsible for pathologies in constructions, penetrates the structures through pores, and alone or in association with other elements or phenomena, it can compromise the useful life of buildings if not identified and avoided early. The study of moisture transfer within civil construction materials and elements is of fundamental importance for the characterization of their behaviour and understanding of their influences on durability, watertightness, thermal and aesthetic performance of buildings in general (Freitas and Peixoto 1992). The creation of a database on the mechanisms of moisture transport in building materials is essential for the adequate numerical simulation of this phenomenon. Previous investigations have treated a masonry wall as a single element in numerical simulations of moisture and heat transport, but the existence of an interface resistance, resulting from the interface between different building materials, reveals that this simulation strategy may not be the most efficient (Freitas and Peixoto 1992). The study developed in the research is important as it investigates the performance in service of an important constructive element that is present in all buildings—the masonry wall of ceramic blocks laid with cement mortar. This theme is in line with the demands of Brazilian performance standards, NBR 15,575 (ABNT 2013). The focus of this technical standard, according to NBR 15,575 (ABNT 2013) “is on the requirements of users for the housing building and its systems, regarding their behaviour in use and not on the prescription of how the systems are built”. The motivations of the research carried out are part of the normative demands of having buildings that, in addition to structural safety in the ultimate limit states, also offer adequate conditions of use and contribute to the quality of life of their users, based on sensory limits. Standardized for weather, sound and visual conditions. Masonry walls are exposed, daily, to incident rain, condensation, and rising dampness. This process of wetting and drying the masonry can result in degradation, such as volumetric expansion, decrease in mechanical strength, abrasion and impact, thermal transfer, mold formation, and presence of fungi and bacteria (Fig. 1). The prevention and correction of damage caused by wall contact with water requires a deep understanding of the water behaviour of moisture transport (Janssen

Moisture Transport Phenomenon in Block Masonry Ceramics …

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Fig. 1 Masonry wall in contact with external water

et al. 2012). If we consider the economic factors of this phenomenon, its study takes on more relevance, since the costs of correcting eventual pathologies associated with the contact of masonry with water increase exponentially when compared to the initial costs of prevention. According to Alves et al. (2012), “quality costs are inversely interrelated. That is, as prevention and evaluation costs increase, the costs of internal and external failures tend to decrease”. In addition to this fact, there is also the repair of apparently harmless pathologies. Turner (2002) reported that a significant amount of financial investment is consumed in the US to carry out mold/fungal repairs in buildings of various uses.

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To properly evaluate the performance of masonry walls subjected to moisture transport inside, it is necessary to understand the interface phenomena (Azevedo 2019). This understanding can lead to more assertive design guidelines. Although masonry walls are composed of multiple layers of bricks and mortar, in most numerical simulations of heat, air, and moisture transfer, the actual masonry composition is often simplified by adopting a strategy of considering a single layer of masonry. Homogeneous brick. This modelling strategy is justified only when the cost and associated computational time are constrained, and to obtain global qualitative information about the investigated phenomenon. On the other hand, when, for example, one wants to investigate the durability of the wall in more detail, the level of complexity of the modelling cannot do without a more detailed modelling that seeks to approach as close as possible to the real conditions of execution (Vereecken and Roels 2013). The heterogeneity of a masonry wall makes the analysis of moisture transfer more complex, requiring knowledge not only of its characteristics individual, but also the conditions of continuity of the interface that separates the different materials (Rego 2014). The study of the hygric resistance generated at the interface has been evolving for decades, as a natural consequence of the process, different approaches have been and have been taken into account to seek an abstraction model of the physicochemical phenomenon associated with the subject of study.

1.1 Research Objectives It seeks to obtain information about the behaviour of moisture transfer and its storage, throughout the life of the system formed by ceramic brick and Portland cement mortar. Additionally, we seek to investigate strategies to meet the performance standards that incorporate more rigorous demands regarding the proper functioning in service of the constructive elements, as well as their aesthetic and energy efficiency performance. In this context, the analysis of the moisture content and how it moves inside masonry walls of ceramic blocks proves to be an important procedure to understand the effect and influence of the main factors involved, namely: the absorption and drying of these materials, through tests with standardized samples. As it contributes to the understanding of the phenomenon of Interface Resistance in the transit of moisture in porous materials, the research carried out advances in the knowledge and characterization of important inputs for the civil construction industry—ceramics and cement mortar. The formation of a database and the appropriate correlation to the methods of analysis provide a basis for reaching a more concise theory close to the real phenomenon. In resume, the main objective of this study is the experimental analysis of the behaviour of moisture transport in samples composed of ceramic brick and cement mortar, with different interface configurations, mortar traces and base dimensions.

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The purpose is to understand how these factors influence the absorption and flow of moisture in these materials.

2 Literature Review This section presents the fundamentals of the different transports of moisture in different phases, as well as the types of interfaces between materials and the test methods for identifying the hygric resistance of the interfaces. Methodological strategies for estimating hygric resistance values of interfaces are also presented.

2.1 Moisture in Porous Materials Most building materials used in building are porous and, therefore, are naturally susceptible to a degradation process due to the constant presence of moisture. Water, being one of the factors that account for most of the pathologies in constructions, penetrates the structures through the pores. Alone, or in association with other elements or phenomena, it can compromise the useful life of buildings if not identified and treated early. The presence of moisture can cause several pathological manifestations in buildings and the most frequent are the following (Straube 2002): • Corrosion of steel in metallic structures, reinforcement in structural masonry structures reinforced concrete and pre-stressed concrete; • Chemical deterioration and dissolution of materials such as plaster coatings, ceilings, wood products and chemical processes such as carbonation and alkaliaggregate reaction in structural concrete; • Efflorescence and leaching; • Deterioration by freezing and thawing cycles in concrete or masonry elements; • Discoloration and stains on coatings and finishes; • Volume changes (swelling, warping and shrinkage) that can cause cracks, detachment of plates, structural failures, aesthetic problems, etc. • Growth of biological forms such as mold, plants and mites. In addition to the pathological manifestations listed above, another recurring phenomenon in buildings is the thermal discomfort caused by humidity, which, in some situations, can be agents that cause diseases in users, with respiratory medicine intercurrences being more frequent. Straube (2002) explains that for a problem related to humidity to occur, at least four conditions are necessary to be satisfied: 1. Availability of moisture source; 2. Existence of a route for the movement of moisture;

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3. Existence of a force that drives the movement of moisture and 4. The susceptibility to moisture deterioration of the building materials used. Thus, in order to prevent pathological manifestations caused by moisture, it is necessary to mitigate at least one of the four conditions necessary for degradation, listed above. This mitigation may seem like a simple task, but in real situations, it is practically impossible to exclude all the above conditions. Most of the time, these conditions occur naturally in various building materials and depend on the location of the building, the climate, among other factors. An example of the difficulties of mitigating or eliminating the conditions listed above is the presence of pores in bricks or concrete, the presence of alkali in the cement or the presence of moisture due to rain. However, even though it is almost impossible to eliminate the listed conditions, the one that plays a more relevant role is the water source and, therefore, should deserve greater attention from the engineer. For Straube (2002), there are four primary sources of moisture in buildings, which can be classified as follows: • Liquid water, from precipitation or leakage from pipes of hydro-sanitary installations; • Water vapour, coming from outside or from the processes taking place inside the building; • Liquid and vapour water from the ground below the building; • Moisture present in the building materials themselves. Therefore, it is essential to have a precise understanding of the behaviour of the animals when they come into contact with water. This is necessary so that you can predict and anticipate problems and, thus, reduce risks and understand their consequences on the durability of materials. According to NBR 15,575 (ABNT 2013), the project life minimum of internal and external sealing systems is 20 and 40 years, respectively. For this requirement to be met in masonry walls, understanding, prediction, and risk reduction and unnecessary maintenance are necessary.

2.1.1

Characterization of the Porous Medium

The fixation and transport of moisture depend on the porous matrix of the materials. The porous matrix of a material consists of the voids within crystalline solids that can have different dimensions, sizes, shapes and ways of communicating with each other. The porosity of a material can be defined as the ratio between the volume of voids and the total apparent volume. The porous structure of bricks and cement-based mortar comes from their manufacturing processes and is therefore unpredictable to some extent. On the other hand, the quality control of these materials prevents the quality of the materials and consequently their porous matrices from being compromised. For moisture to propagate through a material it is necessary that the pores are connected to each other, although there may be the possibility of isolated pores

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Fig. 2 Scanning electron microscopy image of a synthesized ceramic containing open and closed pores

without any interconnection. Therefore, pores with connections to each other are defined as open porosity and isolated pores as closed porosity Freitas et al. (2014). Figure 2 represents the two types of porosity. Porosity is open when there is a volume of pores accessible to a given molecule of fluid and it is said “closed” when there is no minimum volume for the fluid flow. According to the radius of the constituent pores of a given material, it can be classified as microporous, mesoporous or macro-porous. Another distinction of materials is associated with the communications of their pores, which can also be considered as open or closed. This definition is established by the international institution entitled International Union of Pure and Applied Chemistry (IUPAC 1994). The IUPAC (IUPAC 1994) characterizes crystalline solids based on the internal radii of the pores, as well as the volume of pores communicable to a fluid, as shown in Table 1. The appearance of pores occurs during the firing process in the manufacture of ceramic bricks. The initial step is the extraction of clay, which is then prepared for moulding, and subsequent drying at a temperature lower than the firing temperature. This is done so that the water that is inside the raw brick comes out, without the appearance of cracks due to shrinkage. Only after this process is the brick taken directly to the oven, at a temperature of approximately 900 °C, for the definitive firing (Bauer). Porosity can be higher due to the presence of materials that disappear with the high firing temperature of the brick, such as organic materials such as wood sawdust and peat. After burning, the place that was occupied by this organic material is empty, making the material more porous (Hentges 2014). The quality control of the manufacture and delivery of ceramic bricks is defined according to the technical standards NBR 7171 and NBR 8042 (ABNT 1992; ABNT 1992).

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Table 1 Types and classification of pores in ceramic materials (IUPCA) (IUPAC 1994) Types/classifications of porous materials

Definition

Microporous

They have pore diameters of less than 2 nm. They are the smallest pores and have no influence on moisture transport because the water they contain is not free. Due to its very small size, surface tensions are so high that the water cannot move

Mesoporous

They have pore diameters between 2 and 50 nm. They are intermediate-sized pores and are also called “capillary pores” or simply “capillaries”. It is through them that liquid water migrates under the influence of capillary forces. Vapour transport also occurs in these pores

Macroporous

They have pore diameters greater than 50 nm. They are the largest pores and are very relevant to the transport of steam. In contrast, net capillary transport is normally not significant in macroporous because the capillary forces are weaker

With open porosity

Pores that have a continuous channel of communication with the outer surface of the body

With closed porosity

Pores that are totally isolated from their neighbours, closed in on themselves, and not available for a external fluid

2.1.2

Transport of Moisture in Liquid and Vapor Phase

Research on the transport of liquids in multilayer composites can be found and the values studied, for the most part, are determined based on the moisture profiles measured during the soaking experiment and are dependent, for example, on the type of mortar used, the w/c factor (water/cement factor), the use of additives, as well as the type of brick, the curing conditions, and the thickness of the mortar joint. These factors can have a potential impact on the interface strength and on the modification of porous material properties (Azevedo 2019). Construction materials can present varying degrees of hygroscopicity (Freitas and Peixoto 1992). Taking this factor into consideration, materials can be classified as: • Hygroscopic—when the amount of water fixed by absorption is relatively important. Plain concrete and plaster are examples of hygroscopic materials; • Non-hygroscopic—when their mass is practically constant regardless of the relative humidity of the environment in which they are found. Clay is an example of a non-hygroscopic material. Water can penetrate a porous material in a liquid or vapour state. In the liquid state, two mechanisms can usually occur: capillarity and/or infiltration. While capillarity is a result of the attraction of water and the surface tension of the liquid, infiltration requires hydrostatic pressure and depends on the permeability of the material (Charola 2000; Freitas et al. 1996). Most porous building materials, such as concrete, mortar or brick, are also hygroscopic materials that are able to attract water vapour from the environment. In the

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case of building materials, hygroscopicity concerns the adsorption of water from the air. Specifically for these materials, adsorption is the process by which water molecules bind with pore surfaces and thus form thin films composed of one or more layers of molecules. Adsorption arises from weak intermolecular forces (Van der Waals forces) that act between the surface of the material and the water (Gonçalves 2007). It is important to understand how water moves after it has penetrated a porous material. If water moves in a liquid state, it will have the ability to transport salts. If the water moves in the form of vapour, it can be retained by hygroscopicity. In the first case, the mechanism depends on capillarity and, in the second case, it depends on diffusion (Charola 2000). In porous building materials, liquid water migrates mainly by capillarity. The capillary mechanism occurs when the attractive forces between the liquid and the solid are stronger than the cohesive forces in the liquid. The capillary transport properties of porous building materials are evaluated on the macro scale. Appropriate experimental parameters are used to express the tendency of the material, under specific conditions, to absorb a certain amount of water or to transport that water to a certain height. In porous hygroscopic materials, the transport of liquids can occur even when there is no contact with the external liquid water, because a (liquid) diffusion process occurs by which the water migrates from a thicker pore to thinner layers of adsorbed water present in smaller pores (Gonçalves 2007). Water vapour transport in porous building materials can be described as a diffusion process, therefore, caused by a water vapour concentration gradient. The diffusion processes are essentially due to the existence of temperature gradients (thermal diffusion or Soret effect) and water vapour pressure (gaseous diffusion itself). Thermal diffusion, which also occurs in the liquid phase, represents only about 0.05% of the total value of moisture transfer in buildings, and can therefore be neglected (Rego 2014).

2.2 Interface—Hygric Resistance Building walls are usually made up of multiple layers of construction materials. The region between one layer and another of a wall is called an interface, and due to the presence of this contact interface, the transport of moisture in multi-layer elements diverges from that found in single-layer elements (Vereecken and Roels 2013). Although masonry walls are composed of brick and mortar, in most heat, air, and humidity simulations, the actual composition of masonry walls is simplified to a homogeneous layer of bricks (Vereecken and Roels 2013). However, several studies prove that the nature of the interface influences the transport of moisture in masonry walls. Considering that each material has different porous matrices, when they come into contact with each other, as in masonry walls, the transport of moisture through them does not occur constantly. The existence of a discontinuity of pores between

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the materials can result in a decrease in the moisture transfer rate and/or a decrease in the total water absorption. This delay that occurs when the wet front reaches the materials interface has been observed in several studies and has been discussed over the years. In the study of moisture transfer in multi-layer elements, the interface can have a significant influence on the pathological manifestations usually associated with this phenomenon, since the behavior of moisture in masonry is highly determined by the interaction of the water characteristics of the two components, and also by the nature of u. In addition, the curing conditions of the mortar also determine the transport characteristics (Brocken et al. 1997; Depraetre et al. 2000; Derluyn et al. 2011). The change in the behaviour of moisture transport proportional to the change in the nature of the interface and in the water properties of the interface led to the definition of a new property/quantity—the hygric resistance of the interface. The concept ‘interface resistance’ (or ‘ hygric resistance’) was primarily used by Freitas (Freitas and Peixoto 1992), defining it as the greater or lesser diffusion of water, translated into maximum flow transmitted in the samples studied, expressed in kg/m2 s. The study identified hygric resistance by observing the lack of continuity at the interface between porous materials. The work of Freitas (Freitas and Peixoto 1992) opened space for further research on the influence of the interface on the transport of moisture in masonry walls, where different materials, curing conditions, material configurations, and ways of identifying the moisture behaviour, in addition to other interface strength calculation methodologies.

2.2.1

Types of Interface Between Materials

According to Freitas (Freitas and Peixoto 1992), there are three types of interface between porous materials: hydraulic continuity, perfect contact and air space. A schematic representation of the interface is presented in Fig. 3. • Hydraulic continuity—occurs when the porous structure of materials interpenetrates, seen in real work situations, when fresh mortar is inserted between layers of bricks, with physical adhesion between them; • Perfect contact—occurs when there is contact between the materials, but without the interpenetration of the porous matrix; • Air space—occurs when the materials do not come into physical contact, with only a few millimeters of air space between them. Freitas’s research (Freitas and Peixoto 1992) exclusively considered the interface resistance present in the configurations of ‘perfect contact’ and ‘air space’, not considering the existence of interpenetration of the porous matrix. However, further research suggests that compared to a monolithic sample, all types of interface between materials somehow interfere with moisture transfer.

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Fig. 3 Types of interface configurations: hydraulic interface (left), perfect contact (center) and air gap (right)

In contrast, Depraetre et al. (2000) consider the existence of four types of interface: perfect hydraulic interface, air space, natural interface and real hydraulic interface. Perfect hydraulic interface is characterized by the continuity of capillary pressure and moisture flow across the interface. If the two materials are identical, the moisture flow is not influenced by the interface. For different porous materials, an influence is found. Natural interface is considered when both materials are in perfect physical contact, while their porous structures do not fit together. However, perfect physical contact is difficult to achieve. If compared with the configuration by Freitas and Peixoto (1992), this type of contact is equivalent to perfect contact. The real hydraulic interface, or just hydraulic interface, is a sum of the ‘hydraulic interface’ and ‘perfect contact’ configurations, where there is interpenetration of the pores of the two materials and the presence of hygric resistance. This type of interface is formed when the mortar is cured between the layers of bricks. The research investigated two variables of real hydraulic interface: perfect and imperfect real hydraulic interface. In other words, the dry brick, guaranteeing total physical adhesion through the pores, and the saturated brick, preventing physical adhesion through the pores, respectively referred to in the research as hydraulic interface and perfect contact.

2.2.2

Identification of the Different Interfaces

What characterizes the existence of a hygric resistance at the interface is the delay in the rise of moisture inside a porous material, which, as a consequence, results in a decrease in the total content of absorbed water and/or a decrease in the rate of moisture rise., when compared to a monolithic material. To identify and quantify the hygric resistance between the layers of a masonry wall, there are some approaches that can be used to characterize the materials and allow identification.

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Next, only one of the most used methods for the identification and quantification of the hygric resistance of the interface will be exposed—the gravimetric method. Other methods that can also be used for this purpose—nuclear magnetic resonance, X-ray analysis and gamma-ray attenuation, are outside the scope of this research. The gravimetric method, also known as imbibition test, is a classic method to determine the transient moisture content (Rijniers et al. 2005). This method consists of calculating the moisture content from the mass difference between dry and wet samples. According to the current standard ISO 15148 (ISO 2002) the test must be performed using prismatic samples of the material to be studied, under specific conditions of temperature, relative humidity and atmospheric pressure. In addition, the standard recommends that the water flow be unidirectional. To ensure the vertical transport of water, the sides of the samples must be waterproofed, leaving free only the base that is in contact with the water slide, and the top, ensuring the potential difference. The sample of the material to be analysed must be dry and with constant mass, being then immersed in a water slide with 5–10 mm in height, for a certain period of time. The sample must be weighed several times during the water absorption in order to plot the moisture content versus time. Despite being straightforward and apparently accurate, the gravimetric method has the disadvantage of being destructive. Cutting a sample after the test, a process necessary to observe the moisture front, produces heat and consequently disrupts the moisture distribution (Azevedo 2019).

2.2.3

Methodology to Calculate the Hygric Resistance of the Interface

Although there are several studies on the hygric resistance of the interface in the transport of moisture in building materials, few are those that quantify this resistance in numbers. In the previous section, the gravimetric method was mentioned, which identifies the existence of a resistance at the interface between two porous materials, but even this methodology does not lend itself to estimating the value of the resistance explicitly. This calculation does not yet exist in a standardized way and several researches have been developed in order to create strategies to estimate this value, based on existing methodologies. The existence of a resistance at the interface, as well as its value, can be obtained in different ways and strongly depend on the case studied. In masonry walls, for example, the type of mortar, brick, wet or dry curing conditions, the thickness of the mortar layer, the distance from the moisture source, among other factors, can influence the properties of the interface and, consequently, in its performance. It is then possible to correlate the phenomenon of interface resistance in capillary absorption, the calculation of hygric resistance is then made from the measurement of moisture flow from the point change of slope of the characteristic curve of the cumulative flow test (or capillary absorption) (Azevedo 2019).

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Fig. 4 Moisture absorption profile and change of direction of the graphs

The hygric resistance (RH) calculated by the gravimetric method is based on the following expression: RH = ΔMw/Δt, where the time variation and also the capillary absorption are measured from the point of change of slope of the characteristic curve of the capillary absorption test. Azevedo (2019) suggested a new way of calculating hygric resistance using the graphs generated by the gravimetric method. The new form of calculation consists of obtaining the equation of the curve generated after the graph changes direction and extracting its derivative, generating an equation that depends on the instant in which the graph changes direction. This methodology considers that the graphs generated by the absorption test behave differently according to the type of interface between the brick and the mortar. The method considers that when the interface type is perfect or air gap, the graph changes direction only once, while the hydraulic interface would show two changes of direction—this is because there are more interfaces in the hydraulic interface (see Fig. 4). Note that in the hydraulic interface there are two changes of direction in the curve, and for this reason the section considered for calculation is the one after the second inflection point. In addition, there is also the mathematical difference between the calculations. In perfect contacts and air space, after changing the direction of the curve, the best representation of the points obtained was in a linear function, where the derivative does not depend on the instant in which there is a change in direction. On the other hand, in hydraulic interface, the function that best represented the points on the graph was the logarithmic function, whose derivative depends on the instant in which the graph changes direction.

3 Experimental Program The experimental work carried out focused on the study of the behaviour of moisture transfer in samples composed of brick and cement mortar, with different geometric configurations and mortar traits. The aim was to understand the influence of the contact area with water, the type of mortar, and the type of contact between the materials on the hygric resistance of the interface.

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The samples were made with two types of interface between the bricks and the mortar—hydraulic interface and perfect contact, with a layer of fresh mortar between two layers of bricks. To ensure the existence of hydraulic interface, totally dry bricks were used for greater interpenetration of the mortar in its pores. On the other hand, in perfect contact, it was decided to use bricks saturated with distilled water, so that the pores were completely filled and the mortar was prevented from penetrating the pores of the bricks. The mortars used were made with Portland cement CP V, hydrated lime, washed sand and distilled water. The traces were defined in mass of cement, lime and sand and are as follows: 1:0.5:4 (Trace 1); 1:1:6 (Trace 2); and 1:2:9 (Trace 3). These proportions were defined based on the work developed by Azevedo (2019), so that it was possible to compare the results of that researcher with the present research. In addition to the difference in interface and trace, there is also the difference in base dimensions. The samples have a square base measuring 5 cm × 5 cm, 7 cm × 7 cm, and 10 cm × 10 cm, approximately. These measurements were chosen to observe the behaviour of humidity when the interface area with water is increased. For each interface configuration, 90 samples were made, 30 for each mortar mix, i.e., a total of 180 samples. Table 2 shows the data of the samples made and tested. All samples had a height of approximately 11 cm, with two layers of ceramic brick of 5 cm in height interspersed with a layer of mortar of 1 cm, as presented in Fig. 5. Table 2 Configuration of samples analysed

Interface

Trace

Dimensions

Perfect hydraulic interface

1:0.5:4

5 cm × 5 cm 7 cm × 7 cm 10 cm × 10 cm

1:1:6

5 cm × 5 cm 7 cm × 7 cm 10 cm × 10 cm

1:2:9

5 cm × 5 cm 7 cm × 7 cm 10 cm × 10 cm

Imperfect hydraulic interface

1:0.5:4

5 cm × 5 cm 7 cm × 7 cm 10 cm × 10 cm

1:1:6

5 cm × 5 cm 7 cm × 7 cm 10 cm × 10 cm

1:2:9

5 cm × 5 cm 7 cm × 7 cm 10 cm × 10 cm

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Fig. 5 Representation of samples

In all the processes of preparation and execution of the experimental program, distilled water was used to avoid contamination of the materials by mineral salts present in natural or filtered water, which could compromise the search results.

3.1 Preparation of the Test Bodies The materials used in the development of the experimental program, such as cement, fine aggregate and coarse aggregate, were characterized in the laboratory. The bricks used to carry out the experiments were solid ceramic pieces with dimensions of approximately 23 cm × 11 cm × 5 cm. To build the samples used in the tests, it was necessary to cut the bricks to make them smaller, with a square cross section, with sides equal to 5 cm, 7 cm and 10 cm. A manual straight cutting machine with a circular diamond saw was used to make the cuts. For each specimen, two pieces of bricks were used, totaling 360 pieces of bricks, 120 for each base area. To ensure perfect contact, it was decided to saturate the bricks so that there is no interpenetration of the fresh mortar in the pores of the bricks. For this, the bricks were immersed in distilled water for 72 h before applying the mortar. In the case of hydraulic interface, the opposite had to be done. Before placing the fresh mortar, the bricks were placed in an oven for 24 h at 100 °C, in order to remove all the water present in the capillary pores. In this way, it was possible to provide physical and chemical adhesions between the materials, ensuring the greatest possible interpenetration of the mortar in the pores of the bricks. Once the drying and saturation process of the bricks was completed, the process of making the samples began. The study was carried out with three different mortar mixes, composed of fine sand, coarse sand, hydrated lime, Portland cement CP V and distilled water. The characterization of the mortar is explained in more detail in Sect. 3.3. The construction was carried out from the base brick layer, adding a thick layer of fresh mortar to the upper face of the brick and supporting the second layer of brick on top of it. In order to guarantee the mortar laying on the entire face of the bricks,

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Fig. 6 Prepared samples

light blows were performed on the upper face of the sample until it reached 1 cm of thickness. The samples ready after curing for seven days can be seen in Fig. 6. To ensure the occurrence of moisture flow in only one direction, the side faces of the samples were waterproofed after the mortar curing period of 28 days. The material used for waterproofing was the Silver Tape type, which was applied transversally to the samples. First in the central part, where the interface between the bricks and the mortar occurs, and later in the rest of the specimen, taking care to avoid air spaces between the materials and the tape. Figure 7 shows the samples waterproofed. After waterproofing, the samples were kept in a place with ambient temperature until the time of the absorption test. Due to the hygroscopicity of the ceramic bricks, the samples were placed in an oven for 48 h at 50 °C and then placed in a room at room temperature for cooling for 72 h, before each test.

Fig. 7 Waterproofed samples

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3.2 Capillary Absorption To carry out this test, parameters from the European standard ISO 15148 (ISO 2002) were used, which directs the terms for determining the coefficient of water absorption by partial immersion of building materials in general. This standard establishes that the samples have a minimum area of 50 cm2 , but recommends that they be 100 cm2 for better accuracy of the results. In addition, it also requires the waterproofing of the side faces and the use of at least six samples when the areas are smaller than 100 cm2 . However, most of the samples in this study have an area smaller than 50 cm2 and for this reason, the procedure of Rilem TC 127-MS (RILEM, Rilem Technical Committees 1998) was also adapted, which indicates the use of samples with a square base measuring 5 cm × 5 cm and waterproofed sides. The two standards have practically identical procedures, with the objective of determining the capillary absorption coefficient. That said, the present work carried out an adaptation/junction of the two procedures, seeking a greater number of measurements for analysis. ISO 15148 (ISO 2002) provides for at least seven weighings during the entire test, five of them in the first 24 h, one at 24 h and one at the researcher’s choice. In this work, 40 weighings were carried out, 28 of them in the first 24 h, in all samples. The containers used to carry out the experiment were made of transparent plastic with a flat-surface bottom, in order to facilitate the maintenance of the water level. At the bottom of the container, a rubber band of about 5 mm thick was fixed with glue for plastic and rubber, perforated with nails and/or stainless screws. The tips of the nails and/or screws, facing upwards, were intended to support and keep the lower surface of the samples always in contact with water, as can be seen in Fig. 8. A marking was made on the side of the container to identify and control the height of the water depth in which the samples were partially immersed, with heights of 5–10 mm above the base of the samples. 1 Related to the waterproofing of samples, the sequence used for the tests was as follows: 1. 2. 3. 4. 5. 6. 7. 8.

Identification of samples; Storage of the samples in an oven for 48 h; Cooling of the samples for 72 h at room temperature; Printing of measurement annotation tables; Preparation and positioning of properly clean and dry containers; Calibration of the scale to be used; Timer preparation for all measurements of the day; Placement of distilled water in the containers up to the established height marking; 9. Weighing, measuring the dimensions of the samples, and recording the values. The process of carrying out the tests itself followed the following steps:

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Fig. 8 Test container

1. Storage of samples immersed in water—five per container, at the established start time; 2. Weighing of samples at the predicted times; i. ii. iii. iv.

Removal of the specimen from the water; Remove excess water with a damp cloth; Carrying outweighing and recording of values; Replacement of the specimen in the container;

3. Checking the water level of the reservoir and levelling it, when necessary; 4. Repetition of the process in the foreseen times.

3.3 Physical and Hygroscopic Characteristics of the Materials For the proper accomplishment of this study, the characterization of the materials is necessary, so that the reference parameters can be obtained and with them to make the correlations between the results obtained in the tests, and, with that, to arrive at a correct interpretation of the phenomenon.

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3.3.1

31

Ceramic Brick

The tests carried out to characterize the bricks used were density, water absorption index and capillary absorption coefficient. • Density To calculate the density, the bricks were dried in an oven at 100 °C until reaching a constant mass, according to NBR 15,270–3 (ABNT 2005b). After the bricks had cooled, they were weighed, then the three dimensions were measured and the values recorded in five different samples. • Water Absorption Index To calculate the water absorption index, the standard NBR 15,270–3 (ABNT 2005b) was used, which indicates that the bricks must be submerged for a period of at least 24 h in water at room temperature until the mass is stabilized. The tests were carried out on three samples of bricks. • Capillary Absorption Coefficient The capillary absorption coefficient was calculated according to ISO 15148 (ISO 2002), using five samples of bricks partially immersed in distilled water, following the same procedures described above. Measurements were performed at the following test times: 5 min, 20 min, 1 h, 2 h, 4 h, 8 h, 10 h, and 24 h. The capillary absorption coefficient (Aw ) is calculated by: Aw =

Mw mt − m0 √ = √ A t A t

(1)

where Aw is the capillary absorption coefficient (kg/m2 s0.5 ), mt is the mass measured after time (kg), m0 is the initial mass of the sample, A is the area of the base (m2 ) and t is the time (s).

3.3.2

Mortar

Mortar is a common building material used for wall construction, and its dosage is one of the most important factors for the workability of this material (Guimarães et al. 2018). The dosages used in this work are in accordance with the Brazilian standard NBR 7200 (ABNT 1998). Laying mortar is the main material used for joining bricks in masonry walls. It contributes to the uniform distribution of loads in a building and to the absorption of deformations resulting from the active forces. In order for the mortar to perform its functions correctly, it is necessary to guarantee, through the proportions of the materials used in its manufacture, that it has the necessary characteristics compatible with the intended function. One of the main

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Table 3 Proportions of the traces of the mortars used Trace

Cement

Lime

Fine sand

Coarse sand

w/c

w/m

1

1

1

2

2

1.15

0.17

2

1

0.5

3

3

1.68

0.17

4

1

2

4.5

4.5

2.51

0.17

characteristics of mortars, regarding the execution, is the workability, which can be defined as the greater or lesser ease of handling it in the fresh state. The mortars used in this study were composed of Portland cement CP V, hydrated lime, washed sand, and distilled water. By way of comparison, three different proportions of materials were used, in order to maintain the water/dry materials ratio, thus ensuring good workability. The volume proportions, the water/cement ratios (w/c) and the water/dry materials ratio (w/m) are described in Table 3. The mortars were prepared according to NBR 13,276 (ABNT 2016), which also prescribes the calculation of the consistency index in the fresh state. Also at this stage, the content of incorporated air and the density in the fresh state were calculated, both according to NBR 13,278 (ABNT 2005). The tests performed to characterize the mortars in the hardened state were the following: density, water absorption index, and capillary absorption coefficient. For all mortar characterization tests, prismatic samples with dimensions equal to 4 cm × 4 cm base, and 16 cm in height were used. • Density The densities of the mortars were calculated according to NBR 13,278 (ABNT 2005), and similarly to the procedures performed with the bricks. Five samples of each mortar mix were tested. • Water Absorption Index To calculate the water absorption index, we chose to use the same method used in the bricks, which indicates that the samples must be submerged for at least 24 h in water at room temperature, until the mass is stabilized. The tests were carried out on three samples of each mortar mix. • Absorption Coefficient As for the bricks, the capillary absorption coefficients were calculated by Eq. (1) and following the procedures determined by the ISO 15148 standard (ISO 2002).

3.4 Hygric Resistance Measurement The hygric resistance calculation was developed from the models described by Azevedo (Azevedo 2019). The first methodology (previous methodology—PM) of

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calculation is based on the capillary moisture absorption rate of the ceramic specimen as a function of time, regardless of the type of interface between the samples. The second (new methodology—NM) in the new method proposed by Azevedo (2019). For the development of PM methodology, one must start from the point of change in the slope of the capillary absorption curve as a function of time. However, as the curve is a polynomial function, some processes had to be adapted for the analysis to be carried out. Based on the information from the tests, an initial time of 25,200 s (7 h) was specified because it is a common point among the nine configurations and is located in the region closest to what most resembles a sudden change in the slope of the curves. As an endpoint, a time equal to 259,200 s was stipulated, which corresponds to 72 h. The exception was for the small specimen of trace 3 which, as it did not have the record for this period, the final time of 255,600 s (71 h) was used. Making use of Eq. (1) and having Mw for the respective cumulative flow values of capillary moisture absorption recorded for the times of t0 and t of 25,200 s and 259,200 s, respectively. The hygric resistance values of the nine sample configurations were calculated from the ratio between the variations in capillary absorption as a function of time. For the calculation of the NM methodology, some adaptations were necessary so that the calculation could be carried out. Unlike what was proposed by Azevedo (2019), the perfect contact in this study presents two inflection points in the curves generated by the absorption test, as well as the hydraulic interface. In this way, both configurations obtained logarithmic functions in their hygric resistance calculations. The time t used for all perfect contact configurations was 86,400 s (24 h). In the hydraulic interface settings, there was a variation in the time in which the graph changes direction, with 79,200 s (22 h) being stipulated for the 5 cm samples with lines 1 and 2, and the 7 cm samples with lines 1 and 3. Other configurations followed with a time equal to 86,400 s. The hygric resistance calculations were performed for the two types of interface and the two methodologies studied in this work, and the respective observed results will be presented in Sect. 4.5.

4 Results and Discussions In this section, the different results obtained in the tests proposed in the experimental program will be analysed in order to achieve the objectives of this work. For the proper analysis of the observed values and understanding of the parameters influencing the recorded performances, it is essential to characterize the samples in advance. Therefore, the first part of this section will serve to expose the results of complementary laboratory tests for characterization of absorption and saturation of samples in the appropriate cases. In the second part, the results obtained for the interface of the hydraulic type will be exposed, considering the nine configurations of preparation of the samples and

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Fig. 9 Bricks detached from the mortar layer

analysed under the aspects of cumulative flow and also the moisture content, at the end of the analysis period of 74 h. This analysis is first seen as a function of time, both for the cumulative flow and for the moisture content, and then specific figures are exposed for a better visualization of the values to be compared, both in terms of the three types of proposed trace and in terms of in relation to the areas of the bases. For samples under hydraulic interface, due to logistical issues, not all samples were tested during the same time. For the analysis of the results, it was established that it was 74 h, as it covered most of the samples and exceeded the minimum time of 72 h (3 days). Four samples from the T1M sample families (Trace 1 and medium size) and T2P (Trace 2 and small base area) did not have measurements at 74 h, for this reason a logarithmic regression was performed to predict the missing results for the analysis. During the curing of the mortar between the bricks that were previously saturated, the physical adhesion was compromised due to the filling of the pores by water, as was already expected for perfect contact. This phenomenon was evidenced when, after seven days of curing, it was possible to observe that the mortar layer came off the bricks in some samples, as shown in Fig. 9.

4.1 Material Results The results obtained provide information that helps to understand in more detail how the transfer of moisture by capillary rise occurs in multilayer materials, such as a masonry wall.

4.1.1

Ceramic Brick

To calculate the water absorption index, the standard NBR 15,270–3 (ABNT 2005b) was used, which indicates submersion of the bricks for 24 h in water at room temperature, until the mass is stabilized. To obtain a better statistical result, the test was performed in triplicate of the brick samples.

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• Water absorption index, saturation and density of ceramic bricks Figure 10 shows the variation of mass measurements as a function of the square root of time. The capillary absorption coefficient obtained was 0.13 kg/m2 .s0.5 . This value is in agreement with other values of this experiment and found in the literature, which vary between 0.05 and 0.29 kg/m2 .s0.5 . Brick saturation was measured for 96 h, and recorded every 24 h. The information collected from the three samples prepared for this test are described in Table 4. The density value obtained by the ceramic bricks was 1615.10 kg/m3 . The result for the water absorption index was 20%. The results of the tests carried out to characterize the bricks are summarized in Table 5.

Fig. 10 Capillary absorption curve (kg/m2 ) of brick samples as a function of the square root of time (t0.5 )

Table 4 Average saturation of bricks

Table 5 Physical–chemical properties of bricks

Time

Mass (mg)

Moisture content (%)

Starter (dry weight)

2222.8

0

24 h

2666.4

20

48 h

2670.5

20

72 h

2671.9

20

96 h

2672.0

20

Property ceramic brick Density (kg/m3 )

1615.1

Water Absorption Index (%) Capillary Absorption Coefficient

20 (kg/m2 s0.5 )

0.13

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Mortar

The mortars were composed of Portland cement CP V, hydrated lime, washed sand and distilled water, and three different proportions of materials were used, in order to maintain the water/dry materials ratio. • Water absorption index, saturation and density of mortars Figure 11 shows the results of the Trace 1 capillary absorption test for the five samples as explained in the experimental program. Table 6 shows the results for the saturation test of the mortar samples from Trace 1, as well as the observed moisture content. Figure 12 shows different results from those observed for Trace 1. The values for the average capillary absorption of the samples, observed for trace 2, are higher than those recorded in Trace 1. Table 7 has the results of the complementary saturation test performed on the mortar samples with trace 2.

Fig. 11 Capillary absorption curve (kg/m2 ) of Trace 1 samples as a function of the square root of time (t0.5 )

Table 6 Average saturation of Trace 1 samples

Time

Mass (mg)

Moisture content (%)

Starter (dry weight)

484.9

0

24 h

532.4

10

48 h

533.3

10

72 h

533.8

10

96 h

534.0

10

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Fig. 12 Capillary absorption curve (kg/m2 ) of Trace 2 samples as a function of the square root of time (t0.5 )

Table 7 Average saturation of Trace 2 samples

Time

Mass (mg)

Moisture content (%)

Starter (dry weight)

484.0

0

24 h

535.6

11

48 h

536.6

11

72 h

536.8

11

96 h

537.1

11

Figure 13 shows that the values obtained with Trace 3 are higher than those recorded for Trace 1. However, there is also a greater range of results among the samples analysed for this proportion of the mixture in relation to the with Trace 2. Table 8 presents the average saturation values of samples prepared with Trace 3 and tested for 4 days. The percentages of observed moisture contents are also reported. In summary, the mortars exhibited capillary absorption values for Traces 1, 2 and 3 were 0.10 kg/m2 s0.5 , 0.11 kg/m2 s0.5 and 0.12 kg/m2 s0.5 , respectively. The registered densities were 1888.6 kg/m3 , 1892.3 kg/m3 and 1870.3 kg/m3 , for traces 1, 2, and 3, respectively. The water absorption index values were 9.8%, 10.7%, and 11.2% for Traces 1, 2 and 3, respectively. The results of the tests performed to characterize the three types of traits are shown in Table 9.

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Fig. 13 Capillary absorption curve (kg/m2 ) of Trace 3 samples as a function of the square root of time (t0.5 )

Table 8 Average saturation of Trace 3 samples

Table 9 Properties of the tested mortars

Time

Mass (mg)

Moisture content (%)

Starter (dry weight)

483.5

0

24 h

537.5

11

48 h

538.5

11

72 h

538.7

11

96 h

539.1

12

Property

Trace 1

Trace 2

Trace 3

Consistency (mm)

126.68

128.93

127.62

Fresh density (kg/m3 )

2056

2080

2096

Hardened density

(kg/m3 )

1888.6

1892.3

1870.3

Water absorption index (%)

9.8

10.7

11.2

Capillary coefficient (kg/m2 s0.5 )

0.10

0.11

0.12

4.2 Hydraulic Interface Comparing the results obtained between the three types of traces, for samples with 5 cm × 5 cm bases, it is possible to verify that Trace 3 presents higher moisture flow

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Fig. 14 Cumulative flow of moisture (kg/m2 ) as a function of the time (t), for the three different traces using samples with dimensions of 5 cm × 5 cm base

values than the others. Trace 2 has the lowest results, with Trace 1 being intermediate between the other two curves, as presented in Fig. 14. Analysing the results for the three types of traces, and comparing the values of cumulative flow of moisture as a function of time, for the samples with a base of 7 cm x 7 cm, similar behaviours are observed. However, with the addition of the base area, the difference between the results for the three traces is reduced, reaching at a certain moment they overlap, obtaining the same or close values, as can be seen in Fig. 15. The overlap of values occurs between the curves representing Traces 1 and 3. Among the samples with larger base dimensions, of 10 cm × 1 cm, the results observed for the cumulative flow of moisture for the hydraulic interface showed a trend more similar to the smaller samples, of 5 cm × 5 cm. Thus, the samples with Trace 2 were the ones that presented the lowest results for the accumulation of moisture as a function of the characteristic exposure time. This is more obvious from Fig. 16. Comparing all the configurations of traces and dimensions of the bases present in the different samples for the interface with hydraulic interface, it is possible to observe that Trace 3 has the highest results of the cumulative flow of moisture as a function of time, for the small specimen. On the other hand, the samples with Trace 2, in the three dimensions studied, are the ones with the lowest cumulative flow of moisture at three days. Trace 1, with a lower proportion of fine aggregates in relation to cement, has lower results for smaller samples, as can be seen in Fig. 17.

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Fig. 15 Cumulative flow of moisture (kg/m2 ) as a function of the time (t), for the three different traces using samples with dimensions of 7 cm × 7 cm base

Fig. 16 Cumulative flow of moisture (kg/m2 ) as a function of the time (t), for the three different traces using samples with dimensions of 10 cm × 10 cm base

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Fig. 17 Cumulative flow of moisture (kg/m2 ) as a function of the time (t), for all experiments

Carrying out the comparative analysis between the three different areas for the same type of trace in the hydraulic interface, it is possible to observe from another perspective the variation of the cumulative flow of moisture as a function of time and, from that, to conjecture about the influencing parameters. For Trace 1, it can be observed that despite the results close to the medium and large samples, the smaller samples showed lower values than the others, indicating less accumulation of moisture, as can be seen in Fig. 18.

Fig. 18 Comparison of the cumulative flow of moisture (kg/m2 ) as a function of the time (t), between the areas of Trace 1

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Fig. 19 Comparison of the cumulative flow of moisture (kg/m2 ) as a function of the time (t), between the areas of Trace 2

The results obtained for Trace 2 are interesting when compared with the others, because for this proportion of the mortar mixture, values very close to the cumulative flow of moisture as a function of time can be visualized. This occurs for the three different dimensions of the bases, indicating that there may be an ideal value for the proportions of the mixtures in the mortar composition, which would not depend on the area exposed to moisture. This trend can be seen in Fig. 19, and it is important to note that the values per se reach 25 kg/m2 at approximately three days (72 h), which can be considered low in relation to those observed in the other traits. Unlike an intuitively expected linear result, when compared to the other traces, the proportions of the mixture called Trace 3 have a greater similarity of the results in relation to Trace 1 than Trace 2. The values obtained are greater than 25 kg/ m2 , reaching to be close to the 35 kg/m2 observed in samples with smaller base dimensions, mainly 5 cm × 5 cm. On the other hand, samples with larger base dimensions, 10 cm × 10 cm, showed lower cumulative moisture flow, being less than 30 kg/m2 observed after three days. The curves shown in Fig. 20 provide a better visualization of this physical behaviour of the analysed ceramic material. It is important to analyse the moisture contents between the different traits so that a better correlation can be obtained on which are the determining parameters that contribute to the transport of moisture, and thus to be able to establish the criteria related to the resistance of the interface. Figure 21 presents the results of the moisture contents for Trace 1 considering the samples in the three base dimensions studied. The smaller volume samples had the highest moisture content value compared to the intermediate samples, which in turn were larger than the wider-based samples. This can lead to the understanding that there is a direct relationship between the area of the base exposed to moisture and the

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Fig. 20 Comparison of the cumulative flow of moisture (kg/m2 ) as a function of the time (t), between the areas of Trace 3

moisture content that the sample will present under specific conditions. The minimum moisture content was 2070.30 kg/m3 for the large samples, and the maximum was 2321.54 kg/m3 for those with a smaller base area. The moisture content observed for the samples made with Trace 2 had similar relationships between the different areas of the bases, presenting higher results for

Fig. 21 Moisture content (kg/m3 ) between samples with Trace 1

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Fig. 22 Moisture content (kg/m3 ) between samples with Trace 2

the small samples in relation to the intermediate ones, which in turn also showed higher values than those observed in the large samples. The larger samples showed moisture content values on average of 1959.9 kg/m3 , and these results are lower than those presented by the samples of the same dimensions, but prepared with the mortar of Trace 1. Figure 22 shows moisture content data for Trace 2. For Trace 3 the results can be considered better than those obtained by Traces 1 and 2, when small and medium samples are observed. However, the large samples of Trace 3 showed higher results of moisture content compared to the samples made with the mortar of Trace 2. The large samples showed an average value of moisture content equal to 1976.8 kg/m3 , which is superior to the same samples with Trace 2. The average results obtained by the samples of Trace 3 in the hydraulic interface for the moisture contents are shown in Fig. 23. It facilitates the visualization of the moisture contents from an analysis of the different traces in comparison using the same area of the base for the samples. This type of analysis allows the results to be seen for the same trace in different samples, observing the variations in the data. It is also possible to compare the data among the three graphs that will address these results. Figure 24 presents the average values obtained with the samples with a base area equal to 5 cm × 5 cm prepared with the three types of trace. It is possible to see that Trace 1 was the one that obtained the highest average value of moisture content among the analysed samples, having been equal to 2321.5 kg/m3 . The small samples with Trace 2 obtained an average value of moisture content equal to 2248.9 kg/m3 . In turn, the samples made with Trace 3, for these proposed dimensions, were the ones that showed the lowest average value, being equal to 2196.2 kg/m3 . The samples with average dimensions, 7 cm × 7 cm, showed lower values than the others with smaller areas, specially if proportionally compared between the three traces for the results obtained among themselves. The medium samples cast with Traces 2 and 3 showed lower moisture content results than the values of the small

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Fig. 23 Moisture content (kg/m3 ) between samples with Trace 3

Fig. 24 Moisture content (kg/m3 ) between 5 cm × 5 cm CP’s

samples. The average sample results for Traces 1, 2, and 3 are shown in Fig. 25 and are equal to 2206 kg/m3 , 2115 kg/m3 , and 2092.1 kg/m3 , respectively. The data obtained by the large samples in relation to the average moisture content were the lowest among the three dimensions of analysed areas, and can be seen in the Fig. 26. The moisture content of 2070.3 kg/m3 observed for these samples when made with Trace 1 was lower than the lowest result presented by the small samples with Trace 3. On the other hand, in this analysis it is possible to visualise that Trace 2 has a lower moisture content value when compared to Trace 3. This behaviour differs from the other two analyses observed in small and medium samples.

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Fig. 25 Moisture content (kg/m3 ) between 7 cm × 7 cm CP’s

Fig. 26 Moisture content (kg/m3 ) between 10 cm × 10 cm CP’s

The results for the hydraulic interface showed that the samples with Trace 2 have a lower cumulative flow of moisture, and showed lower moisture contents after three days.

4.3 Perfect Contact In addition to the contact interface with previous saturation called hydraulic interface, samples whose faces were dry were also analysed, allowing the flow of water of

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Fig. 27 Comparison of the cumulative flow of moisture (kg/m2 ) as a function of the time (t), for different traces with dimensions 5 cm × 5 cm

hydration of the mortar along with the fines, percolating through the open pores of the ceramic material. Figure 27 shows the results of cumulative moisture flow as a function of time for samples with base dimensions equal to 5 cm x 5 cm for perfect contact. At the end of the three-day period (74 h), Trace 3 showed the highest readings, approximately 35 kg/m2 . Traces 1 and 2 showed similar performance with experimental results of approximately 30 kg/m2 . The performance of the average samples, with base dimensions equal to 7 cm by 7 cm, showed very similar results for the three different types of trace studied, with the values of the curves shown in Fig. 28 being in line. The results were slightly higher with a value of 30 kg/m2 . The large samples, with base dimensions equal to 10 cm × 10 cm, showed a very similar performance to the other samples, and presented values between 30 kg/m2 and 35 kg/m2 , as can be seen in Fig. 29. When comparing all the samples configurations, which are made by grouping the three types of trace and the three different base dimensions of the samples, it is possible to better visualize the performances. It is then possible to verify that the T3Ptype samples, that is, prepared with Trace 3 and with smaller base dimensions, are the ones that presented the highest values of cumulative moisture flow as a function of time. It is also possible to observe that the samples made with Trace 1 were the ones that obtained the lowest values of this transport of accumulated moisture. Figure 30 shows the nine sample configurations and the respective cumulative moisture flux values as a function of time. In this section, an analysis of the three types of traces in comparison of the different areas of the bases was also carried out for the perfect contact, as well as for the hydraulic interface. For Trace 1, it is possible to see in Fig. 31 that the smaller

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Fig. 28 Comparison of the cumulative flow of moisture (kg/m2 ) as a function of the time (t), for different traces with dimensions 7 cm × 7 cm

Fig. 29 Comparison of the cumulative flow of moisture (kg/m2 ) as a function of the time (t), for different traces with dimensions 10 cm × 10 cm

samples obtained lower cumulative flow values as a function of time than the large base samples. For Trace 2, Fig. 32 shows that the performances of the smaller samples were better at the end of the 72 h study period, however the samples with the lowest base showed an atypical behaviour when compared to the other graphs. Although at the

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Fig. 30 Cumulative flow of moisture (kg/m2 ) as a function of the time (t), for all experiments

Fig. 31 Cumulative flow of moisture (kg/m2 ) as a function of the time (t), of samples from different areas with Trace 1

end of the three days the results obtained between the medium and small samples were close, in the first 24 h the cumulative flow of moisture in the samples was much higher than that presented by the medium samples. For Trace 3, it is possible to see in Fig. 33 that the larger samples were the ones that showed the lowest values of cumulative moisture flow as a function of time. These results lower than those obtained by the smaller specimen, of approximately 35 kg/m2 at the end of the analysis period.

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Fig. 32 Cumulative flow of moisture (kg/m2 ) as a function of the time (t), of samples from different areas with Trace 2

Fig. 33 Cumulative flow of moisture (kg/m2 ) as a function of the time (t), of samples from different areas with Trace 3

In order to better visualize the performance of the samples, analyses of the average moisture contents were also carried out for each type of trace as a function of the dimensions of the sample bases. In Fig. 34 it is possible to visualize the results obtained by the samples of Trace 1 in the three configurations of the bases. It is possible to observe that the average samples had lower moisture content results than the other two, with the small base sample the one that presented the highest value among the three analysed, equal to 2023.5 kg/m3 .

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Fig. 34 Moisture content (kg/m3 ) between samples with Trace 1

The results observed for Trace 2 showed that the samples with the largest base dimension were the ones that had the lowest moisture content among the three different areas analysed, being equal to 1929.6 kg/m3 . Figure 35 also shows that the samples with the smallest area of the base were the ones that obtained the highest value of moisture content at the end of the analysis period, being equal to 2072.6 kg/ m3 . Figure 36 shows the results obtained for the samples with the perfect contact in the three base dimensions studied, and using the mixture of Trace 3. It is possible to verify that for this trace the results obtained by the medium and large samples had values very close to 1903.4 kg/m3 and 1905.7 kg/m3 , respectively. The small base area sample obtained moisture content results for Trace 3 equal to 1977.9 kg/m3 .

Fig. 35 Moisture content (kg/m3 ) between samples with Trace 2

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Fig. 36 Moisture content (kg/m3 ) between samples with Trace 3

Another point of view can be adopted by comparing the three types of trace in relation to a single area of the base, so that it is possible to have a visualization of the moisture content of the samples as a function of their dimensions for the same mixture. Figure 37 presents an analysis for the samples with base dimensions equal to 5 cm × 5 cm, with the three studied traits, and under the type of perfect contact. It is possible to verify that Trace 3 obtained the lowest result for the moisture content at the end of 72 h, equal to 1977.9 kg/m3 . Trace 2 had a result equal to 2072.6 kg/ m3 , which is the highest value among the three traces analysed for the same base dimension.

Fig. 37 Moisture content (kg/m3 ) between 5 cm × 5 cm CP’s

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A different behaviour was observed in the analysis of the average samples, with base dimensions equal to 7 cm x 7 cm. Trace 1 showed the lowest moisture content value in the period, equal to 1888.2 kg/m3 , this result being lower than the 1903.4 kg/ m3 recorded for trace 3. The highest value observed for the average samples under this analysis was of the samples with Trace 2, being equal to 1976.3 kg/m3 , as can be seen in Fig. 38. The moisture content observed for the large samples, with base dimensions equal to 10 cm x 10 cm, is shown in Fig. 39, and allows the visualization of the results for these samples of larger base area in relation to the three types of traces and under perfect contact. It is then verified that Trace 3 obtained the lowest result of moisture content equal to 1905.7 kg/m3 , on the other hand, the highest value observed was for Trace 1 equal to 1939.4 kg/m3 .

Fig. 38 Moisture content (kg/m3 ) between 7 cm × 7 cm CP’s

Fig. 39 Moisture content (kg/m3 ) between 10 cm × 10 cm CP’s

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Unlike the last two analyses demonstrated for the medium and small samples, in the case of large samples it was found that Trace 2 did not obtain a higher moisture content, recording 1926.6 kg/m3 .

4.4 Comparison Between Hydraulic Interface and Perfect Contact A summary of the results obtained in the analyses of the cumulative flow of moisture of the samples with hydraulic interface, for the three different traces and dimensions of the areas of the bases, is shown in Fig. 40. It is possible to verify that the highest value of humidity per cumulative flow was 40.3 kg/m2 and it was observed for the samples of Trace 3 and with small area, of dimensions 5 cm × 5 cm. It is demonstrated that the lowest value was obtained by the samples of Trace 2 and also with the smallest area of the base, being equal to 23.4 kg/m2 , which corresponds to a little more than half of what was verified by the small specimen and trace 3. Trace 1 showed lower cumulative moisture flux results than compared to the values observed in Trace 3. Analysing the average moisture content for each base dimension of the samples and the three types of traces, it is possible to observe that the highest value obtained was for the samples with Trace 1 and with a small base area. For this sample, the average moisture content was 2321.5 kg/m3 . The lowest value observed was for Trace 2 with the largest area of the base, 10 cm × 10 cm, being approximately equal to 1960 kg/m3 . The results obtained by Trace 3 also presented significant relatively low data, mainly for the larger samples of the base, as can be seen in Fig. 41.

Fig. 40 Cumulative flow of moisture (kg/m2 ) as a function of the time (t), for all configurations for hydraulic interface

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Fig. 41 Moisture content (kg/m3 ) of all configurations for hydraulic interface

Analysing all nine sample configurations under the aspect of perfect contact, it is possible to visualize which ones had the highest and lowest values as results. Figure 42 allows us to verify that the small sample with Trace 2 was the one that obtained the highest moisture content result among the study, equal to 2072.6 kg/ m3 . The lowest result was verified for the average specimen made with Trace 1 being equal to 1888.2 kg/m3 . The cumulative flow of moisture in the studied period of 72 h for the nine sample configurations can be seen in Fig. 43 and allows to observe similar performances for some cases of the same trait, and also opposites or inverses between two others. It is possible to verify that the samples with Trace 1 obtained low and very approximate

Fig. 42 Moisture content (kg/m3 ) of all configurations for perfect contact

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Fig. 43 Cumulative flow of moisture (kg/m2 ) of all configurations for perfect contact

values for the small and medium samples, being equal to 30.9 kg/m3 and 30.8 kg/ m3 , respectively. In Trace 2, it can be seen that the lowest result of moisture content was observed in the specimen with a smaller area, equal to 30.7 kg/m3 , which is also the lowest value among the nine configurations of samples analysed under perfect contact. Trace 3, contrary to the aforementioned one, showed lower results for the large models, however, still superior to those seen in the other two traces.

4.5 Resistance Values Using the methodologies described in Sect. 3.4, hygric resistance values were calculated for all samples configurations, using both methodologies. Table 10 and Fig. 44 bring the results of the calculations development, both for the hydraulic interface and for the perfect contact. Among the values calculated for the hygric resistances of the nine configurations of the samples, and for both types of interface contact, the smallest and greatest results can be highlighted. T3M sample, with Trace 3 and average dimensions of 7 cm x 7 cm, under the type of hydraulic interface, was the one that obtained the highest result of hygric resistance in the two calculation methodologies, being equal to 7.46 × 10–5 kg/m2 s with the previous methodology and 3.74 × 10–5 kg/m2 s with the new methodology. The lowest value observed was from the T2P sample, with Trace 2 and small dimensions of the base area equal to 5 cm × 5 cm. However, when using the previous calculation methodology, the lowest value was recorded under the type of hydraulic interface, and when using the new methodology, perfect contact

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Table 10 Hygric resistance for the nine configurations of the samples in relation to the dimensions of the bases and traces used, and also the type of interface contact Interface

Dimensions

Trace

Hygric resistance—PM

Hygric resistance—NM

Hydraulic interface

5 cm × 5 cm

1

4.60 × 10–5

2.02 × 10–5

2

4.39 × 10–5

1.98 × 10–5

3

5.35 ×

10–5

1.74 × 10–5

1

6.63 ×

10–5

2.85 × 10–5

2

4.86 × 10–5

1.77 × 10–5

3

7.46 ×

10–5

3.74 × 10–5

1

7.19 ×

10–5

3.11 × 10–5

2

5.16 × 10–5

2.41 × 10–5

3

6.61 ×

10–5

2.66 × 10–5

1

6.79 ×

10–5

2.65 × 10–5

2

6.02 × 10–5

1.10 × 10–5

3

7.36 ×

10–5

2.66 × 10–5

1

7.28 ×

10–5

2.52 × 10–5

2

6.30 × 10–5

2.39 × 10–5

3

6.63 ×

10–5

2.92 × 10–5

1

7.00 × 10–5

3.00 × 10–5

2

7.28 ×

10–5

3.11 × 10–5

3

6.64 ×

10–5

2.62 × 10–5

7 cm × 7 cm

10 cm × 10 cm

Perfect contact

5 cm x 5 cm

7 cm × 7 cm

10 cm × 10 cm

Fig. 44 Comparison between the values of hygric resistance, a hydraulic interface PM; b; hydraulic interface NM c perfect contact PM and d perfect contact NM

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got the lowest result. This specimen recorded a hygric resistance equal to 4.39 × 10–5 kg/m2 s (PM) and 1.10 × 10–5 kg/m2 s (NM). Furthermore, it is possible to notice that using the new methodology the resistance values are 2–3 times smaller than the values calculated with the previous methodology. However, in the case of very small values, they maintain the same order of magnitude and therefore are mathematically close values.

5 Conclusions This research work provided the visualization of the effect of the interface resistance in masonry samples of ceramic brick and mortar, for the transport of capillary moisture. From the analysis of the results obtained with the experimental program, it is possible to show that for both cases analysed, i.e., perfect and hydraulic interface, the hygric resistance has very close values, ranging from 4.0 × 10–5 kg/m2 s and 8.0 × 10–5 kg/m2 s in the first calculation methodology and between 1.0 × 10–5 kg/m2 s and 4.0 × 10–5 kg/m2 s in the second calculation methodology. When comparing the traces in relation to the areas of the bases, there is a decrease in the moisture content and the flow from Trace 1 to Trace 2, suggesting that the samples with Trace 1 absorb more water than those with Trace 2. However, comparing samples with traces 2 and 3, it is possible to observe an increase in the moisture content and in the cumulative flow of the samples, indicating that Trace 3 absorbs more water than Trace 2. It was expected that the higher the proportions for the trace of the mortar, the greater would be the transport of moisture and the amount of water absorbed. Under the analysis of only the hydraulic interface, that is, in which there is an interpenetration of the pores, the samples of smaller areas of the base, of 5 cm × 5 cm, as well as those of area equal to 7 cm x 7 cm, having the bodies of proof with trace 3 were the ones that most absorbed water. Different performance from that observed for samples with a base equal to 10 cm × 10 cm. In samples with a greater base area, the weak trace (Trace 3) absorbs less water than the strong trace (Trace 1) but transports more water than the medium trace (Trace 2). When comparing the different areas of the specimen bases for each trace, in all cases the absorption (moisture content) of water increases as the area is increased. In all cases, the average trace (Trace 2) is the one with the lowest absorption and lowest fluxes.

References ABNT (1992) Brazilian association of technical standards. NBR 8042: ceramic block for masonry— shapes and dimensions. Rio de Janeiro, Rio de Janeiro

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ABNT (1998) Brazilian association of technical standards. NBR 7200: execução de revestimento de paredes e tetos de argamassas inorgânicas—procedimento. Rio de Janeiro ABNT (2013) Brazilian association of technical standards. NBR 15575: residential buildings— performance. Rio de Janeiro, Brazil ABNT (1992) Brazilian association of technical standards. NBR 7171: ceramic block for masonry. Rio de Janeiro, Rio de Janeiro ABNT (2005) Brazilian association of technical standards. NBR 13278: Mortar for laying and coating walls and ceilings—determination of mass density and incorporated air content. Rio de Janeiro, RJ ABNT (2005b) Brazilian association of technical standards. NBR 15270–3: Ceramic components. Part 3: ceramic blocks for structural and sealing masonry—test methods. Rio de Janeiro, RJ: . Disponível em: www.abnt.org.br ABNT (2016) Brazilian association of technical standards. NBR 13276: mortar for laying and coating walls and ceilings—determination of consistency index. Rio de Janeiro, RJ Alves CET, Trindade de DCAC (2012) Custos da qualidade: análise da estrutura e componentes dos custos da qualidade. [S. l.: s. n.] Azevedo AAC (2019) Interface influence on moisture transport in building components. Ph.D. Thesos, FEUP, Porto, Portugal. Available in: http://www.fe.up.pt Bauer LAF, Building materials, vol 2, 5th edn. Rio de Janeiro, LTC, Brazil, 994 Brocken HJP, Adan OCG, Pel L (1997) Moisture transport properties of mortar and mortar joint: a NMR study. Heron [s. l.] 42(1):55–69 Charola AE (2000) Salts in the deterioration of porous materials: an overview. J Am Inst Conserv [s. l.] 39(3):327–343 Depraetre W, Carmeliet J, Hens H (2000) Moisture transfer at interfaces of porous materials: measurements and simulations. [S. l.: s. n.] Derluyn H, Janssen H, Carmeliet J (2011) Influence of the nature of interfaces on the capillary transport in layered materials. Constr Build Mater 25(9):3685–3693 Freitas V, Peixoto MA (1992) Moisture transfer in building walls—interface phenomenon analysis. Ph.D. Thesis, Faculty of Engineering, Porto, Portugal Freitas V, Peixoto, Guimarães AS (2014) Treatment of ascensional moisture in historical heritage. Revista ALCONPAT, [s. l.] 4:1–12 Freitas VP, Abrantes V, Crausset P (1996) Moisture migration in building walls—analysis of the interface phenomena. Build Environ [s. l.] 31(2):99–108 Gonçalves TCD (2007) Salt crystallization in plastered or rendered walls. Ph.D. Thesis, Lisboa, Portugal Guimarães AS et al (2018) Interface influence on moisture transport in buildings. Construct Build Mater [s. l.] 162:480–488 Hentges G (2014) Influence of porosity of ceramic bricks on the emergence of pathologies due to rising humidity. Alegrete/RS ISO (2002) International organization for standardization. ISO 15148: hygrothermal performance of building materials and products—determination of water absorption coefficient by partial immersion, Geneva. https://standards.iteh.ai/catalog/standards/sist/5ab182e2-a7ad-428c-87e140fe97b42300/iso-15148-2002 IUPAC (1994) International union of pure and applied chemistry. Recommendations for the characterization of porous solids. [S. l.: s. n] Janssen H, Derluyn H, Carmeliet J (2012) Moisture transfer through mortar joints: a sharp-front analysis. Cement Concrete Res [s. l.] 42(8):1105–1112 Rego TSMR (2014) Effect of saline aqueous solutions on the soaking processes of walls with multiple layers. MSc. Thesis, FEUP, Porto, Portugal. Available in: http://www.fe.up.pt Rijniers LA et al (2005) Experimental evidence of crystallization pressure inside porous media. Phys Rev Lett [s. l.] 94(7) RILEM (1998) Rilem technical committees. TC 127-MS: tests for masonry materials and structures. Mater Struct [s. l.] 31:2–119

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Straube JF (2002) Moisture in buildings. ASHRAE J [s. l.]. Available in: https://www.researchgate. net/publication/271706272 Turner F (2002) Moisture and Mold. ASHRAE J [s. l.] Vereecken E, Roels S (2013) Hygric performance of a massive masonry wall: how do the mortar joints influence the moisture flux? Constr Build Mater 41:697–707

Electrical Model of a Bulk Concrete and Analysis of Its Frequency-Dependent Electrical Resistivity C. E. T. Balestra, A. Y. Nakano, G. Savaris, F. W. D. Pfrimer, and R. Schneider

Abstract Electrical resistivity (ER) becomes an essential tool for decision- making by managers responsible for plans and strategies for concrete structures maintenance. ER is a non-destructive technique for evaluating reinforced concrete structures, mainly regarding reinforcement corrosion risk due to its easy operation, reliability, and quick and low-cost results. Although ER is a widely used technique, little clear information is discussed in the literature regarding the concrete role as an electrical circuit component. Thus, this chapter presents concepts about circuit types applied to understand electrical resistivity and a comprehensive analysis regarding the concrete role in different electrical circuit types. The main parameters that most influence concrete resistivity are discussed. Keywords Electrical resistivity · Reinforced concrete structures · Reinforcement corrosion · Non-destructive tests · Service life · Durability

C. E. T. Balestra (B) · A. Y. Nakano · G. Savaris · F. W. D. Pfrimer · R. Schneider Federal University of Technology—Paraná, Toledo, Brazil e-mail: [email protected] A. Y. Nakano e-mail: [email protected] G. Savaris e-mail: [email protected] F. W. D. Pfrimer e-mail: [email protected] R. Schneider e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 J. M. P. Q. Delgado (ed.), Concrete Structures: New Trends and Old Pathologies, Building Pathology and Rehabilitation 27, https://doi.org/10.1007/978-3-031-38841-5_3

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1 Introduction The adoption of less invasive techniques to structures, known as non-destructive tests (NDT), has been one of the main lines of research regarding the service life of concrete structures since these techniques allow obtaining quick, reliable, and easy results to evaluate and help the decision makers about the maintenance or rehabilitation actions. Thus, concrete’s electrical (ionic) resistivity and its correlation with probable reinforcement corrosion risk is one of the main used non-destructive techniques to evaluate field structures (Mehta and Monteiro 2006; Balestra et al. 2019; Akhtar and Sarmah 2018; Neville and Brooks 2010; Nguyen et al. 2017, 2018; Chen et al. 2014; Sengul 2014). Electrical resistivity (or, in this case, of concrete, ionic resistivity) is an intrinsic characteristic of the material, related to its ability to oppose the passage of electrical current, governed by Ohm’s law. When the material is subjected to a potential difference, an electric current characterized by the free flow of electrical charges is established. In this way, free electrons collide with each other and against atoms of the conductor, making the passage of electric current difficult, called electrical resistance (Nguyen et al. 2017, 2018; Chen et al. 2014; Sengul 2014). Concrete can present different electrical resistivity values depending on the degree of pores saturation, cement type, water/binder ratio, reinforcement characteristics, and others. However, the moisture present in the pores is one of the main parameters since it can act as a complex material, with electrical resistivity of the order of up to 102 Ω m, whereas, when dried in a kiln, the electrical resistivity can be of the order of 109 Ω m (Neville and Brooks 2010). Although concrete electrical resistivity has been used as NDT to evaluate field structures, little clear information regarding circuit concepts and concrete’s role are presented in the literature. In this sense, this chapter fits in this gap, aiming to analyse and elucidate the concrete’s role in different electrical circuits in a comprehensive way.

2 Resistor–Capacitor Circuit Figure 1 presents a resistor–capacitor (RC) circuit with a power supply v(t) with a small internal resistance (rs) connected to a discharged capacitor (C). A capacitor is an element that stores energy in the electric field between its conductive plates (Nguyen et al. 2018; Chen et al. 2014; Sengul 2014; Andrade and Alonso 1996; Cabeza et al. 2002; Hu et al. 2019; Liu et al. 2015; Wang et al. 2022; Xie et al. 1993). The output v(t) can be modelled by a first-order linear differential equation whose solution is given by Eq. (1).   t vo (t) = 1 − e− r vs (t)

(1)

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Fig. 1 RC circuit

in volts (V ) where r = rsC is the time constant. The lower r, the faster the capacitor’s charging or discharging. For t = r, v(τ ) ≈ 0.632vs (τ ), which means that the capacitor is 63.2% charged, and after 5r, the capacitor is almost fully charged. Focusing on DC analysis, assuming v(t) = u(t), the Heaviside step function define by { u(t) =

0, t < 0 , 1, t > 0

Figure 2 presents charging curves considering rs = 100 Ω and some arbitrary capacitance values. As can be seen, the intersection of each curve with 0.632 V level gives the r, and the capacitance can be experimentally estimated by the charging curve by Eq. (2). C=

c rs

(2)

in faradays (F). The capacitor current (t) can be determined by Eq. (3) i (t) = C

d vs (t) − t vo (t) = e r dt rs

(3)

in amperes (A) which tends to zero as the capacitor charges, as seen in Fig. 3. It is important to note that the same current flows in all circuit elements. However, in rs current is observed due to free charges, and inside the capacitor, the actual current is modelled by the displacement current. As long as the electric field varies inside the capacitor, there will be displacement current. Once the capacitor is fully charged, the internal electric field no longer varies, and the circuit reaches its steady state with no more current. This brief discussion helps to understand the RC circuit and voltage and current characteristics of a capacitor in DC analysis. On AC analysis, the same circuit models

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Fig. 2 Capacitor charging curves considering rs = 100 Ω

Fig. 3 Capacitor displacement current curves considering rs = 100 Ω

a low-pass filter showing frequency-dependent features. Thus, this simple electrical model with some considerations will be used to understand how the electrical bulk resistivity of concrete changes over frequency in a two-plate measurement setup.

3 Electrical Model of a Two-Plate Configuration The configuration to measure the concrete bulk resistivity is illustrated in Fig. 4a, where two conductive plates are attached to the extremities of the concrete specimen. The resistance between the plates is estimated by the ratio of the voltage at the voltmeter and the current at the ammeter. Figure 4b presents an initial electrical

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Fig. 4 Resistivity measurement. a setup; b concrete basic electrical model; c concrete electrical model considering polarization; d concrete model considering polarization in DC analysis after reaching steady-state; e concrete model considering measurement in high frequency

model based only on the electrical resistance of the specimen Rsp and the electrode ohmic resistance r. It is reasonable to consider rx « Rsp, so the ratio of vo at the voltmeter by i at the ammeter in a cylindrical specimen with cross-section S and height h is given by Eq. (4). h vo = ρ ≈ Rsp i s

(4)

where Rsp is given in ohms (Ω), and resistivity (ρ) is given by Eq. (5). ρ=

vo S i h

(5)

in Ω m is the bulk electrical resistivity of the concrete. Note that the polarization effect in the specimen and the conductive plates are not considered. The accumulation of charges on the surface of the conductive plates due to the power supply generates an electric field between them, inducing bound charges in the specimen and causing the polarization of the concrete in the same way as occurs in the capacitor dielectric. Additionally, concrete is a mixture of several elements,

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and it has ions and free charges in its composition, which are responsible for some conduction or convection currents. Thus, at the setup, the specimen can be seen as a dielectric with permittivity ε due to polarization and a material with electrical resistivity ρ due to the flow of charges. Therefore, the electric model of the concrete can be described by the polarization effect modelled by a capacitance C and by an electrical resistivity modelled by the resistance Rsp, as seen in Fig. 4c. It is worth noting that the ρ is due to Rsp, but its experimental determination can be compromised by the dielectric polarization where the displacement current is observed. Then, DC and AC theoretical analyses were performed to understand the polarization effect in determining electrical resistivity. In this study, the impact of the polarization is separated from the resistivity in a linear electrical model, as illustrated in Fig. 4c.

3.1 DC Analysis In the model in Fig. 4c, C is unknown, so it needs to be estimated. Taking only C as the load in the circuit, Fig. 5 presents the Thévenin equivalent model. The Thévenin-equivalent resistance and Thévenin-equivalent voltage source are presented, respectively, in Eqs. (6) and (7). RT H = (r S + r x )//Rsp =

(rs + r x )Rsp (rs + r x ) + Rsp

Rsp  VT H =  vs rs + r p + Rsp

(6) (7)

The Thevénin equivalent model is similar to the RC circuit presented in Sect. 3, but vC is given by Eq. (8).   t vc(t) = 1 − e− r VT H Fig. 5 Thevénin model

(8)

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which tends to VTH as t tends to ∞. Considering rx « rs < (rs + r) « Rsp, RTH in Eq. (6) can be simplified to RTH ≈ r s . By Fig. 4c, VTH is the open-circuit voltage, and considering rx « Rsp, it is approximately the measured voltage by the voltmeter after the circuit reaches steadystate, as presented in Fig. 4d. Therefore, the capacitance can be estimated by Eq. (9). C=

c RT H

(9)

where r can be determined by the charging curve vC(t) (or vo(t) in Fig. 4c). The capacitance or, equivalently, the permittivity ε describes the level of polarization and for parallel conductive plates of area S separated by h (considering the height of the concrete specimen), the capacitance is given by Eq. (10). C =ε

S h

(10)

which shows that the stronger the dielectric polarization, the greater the capacitance, which can affect the resistivity estimation. Equation (10) is a reasonable estimate when h is much less than the diameter of S or when the electric field is wholly confined between the parallel plates. In DC analysis, the dielectric polarization causes the capacitor to be modelled by an open circuit in steady-state, as seen in Fig. 4d, so all charges flow to Rsp and none to C. In this case, i = iR and vo/iR leads to Eq. (4), and the resistivity can be estimated by Eq. (11). ρ=

vo S iR h

(11)

3.2 AC Analysis In AC analysis, frequency-dependent characteristics are observed. The specimen impedance (s) in the electrical model presented in Fig. 4c, considering the joint effect of polarization and resistivity using a sinusoidal input signal, is modelled in the s-domain by Laplace transform as Eq. (12). Z (s) = Rsp //

Rsp 1 = sC Rsp Cs + 1

(12)

Where 1/ sC represents the capacitive impedance, and W (s) = Z(s) + r x , considers the electrodes’ contribution to the impedance. A voltage divider can describe the output voltage as Eq. (13).

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Vo (s) =

W (s) Vs (s) W (s) + Rs

(13)

where Vs (s) and Vo (s) are, respectively, the representation of vs(t) and vo(t) in sdomain. The transfer function is given by Eq. (14). H (s) =

W (s) v0 (s) = vs (s) W (s) + rs

(14)

that will lead to Eq. (15).   r x Cs + 1 + Rrspx   H (s) = x) (rs + r x )Cs + 1 + (rsR+r sp

(15)

Ordinarily, rx « (r + rx) « Rsp, so Eq. (15) can be approximated by Eq. (16). H (s) =

r x Cs + 1 (rs + r x )C S + 1

(16)

Substituting s = jω the frequency response, which describes the ratio of the output voltage by the input source in the frequency domain, will be given by Eq. (17). H (ω) =

j ωr x C + 1 j ω(rs + r x )C + 1

(17)

where ω = 2πf is the angular frequency whose cut-off frequency fc is given by Eq. (18) in hertz (Hz). fc =

/

1

(18)

2π C (rs + r x )2 − 2r x2

Figure 6 presents the low-pass characteristic of |(ω)| considering rs = 100 Ω, rx = 1 Ω, and arbitrary capacitance values. The higher the polarization, the higher the capacitance and the lower the cut-off frequency. Additionally, the higher the frequency for a given polarization case, the higher the possibility that the polarization can influence (s) and, consequently, affect the resistivity estimation. By the electrical model presented in Fig. 4c, it is easy to show that the ratio of V0 (s) and I(s) is given by Eq. (19). V0 (s) = W (s) I (s)

(19)

where Vo (s) and I(s) are s-domain representation of vo(t) and i(t), respectively. To check the frequency dependency, we substitute s = jω obtaining Eq. (20) and, finally,

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Fig. 6 Frequency responses considering rs = 100 Ω and rx = 1 Ω

the resistivity can be determined by Eq. (21). W (ω) =

R Sp Vo(ω) = rx + I (ω) j ω Rsp C + 1 | | | Vo (ω) | S | | ρ(ω) = | I (ω) | h

(20) (21)

| | | (ω) | where | VIo(ω) | is the ratio of the values measured by the voltmeter and ammeter in AC scale. In Eq. (20), as the frequency increases, the second term on the right- hand side decreases, (ω) tends to zero, and W (ω) converges to rx. This effect can be noted in Fig. 4e, where the capacitance is equivalent to a short circuit in parallel with Rsp. Figure 7 presents the magnitude of (ω) given by Eq. (20) considering Rsp = 104 Ω, rx = 1 Ω, and arbitrary capacitance values. As expected, the electrical resistance Rsp is dominant in low frequencies observed in the plateau in Fig. 7. However, as frequency increases, the capacitive reactance decreases, reducing the total impedance (ω). Thus, the lower the polarization or, the lower the capacitance, the lower the error in the resistivity estimation. Considering an actual cylindrical concrete specimen dimension (height of 20 cm and radius of 5 cm), Fig. 8 presents the electrical resistivity variation given by Eq. (21) considering Rsp = 104 Ω, rx = 1 Ω, and arbitrary capacitance values. The higher the polarization effect, the lower it will be (ω) so the measured frequency must be defined to consider it. For comparison purposes, a parallel plate capacitor with a height of 20 cm and radius of 5 cm with air as dielectric, εair ≈ ε0 , has a capacitance given by Eq. (22). C0 = εair πr 2 / h ≈ 0.34 p F

(22)

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Fig. 7 ||W (ω)| versus frequency considering Rsp = 104 Ω and rx = 1 Ω

which is the theoretical lower bound presented in Figs. 7 and 8. In the same conditions, the theoretical resistivity considering Rsp = 104 Ω should be given by Eq. (23) ρ = Rsp πr 2 / h ≈ 392.5 Ω m

(23)

which is the value indicated in the plateau in Fig. 8. On the one hand, if an operator uses a 10 Hz sinusoidal source to estimate the resistivity using Eq. (21), the specimen should have at most 1 μF to get a reliable result. On the other hand, in low-frequency measurement, for instance, at 0.01 Hz, the operator does not need to focus on the polarization effect to obtain a reasonable estimate of the resistivity. Fig. 8 Resistivity versus frequency considering Rsp = 104 and rx = 1 Ω

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4 Discussion This study used a simplified model based on electromagnetic and electric circuit theory to explain the frequency dependency of the concrete bulk resistivity. The study was not focused on the solid interface, pore (liquid) interface, or solid- liquid interfaces of the concrete system but assumed that the overall system was a material where an electric current can be observed under the effect of an electro- magnetic field created by a power supply. Based on the experimental setup, the material between two conductive plates can be viewed as a dielectric with some resistivity that takes us to the model with parameters {r, Rsp, C} illustrated in Fig. 4c. The component Rsp indirectly models the resistivity, the component rx models the conductive plates, and the capacitance component C models the dielectric. Hence, the objective was to estimate Rsp and, consequently, the resistivity ρ. The internal resistance rs of the power supply can influence the measurement of v(t). Figure 6 shows that the system has a low-pass characteristic, and the cut- off frequency defined in Eq. (18) is dependent of r. So, it is essential that, rx « rs « Rsp, to guarantee that v(t) has a measurable value within the measurement scale. Note that with increasing frequency, more attenuated will be v(t), so measurements at higher frequencies should be avoided. In the setup, the current (t) from the power supply can be measured by an ammeter and the voltage vo(t) on the material and conductive plates by a voltmeter. Note that the voltage on the material is not directly accessible, so the impact of rx needs to be evaluated. In DC analysis, the effect of rx is negligible. Thus Eq. (4) is a reasonable estimation of Rsp, and the resistivity can be estimated by Eq. (5). In AC analysis, due to frequency dependency, rx will be the lower bound of the total impedance |(ω)| on W (ω) = Z(ω) + rx as frequency in- creases. So, in very-low frequencies, rx is negligible, and as the frequency increases rx becomes significant. This behaviour can be observed in Fig. 7, wherein very-low frequencies |(ω)| is approximately Rsp, and Eq. (21) can give a good estimation. As frequency increases |(ω)| tends to rx, and Eq. (21) cannot be used to estimate the resistivity. The bulk resistivity will be strong or weak related to the dielectric characteristics modelled by the capacitance C. The larger the C value, the stronger the resistivity frequency dependency, and vice versa. In Fig. 7, it is worth noting that for each curve, as frequency increases, the total impedance decreases from Rsp to- wards rx, and as C decreases, curves are shifted to the right, that is, moved to higher frequencies. It means that if C has a small value, the frequency will have a weaker relation to the resistivity estimation, and the ratio of v(t) and i(t) will still give a reasonable estimate of Rsp. Conversely, if C increases significantly, the ratio can give a misleading estimate of Rsp. So, the lower the frequency, the better the Rsp estimation and the weaker the influence of C. Analyses show that measurement frequency is essential in obtaining an accurate estimate of resistivity. Measurements must be performed at low frequencies; however, different commercially available resistivity meters operate at different frequencies, such as the Giatec RCONTM Resistivity Meter that runs from 1 to 30 kHz, the

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Merlin Bulk Resistivity Meter that runs at 325 Hz, CNS FARNELL Resistivity Meter that runs at 13 Hz, the Proceq Resipod Resistivity Meter that runs at 40 Hz, and Giatec SurfTM Resistivity Meter that runs from 10 to 100 Hz, have different operating frequencies. If measurements were made with the same instrument on different specimens, a fair comparison could be made between the measures. If different instruments were used, looking for a scale factor is necessary to make a fair comparison. Thus, different results are expected to be obtained using different instruments for the same concrete specimen. However, if the operating frequency could be adjusted to a lower frequency, the results would con- verge to the same value. The dependency of the concrete bulk resistivity over the frequency can be studied by another technique called AC Impedance Spectroscopy (ACIS), where the frequency is swept from very low (millihertz) to high frequencies (Megahertz). This technique allows the study of hydration properties, the interfacial properties of the cement, and the characterization of the material’s microstructure. Usually, simple or complex electric circuits represent the material. Still, no consensus exists on associating each electric component with the bulk. The ACIS is a promising technique for understanding cement-based material, but it is beyond the scope of this work.

5 Conclusion A simple electric circuit modelled the concrete bulk, and theoretical analyses were performed on a two-plate configuration setup. In the model, solid interface, pore (liquid) interface, solid–liquid interfaces, hydration, crossing pores, occluded pores, and electrode contacts are concentrated in two aspects: the polarization related to the permittivity of capacitance dielectric, and the resistivity related to resistance. Resistivity is associated with the motion of charges under the effect of an electromagnetic field, and permittivity is associated with how the electromagnetic field polarizes the material so that the bulk can be studied by a linear model separating the resistivity and the polarization effect. The low-pass characteristics of the setup indicate that the material under test undergoes polarization so that resistivity measurement can be affected by the chosen operating frequency. Simulations show that a low polarizable material is weakly affected by the frequency, while the frequency strongly influences a highly polarizable material in resistivity estimation. However, the polarization does not affect the resistivity estimation at a very low frequency. Finally, a misleading estimate can be obtained if the measurement frequency is not correctly defined.

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References Akhtar A, Sarmah AK (2018) Construction and demolition waste generation and properties of recycled aggregate concrete: a global perspective. J Clean Prod 186:262–281 Andrade C, Alonso C (1996) Corrosion rate monitoring in the laboratory and on-site. Constr Build Mater 10(5):315–328 Balestra CET, Nakano AY, Savaris G, Medeiros-Junior RA (2019) Reinforcement corrosion risk of marine concrete structures evaluated through electrical resistivity: proposal of parameters based on field structures. Ocean Eng 187:106167 Cabeza M, Merino P, Miranda A, Nóvoa XR, Sanchez I (2002) Impedance spectroscopy study of hardened Portland cement paste. Cem Concr Res 32(6):881–891 Chen CT, Chang JJ, Yeih W (2014) The effects of specimen parameters on the resistivity of concrete. Constr Build Mater 71:35–43 Hu X, Shi C, Liu X, Zhang J, de Schutter G (2019) A review on microstructural characterization of cement-based materials by AC impedance spectroscopy. Cement Concr Compos 100:1–14 Liu Y, Paredes M, Deuble A (2015) Review and evaluation of techniques for measurements of concrete resistivity. In: Proceedings of the transportation research board (TRB) 94th annual meeting, Washington, DC, USA, pp 11–15 Mehta PK, Monteiro PJM (2006) Concrete: microstructure, properties and materials, 3th edn. McGraw Hill, New York, 674 p Neville AM, Brooks JJ (2010) Concrete technology, 2st edn. Pearson. London, 448 p Nguyen AQ, Klyz G, Derby F, Balayssac J-P (2017) Evaluation of water content gradient using a new configuration of linear array four-point probe for electrical resistivity measurement. Cem Concr Compos 83:308–322 Nguyen AQ, Klyz G, Derby F, Balayssac J-P (2018) Assessment of the electrochemical state of steel in water saturated concrete by resistivity measurement. Constr Build Mater 171: 455–466 Sengul O (2014) Use of electrical resistivity as an indicator for durability. Constr Build Mater 73:434–441 Wang R, He F, Shi C, Zhang D, Chen C, Dai L (2022) AC impedance spectroscopy of cement-based materials: measurement and interpretation. Cem Concr Compos 131:104591 Xie P, Gu P, Xu Z, Beaudoin JJ (1993) A rationalized AC impedance mod- el for microstructural characterization of hydrating cement systems. Cem Concr Res 23(2):359–367

Studies on Rheological Properties of High-Flowable Concrete Nagaraj Ajay, S. Girish, Ashwin M. Joshi, and Namratha Bharadwaj

Abstract Self-compacting concrete (SCC) has considerably lower yield stress as compared to the conventional vibrated concrete (CVC) in their fresh condition and this forms one of their primary differences. To place CVC and SCC via pumping, the latter would require a lower pumping pressure to pump and place as it requires lower yield stress in comparison. Pumping is one of the most preferred methods of conveying and placing concrete due to the field requirements of reaching heights and less accessible places. It is obvious that the intensity of pumping pressure might affect the state of fresh properties of concrete, while being pumped and/or placed. Currently, Rheometers are available to measure the fresh properties of pumped concrete under dynamic condition, i.e., while the mixes are being agitated and pumped; similar instruments are not extensively available or used after pumping and placing concrete i.e., when concrete is at rest when supported on a formwork post pumping and placing. It is necessary to study the fresh properties of placement of concrete at rest i.e., under static condition to understand the actual phenomenon under said condition. The current experimental study attempts to determine the fresh properties of concrete under rest i.e., static condition using shear box test. The concrete mixes were proportioned using volume fraction technique and their characteristics were evaluated using both empirical and material science approach. The results show the uniqueness of the approach for determining the rheological properties of CVC and SCC mixes under static conditions. The study exhibits an

N. Ajay Civil - Structural Consultant, Advaitha Consultants, Bengaluru 560098, India e-mail: [email protected] S. Girish Department of Civil Engineering, BMS College of Engineering, Bengaluru 560019, India e-mail: [email protected] A. M. Joshi (B) Gleeds Consulting (I) Pvt. Ltd., Bengaluru 560005, India e-mail: [email protected]; [email protected] N. Bharadwaj BMS College of Architecture, Bengaluru 560019, India e-mail: [email protected]; [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 J. M. P. Q. Delgado (ed.), Concrete Structures: New Trends and Old Pathologies, Building Pathology and Rehabilitation 27, https://doi.org/10.1007/978-3-031-38841-5_4

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interesting finding, which is the invalidation of the use of Bingham model for SCC with a flow value of 800 mm and beyond. Keywords Bingham parameters · Shear box · Plastic viscosity · Rheology of concrete · Yield stress · Volume fraction method

1 Introduction Concrete is a vital construction material and plays a most important role in the quality of buildings and/or structures. With the availability of advanced equipment, mixing concrete may be easy but it’s not enough. It is important that a concrete mixture is properly designed, batched, mixed, and transported to the site. It is also equally important to properly place the concrete. Concrete placement is an important operation because it determines its quality and durability. Hence concrete placement must be done systematically and efficiently to give the best results desired. It is a challenging task to place the concrete for modern-day constructions as it’s demanding. The high-rise construction specifically requires pumping of the concrete to greater heights. In these construction sites, pumped concrete is preferred since it is fluid in nature and highly workable, allowing for more effective pumping through pipes and/ or flexible pipes. In high-rise building construction, it is challenging to attain uniform mix design, placement, and curing. Especially placing of the pumping concrete into slender column, deep beams and concrete walls, in fact aggravate the tendency of mixes to bleed and produce laitance. Without proper placing procedures, even the designed concrete mixes will segregate and bleed improperly, leading to honeycombing, poor bond to steel, and other problems. Figure 1 demonstrates that it is more difficult to maintain constant mix workability when pouring concrete before and after pumping. Concrete is a composite material, and its hardened property is influenced by its fresh property, and workability remains a crucial property of concrete. The diverse requirements of mobility, compactability and stability of fresh concrete are collectively referred to as “workability” of concrete. Workability is mainly governed by mix proportion, process, and quality control. Workability not only depends on the ingredients of concrete, but also on the nature of the applications. The fresh properties of concrete influence the quality, constructional cost, strength, and durability of structure. For better understanding, it is interesting to note there are little more than 60 test methods available to measure workability of CVC (Koehler and Fowler 2003) and some tests are approved by American Society for Testing and Materials (ASTM), British Standards (BS) and Bureau of Indian Standards (BIS). Slump test, compaction test, Vee-bee test are some of the popular tests used in practice for fresh concrete. Among the test methods, the slump test in more commonly used and accepted test method (Koehler and Fowler 2003). Figure 2 shows the slump test apparatus and test methodology (IS 1199).

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Fig. 1 Placing of concrete

Unfortunately, the slump test does not indicate any small variations in mix proportioning, that can lead to issues related to workability of concrete mixes, which can affect the workability, strength and durability. Concretes with the same slump can exhibit different behavior when tapped with a tamping rod (Girish and Ajay 2017). Now slump test is less relevant for newer advanced concrete mixes than for more conventional mixes. The slump test is now viewed as incapable of providing an adequate characterization of the workability of today’s much more advanced concrete mixtures. In 1983, Tattersall was carried out systematic studies have been summarized in a book (Koehler and Fowler 2003) and continually argued all existing test methods are empirical and indicate single value with respect to either time or distance. In fact, concrete with the same slump may flow differently and may have different workability and as such concrete flow cannot be described by a single parameter. In 2008, ACI: 238-01R (ACI Committee 238 2008) recommended the material science approach for better understanding and measuring the workability of fresh concrete. In this method there are many approaches available, but most popular and widely using is rheological technique.

2 Rheology of Fluids Rheology is a branch of science which deals with “Study of flow and deformation of complex materials” (Tattersall and Banfill 1983). The term ‘rheology’ was coined by Prof. Bingham and is based on the theory of continuum mechanics. “Rheo” is derived from the Greek words “pantarhei”, meaning ‘everything is in flow’, so the name rheology means the theory of deformation and flow of matter.

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Fig. 2 Slump test apparatus

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Fig. 3 Behavior of Newtonian and Non-newtonian fluids

Rheology’s primary goal is to forecast the flow that would result from applied forces in a complex fluid. Rheology has broad applications in a variety of industries, including those that make ceramics, paint, polymers, food, medicine, lubricants, and concrete, particularly to study the flow of fresh concrete. It is most frequently used to characterize the fluid’s flow characteristics in relation to shear stress and shear rate. In Fig. 3, the fundamental fluid behaviour is classified as Newtonian or Non-Newtonian fluid. The viscosity law of Newton is observed by Newtonian fluids. According to Newton’s law of viscosity, the relationship between shear rate and shear stress is linear. If there is a relationship between shear rate and shear stress are non-linear and it does not obey the New-ton’s law of viscosity such fluid is called as non-Newtonian fluids (Tattersall and Banfill 1983). These non-Newtonian fluids are highly viscous, and viscosity is no longer constant for all shear rates and difficult to describe the viscosity by using simple Newtonian equation. Therefore, for such complex fluids, constitute equations or mathematical models are used for better characterizations of flow and it describes the viscosity of fluids (Tattersall and Banfill 1983).

3 Rheology of Fresh Concrete The concrete in its fresh state is assumed as a non-Newtonian fluid. It can be considered as a complex behaviour material, where concentrated suspension of aggregates in cement paste. However, the characterization of its rheology is too complicated. The flow of concrete from its constituents cannot be predicted with any certainty due to this complexity. Therefore, a better understanding of the flow properties of concrete is needed to be able to predict the flow of concrete from the properties of the components. There are six flow curves, and the Bingham model is the one that is most frequently used for describing how fresh concrete flows (Tattersall and Banfill 1983). Figure 4 illustrates the general structure of the Bingham model graphically.

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Fig. 4 Behavior of Bingham Non-newtonian fluids

The Bingham model provides two parameters namely yield stress (τ0 ) and plastic viscosity (μ). The plastic viscosity is correlated to the time of concrete placing and the yield stress is correlated to concrete slump (Tattersall and Banfill 1983). The minimal force necessary to disassemble a structure and start a flow is defined as the yield stress, and it is associated with concrete slump (Tattersall and Banfill 1983). Static and dynamic yield stress are dependent on the flow operation. Concrete must experience shear stress when it is “at rest” in order for flow to begin. Static yield stress increases resistance to segregation while lowering formwork pressure. For ease of pumping, placement, and self-consolidation, a low dynamic yield stress is necessary. Another parameter plastic viscosity describes the resistance to flow once the concrete is flowing and it is related to the time of concrete slumping (speed of the flow) during the testing. In 1962 Ritchie (Girish et al. 2021) applied rheology concept for the first time to the fresh concrete and divided under three fundamental properties, namely: stability, compatibility, and mobility. The stability is represented in-terms of bleeding and segregation. Compatibility is represented by relative density. Similarly, the mobility is represented in terms of internal friction angle, bonding force, and viscosity. Ritchie’s work was innovative, but it had one major drawback, that is, the parameters associated with the rheology of fresh concrete had been identified but, there was no apparent relationship among them. In 1976, Tattersall (Girish et al. 2021) for the first time carried out systematic study on rheological studies on fresh concrete. He considered fresh concrete as a non-Newtonian Bingham fluid and suggested the Bingham model for the flow characterization of fresh concrete, as fresh concrete appropriately behaved like Bingham fluid that exhibited yield stress and plastic viscosity. The yield stress is related to

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the slump of concrete, and the resistance to flow or flow rate represents the plastic viscosity of fresh concrete and these parameters were determined by experimentally using two-point rheometer. Later, many researchers carried out systematic studies towards measuring the rheological properties of fresh concrete using rheometers and other test methods. However, compared to empirical methods, rheological method is providing better characterization of the flow properties of fresh concrete.

4 Measurement of Rheological Properties There are two types of measurements for concrete rheology: the flow curve test and the stress growth test. In general, concrete rheology is measured by flow curve test using rheometers (Girish et al. 2021). Rheometers are typically used to conduct flow curve tests to determine the rheology of concrete (Girish et al. 2021). Rheometers detect the shear stress of concrete at different shear rates. These measured values are then fitted into flow curves to establish the mix’s rheological characteristics (see Fig. 5). For concrete, rotational rheometers are used especially for concentrated suspensions like gels, cement paste and concrete. Concrete rheometers fall into three different configurations—coaxial cylinders, parallel plate, and impeller-type and are shown in Fig. 6 (Tattersall and Banfill 1983). Majority of rheometers measure the dynamic yield stress, and few rheometers measure the static yield stress. There are various rheometers are available and each having its own advantages and limitations (Ajay and Girish 2021). Researchers attempted various studies on rheological properties using different approaches

Fig. 5 Schematic representation of determining the rheological properties by flow curve method

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Fig. 6 Different configuration of rotational rheometers (Tattersall and Banfill 1983)

like numerical simulation, analytical finite element models, correlations between empirical and rheological properties, etc., to overcome the limitation of rheometers. The result of study conducted by Ferraris (Ajay and Girish 2021), by considering the same material using different rheometers is shown in Table 1. As can be seen from values there is no concurrence on yield strength & plastic viscosity and no agreement of the measured values among the different types of rheometers. During pumping of concrete, it is subjected to dynamic condition i.e. dynamic yield stress is measured. Whereas, placing of concrete in the formwork, it is subjected to static condition i.e. static yield stress is measured. There is a need to study the Table 1 Yield stress and plastic viscosity values obtained with different rheometers (Ajay and Girish 2021) Mix

BML

BTRHEOM

Two-point

Yield stress (Pa)

Plastic viscosity (Pas)

Yield stress (Pa)

Plastic viscosity (Pas)

Yield stress (Pa)

Plastic viscosity (Pas)

1

738

114

1619

181

10.84

14.72

2

76

17.4

406

18

0.34

5.34

3

408

82.4

771

136

3.67

13.20

4

840

72

2139

51

7.44

11.65

5

910

108

1753

94

3.91

14.61

6

139

45

505

78

1.80

10.31

7

90

32.7

549

54

0.86

9.31

8

717

29

1662

67

5.71

8.84

9

125

15

624

25

0.95

6.06

10

248

35.9

740

50

1.98

8.88

11

442

29

1189

27

3.97

6.57

12

584

39

1503

38

6.23

9.07

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flow properties of fresh concrete by static condition to correlate its behavior for field applications.

4.1 Shear Box Test The shear box instrument (see Fig. 7) used to study the rheological studies of concrete mixes under static condition (Girish et al. 2021). In brief, the shear box consists of a bed, on which Strain Linear Variable Differential Transformer (LVDT), load cell for applying the displacement rate and pneumatic actuator for normal stress application, are mounted. A thrust piece having threads for load cell, which has ring at one end and spherical end at the other end passes through the guide. Screw adapter is fixed at one end of load cell and the load cell is held between the thrust piece and the end of lead screw. The advancement of the lead

Fig. 7 Shear box test apparatus

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Fig. 8 Working principle and schematic representation of shear box

screw applies the shear force on the specimen. The servo controlled motor and normal stress regulator are mounted on the right end of the frame. The normal stress and shear force (in terms of displacement rate) are applied through a pneumatic actuator and stress regulator. A strain LVDT and S-type load cell measures the displacement (mm) and shear resistance (kN) respectively and the same is captured by the data acquisition system (Girish et al. 2021). The shear box (see Fig. 8) was employed to assess the rheological properties of fresh concrete mixtures at rest condition. The operation idea of a shear box is straightforward. Applying normal stresses and displacement rate to a 150 mm × 150 mm × 150 mm concrete sample and measuring the shear resistance force (kN) and displacement (mm).

5 Case Study on Shear Box Test Method In this work, the rheological properties of low workable and high flowing concrete (SCC) were determined systematically using a shear box under static condition using Bingham model for different flow values.

5.1 Materials The characteristics of the materials used are shown in Table 2. The physical test properties of materials are conducted as per the provisions of code of practices recommended by the Bureau of Indian Standards (BIS). The gradation curves for fine and coarse aggregate is shown in Fig. 9.

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Table 2 Material properties Materials

Specific gravity

Specific surface

Water absorption

Ordinary portland cement—53 grade

3.13

280 m2 /kg

–

Fine aggregate—natural river sand

2.60

–

2.0%

Coarse aggregate—crushed granite angular coarse aggregate (max. size 20 mm)

2.60

–

0.9%

Ground granulated blast slag (GGBS)

2.90

425 m2 /kg

–

Superplasticizer (SP)—PCE based

1.08

–

–

Fig. 9 Grading curves for aggregates

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Fig. 10 Mix design parameters—CVC and SCC

5.2 Mix Design In the current experimental program, about 12 different CVC mixes and 27 different SCC mixes were proportioned and developed. The CVC and SCC mixes with different ingredients were developed based on absolute volume fraction method (Girish et al. 2010). The mix design parameters are given in Fig. 10. The marsh cone test was carried out to optimize the dosage of super plasticizer (SP) and the dosage was kept constant throughout the experimental program. The mix proportion details for CVC and SCC mixes are presented in Table 3. A modified mixing procedure was adopted in the present work based on the previous studies carried out by Girish et al. (2010). Test methodology to conduct the experimental work on CVC and SCC mixes is shown in Fig. 11.

5.3 Test Methodology The methodology followed to determine the Bingham parameters of SCC mixes using shear box was based on previous studies. Figure 12 shows the procedure for finding the rheological properties of fresh concrete mixes.

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Table 3 Details of mix proportions of CVC and SCC mixes Mix

Cement (kg/m3 )

GGBS (kg/m3 )

Water (l/ m3 )

SP (%)

w/c

Vp

Fine aggregate (kg/m3 )

Coarse aggregate (kg/m3 )

115

–

0.38

0.21

710

1310

CVC mixes M1

300

–

M2

375

–

–

0.30

0.23

685

1271

M3

450

–

–

0.25

0.26

663

1230

M4

300

–

–

0.43

0.22

695

1284

M5

375

–

–

0.34

0.25

675

1243

M6

450

–

–

0.28

0.27

650

1203

M7

300

–

–

0.48

0.24

682

1258

M8

375

–

–

0.39

0.26

660

1219

M9

450

–

–

0.32

0.29

635

1180

M10

300

–

–

0.53

0.25

667

1235

M11

375

–

–

0.43

0.28

647

1193

M12

450

–

–

0.35

0.30

625

1152

130

145

160

SCC mixes M13

300

279

175

0.75

0.58

0.37

945

655

M14

300

337

175

0.75

0.58

0.39

915

634

M15

300

395

175

0.75

0.58

0.41

885

613

M16

300

250

185

0.60

0.61

0.37

945

655

M17

300

308

185

0.65

0.61

0.39

915

634

M18

300

366

185

0.95

0.61

0.41

885

613

M19

300

221

195

0.45

0.65

0.37

945

655

M20

300

279

195

0.50

0.65

0.39

915

634

M21

300

337

195

0.55

0.65

0.41

885

613

M22

375

207

175

0.50

0.46

0.37

945

655

M23

375

265

175

0.55

0.46

0.39

915

634

M24

375

323

175

0.57

0.46

0.41

885

613

M25

375

178

185

0.40

0.49

0.37

945

655

M26

375

236

185

0.50

0.49

0.39

915

634

M27

375

294

185

0.65

0.49

0.41

885

613

M28

375

149

195

0.40

0.52

0.37

945

655

M29

375

207

195

0.55

0.52

0.39

915

634

M30

375

265

195

0.60

0.52

0.41

885

613

M31

450

136

175

0.65

0.38

0.37

945

655

M32

450

194

175

0.85

0.38

0.39

915

634

M33

450

252

175

0.95

0.38

0.41

885

613 (continued)

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Table 3 (continued) Mix

Cement (kg/m3 )

GGBS (kg/m3 )

Water (l/ m3 )

SP (%)

w/c

Vp

Fine aggregate (kg/m3 )

Coarse aggregate (kg/m3 )

M34

450

107

185

0.45

0.41

0.37

945

655

M35

450

165

185

0.60

0.41

0.39

915

634

M36

450

223

185

0.65

0.41

0.41

885

613

M37

450

78

195

0.40

0.43

0.37

945

655

M38

450

136

195

0.40

0.43

0.39

915

634

M39

450

194

195

0.55

0.43

0.41

885

613

Fig. 11 Testing methods: fresh properties of concrete mixes

6 Experimental Results and Discussion Table 4 shows the rheological properties of the CVC and SCC mixtures with their empirical values. It can be observed from the results presented in Table 4, for different mixture compositions, the slump test has not shown any difference in workability values. But it is considerable to note that the rheological values of these mixtures obtained from the shear box test show a clear difference among the mixtures. Further, it is interesting to note that the slump test has failed to differentiate these mixtures when compared to the shear box test. The same observation also with the SCC mixtures. Whereas M22, M23, M26, and M30 have the same slump flow even though the mixture ingredients are different, whereas the shear box test results clearly differentiate the mixtures. This demonstrates the importance of the scientific method of assessment to overcome the shortfall of empirical tests.

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Fig. 12 Procedure for finding the Bingham parameters of fresh concrete (Girish et al. 2021)

In addition to the above for SCC, the slump flow of 800 mm and above show a negative trend beyond that. This is physically not possible and brings out the limitations in using the Bingham model at a higher flowability for the materials used in this study. Results from the concrete shear test have clearly demonstrated the limitations of the Bingham model for a higher flow of 800 mm and above. The validation of the Bingham model up to a flow of 800 mm is a new finding, hitherto not mentioned explicitly by other researchers. The findings are for the type of the materials used in this study. Figure 13 illustrates a power law-based generalized relationship between yield stress and slump flow with a regression coefficient R2 = 0.92. When the slump flow is lower, the yield stress is higher, and vice versa. Several researchers that used various rheometers and found a similar association (Ajay 2019; Szecsy 1997). At various Vp, the plastic viscosity falls as the slump flow rises. Plastic viscosity and slump flow exhibit an association (R2 = 0.65) based on the generalized relation. With slump flow, the plastic viscosity generally falls, with only a few isolated places exhibiting the opposite trend. Similar findings were found in the writings of Murata, Kikukawa, and Wallevick (Ajay 2019; Szecsy 1997). The outcomes are based on test results obtained with rheometers. Typically, the relationship between plastic and slump flow is poor (Ajay 2019; Szecsy 1997) and results are based on the test values using rheometers. The rheological studies using shear box test shows the average correlation between plastic viscosity and slump flow (R2 = 0.65), which is good, considering the actual correlation of plastic viscosity with slump flow from the published literature. The

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Table 4 Rheological properties of CVC and SCC with empirical test results Mix

Cement (kg/m3 )

GGBS (kg/m3 )

Water (l/m3 )

SP (%)

w/c

Vp

Slump/ Slump flow (mm)

T50 (s)

Yield stress Pa × 103

Plastic viscosity (MPas)

115

–

0.38

0.21

0

–

88.50

15.3

–

0.30

0.23

0

–

75.10

6.3

–

0.25

0.26

0

–

60.40

14.4

–

0.43

0.22

0

–

81.50

–

0.34

0.25

0

–

79.20

22.5

–

0.28

0.27

0

–

76.90

39.6

–

0.48

0.24

5

–

71.20

40.5

–

0.39

0.26

3

–

67.50

31.5

–

0.32

0.29

0

–

66.70

54.0

–

0.53

0.25

18

–

54.70

12.6

CVC mixes M1

300

–

M2

375

–

M3

450

–

M4

300

–

M5

375

–

M6

450

–

M7

300

–

M8

375

–

M9

450

–

M10

300

–

M11

375

–

–

0.43

0.28

20

–

51.30

37.8

M12

450

–

–

0.35

0.30

25

–

47.30

44.1

130

145

160

4.50

SCC mixes M13

300

279

175

0.75

0.58

0.37

750

4.7

6.40

9.90

M14

300

337

175

0.75

0.58

0.39

750

3.8

6.00

M15

300

395

175

0.75

0.58

0.41

850

3.5

−5.50

M16

300

250

185

0.60

0.61

0.37

700

4.3

12.30

3.60

M17

300

308

185

0.65

0.61

0.39

750

3.0

5.40

4.50

M18

300

366

185

0.95

0.61

0.41

780

2.6

4.80

7.20

M19

300

221

195

0.45

0.65

0.37

700

2.0

12.20

3.60

M20

300

279

195

0.50

0.65

0.39

730

2.2

8.20

14.40

M21

300

337

195

0.55

0.65

0.41

750

2.5

6.60

20.70

M22

375

207

175

0.50

0.46

0.37

680

3.2

24.30

13.50

M23

375

265

175

0.55

0.46

0.39

730

3.6

8.30

37.60

M24

375

323

175

0.57

0.46

0.41

780

3.0

3.10

5.40

M25

375

178

185

0.40

0.49

0.37

650

2.85

39.30

16.20

M26

375

236

185

0.50

0.49

0.39

710

2.1

9.20

6.30

M27

375

294

185

0.65

0.49

0.41

740

2.0

7.40

2.70

M28

375

149

195

0.40

0.52

0.37

660

2.4

34.40

7.20

M29

375

207

195

0.55

0.52

0.39

750

2.2

6.50

10.80

M30

375

265

195

0.60

0.52

0.41

780

2.0

3.10

0.30

M31

450

136

175

0.65

0.38

0.37

700

3.2

12.40

1.80

M32

450

194

175

0.85

0.38

0.39

800

3.0

−7.20

6.30

M33

450

252

175

0.95

0.38

0.41

850

2.8

−6.90

6.00

8.10 34.2

(continued)

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Table 4 (continued) Mix

Cement (kg/m3 )

GGBS (kg/m3 )

Water (l/m3 )

SP (%)

w/c

Vp

Slump/ Slump flow (mm)

T50 (s)

Yield stress Pa × 103

Plastic viscosity (MPas)

M34

450

107

185

0.45

0.41

0.37

710

2.4

10.70

M35

450

165

185

0.60

0.41

0.39

740

2.7

7.70

M36

450

223

185

0.65

0.41

0.41

780

2.2

3.50

0.90

M37

450

78

195

0.40

0.43

0.37

680

2.7

26.90

3.60

M38

450

136

195

0.40

0.43

0.39

700

2.3

13.30

6.30

M39

450

194

195

0.55

0.43

0.41

730

2.4

8.70

14.40

2.70 23.4

shear box test results thoroughly demonstrate the instrument’s efficiency, which is further supported by the findings of the study for various parameters.

7 Concluding Remarks This study has demonstrated the flaws or restrictions of the slump test or, more generally, the empirical test by clearly highlighting the yield stress value derived from the shear box test. Also, it demonstrates how the Bingham model can be used effectively to determine the rheological characteristics of fresh concrete (stiff to flowable mixes). The study also highlights the drawbacks of applying the Bingham model at higher flowabilities. The findings have clearly demonstrated that slump flow and yield stress are correlated.

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Fig. 13 Relationship between slump flow and yield stress and plastic viscosity of SCC mixes

References ACI Committee 238 (2008) Report on measurements of workability and rheology of fresh concrete Ajay N (2019) Feasibility studies on the use of concrete shear box for measurement of rheological properties of SCC mixes. Ph.D. Thesis, Visvesvaraya Technological University, Karnataka, India

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Ajay N, Girish S (2021) Rheology of fresh concrete—a review. J Rehab Civ Eng 9(3):122–132. https://doi.org/10.22075/jrce.2021.20557.1425 Girish S, Ranganath RV, Jagadish V (2010) Influence of powder and paste on flow properties of SCC. Constr Build Mater 24:2481–2488 Girish S, Ajay N, Achutha A (2021) Concrete shear box: new instrument to assess stiff to flowing concrete using Bingham model. ACI Mater J 118(6):227–240. https://doi.org/10.14359/517 34148 Girish S, Ajay N (2017) Importance of rheological properties of fresh concrete—A review. Indian Concr J 91(9) IS 1199 (1999) Methods of sampling and analysis of concrete, no. Reaffirmed Koehler EP, Fowler DW (2003) Summary of concrete workability test methods Szecsy R (1997) Concrete rheology. Ph.D. Thesis, University of Illinois Tattersall GH, Banfill PFG (1983) The rheology of fresh concrete, 1st edn. Pitman, Boston, London, Melbourne

Sewage Sludge: Some Applications in Civil Engineering M. C. A. Feitosa, S. R. M. Ferreira, J. M. P. Q. Delgado, F. A. N. Silva, J. T. R. Oliveira, P. E. S. Oliveira, and A. C. Azevedo

Abstract The use of civil construction waste has been consolidated as a way to achieve sustainability in civil construction, as well as reduce the environmental impacts resulting from the improper disposal of this material. Due to the specificities of its products, civil construction has a large field where this waste can be used as raw material. The objective of this work is to contribute to studies on the possibilities of using sewage sludge as a way to improve the characteristics of the soil in collapse and as small concrete aggregates. Sewage sludge with 25, 50 and 75 mg/ha from the Mangueira and Curado treatment stations was used with an addition of about 5%, 10%, and 15%. In order to characterize the properties of sewage sludge and analyze its interaction with the soil and concrete specimens, several tests were carried out, such as: physical and chemical tests, scanning electron microscopy tests, hydraulic conductivity tests, chemical mobility tests, compressive strength tests, sclerometric M. C. A. Feitosa · F. A. N. Silva · J. T. R. Oliveira Civil and Engineering Department, Catholic University of Pernambuco, Recife, Pernambuco, Brazil e-mail: [email protected] F. A. N. Silva e-mail: [email protected] J. T. R. Oliveira e-mail: [email protected] S. R. M. Ferreira · P. E. S. Oliveira Departamento de Engenharia Civil, UFPE, Av. Acadêmico Hélio Ramos, s/n. Cidade Universitária, Recife, Brazil e-mail: [email protected] P. E. S. Oliveira e-mail: [email protected] J. M. P. Q. Delgado Construct, Departamento de Engenharia Civil, Universidade do Porto, Rua Dr. Roberto Frias, s/n, 4200-465 Porto, Portugal e-mail: [email protected] A. C. Azevedo (B) Instituto Federal de Ciências de Educação e Tecnologia de Pernambuco (IFPE), Recife, Brazil e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024 J. M. P. Q. Delgado (ed.), Concrete Structures: New Trends and Old Pathologies, Building Pathology and Rehabilitation 27, https://doi.org/10.1007/978-3-031-38841-5_5

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tests, and ultrasonic pulse velocity tests. The results obtained allowed us to conclude that the addition of sewage sludge to the soil contributed to reduce its collapsibility, showing that this procedure can be useful for improve the performance of collapsible soils. It was also observed that when the proportion of sewage sludge was increased in substitution for small-size concrete aggregates, the compressive strength and water absorption decreased when compared to a concrete block made with usual aggregates. The behavior obtained indicates that the use of sewage sludge to replace the small-sized concrete aggregate part should be used with caution, even in small-sized buildings, requiring advanced studies to explore its use as a material building. Keywords Sewage sludge · Soil-sludge mixture · Concrete · Civil engineering · Building industry

1 Introduction One of the biggest environmental problems to be faced by humanity in this century is the large amount of waste generated in urban centers. Solid and liquid waste (garbage, STP waste, and industrial treatment), often accumulated in the environment without adequate treatment or use that allows recycling, have become and among others, agents that cause pollution in large urban areas (Geyer 2001). No having destiny right, parts of this waste ends being forwarded to the landfills Sanitary urban when these landfills has capacity. As sustainable development is the only alternative to conceive the survival of the planet, taking into account the technological development and the conditions necessary for the continuity of life. The authorities made several laws to protect the environment with a relationship between the management of slime and waste. In large cities, environmental legislation increasingly restricts the disposal of sludge in landfills, as well as the scarcity of adequate locations tall costs. Then necessary, the development and implementation of alternatives that replace efficient the simple disposal of this waste in landfills (Santos 2003). Agenda 21 at the World Environment Conference—Rio 92, according to Fernandes (1999), on the topic “Environmentally sound management of waste and issues related to sewage”, recognizes the importance of the waste destination. The Agenda defines four programs as priorities: the reduction of waste production, the maximum reuse and recycling, the promotion of environmentally healthy deposits and treatment, and the expansion of the reach of services that was occupied with waste. In Brazil, the Ministry of the Environment estimates that around 10% of urban sewage is treated in sewage treatment plants (STPs) before being released into rivers. This treatment results in the production of a sludge rich in organic matter and nutrients, called sewage sludge, whose final disposal is problematic, even representing 60% of the operation cost of the treatment plants (Camargo and Bettiol 2000).

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The inadequate final disposal of this waste partially nullifies the benefits of collecting and effluent treatment. Therefore, an adequate destination must be given to this residue and, in order to solve this problem several studies have been carried out in order to recycle this residue as a material for the production of other materials. The search for economically and environmentally advantageous solutions for the different types of solid waste generated continues to be a challenge, and among them is the final disposal of sludge from sewage. It is in this context that this work seeks alternatives capable of assisting in the discussion of the management of the final disposal of sewage sludge through its recycling and use in the manufacture, in materials in construction civil as lightweight aggregate, and in the improvement of soils.

2 Literature Review 2.1 Sewage Water Classification Demographic expansion and technological development bring as an immediate consequence the increase in water consumption and the constant increase in the volume of wastewater. These waters, together with surface runoff and possible underground drainage, will form sewage flows or simply sewage. According to its origin, sewage can be classified into sanitary or domestic sewage, which originates from the flow corresponding to the performance of domestic activities, industrial sewage that is generated through industrial activities and storm sewage that has its flow generated from the collection of surface runoff water from rainfall and, in some cases, washing of streets and underground drains (Azevedo Netto 1977).

2.2 Sewage Systems According to Pera (1977), what is called a sewage system is a structural set that includes collecting pipes functioning by gravity, treatment and discharge units when essential, transport and final discharge works, in addition to a series of accessory organs indispensable for the system works and is operated efficiently, quickly and safely. A collection network is a set of conduits and works designed to collect and transport flows to a given location, that is, the collection network is just one component of the sewage system.

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2.3 Evolution of the Sewage Systems According to Azevedo Netto (1984), the collection of wastewater was already a concern of ancient civilizations. In 3750 BC, sewers were built in Nipur (India) and Babylon. And, in 3100 BC there were already bathrooms with sewers channeled in ceramic shackles grouted with plaster. At the end of the twelfth century, the construction of public drainage systems for surface runoff water and underground plumbing for wastewater were resumed, initially for domestic septic tanks and later for rainwater channels; and from the fourteenth century, the first public laws on the installation, control, and use of these services originated (Metcalf and Eddy 1977). The destination of sewage and urban waste was already considered a problem from the sixteenth century onwards, with the increasing pollution of water sources. The development of water supply, the pumping system with steam-powered machines and the use of iron pipes to repress the water began to be used (Azevedo Netto 1984). At the end of the seventeenth century, agricultural transformations and the industrial revolution caused profound changes in city life and, consequently, in sanitary facilities. The distribution of water and water discharges to evacuate sewage caused soil saturation, contaminating the streets and the water. First, some cities tried to use individual septic tanks, which without proper maintenance became sources of disease generation (Azevedo Netto 1984). The decades from 1830 to 1840 can be highlighted as the most important in the history of Sanitary Engineering. In 1847, it became compulsory to discharge all wastewater into public galleries. This is how the unitary exhaustion system came about. The absolute separator system was invented later, in 1879, and applied for the first time in the city of Memphis, Tennessee, United States (Gherghel et al. 2019). In Brazil, thanks to the work developed by Saturnino de Brito and other engineers, from 1912 the absolute separator system became general. The scientific and technological development of humanity has made man aware of the need to create effective sanitation systems where the supply of drinking water and collection of wastewater are guaranteed, as well as favorable conditions for recycling in nature.

2.4 Sewage Sludge In Brazil, the sewage collection and collective transport system does not include rainwater, as the absolute sewage system is used. Constituent parts of this system are the collection and transport of sewage, treatment, and final disposal.

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99

Sewage

The collected sewage is conducted through pipes to the Sewage Treatment Plants (STP). Normally, these pipes function as free conduits, and may also function as forced conduits in some stretches. Sewage is collected and transported from the buildings that lead the effluent to the collection network through building branches. Through secondary collectors, these sewages are released into the collection network that forwards them to the trunk collector that receives these contributions and transports them to an interceptor or outfall (Fontes 2003).

2.4.2

Sewage Treatment

According to Pergorini et al. (2003), approximately 40% of the Brazilian population has sewage collection, and only about 10% of the collected sewage undergoes some treatment process. Sanitary sewage consists of 99.9% water and 0.1% total solids (organic and inorganic, suspended and dissolved), in addition to microorganisms. Due to this 0.1% of solids present in the sewage, it is necessary to treat it (Tsutiya and Hirata 2001; Sperling 1996). Sewage treatment can be divided into two phases: liquid phase and solid phase. The liquid phase can be composed of domestic sewage, industrial sewage, and storm sewage. The solid phase is composed of by-products generated during the treatment of the liquid phase (Fontes 2003). The levels of treatment, as well as their efficiency, limit the removal of pollutants in order to adjust the release to a desired quality.

Treatment of the Liquid Phase The treatment levels in the liquid phase, according to Von Sperling (Sperling 1996), are: preliminary, primary, secondary, and, eventually, tertiary. These treatment levels are summarized below: 1. Preliminary: constitutes the removal of coarse suspended solids (larger materials and sand). The removal of coarse solids is usually done by means of grates and the sand is removed through units called sandbox or desander; 2. Primary: removes part of the sedimentable suspended solids and part of the organic matter, using physical options such as sieving and sedimentation, reducing the organic matter in the effluent. The sewage flows slowly through the decanters, allowing the higher-density solids to gradually settle to the bottom, forming the raw primary sludge with floating materials such as greases and oils, of lower density. 3. Secondary: mainly removes suspended and dissolved solids and sedimentable organic matter and, eventually, nutrients such as nitrogen and phosphorus. Mainly

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used are treatment processes such as stabilization pond systems, activated sludge systems and aerobic systems with biofilms. The main sewage treatment systems at secondary levels stand out: (a) Stabilization of pond systems It is a sewage treatment system widely used in Brazil due to its low cost, operational simplicity and climatic conditions; and it can be done in five different ways: • Facultative Pond: In this type of system, the soluble and finely particulate BOD (biochemical oxygen demand) is anaerobically stabilized by bacteria dispersed in the liquid medium, while the suspended BOD is stabilized by bacteria at the bottom of the pond. • Anaerobic Lagoon: BOD is around 50% stabilized in this lagoon, which is deeper and with greater volume, while the remaining BOD is removed by the facultative lagoon. The anaerobic lagoon has a depth of around 4.5 m and a reduced surface area. • Facultative Aerated Pond: The BOD removal mechanisms are similar to those of a facultative pond. In this system oxygen is provided by mechanical aerators rather than photosynthesis. • Complex mixture aerated lagoon—Facultative lagoon: The energy introduced per unit volume of the lagoon is high, which causes the solids, mainly the biomass, to remain dispersed in the liquid medium, or in complete mixture. The resulting higher concentration of bacteria in the liquid medium increases the efficiency of the BOD removal system, which allows the pond to have a smaller volume than that of a facultative pond. • Complex mixture aerated lagoon—Aerated lagoon: Lagoon similar to the previous system, with the difference that the decantation unit consists of a smaller lagoon, where the sludge must be removed in periods not exceeding 5 years. (b) Activated sludge systems It is a type of sewage treatment system using activated sludge that has been increasingly used, especially in large urban centers, as it allows for treating large amounts of sewage in small areas. It can be performed in three different ways (Andreoli et al. 1999), namely: • Conventional activated sludge: It comprises a primary decanter, aeration tank, secondary decanter, sludge densifier, anaerobic digester and sludge dewatering. The biomass concentration in the reactor is quite high, due to the recirculation of solids (bacteria) settled at the bottom of the secondary decanter. The biomass remains in the system longer than the liquid, which ensures high BOD removal efficiency. • Sludge activated by prolonged aeration: Similar to the conventional system, with the difference that the biomass remains longer in the system, requiring larger aeration. With this, there is less BOD available for the bacteria, which causes them to use organic matter from the cellular material itself for their maintenance.

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• Intermittent flow-activated sludge: The system operation is intermittent. The reaction and sedimentation steps take place in the same tank, in different phases, where the aerators are turned on and off, respectively. When the reactors are turned-off, the solids settle when the effluent (supernatant) is removed. When the aerators are reconnected, the sedimented solids return to the liquid mass, which eliminates the need for recirculation pumps. In this method, there are no secondary decanters. (c) Biological filter systems The stabilization of organic matter is carried out by bacteria that are adhered to the support of stones or synthetic materials. The elimination of pathogens is between 60 and 90% (Lessa 2005). (d) Simplified anaerobic system It consists of a system similar to the anaerobic filter. (e) Land disposal system It is a simplified system that requires large areas. This method is not used due to the great environmental implications, contamination of surface and groundwater, vegetation, etc. 4. Tertiary: This level of treatment is little applied mainly due to its high implementation cost, although it has already been used in some developed countries. It consists of greater efficiency in the removal of nutrients, pathogens, non-biodegradable compounds, heavy metals, dissolved inorganic solids and remaining suspended solids. Treatment of the Solid Phase The sludge generated in the sewage treatment plant, despite not being the only byproduct, is the most important one, as it is a waste that is difficult to treat and dispose of, given the large amounts that are generated, the difficulty in finding suitable places for its final disposal, transport distance, and environmental impacts, among others (Jordão and Pessôa 1995). Despite having more than 95% water, by convention, the sludge is called the solid phase (Andreoli et al. 2001a). The main steps for the treatment of the solid phase are densification, stabilization, conditioning, dewatering, cleaning, and final disposal. Should be mentioned that what determines which steps that will be implemented or not, are the characteristics of the sludge to be generated and the product end wants to obtain, in addition to the costs. The costs represent around 20–60% of the total spent on the operation of a sewage treatment plant (Fontes 2003; Tsutiya and Hirata 2001; Andreoli et al. 2001a). Sludge is composed by water and solids. Solids are divided into suspended solids and dissolved solids, most of them being the former. As for the organic matter, solids divide into fixed or inorganic solids and volatile or organic solids. The solids content is considered by several authors to be the total solids content or solids content

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Fig. 1 Decanter existing in the STP of Curado

dried (Andreoli et al. 2001a). Being the volatile solids/total solids ratio, a good recommendation of the organic matter content in the sludge. (a) Consolidation of the sludge Densification or thickening is a physical process of concentration of solids that has with the objective of reducing moisture and consequently the volume of the sludge, which in turn time facilitates the following units, as sludge become more compact due to the reduction of the volume. The most used types of sludge densifiers are gravity densifiers and the flotation thickeners (Tsutiya and Hirata 2001). • Densifiers per gravity The efficiency of these units is greater when the units use sludge from treatment primary. These are units similar to a primary decanter, in which the sludge settles and it is dense at the bottom of the tank, being removed by scrapers and sent to the stabilization unit (see Fig. 1). • Densifiers per flotation This process consists of injecting air bubbles into the liquid medium. These bubbles adhere to solid particles, causing their density to decrease and the same to be dragged to the surface, where are removed by scrapers (Jordão and Pessôa 1995). (b) Sludge stabilization Stabilization aims to remove pathogens, facilitate dehydration and prevent the emanation of bad odors at the process in treatment of sludge, through from the matter organic biodegradable. It can be done through three processes: biological stabilization, chemical stabilization and thermal stabilization. The most used currently is the biological stabilization (Andreoli et al. 2001a).

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Fig. 2 Drying bed of the STP of Curado

(c) Conditioning and dehydration of the sludge Conditioning is a preparatory process in which chemicals (coagulants) are added to the sludge, aiming to increase the capture of solids in the dehydration processes. O sludge conditioning can be performed through the use of organic polymers, products inorganic chemicals or of heat treatment (Andreoli et al. 2001a). Dewatering sludge is a physical process through which the sludge content sludge moisture is reduced. The main processes used for sludge dewatering sludge are by drying natural or by drying mechanics. • Drying Natural—the drying bed and the sludge drying ponds are part of the dewatering process by natural drying (see Fig. 2). • Mechanized drying—it is used in medium and large sewage treatment stations size depending on the amount of sludge generated. This system is capable of producing a sludge called the “sludge pie”, where the concentration of total solids is around 20–30%. The most frequently used equipment is a filter press, filter mat, and centrifuges (Jordão and Pessôa 1995). (d) Disinfection or cleaning and final disposal of sludge Disinfection is a necessary operation if the destination of the sludge is agriculture, seeking complement aerobic or anaerobic digestion in reducing the level of pathogens to levels acceptable. The final destination of sewage sludge is a serious economic and environmental problem worldwide, for presenting in its composition pathogenic germs, heavy metals, and other compounds toxic, even after the treatment process. This residue, when disposed of inadequately, can cause damage to the environment and human health. The knowledge of production, physical and chemical constitution, as well as other characteristics of waste collected solids, constitutes a fundamental factor for the orientation and planning of a discard safe it’s adequate for these waste (Jonh and Ângulo 2003).

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Currently, there are many possibilities for the use or final disposal of sludge from sewage, through disposal or beneficial use. Some ways of final disposal of sewage sludge will be discussed, such as sanitary landfill, landfarming, agricultural use, recovery of degraded areas, and incineration. • Sanitary landfill—The inadequate planning of a sanitary landfill can cause several environmental impacts, such as the pollution of groundwater and surface water due to the leaching and runoff of percolated liquids that may contain toxic substances, air pollution through the production of gases in landfills and the soil. These impacts can be avoided through well-designed projects, choice of suitable sites, monitoring of the landfill even after its closure, and elements of environmental protection (Tsutiya and Hirata 2001; Andreoli et al. 2001a). There are two types of sludge disposal in landfills: the exclusive sanitary landfill, which only receives sludge, whose solids content must be greater than 30% or even thermally dry; and co-disposal with solid urban waste, where the sludge is mixed with solid urban waste. According to Andreoli et al. (2001a) the solids content must be at least 20%, as the sludge with very high moisture (above 80%) increases the production of leachate in the landfill, reducing the stability of the slopes, in addition to making it difficult to compact the garbage. • Landfarming—According to Santos (2003), this type of sludge disposal in the soil is also known as soil treatment. It aims to biodegrade organic waste and retain heavy metals in the surface layer of the soil. In this type of system, the soil is used as a mere support, with no use of nutrients and organic matter for agricultural purposes, which allows applications of high amounts, accompanied by technological intervention in environmental control. • Agricultural use—According to Andreoli et al. (2001b), to use the term biosolids, it is necessary that the biological or secondary sludge is composed mainly of biological solids, in addition to having a chemical and biological composition compatible with some productive use. Biosolid is treated or processed sludge, with characteristics that allow its recycling in a rational and environmentally correct way (Andreoli et al. 2001b). Therefore, to use it safely, it is necessary to evaluate its quality, in addition to the environmental characteristics of the places in order to avoid possible contamination of the environment. According to Pergorini et al. (2003), agricultural recycling has stood out worldwide, for reducing the pressure of exploitation of natural resources and reducing the amount of waste with environmental restrictions. The use of sewage sludge in agriculture has been much studied and in Brazil there are already advances in the states of São Paulo, Paraná, and Brasília (Santos 2003). The most recommended crops are cereals, as cereals go through industrial processes before reaching the consumer, and those that pose the most risks are those in which the product has direct contact with the soil and which can be consumed raw, such as lettuce, carrots, beets, onions, turnips (Andreoli et al. 2001b).

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Several studies have been carried out with sewage sludge in agriculture in the state of Pernambuco. The research carried out by Silva (2008) evaluated the influence of sewage sludge on the dosage of nutrients in plant cultivation soil, in the state of Pernambuco. The verification of the influence of sewage sludge on the fertility attributes of soil cultivated with radish and açaí by Ferreira (2008) and in the development of Cowpea according to Barboza (2007) and, the soil-sewer sludge interaction: physics, chemistry, microstructural and hydraulic conductivity (Ferreira 2008). • Recovery of degraded areas—ETE sludge can also be used in the recovery of degraded areas, since it contains organic matter and nutrients that contribute to various aspects, such as the formation of aggregates, air and water circulation that promote soil aeration, favoring the recovery and reappearance of vegetation (Tsutiya and Hirata 2001; Andreoli et al. 1999). In São Paulo, in the city of Franca, it was registered by Tsutiya and Hirata (2001), experience with the practice of this alternative where the sludge produced in the STP of Franca was used in the urban perimeter of the city, to control 14 large eroded areas. • Incineration—During the incineration process, volatile solids are converted to carbon dioxide and water in the presence of oxygen and fixed solids are turned into ash. Incineration has the main advantage of reducing the volume of sludge, which reaches approximately 10–20% of the total volume of sludge (Fontes 2003; Garcia-Lodeiro et al. 2016). According to Tsutiya and Hirata (2001), during the decomposition process, despite the elimination of pathogenic organisms and toxic organic compounds, heavy metals are still present in the ashes and, therefore, an adequate final disposal is necessary. According to Andreoli et al. (2001a), the ashes of the sludge must be disposed of in sanitary landfills, or be used as co-incinerators in cement kilns or thermoelectric plants, or also in mixtures with cement that are currently being carried out in Japan and Europe. Studies have also been carried out with the objective of taking advantage of the ashes and partially substituting cement for the production of mortars and concrete (Geyer 2001; Fontes 2003). The emission of pollutants into the atmosphere is the main impact of incineration according to Andreoli et al. (2001b), which can be controlled by improving the combustion process and using filter systems before the gases are released into the atmosphere.

2.5 Current Legislation According to Duarte (2008), there is no legislation in Brazil that regulates the use of sludge as a material in civil construction. However, NBR 10004 (2024) can provide parameters for the analysis of the environmental risk of this type of destination,

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considering that the construction materials, after their use and subsequent demolition, constitute waste. NBR 10004 (2024) establishes the criteria for classifying solid waste according to its dangerousness. This characteristic is a function of the physical, chemical or infectious-contagious properties of the waste, and results in: • risk to public health, causing mortality, incidence of diseases or increasing their rates; • risks to the environment, when the waste is managed improperly. According to NBR 10004, waste is classified as: • Class I Waste: Hazardous. These are wastes that, due to their physical, chemical or infectious-contagious properties, may pose risks to public health, causing an increase in mortality or incidence of diseases (hazardousness) and/or risks to the environment when the waste is handled or disposed of in an appropriate manner inadequate, or when the residue has one of the following characteristics: flammability, corrosivity, reactivity, toxicity and pathogenicity. • Class II Waste: Non-Hazardous. Non-hazardous waste can be divided into: – Class II A Waste: Non-inert: those that do not fit the characteristics of either class I or class II B. This type of waste may have characteristics such as: combustibility, biodegradability or solubility in water. – Class II B: Inert: waste that, when placed in contact with distilled or deionized water, at room temperature, none of its constituents are solubilized at concentrations higher than the standards for potable water, except for appearance, color, turbidity, hardness and flavor. Sewage sludge, according to this standard, fits into class II, not inert, and according to Santos (2003) the leaching, solubilization and gross mass analyzes of various sludge’s showed that sludge’s in general are not hazardous waste.

2.6 Treatment Process in the STP Mangueira and STP Curado The STP of Mangueira shown schematically in Fig. 3 is composed of a pumping station, which has the function of raising, by means of pumps, the sewage from the network to the ETE: Bar Grade, which is the equipment used to retain coarse material, not retained in the pumping station and harmful to the treatment process. A sandbox (desander) is also part of the system, which is intended for the retention of sand carried from the sewers, in addition to the anaerobic reactor of upward flow and sludge blanket (UASB) and polishing pond, with natural dehydration of the excess sludge UASB and drying beds, with a production of approximately 10 ton/ month (dry mass with 60% moisture) of sewage sludge. The sludge formed in the

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UASB reactor results from the treatment of typically domestic sewage. According to Faustino (2007), for an urban region, with basically domestic sewage sludge, the use of sewage sludge in the production of seedlings for afforestation is more viable for the sludge produced in this STP. Thus, in order to meet environmental and technical restrictions, a sludge management plan at the STP of Mangueira was prepared with the aim of enabling its safe and controlled agricultural recycling, compatible with human, financial and technological resources. In the chemical mobility test carried out by Silva (2008), using the sludge from the STP of Mangueira and soil-sludge mixtures in the proportions of 25, 50, and 75 mg/ha. The author obtained the results shown in Tables 1 and 2. In the soil-sludge mixture, the pH variation has the opposite behavior to that observed between EC, Cu2+ , Zn2+ , Fe2+ and Cd2+ . The pH decreases with increasing

Fig. 3 STP of Mangueira

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Table 1 Values of pH, electric conductivity and cations of the soil and mixtures soil-sludge Determination

Soil initial

Soil final

Soil-sludge mix (mg/ha) 25

pH water 1:2.5

Top

6.3

Base EC (μS/cm)

Top

–

Base Cu2+ (mg/ml)

Top

1.5

Base Fe2+

(mg/ml)

Top

1.8

Base Fe2+ (mg/ml)

Top

160

Base Cd2+ (mg/ml)

Top Base

–

50

75

5.85

6.05

5.09

6.13

6.30

5.61

5.09 5.31

9.80

33.9

52.97

77.23

10.43

25.37

45.57

69.77

0.15

0.31

0.28

0.30

0.22

0.10

0.22

0.23

0.83

0.90

1.50

1.58

0.52

0.37

0.49

0.45

26.63

28.75

28.96

37.23

30.44

24.56

23.74

23.76

0.18

0.02

0.08

0.18

0.01

0.02

0.10

0.02

dose; however, the other attributes increase when the levels used increase. It should be noted that for the macroelements (K+ , Na+ , Mg2+ , Ca2+ , Al3+ , P, N), as well as for cadmium—Cd and EC, there is also an increase in the values obtained with the increase in doses, in relation to raw soil, the opposite occurring for pH. The highest concentrations of tested elements were found at the top of the samples, with a retention of the same in the first centimeters of the soil, in concentrations of 25, 50 and 75 mg/ha in relation to the natural soil. There is a contrast between samples with higher concentrations. There is also a contrast between pH and EC variables and a direct correlation between EC and element concentration. This shows that the lower the pH, the greater the availability of the studied element.

2.6.1

STP of Curado

At the STP of Curado, the sanitary effluent undergoes preliminary treatment, consisting of a grid of bars and a sandbox. Then it goes to the maturation vat, whose detention time is approximately 3 days. It then passes through the up-flow anaerobic filter from where it goes to the decanter. After decantation, the decanted effluent goes to the drying bed. The sludge is the result of secondary decantation after the anaerobic filter of ascending flow, being mixed in the composting unit with solid residues. This station treats organic waste from sewage sludge and industrial sludge. The chemical, physical, mineralogical and microbiological characterization of the sewage sludge must be carried out so that the sewage sludge can be classified according to ABNT 10004 and so that no risk occurs with the handling and use of this material. For comparison purposes, the limits for heavy metals in sewage are verified according to CONAMA 375/06, and values obtained at STP of Mangueira and Curado, and shown in Table 3.

1.65

0.21

Fe2+ (mg/ml)

Cd2+

0.11

1.17

0.16

6.69

353.33

22.19

37.26

0.03

0.08

7.65

0.25

pH water (1:2.5)

EC (μS/cm)

P (mg/kg)

Na+ (mg/kg)

Cu2+ (mg/ml)

(mg/ml)

Zn2+

Fe2+ (mg/ml)

Cd2+ (mg/ml)

0.06

0.88

0.14

0.11

38.01

22.47

1466.00

6.61

25 (mg/ha)

0.02

0.72

0.07

0.08

36.91

21.96

2233.3

6.70

50 (mg/ha)

0.99

1.57

0.03

0.03

0.03

0.73

0.13

0.06

37.39

22.20

3213.3

6.67

75 (mg/ha)

0.01

2.53

0.03

0.16

119.67

26.67

0.09

9.45

0.10

0.13

30.00

18.33

407.0

0.13

0.53

0.09

0.05

35.00

21.33

774.33

6.92

25 (mg/ha)

0.04

1.68

0.06

0.05

37.44

22.21

149.11

6.66

0.02

0.08

0.06

0.07

37.24

22.12

324.67

6.68

25 (mg/ha)

0 (mg/ha)

0.05

(mg/ml)

Zn2+

0.05

119.33

24.3

620.0

7.22

0 (mg/ha)

0.05

Cu2+ (mg/ml)

137

26

760.0

7.74

75 (mg/ha)

4th 15 days in leaching (day 45)

138.7

Na+ (mg/kg)

741.0

7.84

50 (mg/ha)

3th 15 days in leaching (day 30)

27.7

P (mg/kg)

(mg/ml)

2.40

EC (μS/cm)

7.45

25 (mg/ha)

0 (mg/ha)

8.05

0 (mg/ha)

pH water (1:2.5)

2nd 15 days in leaching (day 30)

1st 15 days in leaching (day 15)

Table 2 Average values of the chemical analysis of the effluents collected with 15, 30, 45 and 60 days in leaching

0.02

0.60

0.07

0.04

37.36

22.18

732.00

6.67

50 (mg/ha)

0.07

1.72

0.09

0.08

41.33

24.00

1311.0

6.32

50 (mg/ha)

0.04

0.27

0.22

0.08

37.35

22.17

1206.67

6.67

75 (mg/ha)

0.03

1.68

0.15

0.32

45.00

21.22

1626.0

6.82

75 (mg/ha)

Sewage Sludge: Some Applications in Civil Engineering 109

110 Table 3 Chemical analysis of the content of the metals in the sludge

M. C. A. Feitosa et al.

Concentration maximum allowed (mg/kg mass dry) Metals

CONAMA 375/06

STP Mangueira

STP Curado

As

41

–

0.41

Ba

1300

–

242.45

Cd

39

–

1.86

Pb

300

–

9.66

Cu

1500

155

20.89

Cr

1000

–

10.49

Hg

17

–

Mo

50

–

23.21

Ni

420

–

8.73

Se

100

–

Zn

2800

548

0.157

0.22 86.54

2.7 Applications of Sewage Sludge in the Civil Construction Industry The use of waste has been shown to be a technically promising possibility as a constituent material in the manufacture of products in the civil construction sector. Durante-Inguza et al. (2006) defend the use of waste as an environmentally correct practice, with a view to reducing the consumption of natural resources—both in the form of raw material and in the form of energy—and the reduction of costs and environmental damage resulting from inadequate final disposal methods (GarciaLodeiro et al. 2016; Durante-Inguza et al. 2006). According to Santos (2003), different ways of recycling sewage sludge as building materials are being suggested internationally as safe alternatives for encapsulating heavy metals, reducing polluting atmospheric emissions, reducing the volumes required in landfills and consequently reducing of costs, in addition to being a way of making beneficial use of available raw materials and energy, causing savings in the extraction of these resources from the environment, even if in small quantities, and thus adapting to the model of sustainable development. In order to investigate the options for managing sewage treatment residues, Santos (2003) made a comparative analysis of the market aspects which are involved in each technically viable recycling system. Competition with other markets, technological innovations, incentives for recycling products/systems, demand for recycled products and aspects of the production system were evaluated. As a result, the most favorable market for the use of sewage sludge samples was the Ceramic Industry, followed by the Civil Construction market (light aggregate) and finally the cement market. Some applications of sewage sludge will be presented below. It is worth noting that no studies were found in the literature using sewage sludge to improve collapsible soils.

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Manufacture of Lightweight Aggregates

Brosch et al. (1976) produced the first lightweight aggregates using sewage sludge. The sewage sludge in this study was first used in its raw state and then digested and dehydrated at the STP of Pinheiros, in the city of São Paulo. The process used was sintering, which consisted of the following steps: sludge drying; pelletization and transformation into light aggregates through sintering, where the agglomerates are calcined by self-combustion. The quality of these aggregates was considered satisfactory in terms of abrasion resistance and mechanical resistance to crushing. The sewage sludge produced in the city of Londrina was used to produce lightweight aggregate. From the studies carried out, it can be concluded that the final product presented characteristics compatible with the requirements and criteria established by the Brazilian specifications regarding the production of concrete elements for masonry, production of structural concrete or for thermal insulation (Morales and Agopyan 1992). The researchers from the Technological Research Institute—IPT, carried out an experimental research on the use of digested sludge from the STP of Pinheiros— São Paulo. This team obtained a material that, after crushing, was classified within the specifications of lightweight aggregate for civil construction purposes, with uses in concrete structures, thermal insulation, filling voids, prefabrication of buildings and blocks for masonry and floors. A semi-industrial installation, whose project was developed by Brazilian companies, was implanted next to the station of Leopoldina (Water Quality Recovery Station, with mechanical and electrical components of national manufacture, and was in operation from June 1979 until the end of 1982 (Santos 2003). The light aggregate production process, based on digested sewage sludge, went through the following unit operations: sludge dehydration; post-drying of centrifuged sludge; dosing and mixing of components; pelletizing; drying the pellets by fluidized bed; sintering; sinter breaking and crushing and sinter stabilization and classification (Brosch et al. 1976). The quality control of ALL—(Light Sludge Aggregate), was carried out by the concrete laboratories of Sabesp—Secretariat of Basic Sanitation of the State of São Paulo. Concretes made with ALL, compared with concretes of the same mix using Cinasita expanded clay, the only competitor in the national market at the time, showed better workability. As for the resistance to axial compression, they obtained maximum values of 29 MPa, only 12% below the concrete produced with expanded clay. ALL was used in works by Sabesp itself, in the concrete of the footbridges on the Anchieta Highway, and as filler in the lowered slabs of Shopping Ibirapuera (Santos 2003). According to Santos (2003), among several works in the manufacture of lightweight aggregates, internationally it is possible to highlight the one developed by Dr. George Harrison for the San Diego Region Water Reclamation Agency. He started to produce a lightweight aggregate from sewage sludge through a process called CCBA (Coordinate Chemical Bonding Adsorption). The process consisted of the following stages: mixing the sewage with clay, aluminum and polyacrylic acid; coagulation and flocculation; decantation (sludge with 45% solids); mixing

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with clay; extrusion; cut to form pellets about 6 mm in diameter; and burns between 1070 to 1095 °C. The lightweight aggregate complied with ASTM standards. From this aggregate, concretes with resistance above 35 MPa and blocks with more than 6.5 MPa were obtained (George 1986). For Fontes (2003), the reduction in compressive strength is small for a replacement of up to 30% of sludge, in relation to the mixture made only with Portland cement; in addition, the absorption capacity of the specimens added with sludge was reduced, resulting in a more durable structure. This phenomenon is explained by the granulometry of the sludge being finer than that of cement. According to Geyer (2001) the possibilities of using ash in concrete are restricted to low strength concrete.

2.7.2

Raw Material for Manufacturing Portland Cement and Pozzolans

A laboratory-scale study sought to develop a Portland cement from sewage sludge (Tay and Show 1997). Portland cement has limestone and clay as raw materials, the latter being replaced in the study by dehydrated sludge. The properties of cement produced in this way, as well as conventional Portland cement, were analyzed. The first step was the drying of the sludge sample, a necessary condition for grinding and adequate mixing with the limestone. Dehydrated sludge samples were dried at 105 °C, soil and mixed with limestone powder in different proportions. These mixtures were soil between 250 and 350 μm, incinerated at different temperatures and detention times. The final product was milled to a granulometry smaller than 80 μm. The properties of cement produced in this way, as well as conventional Portland cement, were analyzed. The best cement produced was the one resulting from the mixture of 50% dry sludge and 50% limestone, by mass, with a firing temperature of 1000 °C and a kiln resistance time of 4 h. Tests revealed that there were no expansion issues. The setting time was fast, which can be attributed to the lack of gypsum addition normally incorporated in conventional cements, and the pozzolanic reactivity was very low. The compressive strength after 28 days reached 6.28 MPa—about 27% of the value obtained for a common Portland cement. Despite the study’s inherent shortcomings, it reveals a potential application. Onaka (2000) tested sludge processing for nine consecutive months in a cement factory, with good results. The process began with drying the sludge, transforming it into pellets, while conserving its organic matter and energy content. These pellets, from 2 to 10 mm in diameter, were thrown into the kiln along with the rest of the cement raw material. The organic matter was used as a complementary source of heat and the inorganic part was integrated into the clinker. Traces of heavy metals were fixed at even more diluted levels in the cement mass. Gas monitoring and product quality control did not indicate any change in relation to the values without the use of sludge. The results reveal that the incorporation of 2% of dry sludge as raw material in clinker kilns would allow consuming all the sludge generated in Japan.

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Another application is the use of calcined sludge ash in a controlled manner in the production of pozzolans that can partially replace cement clinker. The pozzolanic reactivity in calcined sludge between 750 and 800 °C, due to the presence of montmorillonite, was confirmed by Morales (1994), who concluded that it was possible to replace up to 35% of Portland cement consumption.

2.7.3

Raw Material for Ceramic Manufacturing

The oldest information found on the industrial scale production of bricks using sewage treatment waste refers to the Fishwater Flats WWTP, Port Elizabeth, South Africa. Since 1979, a brickyard located 15 km from the ETE has produced more than 120 million bricks from a mixture by volume of 30% sludge with 70% clay, for common bricks, and 5–8% of sludge for bricks finishing (Slim and Wakefield 1991; Werther and Ogada 1999). The sludge sample mixed with clay are soil into a dough; this homogeneous mass receives water and its moisture is adjusted to 20%, the mass is extruded and the bricks are cut. The next stage is drying in a covered environment at room temperature for two weeks, or in ovens for two days, at a temperature between 60 and 65 °C; proceed to burning, cooling and storage. In a continuous kiln, the bricks molded from the mixture of sludge and clay are heated until the samples reach a temperature of around 150 °C. At this point, the sludge begins to pyrolyze and the combustion of volatiles begins, rapidly increasing the temperature of the blocks to 800 °C. point in the kiln where the sludge is completely burned and the thermal gradient decreases, an external fuel is burned to raise the temperature to 960 °C. The use of sludge in this factory is responsible for a saving of 55 L of fuel oil for every 1000 bricks produced (Werther and Ogada 1999). Such bricks are recognized for their excellent quality; uniform color and texture, absence of cracks and are indistinguishable in appearance and odor. Compressive strength values for exposed and non-exposed bricks are respectively 40.7 and 38.3 MPa—values that are extremely superior to local standards, which are 17.0 and 14.0 MPa. The water absorption in 24 h was 13%, 30% higher than the bricks manufactured in the region, which added advantage to the product, as it increased its adherence to mortars and increased thermal and acoustic comfort. The advantages of the process are water savings, production of lighter bricks, reduction of transport costs, fuel savings in the kiln and the use of burning gases to dry the sludge sample (Werther and Ogada 1999). Herek et al. (2005) analyzed ceramic blocks of a six-hole brick, on a reduced scale, made with dry sludge from a textile industry ETE. It has been demonstrated that the manufacture of blocks can be a viable alternative, since the presence of textile fibers in the sludge must have contributed to the increase in the compressive strength of the specimens manufactured with 10% sludge. Many other studies of incorporation of dehydrated sludge and sludge ash have been carried out. According to Onaka (2000) in Japan about 70% of sludge samples are

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incinerated, and part of the ashes is used in the production of bricks and interlocking floor blocks. According to Fontes (2003), one way to reduce the volume of sewage sludge generated is incineration, with a volume reduction of around 85%. A smaller area is required for disposal and a possible use of ash in civil construction due to the elimination of organic matter and the possibility of generating energy, despite the high cost.

3 Materials and Methods In this work, one soil and two types of sludge were used. The soil was collected from Itapirema Experimental Station of the Pernambuco Agronomic Institute (IPA), Goiana/PE, and the sludge’s were collected at the STP of Mangueira and STP of Curado, all STPS located in Region metropolitan of Recife, Pernambuco.

3.1 Experimental Program: Soil, Sludge and Soil-Sludge Mixture The experimental program was carried out with samples of soil, sludge and soilsludge mixtures, and the experimental campaign is presented in Table 4. In order to analyze the physical, chemical, microstructural characterization and hydraulic conductivity, the sludge from the STP of Mangueira was used in the soil— sludge interaction and for the physical, chemical, compressibility, collapse and as an aggregate in concrete characterization it was used the sludge from the STP of Curado.

3.2 Preparation of the Samples of Soil and Soil-Sludge Mixture For the joint granulometry test by sieving and sedimentation, as well as for determining consistency limits, the materials were air-dried and manually crushed. The preparation of soil samples for the physical characterization tests followed the ABNT standards. The sludge sample collected from the STP of Mangueira was air-dried, crushed and passed through a 4 mm mesh sieve according to Silva (2008) and supplied to the Laboratory of Geotechnics already dry and in lumps. The sludge from the STP of Curado came from the STP drying bed and then packed in plastic bags to be transported to the laboratory of the Catholic University

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Table 4 Description of the experimental campaign Tests

Description

Qt. STP sludge STP STP Mangueira Curado

Physical description of Granulometry tests with deflocculant, soil, sludge, and consistency limits, real specific weight of soil-sludge the grains and compaction

20

X

X

Edometric simple test

Edometrics tests were performed with different vertical tensions of inundation, with samples compressed and flooded with distilled water

56

–

X

Edometric double test

Edometrics tests were performed with 16 samples compressed. The moisture constant was previously flooded with distilled water

–

X

10

X

–

Hydraulic conductivity Determination of the hydraulic conductivity 08 of the soil and soil-sludge mixture

X

–

Chemical mobility

Test to evaluate the mobility of the chemical 12 elements

X

–

Chemical description

pH in water, in KCl, and in CaCl2 ; Organic 29 carbon, aluminum exchangeable (Al3+ ), calcium exchangeable (Ca2+ ), magnesium exchangeable (Mg2+ ), sodium exchangeable (Na+ ), potassium exchangeable (K+ ), saturation percentage of sodium (Na+ Al3+ ), attack sulfuric, percentage of iron at the extract sulfuric (Fe2 O3 ), silica at the extract sulfuric (SiO2 ), percentage of aluminum in the sulfuric extract (Al2 O3 ), electrical conductivity in the saturation extract

X

X

Mechanical tests

Resistance to compression, sclerometric index, ultrasonic velocity and capillary absorption

–

X

Electronic microscopy Microstructural analysis of the soil, sludge and soil-sludge mixture

72

of Pernambuco and placed to dry in the air and after drying it was crushed and passed through the sieve with 4 mm mesh opening (see Fig. 4). The soil-sludge mixture using sewage sludge from the STP of Mangueira was carried out in proportions equivalent to 25, 50 and 75 mg/ha, these concentrations from the FIUC research whose purpose was the use of sewage sludge in the soil for of agriculture (Ferreira 2008). As these proportions are extremely small for civil engineering purposes, the proportions of dry weight of 5%%, 10% and 15% of sludge from the STP of Curado were chosen, to be used in partial replacement of the fine aggregate weight. The granulometry of the sewage sludge from the STP of Mangueira and the STP of Curado was evaluated following the ABNT recommendations and the moisture was

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Fig. 4 a Dry sludge—STP of Curado, and b Sieved sludge—STP of cured

evaluated at a temperature of 45 °C to constant weight, with consecutive weighing of 24 h.

3.3 Methods 3.3.1

Physical Description

After the preparation of the mixture, the physical characterization tests were carried out according to the Brazilian standards: Sample preparation [NBR 6467 (2009)], Granulometric analysis [NBR 7181 (2018)], Soil grain specific mass [NBR 6458 (2016)], Liquid limit [NBR 6459 (2017)], Plasticity limit [NBR 7180 (2020)], Compression test [NBR 7182 (2020)], by simple edometric test and double edometric [NBR 16853 (2020)]. Figure 5 shows the natural soil used in the experimental campaign. Fig. 5 Natural soil (sand silty)

Sewage Sludge: Some Applications in Civil Engineering

117

Fig. 6 PVC columns with natural soil samples and with soil-sludge mixtures equivalent to 25, 50, 75 mg/ha

3.3.2

Chemical Mobility

In these experimental tests, the experimental results were carried out by Silva (Silva 2008), which used the same soil and the sludge from STP of Mangueira. The mobility of the chemical elements was evaluated using 0.10 m PVC tubes diameter, using up to 0.21 m high samples of natural soil and soil-sludge mixtures with an equivalent of 25, 50, and 75 mg/ha. The experimental tests were done with 3 of each sample, totaling 12 columns (see Fig. 6). The sludge was mixed with the soil in the first 50 mm, simulating the disposal of the residue on the surface. In each column, daily and for 60 days, deionized water was applied relative to the field capacity of the soil, and the effluents were collected fortnightly under the base of the column for complete chemical analysis, according to Teixeira et al. (2017). After 60 days and for 5 consecutive days, the same amount of water was placed and the total amount of effluents was measured in a graduated cylinder. After the end of the tests, the moisture of the natural soil and of the soil-sludge mixtures at the top (0–0.10 m) and at the base (0.10–0.20 m) of each column were determined, the dimensions, height and diameters, at eight different points of each sample in the columns for volume evaluation, as well as determination of the wet weight of the samples.

3.3.3

Scanning Electron Microscopy Test

The microstructure of the soil and soil-sludge mixtures of the STP of Mangueira were observed from the samples collected at the top and bottom of the columns. The samples were carefully removed and placed to dry in the air, where three prismatic specimens with a base of 9.8 mm and a height of 8 mm were prepared. The specimens were molded so that no sharp or pointed instrument touched the observation surface, using the same technique described by Ferreira (2008). The specimens were fixed

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in an aluminum cylinder with a diameter of 9.8 mm and a height of 11 mm using 3 M tape and reinforced with a small amount of glue in contact. The specimens were placed in a vacuum bell type Fine Coat Ion Sputter JfC 1100 for metallization, where the specimens received a thin gold film whose purpose was electrostatic charging, providing good conduction of the electron beam. In some specimens it was necessary to carry out a second metallization, because the first one did not completely cover the sample and a higher resolution could not be obtained. After the metallization process, the surfaces of the samples were observed and photographed in the JSM LV1600 Sconning Microscope equipment by Joel from UNICAP, operating at 15 kV.

3.3.4

Hydraulic Conductivity Test

The hydraulic conductivity was determined in the laboratory using the permeameter of flexible walls, in samples of natural soil and soil-sludge mixture under the same conditions of average relative moisture and average dry specific weight of the samples of the columns. The permeameter system comprises a main control panel and is capable of testing one sample while functioning as a controller for other samples. The panel increases system capacity without duplicating key functions. The equipment can perform up to three tests simultaneously, with different pressures, as presented in Fig. 7. Samples of natural soil and soil-sludge mixtures were statically compacted at average moisture content and average dry specific weights obtained from tests on the experiment’s columns. The specimens had an average height of 109 mm and an average diameter of 98 mm. In the cell, the specimen was placed in contact with filter paper and porous stone at the top and bottom and coated with a protective latex

Fig. 7 Permeameter of flexible walls to obtain hydraulic conductivity

Sewage Sludge: Some Applications in Civil Engineering

119

membrane. Care was taken during the lining of the specimen, using rubber alloy to improve the fixation and offer security to its side, avoiding contact with water on this face. After assembling and connecting the cell to the control panel, it began to fill with water, applying lateral pressure to remove air from the porous stones and pipe lines, draining a little water from the set, with the purpose of remove air bubbles from the surface. The saturation of the samples was practically immediate, being verified through the parameter B = Δu/Δσ3 , where Δu is the increased pore-water pressure and Δσ3 is the increased and confining tension), using a transducer with external reading of pore-pressure. After saturation, a confining voltage Δσ3 , from 0, 15, 25, 50, 75, 100, 150, and 200 kPa, in stages. Between each step, and after consolidation, the hydraulic conductivity was determined. To establish the water flow in the sample, a tension difference between the base and the top of 5 kPa was applied, when, then, the time necessary for a volume of 5000 mm3 of water crossed the specimen, a process repeated until three equal time intervals were obtained.

3.3.5

Double and Single Edometric Tests

Preparation of Samples The natural soil sample was placed to dry in the open air, crushed and passed through a No. 10 sieve. To determine the hygroscopic moisture, a sample of approximately 1 kg was separated from the natural soil and the sludge. After determining the natural soil hygroscopic moisture of 1.60 and 2.48% of the sludge, water was added to the natural soil sample and to the three mixtures with 5%, 10% and 15% so that it reached the value of moisture of 5.0%. The samples were placed in the capsules and taken to a humid chamber for 24 h and after that time the moisture was checked. With the samples of soil and soil-sludge at the desired moisture content, the volumes of soil necessary for compaction of the test specimens with specific dry weights of 15.00 kN/m3 and 17.00 kN/m3 with degrees of compaction of 82% and 94%, respectively, were calculated, at 5% moisture, corresponding to an optimal moisture deviation of 3.66%. As it is sand, to minimize moisture and soil losses due to mold handling, the specimens were compacted in the rings of the edometer cells, which had an average height of approximately 20.00 mm and a diameter of 76.25 mm. The compaction was carried out statically in a manual CBR type press with a capacity of 40 kN. The previously calculated volume of soil was placed in the ring and fitted into the compaction mold. The mold has 2.5 times the value of the height of the test specimens, for placing the soil that has not yet been compacted. The shape of the mold ensures that the soil is not compacted beyond what is necessary, due to the safety system at the top, where the piston contacts the top of the mold, preventing the piston from compacting the soil further (see Fig. 8).

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(a)

(b)

Fig. 8 Compression mold at the beginning and after static compaction. a Mold in the press at the beginning of compaction; b Mold after compaction

Procedures Edometric tests, single and double, were carried out to determine the compressibility and collapsibility parameters of natural soil samples and soil-sludge mixtures in the proportions of 5, 10 and 15%, with moisture of approximately 5.0% and weights specific 15.00 and 17.00 kN/m3 . Samples were confined laterally, and distilled water was used for flooding. Fifty-six specimens were used for use in single edometric tests and sixteen specimens for double edometric tests. The tests were carried out in the Geotechnics laboratory of the Catholic University of Pernambuco, in conventional Bishop type presses, with a loading system using weights and a strut, with a ratio of 1:10, and fixed ring-type edometric cells. The strain readings were monitored using an extensometer, with a sensitivity of 0.01 mm. The assembly procedures were the same for all tests. The specimen compacted in the ring was placed on the filter paper (see Fig. 9), placed on the porous stone (air-dried) and the assembly mounted on the edometric cell. After assembly, the top of the cell was wrapped in plastic affixed with rubber bands to prevent moisture loss; this procedure was initially adopted by Jennings and Knight (1957), and used until today by several authors (Guimarães Neto 1997; Motta 2006; Souza Neto 1998; Futai 1997). Only in the double tests, with the sample previously flooded, it was not necessary to protect the top of the cell. At the beginning of the tests, single or double, a minimum tension of 3.75 kPa was applied to the system for settlement and for the initial reading of the deformation process. The settlement resulting from this tension was attributed to the accommodation of the system, not being considered in the calculation of the deformations. Vertical stresses (σvi ) were applied incrementally (Δσ/σ = 1). Different specimens were flooded at tensions of 10, 20, 40, 80, 160, 320 and 640 kPa. The duration of each stress stage was such that the deformation between two consecutive time intervals (Δt/t = 1) was less than 5% of the total soil deformation occurred up to the previous time, according to Ferreira (2008). When that time was less than one hour, at least one hour was allowed. Flooding was done from the base to the top of the cell. The deformations due to flooding were monitored until stabilization and the readings

Sewage Sludge: Some Applications in Civil Engineering

(a)

(c)

121

(b)

(d)

Fig. 9 Edometer cells assembly procedure: a specimen in the edometer cell; b edometer cell after assembly; c cell with protection for avoid loss of moisture; d press where will be placed the edometer cell

were taken during 24 h, in times of 0.6; 0.25; 0.50; 1; two; 4; 8;15; 30; 60; 120; 240; 480 and 1440 min. At the end of the test, 24 h after the start of flooding under different stresses, the cells were drained and disassembled and the specimens removed and weighed to determine the moisture content of the soil and soil-sludge mixtures. In the double edometric tests, two loading conditions were tested: in natural moisture (constant moisture), and with the specimen previously flooded. The first condition follows the entire sequence described for the simple edometric test, but without flooding, with loading up to 640 kPa and then unloading to 320 kPa, 80 kPa and 20 kPa, then it was disassembled to remove the specimen and determine the content of soil moisture and soil-sludge mixtures. In the second condition, the specimen, under a minimum tension of 3.75 kPa, was flooded and its deformations were monitored until stabilization. Only 24 h after the flooding were the loading stages started, with the objective of the soil reaching saturation. The vertical tensions were applied in the same incremental way as in the simple edometric tests (Δσ/σ = 1), starting with 10 kPa up to the tension of 640 kPa and unloading to 320 kPa, 80 kPa and 20 kPa. With the same duration time for each voltage stage of the previous item.

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Chemical Characterization of Soil, Sludge and Soil-Sludge Mixture

The chemical tests of the soil, sludge and soil-sludge mixture were carried out at the Chemical Analysis laboratory of the Catholic University of Pernambuco and the methods used are in accordance with the soil analysis methodology adopted by the National Service for Soil Survey and Conservation, in accordance with the Soil Analysis Methods Manual of the Brazilian Agricultural Research Corporation (Teixeira et al. 2017). These tests were carried out on the soil and soil-sludge mixtures of the STP of Curado. The sample preparation procedure was the same for both soil and sludge. The collected samples were spread on trays to dry and crumbled with the aid of a mortar grade hand. After identification, the samples were sent to the Chemical Analysis laboratory to carry out the tests. Assays were performed in triplicate and the difference between results did not exceed 0.1% of the value in relation to the titers. Some tests are described according to Paiva (2008).

Hydrogenionic Potential—pH In the test, a Marconi brand equipment (model MOD 2006) with combined electrode was used. The pH in soil and sludge samples serves to determine the presence of exchangeable aluminum and also the predominance of clay in weathering process which is verified by changing the pH in water and the pH in KCl. It also verifies the tendency of systems with high concentrations of H+ and Al3+ to flocculate.

Organic Carbon and Organic Matter In determining this test, a digester block was used to carry out the reaction of potassium dichromate (K2 Cr2 O7 ) with the organic matter in a strongly acidic medium (H2 SO4 ) to then be titrated with ammoniac ferrous sulfate. As the amount of organic matter in the soil defines the formation of a greater or lesser amount of aggregate in the structure, aggregates formed by an organic matter content > 3.5% are considered unstable. And the organic carbon content varies with the clay content in the mineral fraction, the organic matter calculation is always 1.724 times greater than the organic carbon.

Exchangeable Acidity The exchangeable acidity (H+ + Al3+ ) corresponds to the acidity released by the reaction with an unbuffered potassium chloride solution, also defined as the actual acidity that is used in the determination of the effective cation exchange capacity

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(ECC), also defined as the sum of bases (Teixeira et al. 2017). It was determined by titration with NaOH and phenolphthalein as an indicator.

Electrical Conductivity and Percentage of Water in the Saturation Extract The electrical conductivity in the saturation extract is used to predict the number of salts ions (cations and anions). The test was carried out by conductivity tract determined by volumetric.

Specific Surface and Methylene Blue Adsorption The aqueous methylene blue solution in contact with the clay minerals forms a layer around the surface, involving every particle, making it possible, through this technique, to calculate the specific surface (SE) and the adsorption of methylene blue. Thus, the greater the specific surface of the clay mineral, the greater the amount of methylene blue adsorbed and the smaller the particle size. The test was carried out through volumetric absorption (Santos 2003; Paiva 2008). It is a quick and simple technique where a methylene blue solution is used to determine the specific surface and the adsorption of methylene blue where the cations that are adsorbed on clay minerals are replaced by methylene blue (Paiva 2008).

3.4 Use of Sewage Sludge as Fine Aggregate in Concrete In this work, the feasibility of using sewage sludge as a partial substitute for sand to produce concrete was studied. In order to evaluate the potential of this residue, physical and mechanical tests were carried out on all mixtures, in the Materials laboratory of the Catholic University of Pernambuco. The experimental procedure was carried out in three stages: characterization of the raw materials (sand, gravel, cement, and sewage sludge), dosage studies for the qualification and selection of four concrete mixes, three of which with different proportions of sludge in relation to the dry weight of sand and a standard mix (reference concrete), without the addition of sludge and, finally, the evaluation of the mixtures in the fresh state and the performance of the concrete in the hardened state. Two mixes were chosen 1:0.54:1.54 for water-cement ratio (w/c = 0.57) and 1:2.5:2.34 and water-cement ratio (w/c = 0.65), in order to compare the results of the present research with other studies using sewage sludge as the Evaluation of the compressive strength of concrete with the use of Construction and Demolition Waste aggregate (1:0.54:1.54:0.57) (Oliveira et al. 2007), and the Study of the Potentiality of sludge ash from Sewage Treatment Plants as a supplementary material for the production of concrete with Portland cement (1:2.5: 2.34:0.65) (Fontes 2003). The components used in the manufacture of concrete were:

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Table 5 Trace and consume of the concrete by m3 (w/c = 0.57) Trace (1: a:l:b)

Mixture

Cement (Kg)

Sand (a) (Kg)

Sludge (l) (Kg)

Gravel (b) (Kg)

Water (Kg)

Sand

1: 1.50: 2.50

423.10

634.65

–

1057.75

241.17

Sand + 5% sludge

1: 1.51: 0.08: 2.59

371.28

560.63

29.70

961.62

211.63

Sand + 10% 1: 1.32: 0.15: 2.47 sludge

388.75

513.5

58.31

960.21

221.59

Sand + 15% 1: 0.80: 0.14 1.57 sludge

395.69

316.55

55.40

621.23

225.54

a—sand; b—gravel; l—sludge

• CP II Z 32 RS sulphate-resistant composite Portland cement, manufactured in accordance with Brazilian standards. • The aggregates used in making concrete were washed quartz sand and 25 mm crushed stone. The main physical parameters of fine and coarse aggregates were analyzed according to NM 1987 recommendations. • The water used for the production of concrete came from the water supply company in the city of Recife. 3.4.1

Concrete Doses

For mixing the concrete, a concrete mixer was used, with a capacity of 110 L, aiming at a compressive strength of 25 MPa at 28 days. First, coarse aggregates were added, followed by fine aggregates and half of the predicted water. The concrete mixer was then activated for 1 min, in order to promote the mixture between the sand and the gravel. Then, the cement and the rest of the water were added. Four traits were made, the first being a reference (without adding sewage sludge), and the other three with sludge in the proportions of dry weight 5%, 10% and 15% in partial replacement of sand. The traces referring to the mixtures as well as the consumption per m3 with a w/c ratio of 0.57 and 0.65 are shown in Tables 5 and 6. For comparison purposes, the same reference trait of the research carried out with concrete using construction and demolition waste (Oliveira et al. 2007) and sewage sludge ashes was chosen (Fontes 2003).

3.4.2

Molding of the Specimens

The casting of the concrete was carried out in accordance with Brazilian standards. For each manufactured concrete, 09 cylindrical specimens of 0.10 m in diameter and 0.20 m in height were molded. Concrete consistency, expressed by measuring the slump of the truncated cone—NM 67/98. The slump was kept constant (90 ± 10 mm), shown in Fig. 10. Then, after a period of 24 h, the specimens were de-molded

Sewage Sludge: Some Applications in Civil Engineering

125

Table 6 Trace and consume of the concrete by m3 (w/c = 0.65) Mixture

Trace (1: a:l:b)

Cement (Kg)

Sand (a) (Kg)

Sludge (l) (Kg)

Gravel (b) (Kg)

Water (Kg)

Sand

1: 2.33: 2.85

342.85

798.84

–

977.12

222.85

Sand + 5% sludge

1: 2.21: 0.12: 2.18 343.88

759.97

41.26

749.66

223.52

Sand + 10% sludge

1: 1.44: 0.16: 2.53 384.91

554.27

61.58

973.82

250.19

Sand + 15% sludge

1: 1.08:0.19: 2.14

453.20

79.73

898.01

272.76

419.63

Fig. 10 Trunk cone slump test

and immersed in a tank with water until the test age was completed, 7, 14, and 28 days.

3.4.3

Carrying Out the Tests

To carry out the tests, 72 specimens were molded, with 0.10 m in diameter and 0.20 m in height. Of the total number of specimens, 48 were used for compressive strength, sclerometry and ultrasonic velocity tests and the remaining 24 for capillary absorption tests. For each execution of the tests, two specimens of each mix and composition were used, except for the absorption test where three specimens were used. Their purpose is to evaluate the performance of concrete in terms of mechanical tests, as described in Table 7. The tests were carried out at the Materials Laboratory of the Catholic University of Pernambuco in accordance with the ABNT standards: Determination of compressive strength (NBR 7222 2011), sclerometry (NBR 7584 2012), ultrasonic propagation velocity (NBR 8802 2019), and water absorption by capillarity (NBR 9779 2020).

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Table 7 Program experimental of concrete for relationship w/c = 0.57 and w/c = 0.65 Mixtures

Physical and mechanical tests

Samples dimensions (cm)

Test time (days)

Number of samples per age

Sand

Axial compression resistance

10 × 20

7, 14 and 28

02

Sclerometric index

Sand + 5% sludge

Sand + 10% sludge

Sand + 15% sludge

10 × 20

7, 14 and 28

02

Ultrasound velocity 10 × 20

7, 14 and 28

02

Absorption by capillarity

10 × 20

7, 14 and 28

03

Axial compression resistance

10 × 20

7, 14 and 28

02

Sclerometric index

10 × 20

7, 14 and 28

02

Ultrasound velocity 10 × 20

7, 14 and 28

02

Absorption by capillarity

10 × 20

7, 14 and 28

03

Axial compression resistance

10 × 20

7, 14 and 28

02

Sclerometric index

10 × 20

7, 14 and 28

02

Ultrasound velocity 10 × 20

7, 14 and 28

02

Absorption by capillarity

10 × 20

7, 14 and 28

03

Axial compression resistance

10 × 20

7, 14 and 28

02

Sclerometric index

10 × 20

7, 14 and 28

02

Ultrasound velocity 10 × 20

7, 14 and 28

02

10 × 20

7, 14 and 28

03

Absorption by capillarity

Compressive Strength Test It was observed that the specimens had some irregularities on the top surface which caused a non-uniform distribution of the compressive stress at certain points, which could interfere with the resistance results. In order to achieve better surface uniformity, that is, to make them as flat as possible, corrections were made on the top and bottom of the specimens. Once the specimens were rectified, the tests were carried out using a Universal Testing Machine, digital with a capacity of 1000 kN. The specimen was placed directly on the bottom plate of the press, so that it was centered in relation to the loading axis. The specimens were broken in compression at the ages of 7, 4 and 28 days, counted from the time of molding. Compressive strength is obtained by dividing the applied load by the cross-sectional area of the specimen. Figure 11 illustrates this test.

Sewage Sludge: Some Applications in Civil Engineering

(a)

(b)

127

(c)

Fig. 11 Compressive strength test: a specimen in the press; b ruptured specimen; c break of specimen

Sclerometry Test To carry out this test, an area of the specimen without irregularities is chosen, where a grid is drawn for the application of the reflection hammer on the surface in a perpendicular position, indicating the readings in which the impact has broken or cracked the surface of the concrete. Nine readings were performed for each specimen. Calculating the arithmetic mean of the reflection values, then determining the sclerometric index, through which information about the surface hardness of the concrete is obtained.

Ultrasonic Velocity Test After preparing the specimens, a thin layer of couplant (vaseline) is applied to the faces of the transducers or to the specimen, with the transducers on opposite faces of the material, if the transmission is direct. The time reading is done in a PUNDIT device, equipment that provides the time elapsed between the emission of the wave and its reception (t) in μs, and knowing the distance between the coupling points of the transducers (L), the wave propagation velocity (V) can be calculated, according to Eq. (1). Figure 12 illustrates the procedure for this test. V = L/t

(1)

where V is the propagation of wave velocity (m/s), L is the distance between the coupling points of the centers of the transducer faces (m), and t is the elapsed time from the emission of the wave until its reception(s).

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Fig. 12 Ultrasonic velocity test

Capillarity Absorption Test After the curing time of 28 days, the specimens were weighed and placed in an oven at a temperature of 105 ± 5 °C for 24 h, and then weighed again until reaching constant mass, according to the standard criteria. Then, the samples were placed in a closed container with a water depth of 5 ± 1 mm, constant, determining the mass of the specimens with 3, 6, 24, 48 and 72 h counted from them in contact with the water. The samples are then broken by diametric compression in order to allow the annotation of the water distribution inside. Figure 13 shows some steps of this test procedure. The water absorption by capillarity was calculated with the following equation: W = (A − B)/s

(2)

where W is the water absorption by capillarity, in g/cm2 , A is the mass of the specimen that remains with one side in contact with the water during one specified period of time, in g; B is the mass of the dry specimen, as soon as it reaches a temperature of (23 ± 2) °C, in g; and s is the area of cross section, in cm2 .

4 Results and Discussions In this section, the experimental results obtained in the tests for the physical, chemical, microstructural characterization of the soil and soil-sludge mixtures are presented and discussed, as well as the mechanical tests in different percentages of sludge, in order to study the use of sludge in soil improvement and in partial replacement of fine aggregate on concrete.

Sewage Sludge: Some Applications in Civil Engineering

(a)

(b)

(c)

(d)

129

Fig. 13 Capillarity absorption test: a specimen immersed in water; b manual press; c ruptured specimen; d absorption by the specimen

4.1 Physical Characterization of Soil, Sludge and Soil-Sludge Mixtures The results of the physical characterization tests of the soil, sludge and soil-sludge mixtures are presented in Tables 8 and 9 and in Figs. 14, 15 and 16. In the Pedological classification the soil used is a Spodosol. A sample of the same soil was separated for tests with sludge from the STP of Mangueira and another with sludge from the STP of Curado. The two soil samples used present practically the same granulometry. The first sample has 92% sand, 4% silt and 4% clay. It is a Silt Sand (SM) in the Unified Classification, non-liquid and non-plastic and in the TRB Classification System it is classified as Gravels and Silt or Clay Sands (A-24). The actual specific weight of the grains is equal to 26 kN/m3 , has an optimum moisture content of 11.90% and maximum apparent dry specific weight of 17.60 kN/m3 , presented in Table 8 and Fig. 14a and used in experiments with sludge from the STP of Curado. The second sample has 88% sand, 3% silt and 9% clay. It is a Silt Sand (SM) in the Unified Classification, non-liquid and non-plastic and in the TRB Classification System it is classified as Gravels and Silt or Clay Sands (A-2-4). The actual specific weight of the grains is equal to 26.16 kN/m3 , has an optimum moisture content of 8.66% and maximum dry apparent specific weight of 18.18 kN/ m3 , shown in Table 8 and Fig. 14b and were used with sludge from STP of Curado.

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Table 8 Dry unit weight (γd ), percentage of sand, silt, and clay in the materials analyzed and physical indexes (ideal moisture. wopt , and maximum apparent dry specific weight, γdmax ) Material

γd (kN/m3 )

Sand (%)

Silt (%)

Clay (%)

Classification Unified

TRB

wopt (%)

γdmax (kN/m3 )

STP Mangueira Soil

26.00

92

4

4

SM

A-2-4

26.00

92

Sludge

–

88

12

0

–

–

–

88

Soil + sludge (25mg/ha)

25.00

65

9

26

SM

A-2-4

25.00

65

Soil + sludge (50mg/ha)

25.00

71

4

25

SM

A-2-4

25.00

71

Soil + sludge (75mg/ha)

25.00

66

4

30

SM

A-2-4

25.00

66

Soil

26.16

88

3

9

SM

A-2-4

8.66

18.18

Sludge

16.27

96

4

0

–

–

–

–

Soil + 5% sludge

23.99

90

3

7

SM

A-2-4

12.34

17.66

Soil + 10% sludge

23.54

92

4

4

SM

A-3

13.28

18.14

Soil + 15% sludge

22.84

92

4

4

SM-SP

A-2-4

12.46

15.85

STP Curado

Table 9 Physical indexes of soil, sludge and soil-sludge mixture Material

Moisture excellent (%)

Weight-specific apparent dry maximum (kN/m3 )

Natural soil

11.90

17.60

Soil + sludge (25 mg/ha)

11.80

17.10

Soil + sludge (25 mg/ha)

11.60

17.50

Soil + sludge (75 mg/ha)

12.90

17.50

8.66

18.18

Sand + 5% sludge

12.34

17.66

Sand + 10% sludge

13.38

18.14

Sand + 15% sludge

12.46

15.85

STP Mangueira

STP Curado Natural soil

Sewage Sludge: Some Applications in Civil Engineering 100

Clay

Silt

Sand

Gravel Sand Sludge Sand +5% Sludge Sand+10% Sludge Sand+15% Sludge

90 Cumulative percentage (%)

131

80 70 60 50 40 30 20 10 0 0.001

0.01

0.1 1 Particle size (mm)

10

100

Fig. 14 Example of the particle size curves—STP of Curado

(a)

(b)

(d)

(c)

(e)

Fig. 15 Electron microscopy of: a natural soil, b sludge, c soil-sludge (25 mg/ha), d soil-sludge (50 mg/ha), and e soil-sludge (75 mg/ha)

132

M. C. A. Feitosa et al. 0.75

0.65

0.65

0.60

0.60

0.55 0.50 0.45 0.40 0.35

10 kPa 20 kPa 40 kPa 80 kPa 160 kPa 320 kPa 640 kPa

0.30 10

0.55 0.50 0.45 0.40 0.35

γd=15 kN/m3 - Sand 100

0.30 10

1000

0.70

0.65

0.65

0.60

0.60

Void index (-)

Void index (-)

0.75

(c)

0.70

0.55 0.50 0.45 0.40 0.35 0.30 10

10 kPa 20 Kpa 40 kPa 80 kPa 160 kPa 320 kPa 640 kPa

10 kPa 20 Kpa 40 kPa 80 kPa 160 kPa 320 kPa 640 kPa

γd=15 kN/m3 - Sand+5% sludge 100

1000

Vertical stress of consolidation (kPa)

Vertical stress of consolidation (kPa)

0.75

(b)

0.70

Void index (-)

Void index (-)

0.75

(a)

0.70

10 kPa 40 kPa 160 kPa 640 kPa

20 Kpa 80 kPa 320 kPa

(d)

0.55 0.50 0.45 0.40

γd=15 kN/m3 - Sand+10% sludge 100

Vertical stress of consolidation (kPa)

1000

0.35 0.30 10

γd=15 kN/m3 - Sand+15% sludge 100

1000

Vertical stress of consolidation (kPa)

Fig. 16 Void index versus vertical consolidation stress in simple edometric tests for apparent dry specific weight 15.00 kN/m3 : a sand b sand + 5% sludge, c sand + 10% sludge, d sand + 15% sludge

The granulometric composition of the sludge from the ETE Mangueira consists of 88% of granules (with dimensions between 4.8 and 0.1 mm) and 12% with dimensions smaller than 0.1 mm. The sludge from the STP of Curado is composed of 96% granules (with dimensions between 4.8 and 0.05 mm) and 4% with dimensions smaller than 0.05 mm, with a real specific weight of the grains equal to 16.70 kN/m3 . Soil mixtures with sewage sludge from STP of Mangueira are also classified as Silt Sand (SM), non-liquid, non-plastic. However, the addition of sewage sludge to the natural soil significantly increased the percentage of the clay fraction of the material, changing from 4% in the natural soil to values between 25 and 30% in the sludge-soil. The actual specific weight of the grains in the soil-sludge decreased a little (25 kN/m3 ), see Table 8. Soil mixtures with sewage sludge from the STP of Curado in the proportions of 5 and 10% are also classified as Silt Sand (SM), non-liquid, non-plastic. In the proportion of 15% it is classified as poorly graded Silt Sand (SM-SP), not liquid, not plastic. In the TRB Classification System, mixtures in the proportions of 5 and 15% are classified as Boulders and Silt or Clay Sands (A-2-4). And the mixture in the proportion of 10% is a Fine Sand (A-3). The real

Sewage Sludge: Some Applications in Civil Engineering

133

specific weights of the grains decreased (23.99 kN/m3 , 23.54 kN/m3 and 22.84 kN/ m3 ) in relation to the soil, see Table 8 and Fig. 14. Table 9 shows the values of the optimum moisture content and the maximum apparent dry weight of the soil and soil-sludge mixtures. It can be seen in that the optimum moisture ranged from 11.60% to 12.90% and the maximum dry apparent specific weight was between 17.10 and 17.60 kN/m3 . There is a small influence of the mixture of sewage sludge with the soil in these indices, in relation to the natural soil, because the amount of sludge placed is small. Observing Fig. 16b, we verify that there is a decrease in the maximum apparent specific weight with the increase in the percentage of sludge, except for the proportion of 10% and that the optimal humidity increases with the increase of sludge up to 10% and subsequent decrease. Adding sludge to the soil decreases the maximum specific weight (γdmax ) and increases the optimum moisture content (Wot ). The influence of sludge addition is significantly higher.

4.2 Chemical Mobility Test of Soil and Soil-Sludge Mixtures—STP of Mangueira Analyzing the physical effects in chemical mobility assays. It is observed that in the natural soil, the humidity at the base of the experimental column is higher than at the top. The water used is not retained in the first 0.10 m of the soil. With the addition of sludge to the soil, water is stored more on the surface (top), in increasing amounts, as the sludge dose is increased, Table 10. The sludge gives the soil a greater capacity to retain water on the surface, according to Melo and Marques (Melo and Marques 2000), increases the degree of saturation, increases the voids index and porosity and decrease specific wet and dry apparent weights, aspects of fundamental importance for the development of plant roots, and to preserve a higher degree of saturation in the soil on the surface. Table 10 Physical indices of natural soil and soil-sludge mixtures Material

Moisture (%)

Sr (%)

e

n (%)

γh (kN/m3 )

γd (kN/m3 )

Base

Top

Natural soil

22.68

19.49

64.28

0.86

46.07

16.98

14.02

Soil + sludge (25 mg/ha)

22.08

22.17

64.60

0.93

48.14

16.45

13.48

Soil + sludge (25 mg/ha)

27.20

31.86

65.30

1.02

50.39

16.41

12.90

Soil + sludge (75 mg/ha)

25.73

33.54

65.72

1.18

54.07

15.49

11.95

Sr —Degree of saturation; e—Index of voids; n—Porosity; γh and γd —Wet and dry apparent specific gravity, respectively

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M. C. A. Feitosa et al.

Analyzing the physical effects in chemical mobility assays. It is observed that in the soil natural, the moisture at the base of the experimental column is higher than at the top. The water used it is not retained in the first 0.10 m of the soil. With the addition of sludge to the soil, the water becomes stored more on the surface (top), in increasing amounts, as the dose of sludge is increased, Table 10. The sludge gives the soil a greater capacity to retain water in the surface, according to Melo and Marques (2000), increases the degree of saturation, increases the void ratio and porosity and decreases the weights specific humid It is apparent dry, aspects those in fundamental importance for the development of plant roots, and to preserve a greater degree of saturation at the soil in surface.

4.3 Microstructural Analysis of Soil and Soil-Sludge Mixture—STP of Mangueira The soil matrix consists of an intense amount of sand grains and little clay. The sand grains are almost entirely quartz, with varying sizes and predominantly rounded shapes with lesser intensity of angular shapes (Fig. 15a). There is a small amount of plasma, predominantly mineral (clay) partially coating the skeletal grains (sand), often not extending or forming bridges between them. This type of porosity is called Simple Packing Pores, i.e., the empty spaces are the result of the joining of particles of different sizes and shapes. The sludge consists of granulates of different shapes that connect directly or through fibers (Fig. 15b). As the amount of sludge in the natural soil increases, the sand grains are progressively coated by the LE reducing direct contact between the quartz grains, the sludge occupies the empty spaces (Fig. 15c, d, and e), taking up the volume of air.

4.4 Hydraulic Conductivity In the natural soil, the hydraulic conductivity decreases with the increase of the confining stress of values that varied from 4.8 × 10–4 m/s to 1.7 × 10–4 m/s. The addition of sewage sludge to natural soil causes a reduction in hydraulic conductivity. The reduction is 60% for a dose equivalent to 75 mg/ha. The effect of adding sludge to the natural soil causes a reduction in hydraulic conductivity equivalent to an increase of 50 kPa of confining stress.

Sewage Sludge: Some Applications in Civil Engineering

135

4.5 Chemical Characterization of the Soil, Sludge and Soil-Sludge Mixture 4.5.1

Sludge from the STP of Mangueira

The chemical characterization of soil, sludge from STP of Mangueira and soil-sludge mixtures at doses equivalent to zero, 25, 50 and 75 mg/ha, carried out after the chemical mobilization tests by Silva (2008) and collected after 60 days of leaching, divided into top (layer from 0 to 0.10 m) and base (layer from 0.10 to 0.20 m from the soil), and presented in Table 11. The pH determined in water is acidic (pH < 7). In natural soil, soil cation exchange capacity is low (CEC = 5.7 cmolcdm−3 ) with low activity (Tb), typical of clay-mineral kaolinite. When adding sludge to the soil, there is an increase in phosphorus, potassium and sodium levels; being larger at the top than at the bottom. The phosphorus content found in the soil is considered low, being observed its increase with the addition of sewage sludge. According to Tomé Júnior (2001), regardless of the type of soil, phosphorus contents will be low, below 3 mg/kg and phosphorus contents above 30 mg/kg will be high.

4.5.2

Sludge from the STP of Curado

The chemical characterization of the soil, sludge from STP of Curado and soil-sludge mixtures in the weight proportions of 5, 10 and 15%, where the determinations were carried out as described in Sect. 3, is presented in Table 12. Natural soil is acidic (pH < 7). The pH of a soil is not a constant and characteristic value as in aqueous solutions. The pH value in Potassium Chloride (pHKCl ) is lower than the pH value in water (pHH2O ) and the pH variation (ΔpH = pHKCl –pHH2O ) is negative, indicating the presence of silicate clays. The amount of organic matter obtained from organic carbon is low (less than 1.0%). The cation exchange capacity is low (Tvalue = CTC < 27 cmolc/kg), also indicating the predominance of the clay mineral kaolinite. The saturation per base expressed as a percentage (value of V) is less than 50% in the case of a Dystrophic soil. The percentage of sodium in the exchangeable complex (100 Na+ T−1 ) of 2.3% is low (2.3%) less than 6%. The electrical conductivity of the saturation extract is high (10 mS/cm/25 °C) greater than 4 mS/cm/25 °C. As sludge is added to the soil from 5 to 15%, the mixtures thus formed have a practically neutral pH (approximately 7), the organic matter content grows but is still low, the cation exchange capacity grows and from the proportion of 10% the mixture has a high CEC (Tvalue = CTC > 27cmolc/kg). The aluminum saturation decreases and the sodium saturation, the amount of water in the saturated extract and the electrical conductivity of the saturation layer increase when the proportion of sludge to the soil is increased.

75 mg/h

12.00

3.33

Base

2.33

Top

12.33

Base

2.33

Base

Top

2.33

50 mg/ha

2100

Top

3.33

Base

25 mg/ha

2.67

Soil-sludge

0.15

Top

Soil

K+ (cmolc /l)

66.67

67.33

69.00

72.67

60.00

68.00

300

67.67

67.67

0.08

Na+ (cmolc /l)

Chemical characterization

Soil (initial)

Sample

0.54

0.67

0.13

0.20

0.13

0.13

1200

0.97

1.14

0.55

Mg2+ (cmolc /l)

3.24

3.14

3.18

3.31

3.28

3.08

9400

3.16

3.01

3.4

Ca2+ (cmolc /l)

Table 11 Chemical characterization of soil, sludge and soil-sludge mixture—STP Mangueira

1.48

1.51

1.37

1.41

0.90

1.81

–

1.58

1.84

0.00

Al2+ (cmolc /l)

2.99

9.05

4.19

7.33

3.26

5.53

45,000

2.87

3.05

20.00

P (mg/kg)

1.12

1.09

1.32

1.02

0.76

0.53

–

1.91

1.12

–

N (mg/kg)

136 M. C. A. Feitosa et al.

Sewage Sludge: Some Applications in Civil Engineering

137

Table 12 Chemical characterization of soil, sludge, and soil–sludge mixture from STP Curado Properties

Soil

Sludge

Soil—sludge mixture 5%

10%

15%

pH in water

6.08

7.22

6.9

7.01

7.13

pH in KCl

6.00

7.30

7.06

7.15

7.18

Organic carbon (g/kg)

1.07

14.29

8.60

9.67

11.46

Organic matter (g/kg)

1.85

24.64

14.82

16.67

19.76

Mg2+ exchangeable (cmol/kg)

3.30

11.00

3.00

0.20

1.50

Na+ exchangeable (cmol/kg)

0.30

185.80

10.40

22.30

26.90

K+

exchangeable (cmol/kg)

0.20

18.40

1.30

1.90

2.20

H+ + Al3+ extracted (cmol/kg)

8.10

8.90

6.01

6.67

7.37

H+ exchangeable (cmol/kg)

7.70

8.80

5.71

6.27

6.95

Value of V (% Sat. of Base)

0.38

0.97

0.76

0.83

0.86

% Fe2 O3 in Ext. Sulfuric (g/kg)

0.50

2.25

0.63

0.75

0.88

% Al2 O3 in Ext. Sulfuric (g/kg)

1.50

3.30

1.50

3.20

3.40

Electrical conductivity (mS/cm at 25 °C)

10

9769

2708

3670

5940

Specific surface (m2 /g)

18.40

14.70

3.70

11.00

11.00

4.6 Compressibility Analysis The values of void ratios, volumetric deformations and potential collapses obtained by conventional edometric tests are shown in this item. The results of the edometric tests are represented with typical graphs, which relate void ratio (e) and specific volumetric strain (εv ), on a linear scale, with the vertical consolidation stress (σv ), on a logarithmic scale. Also presented are the curves of the variation of the collapse potential (εc ), in percentage, with the vertical consolidation stress (σv ), in a logarithmic scale for the simple edometric tests.

4.6.1

Edometric Tests

Simple Edometric Tests Simple edometric tests were carried out aiming to determine the collapse strains (εc ) under different flood stresses (σvi ). The compaction process and the moisture control allowed to obtain specimens, with apparent dry specific weights and moisture very close to the desired ones, as well as the repeatability of the results. The figures, void ratio versus vertical consolidation stress, specific volumetric strain versus vertical consolidation stress, of the soil and soil-sludge mixtures flooded with distilled water with dry apparent specific weights of 15.00 kN/m3 and 17.00 kN/m3 are shown in Figs. 16, 17, 18 and 19.

138

M. C. A. Feitosa et al. 0 (a) 2 4 6 10 kPa 20 kPa 40 kPa 80 kPa 160 kPa 320 kPa 640 kPa

8 10 12

γd=15 kN/m3 - Sand

Specific volumetric deformation (-%)

Specific volumetric deformation (-%)

0

14

4 6 10 kPa 20 kPa 40 kPa 80 kPa 160 kPa 320 kPa 640 kPa

8 10 12

γd=15 kN/m3 - Sand+5% sludge

14 10

100 Vertical stress of consolidation (kPa)

1000

10

100 Vertical stress of consolidation (kPa)

1000

0 (c)

2 4 6 10 kPa 20 kPa 40 kPa 80 kPa 160 kPa 320 kPa 640 kPa

8 10 12

γd=15 kN/m3 - Sand+10% sludge

Specific volumetric deformation (-%)

0 Specific volumetric deformation (-%)

(b) 2

(d) 2 4 6 10 kPa 20 kPa 40 kPa 80 kPa 160 kPa 320 kPa 640 kPa

8 10 12

γd=15 kN/m3 - Sand+15% sludge

14

14 10

100 Vertical stress of consolidation (kPa)

1000

10

100 Vertical stress of consolidation (kPa)

1000

Fig. 17 Specific volumetric deformation versus vertical consolidation stress in edometric tests simple for apparent dry specific weight of 15.00 kN/m3 : a sand b sand + 5% sludge, c sand + 10% sludge, d sand + 15% of sludge

The collapse potential values were calculated using Eq. (3), for vertical flood stresses of 10, 20, 40, 80,160, 320 and 640 kPa, from simple edometric tests, with compacted samples for specific weights of 15.00 kN/m3 and 17.00 kN/m3 are presented in Table 13. The variation of the collapse potential with the vertical consolidation stress of the flooded soil with different silt proportions is shown in Fig. 20. C P(%) = 100%. ΔH/Hi

(3)

where: ΔH is the variation in height of the specimen due to flooding (mm) and Hi is the height of the specimen before flooding In the soil without sludge addition for the dry specific weight of 15.00 kN/m3 , the collapse increases reaching a maximum value of 6.61% at the stress of 320 kPa and then decreases. This is the critical stress for maximum collapse. Soil compaction to a specific weight of 17.00 kN/m3 significantly reduced the collapse potentials to maximum values of 1.64% for a stress of 640 kPa. Adding silt to the soil decreases the potential for collapse. For the dry specific weight of 15.00 kN/m3 and tension of 10 kPa, the addition of 10% and 15% of sludge

Sewage Sludge: Some Applications in Civil Engineering 0.55

139

0.55 (b)

0.50

0.50

0.45

0.45

Void index (-)

Void index (-)

(a)

0.40 10 kPa 20 kPa 40 kPa 80 kPa 160 kPa 320 kPa 640 kPa

0.35 0.30 0.25

0.35

10 kPa 20 Kpa 40 kPa 80 kPa 160 kPa 320 kPa 640 kPa

0.30 0.25

γd=17 kN/m3 - Sand

γd=17 kN/m3 - Sand+5% sludge

0.20

0.20

0.55

100 Vertical stress of consolidation (kPa) 10 kPa 20 Kpa 40 kPa 80 kPa 160 kPa 320 kPa 640 kPa

0.50 0.45 0.40

10

1000 0.55 0.50

0.35 0.30

100 Vertical stress of consolidation (kPa) 10 kPa 20 Kpa 40 kPa 80 kPa 160 kPa 320 kPa 640 kPa

(c)

Void index (-)

10

Void index (-)

0.40

0.45 0.40

1000

(d)

0.35 0.30

0.25

0.25 γd=17 kN/m3 - Sand+10% sludge

0.20 10

100 Vertical stress of consolidation (kPa)

γd=17 kN/m3 - Sand+15% sludge

0.20 1000

10

100 Vertical stress of consolidation (kPa)

1000

Fig. 18 Void index versus vertical consolidation stress in simple edometric tests for apparent dry specific weight 17.00 kN/m3 : a sand b sand + 5% sludge, c sand + 10% sludge, d sand + 15% sludge

to the soil caused a small expansion. A similar behavior was observed for the dry specific weight of 17.00 kN/m3 at tensions of 10 kPa, 20 kPa with sludge addition of 10% and 15%. The average of the initial physical indices of the eight soil specimens of each soil-sludge mixture and each apparent dry specific weight was calculated. From the average values of the physical indices, the percentage of volume of each component of the mixture was calculated in percentage corresponding to soil, sludge, water and air. The experimental values are shown in Table 14 and Fig. 21. Adding sludge works efficiently to reduce collapse, similar to increasing specific gravity. For the specific weight of 15.00 kN/m3 the reduction of natural soil collapse in relation to the addition of sludge in 5%, 10% and 15% were 6.2%, 51.6% and 56.4%, respectively. For the same dry apparent specific weight, the addition of sludge increases the volume of solid particles and reduces the volume of voids. As the volume of water had small variations, the reduction that occurs in the volume of voids is due to the reduction in the volume of air. On the other hand, the volume increase that occurs of solid particles in the mixture in relation to the natural soil is significantly influenced by the difference in the actual specific weight of the soil grains (26.16 kN/m3 ) when

140

M. C. A. Feitosa et al. 0

0 2 4 6 10 kPa 20 kPa 40 kPa 80 kPa 160 kPa 320 kPa 640 kPa

8 10 12

(b)

Specific volumetric deformation (-%)

Specific volumetric deformation (-%)

(a)

γd=17 kN/m3 - Sand

2 4 6

10 12

γd=17 kN/m3 - Sand+5% sludge

14

14 10

100 Vertical stress of consolidation (kPa)

10

1000

100 Vertical stress of consolidation (kPa)

1000

0

0 (c)

Specific volumetric deformation (-%)

Specific volumetric deformation (-%)

10 kPa 20 kPa 40 kPa 80 kPa 160 kPa 320 kPa 640 kPa

8

2 4 6 10 kPa 20 kPa 40 kPa 80 kPa 160 kPa 320 kPa 640 kPa

8 10 12

γd=17 kN/m3 - Sand+10% sludge

(d) 2 4 6 10 kPa 20 kPa 40 kPa 80 kPa 160 kPa 320 kPa 640 kPa

8 10 12

d=17

kN/m3 - Sand+15% sludge

14

14 10

100 Vertical stress of consolidation (kPa)

10

1000

100 Vertical stress of consolidation (kPa)

1000

Fig. 19 Specific volumetric deformation versus vertical consolidation stress in edometric tests simple for apparent dry specific weight of 17.00 kN/m3 : a sand b sand + 5% sludge, c sand + 10% sludge, d sand + 15% of sludge Table 13 Collapse potential of simple oedometer tests Vertical flood stress (kPa)

Dry specific weight—15.0 kN/m3

Collapse potential—CP (%) Dry specific weight—17.0 kN/m3

0% Sludge

5% Sludge

10% Sludge

15% Sludge

0% Sludge

5% Sludge

10% Sludge

15% Sludge

10

0.11

0.13

−0.49

−0.92

0.11

−0.11

−0.37

−1.12

20

0.50

0.16

−0.06

−0.04

0.41

−0.05

−0.29

−0.60

40

1.30

0.40

0.52

0.05

0.45

0.32

0.02

−0.31

80

3.75

1.30

1.03

0.29

0.61

0.49

0.76

0.65

160

4.99

2.15

1.30

0.80

0.63

0.63

0.78

1.26

320

6.61

4.50

1.96

1.67

0.88

0.53

0.79

1.61

640

5.81

5.45

2.81

2.53

1.64

0.41

1.08

2.21

Sewage Sludge: Some Applications in Civil Engineering -2

-2 (a)

γd = 15.0 KN/m3

γd = 17.0 KN/m3

(b)

-1

Potential for Collapse or Swell (%)

-1

Potential for Collapse or Swell (%)

141

Swell

0 1

Collapse

2 3 4 5

Sand Sand + 5 % Sludge Sand + 10 % Sludge Sand + 15 % Sludge

6

Swell

0 Collapse

1 2 3 4 5

Sand Sand + 5 % Sludge Sand + 10 % Sludge Sand + 15 % Sludge

6

7

7

10

100

1000

Consolidation Vertical Tension (kPa)

10

100

1000

Consolidation Vertical Tension (kPa)

Fig. 20 Collapse potential versus vertical consolidation stress in simple edometric tests for specific dry apparent weight of: a 15.00 kN/m3 and b 17.00 kN/m3

Table 14 Percentage in volume of each component from the mixture Sample

Percentage in volume Specific dry apparent weight 15 kN/m3

Specific dry apparent weight 17 kN/m3

Solid

Sludge

Water

Air

Solid

Sludge

Water

Air

57.44

0.00

7.46

35.10

65.23

0.00

8.18

26.59

Sand + 48.45 5% sludge

14.42

7.41

29.71

54.85

16.33

8.61

20.21

Sand + 10% sludge

46.26

17.72

7.61

28.40

52.47

20.10

8.61

18.82

Sand + 15% sludge

42.84

23.17

7.39

26.61

48.55

26.25

8.60

16.60

Sand

compared to the sludge (16.27 kN/m3 ). Therefore, for the same dry apparent specific weight, the addition of sludge to the soil increases the number of particles in the contacts between the grains, reducing the pores and providing greater stability to the soil structure, reducing collapse. This was shown through the scanning electron microscopy test described in Sect. 4.3.

142

M. C. A. Feitosa et al.

Fig. 21 Percentage in volume of each component from the mixture

Double Edometry Tests The double edometry tests were carried out with the soil and soil-sludge mixtures compacted with dry specific weight of 15.00 and 17.00 kN/m3 . The following figures show the relations between void ratio and vertical consolidation stress, and deformation specific volumetric and vertical consolidation stress obtained in tests on soil samples in natural moisture (constant), and flooded, are shown in Figs. 22, 23, 24 and 25 (using distilled water as flood liquid). From the results of the double edometric tests, the compression index (Cc ), the expansion index (Cs ), and the pre-consolidation stress of the soil and soil-sludge mixtures were determined, presented in Tables 15 and 16. It is observed that the parameters obtained from the tests in natural moisture were lower than those obtained from the flooded tests. For the dry specific weight of 15.00 kN/m3 , the compressibility in the natural and flooded condition increases with the addition of sludge up to 5% and decreases later with the increase of the sludge percentage. For the dry apparent specific weight of 15 kN/m3 , the pre-consolidation stress in the non-flooded soil increases with the addition of sludge to the soil up to 5% and then decreases. In the flooded soil, however, the pre-consolidation stress increases with the addition of sludge to the soil up to 10% and then decreases. For the apparent dry specific weight of 15.00 kN/m3 in the natural condition, the addition of sludge to the soil in the proportion of 5% increases the pre-consolidation stress by 30% and subsequently decreases. Showing similar behavior when flooded, with an increase in the Pre-consolidation stress of 70% for the addition of 5% of sludge, decreasing with the proportions of 10% and 15% of the sludge.

Sewage Sludge: Some Applications in Civil Engineering 0.75

0.75 (a)

0.70

0.65

Void index (-)

Void index (-)

0.60 0.55 0.50 0.45 0.40

0.30 10

Natural soil Flooded soil

100 Vertical stress of consolidation (kPa)

0.55 0.50 0.45 0.40

0.30 0.25 10

1000

0.70 0.65

0.60

0.60

Void index (-)

0.65

0.55 0.50 0.45 0.40

0.30 0.25 10

Natural soil Flooded soil

γd=15 kN/m3 - Sand+5% sludge

100 Vertical stress of consolidation (kPa)

1000

0.75 (c)

0.70

Void index (-)

0.60

0.35 γd=15 kN/m3 - Sand

0.75

0.35

(b)

0.70

0.65

0.35

143

(d)

Flooded soil

0.55 0.50 0.45 0.40 0.35

Natural soil Flooded soil

Natural soil

γd=15 kN/m3 - Sand+10% sludge

100 Vertical stress of consolidation (kPa)

1000

0.30 0.25 10

γd=15 kN/m3 - Sand+15% sludge 100 Vertical stress of consolidation (kPa)

1000

Fig. 22 Variation of the void index with the vertical stress of consolidation obtained through double oedometer tests, for dry apparent specific weight of 15.0 kN/m3 : a sand, b sand plus 5% sewage sludge, c sand plus 10% sludge, d sand plus 15% sludge

It can also be observed that with the dry specific weight of 17.00 kN/m3 the parameters obtained from the tests in natural moisture were lower than those obtained from the flooded tests. With a dry specific weight of 17.00 kN/m3 , compressibility increases with the increase in the percentage of sludge both in natural and flooded conditions. The addition of sludge in the natural condition decreases the Pre-consolidation stress by 13%, 20% and 14% in proportions of 5%, 10% and 15%, respectively, in relation to the Pre-consolidation stress of the natural soil. In the flooded condition it reduced the Pre-consolidation stresses by 10%, 76% and 71% in the proportions of 5%, 10% and 15%, respectively. In order to maintain the same dry specific weight in the soil, the increase in the percentage of sludge causes a reduction in the soil voids index, justifying a lower compressibility due to the addition of sludge.

144

M. C. A. Feitosa et al. 0 (a) 2 4 6 8

10 12 Natural soil Flooded soil

14 16 10

γd=15 kN/m3 - Sand

Specific volumetric deformation (-%)

Specific volumetric deformation (-%)

0

4 6 8 10 12 Natural soil

14

Flooded soil 16

100 Vertical stress of consolidation (kPa)

1000

10

γd=15 kN/m3 - Sand+5% sludge

100 Vertical stress of consolidation (kPa)

1000

0 (c)

2 4 6 8 10 12 Natural soil

14

Flooded soil 16 10

γd=15 kN/m3 - Sand+10% sludge

100 Vertical stress of consolidation (kPa)

1000

Specific volumetric deformation (-%)

0 Specific volumetric deformation (-%)

(b) 2

(d) 2 4 6 8 10 12 Natural soil

14

Flooded soil 16 10

γd=15 kN/m3 - Sand+15% sludge

100 Vertical stress of consolidation (kPa)

1000

Fig. 23 Variation of the void index with the vertical stress of consolidation obtained through double oedometer tests, for dry apparent specific weight of 17.0 kN/m3 : a sand, b sand plus 5% sewage sludge, c sand plus 10% sludge, d sand plus 15% sludge

5 Application of Sludge for the Substitution of Fine Aggregates for Concrete 5.1 Physical Characterization of Fine and Coarse Aggregate The granulometric curves referring to the fine aggregate used in this study and the sludge that will partially replace the sand and the coarse aggregate are shown in Fig. 26. The fine aggregate has a fineness modulus of 2.57 and specific mass of 2.65 g/cm3 and the coarse aggregate has a fineness modulus of 7.28.

5.2 Ultrasonic Velocity The velocity values for traces with respect to w/c = 0.57 and w/c = 0.65 are shown in Table 17. The graphs of ultrasonic velocity versus age, obtained in the tests, are

Sewage Sludge: Some Applications in Civil Engineering 0.55

145

0.55 (b) 0.50

0.45

0.45

Void index (-)

Void index (-)

(a) 0.50

0.40 0.35 0.30 0.25 0.20

0.40 0.35 0.30 0.25 0.20

Natural soil 0.15 0.10 10

Flooded soil

γd=17

kN/m3

0.15

- Sand

100 Vertical stress of consolidation (kPa)

0.10 10

1000

0.55

Natural soil Flooded soil

γd=17 kN/m3 - Sand+5% sludge

100 Vertical stress of consolidation (kPa)

0.55 (d) 0.50

0.45

0.45

Void index (-)

Void index (-)

(c) 0.50

0.40 0.35 0.30 0.25 0.20 0.15 0.10 10

1000

0.40 0.35 0.30 0.25 0.20

Natural soil Flooded soil

γd=17 kN/m3 - Sand+10% sludge

100 Vertical stress of consolidation (kPa)

1000

0.15 0.10 10

Natural soil Flooded soil

γd=17 kN/m3 - Sand+15% sludge

100 Vertical stress of consolidation (kPa)

1000

Fig. 24 Variation of specific volumetric deformation with the vertical consolidation stress obtained through double oedometer tests, for dry apparent specific weight of 15.0 kN/m3 : a sand, b sand plus 5% sewage sludge, c sand plus 10% sludge, d sand plus 15% sludge

shown in Fig. 27. Also included are results of Oliveira et al. (2007) with CDW, for comparison purposes. Adding a percentage of sludge to concrete as an aggregate decreases the ultrasonic velocity, although it is higher than in concrete using CDW. The values of the ultrasonic speeds for the two concretes were within the values that characterize the concretes as of good quality, according to Table 18, which shows the classification of the quality of the concrete according to the ultrasonic speed.

5.3 Sclerometer Index The mean values of the sclerometric index are presented in Table 19. The values of the sclerometric index versus age, obtained in the tests, are shown in Fig. 27 with the results of Oliveira et al. (2007) for comparison.

146

M. C. A. Feitosa et al.

4 6 8 10 12 14 16 10

Natural soil Flooded soil

γd=17 kN/m3 - Sand

100 Vertical stress of consolidation (kPa)

Specific volumetric deformation (-%)

0

4 6 8 10 12

16 10

γd=17 kN/m3 - Sand+10% sludge

100 Vertical stress of consolidation (kPa)

4 6 8 10 12 14

Natural soil Flooded soil

γd=17 kN/m3 - Sand+5% sludge

100 Vertical stress of consolidation (kPa)

0

(c)

Natural soil Flooded soil

(b)

2

16 10

1000

2

14

0 Specific volumetric deformation (-%)

(a)

2

1000

Specific volumetric deformation (-%)

Specific volumetric deformation (-%)

0

1000

(d)

2 4 6 8 10 12 14 16 10

Natural soil Flooded soil

γd=17 kN/m3 - Sand+15% sludge

100 Vertical stress of consolidation (kPa)

1000

Fig. 25 Variation of specific volumetric deformation with the vertical consolidation stress obtained through double oedometer tests, for dry apparent specific weight of 17.0 kN/m3 : a sand, b sand plus 5% sewage sludge, c sand plus 10% sludge, d sand plus 15% sludge

It is possible to observe that the sclerometric indices decrease with the increase in the percentage of sludge both for the factor w/c = 0.57 and for the factor w/c = 0.65. These values are compared with the concrete CDW by Oliveira et al. (2007), and it is possible to observe that these results higher values. Adding a percentage of sludge to concrete as an aggregate decreases the sclerometric index for the same curing date. The water/cement factor was not sensitive to the soil-sludge mixture (Fig. 28).

5.4 Compressive Strength Resistance values are shown in Table 20. The graphs of resistance to compression versus age, obtained in the tests, are shown in Fig. 29, and also the results refer to the CDW (Oliveira et al. 2007). Adding a percentage of sludge to concrete as an aggregate decreases the compressive strength and presents values close to those obtained in concrete with CDW* aggregate, Fig. 29a.

Sewage Sludge: Some Applications in Civil Engineering

147

Table 15 Coefficients and parameters of the double oedometer tests with soil samples and soil– sludge mixtures with a dry specific weight of 15.0 kN/m3 Samples

Sand + 0% sludge

Test type

Natural Flooded

Sand + 5% sludge

Natural Flooded

Sand + 10% sludge

Natural Flooded

Sand + 15% sludge

Natural Flooded

Coefficients and parameters Compression index

Vertical stress range (kpa)

Expansion index

Compression index

0.046

10–80

0.015

115.61

0.055

160–640

0.111

10–80

0.021

73.96

0.129

160–640

0.044

10–80

0.016

150.31

0.090

160–640

0.111

10–80

0.021

125.89

0.165

160–640

0.040

10–80

0.018

81.85

0.078

160–640

0.091

10–80

0.021

64.82

0.165

160–640

0.038

10–80

0.015

80

0.071

160–640

0.096

10–80

0.021

40

0.109

160–640

According to Metha and Monteiro (2013) the most used resistance in structures is moderate, in which the compressive strength varies between 20 and 40 MPa. Helene and Terziani (1995) confirm that the strength to guarantee the viability of the concrete must be greater than 20 MPa, a limit reached after 28 days for a proportion of 5% (w/ c = 0.57). The resistances in the proportions of 10 to 15% resulted below this value. For w/c = 0.65, the resistance has not reached this limit. With regard to compressive strength, we observed that it decreases with the increase in the percentage of sludge up to 10% and then increases for w/c = 0.57, which is slightly higher compared to the results of the CDW* (Oliveira et al. 2007). For w/c = 0.65, with an increase in the percentage of sludge, resistance decreases, and in relation to CDW* (Oliveira et al. 2007) it is lower.

5.5 Absorption by Capillarity The results of the water absorption values by capillarity after 72 h and the absorption by capillarity considering a time of 3 to 72 h, according to the norm, is shown in Table 21 and the results of absorption by capillarity versus time, illustrated in Fig. 30.

148

M. C. A. Feitosa et al.

Table 16 Coefficients and parameters of the double oedometer tests with soil samples and soil– sludge mixtures with a dry specific weight of 17.0 kN/m3 Samples

Test type

Sand + 0% sludge

Natural Flooded

Sand + 5% sludge

Natural Flooded

Sand + 10% sludge

Natural Flooded

Sand + 15% sludge

Natural Flooded

Clay

Coefficients and parameters Compression index

Vertical stress range (kPa)

Expansion index

Compression index

0.023

10–80

0.014

147.23

0.042

160–640

0.049

10–80

0.017

231.06

0.079

160–640

0.035

10–80

0.015

128.33

0.057

160–640

0.070

10–80

0.018

207.49

0.089

160–640

0.039

10–80

0.016

118.23

0.066

160–640

0.052

10–80

0.018

54.50

0.092

160–640

0.039

10–80

0.021

126.64

0.069

160–640

0.076

10–80

0.025

66.15

0.110

160–640

Silt

Sand

Gravel

100

Cumulative porcentage (%)

90 80

Sludge Sand Gravel

70 60 50 40 30 20 10 0 0.001

0.01

0.1 1 Particle size (mm)

Fig. 26 Granulometric curves of the aggregates

10

100

Sewage Sludge: Some Applications in Civil Engineering

149

Table 17 Values of the ultrasonic velocity Healing time (days)

Ultrasonic velocity (km/s) w/c = 0.57

w/c = 0.65

0% sludge

5% sludge

10% sludge

15% sludge

0% sludge

5% sludge

10% sludge

15% sludge

7

4.51

4.22

3.92

3.54

4.53

4.06

3.84

3.73

14

4.62

4.20

4.04

3.80

4.64

4.08

3.94

3.90

28

4.68

4.54

4.26

3.90

4.77

4.07

4.01

3.94

Note that the ultrasonic velocity values decrease with increasing sludge percentage. However, these values are higher than the values obtained by Oliveira et al. (2007)

5000

5000

(b) w/c= 0.65

Ultrasonic Velocity (m/s)

Ultrasonic Velocity (m/s)

(a) w/c= 0.57

4000

3000

Sand Sand+5 % Sludge Sand+10% Sludge Sand+15% Sludge Concrete with CDW [51]

2000 0

7

14 21 Healing time (day)

4000

3000 Sand Sand+5 % Sludge Sand+10% Sludge Sand+15% Sludge

2000

28

0

7

14 21 Healing time (day)

28

Fig. 27 Ultrasonic velocity versus healing time for: a conventional concrete, concrete with sewage sludge, and with CDW (Durante-Inguza et al. 2006) for w/c = 0.57; and for b conventional concrete and concrete with sewage sludge for w/c = 0.65

Table 18 Classification of concrete quality according to the ultrasonic velocity values

Ultrasonic velocity (m/s)

Concrete quality

V > 4500

Great

3500 < V < 4500

Good

3000 < V < 3500

Regular (dubious)

2000 < V < 3000

Generally bad

Bottom < V < 2000

Bad

Note that there is a reduction in the values obtained with an increase in the percentage of sludge around 63% for the factor w/c = 0.57 and for the factor w/ c = 0.65 around 52%. The values found for concrete in the proportions of 5%, 10% and 15% are of the same order of magnitude. Adding a percentage of sludge to concrete as an aggregate decreases absorption regardless of the percentage of sludge added.

150

M. C. A. Feitosa et al.

Table 19 Values of the sclerometry index Healing time (days)

Sclerometry index values (average) w/c = 0.57

w/c = 0.65

0% sludge

5% sludge

10% sludge

15% sludge

0% sludge

5% sludge

10% sludge

15% sludge

7

26.50

24.50

18.50

20.00

23.00

17.00

19.50

19.00

14

28.50

25.00

20.50

19.50

25.50

19.50

19.00

19.00

28

30.00

25.00

20.50

20.50

26.00

22.00

21.00

20.00

35

Sand Sand+5% Sludge Sand+10% Sludge Sand+15% Sludge Concrete with CDW [51]

30

Sclerometer Index

Sclerometer Index

35

25

Sand Sand+5% Sludge Sand+10% Sludge Sand+15% Sludge

30

25

20

20 (a) w/c= 0.57

15 0

7

14 21 Healing time (day)

(b) w/c= 0.65

15 0

28

7

14 21 Healing time (day)

28

Fig. 28 Sclerometer index versus healing time: a conventional concrete, with sewage sludge and with CDW (Oliveira et al. 2007), w/c = 0.57 and b conventional concrete with sewage sludge, w/c = 0.65 Table 20 Compressive strength values Healing time (days)

Compressive strength (MPa) w/c = 0.57

w/c = 0.65

0% sludge

5% sludge

10% sludge

15% sludge

0% sludge

5% sludge

10% sludge

15% sludge

7

20.04

16.08

12.20

11.50

19.30

14

25.86

19.99

14.50

13.60

21.50

14.64

11.75

10.76

16.18

12.60

28

27.84

22.83

16.36

17.60

23.06

14.95

11.69

12.69

12.80

According to Neville (2015), absorption is not considered a measure of concrete quality, however, it is observed that good quality concrete presents absorption below 10%, as a good quality concrete.

Sewage Sludge: Some Applications in Civil Engineering 30

30 (b) w/c= 0.65

25 Compressive Strenght (MPa)

Compressive Strenght (MPa)

(a) w/c= 0.57

20 15 10 Sand Sand+5% Sludge Sand+10% Sludge Sand+15% Sludge Concrete with CDW [51]

5 0 0

7

151

14 21 Healing time (day)

25 20 15 10 Sand Sand+5% Sludge Sand+10% Sludge Sand+15% Sludge

5 0

28

0

7

14 21 Healing time (day)

28

30

Compressive Strenght (MPa)

(c) w/c= 0.65 25 20 15 10 5

Concrete with SSA [61] Concrete with SS

0 0

5 10 15 Percentage of SSA and SS (%)

20

Fig. 29 Compressive strength versus healing time: a conventional concrete, with sewage sludge and with CDW (Oliveira et al. 2007), w/c = 0.57; b conventional concrete with sewage sludge, w/c = 0.65.; and c concrete with sewage sludge (SS) and sewage sludge ash (SSA) (Silva et al. 2021), w/c = 0.65 Table 21 Capillary absorption test result after 72 h

Samples

Capillary water absorption (%) w/c = 0.57

w/c = 0.65

Sand

2.78

2.09

Sand + 5% sludge

2.12

1.33

Sand + 10% sludge

1.87

1.57

Sand + 15% sludge

2.41

1.49

152

M. C. A. Feitosa et al. 1.6 (a) w/c= 0.57

1.4

Capillary Pressure (KPa)

Capillary Pressure (KPa)

1.6

1.2 1.0 0.8 0.6 Sand Sand+5% Sludge Sand+10% Sludge Sand+15% Sludge

0.4 0.2 0.0

(b) w/c= 0.65

1.4 1.2 1.0 0.8 0.6 0.4

Sand Sand+5% Sludge Sand+10% Sludge Sand+15% Sludge

0.2 0.0

0

12

24

36 48 Time (h)

60

72

0

12

24

36 48 Time (h)

60

72

Fig. 30 Absorption by capillarity versus time, with conventional concrete, and concrete with sludge: a w/c = 0.57 and b for factor w/c = 0.65

6 Conclusions The conclusions presented should not be taken in an absolute way, as these conclusions refer only to the data obtained in the analysis of the sludge generated in the STPs of Mangueira and Curado, Pernambuco (Brazil), and which constitutes data and information in the execution of new researches that present results that can complement and/or confirm the data obtained in this study. • The sludge cannot be considered as a single waste, as it constitutes a family of different sludge’s from different STPs, and consequently, each STP sludge must be treated as unique, in a process of reuse or recycling. • There are physical, chemical, and microstructural changes in the soil with the addition of sewage sludge to the natural soil. • The hydraulic conductivity of the soil decreases with the addition of sludge, reaching 60% when a dose equivalent to 75 Mg/ha of sludge is added to the natural soil, equivalent to an increase in the confining tension of 50 kPa to the soil. • In order to maintain the same apparent dry weight of the soil-sludge mixture, the addition of the sludge percentage provides a reduction in the soil voids index, justifying a lower compressibility due to the addition of sludge. Proving to be suitable for improving collapsible soils. • The compressive strength of concrete decreases with increasing sludge content, the effect being more expressive for the addition of 10% of sludge, when compared to the reference concrete of 25 MPa. • Concretes with the addition of sludge above 5% restrict their application, mainly because these samples do not have mechanical properties for their use, which is less than 15 MPa. • It was found that the addition of STP sludge in concrete can be a viable and environmentally correct alternative, as it promotes the reduction of considerable amounts of this material to be disposed of in landfills or returned to watercourses,

Sewage Sludge: Some Applications in Civil Engineering

• • • • •

153

as well as significant reductions in the consumption of natural aggregates. It can be used in small works. Finally, some suggestions for future research are listed in order to increase the knowledge in this field: Detailed studies of the physical, chemical and mineralogical characteristics of the sludge from the ETEs and study. Continuation of research in order to study the use of sludge in a concrete way, that is: in the manufacture of floors, walls, sidewalks and others. It is recommended that other tests be carried out to verify the concrete’s other properties, including: tensile strength by flexion and diametral compression, static deformation modulus and leaching. The results obtained in the research, with regard to the environmental aspect, that is, regarding the ability to safely retain the harmful compounds present in the sludge, should be analyzed, through tests of solubilization, leaching, X-Ray diffraction, and others.

Acknowledgements This work was supported by: Base Funding—UIDB/04708/2020 and Programmatic Funding—UIDP/04708/2020 of the CONSTRUCT—Instituto de I&D em Estruturas e Construções—funded by national funds through the FCT/MCTES (PIDDAC) and by FCT— Fundação para a Ciência e a Tecnologia through the individual Scientific Employment Stimulus 2020.00828.CEECIND.

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