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Case Studies in Building Rehabilitation [1st ed.]
 9783030492014, 9783030492021

Table of contents :
Front Matter ....Pages i-vii
Rehabilitation of K. G. Road Complex at New Delhi, India (Prafulla Parlewar)....Pages 1-15
Characterization of Ancient Mixed Masonry Structures of Brickwork Infilled by Cobblestone Wall (I. Lombillo, Y. Boffill, J. Pinilla, E. Moreno, H. Blanco)....Pages 17-37
Rehabilitation of Historic Chancery Building, Yangon, Myanmar (Prafulla Parlewar)....Pages 39-58
Rehabilitation Operations in Residential Buildings in La Mina Neighborhood (S. Adrià del Besòs, Barcelona) (C. Díaz, C. Cornadó)....Pages 59-88
Repair of Face Brick Facades Sustained in Reinforced Concrete Slabs (C. Díaz, C. Cornadó)....Pages 89-103
Influence of Environmental Factors on Deterioration of Mural Paintings in Mogao Cave 285, Dunhuang (D. Ogura, T. Hase, Y. Nakata, A. Mikayama, S. Hokoi, H. Takabayashi et al.)....Pages 105-159

Citation preview

Building Pathology and Rehabilitation

J. M. P. Q. Delgado   Editor

Case Studies in Building Rehabilitation

Building Pathology and Rehabilitation Volume 13

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.

More information about this series at http://www.springer.com/series/10019

J. M. P. Q. Delgado Editor

Case Studies in Building Rehabilitation

123

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

ISSN 2194-9832 ISSN 2194-9840 (electronic) Building Pathology and Rehabilitation ISBN 978-3-030-49201-4 ISBN 978-3-030-49202-1 (eBook) https://doi.org/10.1007/978-3-030-49202-1 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 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

Preface

Building pathology is the scientific study of the nature of building failure and its causes, processes, development and consequences, to help create the right remedial and management resolutions. Rehabilitation is a strategic area that is concerned not only with the monumental heritage and 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 evolution of degradation can be interpreted as the continuous reduction in performance over time. The main purpose of this book, Case Studies in Building Rehabilitation, is to provide a collection of recent research works, case studies and real-life experiences of building pathology, to contribute to the systematization and dissemination of knowledge related to building pathologies (structural and hygrothermal), durability and diagnostic techniques and, simultaneously, to show the most recent advances in this domain. It includes a set of new developments in the field of building pathology and rehabilitation, bridging the gap between current approaches to the surveying of buildings and the detailed study of defect diagnosis, prognosis and remediation. It features a number of case studies and a detailed set of references and further reading. The book is divided into six chapters that intend to be a resume of the current state of knowledge for the benefit of professional colleagues, scientists, students, practitioners, lecturers and other interested parties to network. At the same time, these topics will be going to encounter a variety of scientific and engineering disciplines, such as civil, materials and mechanical engineering. Porto, Portugal

J. M. P. Q. Delgado

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Contents

Rehabilitation of K. G. Road Complex at New Delhi, India . . . . . . . . . . Prafulla Parlewar

1

Characterization of Ancient Mixed Masonry Structures of Brickwork Infilled by Cobblestone Wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I. Lombillo, Y. Boffill, J. Pinilla, E. Moreno, and H. Blanco

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Rehabilitation of Historic Chancery Building, Yangon, Myanmar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prafulla Parlewar

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Rehabilitation Operations in Residential Buildings in La Mina Neighborhood (S. Adrià del Besòs, Barcelona) . . . . . . . . . . . . . . . . . . . . C. Díaz and C. Cornadó

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Repair of Face Brick Facades Sustained in Reinforced Concrete Slabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Díaz and C. Cornadó

89

Influence of Environmental Factors on Deterioration of Mural Paintings in Mogao Cave 285, Dunhuang . . . . . . . . . . . . . . . . . . . . . . . . 105 D. Ogura, T. Hase, Y. Nakata, A. Mikayama, S. Hokoi, H. Takabayashi, K. Okada, B. Su, and P. Xue

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Rehabilitation of K. G. Road Complex at New Delhi, India Prafulla Parlewar

Abstract The Kasturba Gandhi (K. G.) road residential complex is a prestigious building located at the New Delhi, India. This building suffered structural deterioration due to the damaged rainwater and drainage system. This research mainly looks into the reasons for the decay of the building, method adapted for the structural analysis and proposed methods of retrofitting. In particular, this research includes assessment of the structural condition for the future viability of the building. Assessment studies were conducted on the building through geometric survey and structural testing. Building was not found suitable for habitation based on the results of assessment. Furthermore, the retrofitting was proposed to strengthen the structure with various methods like use of micro concrete, mild steel jacketing and repair of spalling.

1 Introduction The Kasturba Gandhi (K. G.) road residential complex is a prestigious building located at New Delhi, India. This five storied building is known for its architectural significance in the contemporary architecture of New Delhi. However, because of damaged drainage system, the building’s structural system deteriorated with the passage of time. The research here looks into the reasons for the deterioration of the building. Then, it delineate the assessment methodology for structural analysis of the building by identifying the correct studies and testing methods. Finally, the paper look into the method of retrofitting for the building with use of latest technology for rehabilitation. The building is assessed for its structural conditions in two sections: (1) geometric studies, and (2) structural testing. The geometric studies documented the damages on each floor of building. The structural testing includes: (a) rebound hammer test, (b) laboratory tests, (c) endoscopic survey, and (d) masonry mortar

P. Parlewar (B) City Development Corporation (P) Ltd., Mumbai, India e-mail: [email protected] © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 J. M. P. Q. Delgado (ed.), Case Studies in Building Rehabilitation, Building Pathology and Rehabilitation 13, https://doi.org/10.1007/978-3-030-49202-1_1

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Fig. 1 a Front view of complex b Block view of complex

test. In this research, the geometric studies are illustrated through drawings and photographs for severity of damages. The geometric studies are based on the field survey conducted to document the building and its damages. Severities of damages were assessed based on the visual observations undertaken in field. These were further documented through photographs and drawings. Rebound hammer test is basically a surface hardness test to measure the compressive stress in concrete. In this research, detail results of rebound hammer test are taken for assessment of the building. Moreover, the core samples are taken from R.C.C. slab and masonry. These samples were submitted to the testing laboratory. It was found that the columns were severely damaged at various locations. Also, the slabs and beam were damaged at various locations. The rebound hammer test results were compiled to show the compressive strength of concrete. The results of rebound hammer test had indicated poor compressive strength of concrete on all floors in the building (Fig. 1).

2 Geometric Studies The geometric studies for the building includes: (a) physical measurements of the building, and (b) visual studies of damages. In physical measurements, the building documentation was undertaken for floor wise arrangement of rooms, beams, columns, slabs, staircases and other elements. This documentation was undertaken on physical map to analyse severity of damages. In case of visual studies, the photographs of the damaged structural part were taken to identify the severity of damage.

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2.1 Physical Measurements The procedure for physical measurement was based on using ultrasonic measuring equipment to document the structural system of the building. A system of floor wise documentation was carried out on site with engineers and architects. Then, drawings were prepared based on these physical measurements. Following are the salient points of the structural system of the building (Figs. 2, 3, 4, 5, 6 and 7): (1) The building is Reinforce Cement Concrete (R.C.C.) construction with three wings. One wing has two room residential units with attached pantry and toilet. Second wing has single room units with toilet. Third wing is separate on the rear side with attached pantry and toilet. The building wings make an arrangement of larger block in front and smaller part at rear part of plot. (2) Ground floor is having reception and pantry with staircase core in the center of the building. A small staircase is also found at the one end of the building. The top of the central staircase is having water tanks which damaged the slab of the building. (3) The structural columns are at center to center span of 5.0 meters at the main part of the building. The existing column size is 500 MM × 340 MM and beam size is 500 MM × 340 MM. (4) In the original design of the building, the column numbers C02, C03, C07, C09, C47 and C49 are around two ducts of toilet and pantry. Water supply and sanitary pipes are located in these ducts. It was found that the leakage in water supply and sanitation has resulted into the severe damage to columns C02, C03, C07, C09, C47 and C49. Also, we predicated that the foundation below these columns may be damaged due to water leakages in the ducts. Hence, the water leakages in the duct was found to be major reason for the deterioration of the building (Fig. 8).

Fig. 2 Ground floor plan

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Fig. 3 First floor plan

Fig. 4 Second floor plan

2.2 Visual Assessment of Damages The visual assessment of building includes visually identifying the damages of the building. These damages are recorded through photographs to identify the severity of damages. The floor wise damages are as follows: (a) Ground floor: At the ground floor, the structural damages are observed in the columns, beams and slab. Our geometric studies documented damages in following location: (a) Ground floor damages were

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Fig. 5 Third floor plan

Fig. 6 Fourth floor plan

found in columns C02, C06, C09, C11, C12, C24, C25, C38, C61, C42, C47 and C49 (Fig. 2). The damages of columns are shown in hatch circle. (b) First Floor: The first floor damages were observed in the columns, beams and slab. These damages were in columns C02, C06, C09, C11, C12, C24, C25, C38, C61, C42, and C49 (Fig. 3). (c) Second Floor: The second floor damages were observed in the columns, beams and slab. The damages are in columns C02, C04, C08, C07, C09, C11, C12, C18, C44, C47, C43 and beam C43–C4 (Fig. 4). (d) Third Floor: The third floor damages were observed in the columns, beams and slab. These damages are in columns C02,

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Fig. 7 Fifth floor plan

Fig. 8 Damages on ground floor (a, b) and first floor (c, d)

C04, C06, C07, C09, C11, C18, C38, C40, C42, C47, and C49 (Fig. 5). (e) Fourth Floor: The fourth floor damages were observed in the columns, beams and slab. These damages in columns are C02, C04, C06, C07, C09, C10, C11, C12, C37, C38, C43, C44, C47 and C49 (Fig. 6). (f) Fifth Floor: On the fifth floor severe damages were observed in the columns, beams and slab. These damages are found in columns C02, C04, C05, C07, C08, C09, C11, C18, C37, C38 and beams in span C05–C08 and C38–C16 (Fig. 7). (g) Terrace Floor: On the terrace floor severe damages were observed in the columns, beams and slab. These damages are found in columns C02, C04, C06, C07, C08, C09, C11, C18, C37 and C38 (Fig. 9).

2.3 Endoscopic Studies The endoscopic studies were conducted with an endoscopic instrument on the damaged columns. An endoscopy instrument is 1.3 Mp waterproof inspection camera. Following are the findings of endoscopic studies: (1) The concrete was corroded severely inside the columns. It can be inferred that the reinforcement corrosion is

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Fig. 9 Damages on ground floor (a, b) and first floor (c, d)

Fig. 10 Endoscopic studies on ground floor

Fig. 11 Endoscopic studies on ground floor

in between 50% and 80%. (2) Endoscopy results shown in Figs. 10 and 11 clearly shows that the reinforcements are fully damages. (3) The endoscopy results inferred that there is no bonding between the concrete and the reinforcement. (4) The stirrups were broken at many location. Stirrups are also fully damaged inside as shown in Fig. 11. (5) The endoscopy show that the concrete was in grey and white color. This colorization also indicates the damages in concrete. (6) Moreover, many cracks were found inside the columns in endoscopy studies.

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3 Structural Testing 3.1 Non-destructive Test (NDT)—Rebound Hammer Test (RHT) The rebound hammer test (IS-13311 Part II 1992, reaffirmed 2004) is principally a surface hardness test. It works on the principle that the rebound of an elastic mass depends on the hardness of surface against which the mass impinges. Rebound hammer test (RHT) gives us a tentative idea about the surface strength of concrete. The variation of 25% is found between the strength of specimen tested by RHT and by convention method. This is because, the results of RHT are affected by factors like surface and internal moisture, carbonation of concrete, age of concrete and type of aggregates. More moisture gives less rebound number.

3.1.1

Rebound Hammer Test (RHT) for Building

The rebound hammer test (RHT) was conducted to understand the general condition of the residential complex building. This test was conducted on structural members like R.C.C. columns and walls with nine points at one location. These nine points were taken on members in a square area to get accurate results. The average results of this nine rebound points were calculated for compression strength of concrete. This test was conducted at 334 locations in the building with nine points each. The Figs. 12, 13 and 14 shows the graphical representation of the results of RHT.

Fig. 12 Rebound Hammer Test (RHT) results

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Fig. 13 Rebound Hammer Test (RHT) results

Fig. 14 Rebound Hammer Test (RHT) results

3.2 Laboratory Tests To understand the structural damages the laboratory tests were conducted on the concrete. These tests include: (1) compressive test of core samples of slabs, (2) test of reinforcement, and (3) brick tests. Because of severity of damages, it was only possible to take the core sample of slab. On site, it was difficult to remove the sample for beams and columns because of severe damages. However, the testing inference on the core sample of the slab gave a clear understanding on the composition and compressive strength of the concrete.

3.2.1

Compressive Test of Core Sample of Slab

As per the IS: 456–2000, the minimum three cores samples were tested for the compressive strength of the concrete. The core testing was conducted as per the IS 516:1959. The following are the criteria for the accepting the strength for the core strength of the concrete members: (a) the average corrected core strength shall not be less than 85% of the equivalent cube strength and (b) the strength of the individual members shall not be less than the 75% of equivalent cube strength.

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Fig. 15 a Concrete Core Samples b Bricks Sample

3.2.2

Core Drilling

A core was cut by means of rotary cutting tool having diamond bits. The machine was firmly supported and braced against the concrete to prevent relative movement which results in distorted and broken core. This process included lubricating the cutter with water supply (Fig. 15).

3.2.3

Length and Diameter of Core

The three samples of the core of following length were taken for laboratory test: (1) 100.70 mm, (2) 106.40 mm and (3) 108.40 mm (Fig. 15). The weight for these core samples are 0.780, 0.895 and 0.880 respectively. The core of diameter 66.5 mm was cut from the slab. The ratio of length to diameter in the core sample was 1: 1.58 (Table 1).

3.2.4

Density of Core

As per the IS 456: 2000, the density of concrete shall be 2500 Kg/m3 . The table below shows the density of the tested cores (Table 2). The average density of concrete was 2329.25 Kg/Cu. M. As the density was found lesser than required, it can be inferred that strength of concrete is reduced in the building. Table 1 Length and diameter of core samples

S/N

Length (mm)

Diameter (mm)

1 2 3

100.70 106.40 108.40

66.50 66.50 66.50

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Table 2 Weight, volume and density of core samples S/N Weight (Kg) Volume (Cu. mm) 1 2 3

0.780 0.895 0.880

349831.80 369633.60 376581.60

Table 3 Results of compressive test of core sample S/N Length (mm) Diameter Weight (mm) (mm) 1 2 3

100.70 106.40 108.40

66.50 66.50 66.50

0.780 0.895 0.880

Table 4 Percent decrease in strength of concrete S/N Percentage decrease in strength over equivalent cube strength 1 2 3

3.2.5

25.00 25.00 25.00

Density (Kg/Cu.m) 2229.64 2421.31 2336.81

Area (sq.mm) Remark 3474 3474 3474

OK OK OK

Average percentage in strength over equivalent cube strength

25.00

Testing of Core

Before test, the core was keept in water for 48 h at 24–30 ◦ C. The core test was undertaken by applying Load of 0.2N/(mm2 /s) to 0.42N/(mm2 /s) at constant rate for calculating compressive strength of concrete. Following are the results of the concrete core tests (Tables 3 and 4): (1) The average corrected core strength is less than 85% of the equivalent cube strength. (2) The strength of the individual members is 75% of equivalent cube strength. (3) The density of the concrete is found to be reduced in the core sample. (4) Thus the compressive strength of concrete is insufficient.

3.3 Test of Reinforcement The laboratory test of three reinforcement samples of 1.0 M length was conducted to understand the content of Carbon, Sulphur, Manganese and Phosphorus. Following are the observation of test of reinforcement (Table 5): (1) The carbon content in the sample is 0.35%. The higher carbon content of 0.3% and above makes the steel bar brittle. Thus, there is reduction in the tensile strength of the reinforcement. (2)

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Table 5 Percentage of carbon, sulphur, manganese and phosphorus S/N Carbon Sulphur Manganese 1

0.35

Table 6 Compressive strength of bricks

0.06

0.85

Phosphorus 0.0775

S/N

Result

Average

1 2 3 4 5

11.80 12.50 10.90 12.00 11.98

11.98

The content of Sulphur also makes the reinforcement brittle. In the test 0.06% of Sulphur was found in reinforcement. (3) The higher content of Manganese increases the tensile strength of the reinforcement. The Manganese content is 0.85% in the reinforcement. (4) The content of Phosphorus also increases the brittleness of the reinforcement. Thus, reducing the tensile strength of reinforcement.

3.4 Test of Bricks The sample bricks were tested for its strength. The three brick samples were removed from the building. The procedure of the testing included keeping the sample immersed in water for five days. Then, axial load of 14 N/mm2 was uniformly applied on the bricks. The test was conducted as per IS: 3495–1992(P-I). The strength of bricks was found to be sufficient in the building. The test results are shown in Table 6.

4 Recommendations for Structural Retrofitting The structural members of the building were proposed to strengthen through following methods: (a) structural strengthening with micro concrete, (b) jacketing and collaring, and (c) repair of spalling and swellings.

4.1 Structural Strengthening with Micro Concrete Jacketing The structural members strengthening was proposed by use of Micro Concrete. The micro concrete is a dry power which requires addition of clean water. This is a ready

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to use dry power which produces a free flowing non shrink repair. This combined with additives provide controlled expansion of concrete with minimum demand of water. It provides high compressive strength than the regular concrete. This also provides high early strength in concrete which give strength in the deteriorated structural member. Moreover, it offers excellent resistance to water. Thus it makes the member highly durable. The retrofitting was proposed in following steps: 1. Prop Supports: The prop were proposed for providing sufficient structural support in slab and floor. These props will provide support to load carrying members like beams, columns etc. 2. Removal of Surrounding brick works: In the first step, the brickwork on the sides of the structural member was proposed to be removed to make space for shuttering. 3. Surface Preparation of Concrete: In this step, all reinforcement bars were proposed to be exposed by chipping the original concrete on the damaged member. This chipping will be to minimum depth of 10 mm behind the reinforcing bars. 4. Cleaning of Reinforcement: The reinforcement was proposed to be cleaned with rust remover made up of zinc rich epoxy based coating with zinc content greater than 84% to existing reinforcement. 5. Provision of extra reinforcement: Additional reinforcement is proposed with an anchor in the concrete by providing adequate shear connectors. 6. Shear Connectors: The shear connectors of 8.0 mm diameter were proposed in holes of 14.0 mm diameter and 75 mm deep at 500 mm c/c on all the faces of the beams. These connectors were proposed be fixed in holes by using polyester resin anchor grout. 7. Primer coating of reinforcement: The Epoxy Zinc Polymer of 40 micron was proposed on the new reinforcement. 8. Epoxy Bonding Agent: The Epoxy resin based bonding was proposed to be applied on the dry concrete substrate using stiff nylon brush uniformly on the surface. This shall be applied before the elapse of time mentioned in the specifications. 9. Formwork and shuttering: The form work was proposed to pour micro concrete. This formwork was proposed to be leak proof and will not permit the flow of micro concrete. 10. Mixing of micro concrete: The micro concrete was proposed as per the manufacturer specifications. The concrete was proposed be mechanically mixed to get homogeneous mix. 11. Pouring of Micro Concrete: The micro concrete mixture will be poured in formwork by use of funnel or hose pipe with good compaction. 12. Curing: The curing needed to be done as per the standard procedure by use of curing compound in water. 13. Tests for effectiveness of repair: It was recommended to check the compressive strength of retrofitted concrete members through rebound hammer test after 28 days.

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14. Jacketing and Collaring in Metal or Pre-cast Members: The structural members were proposed to be jacketed and collared by use of metal or pre-cast members anchored with the beam, column or slab. 15. Repair of Spallings and Swellings: It was suggested to repair these damages by re concreting the ceiling with following method: (A) the loose mortar shall be removed from the surrounding from spalled surface. Sufficient cleaning was proposed of surrounding area with brush. (B) Two coats of anti-corrosive paint was proposed to be applied on the exposed reinforcement surfaces. One coat of polymer bonding agent need to be applied over the entire area of steel and concrete. (C) Above this polymer, 1:3 cement mortars was proposed to be applied over the reinforcement. This concrete was proposed to be cured for minimum 15 days. (D) A water proofing coat was proposed to be applied before finishing of this ceiling surface.

5 Conclusion The following are the conclusion of structural assessment and rehabilitation of the residential complex based on visual studies and structural testing: 1. It was found through visual studies and structural testing that the severity of damages were high in the columns and beams. 2. The shear cracks, flexural cracks etc. were found in columns and beams of the structure. 3. The design load required for the building is 20 N/mm2 for compressive strength of M 20 grade of concrete as per IS 456: 2000. 4. The compressive strength of concrete members like beam, columns, and slabs were found to be poor in compression. This strength was less than the design load of 20 N/mm2 . So the strength of R.C.C. members in compression is insufficient. 5. The core test has indicated insufficient compressive strength. The average corrected core strength was less than 85% of the equivalent cube strength. As per IS 516:1959, the corrected core strength shall not be less than 85%. 6. As per the endoscopic studies, the reinforcements were corroded at many locations. It can be assume that reinforcement corrosion was between 50% and 80%. This has resulted into poor tensile strength of reinforcement. 7. The laboratory test for reinforcement had also indicated into poor tensile strength of reinforcement. 8. The building is situated in Seismic Zone 4. As per the IS 13920 (1993) for ductile design code, spacing of stirrups shall be minimum 100 mm center to center. But during survey, the spacing was found to be 175–200 mm center to center. Moreover, based on visual studies and structural testing, the failure of structure was possible in event of earthquake. 9. The structural retrofitting was proposed for columns and beams by using micro concrete and mild steel jacketing. Inspection and strengthening of foundation was

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also proposed to investigate damages and uneven settlement in the foundation. The proposed retrofitting could provide long term strength in the structural members. Thus based on above assessment, residential complex was declared unfit for habitation. Moreover, the urgency for retrofitting was proposed after vacating the premises. Further, similar approach for research is undertaken for buildings deteriorated by rain and weather conditions in Myanmar. Similar research methodology is adapted to analyse historic buildings in downtown Yangon in Myanmar.

Characterization of Ancient Mixed Masonry Structures of Brickwork Infilled by Cobblestone Wall I. Lombillo, Y. Boffill, J. Pinilla, E. Moreno, and H. Blanco

Abstract A great part of the Architectural Heritage is constructed with masonry walls. Certain interventions in this Heritage make it necessary to characterize the mechanical properties of these load-bearing elements. This article has the aim of proposing and using several complementary methods applicable to the characterization of the materials forming historical masonry structures, applying them to mixed masonry made up of bricks, lime mortars and cobblestones. In this research, tests were carried out on a building constructed in two clearly differentiated periods, 15–18th century and 19–20th century. A sample-taking campaign was done on bricks, mortars and portions of masonry, for later physical-chemical-morphologicalmechanical testing in laboratory, and an in situ experimental minimally-intrusive campaign using techniques such as flat-jack, sclerometer and penetration-meter on mortars. The mechanical results obtained enabled the evaluation of the validity of some experimental formulas for estimating the strength of masonries from the strength of their component materials (brick and mortar), when applying them to historical constructions. In the same way, the physical-chemical characterization tests carried out enabled the justification, economically and minimally intrusively, the differentiation of the materials employed in the two construction periods.

I. Lombillo (B) · Y. Boffill · H. Blanco University of Cantabria, Civil Engineering School, 39005 Santander, Spain e-mail: [email protected] Y. Boffill e-mail: [email protected] H. Blanco e-mail: [email protected] J. Pinilla · E. Moreno Polytechnic University of Madrid, School of Architecture, 28040 Madrid, Spain e-mail: [email protected] E. Moreno e-mail: [email protected] © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 J. M. P. Q. Delgado (ed.), Case Studies in Building Rehabilitation, Building Pathology and Rehabilitation 13, https://doi.org/10.1007/978-3-030-49202-1_2

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Keywords Masonry structures · Architectural heritage · Laboratory experiments · In situ campaign

1 Introduction Within the intervention process, previous knowledge is fundamental when choosing the most suitable techniques and materials applicable in preservation and damage prevention in Cultural Heritage (Binda et al. 1999, 2009). Therefore, the refurbishment process should be based in precise previous investigation (Binda et al. 2008). The masonry structures are composed of petrous or ceramic pieces joined in most cases by a conglomerate. The mechanical strength of the masonry depends on several factors such as the strength of the pieces and of the conglomerate, the size of the pieces, the humidity content, the emplacement method, etc. (Martínez et al. 2001). Specific interventions on architectural heritage presuppose a modification of the forces on the load-bearing walls, so in many cases it is necessary to know their mechanical properties when establishing the most suitable intervention criterion. There are diverse ways of obtaining the mechanical properties and strength of masonry, from in situ N-MDT (Non-Minor Destructive Techniques) (Binda et al. 2000; Lombillo et al. 2013), experimental approximations based on breaking samples in the laboratory, or through the use of formulas. Thus, numerous attempts have been made to obtain empirical formulas that provide the masonry strength from the geometrical and mechanical characteristics of the components. Among the most notable are: Hendry and Malek (1986), the one proposed in Eurocode 6 (EN 1996-11:2005), BD 21/93 (1993) or ACI 530/99 (1999). There are also phenomenological formulas that have the advantage over the empirical ones of adapting to distinct typologies of masonries and materials, and not only the conditions under which the empirical formulas were obtained. Among these, Olher’s formula (Hendry 1998) and the UCI one (1995) should be mentioned. The most rigorous way of obtaining the properties of the historical masonries is through the use of in situ diagnostic techniques, such as the techniques based on flat jacks, given that they enable the masonries to be tested under real conditions, avoiding the extraction of samples for later testing in the laboratory, a process that can significantly affect the results obtained. In fact, the existing formulas require the extraction of samples for testing the pieces and the mortar of the masonry. In the case of ceramic bricks, their compressive strength depends on the density, which in turn depends on the raw material and the temperature of manufacture. Thus, the physical-chemical characterization of the materials is a tool that helps in the interpretation of the results obtained in the mechanical tests. As for the mortars, their strength can be estimated indirectly through tests such as rebound index or penetration index. The compressive strength of mortar depends on multiple factors such as the density, the type of conglomerate, the water/conglomerate ratio and the conglomerate/aggregate ratio or the curing conditions.

Characterization of Ancient Mixed Masonry …

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This research aims to evaluate the validity of different techniques and methods generally applied in assessment of existing masonry buildings, applying them to the specific case of mixed masonry structures of brickwork infilled with lime mortar and cobblestones, a construction type which has been studied very little by the scientific community. Therefore, as a practical application, the characterization tests carried out on the load-bearing walls of a historical building, ‘Los Aragoneses’ mill, are reported. Its current structure is the result of the union of two different volumes with diverse reforms, Fig. 1. The oldest dates from the middle of the 15th century, having being rebuilt some years later. The second part was attached to the first around 1780 with the aim of providing a new production module with a mill and a chapel. What is more, at the end of the 18th century the whole building was remodeled, with no information about whether remains of the original building were maintained. Finally, between the 19 and 20th century, a neo-mudejar-style back building was added, to house a steam engine press. Independently of the construction era, the load-bearing walls of the building, both exterior and interior, are of mixed masonry structures of brickwork infilled with lime mortar and cobblestones, Fig. 2, with variable thicknesses between 35 and 80 cm, composed of: • Masonry of brick and lime-based mortar: in vertical pilasters every 4–5 m and at the corners, in horizontal rows every 1–1.5 m, and in the edges of windows and doors. The bricks are solid of dimensions 28 × 14 × 3–5 cm, with bed joints of mortar ranging from 3–6 cm.

Fig. 1 General perspective of the emplacement of the ‘Los Aragoneses’ mill, Monachil (Spain)

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Fig. 2 Mixed masonry of brickwork infilled with cobblestones and lime mortar

• Masonry of infilled cobblestones and lime-based mortar outlined by bricks. A total of 4 manual trial pits were made to verify the conditions of the foundations of the load-bearing walls. Thus, what could be original foundations of the first construction are made of lime mortar and cobblestone masonry of depths ranging from 60–80 cm, while the more modern ones are made of brick masonry of depths greater than 90–120 cm. In the physical-chemical-morphological characterization of materials, the following tests have been used: hydric to establish physical properties, X-Ray Diffraction (XRD) to find the crystalline structure, Polarized Optical Microscopy (POM) to obtain information about mineralogy, Scanning Electron Microscopy (SEM) for chemical and morphological characterization, and Thermal Gravimetric Analysis (TGA/DTA) to find out the proportion of each component. Moreover, several compressive strength tests were carried out on pieces, mortars, and portions of masonry in the laboratory and various in situ N-MDT tests were done (flat jack, sclerometry and mortar penetration tests) oriented to estimate the mechanical characterization of the masonry structure.

2 Materials and Methods This section describes the tests used with the aim of obtaining useful information about the physical, chemical, morphological and mechanical characterization of the materials used in the existing masonries, and the methodologies used in situ for the mechanical characterization of the masonry walls.

Characterization of Ancient Mixed Masonry …

21

The walls, pieces and mortars in the building have been denominated according to the date of construction figuring in the historical studies, thus, being either of the period 15–18th or 19–20th.

2.1 Characterization of Materials in the Laboratory Twenty-three samples of materials were extracted manually (6 corresponded to complete brick samples, 12 samples of mortars, 3 of stone and 2 of brickwork) and 7 cylindrical samples of walls were obtained using a hollow-crown coupled to a perforator.

2.1.1

Physical-Chemical-Morphological Characterization of Materials

Hydric tests were carried out, with a hydrostatic balance, to calculate the apparent density, the coefficient of absorption and the accessible porosity. The real volume was also obtained using the Le Chatelier volumenometer, calculating the real density of the samples. With the aim of finding the crystalline phases in the samples analyzed and, therefore, their chemical composition, X-Ray Diffraction (XRD) techniques were used (Lombillo et al. 2013; Middendorf et al. 2005; Isebaert et al. 2016; Arizzi et al. 2013; Van Hees et al. 2004; Nóbrega De Azeredo et al. 2015; Franzoni et al. 2017). For this purpose, a Bruker D8 Advance powder diffractometer was used fitted with a highstability copper anode X-Ray supply, and a SOL-X detector of energy dispersion and large active area for X-Ray diffraction, enabling a shorter measurement time than other detectors combined with a low background level. Using a Scanning Electron Microscope (SEM) (Lombillo et al. 2013; Middendorf et al. 2005; Arizzi et al. 2013; Van Hees et al. 2004; Nóbrega De Azeredo et al. 2015; Franzoni et al. 2017; López-Arce et al. 2016) a morphological examination of the topographical structure of the fracture planes of the samples was performed. Moreover, managing a range of augmentation scales, a view of both the whole element and of the details was obtained. In the same way, coupling a dispersive energy XRay spectrometer, the elemental analysis of the samples was made possible. The study was done with a Jeol JSM-820 microscope operating at 20 kV and equipped with Oxford EDX analysis. The samples were covered with Au (Emitech K550X metalizer) to ensure good conductivity of a beam of electrons. Complementarily, using a Polarized Optical Microscope (POM) (Middendorf et al. 2005; Arizzi et al. 2013; Van Hees et al. 2004), information was obtained about the mineralogy of the samples under study (petrographic analysis). Thus, to identify aggregates and binder through observation of thin laminas, a Kyowa, mod. BIO-POL, transmitted and polarized light petrographic microscope was used. The photographs were taken with a 5Mpixel Moticam, model 2300.

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Finally, Thermal Gravimetric Analysis (TGA) and Differential Thermal Analysis (DTA) (Middendorf et al. 2005; Nóbrega De Azeredo et al. 2015; Franzoni et al. 2017; Verstrynge et al. 2011) enabled the estimation of the proportion of each component, so the dosage of the mortars and presence of unfired clays could be estimated.

2.1.2

Mechanical Characterization

Mechanical compression tests were performed using a hydraulic press on a part of the samples extracted (7 bricks, 4 of mortar and 4 masonry testpieces). To this end, the samples were cut with a circular saw and capped with Betolevel 15 CT-C30-F6 self-leveling mortar whose compressive strength is over 30 MPa. The testing machine used for the tests on bricks and masonry testpieces was an Ibertest MIB-60 servohydraulic press in accordance with the norm UNE-EN 772–1 (2011). The breaking of mortars was done with two test presses, an Autotest 200–10 SW and another Wykeham Farrance, in accordance with the norm UNE EN 1015-11 (2007).

2.2 In Situ Experimental Campaign 2.2.1

Flat Jack Test

The flat jack technique was developed by the Italian researcher Paolo Rossi in the early 1980s (Rossi 1982), although it was not until 1985 that the first application in situ took place on the brick walls of the ‘Palazzo della Ragione’ de Milan (Rossi 1985). Later, tests were performed on other construction types (Lombillo 2010) such as ashlars, irregular rubblestones and even rammed-earth (Lombillo et al. 2014), which contributed to the progressive calibration of this technique. Following the criterion for characterizing the masonry walls of the constructions built in the 15–18th and 19–20th centuries, the tests were performed at the points shown in Fig. 3.

2.2.2

Sclerometer and Penetrometer Tests on Mortars

The use of a pendulum sclerometer provides a rapid qualitative indication of the quality of mortar through the correlation with the energy absorbed by the mortar during the impact (Tavares et al. 2008; Tavares and Veiga 2007). It is considered as a low-impact test for monitoring the quality of mortars through the evaluation of its surface hardness. The equipment utilized in this study was a SCHMIDT PM-type pendulum hammer. Another test used for the in situ characterization of mortars was the penetrometer technique, for which a portable PNT-G penetrometer was utilized. The penetrometry of mortars used, based on the PNT-G method developed by Gucci and Barsotti (1995),

Characterization of Ancient Mixed Masonry …

23

Fig. 3 Floorplan of emplacement of the flat jacks. SFJ-01 and DFJ-01 were performed in the semibasement of SE wall of the 19–20th century building, while SFJ-02 and DFJ-02 were performed on the ground floor of the SW wall of the 15th century building, supposedly remodelled in the 18th century

Gucci and Sassu (2002), provides a rapid qualitative indication of the compressive strength of the material through the correlation with the energy necessary for performing a standardized perforation. The procedures followed to carry out the previous tests are included in the RILEM MS-D.7 (1997) and RILEM MDT. D.1 (2004) recommendations respectively.

3 Results Table 1 details the experimental campaign carried out. The stones analyzed correspond to the columns of the central patio and the ashlars of the main wall.

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Table 1 Experimental campaign carried out Material

XRD

SEM

POM

TGA/DTA

Mech. character SCL Lab.

Brick

X

X

X

X

X

Mortar

X

X

X

X

X

Stone

X

X

X

Masonry structure

X

PEN

DFJ X

X

X

XRD: X-Ray Diffraction; SEM: Scanning Electron Microscopy; POM: Polarized Optical Microscopy; TGA/DTA: Thermal Gravimetric Analysis and Differential Thermal Analysis; DFJ: Double Flat Jack; SCL: Sclerometry; PEN: Penetrometry

3.1 Results of the Characterization of Materials in the Laboratory 3.1.1

Physical-Chemical-Morphological Characterization of Materials

Table 2 shows the compounds identified in the XRD analysis. 15–18th century bricks and mortars, 19–20th century bricks and mortars, and stone were studied. In the case of the mortars, the fine and coarse fractions were analyzed. Because of the microstructure of cementitious materials is so heterogeneous, Polarized Optical Microscopy (POM) was firstly used to quantitative image analysis about volume fractions of phases of epoxy-impregnated and polished samples. After that, in particular areas, Scanning Electron Microscopy analyses (SEM) were carried out. As an example of obtained results of the petrographic thin section study (POM), Fig. 4 shows the analysis by parallel nicols, NP × 40, of 15–18th century mortar, and Fig. 5 shows the analysis by crossed nicols, XP × 40, of 19–20th century mortar. Table 3 shows the results of the Scanning Electron Microscopy analyses carried out. From the POM and SEM analyses, it can be seen that the mortars of the 15–18th century period are basically composed of calcium-dolomite aggregate and smaller quantities of additions of siliceous aggregate (quartz and feldspar). The mortars of the 19–20th century period are composed of crushed calcium aggregate, and a smaller proportion of silica, especially in one of the samples analyzed. In this sample, clays of varied mineralogy were also found (based on an XRD analysis using oriented aggregates Mica/Paragonite: 60%, Smectite: 28% and Chlorite: 12%). Moreover, the SEM images showed that in none of the mortars was SCH gel present (calcium silicate hydrates). No crystals of Ca(OH)2 was observed either, which indicates that all the lime had been carbonated. The Thermal Gravimetric Analysis (TGA/DTA) were used to find out the dosages of the mortars. Up to 420 °C, losses due to absorbed water and crystallization of salts were found. Results above 700 °C showed the decomposition of magnesium carbonate of the dolomite, and at 800 °C the decomposition of the calcite.

CaSiO3

Ca(Mg,Al)(Si,Al)2 O6

Fe2 O3

Wollastonite

Diopside

Hematite

3.34

8.21

2.56

8.09

16.90

19.01

11.72

9.12

Ca2 Al2 SiO7

Galenite

85.24

4.14

CaCO3

Calcite

98.48





Phyllosilicates (K0.82Na0.18)(Fe0.03Al1.97)(AlSi3 )O10(OH)2 11.62

SiO2

Quartz





7.01

(Na0.84Ca0.16)Al1.16Si2.84O8

Plagioclase

Mortar 19–20th









5.36

56.67

74.15

6.93

77.13









3.50

82.00

72.96

3.00

83.64









0.75 1.32 0.31

15.86 24.33 7.69

39.93 17.54 10.20

1.77 1.13 0.50

81.18 85.35 77.82









3.85 1.55 1.82

81.49 81.56 46.61

71.14 30.03 63.29

3.07 1.33 1.81

62.49 27.08 30.43

Coarse fraction Fine fraction Coarse fraction Fine fraction

15–18th 19–20th 15–18th

Brick

33.85

CaMg(CO3 )2

Dolomite

Compounds identified

Table 2 Compounds identified using XRD (%)











84.07

11.68





Stone

Characterization of Ancient Mixed Masonry … 25

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Fig. 4 Analysis by parallel nicols, NP × 40, of 15–18th century mortar

Fig. 5 Analysis by crossed nicols, XP × 40, of 19–20th century mortar

Table 3 Analysis of SEM results (%Components) Material

Sample

CO2

MgO

SiO2

CaO

Al2 O3

K2 O

FeO

Aggregate

15–18th century mortars

01

23.19

22.34

7.13

47.34







Calcium

19–20th century mortars

01



7.04

17.93

67.25

7.77





Calcium

02

27.01

4.97

2.99

65.03







Calcium

03

16.43

2.07

4.44

77.06







Siliceous

15–18th century brick

01

15.13

1.41

39.54

11.6

20.19

6.96

5.17



Stone

P

100



Characterization of Ancient Mixed Masonry …

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Fig. 6 TGA/DTA analysis of the 15–18th century brick

This (TGA/DTA) technique was similarly used on samples extracted from the pieces of brick. Figures 6 and 7 show a loss of weight due to evaporation of water up to 100 °C, indicating greater humidity and thus porosity in the sample from the first period, 15–18th century, with respect to the second period, 19–20th century. The loss of weight at 800 °C indicates the presence of calcium carbonate caliches, the samples from the first period showing greater presence of caliches than in those of the second period. In the first period brick, a greater number of endothermic peaks was observed, which indicates the presence of a greater quantity of clays that have not been fired, given that in their manufacture they underwent lower temperatures.

3.1.2

Mechanical Characterization

Table 4 details the compressive strengths obtained in the laboratory. The mortars of the 15–18th century provide an average compressive strength of 0.96 MPa and the 19–20th century ones of 3.16 MPa. The great variability shown by the 15–18th century mortars are related partly to the effect on the material of the extraction from the masonry and, partly to the conditioning and preparation of the samples before the test. In the case of the 15–18th century half-bricks tested, the value was 15.94 MPa with a notable variability of 21.25%, which was reasonable given its manufacture period. As for the 19–20th century bricks, the average compressive

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Fig. 7 TGA/DTA analysis of the 19–20th century brick Table 4 Compressive strengths of the samples of materials and masonry structures under study Material 15–18th century mortar

19–20th century mortar 15–18th century brick

Pmax (kN)

Area (cm2 )

fc Average Std. deviation Var. Coef. (MPa) (%) (MPa) (MPa)

1.93

15.95

1.21

1.66

16.00

1.04

1.01

16.00

0.63

5.57

17.63

3.16

280.6

197.74 14.19

0.96

0.30

31.12%

3.16





15.94

3.39

21.25%

18.67

2.12

11.36%

4.50

0.47

10.37%

286.32 207.78 13.78 578.89 291.78 19.84 19–20th century brick

607.56 290.14 20.94 581.58 300.09 19.38 491.38 309.43 15.88 351.61 190.37 18.47

19–20th century brick masonry

40.49

99.98

4.05

50.41 100.02

5.04

47.34

99.87

4.74

41.73

99.83

4.18

Characterization of Ancient Mixed Masonry …

29

strength was 18.67 MPa with an optimum variability coefficient of 11.36%. Finally, the 19–20th century masonry workpieces provided an average compressive strength of 4.50 MPa with a variability coefficient of 10.37%, which was quite low for the type of construction analyzed. It should be noted that 15–18th century masonry samples could not be extracted for later testing in the laboratory due to the low quality of the mortars.

3.2 Results of the in Situ Experimental Campaign 3.2.1

Estimation of Stress Levels

Figure 3 shows the emplacement of the flat jacks. In the case of emplacement 01, the portion of the masonry wall under study corresponds to the inside of the external brick wall, which is a semi-basement, belonging to the part attached in the 19–20th century (over ground level, the wall is a mixed masonry of brick of 28 × 14 × 5cm with lime-based mortar in bed joints of 3 cm and cobblestones also with lime-based mortar). As for emplacement 02, the tests were carried out on the ground floor, on part of the inside of an external mixed masonry brick wall, of 28 × 14 × 3 cm with lime-based mortar in bed joints of 4 cm, and cobblestones also with lime-based mortar, belonging to the original part (15th century) supposedly remodeled in the 18th century. The stress levels measured were 0.56 MPa in test SFJ-01, and 0.26 MPa in test SFJ-02.

3.2.2

In Situ Mechanical Characterization of the Masonry Structures

Test DFJ-01 had the aim of determining the modulus of deformation and Poisson’s ratio of the inner leaf of the brick masonry forming one of the load-bearing walls of the extension built in the 19–20th century. While test DFJ-02 allowed to determine the equivalent parameters in the inner leaf of the 15th century load-bearing wall, supposedly remodeled in the 18th century, built of a mixed masonry of brickwork infilled with cobblestone and lime mortar. A comparison of the average σ-ε laws obtained in the tests is shown in Fig. 8. From the curves shown in Fig. 8, it can be seen that in the case of DFJ-01 there is linear behavior until around 1.20 MPa, so that magnitude is related to the elastic limit of the masonry. From the study of the envelope curve of the non-linear behavior zone (Lombillo et al. 2013, 2014), a compressive strength of 3.88 MPa can be estimated associated to a deformation of 3‰ (Tassios 1988), a congruent value bearing in mind that the first fissure affecting one of the pieces forming the wall developed at a working pressure of the pump of 4 MPa. The secant modulus of elasticity determined was 3674 MPa and its Poisson’s ratio was 0.06. In the case of DFJ-02, the elastic limit was of 0.40 MPa and, carrying out an analogous study to the previous one, the

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Fig. 8 Comparison of the average σ-ε laws obtained in test DFJ-01 (19–20th century wall) and in DFJ-02 (15th century wall supposedly remodelled in the 18th)

compressive strength was estimated to be 1.02 MPa, the secant modulus of elasticity was of 1513 MPa and Poisson’s ratio 0.47.

3.2.3

Penetrometric and Sclerometric Tests on Mortars

The tests were carried out in areas near the flat jack test zones. In each test multiple repetitions were performed to, as far as possible, reduce the uncertainty of the average value obtained. The values registered are shown in Table 5. In the penetrometric test, the table includes the compressive strength value of the mortar, Rc , determined from Gucci’s relationship, Rc = (PI + 22)/134 (Gucci and Barsotti 1995), which proposes a relationship between the values of the penetrometric index (PI) and the compressive strength of the mortar, in the case of mortars with a compressive strength less than 4 MPa.

4 Discussion of Results In summary, Table 6 provides details about the most representative properties of the different materials studied in the laboratory.

Characterization of Ancient Mixed Masonry …

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Table 5 Penetrometric index (PI) and surface hardness values obtained in the area of the flat jack tests Position

DFJ-01 (19–20th century)

DFJ-02 (15–18th century)

Penetrometric index (PI)

267

1115

1441

1399

96

124

68

105

814

1139

2383

2093

60

54

20

12

887

2040

680

1069

193

61

39

291

763

2297

582

890

183

60

86

106

1038

1441

1226

1636

31

26

149

37

Average (PI)

1260.00

90.05

Rc (MPa)

9.57a

0.83

Rebound index (RI)

26

17

20

15

14

18

12

14

25

12

15

42

16

24

14

18

25

35

25

40

18

20

22

17

25

35

23

22

17

15

16

19

Average (RI)

25.13

17.13

Class

B–Moderate (25–35)

A–Weak (15–25)

a In this respect, it should be commented that the value of R in the area of DFJ-01 must be considered c

questionable given that it is above 4 MPa, the maximum value established by Gucci for the use of his correlation equation

The tests carried out confirmed that all the mortars analyzed were of limes with dolomite and/or silicate aggregates (quartzes and feldspars). Moreover, coincidentally with the periods of construction of the building (Torices et al. 2015), 2 types of mortars were found, clearly differentiated, some poorer, with lime:aggregate (l:a) ratios between 1:2 and 1:2.5 and densities around 1.23 g/cm3 , corresponding to the 15–18th century walls, and other richer ones, with a l:a ratio of 1:1.3 and an apparent density more than 1.78 g/cm3 , in the 19–20th century walls. The presence of calcium silicate hydrates (CSH gel) or calcium aluminate hydrates (CAH compounds) was not detected, so the presence of Portland cement or natural cements was totally discarded, which dates these masonries in the 19th century or the beginning of the 20th century, given that the first Portland cement masonry was used in the Spanish region of Andalucía by the ‘Sociedad Financiera y Minera de La Caleta’ in Malaga in 1921, and in Granada by ‘Inocencio Romero de la Cruz’, in Atarfe, also in 1921 (Puche and Mazadiego 2000). The samples of 15–18th century mortar provided an average compressive strength of 0.96 MPa and the 19–20th century ones of 3.16 MPa. This considerable difference in values can be explained by the physicalchemical characterization, given that the mortars of the 15–18th century have a low density due to the sandiness of the mortar, which was induced by the low content of conglomerate (low l:a ratio).



Well-preserved mortar

lime mortar, with 44% dolomite

Dolomitea lime mortar, with 20% dolomite

Made with clay with high content of siliceous sand and high presence of caliches

Made with clay with high content of siliceous sand and low presence of caliches

15–18th century mortar

19–20th century mortar

15–18th century brick

19–20th century brick



19–20th century brick wall









1:1.3

1:2

1:2.5

l:a





10.23

18.89

11.13–15.87



30.88

A (%)





18.32

29.98

21.89–28.48



37.96

P (%)

– –

4.5b





9.57

0.83



PEN



18.67

15.94

3.16

0.96



Lab

Compressive strength (MPa)

3.88

1.02







DFJ









B– Moderate (25-35)

A–Weak (15-25)



SCL (class)

D: Apparent density; l:a: lime:aggregate ratio; A: Absorption coefficient; P: Accessible Porosity; PEN: Penetrometry; DFJ: Double Flat Jack; SCL: Sclerometry a Dolomite: calcium carbonate with magnesium common in many limes b Average compressive strength obtained from 4 experimental tests in the laboratory (Table 4)



15–18th century brick wall infilled with lime mortar and cobblestone

1.80

1.59

1.78–1.97

1.23

Very sandy mortar

Dolomitea

Well-preserved mortar

D (g/cm3 )

Description

Material

Table 6 Most representative properties of the materials studied in the laboratory

32 I. Lombillo et al.

Characterization of Ancient Mixed Masonry …

33

As for the bricks, all of them have been made with the same type of clay and siliceous sand. However, different firing temperatures have been observed corresponding to the 2 periods of construction identified. The bricks from the zones built in the 15–18th century were fired at low temperature, with a less purified raw material, and greater content of caliches, a high content of unfired clay (XRD detected greater presence of phyllosilicates, as well as quartz, calcite and clays) and high porosity. In contrast, the bricks used in the 19–20th century show lower content in caliches, a lower unfired clay content and a lower porosity, indicating a higher firing temperature. Their mineralogical composition shows greater presence of silicates and little calcite. The average compressive strength found for the 15–18th century bricks tested was 15.94 MPa with a variability coefficient of 21.25%. As for the 19–20th century bricks, it was 18.67 MPa with an optimum variability coefficient of 11.36%. With respect to the mechanical characterization tests in the laboratory and the flat jack tests carried out, the different mechanical behavior of the 15–18th century and 19–20th century walls was evident. Table 7 details the mechanical parameters obtained in the masonry structures. Table 7 Mechanical parameters obtained for the load-bearing walls of masonry Mechanical parameter

15–18th century

19–20th century

Type of masonry

Brickwork infilled with lime mortar and cobblestones

Brickwork (lime mortar)

Elastic limit (MPa)

0.40

1.20

Compressive strength (MPa)

(a) Double flat jack (σfailure )

1.02

3.88

1.00*

(b) Tests of Average value masonry fk workpieces (c) Piet70 Estimation, fk (p.i.e.t. 1971)



4.50



3.74

0.96*



4.25

1.10*

(d) Eurocode 6 estimation, fk (EN 1996-1-1:2005)



6.03

1.55*

Elastic modulus through DFJ (MPa)

1513

3674

Poisson’s ratio through DFJ

0.47

0.06

* Relation

with respect to the value estimated in the double flat jack test, as it is considered the closest to the real behavior of the masonry (a) The compressive strength provided by the flat jack (σfailure ) are not characteristic values (fk ) as they are from only one test (b) In the case of laboratory tests on masonry testpieces, the characteristic compressive strength, fk , was obtained from the tests listed in Table 4, in which an average strength of 4.50 MPa and variability coefficient of 10.37% were obtained (c) As for the piet70 (1971), the value indicated corresponds to the characteristic strength, fk (d) Finally, with respect to Eurocode 6, EC6 (EN 1996-1-1:2005), the value indicted corresponds to the characteristic strength, fk , obtained considering pieces of fired clay (group 1) and ordinary mortar

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I. Lombillo et al.

In this case, it can be seen that the compressive strength of the masonry samples tested in the laboratory provided similar results to the in situ double flat jack test. However, the estimations of strength included in the piet70 and EC6, envisaged for new construction, give rise to higher values than those obtained in the tests, which casts doubt on the validity of estimating values of strength of historical masonries. The referred Fig. 8 allows to visualize this differential behavior of the two masonries under study directly, where the greater rigidity (2.4 times) of the 19–20th century masonry can be seen compared to the 15–18th century one as too its better mechanical performance (with a compressive strength 3.8 times greater). With respect to the stress levels obtained through SFJ, above all in the case of SFJ-01, it can be stated that they were greater than those estimated theoretically. However, it is notable that, in cases such as this, when a high service stress is not foreseen (due to the low weight of the existing walls themselves), the results of the simple flat jack tests should be treated cautiously. As for the mechanical characterization NDTs on the mortar of the masonries under study (penetrometric and sclerometric), the dispersion of the results in the two test zones should be highlighted. Generally, it was found that the mortar in the zone of test DFJ-01 (19–20th century) was of better quality than that in the zone of test DFJ-02 (15–18th century). In this respect, the correspondence with the results for the samples of mortar tested in the laboratory to compression and with those found for the masonries studied through S/D-FJ tests should be noted, where clearly different behavior was found in the two masonries. The compressive strength of the mortars (Rc ) obtained in the penetrometric test using Gucci’s equation, Table 5, was 0.83 MPa for the 15–18th century mortars (a value close to the one obtained in the laboratory, 0.96 MPa) and 9.57 MPa for the 19–20th century mortars. In this latter case, given the estimated strength through the above-mentioned equation is greater than 4 MPa, the maximum value established by Gucci for its use, this value should be treated cautiously. With respect to the results obtained with the sclerometric tests, they behave in a similar way to those obtained in the penetrometric test. Better classification of the mortars is obtained in the zone of the test DFJ-01 (19–20th century) with Class B–Moderate, compared to the zone of DFJ-02 (15–18th century) with Class A–Weak.

5 Conclusions From the tests performed on the masonries existing in the ‘Los Aragoneses’ mill in Monachil, Southern Spain, it can be concluded that there are 2 types of masonries, corresponding to a construction in two phases: 18th century (and before) and 19th and beginning of the 20th century, with materials of better performance. Through XRD, it was possible to find the crystalline phases existing in the samples analyzed and their chemical composition. Through SEM, a morphological examination of the topographical structure of the fracture planes of the testpieces and elemental analysis of the distinct materials making up the walls were carried out.

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Through POM, complementary information was found about the mineralogy of the samples. Finally, the TGA-DTA tests enabled the characterization of the properties of the materials that directly influenced the mechanical properties of the materials making up the historical masonries in question. In this way, the lime:aggregate ratio of the mortars and the firing temperature of the ceramic bricks was found. The compressive strengths obtained when breaking masonry testpieces, in this specific case, were lower than those obtained in flat jack tests. This difference can be explained both by the weakening of the masonry piece caused by extraction from the wall and the lack of lateral confinement of the test pieces during the tests in the laboratory. The estimations of strength obtained from experimental formulas considering the mechanical strength of the pieces of brick and the mortars, piet70 and EC6, give rise to disparate values. With respect to the NDTs applied to the characterization of the mortars, the dispersion of the results should be highlighted. However, both with the sclerometric tests, and with the penetrometric ones, it was demonstrated that the mortars of the 19–20th century were of higher quality than those of the 15–18th century, which is in line with the clearly different behavior of the two masonries. Acknowledgments This work was partially supported through the project “Study of the ‘Casa de los Aragoneses (Monachil, Granada)’ to assess the state of the structure and materials in order to carry out their refurbishment” funded by the ‘Organismo Autónomo de Parques Naturales’.

References ACI committee 530 (1999) Building code requirements for masonry structure. American Concrete Institute, Farmington Hills, MI Arizzi A, Martínez J, Cultrone G (2013) Ultrasonic wave propagation through lime mortars: an alternative and non-destructive tool for textural characterization. Mater Struct 46(8):1321–1335 Binda L, Lualdi M, Saisi A (2008) Investigation strategies for the diagnosis of historic structures: on-site tests on Avio Castle, Iatly, and Pisece Castle. Slovenia. Can J Civ Eng 35:555–566 Binda L, Saisi A, Tiraboschi C (2000) Investigation procedures for the diagnosis of historic masonries. Constr Build Mater 14:199–233 Binda L, Baronio G, Gambarotta L, LagomarsinoS, Modena C (1999) Masonry constructions in seismic areas of central Italy: a multi-level approach to conservation. In: 8th North American masonry conference. Austin, pp 44–55 Binda L, Anzani A, Cardani G (2009) Methodologies for the evaluation of seismic vulnerability of complex masonry buildings: case histories in the historic centre of Sulmona. In: Brebbia CA (ed) Proceedings of 11th international conference on structural repairs and maintenance of heritage architecture (STREMAH 2009). Wessex Institute of Technology Press, Ashurst, United Kingdom, pp 395–405 British Standard BD 21/93 (1993) The assessment of highway bridges and structures. Department of transport, Her Majesty’s Stationery Ofc., London Code UIC 778–3 (1995) Recomendations pour l’evaluation de la capacité portante des ponts-voûtes existants en maçonnerie et beton. Union Internationales des Chemins de fer EN 1996–1–1 (2005) Eurocode nº 6: Design of masonry structures, Part 1–1: General rules for reinforced and un-reinforced masonry structures

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Franzoni E, Leemann A, Griffa M, Lura P (2017) The “Terranova” render of the Engineering Faculty in Bologna (1931–1935): reasons for an outstanding durability. Mater Struct 50:221 Gucci N, Barsotti R (1995) A non-destructive technique for the determination of mortar load capacity in situ. Mater Struct 28(5):276–283 Gucci N, Sassu M (2002) Resistenza delle murature: valutazione con metodi non distruttivi, il Penetrometro PNT-G. L’Edilizia 16(2):36–40 Van Hees RPJ, Binda L, Papayianni I, Toumbakari E (2004) Characterisation and damage analysis of old mortars. RILEM TC 167-COM: ‘Characterisation of Old Mortars with Respect to their Repair’. Mater Struct 37:644–648 Hendry AW, Malek MH (1986) Characteristic compressive strength of brickwork from collected test results. Masonry Int 7:15–24 Hendry AW (1998) Structural Masonry. Macmillan Press Ltd Isebaert A, De Boever W, Cnudde V, Van Parys L (2016) An empirical method for the estimation of permeability in natural hydraulic lime mortars. Mater Struct 49:4853–4865 Lombillo I, Thomas C, Villegas L, Fernández-Álvarez JP, Norambuena-Contreras J (2013) Mechanical characterization of rubble stone masonry walls using non and minor destructive tests. Constr Build Mater 43:266–277 Lombillo I, Villegas L, Fodde E, Thomas C (2014) In situ mechanical investigation of rammed earth: calibration of minor destructive testing. Constr Build Mater 51:451–460 Lombillo I (2010) Theoretical–experimental research about minor destructive tests (MDT) applied to the mechanical on-site characterization of historic masonry structures. Dissertation, University of Cantabria López-Arce P, Tagnit-Hammou M, Menéndez B, Mertz J-D, Kaci A (2016) Durability of stonerepair mortars used in historic buildings from Paris. Mater Struct 49:5097–5115 Martínez JL, Martín-Caro JA, León J (2001) Comportamiento mecánico de la obra de fábrica. Universidad Politécnica de Madrid, Madrid, Departamento de Mecánica de los Medios Continuos y Teoría de Estructuras Middendorf B, Hughes JJ, Callebaut K, Baronio G, Papayianni I (2005). Investigative methods for the characterisation of historic mortars-Part 1: Mineralogical characterisation. RILEM TC 167-COM: Characterisation of Old Mortars with Respect to their Repair. Materials and Structures 38(38):761–769 Nóbrega De Azeredo AF, Struble LJ, Carneiro AMP (2015) Microstructural characteristics of lime-pozzolan pastes made from kaolin production wastes. Mater Struct 48:2123–2132 Puche O, Mazadiego LF (2000) Las canteras históricas de Morata de Tajuña y la cementera Portland Valderribas. 1st Simposio Ibérico sobre Geología. Patrimonio y Sociedad, Tarazona, Spain, pp 109–123 RILEM Recommendation MS-D.7 (1997) Determination of pointing hardness by pendulum hammer. RILEM TC 127-MS: Tests for masonry materials and structures. Materials and Structures 30:323–328 RILEM Recommendation MDT. D.1 (2004) Indirect determination of the surface strength of unweathered hydraulic cement mortar by the drill energy method. RILEM TC 177-MDT: Masonry durability and on-site testing. Materials and Structures 37:485–487 Rossi PP (1982) Analysis of mechanical characteristics of brick masonry by means of nondestructive in-situ tests. In: Proceedings of 6th international brick masonry conference. Rome, pp 77–85 Rossi PP (1985) Flat-jack test for the analysis of mechanical behaviour of brick masonry structures. In: Proceedings of 7th internacional brick masonry conference, vol 1. Melbourne, pp 137–148 Tassios T (1988) Mecánica delle muratura. Liguori Editore, Napples Tavares M, Magalhães AC, Veiga MR, Velosa A, Aguiar A (2008) Repair mortars for a maritime fortress of the 17th century. In: Medachs–Construction Heritage in Coastal and Marine Environments: damage, diagnostics, maintenance and rehabilitation, Lisbon, LNEC

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Tavares M, Veiga MR (2007) A Conservação de Rebocos Antigos - Restituir a Coesão Perdida através da Consolidação com Materiais Tradicionais e Sustentáveis. In: VII SBTA–Seminário Brasileiro de Tecnologia de Argamassas, Recife–Pe, ANTAC Torices N, Gómez JJ, López L (2015) Informe histórico-artístico y arquitectónico del Molino de los Aragoneses de Monachil (Granada) UNE-EN 771–1 (2011) Especificaciones de piezas para fábrica de albañilería, Parte 1: Piezas de arcilla cocida. AENOR UNE-EN 1015–11 (2007) Métodos de ensayo de los morteros para albañilería, Parte 11: Determinación de la resistencia a flexión y a compresión del mortero endurecido. AENOR Verstrynge E, Schueremans L, Van Gemert D (2011) Time-dependent mechanical behavior of lime-mortar masonry. Mater Struct 44:29–42 p.i.e.t. 70 (1971) Prescripciones del Instituto Eduardo Torroja ‘Obras de Fábrica’. Instituto Eduardo Torroja de la Construcción y del Cemento (IETcc), Madrid

Rehabilitation of Historic Chancery Building, Yangon, Myanmar Prafulla Parlewar

Abstract The historic Chancery Building is located on Merchant Street in downtown Yangon, Myanmar. This building was originally constructed as office of the Oriental Life Assurance Company of Calcutta, India. The research here investigates the physical conditions, structural damages and causes for deterioration of the building. The main reason for the structural deterioration of building was the damaged rainwater drainage system. This structural deterioration was investigated through geometric studies and Non-destructive Test. Also, the building had damages in exteriors, problems of termites, dampness and seepages. Based on this research, rehabilitation was proposed for the building by retrofitting the structural members with latest technology. Moreover, the building rehabilitation included redesigning of roofing system, water proofing and repair of drainage.

1 Introduction The historic Chancery building was originally constructed as offices of the Oriental Life Assurance Company of Calcutta, India. This five storied building was completed in year 1914 (Fig. 1). The Embassy of India occupied this building in May 1957 (Bansal and Fox 2016). This building is located on Merchant Street and 36th street in downtown Yangon. It is 12th building in Yangon to be commemorated by Yangon Heritage Trust (YHT) by a Blue Plague (Tun 2019). This chapter mainly investigates the reasons for the deterioration, structural assessment, and based on these investigation proposes rehabilitation of the building. The main reasons for the deterioration of the building were the damaged rainwater drainage system, water proofing of terrace and exterior damages. The research here assess the building through geometric studies and Non-destructive Test (NDT). The geometric studies include visual analysis which identifies defects in the structural members such as columns, beams and slab at each floor. Hence, floor-wise analysis of P. Parlewar (B) City Development Corporation (P) Ltd., Mumbai, India e-mail: [email protected] © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 J. M. P. Q. Delgado (ed.), Case Studies in Building Rehabilitation, Building Pathology and Rehabilitation 13, https://doi.org/10.1007/978-3-030-49202-1_3

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Fig. 1 a View from merchant street and b View from 36th street

these structural members is presented in this chapter. The damaged rainwater system had not only resulted into the damages to the structural members but also developed dampness, seepages and termites in the building. Rebound hammer tests (RHT) were conducted to investigate the condition of structural members in the building. The results of RHT had indicated poor compressive strength of concrete in columns. Some of the columns were found to be critical. The building is having composite columns with “I” steel sections covered with concrete. During the studies, it was observed that these “I” sections were corroded in columns. The beams were also found to have cracks at various locations. In year 2016, majority of damages were found on the fourth floor slab. These damages include spallings of the concrete and exposure of the corroded steel reinforcement. The dampness and seepages were found in all the floors of building. The causes of dampness and seepages were summarised as follows: (a) The rainwater drainage pipes were damaged at various locations on the exterior walls of the building. These broken pipes drains water on the wall surfaces which lead to internal seepage on walls and slabs. (b) The vegetations were developed on the external walls, cornices and slabs of the building. During rain, water find easy passage through cracks developed by roots of vegetation. (c) A open duct was found in the building for the water supply and sanitation pipes. Rainwater caused seepages on walls of this duct. (d) The concealed water supply pipes were damaged which leads to seepages in many locations in the building. (e) The other important cause of seepages in the building was the damaged roofing system. The roofing was made of wooden trusses and GI sheets. Many places, the trusses and metal sheets were damaged in the roof. The valley gutters were repaired from time to time. But still, there were damages in the valley gutters. The building was facing major problem of termites at various locations. Main causes for termites were dampness, wooden furniture, wall panels and cracks in exteriors of building. Damages in exteriors of building were carbonation, vegetation and cracks. It was important to treat the walls with water proof coating to reduce seepages inside the building.

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The rehabilitation of building was proposed by retrofitting of damaged structural members with latest technology. The method for retrofitting included use of Carbon Fibre Reinforced Polymer (CFRP), micro concrete, and jacking. Furthermore, the rehabilitation proposal included repair of roofing system, renewal of rainwater, renewal of sanitation system, repair of dampness and seepages, treatment of termites, exterior repairs and repair of various other parts of the building.

2 Building Profile Historic Chancery Building is located at downtown Yangon formerly know as city of Rangoon. The city was capital city in Myanmar (Burma) with a downtown area also called a Central Business District (CBD). The city is located in Lower Myanmar at the convergence of the Yangon and Boda Rivers. This downtown has many Colonialera buildings existing with heritage architecture. British conquered Yangon after the war of 1852 (Rhoden 2014), and later planned the downtown area into a commercial, political and administrative area. The downtown was design by the army engineer Lieutenant Alexander Fraser. He designed the downtown into a grid iron pattern. The climate in Yangon has a tropical monsoon with rainy season from May to October. During monsoon, the city experience rain fall upto 600 mm in month of August. The average temperature, highs ranges from 29 to 36 ◦ C (84–97 ◦ F) and lows ranging from 18 to 25 ◦ C (64–77 ◦ F). This former British capital has highest number of colonial building in SouthEast Asia. In year 1996, Yangon City Development Committee (YCDC) created a Yangon City Heritage List of old buildings which need an approval for modification and rehabilitation. Later, Thant Myint-U founded the Yangon Heritage Trust (YHT) as an NGO to conserve the heritage buildings in the downtown area. The YCDC and YHT are the core bodies which regulates the heritage buildings in down town Yangon. The Chancery building is a landmark building in the historic downtown. This building is attached to historic Corporate Tax Office of Yangon (Fig. 2a). On May 30, 2016, the Chancery building was commemorated with Blue Plague by Yangon Heritage Trust (YHT) as a symbol of historic significance of the building. The ground floor of the building have two entries, one as main entry under the porch for the general public and other for administrative staff (Fig. 2b). A reception lobby located at ground floor has waiting area for visitor and a hall which is converted into an auditorium. Some of the rooms on the ground floor are kept locked from long time. A library is located at rear end of the building. This library have an access from the 36th street and open to public on all working days. Columns in the library were found to be severely damaged. The main problem for the damages of the columns in ground floor library were due to storages kept in the Hindi book store. In year 2016, major cracks were observed in the columns in the library. Initially, the retrofitting was done by plastering the columns. This retrofitting was not sufficient to strengthen the columns. This floor is a public area, and the cracks and damages in columns were found dangerous to the public safety. Behind the library there is service corridor with

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Fig. 2 a Site plan, b Ground floor plan and c Mezzanine floor plan

drainage and sanitation services. However, this service passage is most damaged area of the site. The first floor of the building has administrative office with a conference hall. The second floor of the building is used for administrative offices. This floor also have many metal storages for keeping the administration files which resulted into the higher loading condition on the floor. The third floor have the offices of higher rank officers of the Chancery. The Fourth floor have the residence for the security along with a large yoga hall. Presently, the terrace floor is not used because of the leakages from roof and termites. Terrace floor is covered with the GI sheets. The profile of the roofing system is aesthetically integrated with the exterior design. Originally, roofing system was not part of the building. This new design had multiple slopes and valley gutters. Because of this, faster run-off of rainwater is restricted during rain.

3 Geometric Studies Geometric studies were based on the field survey conducted to document the building and its damages. Severities of damages were assessed based on the visual observations undertaken during field work inside the building. These were further documented through photographs and drawings.

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3.1 Physical Measurements Physical measurements were based on delineating accurately the structural system of columns and beams. These columns and beams were measured in the grid to understand the historic design. Then, the physical measurement were taken by ultrasonic measuring equipment. A system of floor wise documentation was carried out on site with engineers and architects. Then, drawings were prepared based on these physical measurements (Figs. 2, 3 and 4).

3.2 Visual Assessment of Damages Structural condition of building was assessed through geometric surveys which include documentation of complete building and identification of damages in columns, beams and slabs. The building is composed of Reinforced Cement Concrete (R.C.C.) with brick work in external and internal walls of the building. The

Fig. 3 a First floor plan, b Second floor plan and c Third floor plan

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Fig. 4 a Fourth floor plan, b Terrace floor plan and c Roof plan

internal walls have lime plaster on the wall surfaces. It was found that the column are composite type with “I” steel section and concrete. The major cracks were identified in columns and beams. Spallings and swelling of concrete was identified in the slabs.

3.3 Structural Damages in Building To understand structural condition of the building, damages were observed and analysed on all floors for severity on scale of three indicators i.e. high, medium and low. (a) Ground Floor Damages: At the ground floor, the structural damages were observed in the columns, beams and slab (Fig. 5a, b). Our geometric studies documented damages in following location: (i) Columns in Library: The damages of columns C39 and C44 were investigated in year 2016. In year 2016, internal steel of these columns were exposed and corrosion was visible (Fig. 6a). During this time, the room above library was having heavy load of storages.

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Fig. 5 a Ground floor damages and b First floor damages

So, it was analysed that the excess loading might had been responsible to cause damages in these columns. Later in year 2016, the excess load was removed and C39 and C44 were retrofitted with standard procedure. But in year 2019, again major cracks were developed in these columns. The severity of damages in columns was high on the ground floor. Thus, it was inferred that the columns were in failure state. (ii) Beams: The cracks were found in the beams J1J2 and L5L4. The spans consist of damaged beams were C5C4–B5B4 and B5B4–A5A4 (Fig. 5a). The severity of damages was medium on these beams. (b) First Floor Damages: The first floor damages in the columns, beams and slab were as follows (Fig. 5b): (i) Columns: The cracks were found in columns C10, C15, and C44. The severity of damage of these columns was high on the first floor. (ii) Beams: The beams K2K3, D5L5 and D1D2 were found to be damaged on this floor. The severity of damage of these beams were determined as medium. (iii) Slab: The swelling were found in various locations in the slabs at this floor.

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Fig. 6 a Damaged C44—year 2016 and b Damaged C39—year 2019

(c) Second Floor Damages: In year 2016, spalling was developed in Head of Chancery (HOC) office (Fig. 3b). This had exposed the corroded reinforcement of the slab. Following were the damages on this floor (Fig. 7a): (i) Spalling: The spalling was observed in the HOC office. Severity of this damage was high on this floor. Reasons for this spalling were leakages in slab and loose concrete. (ii) Beams: The beam H2H1 was found to be damaged on this floor. The severities of damages of these beams were medium (Fig. 7a). (iii) Slab: The spalling and swellings were found in slabs at this floor. These were found in spans K4K3–J4J3, K1K2–J1J2, J1J2–I1I2, I1I2–H1H2, C1C2–B1B2, B1B2–A1A2, and B5B3–A5A3, The severity of damages of these spalling and swellings in slabs were medium. (d) Third Floor Damages: The third floor damages were observed in the columns, beams and slab (Fig. 7b). These damages were as follows: (i) Columns: The cracks were found in columns C14, C41 and C44. The severity of damage of these columns were observed as high like on the other floors. (ii) Beams: The beams G2G1 and A1A2 were found damaged on this floor. The severity of damage of these beams were medium. (iii) Slab: The swelling was found in various slabs at this floor. The severity of this swelling was medium. (e) Fourth Floor Damages: The damages at fourth floor were observed as follows (Fig. 8a): (i) Columns: The cracks was found in columns C44. The severity of damage of these columns were determined as high like on the ground floor. Studies indicated that this column was damaged on all floors. It was suggested that the critical condition of this column may be not related to excess loading.

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Fig. 7 a Second floor damages and b Third floor damages

But, it was because of the failure of the concrete member. (ii) Beams: The beams K2J2, J2J3, I2I3, F1F2, C1C2, J1J2 and C5B5 (Fig. 8a) were found to be damaged on this floor. Also, spans C1C2–B1B2, and B1B2–A1A2 were observed with damaged beams. The severity of damages of these beams were ranging between medium to high. (f) Terrace Floor Damages: On the terrace floor, severe damages were observed in the columns, beams and slab (Fig. 8b). These damages were as follows: (i) Columns: The cracks were found in columns C06 and C16. The severities of damages of these cracks were high on terrace. (ii) Beams: The beam in K2J2, J2J3, J1J2, J2I2, and E2E3 were found to be damaged on this floor (Fig. 8b). The span G3G2–F3F2 were having damaged beam. The severities of damages of these beams were high. (iii) Slab: The swelling was found in spans J1J2–I1I2, I2I3–H2H3, and E1E2–D1D2 slabs at this floor (Fig. 8b).

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Fig. 8 a Fourth floor damages and b Terrace floor damages

3.4 Damages in Exteriors of Building Damages in exteriors of building were carbonation, vegetation and cracks. The main reason for the carbonation was heavy rain in Yangon. The cracks were caused mainly due to growth of vegetation on walls (Fig. 9).

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Fig. 9 Damages in exteriors

4 Structural Testing 4.1 Non-destructive Test—Rebound Hammer Test Rebound hammer test (IS-13311 Part II 1992, reaffirmed 2004) was conducted on the columns of the building (Indian standard 2004). This test is principally surface hardness test that works on the principal of rebound of an elastic mass (Katalin et al. 2015). Variation of 25% is found in strength of specimen tested by RHT. This is because factors like surface and internal moisture, carbonation of concrete, age of concrete and type of aggregates. RHT result indicated that the structural condition of building requires immediate attention for retrofitting and repairs. As per British Code 8110-1-1997 (Updated) (British Standard Institute 1997), 20 Mpa is the load criterion for load design of historic buildings. However, some of the structural members were found to have strength below 20 Mpa. RHT results had shown low strength of the structural member. RHT was conducted on columns with nine points at one location. These nine points were taken on members in a square area to get accurate results. The compressive strength of concrete was average of these nine rebound numbers. This test was conducted at fifty three locations in the building. The results of the NDT are as follows: (a) It may be assumed that grade of concrete is C25 and design load may be 20 Mpa as per BS code 8110-1-1997 (updated). (2) The results of rebound hammer test for compressive stress of concrete in columns were found to be below 20 Mpa. (3) Compressive stress for concrete in structural members C06, C09, C10, C27, C35, C39, C40, C42, C43, and C44 were found in critical state (Figs. 10, 11 and 12). (4) It can be assumed that foundations are in good situation because of no uneven settlement.

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Fig. 10 Results of RHT (G = Good, A = Average and C = Critical)

Fig. 11 Results of RHT (G = Good, A = Average and C = Critical)

Fig. 12 Results of RHT (G = Good, A = Average and C = Critical)

5 Dampness and Seepages Dampness and seepages were major problem which damaged the structural members. The reasons for dampness and seepages in the Chancery building were as follows: (a) Damaged Rainwater Drainage System: Rainwater drainage system of the building was composed of GI metal roofing on king post wooden trusses. This roofing was planned such that exteriors of building aesthetically integrate with the roof.

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(b)

(c)

(d)

(e)

(f)

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Some of the observations on the roofing of the building were use of thin roofing sheets, multiple valley gutters, and damaged trusses. Damage Water Supply Pipes: The water supply pipes to the building were through a internal duct. Many places the old pipes were damaged causing the seepages on the walls. Leakages in these pipes results into severe dampness in the building. Open Duct: The building had service ducts for water supply and sanitation pipes (Fig. 16a). This duct did not had any protection from rainwater. During heavy rain, the water spreads on the walls of the duct which results into dampness in the wall. Cracks in External Walls: Various cracks were found in different locations in exterior walls on rear side. Some of these cracks were in the plaster surfaces. These were also causing dampness in the internal walls. Vegetation on External Walls: The external walls on rear side of the building were not repaired from long time. So, small and medium vegetation were grown on the wall and cornices of the building. Most of these trees were Peepla trees. Roots of these trees grow faster. Thus, it was causing cracks in the cornices and joints in the building. These cracks becomes easy passage for rain water in walls. Toilet Grouts and Water Proofing: Toilet grouts between the tiles were also causing seepages in the slab. Waterproofing of toilets was deteriorated which results into dampness and seepages.

The dampness and seepages were documented in all the floors (Figs. 13, 14, 15 and 16). The floor wise observation of seepages and dampness were as follows: (a) Ground Floor: The ground floor dampness and seepages were located on side wall of corridor near stairs case. These dampness and seepages were found in span D5D3–L5L4, L5L4–C5C4, and C5C4–B5B4 (Fig. 14a, b) First Floor: The dampness and seepages on first floor were observed in spans K3K2–J3J2, K2K1–J2J1, E2E1– D2D1, D2D1–C2C1, C5C3–B5B3, and B5B3–A5A3 (Fig. 13b). Main reason for this dampness was the rainwater falling on rear wall surface. Also, the cracks in cornices were developed due to vegetation. Seepages were found below toilets. The reason for these seepages were damaged water proofing of toilet and damaged water pipes. (c) Second Floor: On this floor dampness were found in span C5C3–B5B3. These dampness were mainly because of exterior cracks and damaged rainwater drain (Fig. 14a, d) Third Floor: The major dampness was found on this floor. Locations of dampness were K4K3–J4J3, K3K2–J3J2, K2K1–J2J1, J4J3–I4I3, J2J1–I2I1, I4I3– H4H3, G2G1–F2F1, F2F1–E2E1, D2D1–C2C1, C2C1–B2B1, B3B2–A3A2, and B2B1–A2A1 (Fig. 14b). Reasons for this dampness were leakages in toilet and cracks in external walls. The severity of dampness was high on same wall and low on others. (e) Fourth Floor: The major dampness was also found on this floor. The locations of dampness were K3K2–J3J2, K2K1–J2J1, J3J2–I3I2, J2J1–I2I1, H2H1–G2G1, G2G1–F2F1, F2F1–E2E1, D2D1–C2C1, C5C3–B5B3 and C2C1–B2B1 (Fig. 15a). Reasons for this dampness were grouts in toilet and cracks in external walls. The severity of dampness was high on all walls.

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Fig. 13 a Ground floor dampness and b First floor dampness

6 Termites in Building Termites were also one of the major problems of the Chancery building. A visual survey was conducted to identify the termite infected areas in the building (Fig. 15b, c). The reasons for termite formation were moisture in the walls, wooden furnitures, partitions, wooden skirting and wall panels. The cracks in exteriors of the building were also causing the termite growth.

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Fig. 14 a Second floor dampness and b Third floor dampness

7 Roofing System and Terrace Floor Damages Terrace floor roof were mainly responsible for deterioration of building which caused dampness, seepages and spallings. To understand the present problems of roofing system, investigations were undertaken on wooden trusses, GI metal sheets, valley gutters, drainage pipes and terrace water proofing. (a) Wooden Trusses: Main structure of the roofing was composed of king post wooden trusses. These trusses were supported by R.C.C. beams at both end of the span. Gable end of the truss was supported on the triangular brick wall which aesthetically balanced the exterior design. The wooden trusses were having wooden purlins to support the metal sheets. These wooden trusses were severely damages.

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Fig. 15 a Fourth floor dampness, b and c Termites in building

(b) GI Metal Sheets: The GI metal sheets were supported on the purlins. These metal sheets were damaged at various locations. These damages were rusting of metal sheets from top side and leakages at various places. Most of these GI metals sheets were of thinner gauge which results into fast rusting and leakages. (c) Valley Gutters: The design of valley gutter did not encourage speedy run-off of rainwater which results into the leakages on terrace floor. (d) Drainage Pipes: PVC drainage pipes were damaged at various locations. Due to multiple bends, design was insufficient for faster run-off of rain water. The rain water drainage pipes were running horizontally on the terrace and the length of the pipes were longer in horizontal runs. Also, the design was insufficient to the intensity of rain in Yangon. (e) Terrace Water Proofing: Water was drained on the terrace for run-off (Fig. 16b). This caused the dampness and seepages in the slab. The terrace floor was not repaired from long time. Also, water proof coating was damaged completely on

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Fig. 16 a Open duct and b Rainwater water drain on floor

terrace floor. Moreover, the terrace floor drainage slopes were not found sufficient for water run-off. The design of roofing system was found to be aesthetically planned with the exterior design (Fig. 1). However, it had resulted into multiple slopes (Fig. 4c). Because of this, faster run-off of rainwater was restricted from the building during heavy rain. Also, in roofing design, multiple joints were existing between the valley gutter, walls, and roof sheets. After few years, these joint are difficult to maintain. Thus, it resulted into seepage of water at the joints.

8 Recommendations for Rehabilitation 8.1 Structural Retrofitting The structural members of the building were proposed to be strengthen through following methods: (a) The damaged columns and beams were proposed to be retrofitted with the Carbon Fibre Reinforced Polymer (CFRP). Because the building was more than 100 years old, low weight material with high strength was recommended for the retrofitting. The proposed retrofitting in CRFP will increase the life of the structural members. Also, this will need minimum supports for retrofitting. The CFRP is composite material of natural carbon with decomposition of organic fibres created at 1315 ◦ C (2400 ◦ F). Retrofitting in CFRP will increase erosion resistivity of the old structural members in the building. (b) The columns in the library were propose to be strengthen with Micro Concrete. This will help in increasing the strength of the structural members in a short

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time. Moreover, the self compacting properties of the concrete can provide early high compressive strength. (c) The structural members on terrace floor were proposed to be jacketed and collared by use of metal or pre-cast members anchored with the beam, column or slab. It was proposed to make a steel reinforcement cage wrap around the damaged column. Then, in situ casting was proposed to increase the compressive strength of the concrete. (d) It was suggested to repair spalling observed on the damaged slabs by re concreting in following steps: (i) The loose mortar was proposed to be removed from the surrounding spalled surface. Adequate cleaning was proposed of surrounding area with brush. (ii) Then, the two coats of anti-corrosive paint was proposed to be applied on the exposed reinforcement surfaces. One coat of polymer bonding agent was proposed to be applied over the entire area of steel and concrete. (iii) Above this, 1:3 cement mortars was proposed to be applied over the reinforcement. It was suggested to cure concrete for minimum 15 days. (iv) Finally, a water proofing coat was proposed on the ceiling surface.

8.2 Dampness and Seepages Dr. Fixit is locally available water proofing treatment which provides comprehensive solution to the dampness. Following were the recommendations for repair of dampness and seepages: (a) Mild dampness was proposed to be repaired by removing the loose material by using iron brush. The loose patches were proposed to be removed up to two feet from the surrounding damp area. Re-plastering was proposed in the exterior. This re-plastering was proposed by use of mix of water proofing materials, sand and plasticizing chemicals. After drying of the plaster, the water proofing coat was proposed to be applied on the surface. (b) Severe dampness were found in many places in the Chancery building. These were seen as damaged plaster with severe damp patches and white chalky deposits on the wall. To repair these severe dampness, all the water leakages were proposed to be removed from both side of wall. The plaster was proposed to be completely removed to apply water proofing on the wall surfaces.

8.3 Termites The comprehensive treatment was suggested for the problems of the termite which included smoke treatment, injection treatment, and treatment by anti-termite spray. It was recommended to undertake annual inspection and maintenance to solve the problems of termites in the building.

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8.4 New Roofing System A new roofing system was proposed to stop further deterioration of building. Following were the suggestions to make the new roofing system: (a) It was suggested to redesign the roof for faster run-off with simplified design to reduce excess turns in pipes. The size of valley gutter and pipes need to be redesigned as per rainfall in Yangon. (b) The locally available GI sheet of higher gauge was proposed be used for better design of the roofing. (c) The old king post wooden trusses were damaged due to rainwater. Also, this trussed were causing termite in building. So, it was proposed to replace these old trusses with the new Mild Steel (MS) angle trusses.

8.5 External Repairs External growth of vegetation and cracks in the building were causing the damages to internal structural members. The recommendations for repair external walls were as follows: (a) All the damaged exterior plaster was proposed to be replaced with new plaster mixed with water proofing compound to avoid dampness in the exterior parts of building. (b) The carbonation on exterior of building was proposed to be removed by use of low to medium pressure non-ionic water. Such water cleaning was proposed to be carefully done without damaging any part of the building. c) In various places in exteriors, small size vegetation was developed due to rain. This vegetation was causing cracks in non-structural elements of the building like canopy and chajjas. It was recommended to remove complete root system, as re-growth decay may result in damages to building. Also, localized chemical treatment of root systems was proposed to reduce any further increase of vegetation. The small Peepla plants were suggested to be removed by use of spray of Glyphosate with one percent solution of Sodium Arsenate. Then the gaps were proposed to be filled and repaired with epoxy.

8.6 Other Damages Toilet floors in building were another major cause for dampness and seepages in building. The old pipes were proposed to be replaced in toilets and pantry. Lime plaster is used in the interior of the Chancery Building. The building was repainted with the oil based paint during previous renovation. This was a major cause for

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increasing the moisture inside the wall. So, the lime based painting was proposed to rehabilitate the building from the problems of dampness, seepages and termites. The old wall panels were made of wood. These panels needed immediate replacement due to problems of termites in the building.

9 Conclusion Thus, the rehabilitation of Chancery building was proposed by undertaking (a) structural repairs, (b) treatment to dampness and seepages, (c) anti-termite treatment, (d) replacement of roofing and (e) other repairs like toilets, exteriors, plastering and painting. The columns, beams and slabs were damaged in the building. Some of these columns were in critical condition. These findings were based on the RHT conducted on various columns of the building. Subsequently, the retrofitting was proposed by use of CFRP, micro concrete, jacketing and repair of spalling of concrete. The roofing system was comprised of metal sheets, wooden king post trusses, and valley gutters. It was proposed to redesign and replace complete roofing system. This redesign was proposed to conserve the heritage value of the building. The dampness and seepages were major problems in the building. It was proposed to re plaster external part of the building. All the damaged toilets were recommended for repair by replacing complete flooring to stop seepages in the building. The termite problems in the building were recommended for anti termite treatment with annual inspection and maintenance. Thus, it was recommended to renovate the Chancery building on priority because of critical structural conditions.

References Bansal B, Fox E (2016) Yangon: architectural guide. DOM Publisher British Standard Institute (1997) Structural use of concrete Part 1: Code of Practice for design and construction Indian standard, non-destructive testing of concrete—methods of test, Part 2 Rebound Hammer (2004) Katalin S, Adorjan B, Istvan Z (2015) Understanding the rebound surface hardness of concrete. J Civil Eng Manag 21(2):185–192 Rhoden TF (2014) A Brief History of Yangon, Yangon and Swedagon Pagoda: other places travel guide. Other Places Publishing, Editor: Benjamin Cook Tun TY (2019) Indian embassy receives blue heritage plaque. Myanmar Times

Rehabilitation Operations in Residential Buildings in La Mina Neighborhood (S. Adrià del Besòs, Barcelona) C. Díaz and C. Cornadó

Abstract This chapter describes the physical operations of reforming and improving the accessibility, habitability and security of La Mina’s buildings. La Mina, which was built between 1968 and 1974, is comprised of 2,727 social dwellings in Sant Adrià del Besòs, a city close to the border of Barcelona. The usual techniques of the time were used in its construction. In the first phase, reinforced concrete was used for the structures and ceramic bricks for the exterior enclosures, and in its second and final phase the tunnel formwork technique, which was then new, and reinforced concrete panels for exterior enclosures were used. In some of the operations that were carried out, specific improvements were implemented. However, many of the rehabilitation operations that are described, such as the renovation of facilities, the addition of elevators or the reduction of energy loss from the exterior enclosure, could be applied in other situations to buildings constructed in the same period and urban context. Keywords Housing estate rehabilitation · Building renovation · Building refurbishment

1 Introduction The neighborhood of La Mina is a group of 2,727 dwellings built between 1968 and 1974. It is next to the mouth of the Besòs River, on one of the boundaries between the town of Sant Adrià del Besòs and the city of Barcelona, within Barcelona Metropolitan Area. It is one of the large housing estates built during the years of high C. Díaz Universitat Politècnica de Catalunya-Barcelona Tech (UPC), Barcelona, Spain e-mail: [email protected] C. Cornadó (B) Grupo de Investigación Rehabilitación y Restauración Arquitectónica (REARQ), Departament de Tecnologia de l’Arquitectura, Universitat Politècnica de Catalunya-Barcelona Tech (UPC), Barcelona, Spain e-mail: [email protected] © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 J. M. P. Q. Delgado (ed.), Case Studies in Building Rehabilitation, Building Pathology and Rehabilitation 13, https://doi.org/10.1007/978-3-030-49202-1_4

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Fig. 1 Urban situation of the neighborhood: a Urban context in an area occupied by linear blocks and towers, between the Besòs river, an industrial area that separates the sea from the end of the urban fabric of Barcelona’s Eixample district. b Aerial photo of the neighborhood, showing its surrounding environment and the location of the buildings

immigration from country to city in Spain (Diaz and Ferrer 1995; Ferrer 1996) and it originally housed low-income inhabitants (Fig. 1). The neighborhood was located in an unpopulated urban expansion area in the delta of the Besòs River. Over time, this area has become part of the City’s urban continuum and its nearby municipalities. The design of La Mina was based on prevailing urban planning models, in which residential, commercial and service uses were separated and isolated blocks and tower buildings of different heights were laid out over the territory (Díaz 1986). In La Mina, dwellings are grouped into linear blocks formed by juxtaposed modules with vertical access and two or four flats on each floor. The functional dwellings’ program includes a living room, kitchen, three or four bedrooms, a bathroom and laundry room, with useful surface area of around 55–67 m2 (Díaz 1986). Two areas are clearly distinguished in the configuration of the neighborhood. La Mina Vieja (The Old Mina) was built in a first phase and is comprised of 855 dwellings, mostly in 6-story buildings with small squares formed between them. A 13-story building, the only tall construction in the area, creates a boundary on one side. Common construction systems of the time were used in the first buildings put up in this area: reinforced concrete portal frames for most of the buildings, and a metal structure in the tall building (Díaz 1986; Díaz et al. 2015). Their outer envelopes are made of two brick sheets that enclose an air chamber, and flat roofs (Díaz 1986; Díaz et al. 2015). The construction of a second area called La Mina Nueva (The New Mina) began in 1972, with 1872 dwellings. It is comprised of six longer 11-story buildings and one 8-story building, all in parallel in the same direction, which create and bound exterior spaces that are larger and less well-defined than in La Mina Vieja. The tunnel formwork technique was used in the construction of all these buildings (Del Águila García 1986; Díaz et al. 2009). This technique was novel in Spain but already known and applied in other European countries. The same technique was used to build some of the blocks in La Mina Vieja (Fig. 2).

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Fig. 2 The two neighborhood areas: a The limits of La Mina Vieja and La Mina Nueva and the arrangement of the buildings in the two areas. b Partial view of the 6-story buildings of La Mina Vieja. c Partial view of the 11- and 8-story buildings of La Mina Nueva. d Construction with tunnel formwork of La Mina Nueva buildings

The Department of Architectural Technology of the Polytechnic University of Catalonia–Barcelona Tech (UPC) received a commission from the Institut Català del Sol (INCASOL) and the neighborhood managers (La Mina consortium and Pla de Besòs SA) to take charge of the design and construction management of physical rehabilitation and improvement actions on the residential buildings of La Mina Vieja and La Mina Nueva. This set of actions was established in the Special Plan for the Reorganization and Improvement of the neighborhood approved in 2002, authored by the team of architects Jornet-Llop-Pastor (Jornet et al. 2005, 2009). The actions were based on guidelines produced in a previous technical study by the same Department, which analyzed the state of the buildings and the maintenance operations that had been carried out during the buildings’ life. In fact, these design and management operations represented the last phase of a long analysis process that included the diagnosis and evaluation of various rehabilitation actions, with the most suitable chosen for the Plan (Díaz et al. 2012). Figure 3 outlines the sequence of actions and the relationship between them. This chapter refers exclusively to improvements in the accessibility, habitability and security of the buildings. The rehabilitation and improvement actions for the buildings considered in the Special Plan covered a range of objectives that can be divided into four main groups (Jornet et al. 2005, 2009). Two of them directly or indirectly affect accesses to La Mina Nueva buildings from the outer urban space. One proposal was to restructure specific aspects of the placement and number of dwellings accessed through the entrances to

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Fig. 3 Sequence of actions carried out in the technical study prior to the designs for improving accessibility, habitability and security in residential buildings

the residential blocks. Another was to create routes in the neighborhood by providing new ways through the three longer blocks, to shorten pedestrian paths. The other two objectives refer to habitability and accessibility. One addresses improvements in the external envelope and the provision of services and general and individual facilities in La Mina Nueva buildings. The other focuses on improving accessibility to La Mina Vieja buildings and installing elevators in the 6-story blocks that did not have any in the past. The rehabilitation actions derived from these objectives, which are described and discussed in more detail below, are only a fraction of the actions established in the Special Plan. The Plan also includes urban reorganization of the neighborhood, better connections with the city through increased public transport, the construction of new services and public facilities and the implementation of a powerful social program. Only comprehensive, combined knowledge of these measures enables us to understand the strategies designed to achieve an improvement in living conditions of the resident population shown in the Plan (Fig. 4).

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Fig. 4 Location of rehabilitation operations in the neighborhood. The figure shows the location of the new entrances and lobbies (reorganization of ground floors) and the situation of the module that was used as a prototype for integral rehabilitations in La Mina Nueva buildings, as well as the layout of the new elevators in La Mina Nueva

2 Restructuring Accesses to the Dwellings The proposed changes in the number and location of accesses completely rearranged all lobbies and ground floors of La Mina Nueva blocks and involved reducing the number of dwellings served by each vertical access. This fostered greater use and appropriation by the inhabitants of each vertical connection (Her Majesty’s Stationary Office 1994). The subdivision also increased the visibility of the buildings’ blind end walls. These operations were carried out at the same time as necessary repairs to the ceramic slabs that partially covered the buildings’ central courtyards, which were strongly affected by corrosion of the metal rods in the reinforced concrete. An example of the poor general condition of the halls before the remodeling can be seen in the photographs in Fig. 5. The image in Fig. 6a shows the situation of one block’s lobbies before rehabilitation. Each ground-floor access led to 80 dwellings distributed in two stairways. Figure 6b shows the situation of the new lobbies that provide access to 40 dwellings, so each lobby leads to a single stairway. In this new distribution, the accesses are

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Fig. 5 Condition of the lobbies before restructuring and rehabilitation. a View from the outside entrance. b Inner courtyard. c Access door to one of the two stairways that converged in each hall. d Detail of corrosion on one of the slabs

Fig. 6 Location of the exterior entrances to vertical accesses. a Situation prior to restructuring. b Situation after restructuring. c Space between the end walls of one of the blocks before the creation of the new access. d Space between the end walls of one of the blocks after the creation of the new access

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located on the two opposite longitudinal facades and on the end walls, in order to revive the exterior public space uniformly and provide a newer more attractive design. The operations involved in creating the new layout of the exterior accesses required partial occupation of some of the interior courtyards on the ground floor and affected the original layout of the existing lattices. These lattices were made from prefabricated concrete pieces (Fig. 5a, b, c) that separated the lobbies from the courtyards and were in very poor condition. All this, combined with moisture problems in the floor slabs covering the rear central courtyards of first-floor dwellings (Fig. 5d), led to general actions that included the repair of the slabs, the complete renovation of the roofs of inner courtyards and full replacement of the concrete lattices, so that all the ground floor communal spaces of La Mina Nueva blocks were completely renovated (Fig. 7). In the lobbies at the ends of the blocks, the outer entrance was moved forwards in relation to the wall that closed the stairwell at ground floor level. This made it possible to accommodate a new interior enclosure covered with concrete slab supported by metal profiles and plates. This metal structure also supported the new exterior enclosure made with perforated sheet protected with anti-corrosion paint (Fig. 7a, b, c, d). The original lattices made from prefabricated hollow concrete pieces, which surrounded the inner courtyards, were replaced by pieces of double-layer molded glass with vertical joints that included reinforcements placed between the metal profiles (Fig. 7e, f). The upper curved profile of this structure forms part of the new perimeter support for the IPN-80 metal joists that functionally replace the ribs of the ceramic slabs affected by corrosion (Fig. 8). All the elements of the reinforcements are hidden by a false ceiling made from laminated plasterboard (Fig. 7f). In each lobby, the interior finishes of the walls and flooring were preserved or replaced totally or partially depending on the state of deterioration. The roofs of the new sections of the lobby were built with solid reinforced concrete slabs supported by metal profiles. Light sloping concrete was laid on the slab, as well as a waterproofing sheet with four layers of liquid rubber and a double layer of ceramic tiles placed with mortar (Fig. 9a). The same solution was applied to the existing roofs of the inner courtyards once all the materials of the old roofs that supported the reinforced ceramic slabs had been removed (Fig. 9b).

3 Comprehensive Rehabilitation of a Residential Module of 40 Dwellings in La Mina Nueva The five 11-story buildings and the 8-story building in the La Mina Nueva neighborhood were built using a large tunnel formwork system (Díaz 1986; Del Águila García 1986; Díaz et al. 2009), called Hunnebeck, which formed the 15 cm-thick load-bearing walls and the 16 cm-deep slabs, all in solid reinforced concrete. This

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Fig. 7 Construction of the new lobbies. a Floor plan of two of the new lobbies. b Section of the same lobbies. c Positioning of the perforated sheet panels. d External enclosure based on perforated sheets placed forward from the plane of the staircase wall. e Positioning of molded glass. f Appearance from the inside of the new enclosure of the inner courtyard based on molded glass

system had been used extensively in other European countries before. In fact, the considerable length of the blocks, three of them of 199.5 m and two 106 m, as well as the linearity and lack of setbacks on the facades responded precisely to the convenience of optimizing the movements of the auxiliary resources of hoisting and horizontal transportation of the formwork. The deltaic characteristics of the land forced the foundations to be made from reinforced concrete piles from 15 to 20 m of length. The structural safety conditions were verified in the technical study prior to the phase of undertaking the rehabilitation projects (Díaz et al. 2012). The exterior enclosures of all buildings are two-leaf: an outer sheet of reinforced concrete panels molded on site and an inner sheet based on pieces of plaster of 40 × 60 cm, 6 cm thick, which encloses an inner air chamber. These same pieces were used to build

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Fig. 8 Repair of ceramic slabs. a Detail of the reinforcing joists’ position between the new edge beam of the molded glass enclosure and the fixings to the perimeter wall. b View of the joists between the edge beam and a U-profile fixed to the perimeter wall, used instead of the metal plates (left image detail) when the joists are correlative

Fig. 9 Technical intervention on the deck of the courtyards. a Phase of arranging the metal rods of the new slab on the wooden board formwork, before concrete placement. b View of the finished rehabilitated roof

the entire interior partition. Both exterior and interior carpentry were wooden, with single pane glass. The maintenance conditions were very varied. However, as the dwellings were public housing (Díaz et al. 2016, 2019), they had been subjected to some general actions aimed at resolving the most widespread problems, such as condensation dampness in the end walls, leaks on roofs and dysfunctions in vertical evacuation facilities. The structure and main partitions of the buildings did not show remarkable damage, although there were abundant cracks in the partitions due to deformations caused by the creep of reinforced concrete slabs. As a module in one of the five 11-story buildings (Fig. 10) was empty for a long time, there was an opportunity to undertake a comprehensive rehabilitation project. In this pilot project, the improvement and rehabilitation actions proposed in the

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Fig. 10 a Standard floor plan of the intermediate modules of the block with 3-bedroom dwellings and the end modules with 4-bedroom dwellings. b The photograph shows the end module in which the intervention was undertaken

technical study could be implemented and integrated into the urban plan that was subsequently approved. The empty dwelling was one of the end modules of a 6-module blocks (Fig. 10). The end modules differ from the middle ones because they contain 4-bedroom dwellings instead of 3-bedroom dwellings. However, all dwellings are sufficiently similar because the structural configuration and all other integral elements are the same, except the thermal conditions of the two dwellings that are in contact with the end walls. The objective of the intervention was to update all the elements of the building that have an impact on aspects of habitability, health, safety and energy efficiency. The aim was to maintain the interior distribution of the dwellings and the external image of the facades of the building, with only formal modification of the end of the block bordering on the aforementioned end walls, to improve its appearance by moving forward the enclosure of the renewed lobby. Consequently, this was a comprehensive rehabilitation operation that can be used as a reference for most of the buildings in La Mina Nueva. The operation included improvement of the thermal and acoustic conditions of the external enclosures, including rehabilitation of the enclosures of the inner courtyard and the roof, as well as complete replacement of all interior and general installations for ventilation, fire protection, electricity and water supply and evacuation. This set of actions resulted in the replacement of all the bathroom and kitchen fittings in the dwellings.

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3.1 Rehabilitation of the Outer Envelope The criterion adopted for the external enclosures prior to any intervention was to evaluate their thermal and acoustic insulation conditions at the time of the technical study and compare the results with the values established in current technical standards (Díaz et al. 2012; Bragança et al. 2007). Figure 11 shows the construction sections of the longitudinal facades and the upper roof, indicating the interventions that were implemented. Longitudinal facades are made of reinforced concrete panels built on site fixed to the transverse reinforced concrete walls of the tunnel formwork and plasterboard. Subsequently, before the technical study and in a general action for all buildings with this type of enclosure, a ribbed metal sheet was added in front of the panels to avoid the breaking and detachment of concrete pieces out of the panels (Fig. 11). In addition, in another of the general actions undertaken in advance, the thermal insulation of the end walls was improved by applying a system based on expanded polystyrene plates on the outside (ETICS). These actions led to the fulfillment of the Catalan NRE AT/87* standard in the buildings, with the exception of the roof enclosure, where the required minimum value of thermal transmittance (0.40 W/m2 K) was

Fig. 11 Rehabilitation of exterior enclosures. a Section of the facades by the living room and terrace of dwellings. In red, the renewed windows and the sealing sheet and thermal insulation added in the pilot intervention. b Concrete panel that forms the railings of the terraces. c Enclosure of the living room of the standard dwelling with the new carpentry

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not met. The thermal transmittance (U) values of all initial and subsequent exterior enclosures after the pilot intervention are indicated in Fig. 12. In situ measurements of the acoustic conditions were carried out to assess the level of exterior noise measurable from the interior of the dwellings closest to the fast road that runs through one of the boundaries of the complex. At the time the neighborhood was built, there were no acoustic regulations and the fast road did not exist. The values obtained (Fig. 13) indicate the insufficient acoustic reduction offered by the glass enclosures of bedrooms and living rooms, since the values exceeded the 30 dBA

Fig. 12 Thermal transmittance values (U) of the original exterior enclosures and those after the pilot intervention

Fig. 13 Sound pressure levels on the exterior and interior of dwellings near the fast road

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and 25 dBA of acoustic pressure in living rooms and bedrooms respectively that are required by Barcelona’s urban regulations. Data on the thermal and acoustic conditions of the dwellings were used to determine which actions to undertake. The selected actions consisted of improving both aspects by changing all the exterior woodwork containing single pane glass (on facades and inner courtyards) for aluminum windows with double glazing and roller blinds (Fig. 14). The other action was increasing the thermal insulation of the upper cover (Figs. 11 and 12). This reduced energy demand by 20.2% in relation to that required by the original building and 9.3% in relation to that required by the building before the intervention. On the facades of the inner courtyard, which did not have the finish of the ribbed metal sheet, all the surfaces needed to be cleaned with pressurized water. Subsequently, a protective film of anti-carbonation and anti-chloride product had to be applied (Fig. 15).

Fig. 14 Facades with the existing ribbed metal sheet and with the new roller blinds and the new lacquered aluminum frames. a Area corresponding to the living room. b Area corresponding to the bedrooms

Fig. 15 Rehabilitation of the inner courtyard enclosures. a Surface cleaning of concrete with pressurized water. Note the difference in color between the cleaned part and the rest. b Aspect of the enclosure once the anti-carbonation and anti-chloride product has been applied and the window frames have been renovated. The darkest part corresponds to the neighboring module that has not been rehabilitated

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Fig. 16 Rehabilitation of the upper roof. a Arrangement of the double waterproof sheet and formation of the endings of the smoke extraction elements and the railings. b Appearance of the roof finished with the protective gravel and protection of the edge railing with ribbed sheet

On the upper roof, the slopes formed with light concrete were slightly increased and their waterproof layer was renewed by placing a double sheet of modified bitumen (LBM). In addition, 4 cm of extruded expanded polystyrene was added, to increase thermal insulation, and covered with gravel for stability (Fig. 16). This set of interventions transformed the existing roof into an inverted roof. Finally, all the endings of projecting elements of the ventilation installation, the walls of the elevator room and the perimeter railings were completely renewed. They were coated with the same sheet metal as the facades as an additional protection resource. Consequently, the existing roof was completely improved including all its unique points.

3.2 Facilities Renovation The state of the building’s facilities was very precarious, uncontrolled and with very little maintenance (Fig. 17). One of the main objectives of the pilot intervention was to assess the difficulties and cost of complete renovation of the facilities to update them so that they comply with current standards and requirements (Labastida 1999). The following repairs and renovations should be carried out on the facilities: – Full renovation of water and electricity supply facilities – Providing the building with natural gas – Renewal of the vertical and horizontal water drainage ducts, both the general pipe and those of each dwelling – Renewal of the entire smoke evacuation system – Providing all telecommunication elements established in the regulations (telephony, TV, collective antenna, etc.) – Adaptation of the fire protection system to the requirements of the Fire Department (emergency stairs, dry column, etc.)

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Fig. 17 State of the facilities before the rehabilitation

One of the changes in the regulations that have occurred since the construction of the building is the need to centralize water, electricity and gas meters in places that can be accessed easily by inspectors, among other requirements (Fig. 18). Therefore, there was a need for one space in the new lobby that met these requirements, although this meant varying the routes to the supply points, to facilitate registration and ease of maintenance. These same criteria were also applied to locate the wastewater and stormwater evacuation elements, with routes and logs in single spaces with easy access. The paths of existing ducts through the slabs were used to provide new drainage and smoke elimination ducts (Fig. 19). The stanchions of the installations of water, gas, electricity, fire protection and telecommunication facilities ran through the rehabilitated enclosures of the interior courtyards of the building (Fig. 20). Obviously, the undertaking of all these operations was accompanied by renovation of the entire bathroom and kitchen equipment of the dwellings, and also involved the reconstruction of its enclosures, which were weakened by the passage of the previous facilities. For the reconstruction, prefabricated composite pieces of hollow ceramic coated with plaster (known as ladriyeso in Spanish) were used, as their format and coating material are similar to the plaster pieces used in the original partition wall. The kitchen equipment and sanitary appliances in the bathrooms were also renewed (Fig. 21), as well as the coating of ceramic pieces. The Ladriyeso application was extended to the reconstruction of other partitions of dwellings affected by breakages due to the creep of the slabs.

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Fig. 18 Centralization of water, electricity and gas meters in the lobby. a Distribution of the network of pipes and cables through the roof of the ground floor to the vertical paths. b View of one of the finished cabinets. c Path of the ventilation ducts to the inner courtyard. d Water supply pipes before installation of the meters

Fig. 19 Use of the paths through the slabs. a Arrangement of water supply and evacuation facilities in the original project. b Arrangement of the new pipes through the existing holes in the slabs

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Fig. 20 Route of the water, gas and dry column supply pipes through the inner courtyard. a Start of the route in the placement phase. b Route through intermediate floors. c Final sections of the pipes. The vents of the gas installation in the kitchens are also shown. On the roof are some of the static extractors of the ducts that circulate through gaps in the slabs

Fig. 21 Interventions in wet rooms. a Reconstruction of the partition walls with partitions based on large-format ceramic pieces covered with plaster. b Kitchen with the equipment in place

Finally, it was decided that the electrical wiring would run through plastic gutters to avoid perforations in both reinforced concrete and plaster walls (Fig. 22).

3.3 Adequacy of Fire Protection Facilities Following the guidelines of the Fire Department, the fire protection conditions of the building were considerably improved to adapt them to the highest current requirements. For this purpose, a fire sector needed to be created in the stairwell, so that it could be subdivided at the level of the 6th floor by a 2 h fire resistant enclosure (RF120, according to Spanish regulations). The emergency stairs for users of the five upper floors start at this level. They are designed to evacuate through the building’s

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Fig. 22 New electrical installation. a Start of the interior installation of a dwelling from the protection and bypass panel. b Connecting elements of the installation and gutter for the passage and protection of the cables. c Detail of junction box and PVC gutters

roof, with possible access to the roofs of the rest of the building’s modules. The new emergency staircase communicates with the vertical access of the building on all the landings of the general staircase above the 5th floor and is supported by metal beams fixed to the reinforced concrete walls of the building. The evacuation of users of the lower floors is expected to be carried out through the lobby, and it is also possible to exit via the Fire Department’s mobile stairs (Fig. 23). These new evacuation conditions were completed with the installation of a dry column through the inner courtyard until the intake next to the building entrance. Fire extinguishers were also placed on each of the 11 floors of the building, together with emergency lighting points and venting devices on floors 5 and 10 to detect and extract smoke in case of fire in each of the two new fire sectors of the general staircase of the building (Fig. 24).

4 New Installation of Elevators in the Buildings of La Mina Vieja Th.e area of the neighborhood called La Mina Vieja was the first to be built and differs morphologically and constructively from La Mina Nueva. In this area, most of the buildings are constructed with conventional techniques of the time, that is, with reinforced concrete structures and ceramic brick enclosures. Most of the buildings in this area are 6-stories high: the ground floor has a commercial use while the five following floors are residential. Many of the buildings do not have elevators. Hence, to improve accessibility, it was decided to provide the buildings with elevators located on the outside (Fig. 25). This operation foresaw the installation of 30 elevators in buildings that lacked them and was completed in three phases between 2004 and 2010. Although the buildings in La Mina Vieja are very similar in appearance and distribution, they can be classified into different types: C, D and E lack an elevator, while B and F were fitted with elevators from the outset (Fig. 26). Each typological

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Fig. 23 New emergency staircase. a Position of the new emergency staircase built in the end module and plan of the situation in the neighboring modules. b View from the street. c Last leg of the emergency stairs. d Exit to the roof. In the background, access to the elevator machinery room

Fig. 24 New fire protection elements. a Dry column in the inner courtyard, in front of the ventilation window of the general staircase. b Location of the junction of the dry column and the venting device on the 5th floor, integrated into the ventilation opening. c Emergency lighting location

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Fig. 25 a Location of the new elevators in Mina Vieja. b Images prior to the installation of the elevators of the six-story buildings

Fig. 26 Housing types in La Mina Vieja and their location in the neighborhood

unit is formed by two symmetrical dwellings with access though a landing that leads to the staircase, which is ventilated through the facade. This makes it difficult to have the landing of the elevator at the level of the dwellings and leaves two possibilities for the installation of the new elevator. The first is to place the elevator on the side of the facade opposite the staircase, making it possible to access the dwellings at the same level. This option would have involved remodeling the ground floor and building a new volume on the facade to provide access to the dwellings through the terraces or kitchens. The second possibility was to place the new elevator adjacent

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to the existing staircase, without an access at the same level, and instead making the elevator landings halfway up each floor. The second option was adopted by the administration for economic reasons. Although universal accessibility was not achieved, accessibility was improved markedly. A unitary design was chosen for the new elevators’ volumes, although the subtle differences between the various types of buildings led to the adoption of different morphological solutions on the ground floor (Figs. 27a and 28c, d). Two of the types (types C and D3) incorporated the building access from the new elevator volume. Each new module that was added to the facade had an elevator and its landing that connected to the existing staircase, so that the ventilation conditions of the existing staircase were maintained (Fig. 27b). It was decided to clearly differentiate the new modules from the original building, using differentiable materials. Ground floors combine concrete and a finishing made of metal grid. The upper floors have an enclosure of reinforced concrete panels.

Fig. 27 a Original floor plans of La Mina Vieja buildings. b Placement of new elevators in standard floor plan, ground floor, front view and sections

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Fig. 28 a, b and c Views from the outside of the new elevators

Volumetrically, the new elevator modules protrude from the cornice line providing access to the roof (Fig. 28).

4.1 Structure The structure of each of the new modules is comprised of five slabs, which form the new landings, and four pillars that limit the elevator travel. The new slabs are supported by the pillars and the concrete floor slabs of the existing staircase’s landing. Each elevator has its own foundation. The fact that the installation of the new elevators was completed in three phases led to changes in their structure. These were due to a process of cost optimization and commissioning. The structure of elevators built in the first phase were made of in situ reinforced concrete (Fig. 29a). This solution was chosen because it was cheaper than a metal structure. However, the costs derived from the small scale of each phase of concreting meant that this option was revised in the second phase. The structure of phase 2 was designed and constructed with a steel profile structure welded in situ (Fig. 29b) with steel and concrete slabs, respecting the same exterior design. The structure of phase 3 optimized phase 2. In this second phase, the construction company suggested a change in commissioning that consisted of building the structure of each new elevator in the workshop and transporting it to the site in two sections (Fig. 29f). This modification reduced the work time on site as it facilitated the assembly of the elevators’ structure.

4.2 Interior and Exterior Finishes Durability was one of the main factors to consider for the choice of both interior and exterior finishes. The exterior enclosures were executed with prefabricated concrete panels supported and fixed to the elevator structure (Fig. 30). Each reinforced concrete panel is anchored by six points to the elevator structure. The central anchor points

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Fig. 29 a Type D elevator structure for phase 1. b Type C elevator structure for phases 2 and 3. c Phase 1 under construction. d Phase 2 under construction e and f. Phase 3 under construction

support the weight of the panel while the two upper points and the two lower points stabilize the piece against horizontal thrusts (Fig. 31a, b). As shown in Figs. 31 and 32, the fixing system did not vary with the change of concrete structure (Fig. 31) to metallic structure (Fig. 32). The only variant was the type of union with the structure: by mechanical anchors in the case of the concrete structure (Fig. 31b) and by welding in the case of the metal structure (Fig. 32). For the interior finishes, the choice was to use thermosetting resin panels placed with aluminum profiles (Fig. 33).

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Fig. 30 a Diagram of fixation of the prefabricated concrete panels to the structure. b Detail of the section of the new elevator volume

Fig. 31 a Image of the process of placing the new panels. b Stabilizer fixation placement. c Support fixing detail

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Fig. 32 Images of the fixings of the panels to the metal structure

Fig. 33 a and b Images of the inner finishing of thermosetting resins. c Type D lobby

5 New Passages in the Long Buildings of La Mina Nueva The project for the creation of new passages in the buildings of La Mina Nueva has not yet been carried out, although it is included in the urban planning. The project considers the creation of passages in the Mart and Llevant buildings (Fig. 34a), whose original length was almost 200 m, and defining a public space between them with little permeability to the outside (Fig. 34b). These blocks are of the typical typology of La

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Fig. 34 a Buildings in which the passages are planned. b Public space between the two blocks. c View of the Mart block

Mina Nueva buildings. They are 11-story linear blocks built with tunnel formwork (Fig. 34c). Each is formed by 12 modules separated by thermal joints, while each module is made of three tunnel formwork widths. Each of the modules has a lobby that gives access to 40 dwellings. The project foresees the suppression of the three lower floors of the central module of each of the blocks. This would involve eliminating the commercial ground floor and eight dwellings (two floors of dwellings) in each of the blocks (Fig. 35c). Each

Fig. 35 a Longitudinal elevation of one of the linear blocks with the location of the passage to be executed. b Detail of the elevation with the affected area. c Affected dwellings

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passage would be 15 m wide and three stories high, to ensure enough visibility and amplitude (Fig. 35a, b). The suppressed module affects two access stairs, and two dwellings would be eliminated from each access (Fig. 35c). The passages will be created between thermal joints, so no structural intervention is required in the adjacent modules. Structural interventions are only concentrated in the module where the passage will be formed. This action must guarantee the support of the 8-story structure above the passages. In addition, the intervention must resolve the accesses to the two affected lobbies and the wall coverings that will be exposed once the demolition is carried out. Figure 36 shows the elevation once the passage has been made in one of the two linear blocks. The completion of each passage requires the elimination of two lateral walls and two central walls of the tunnel formwork and the shoring of these walls (Fig. 36b, d). To achieve this, a structure made of metallic frames replaces the suppressed walls. These portal frames will be braced by metallic crosses that stabilize them in a transverse direction to the horizontal forces (Fig. 36c). A suspended ceiling will cover all these elements. All this structural intervention is expected to be carried

Fig. 36 a Longitudinal front view of one of the linear blocks with the passage. b Front view detail of one of the passages. c Longitudinal section of one of the passages. d Floor plan of one of the passages e Volumetry of one passage

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out without the need to relocate the inhabitants of the upper floors, for which it will be necessary to enable temporary access to the existing stairways. The access halls that lead to the passages will be remodeled with an image similar to that adopted in the remodeling of the ground floors in the rest of La Mina Vieja, with an extension of the access space (Fig. 36d). The walls that will be exposed after the demolition of the three floors will be protected by cladding and equipped with thermal insulation. The passages will have a false ceiling and will be illuminated by new lamps located on metal pillars. The pavement of the passages will be the same as that of the adjacent streets to give an image of continuity.

6 Epilogue The rehabilitation actions included in the Special Plan for the Realignment and Improvement of the neighborhood, approved in 2002 (Jornet et al. 2005, 2009), have not been completed. In addition to the execution of the passages through the blocks, the demolition of one of the 6-module blocks with 240 dwellings is pending execution. As in many other large housing estates with similar physical and social characteristics to La Mina, the programming of the various phases and operations included in the planning depend on complex management and budgetary activities. Other factors that need to be considered include changes in the users’ vicissitudes, which can almost always be explained by considering a much broader context than the strictly technological framework. However, if the experience is focused on more specific aspects, such as the discussion of demolition-rehabilitation options, which are almost always present in interventions of these characteristics (Belmessou et al. 2005; Power 2008; Wassenberg 2011; Cervero and Hernández 2015; García-Vázquez et al. 2016), we can verify (taking as a reference the action of integral rehabilitation in one of the modules) that the cost of the described intervention added to the set of maintenance operations completed in advance represents 63% of the cost of replacing the building, rebuilding the module with the same number of square meters as demolished. This result, which can be added to previous ones obtained by the REARQ Research Group, confirms from a strictly economic perspective the rationality of prioritizing maintenance, rehabilitation and improvement of buildings (Díaz et al. 2012). This conclusion is evident when such operations are compared to the more radical, less sustainable options of building demolition and reconstruction. Finally, it is extremely difficult to evaluate the results of the interventions undertaken in these kind of cases (Estany 2014); La Mina is no exception. Indeed, a solution based solely on material qualities is usually insufficient for issues related to correction, adequacy and durability. The adequacy of related issues of use and maintenance also needs to be considered, taking into account users’ idiosyncrasies and acceptance. These aspects are often of a more subjective nature with greater variability than the previous ones.

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Acknowledgments Many colleagues and scholarship students participated in the long process of execution of the various works that are summarized on the previous pages. We thank them for their dedication and commitment, which went beyond merely completing the commission. They include the architects E. Hormías, F. Pardo, J. I. Llorens, R. Gumà, M. Urbiola, E. Simó and J. Pérez-Mellado; the technical architects, J. Fusté de TRAM Ass., X. Oliva, J. Iglesias and M. Hierro de COTCA, S. A.; and the scholarship students E. Llaneras and M. De la Nogal. We also appreciate the trust placed in our University Department by the Institut Català del Sol (INCASOL), a Government of Catalonia agency, and the managing bodies of the neighborhood: the Consorcio de La Mina and Pla de Besòs S. A.

References Belmessou F, Chignier-Riboulon F, Commercçon N, Zepf M (2005) Demoliyion of large housing estates: an owerview. In: Restructuring large housing estates in Europe, Chap. 10 193–210, The Policy Press, London, UK Bragança L, Wetzel C, Buhagiar V, Verhoef LGW (2007) Improving the quality of existing building envelopes; Facades and Roofs, COST C16, vol 5. Delft University Press, The Netherlands Cervero N, Hernández L (2015) Remodelación, transformación y rehabilitación. Tres formas de intervenir en la vivienda social del siglo XX. Informes de la Construcción, Instituto de Ciencias de la Construcción Eduardo Torroja (IETcc). v67 Extra-1. https://dx.doi.org/10.3989/ic.14.049. ISSN 0020–0883 Del Águila García A (1986) Sistemas de grandes encofrados en la edificación. In: Las tecnologías de la industrialización de los edificios de vivienda. Colegio Oficial de Arquitectos de Madrid, Spain, pp 133–160 Diaz C, Ferrer A (1995) Edificació, urbanització i població en les àrees urbanes perifèriques i centrals de la Regió Metropolitana de Barcelona. Forum ISSN 1134–8356(2):82–93 Díaz C, Ravetllat PJ, García-Almirall P, Cornadó C, Vima S (2016) Refurbishment in Large Housing Estates: a Review on Restructuring and Upgrade. Procedia Eng 161:1932–1938. https://doi.org/ 10.1016/j.proeng.2016.08.776 Díaz C, Cornado C, Vima Grau S, Ravetllat P, Garcia Almirall P (2019) Intervenciones de rehabilitación en grandes conjuntos habitacionales construidos durante el periodo 1950–1975. ACE: Arquitectura, Ciudad y Entorno 14(41).http://dx.doi.org/10.5821/ace.14.41.6538 Díaz C (1986) Aproximació a l’evolució i al comportament derivat de les tècniques constructives utilitzades en els tipus edificatoris exempts destinats a habitatge econòmic a Catalunya. Periode 1954–1976. ThD, Escola Tècnica Superior d’Arquitectura de Barcelona, Universitat Politècnica de Catalunya, Barcelona-Tech, Spain. http://www.mec.es/teseo/ Díaz C, Cornadó C, Vima S (2015) El uso del hormigón armado en los sistemas estructurales de los edificios residenciales modernos del Área Metropolitana de Barcelona, In: Proceedings IX Congreso Nacional and I Congreso Internacional Hispanoamericano de Historia de la Construcción, vol I. Segovia, Spain, pp 531–540. https://doi.org/10.13140/rg.2.1.3719.4328, http://hdl. handle.net/2117/79239 Díaz C, Cornadó C, Hormías E (2009) Rehabilitación de edificios construidos con encofrado-túnel en el barrio de La Mina (Barcelona, España). In Proceedings of X Congreso Latinoamericano de Patología y XII Congreso de Calidad en la Construcción, CONPAT, Valparaíso, Chile Díaz C, Cornadó C, Llorens J, Pardo F, Hormías E (2012) Un estudio de caso: la rehabilitación de los edificios de viviendas del barrio de La Mina en Sant Adrià del Besòs (Barcelona). Análisis funcional y de las condiciones de seguridad, habitabilidad y mantenimiento. Informes de la Construcción, Instituto de Ciencias de la Construcción Eduardo Torroja (IETcc) 64(525):19–34. http://dx.doi.org/10.3989/ic.11.005. ISSN 0020–0883)

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Estany C (2014) De paquet d’habitatges al projecte de ciutat. Universitat Politècnica de Catalunya, Barcelona Tech, Spain, Estratègies per a la recuperació urbana dels polígons de Barcelona. ThD Ferrer A (1996) Els polígons de Barcelona. Edicions de la Universitat Politècnica de Catalunya, Barcelona, Spain García-Vázquez C, Pico R, Sendra J et al (2016) Intervención en barriadas residenciales obsoletas. Manual de buenas prácticas. Abada, Madrid, Spain Her Majesty’s Stationary Office (HMSO) (1994) High expectations. A guide to the development of concierge schemes and controlled access in high rise social housing, Department of the Environment, London, UK Jornet S, Llop JM, Pastor E (2005) Pla especial de reordenació i millora del barri de La Mina. In: Plans molt especials, Col·legi d’Arquitectes de Catalunya, Papers Sert 16:110–151 Jornet S, Llop C, Pastor E (2009) La rehabilitación de la ciudad existente. El Plan Especial de reforma y reordenación del barrio de La Mina y documentos complementarios 2000–2006. In: Ordenar el territorio, proyectar la ciudad, rehabilitar los tejidos existentes. Ministerio de la Vivienda, Madrid, Spain, pp 121–172 Labastida F (1999) Las operaciones de mantenimiento y sus plazos en los edificios de viviendas. In: El mantenimiento de los edificios., desde el inicio del proyecto al final de su vida útil. Colegio de Arquitectos de Cataluña, Fundación Politécnica de Cataluña, Barcelona, Spain, pp 65–76 Power A (2008) Does demolition or refurbishment of old and inefficient homes help to increase our environmental, social and economic viability? Energy Policy 36:4487–4501 Wassenberg W (2011) Demolition in the Biljmermeer: lessons from transforming a large housing estate. Build Res Inform 39(4):363–379. http://dx.doi.org/10.1080/09613218.2011.585104

Repair of Face Brick Facades Sustained in Reinforced Concrete Slabs C. Díaz and C. Cornadó

Abstract In recent decades face brick facades have been one of the architectural forms used to build the vertical exterior enclosures of buildings. However, some support solutions in the slabs have led to specific problems, especially in high buildings, which have sometimes required very expensive repairs. This chapter presents and briefly discusses the numerous agents that can influence the anomalous behavior of these facades and the most common damage. The knowledge of agents involved in each case in the formation of damage is considered essential to analyze the repair systems that have been applied so far. The information obtained over time on the results of repairs can be used to draw up guidelines on the most appropriate solutions. Keywords Face-brick facades · Masonry veneer walls · Building envelope repair · Building pathology

1 Introduction In recent decades, non-structural ceramic face-brick facades with a continuous appearance throughout the building’s height have been a common solution in the buildings of many European, North and South American countries. In these facades, bricks usually form the outer sheet of an enclosure that is approximately 12–15 cm thick. This layer can be complemented by thermal insulation on the intrados. A second thinner inner sheet completes the facade and is usually made of hollow ceramic brick, concrete block, plaster cast or sheet plaster, among other options (Fig. 1a, b, c) (Bernstein et al. 1982). C. Díaz Universitat Politècnica de Catalunya - Barcelona Tech (UPC), Barcelona, Spain e-mail: [email protected] C. Cornadó (B) Grupo de Investigación Rehabilitación y Restauración Arquitectónica (REARQ), Departament de Tecnologia de l’Arquitectura, Universitat Politècnica de Catalunya - Barcelona Tech (UPC), Barcelona, Spain e-mail: [email protected] © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 J. M. P. Q. Delgado (ed.), Case Studies in Building Rehabilitation, Building Pathology and Rehabilitation 13, https://doi.org/10.1007/978-3-030-49202-1_5

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Fig. 1 Types of face brick facade: a The outer sheet is located ahead of slab edges. b and c The outer sheet is partially supported by the slabs. d Building with facades partially supported by slabs (La Pau neighborhood, Barcelona)

One of the key aspects of these facades is the conditions of the encounter between the outer brick sheet and the successive slabs. The outer brick sheet can be placed ahead of the edges of the slabs or it can be only partially supported by a variable section thickness so that the rest of the sheet passes in front of the floor slab. This can be resolved in the form of cut ceramic pieces or ceramic strips adhered to the floor slab (to achieve the visual continuity of the ceramic material throughout the wall height) (Monjo 2010; Pellicer). In Fig. 1, typical details of both types of encounters can be observed. Of these types of encounters, the solution of partially supporting the wall on the slabs has presented the most problems (Fig. 1b, c, d). In fact, a huge number of buildings have required specific interventions to solve situations that involved risk of detachment and fall of wall sections of greater or lesser magnitude (Adell and Vela 2005). In this chapter, reasons for this type of problem and ways that it usually appears externally will be presented. Knowledge of potential causes in these cases and their interrelation is required to interpret the repair procedures that are usually applied to solve these problems. The repair solutions will be listed and discussed later from a general perspective.

2 Agents that Generate the Most Frequent Damage Pathological processes that are usually found in the problem in the facades treated here are not generally due to a single agent. It is vital to know the effects of each agent to correctly determine the most suitable repair in each case (Adell and Vela 2005; Mañà 2004). The agents can be divided into three main groups: physical agents that generate additional stresses on the facade, those that are related to deficiencies

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Fig. 2 Movements or formation of bulging in thinner sections of the wall

in construction and installation and those that are related to geometry, that is, height, length, slenderness and general form. Obviously, both those of the second group and those of the third group have an indirect impact on the increase in additional stresses supported by the facades. Additional stresses that may affect these facades have various origins. The most frequent is an excess of vertical compression that causes the descent and transfer of loads through slabs due to lack of rigidity of its edge nerves or its creep movements. These stresses can be increased when there is no contact with the section of the wall below the floor, which causes all loads to transmit through the sections that pass in front of the floor edge (Fig. 2) (González Valle 1982; Díaz and Alegre 1993; del Rio 2017). Thermal expansion and contraction movements also generate stresses and bulging when their movement is restricted. These stresses are greater the greater the section of wall that cannot move, both vertically and horizontally (Díaz et al. 2015). Expansion caused by humidity of the ceramic material has an effect equivalent to dilation and is sometimes the determining factor in damage formation. In tall buildings, compression stress effects generated by the shortening of reinforced concrete pillars in loading and subsequent creep stages must also be considered (Pellicer 2002; de Isidro 2004; Mola and Pellegrini 2010). Some aspects of the implementation of both slabs and walls must be considered so these are factors that influence the formation of anomalies. In addition to the lack of contact between upper section of the walls and the slabs, another important aspect to consider in the execution process is the vertical alignment of slab edges (Mañà 2004). The facade location will be determined by the most protruding slab edge, leading to a lower surface support on the rest of the floors (Fig. 3). When this happens, unforeseen load transmission can occur in these areas. Other factors to be considered in anomalies can be the excessive rigidity of mortar used in the construction of walls and the poor adhesion to concrete or ceramic of the mortar used for fixing the coating pieces or tiles (Pellicer 2002; Díaz 2002, 2004).

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Fig. 3 Facade construction: a defect diagram of the vertical alignment of slab edges. b Thermal expansion movement diagram when the facade loses contact with the slabs. c, d Buildings that have suffered collapses caused, among other possible agents, by the thermal effect and the implementation of the facade-slabs contact

Finally, geometric aspects have a clear impact on the level of mechanical stresses on facades, since the greater the length or width of the facade without the possibility of free deformation or the greater its slenderness, the higher the order of magnitude of tensions that can be reached in the sections (Adell and Vela 2005; Mañà 2004; del Rio 2017). Curvilinear forms of walls can produce non-compensated horizontal thrusts towards the outside that also facilitate the formation of anomalous behaviors (Mañà 2004; Díaz et al. 2015).

3 Damage Typology Damage diagnosis in these facades and its consequent repair must consider all agents that may be involved in its formation. In certain cases, visual damage inspection provides enough information to determine all or some of the causative agents, although the execution of openings and previous tests are sometimes required to define these agents sufficiently. Table 1 summarizes and graphically depicts the basic typology of damage that may evolve and lead to risk situations of detachment and falling of facade sections or ceramic pieces, including the various agents that can be involved in their formation (Díaz et al. 2020). From this first level of assessment of potential causative agents, it is necessary to have additional information on each specific case in order to determine with sufficient rigor the origin of damage. The graphics in Table 1 showing the various types of damage are taken from real cases.

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Table 1 Damage typology. Description and causative agents involved in damage formation Damage description

Causative agents

Type 1

Vertical cracks in the corners of the lower sections of the facades. They are usually thicker in the central part of their path. If the façade section is supported by a cantilever floor, they can have a parabolic shape

• Deformation of slabs due to overloads • Creep movement of slabs • Little support of the facade on the slabs • Number of floors • Vertical thermal movement of the facade • Ceramic moisture expansion • Pillar shortening or buckling • High mortar rigidity

Type 2

Vertical cracks in the corners that appear in the middle section of the facade or in all its height. They are usually thicker in the central part of their path. They can also appear at a random height of the building specially in sections of the wall that are supported by the most protruding slab edges

• Vertical thermal movement of the facade • Little support of the facade on the slabs • Deformation of slabs due to overloads • Creep movement of the floors • Ceramic moisture expansion • Pillar shortening or buckling • Height of façade and number of floors • High mortar rigidity

Type 3

Vertical cracks of homogeneous thickness, which usually appear on the entire height of the facade in singular locations such as concave or protuding corners, in the vertical part of the jambs of a certain vertical alignment of windows, in sections coinciding with changes in thickness of the wall such as those covering the pillars, etc.

• Ceramic moisture expansion • Horizontal thermal movement of the facade • Distance between thermal joints • Pillar shortening or buckling • High mortar rigidity

Type 4

Bulges located in horizontal sections that have a smaller section than the total wall thickness, coinciding with the overhangs of the slabs or extending above or below them

• Vertical thermal movements • Ceramic moisture expansion • Little support of the facade on the slabs • Deformation of slabs due to overloads • Creep movement of the floors • Lack of adhesion of the tiles to the slabs • High mortar rigidity

Type 5

Relative horizontal displacements • Curvilinear form between facade sections and the • Horizontal thermal movement of sections of slab edge covering. They the facade appear especially on curved facades • Distance between thermal joints • Ceramic moisture expansion • High mortar rigidity (continued)

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Table 1 (continued) Type 6

Damage description

Causative agents

Detachment of the brick-clad, ceramic pieces or tiles to the edges of the slabs

• Low adhesion of the ceramic coating to the edges of the slabs • Creep movement of the floors • Curvilinear form, • Pillar shortening or buckling

4 Intervention Methods A wide range of conceptual bases and forms have been chosen to solve the problems described above. We describe and discuss various forms of intervention used in buildings affected by types of damage described above, grouped by repair technique.

4.1 Crack Clamping Clamping has been used particularly for vertical cracks of the first three types presented. Two types of metal clamps can be distinguished: metal rods placed along the mortar joints to hide them or metal plates fixed on the outside (Fig. 4). This technique has also been used in some cases to repair inclined cracks of Type 1. The placement of clamps can be justified technically when the crack has ceased its movement or, in any case, when it is certain that the agent that has caused the damage will not generate tensile stresses in the future that exceed those that the masonry can withstand (Brufau 2010; Orcajo 2014).

Fig. 4 Examples of cracks repaired with a clamps or b and c metal plates

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Fig. 5 Formation of horizontal joints in US buildings. a Joints formed a posteriori. b Horizontal joints made in a recently constructed building. c View of the support angle on each floor in a building under construction (Brooklyn, NYC)

4.2 Formation of Horizontal Movement Joints The formation of horizontal joints at a later stage has been used to reduce load accumulations in lower floors and vertical thermal stresses. The arrangement of the joints follows systematic approaches, in which they are placed on each floor or every two floors, or depending on the damage location observed at the time of repair. The solution has been widely applied in high-rise buildings in the United States, and is currently common practice in new buildings (Fig. 5). New joints must allow free facade vertical movement between two consecutive joints, so they must be sealed on the outside with elastic material. Their location can coincide with the horizontal line of the door lintels and window openings to reduce the meters of mortar joint sawing in the masonry (Fig. 6) or with the last horizontal joint below the slab’s edge, if the ceramic pieces of the coating are adhered to it. It is important to consider the equilibrium conditions of facades to bear horizontal forces (wind, earthquake and interior impacts) once disconnected from the slabs, when the entrances and projections of the facade itself do not confer enough rigidity. In this case, a type of support must be designed that can withstand the aforementioned horizontal forces and, at the same time, allow the facade to deform freely vertically. Figure 6 shows an example of fastening that meets these requirements.

4.3 Placement of Metal Support Angles One very common technique is to place metal angles to complement the support surface of the wall in front of the slabs, either based on previous tests to verify the measure of the support or coinciding only with the location of damaged sections. Profiles are usually positioned in these cases without the parallel formation of a horizontal elastic joint, so as not to modify the equilibrium conditions of the lower facade sections (Herrera Cardenete et al. 2012). When profiles are placed along the entire facade section, they can perform a rigid edge nerve function in addition to complementing the support, which may be insufficient to reduce the transmission of

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Fig. 6 Subsequent formation of horizontal joints on all floors of a building with Type 1 fissures by accumulation of loads on lower floors (Albacete, Spain). a Repaired building view. b Detail of the designed support. c View inside the metal support. It includes the angular support of the wall in the lintels’ horizontal line and a clamping mechanism using movable screws and slotted holes in the lower section supported in the slab. d View of the support and elastic formation joint from the front of the horizontal fin of the profile (Díaz 2006)

loads through slabs and the facade. A facade fastening made of angles arranged on the inside sometimes complements or replaces the arrangement of the support angle on the outside (Fig. 7).

Fig. 7 Examples of metal angle provision to complement the surface of support on the slab. (Barcelona, Spain)

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Fig. 8 Examples of the subsequent execution of vertical joints. Observe in detail the retaining cable fastenings fixed to pillars that coincide with the situation of new joints to restrict the horizontal movement towards the outside of the curved wall (Granollers, Spain) (Díaz 2006)

4.4 Formation of Vertical Movement Joints The formation of vertical joints has been used to reduce the effects of horizontal thermal stresses on walls and the moisture expansion of ceramic. Both effects can overlap and cause damage of Type 3. The new vertical joints are usually arranged to coincide with the location of cracks or subdivide the facade into sections of similar length. Facades with curved shapes are especially prone to experience horizontal movements due to thermal expansion (Type 5) that generate very diverse cracks and anomalies (relative movements between the continuous parts of the wall and those interrupted by windows, movements of sills and jamb coatings, etc.), which can be limited by the formation of vertical movement joints (Fig. 8) (Díaz et al. 2015; Luzón 2001).

4.5 Replacement of Bulging Masonry Sections In some cases, repairs of bulging areas of the wall (Type 4) that generally coincide with the covering of slab edges and adjacent sections have been carried out by removing ceramic pieces. These are then replaced with pieces that have the same appearance and are fixed to the concrete with special mortar-based systems with high adhesive capacity (Díaz 2006). However, the effectiveness of this technique is limited to the assumption that new bulging areas will no longer form after repair (an issue that is difficult to predict), since there is no absolutely reliable evidence of rheological duration of the processes that generate this type of damage in the presence of cyclic environmental agents or one-off, extreme events that may affect the deformability characteristics of vulnerable facade sections (Fig. 9). In other cases, the solution consists of totally replacing sections susceptible to bulging. These actions, which are usually much more expensive than the previous ones, allow intervention approaches that cancel the effects of agent that may have

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Fig. 9 Repair of bulging areas affected by damage at the time of the intervention (Barcelona, Spain)

Fig. 10 Total replacement of ceramic sections of a partially bulged facade using polymeric concrete pieces fixed to the slab edge with prior arrangement of a self-sealing sealing sheet (Granollers, Spain) (Díaz et al. 2015)

been involved in the anomaly’s formation (thermal effects, expansion of ceramic moisture, transmission of loads to the facades, etc.). An additional aspect to consider in the design of the intervention is the impact on the building’s image when the material that is chosen is not the same as the original facade (Fig. 10).

4.6 Replacement of Detached Ceramic Coating Pieces Replacement of detached coating pieces of slab edges- damage referred to as Type 6—has often needed complementary operations to guarantee the maximum thickness requirements of the adhesive mortar, to eliminate risks of the expansive effect of concrete corrosion reinforcements, or to achieve additional safety offered by the adhesive qualities of the grouting mortar (Díaz 2006).

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Fig. 11 Repair of unattached ceramic coatings. a Metal rod arrangement in front of the floor slab before concreting. b Surface appareance after concreting and preparation of the adhesion surface. c Appearance of ceramic coating already adhered before joint grouting (S. Adrià del Besòs, Spain)

Fig. 12 Building with sections of ceramic pieces detached. a Appearance of a building with some sections of floor slab whose covering has been removed. b One of the ceramic pieces with a metal fixing being introduced into a hole previously filled with epoxy compound. c Detail of ceramic piece attachment to the slab edge with the mortar and the fixing located in the drilled hole made in the first brick course. The repair forecast for rusty reinforcements is also displayed (Barcelona, Spain) (Luzón 2001)

In extreme cases, replacement of the vertical plane of adhesion to reduce the thickness of the grouting mortar can force prolongation of the slab by providing new reinforcement rods that will be embedded into the newly added concrete (Fig. 11). On other occasions, it may be advisable to increase the security offered by the mortar adhesion to the surface of slab edges by placing metal fixings firmly attached to each of the pieces introduced into work that has been drilled previously (Fig. 12).

4.7 Total Replacement of Damaged Facades The entire damaged facade can be replaced when damage affects a large sector or the entire building or when repair work inside is not compatible with daily use. In some cases, substitution is chosen because the results of previous partial repair options have not lasted. Three examples of intervention in Figs. 13, 14 and 15 show buildings that presented the three cases respectively (Díaz 2006).

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Fig. 13 Substitution of a wall in a hospital building (Barcelona, Spain). a Overview of the repaired building. b Crack in the central section, next to the corner. c Detail of the wall-slab encounter. Location of support angles, horizontal joints and flexible fixings for upper wall retention. d Vertical section of the as-built wall with the elements of the repair carried out. e Floor plans and front view of the wall with an inner section of the chamber that extends to the axis of symmetry. The masonry coursing, the pilasters’ separation and the upper fasteners can be seen (Díaz 2006)

Figure 13 shows the example of a 10-story wall in a hospital building that is poorly supported by slabs and affected by a general bulge due to vertical thermal expansion (Type 2). The building use prevented entry into the interior to carry out repair work. The solution reconstructs the wall in its entirety with a 14 cm-thick stacked wall with pilasters of 15 × 30 cm to reduce its slenderness, maintaining the interior partition that separates it from hospital work units. In the new wall, horizontal movement joints are arranged along the slab’s lower part so that movement of the covering pieces becomes independent. They are fixed to the edge and the transmission of loads through them is prevented by placing another horizontal joint in the upper part. These horizontal joints are made along horizontal courses and contain the metal angles that supplement the wall supports on each floor. The solution also tries not to modify the exterior appearance of the replaced face brick wall.

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Fig. 14 New exterior skin in university building (Barcelona, Spain). a, b, c Facades with serious problems of bulges repaired unsuccessfully with various replacement systems of affected areas. d, e Arrangement of a second skin based on ceramic plates attached to a new metal substructure of metal supports placed in front of the existing facade and fixed to the structure

Fig. 15 New exterior skin in a university building (San Sebastian, Spain) a, b Building after facade failure c, d Building after facade replacement

Figure 14 shows a university building with serious bulging damage coinciding with the edges of the slabs. Repeated repairs carried out for years, consisting of zonal replacement of the damaged areas using different techniques to achieve the adherence of new ceramic pieces did not achieve lasting results and new bulging areas that had not been the object of repair continued to appear. Finally, the solution consisted of providing an outer skin based on ceramic plates fixed to a metal substructure, fixed to the pillars and reinforced concrete slabs of the building. Finally, in Fig. 15, a university building with a problem like that of Fig. 13 underwent complete replacement of the 12 cm-thick face brick facades with clear thermal expansion damage (Fig. 3b). They were completely replaced by new facades based on aluminum sandwich panels.

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5 Final Considerations For the correct choice of a repair solution in each case it is necessary to consider the many agents that may have been involved in the damage formation, even in cases where, apparently, considering the effects of one of them is enough to respond to some of the cause-effect relationships in the pathological event. Agents that are responsible for the accumulation of loads in the lower slabs of the building include the potential incidence of slab deformation, the inadequacies of support on the facade and the vertical thermal expansion of the wall. The current perception of repaired buildings and knowledge of the intervention processes in some damaged buildings indicate that partial repairs (according to the observed damage at the time of repair) do not always mean the end of the pathological manifestation of the actions that generated the anomalous behavior. New bulges or fissures are often observed specifically in the lower and middle third of the facades of repaired buildings. However, it has not been possible to establish with sufficient certainty minimum periods of time between the completion of works and the partial repair that absolutely guarantee the intervention’s effectiveness, even in cases where the intervention is initiated on dates after those in which the creep phases effects on concrete elements could be minimal. From the above, we can deduce the desirability of prioritizing interventions that solve the existing problem not only in directly damaged areas but also in all the elements or facade areas that are in a similar situation of exposure or risk of future formation of the anomaly. In other words, in most cases, systematic or general solutions tend to be adopted that rectify or vary the initial design of the facade, thereby eliminating the origin of the damage that has occurred.

References Adell JM, Vela S La (2005) fachada contemporánea con ladrillo: Cerramientos tipo. Informes de la Construcción 56(495):13–31 Bernstein D, Champetier JP, Peiffer F (1982) La maçonnerie sans fard. Ed. Du Moniteur, Paris, France Brufau R (2010) La reparación de grietas y fisuras. In: Rehabilitar con acero. Asociación para la Promoción Técnica del Acero. Madrid, Spain, pp 145–154 Díaz C, Cornadó C, Albareda A (2020) Damage in face-brick facades placed between concrete slabs. J Build Eng. https://doi.org/10.1016/j.jobe.2020.101312 Díaz C (2002) Non-structural pathology in modern residential building. In: XXX IAHS world congress on housing, vol III. Coimbra, Portugal, pp 1795–1802. https://doi.org/10.13140/2.1. 1540.8162 Díaz C (2004) Patología de los recubrimientos cerámicos. In: VIII Congreso Mundial de la Calidad del Azulejo y del Pavimento Cerámico QUALICER-2004, Castellón, Spain, Tomo 1, pp. M.D.3– M.D.10. https://doi.org/10.13140/2.1.2466.5121 Díaz C (2006) Patología e intervención en fachadas de ladrillo visto. In: II Encontro de Patología e Reabilitaçao de Edificios PATORREB-2006, vol I. Porto (Portugal), pp 9–18. https://doi.org/10. 13140/rg.2.1.1630.4724

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Díaz C, Alegre V (1993) Reología de los forjados reticulares planos de hormigón armado objeto de operaciones de desatraque de los cerramientos verticales. In: II Congreso Iberoamericano de Patología de la Construcción y V de Control de Calidad (CONPAT-93), Barquisimeto (Venezuela), pp 252–257 Díaz C, Cornadó C, Gumà R (2015) Repair of face brick facades in two ovoid-shaped residential buildings in Granollers (Barcelona). In: 1st international symposium on building pathology. Porto, Portugal, DVD, pp 539–345. ISBP-2015 González Valle E (1982) La flexibilidad de los forjados de hormigón armado de edificación: evaluación de la situación actual-. Informes de la Construcción 34(343):5–11 Herrera Cardenete E, Martínez Ramos R, Herrera Fiestas E, García JF (2012) Un problema constructivo no resuelto en fachadas de fábrica vista de ladrillo. In: 4º Congreso de Patología y Rehabilitación de Edificios. PATORREB-2012. Santiago de Compostela, Spain de Isidro F (2004) Determinación de la expansión por humedad de los productos cerámicos de uso estructural. Conarquitectura 11:73–88 Luzón JM (2001) Juntas de dilatación en cerramientos de fachadas de ladrillo. Distancias, detalles constructivos y ejecución. Cuadernos INTEMAC 44 Mañà F (2004) La fachada de obra vista. In: La seguridad en las estructuras de fábrica. Collegi d’Aparelladors i Arquitectes Tècnics de Tarragona, Cap 12:101–108 Mola F, Pellegrini LM (2010) Effects of column shortening in tall reinforced concrete buildings. In: 35th conference on our world in concrete and structures. Singapore Monjo J (2010) La rehabilitación de las fachadas de ladrillo visto. Conarquitectura (10):97–108 Orcajo J (2014) La evolución de las lesiones en las fachadas de ladrillo visto y su relación con los cambios en los sistemas constructivos. Universidad de Valladolid, Valladolid, Spain, PhD Pellicer D (2002) Notas sobre patología por dilatación potencial del ladrillo cerámico en paramentos de fábrica. Revista de Edificación 31–32(04):29–34 Pellicer D, Cerramientos de fábrica no portante de ladrillo cerámico a cara vista. Asociación de Seguros Mutuos de Arquitectos Superiores (ASEMAS), Report, Fachadas 4 del Rio C (2017) Transmisión del peso propio de las fachadas de ladrillo. Conarquitectura 62:76–80

Influence of Environmental Factors on Deterioration of Mural Paintings in Mogao Cave 285, Dunhuang D. Ogura, T. Hase, Y. Nakata, A. Mikayama, S. Hokoi, H. Takabayashi, K. Okada, B. Su, and P. Xue

Abstract The Mogao caves in Dunhuang, located in the inland desert region of China, are a UNESCO World Heritage Site. Within this site, cave 285 is one of the most important caves. As a great deal of deterioration has taken place in this cave, a large amount of research has been carried out on the environmental effects D. Ogura · T. Hase · Y. Nakata Department of Architecture and Architectural Engineering, Graduate School of Engineering, Kyoto University, Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto, Japan e-mail: [email protected] T. Hase e-mail: [email protected] Y. Nakata e-mail: [email protected] A. Mikayama Daiken Co., Kaigandori 2-5-8, Minami, Okayama 702-8045, Japan e-mail: [email protected] S. Hokoi (B) School of Architecture, Southeast University, No. 2, Sipailou, Nanjing, China e-mail: [email protected] Kyoto University, Yoshida-Honmachi, Sakyo, Kyoto 606-8501, Japan H. Takabayashi Faculty of Fine Arts, Kyoto City University of Arts, 13-6 Kutsukake-cho, Oe, Nishikyo-ku, Kyoto 610-1197, Japan e-mail: [email protected] K. Okada National Institutes for Cultural Heritage, 13-9 Ueno Park, Taito-Ku, Tokyo 110-8712, Japan e-mail: [email protected] B. Su · P. Xue The Conservation Institute, Dunhuang Academy, Dunhuang, Gansu, China e-mail: [email protected] P. Xue e-mail: [email protected] © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 J. M. P. Q. Delgado (ed.), Case Studies in Building Rehabilitation, Building Pathology and Rehabilitation 13, https://doi.org/10.1007/978-3-030-49202-1_6

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that caused these changes. The deterioration such as changes in color and cracks in the mural paintings are due to physical environmental factors. In this work, the influence of the hygrothermal and light environments on the deterioration of the mural paintings in cave 285 was examined through several experiments using simulated mural paintings, focusing on the time period when the entrance hall had collapsed. In the drying experiments, many cracks in the Bengal red, a few in the lapis lazuli, were observed but none could be seen in the others. White crystals appeared in all the paint layers mixed with salt, and a herpetiform swell appeared in the talc substrate to which the saturated NaCl solution was added. The UV radiation caused the chroma saturation changes in most of the paint layers, showing a significant change in the case of the organic pigments. To examine the influence of light on the deterioration of the mural paintings, the simulation of illuminance under natural lighting condition during the period when the entrance hall collapsed was conducted, and the calculated results were compared with the visual observation. It was found that many discolored paintings or color changes of the layers are related to the large amount of annually integrated illuminance. Previous researches show that the East wall has been least affected by moisture, solar radiation, and sunlight compared to the other walls and ceiling. However, the effects of deterioration, including scratches, detachment, and discoloration, are also seen on the east wall. Hence, we investigated the effects of adhesion and the collision of windblown sand as factors contributing to the deterioration of the east wall. We conclude that sand blown by high velocity wind has led to detachment, flaking, and losses including fading of the paintings. To examine the effects of the hygrothermal environment on the deterioration of the mural paintings in cave 285, simulations of heat, moisture, and salt transfer were conducted for the time before and after the fall of the entrance hall. It was shown that the cracks caused by drying shrinkage were mainly created soon after the production of the paintings. The cracks caused by thermal expansion are likely to keep increasing; biodegradation and destruction due to freeze-thaw are scarcely progressing currently but they probably occurred more frequently when the entrance hall had collapsed. A part of the paintings on the west wall deteriorated due to the crystallization of the salt contained in the paintings (or the soil wall) just after the production of the paintings. Regarding the relationship between temperature in the cave and insect excrement or secretion, the black-spotted soiling spread over the entire walls and the brown deposit seen in the cracks or peeled parts on the ceiling is considered to be the results of the excrement or secretion of insects on the wall paintings. The inside of the main chamber where temperature is stable throughout the year provides the insects a suitable space to live in. Keywords Dunhuang · Mogao caves · Deterioration · Lighting · UV · Windblown sand · Heat and moisture · Salt · Insect

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Symbols c Cs Dse Fw jl r T t ρ, ρw , ρs λ λ’μ , λ’T  w,  s μ σ

Specific heat [J/kg K], Salt concentration [kg/kg] Effective diffusion coefficient of salt [m2 /s] Gravity force exerting on 1 kg of water [N/kg], Liquid water flux [kg/m2 s] Latent heat of phase change from water vapor to liquid water [J/kg], Absolute temperature [K], Time [s], Density of material, liquid water, and salt, respectively [kg/m3 ], Thermal conductivity [W/m K], Moisture conductivities related to water chemical potential and temperature gradients, respectively [kg/m2 s (J/kg)], [kg/m s K], Volumetric moisture and salt content, respectively [m3 /m3 ], Chemical potential of water [J/kg] reflection coefficient of solute [nd]

1 Introduction 1.1 Mogao Caves, Dunhuang The Mogao caves (UNESCO HP) (see Fig. 1) are a series of Buddhist sites on a cliff in Mingsha mountain on the eastern side of the Taklamakan Desert. This cave system was listed as a State Priority Protected Site by the State Council of China

Fig. 1 Overview map of the region surrounding the Mogao caves (Google map, Mogao caves)

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in 1961 and was named as a UNESCO World Heritage Site in 1987 (Jianjun et al. 2014; Takabayashi et al. 2008). More than 700 caves remained in the upper, middle, and lower areas of this cliff between the fourth and fourteenth centuries; paintings and colored statues are present in 492 caves. The cave surveyed for this study, cave 285 (Fig. 2), also has paintings on all its walls and ceiling, and is regarded as one of the most precious because its period of construction is known. This cave is located within the middle layer at the site, so the effects of moisture, including rain and groundwater, are minimal and the condition of the paintings remains relatively good. Evidence for deterioration, including cracks, detachment, discoloration, salt weathering, and the adhesion of sand and insect secretions, are nevertheless present. Thus, a large number of studies focused on the mural paintings in cave 285 and their deterioration have been carried out; Takabayashi et al. (2008, 2009) investigated the materials and techniques used to create these mural paintings, as well as their state of preservation, using optical approaches aimed at reconstructing their original condition, while Oba et al. (2009) classified the deterioration visually. These workers (Oba et al. 2009) provided an overview site investigation, including the factors leading to deterioration, and clarified that both the environment and material properties had exerted strong influences on cracks in the coloring layer. Furthermore, Oba et al. (2009) clearly noted that temperature, humidity, and solar radiation should be considered key environmental factors leadings to deterioration. Ogura et al. (2013) went further to simulate temperature and humidity in the cave using a hygrothermal model, while Uno et al. (2010) and Nakata (2014) calculated the integrated amount of solar radiation reaching the walls and compared it with the degree of deterioration. These workers concluded that because the effects of solar radiation on the east wall were minimal, other factors such as the adhesion and collision of windblown sand should be investigated. Wang et al. (2014) clarified mechanisms of the damages to cultural relics in terms of ethology and bionics. In contrast, a number of studies have been carried out that discuss controlling the movement of Gobi Desert sand in order to protect the Mogao Grottoes from windblown deterioration (Jianjun et al. 2001; Li et al. 2014). They concluded that

Fig. 2 The external appearance of the Mogao caves, including cave 285, in 2010 (a, b) and in 1914 (c) (Xianlin et al. 1980)

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the construction of the fence in 1980s significantly cut off the windblown sand from Mingsha Mountain. Issues related to the buried walls of some of these caves were recognized by Fan (Jinshi 2014), who argued that windblown sand may have caused these problems, especially when doors and windows were absent. However, Jinshi and Yongseng (2003) did not explain how much sand had flowed into the cave and how this windblown sediment behaved near to the site and wall surfaces.

1.2 Mogao Cave 285 The floor plan and east-west section of cave 285 are shown in Fig. 3 (UNESCO HP). The main room of cave 285 has an almost square floor that is 6.4 m wide and 6.3 m deep, and a cone-shaped ceiling that is 5.0 m high. There are three niches on the west wall and four monk rooms on the north and south walls of the main room, and the entrance is on the east side. The cave wall is thin between the center of the north side of the east wall and the neighboring cave 287, while the other adjacent cave, 286, is located directly above the doorway to cave 285, which is 1.2 m wide, 1.4 m deep, and 2.0 m high. The entrance hall collapsed at an as yet unknown time in the past, confirmed by a photograph taken by a Russian expedition team between 1914 and 1915 (Fig. 2c). There was no entrance hall at this time, and the doorway was directly connected to the exterior; thus, the present entrance hall with a new door was constructed within approximately 10 years from 1956. The collapse of the entrance hall meant that the outdoor air and sunlight could easily enter the main chamber, and the mural paintings might have been affected by it (Fig. 4). Thus, we investigated their influence on the deterioration. This research deals with the time period when the entrance hall was missing.

Fig. 3 The shape of cave 285: a Floor plan; b East-west section (Dunhuang Art Collection Offhand 2000)

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Fig. 4 West wall of cave 285 (Ogura et al. 2013)

1.3 Deterioration of Mural Paintings and Factors Related to Deterioration The deterioration of the mural paintings in cave 285 and the possible causes related to the deterioration are summarized in Table 1. The deterioration phenomena of the mural paintings in the Mogao Caves, such as changes in color fading, cracks, peeling, and flaking, are due to physical environmental factors such as light, heat, moisture, and so on. In addition, it is estimated that sand particle collisions on the wall surface Table 1 Deterioration phenomena and their causes in cave 285

Phenomenon

Causes of deterioration

Change in Color, Discoloring Chemical alteration due to light, temperature, humidity, etc. Crack, Peeling, Exfoliation

Physical degradation due to light Thermal expansion and shrinkage Moistness expansion and dry shrinkage Freezing and thawing, salt crystallization

Mechanical Damage

Contact by birds, insects, humans, etc. Collision of sand particles due to air flow

Adhered Dirt

Excretions and secretions by living beings Graffiti, ectype trace

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by airflow may cause deterioration of the mural paintings. The sand particles may accumulate on or stick to the walls and cause discoloration. So far, we have investigated the following issues to clarify the causes of the deterioration of the mural paintings in cave 285, and show the results in the following sections. (1) The influence that the hygrothermal environment now and during the collapse of the entrance hall has/had on the deterioration of the mural paintings: investigated using onsite measurements and hygrothermal simulations. (2) Estimation of the reason for salt crystallization on the west wall using heat, moisture, and salt transfer simulations. (3) The influence of sunlight on the deterioration of mural paintings; explored via onsite surveys, laboratory experiments, and light simulations. (4) The influence that the wind-driven sand inflow has on the (visual) deterioration: investigated using onsite surveys and Computational Fluid Dynamics (CFD) simulations. (5) The relationship between temperature and the attachment of insect excrement and secretions: studied using onsite surveys and measurements of the vertical temperature distribution.

2 Purpose and Procedures In Sect. 3, the influence that the hygrothermal environment has on the deterioration of the mural paintings was examined through laboratory and outdoor exposure experiments using simulated mural paintings, and the influence that the lighting environment has on the deterioration of the mural paintings was examined by an onsite survey and lighting simulation, focusing on the period when the entrance hall had collapsed. In Sect. 4, the distribution of the light intensity in the main chamber of cave 285 is simulated, and the correlation with the observed deterioration is examined. In Sect. 5, we investigate the effects of adhesion and the collision of windblown sand as factors contributing to the deterioration of the east wall, including scratches, detachment, and discoloration. First, the air flow distribution near the paintings, which is caused by the wind flowing into the cave, and the movement of the sand particles are simulated. Then the calculated results are compared with the deteriorated situation. In Sect. 6, we first propose a model of simultaneous transfer of heat, moisture, and air in the spaces and the surrounding ground, and validate the proposed model by reproducing the present hygrothermal environment in cave 285. Next, the annual changes in temperature and humidity on the surfaces of the walls, that have significant influence on the deterioration of the mural paintings, are calculated by using the proposed model. Finally, the locations where the cracks or exfoliation of the mural paintings are likely to occur are predicted based on the calculated results for the integrated evaluation of the deterioration. The same kinds of simulation and evaluation

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are also conducted for the period when the entrance hall had collapsed. Furthermore, regarding the west wall, heat, moisture, and salt transfer in the ground is simulated and the amount of salt precipitation on the wall surface is estimated based on the calculated evaporation rate and salt concentration. This result is used for identifying the reason for and mechanism of the deterioration of the mural paintings caused by the salt precipitation. In Sect. 7, black-spotted soiling and brown deposit on the mural paintings are connected with the activities of the insects based on visual inspection, and the relationship between the temperature in the cave and insect lives are examined. In Sect. 8, we try to estimate the deteriorating process of the mural paintings arriving at the current state by integrating the results so far.

3 Deterioration Experiments Using Simulated Paint Layers In this section, four types of experiments-drying, cyclic temperature change, UV irradiation, and sun exposure-were carried out using simulated paint layers to show the relationship between the degradation of the paint layers and the environmental conditions such as temperature, UV, and natural light (Ogura et al. 2019).

3.1 Production of Simulated Paint (Pigment) Layers The simulated paint layer was produced as follows. A glue solution with 13% concentration and talc (Mg3 Si4 O10 (OH)2 ) were mixed at a mass proportion of 3 to 2, which corresponds to 21 g to 14 g per panel with dimensions of 227 mm by 158 mm, in a mortar using a pestle. After the mixture had slightly solidified, the same amount of water (14 g) was added to the mixture and was mixed using the pestle, which led to the completion of the substrate material. This substrate material was painted on a wooden panel (227 mm × 158 mm) using a brush and left to dry for two hours. This process was repeated three times before the completion of the substrate layer. A mixture of pigment and glue solution was applied by brush on the substrate and then left to dry for two hours. This process was repeated twice and then the simulated paint layer was finished. The pigments estimated to have been used in cave 285 were used (see Table 2).

3.2 Drying Experiment Simulated paint layers made using Bengal red, red lead, cinnabar, verdigris, and coarse and fine lapis lazuli (pigment made using natural lapis lazuli) were produced.

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Table 2 Pigments estimated as having been used in cave 285 Color

Pigment

Main ingredient

White

Talc (substrate)

Talc, pagodite: silicon and magnesium are the main ingredients

Red

Cinnabar

Cinnabar mercury HgS

Red lead

Lead oxide Pb3 O4

Bengal red

Iron oxide Fe2 O3

Organic pigment

Not identified

Yellow

Orpiment (synonym: arsenious sulfide)

Arsenic sulfide Ag2 S3 Copper oxide CuO

Green

Verdigris

Orpiment+indigo

Arsenic sulfide Ag2 S3 +indigo C16 H10 N2 O2

Blue

Lapis lazuli (synonym: azure)

Indigo (organic pigment)

C16 H10 N2 O2

Black

Chinese ink

Main ingredient: blue gold, sodalite, hauynite, noselite Subspecies: calcite, iron pyrite Carbon, glue

They were set in an oven at 95 °C for two hours to investigate their characteristics under the drying shrinkage process (Figs. 5 and 6). Cracks detectable by visual inspection appeared in the Bengal red and lapis lazuli. The number of cracks significantly differed depending on the pigments: many in the Bengal red, a few in the lapis lazuli, and none in the others. These cracks seemed to be caused by drying shrinkage of the glue solution, because the pigments are insoluble in water. The difference in crack size depending on the pigments is likely due to the difference in the specific surface area decided by the particle size and/or shape, judging from the fact that more cracks were found in the Bengal red, with its smaller particle size. Fig. 5 Cracks: Bengal red

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Fig. 6 Cracks: Lapis lazuli

3.3 Experiment Using Cyclic Temperature Changes The experiments where the ambient air temperature was cyclically changed were carried out using the paint layer samples of Bengal red, red lead, lapis lazuli (coarse and fine), verdigris (coarse and fine), cinnabar, and organic pigments (safflower (Carthamus tinctorius) and dark red). In an incubator (KCL-2000A, Tokyo-RikaKikai Ltd.), temperature changes over a 24 h cycle were applied (70 °C for 5 h, changed to 20 °C in 2 h, then 20 °C for 15 h) (see Fig. 7). Figure 8 presents an example of the experimental results, showing the cracks in the paint layer. Such cracks were found after 5 cycles for verdigris (fine), 5 cycles for red lead, and 51 cycles for lapis lazuli (fine). Since the cracks were also generated during the drying experiments using verdigris (fine) and lapis lazuli (fine) layers, these paint layers are regarded as being sensitive to temperature. Regarding the red lead, cracks were not generated during the drying experiment; therefore, the cyclic Fig. 7 Cyclic temperature and humidity input

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Fig. 8 Cracks in verdigris

change seems to be an influential factor for this pigment. As for the organic pigments, the safflower showed discoloration.

3.4 Influence of Salt The herpetiform peeling found on the mural paintings on the west wall in cave 285 is considered to have been caused by salt crystallization. Therefore, by adding an NaCl solution to the substrate and/or paint layer using Bengal red, red lead, and cinnabar (coarse) as the pigments of the simulated paint layers, the influence of salt was observed. The salt was added by replacing the pure water with saturated NaCl solution in the substrate production process, or by dropping the NaCl solution into the mixture of the pigment and glue water in the paint layer production process (see Fig. 9). Fig. 9 Simulated paint layer with/without salt

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Fig. 10 Precipitation of white crystal (magnified by 1000)

Fig. 11 Spotted pattern in talc substrate

One day after the production of the paintings, white crystals appeared in all paint layers mixed with the salt (see Fig. 10). Also, a spotted pattern appeared in the talc substrate to which the saturated NaCl solution was added (see Fig. 11). The white crystals seemed to be salt that had precipitated due to the evaporation of the water in the paint layer. Because the spotted pattern did not appear in the substrate not mixed with the salt solution, it must have been caused by the salt, although the mechanism has not yet been clarified. Since the same sort of spotted pattern was found in the white substrate on the east ceiling in cave 285, salt seems to have influenced the mural paintings on the ceiling of this cave.

3.5 UV Irradiation Experiment The discoloration and fading of the mural painting in cave 285 are considered to have been strongly influenced by UV irradiation. Therefore, by setting simulated paint layers made using Bengal red, red lead, Taisha, lac, orpiment, indigo, atacamite,

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Orpiment

Orpiment+Indigo Safflower

Safflower

Dark red

Safflower

Dark red

Bengal red

Red lead/ Actamite

Bengal red

Red lead/ Atacamite

Red ocher

Indigo

Red ocher

Indigo

lac Without irradiation

lac With irradiation

Fig. 12 Appearance of paint layers after a year with/without UV irradiation

dark red, and safflower in a UV irradiation apparatus and taking photos along with the measurement of L*a*b* using a soil color meter (Konica Minolta SPAD–503), the changes in the paint layers could be observed. For the UV irradiation, a UV lamp for sterilization, model GL-10 (Toshiba), which effectively put out 253.7 nm UV rays, was used. The output of the lamp was 2.7 W and the irradiation intensity of the UV rays at a position 1 m away from the lamp was 29 μW/cm2 . The simulated paint layers were set 38 cm away from the lamp. Photos after about one year with and without UV irradiation are shown in Fig. 12, and the time profile of the chroma saturation is shown in Fig. 13. After UV irradiation for more than one year, all of the paint layers except for Bengal red and Taisha showed chroma saturation changes. The degree of discoloration and fading differed depending on the pigment, showing a significant change in the case of the organic pigments (safflower and dark red) and red lead. Their chroma saturations changed in a few months. The orpiment, a pigment that has faded in cave 285, also showed a chroma saturation change. The red lead painting, which is discolored in the cave, changed color from orange to black.

3.6 Sun Exposure Experiment An acrylic case (box), in which the simulated paint layers made using Bengal red, red lead, cinnabar (coarse and fine), verdigris (coarse and fine), lapis lazuli (coarse and fine), safflower, and dark red were placed, was set on the roof of a four-story

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Fig. 13 Changes in chroma saturation

building not surrounded by any obstacles (January 10th, 2013), and the changes in the paintings due to solar radiation were observed. In the acrylic case, a solar radiometer and a handy-type hygrothermometer were set to measure the solar radiation, temperature, and relative humidity in the case. The chroma changes of the paint layers were checked by visual inspection, photos with a digital camera, and L*a*b* measured by a soil color meter. The chroma saturation changes were significant for the safflower and dark red paint layers (see Fig. 14), similar to the UV irradiation experiment. However, the significant discoloration seen in the UV irradiation experiment did not occur in the red lead paint layer. After one month, cracks were seen in some paint layers. The cracks increased over time, and they were found in all paint layers after three months. These seem to have been caused by drying shrinkage of the glue due to the surface temperature increasing because of the solar radiation.

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Bengal red Red lead Safflower Lapis Lapis lazuli(fine) lazuli(coarse)

Verdigris(fine) Verdigris(coarse)

Cinnabar (fine) Cinnabar (coarse)

Before exposure

After 295 days of exposure

Fig. 14 Changes due to exposure to the sun

4 Influence of Light Environment on Deterioration of Mural Paintings 4.1 Lighting Experiment in Cave 285 Although the cone-shaped ceiling has the same motifs on all planes (orientation), the level of deterioration differs depending on the orientation. One of the main reasons for the deterioration and its orientation difference was estimated to be the sunlight, and a lighting experiment, as shown in Fig. 15, was carried out assuming the situation where the entrance hall had collapsed. Fig. 15 Lighting experiment on site (> Projector)

Projector

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Two projecting lamps simulating sunlight were used to radiate the inside of the main chamber. As shown in Fig. 16, the brightness in the irradiated and nonirradiated areas was clearly different, which indicates that the deterioration of the mural paintings also differs between the irradiated and nonirradiated areas. Therefore, the deterioration of the same motif on the planes of the ceiling and walls was compared. As shown in Fig. 17, the motif on the irradiated area is more discolored than that on the nonirradiated area. The same is true of the west wall (Fig. 18), where the irradiated and shaded areas are adjacent to each other. The discoloration of the mural painting under irradiation is much worse than that in the shaded area.

Fig. 16 Irradiated and nonirradiated areas

Non-irradiated motif

Irradiated motif Fig. 17 Comparison of brightness and discoloration of the same motif (ceiling)

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Fig. 18 Comparison of brightness and discoloration of the same motif (west wall) Table 3 Reflectance of floor, walls, and ceiling

Diffuse reflection (%)

Normal reflection (%)

Floor

30

10

Entrance wall

30

10

Walls, ceiling

40

0

4.2 Simulation of Natural Lighting Environment During Period When Entrance Hall Collapsed Sunlight is considered as one of the main reasons causing the deteriorations of the mural paintings in cave 285. When the entrance hall collapsed, the amount of the solar light incident on the walls through the entrance, was considered to be much more than today and to have had a huge impact on the mural paintings. We estimated the lighting environment in cave 285 at the time by lighting simulation, and compared the results with the current deterioration status. A general-purpose simulation program (Lumicept 6.0, Integra Co. Ltd.) was used for the simulation. The reflectivity of each surface is listed in Table 3. The calculated annual integrated illuminance (AII, hereafter) (lx・h)1 is shown in Fig. 19. On the west wall, AII is more in the lower part than that in other parts. This indicates that the reflected diffused component of the sky and direct radiations have a larger influence than the normal reflection of the direct radiation on AII. In the upper part of the west wall, AII in the northern part is larger than that in the southern part, which is because the reflected component of the direct light is not incident on the southern part on the west wall due to the shape of the cave. On the north and south walls, AII is more in the western part than the eastern part, and more in the lower part than the upper part. 1 In

CIE, the deterioration by UV is evaluated based on energy [CIE157:2004].

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Fig. 19 Annual integrated illuminance (AII) on each wall (lx・h)

In the area centered by the east wall, AII of the whole east wall is a little because of the shape of the cave. In the east ceiling, AII in the northern central part is large, while small at the south-eastern and north-eastern corners. AII in the west wall is larger than those in other walls, and that in the north wall is larger than that in the south wall because the direct light is incident longer period on the north wall.

4.3 Influence of Natural Light on Deterioration of Mural Paintings in Cave 285 By comparing the results of the pigment change in the experiment using simulated mural paintings and the calculated results in the solar illuminance simulation, the deteriorating factors in cave 285 was examined. Figure 20 compares the northern and southern parts in the upper area of the west wall. The deterioration in the northern part is more severe than that in the southern part, which corresponds to the larger AII in the northern part. Figure 21 shows the grappers at the lower part of the north wall. The color of the two eastern grappers remains better than that of the three western grappers, which corresponds to the larger AII on the western part than that on the eastern part. Figure 22 compares the state of deterioration and AII on the side wall of the doorway. The photo shows that the upper part on the main room side is better conserved than the lower part on the entrance hall side, which corresponds well with the distribution of AII. The same situation can be seen in the other caves. Figure 23 shows the deteriorated state of red-colored

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Fig. 20 Upper part of west wall: left-south, right-north

West

Fig. 21 Comparison of grappers on the north wall

Fig. 22 Side wall of door way: left-photo, right-AII

East

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Fig. 23 Deterioration status of “Unkimon” (Takabayashi et al. 2013)

“Unkimon,” an ancient Chinese cloud design of curling figures on the ceilings. The results are well correlated with the AII distribution in the following aspects: the color on the east ceiling remains better than that on the west ceiling, and the color on the south ceiling remains more than that on the north ceiling, and the color on the northern part remains less than any other part on the east ceiling. However, the conserved state of “Unkimon” on the eastern part of the ceiling is better than any other part, even though AII on the eastern part is more than other ceilings. On the upper part of the entrance to cave 285, the rock extrudes about 2 m (see Fig. 24). Because the reflected light incident on the east ceiling decreases when the shading effect of this rock is considered (in the simulation), it may be one of the reasons for the poor correlation between the deterioration state and AII. As mentioned above, a strong correlation can be found between the locations with large AII and the heavily deteriorated or color changed locations. Fig. 24 Cave 285 at the time when the entrance hall collapsed (Paul 1921)

Cave 285

rock-bed above entrance

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5 The Effects of Windblown Sand on the Deterioration of Mural Paintings in Cave 285 In this section, we investigate the effects of adhesion and the collision of windblown sand as factors contributing to the deterioration of the east wall, including scratches, detachment, and discoloration (Mikayama et al. 2018). The air flow distribution near the paintings, which was caused by the wind flowing into the cave, and the movement of the sand particles are simulated. The calculated results are compared with the deteriorated situation. We first measured wind velocity, wind direction, and sand particle size, and observed the deterioration and uneven shape of the east wall of cave 285 in detail. Next, under the most frequently occurring and strongest southerly wind, we simulated airflow and the movement of sand particles by using computational fluid dynamics (CFD) software. Finally, we compared the distributions of airflow and sand particle concentration adjacent to the east wall with the spatial distribution of deterioration.

5.1 Deterioration of Paintings on the East Wall of Cave 285 and Its Uneven Surface The spatial distribution of deterioration on the east wall of cave 285 is shown in Fig. 25. Fine scratches are widespread on the east wall of cave 285, varying in direction from horizontal to vertical. According to the previous research (Wang et al. 2014), it may be caused by creatures such as birds. Observations of the east wall of cave 285 also reveal a great deal of detachment as well as flaking of coloring and substrate layers in the lower portion, particularly near to the doorway. The intensity of damage is more severe on the southern side than on the northern side; at an intermediate height, similar widespread deterioration near to the cave doorway can be seen on the northern side, while losses to the surface represent the most serious damage on the southern side. A great deal of sand adhesion is also evident on the east wall of cave 285, at higher densities in both lower and upper sections. However, little adhesion is evident at an intermediate height, as well as in any other location than on the northern side near to the doorway. We therefore hypothesized that the volume of sand adhesion is related to the inclination of the wall, and so checked the uneven shape of the east wall surface. Observations show that the east wall is convex at upper and lower heights, while it is concave at an intermediate height. Because thick sand adhesion can be seen in the convex areas, it seems likely that the uneven shape of the wall is closely related to volume in this case.

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Fig. 25 Images to show the distribution of east wall deterioration within cave 285 (Watanabe et al. 2011): a Flaking and scratches; b Sand adhesion

5.2 Airflow Around the Mogao Caves Including Cave 285 5.2.1

Wind Around the Mogao Caves

Two weather stations are installed by Dunhuang Academy. One is located on the cliff, approximately 50 m above cave 85, and the other is located in front of cave 72 in a lower position, at a height of approximately 2 m (see Fig. 1). Wind velocity and direction data measured at the weather station on the cliff between 2012 and 2014 are presented in Fig. 26. These data show that the mean wind velocity over the last three years was approximately 4.1 m/s on the cliff compared to approximately 0.74 m/s at the lower cliff height. Wind velocity infrequently exceeded 10 m/s, to a recorded maximum of nearly 20 m/s. The main wind direction was from the south, encompassing approximately 40% of measurements, and tended to exhibit a faster velocity.

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Fig. 26 Distribution of wind directions recorded at the weather station on the cliff: a Rose diagram of wind directions; b Frequency distribution of wind velocities and directions

As shown in Sect. 5.2.2, data show that the wind direction was from the south in front of cave 285 and from the west at the weather station at the lower cliff height, when a southerly wind was blowing on the cliff.

5.2.2

Air and Temperature Distributions at the Present Opening of Cave 285

We measured wind velocity and recorded the state of six streamers placed around the doors of the present-day entrance hall of cave 285 between 14:00 and 14:30 on September 4, 2013. The most frequently recorded wind direction during the measurement period was from the north, while the next most frequent was from the south. The airflow distribution around the doors is shown in Fig. 27. Data show that the

Fig. 27 Illustration to show the state of streamers at the present cave opening

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distributions of north and south airflow directions were almost symmetric; in both cases, the wind flew into the cave from the upper leeward side and left via the lower part. Measured wind velocities were less than 1 m/s, rarely exceeding 2 m/s, although sometimes calm periods were recorded. During these periods, the air distribution at the present cave opening exhibited a flow pattern typical to buoyancy ventilation, blowing into the cave from the top and out from the bottom, as the result of inside and outside temperature differences. The average temperature recorded inside the case is 4.6° lower than the outside temperature.

5.3 Sand Particle Size Distribution Micrographs of sand particles collected from the desert at the foot of Sanwei mountain and at points A to E within cave 285 (Fig. 3) are shown in Fig. 28. The results of this analysis show that smaller sand particles come from deeper positions inside cave 285. In addition, sand particles collected from outside the screen door (Fig. 3b) were slightly larger than those collected inside (compared point A data with point B data), and there was little difference between upper and lower heights (compared point B data with point C data). The diameter of the largest sand particle recorded at points A, B, and C was approximately 0.1 mm while the smallest was less than 0.01 mm. In contrast, sand particle diameters inside the main room of cave 285 were very narrowly distributed around 0.01 mm. Thus, we used sand particle diameters between 0.1 mm and 0.01 mm in our simulations.

Fig. 28 Sand particle micrographs

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5.4 Simulation of Airflow and Sand Movement 5.4.1

Outline of Simulation

We initially simulated airflow and sand movement around the Mogao caves using the CFD model Flow Designer 12 (Advanced Knowledge Laboratory 2015). Taking topography into account, Mingsha mountain was placed in the southwestern part of the domain for analysis, while the desert at the foot of Sanwei mountain was located to the east and was simulated using planes at altitudes of 10 m, 20 m, and 30 m. We assumed that horizontal desert planes at heights of 10 m, 20 m, and 30 m, as well as the 50 m high cliff, were all sand generating panels, and placed approximately 13 m high trees approximately 20 m to the east of the cliff. Cave 285 is located 1,451.8 m to the north from the southern edge of the analysis domain, 5 m above the ground level, while the uneven shapes of all wall surfaces were approximated by a staircase within the cave (Figs. 29 and 30). We next simulated the airflow and sand movement around cave 285 in detail. In this case, the nesting domain space superseded the results of the previous simulation. Our nesting domain is 50 m wide, 32 m deep, and 40 m high, as is shown as the circled area in Fig. 29. We performed a steady state calculation using a high-Reynolds number k-ε turbulence model. The southern margin of the analysis domain of this model around the Mogao caves was defined as the inlet boundary, while the northern margin was set as the outlet boundary. Thus, as the most frequently encountered southerly wind with

Fig. 29 Details of simulation model and boundary conditions of the domain around the Mogao caves

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Fig. 30 Details of simulation model and boundary conditions of nesting domain around the Mogao caves

the largest velocity is likely to most influence deterioration of the east wall, a wind from this direction at 10 m/s at a 50 m height was assumed at the inlet boundary. We also set sand concentrations at 10,000 ppm on outbreak panels for 0.01 mm, 0.05 mm, and 0.1 mm diameters, respectively. We assumed that sand is affected by gravity and settled at a sedimentation rate that varied according to its size while diffusing. The density of sand particles was set at 1,510 kg/m3 (JSME Data 2009) in all cases.

5.4.2

Results and Discussion of the Simulation

(1) The airflow distribution and distribution of sand concentration around the Mogao caves The airflow distribution and the distribution of sand concentration around the Mogao caves are shown in Figs. 31 and 32. Simulation results show that the southerly wind flows in from the inlet boundary at the southern end of the model and generally moves northwards. However, local flow parallel to the cliff can also be seen within the narrow region approximately 100 m to the east, creating a large number of complicated circulation patterns. Results show that this complex airflow explains why the northerly wind was most frequent during the measurement period in front of cave 285 even though the dominant wind direction was from the south. Measurements at the cliff-based weather station show an average wind velocity of about 6.5 m/s and a predominant southerly wind direction. However, in front of cave 285, this southerly wind flows at about 2.0 m/s while a southwesterly wind at 0.4 m/s was recorded at the

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Fig. 31 Airflow distribution around the Mogao caves

lower cliff weather station. Calculated wind velocities and directions at the weather stations and in front of cave 285 agree well with measured results. Results show that sand generated in the Sanwei mountain area flows first to the northwest, before turning to the north as it is affected by the southerly wind. This pattern is illustrated in the right-hand side sections of the density distributions in Fig. 32; this sand does not reach 500 m away from the cliff. Similarly, sand generated in the Mingsha mountain area flows first to the northern region at the foot of the cliffs before flowing northwards, as illustrated in the left-hand side sections of the density distributions in Fig. 32. Results show that the concentration of 0.01 mm diameter sand is nearly uniform at a given height, and that there is very little difference in density distribution between 1 m and 30 m heights (Fig. 32). Data further show that 0.05 mm or 0.1 mm diameter sand particles settle down quickly so the concentration of these sizes at a height of 1 m is higher than that of their smaller counterparts. Finally, most sand particles with a diameter of 0.05 mm drop onto the floor in the doorway, although some migrate into the room.

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Fig. 32 Sand density concentrations around the Mogao caves

(2) Distributions of airflow and sand concentrations in cave 285 Distributions of airflow and sand concentrations in cave 285 are shown in Figs. 33 and 34. Simulation results show that initially a southerly wind flows into cave 285 from the northern section of the doorway, before passing deep down into the space and being deflected to the south. This wind then passes up close to the western wall and returns to the east side of the cave via the upper region of the main room, before finally flowing out via the lower southern area of the doorway. Data show that the wind velocity in front of cave 285 would have been about 2.0 m/s, and as slow as 0.1 m/s within most areas of the cave. The airflow distribution calculated at the doorway agrees well with measurement results.

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Fig. 33 Airflow distribution in cave 285

Results show that the concentration of 0.01 mm diameter sand is the highest inside the cave. This sand particle size is present close to the ceiling because it does not settle easily compared to in the main room, 1 m inside from the doorway. Data suggest that just small sand particles 0.01 mm in diameter are able to reach into the main room, in agreement with survey results. Sampling inside the cave does show that 0.1 mm diameter sand particles are not found within the main room, although this situation can be expected to have changed since the collapse of the original entrance hall. (3) Distributions of airflow and sand concentrations near the east wall of cave 285 Distributions of airflow and sand concentrations within a vertical Sect. 5 mm from the surface of the east wall are shown in Fig. 35. Simulations show that air velocity was fastest near to the doorway of cave 285, reaching 0.1 m/s adjacent to the southeast corner of this entrance. Data show that at the northeast corner of this doorway, air velocity exceeded 0.05 m/s across a wider area than in the southeast region. Therefore, across the whole southern and northern sides of the east wall, it is clear that wind velocity was faster in the former region compared to the latter. Data also show that the concentration of 0.01 mm diameter sand is highest in the lower area on the south side, and second highest in upper areas on both the southern and northern sides. These regions are inclined upward (Fig. 30), so sand tends to accumulate in these regions due to the uneven shape of the wall surface. Similarly,

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Fig. 34 Sand concentrations in cave 285

concentration of this size of sand is low at the intermediate height on the north side of the wall because this region is inclined downwards, while sand with a diameter of 0.05 mm is not present 1 m above the floor. The concentration of this size of sand is highest in the lower region on the southern side of the east wall, although it is still just half that of 0.01 mm sand. Simulations show that the concentration of 0.05 mm diameter sand is 30% that of 0.01 mm diameter sand on the northern side of the wall near the door way, while the concentration of 0.01 mm sand is high on the lower southern and northern sides near the door way, but still less than half that of 0.05 mm sand.

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Fig. 35 Distributions of airflow and sand concentrations within a vertical section 5 mm from the surface of the east wall

5.5 Discussion 5.5.1

The Relationship Between Calculation Results and the Distribution of Detachment, Flaking

Compared with the results in Fig. 25a, the simulation results in Fig. 35 show that concentrations of 0.01 mm and 0.05 mm diameter sand particles are higher within lower regions near to the doorway where lots of detachment and flaking are seen, and that air velocity is also enhanced in these areas compared to surroundings. Thus, an increased level of deterioration is likely to be caused by windblown sand. This higher observed concentration also agrees well with the degree of deterioration seen on the lower southern side compared to the lower northern side; windblown sand is also likely to have had an effect on deterioration across the whole northern side near to the doorway; although, on the upper southern side, also close to the entrance where most severe losses are seen, the concentration of sand of all diameters is not high.

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The Relationship Between Results Close to the East Wall and the Distribution of Sand Adhesion

When the simulation results in Fig. 35 compared with that in Fig. 25b, sand concentrations correspond very well with amounts of adhesion in the lower southern and northern sections close to the cave doorway. It remains unclear if this could lead to fading of paintings due to sand adhesion in addition to the detachment or flaking described above. High concentrations of 0.01 mm diameter sand particles also correspond well with the amount of adhesion seen in the upper parts on both southern and northern sides of the doorway. However, a lot of adhesion can also be seen in the lower northern region even though the concentration of sand is not so high. This could be explained by the possibility that the airflow distribution in the cave given a northern wind will be symmetrical versus a southern wind, and so adhesion in the lower northern region may occur in the former situation. Thus, albeit less frequent, additional wind directions should also be taken into consideration. Moreover, we assumed that all of the sand particles coming into contact with the wall surfaces are attached to the wall, in order to pay attention to sand adhesion. We think the restitution coefficient is probably not zero, and its effect must be considered. It is one of the remaining issues.

6 The Effects of Hygrothermal Environment on the Deterioration of Mural Paintings in Cave 285 In this section, we first propose a model of simultaneous transfer of heat, moisture, and air in the spaces and the surrounding ground, and validate the proposed model by reproducing the present hygrothermal environment in cave 285. Next, the annual changes in temperature and humidity on the wall surfaces that have significant influence on the deterioration of the mural paintings are calculated by using the proposed model. Finally, the locations where the cracks or exfoliation of the mural paintings are likely to occur are predicted based on the calculated results for the integrated evaluation of the deterioration. The same kind of simulation and evaluation are also conducted for the time when the entrance hall collapsed. Furthermore, regarding the western wall of cave 285, heat, moisture, and salt transfer in the ground is simulated and the amount of salt precipitation on the wall surface is estimated based on the calculated evaporation rate and salt concentration. This result is used for identifying the reason and mechanism of the deterioration of the mural paintings caused by the salt precipitation.

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6.1 Meteorological Conditions Around the Mogao Caves The meteorological data measured at weather stations located on the cliff in 2008 were used as the typical conditions around the Mogao grottos (Figs. 36 and 37). The annual average temperature is 10.8 °C with the highest at 37.3 °C in early August and the lowest at –23.2 °C in the later part of January. The annual average of relative humidity is 31.5% with the monthly highest RH 60.6% in January and the lowest RH 14.0% in April. The horizontal global solar radiation amounts to 1000 W/m2 in summer. The annual amount of precipitation was 8.1 mm, less than the usual value of 30.0 mm.

Fig. 36 Outdoor temperature in 2008

Fig. 37 Outdoor relative humidity in 2008

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6.2 Criteria for Occurrence of Deterioration of Mural Paintings Although various kinds of deteriorations have been found in the mural paintings of cave 285 (see Figs. 38, 39, 40, 41), the cracks, exfoliation, salt weathering, biodegradation, and freeze-thaw destruction are dealt with in this section. The conditions under which these deteriorations occur have not been fully identified yet, but we evaluated the occurrence using the conditions listed in Table 4 following previous literature (Holbein Works 2004; Sawada 2002; Kigawa et al. 2006; Emoto 1985; Miura 1985). Fig. 38 Cracks (Oba et al. 2009)

Fig. 39 Exfoliation (Oba et al. 2009)

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Fig. 40 Herpetiform spalling

Fig. 41 Herpetiform uplift

Table 4 Conditions for deterioration occurrence Deterioration phenomenon

Conditions for deterioration occurrence

Cracks

Temperature change (thermal expansion shrinkage) Moisture content change (drying shrinkage)

Exfoliation

Frequency of crack occurrence. Relative humidity75% (decrease in adhesive force of glue)

Biological degradation

Temperature0 °C and relative humidity60%

Salt weathering

Amount of precipitated salt (evaporated water × salt concentration of solution)

Free-thaw destruction

Number of crossing of temperature across freezing point

6.3 Model of Simultaneous Transfer of Heat, Moisture, and Salt in the Ground The following simultaneous transfer equations of heat, moisture, and salt in porous materials were used (Matsumoto 1984; Abuku et al. 2008; Oda et al. 2011; Iwamae 1995).

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  ∂T = ∇ λ + r λT g · ∇T + ∇r λμg (∇μ − Fw ) ∂t

(1)

ρw

  ∂ψ = ∇λμo ∇μo − Fw + ∇λ μc ∇μc + ∇λT ∇T ∂t

(2)

ρs

∂ψs = ∇{(1 − σ ) · Cs Jl } = ∇(ρw ψw Dse · ∇Cs ) ∂t

(3)



6.4 Validation of the Proposed Model: Reproduction of the Current Hygrothermal Environment in Cave 285 in the Middle Layer By reproducing the present temperature and humidity in cave 285 using the basic equations, the proposed model is validated first, and then the deterioration mechanism of the mural paintings is evaluated. (1) Schematics of model for analysis The object analyzed was modeled as a two-dimensional system consisting of three (upper, middle, and lower) layers, including cave 285 (see Fig. 42). Cave 285 in the middle layer consists of the entrance hall and main chamber, and the upper and lower caves consist of one chamber. Each chamber is modeled as one node. The air exchange is assumed to take place between each chamber and outdoor, and between the entrance hall and main chamber. Fig. 42 Analyzed model and boundary conditions

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(2) Boundary and initial conditions At the boundary adjacent to the outdoor air, the third kind of boundary conditions were used, and solar radiation and rain are incident on the horizontal surfaces while only solar radiation was on the vertical surfaces. The vertical boundary of the background was assumed as adiabatic and impermeable to moisture. At the bottom of the ground, the first kind of boundary condition was used, where the temperature was assumed equal to the annual average of the outdoor temperature (meteorological data in 2008) and the relative humidity was set as 90% (Ogura 2000). (3) External climatic conditions The temperature, relative humidity, solar radiation and precipitation (2008) given in Figs. 36 and 37 were used as the external climatic conditions. (4) Material properties and other physical constants A sandy soil was assumed around cave 285, and the hygrothermal properties of Plainfield Sand (Iwamae 1995; Ogura 2000) were used. The values of the heat and moisture transfer coefficients at the external surfaces of the ground and the inside surface of the chambers were referred to the literature (Hokoi et al. 2003). The air exchange rates of the chambers were estimated referring to the velocity measured by Uno et al. in cave 285 (Uno 2009), which is 0.04 m/s between outdoor and the entrance hall and 0.02 m/s be-tween the entrance hall and the main chamber. (5) Comparison between calculated and measured results By conducting simulations for 20 years, cyclic steady state results were obtained. The calculated temperature and humidity of the main chamber are shown with the measured results in Figs. 43 and 44, respectively. Both the calculated temperature and humidity agree well with the measured results.

Fig. 43 Temperature in main chamber

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Fig. 44 Absolute humidity in main chamber

(6) Temperature and humidity of wall surfaces in Cave 285 Temperature (Fig. 45 upper): All surface temperatures show the annual changes similar to that of the air in the main chamber. The amplitude of the annual change is about 18 °C. The temperature of the east wall shows a larger annual change than that of the west wall. It is lower by one degree in the second decade of February, and higher by 0.5° in the second decade of August than those of the west wall, because the east wall is next to the entrance hall with much larger fluctuations. Relative humidity and moisture content (Fig. 45 lower left and right): Like the temperatures, both humidity and moisture content of all the wall surfaces also change

Fig. 45 Wall temperatures, relative humidity, and moisture content in main chamber

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with the air humidity in the main chamber. The relative humidity of the wall surfaces is lower than 60% throughout the year, and lower than 50% except for the period from the later part of July to August. The moisture content is also lower than 0.004 m3 /m3 .

6.5 Evaluation of the Effect of Hygrothermal Condition on Deterioration Process of Mural Paintings in Cave 285 at the Current Situation (1) Cracks caused by thermal expansion: Depending on the expansion coefficients of pigments, glue, and substrate layer, the cracks may be generated. From the production time of the paintings to the present, expansion and shrinkage have been repeated for a long period, thus the crack generation process may have been progressing. (2) Cracks caused by drying shrinkage: Compared with the saturation moisture content (0.375) at the time of production of the paintings, the moisture content of the wall is currently very low, at 0.003 m3 /m3 . Thus, the possibility of crack generation caused by drying is not high. (3) Exfoliation: Since the relative humidity does not increase over 75% in any wall, the exfoliation caused by the decrease in adhesive force of the glue is not likely to occur anymore. (4) Bio-deterioration: Although the wall temperatures are higher than 0 °C throughout the year, the possibility of the bio-deterioration is low since the indoor relative humidity is less than 60%. However, depending on the moisture generation by the human activities (visitors, etc.) in the cave or sudden increase in the outdoor humidity, bio-organisms may grow. (5) Freeze-thaw fracture: Since the wall temperature of the main chamber are higher than 0 °C throughout the year, the damages caused by freeze-thaw process is not likely to occur. But under the situation where the outdoor temperature is lower than the assumed input values, freeze-thaw may happen.

6.6 Temperature and Humidity in Cave 285 at Times When Entrance Hall Collapsed (1) Schematics of model for analysis In this case, cave 285 is modeled as only one room, i.e. main chamber to simulate the time period when the entrance hall collapsed. Regarding the initial and boundary conditions, material properties and so on, the same conditions were used as those in the Sect. 6.4. It should be noted that the solar radiation directly incident onto the main chamber is not considered in this simulation either.

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(2) Calculated results Comparison of the temperature and relative humidity in the main chamber between the cases with and without the entrance hall are shown in Figs. 46 and 47. The air temperature in the main chamber becomes closer to the outside temperature when the entrance hall is missing, and the annual average differs by 1.2 °C depending on the presence of the entrance hall. Furthermore, the amplitude of the annual temperature change in the case without the entrance hall reaches to 47.6°, which is significantly higher compared to 22.2° when the entrance hall was there. When there is no entrance hall, the annual average, highest, and lowest relative humidity of the main chamber are 29.1%, 73.8%, and 3%, respectively, with significantly large fluctuations. It is

Fig. 46 Temperature in main chamber

Fig. 47 Relative humidity in main chamber

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high from the second decade of December to the later part of February, and low from the early April to the end of July. The calculated temperatures, relative humidity, and moisture content of the wall surfaces are shown in Figs. 48, 49, 50, respectively. The wall surface temperatures show the similar annual changes with the air temperature in the main chamber. Their amplitude is about 44°, more than two times larger than that of the entrance hall. The temperature difference between east and west walls is slightly larger than that in the case with the entrance hall which is 1.2° in the second decade of February and 0.6° in the second decade of August. Similarly, the relative humidity and the moisture content change in a similar manner with the air humidity in the main chamber.

Fig. 48 Wall temperatures

Fig. 49 Wall relative humidity

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Fig. 50 Wall moisture content

6.7 Evaluation of the Effect of Hygrothermal Condition on Deterioration Process of Mural Paintings in Cave 285 at Times When Entrance Hall Collapsed (1) Cracks caused by thermal expansion The possibility of crack generation may be higher than the current situation with the entrance hall, depending on the expansion coefficients values of pigments, glue, and substrate layer. Moreover the solar radiation incident on the walls in the main chamber increases damages done by cracks. (2) Cracks caused by drying shrinkage Compared with the current situation with the entrance hall, the moisture content of the walls slightly increases in winter, but very low at 0.004. The possibility of cracks due to drying is low. (3) Exfoliation The relative humidity does not increase over 75% in any wall, but the maximum value of the east wall and the ceiling becomes over 70%. If the conditions used in the simulation could be different from the real situation, or if the rain hits the external wall of the main chamber or upper caves, the relative humidity of the walls may be over 75%. In such cases, the exfoliation may occur due to the decrease in adhesive force of the glue at the east wall, and east facing and top surfaces of the ceiling.

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(4) Biodeterioration The temperatures of all walls are higher than 0 °C from early March to the end of November. From the second decade of September, the indoor relative humidity sometimes becomes higher than 60%, and the wall temperature is relatively high at around 20 °C. Therefore, the possibility of the biodeterioration may be high during this time of the year. (5) Freeze-thaw fracture All the walls experience the temperature lower than 0 °C from the early to the second decade of December and at the end of February, and hence the possibility of freeze-thaw fracture is high.

6.8 Amount of Salt Precipitating on West Wall of Cave 285 A part of the west wall in cave 285 is deteriorated by salt precipitation. In this section, the amount of the salt precipitated on the surface of the wall was examined to analyze the origin of the salt. Two possibilities were considered: the salt dissolved in the water in the ground (case A) and the salt dissolved in the paint used during the production process of the paintings (case B). (1) Salt examined and concentration of salt solution The rock salt (NaCl) found in Mogao grotto was examined (Kuchitsu and Duan 1993). In the surface water around Mogao grotto, chloride ions of 963 mg/l were present (Kitano et al. 1994). If the proportion of chloride ions and sodium ion was 1 to 1, the mass (salt concentration) of the NaCl in the surface water 1 m3 was estimated as 1.587 [kg/m3 ]. (2) Schematic model for analysis and calculation conditions The region from the surface of the west wall to the 10 m deep ground behind the west wall was modeled as horizontal one-dimensional system. On the surface of the west wall, the air temperature and relative humidity of the main chamber were given as the boundary conditions, and the annual average of the temperature and relative humidity of the ground 10 m deep (from the Sect. 6.4) were used at the other boundary. For the initial conditions of the temperature and relative humidity of the ground and the main chamber, the calculated results in Sect. 6.4 were used. But, the relative humidity of the surface cell of the west wall was set at 100% (saturated moisture content 0.375 m3 /m3 ) in case B. The salt concentration was set at 1.587 kg/m3 for all cells except for the surface one in the case A, and in case B, it was set at 1.587 kg/m3 only at the cell of the west wall surface.

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(3) In the case of salt dissolved in the ground water For case A, a simulation for 20 years was conducted and the cyclic steady state was obtained. Following are the simulated results at the twentieth year: Salt Precipitation Process Large amount of salt precipitated between April and November when a lot of water evaporated. As a result, the amount of the contained salt, and the salt concentration of the surface cell decreased (Figs. 51 and 52). On the other hand, the salt was supplied to the surface by water convection or advection from the inside of the ground, and the salt concentration recovered almost to the initial value. By the repetition of this cycle, the salt precipitates every year.

Fig. 51 Evaporation rate from west wall

Fig. 52 Precipitating and contained salt at west wall surface

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Fig. 53 Distribution of salt concentration in the whole ground

Distributions of Moisture Content and Salt Concentration in the Whole Ground At the surface, the salt concentration is very low (Fig. 53) because the salt transfer from inside the ground is very slow. Amount of Salt Precipitated at the Surface of West Wall The total amount of the salt precipitated at the west wall surface for one year was 1.12 × 10–7 kg/m2 . Assuming that cave 285 was constructed in the year 535, the accumulated amount of the precipitated salt would have been 0.17 g/m2 in the year 2012. This is too small compared with the amount of the salt present at the moment. Therefore, the possibility that the salt currently present on the surface of west wall has resulted from the precipitation of the salt which once dissolved in the ground water is very low. (1) In the case of salt dissolved in the paint One-year simulation was conducted under the conditions of case B. Salt Precipitation Process At the early stage of the simulation, the water evaporates from the wall surface to the air in the chamber (Fig. 54), causing the decrease in the moisture content at the surface. However, because the relative humidity at the surface remains almost 100% for a while, the evaporation rate is nearly constant, and the decreasing rate of the moisture content on the surface also remains constant (Fig. 56). Since the salt precipitates due to the water evaporation to the main chamber, the amount of salt on the surface of the wall surface also decreases (Fig. 57). This process continues for about six and a half days from the start of the simulation. After that, the moisture content reaches a threshold value where the relative humidity drastically decreases, and the evaporation rate from the surface of the west wall decreases with the decrease

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Fig. 54 Evaporation rate from west wall (positive value)

in relative humidity. Before this point, most of the dissolved salt precipitates because most of the water on the surface evaporates (Fig. 55). Total Amount of Salt Precipitated at the Surface of the West Wall The total amount of the salt precipitated at the surface was 99.8% of the input amount of 1.485 × 10–2 kg/m2 , and it is very little compared with that recognized in cave 285. Since the salt concentration was assumed to be 1.587 kg/m3 in the present simulation and if the mural paintings were produced using the paint dissolved with near-saturated NaCl solution (saturation concentration of 360 kg/m3 ), the salt may precipitate to the present amount.

Fig. 55 Salt precipitation rate at west wall surface

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Fig. 56 Moisture content and relative humidity at west wall surface

Fig. 57 Amount of salt contained and salt concentration at west wall surface

7 Relationship Between Temperature in Cave and Insect Excrement or Secretion As pointed out in the survey of the cave, black-spotted soiling was found all over the mural paintings. On the ceiling, a lot of brown deposits were seen in the cracks or peeled part of the paintings (see Fig. 58). These show that the insects stayed on the wall and attached their excrement or secretion to the wall paintings. Figure 59 shows the annual change in the vertical temperature distribution in the main chamber of cave 285. The temperature in the main chamber is lower in the summer and higher in the winter compared with that of the outdoor temperature. Thus, it is more stable than the outside throughout the year. The temperature at the upper part of the main chamber is higher than that at the lower part throughout the year, and the difference in the vertical temperature increases particularly from fall to winter until about 4 °C. During the survey in November 2012, we confirmed that

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Fig. 58 Black soiling at peeled part of ceiling

Fig. 59 Vertical temperature distribution in main chamber of Cave 285 (August, 2010–August, 2011)

the insects stayed on the ceiling. The indoor environment of the cave seems suitable for the insects to live in, because the temperature in the main chamber is more stable than the temperature outside.

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8 Appearance Changing Process of Mural Paintings By integrating the results so far, we tried to estimate the deteriorating process of the mural paintings until the present state.

8.1 At Early Stage After Production of Mural Paintings (1) Shrinkage of paintings due to drying: With the evaporation of the water contained in the substrate and paints in the production stage, small cracks were generated in the paint layers of Bengal red and lapis lazuli with the drying of the paints. A lot of cracks were generated particularly in fine Bengal red. (2) Salt precipitation caused by drying: With the drying of the substrates and paint layers, the salt precipitated at the paintings on the niche surface of the west wall several weeks after the completion of the paintings. The present herpetiform cracks and peelings were formed at this early stage.

8.2 For Several Decades After Production of Paintings (1) Solar radiation through entrance: Although limited to several mornings before and after the spring and autumn equinoxes, the direct solar radiation hit the lower central part of the west wall for a short time if the door of the entrance hall was open at the same time. It caused the discoloration of the paintings due to the ultraviolet ray. The paint layer of Buddha statues was also discolored. In particular, the organic pigments such as safflower, dark red, and orpiment were significantly discolored, while blackening of red lead progressed slowly. However, in this stage, there was a column at the center of the main chamber which interrupted the solar radiation and did not allow it to fall on the center of the west wall directly. But its reflected radiation hit mainly the east wall, and the eastern part of the north and south walls. In addition to the direct component, the sky radiation was incident on the area centered at the center of the west wall through the entrance throughout the day. Although the intensity of this radiation is weak, the total amount of the irradiated energy increased proportionally to the period during which the door was opened, and it discolored the paintings around the Buddha statues very slowly but gradually. (2) Progress of drying: The drying progressed for a period of about 10 years, and the cracks were slowly enlarged. (3) Sand dust: Although the sand dust flew in due to people entering and exiting, there was not a significant deposit of the sand dust protected by the entrance hall. However, the sand dust entered the main chamber during sandstorm which occurred several times a year, and was deposited on the floor and the wall

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surfaces, especially on the upward facing parts of the east, west, and south wall surfaces. This deposit of the sand dust slowly reduced the chrome of the paint layers. (4) Salt crystallization in white substrate on the ceiling: Along with a slow progress of drying, the salt crystallized in the white talc substrate formed herpetiform pattern.

8.3 Several Decades After Production of Paintings—Just Before Collapse of Entrance Hall (1) Effect of people entering and exiting: Due to the heat and moisture generation caused by people entering and exiting for discipline, praying, and producing mural paintings, and the burning of candles, condensation occurred on some parts of the walls of the monk rooms and change in color to brown occurred there. (2) Expansion and shrinkage caused by drying/wetting: Due to the daily and annual changes in the temperature and humidity, the color changes and discoloration of red lead and safflower, and the enlargement of the cracks of verdigris and lapis lazuli continued. (3) Insects: Along with the human activity in the cave, the insects also spent their lives. Their excrement or secretion were attached to almost all the paintings, then dried and changed into small black spots. Therefore, the brightness of the paintings dropped with time, and the chrome also continued to decrease slowly. (4) Temperature and humidity: At the center of the east wall, where the influence of the outdoor temperature changes through cave 287 was relatively large, blackening progressed very slowly.

8.4 Just After Collapse of Entrance Hall Due to the collapse of the entrance hall, the external impacts such as wind, rain, temperature and humidity, solar radiation, and sand directly worked to the main chamber, causing drastic changes in the mural paintings. (1) Incidence of solar radiation: The solar radiation caused the temperature change, but the discoloration and color change caused by ultraviolet radiation was the most concerning effect. The solar radiation which was incident only through the doors at the entrance hall and the doorway drastically increased after the collapse of the entrance hall. The impact area of the radiation significantly extended from a small central part of the west wall to most of the west wall and the western parts of the south and north walls. Furthermore, because the column at the center of the chamber disappeared until this time, the reflected radiation from the floor and the side walls of the doorway was shed on the ceiling, which

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discolored and changed the color of the paintings rapidly. These changes were drastic particularly at lower part of the west wall and the western parts of the north and south walls. On the ceiling, the influence was serious in the order of west, north, and south, which is clearly shown by the remaining fraction of “Unkimon.” (2) Temperature and humidity changes: Large fluctuations of the temperature and humidity almost equal to those of the outdoor air prevailed inside the main chamber, causing the increase in drying rate and wetting (absorption) at the same time. Coupled with the drying by solar radiation, the drying shrinkage became significant, leading to the larger cracks and exfoliation. The paintings on the side walls of the doorway were seriously damaged. (3) Inflow of sand dust: The sand dust directly entered the main chamber, and the small sand particles (smaller than 0.01 mm) rapidly accumulated on the upper faced surfaces of the walls and the horizontal surfaces. Furthermore, scratches were caused on some parts of the paintings due to the physical force exerted by relatively large sand particles during a strong sandstorm.

8.5 After Reconstruction of Entrance Hall to Present After the entrance hall was reconstructed, the external impacts decreased and the deterioration has slowed down and it is similar to the situation before the collapse of the entrance hall. However, the fouling and damages caused by touching the paintings have increased with the increase of the people visiting the cave. More insects started living in the cave, particularly near the ceiling as the temperature in the main chamber increased after the reconstruction of the entrance hall. The brown excrement or secretion became prominent at the cracks or exfoliated layers of the paints.

9 Conclusions In this work, the influence of the hygrothermal, light, and wind environments on the deterioration of the mural paintings were examined through experiments using simulated mural paintings, on-site survey and simulation focusing on the period when the entrance hall had collapsed. The following results were obtained: (1) In the drying experiments using the simulated paint layers made with Bengal red, red lead, cinnabar, verdigris, and lapis lazuli (coarse and fine pigments), the number of cracks differed depending on the pigments: many in the Bengal red, a few in the lapis lazuli, and none in the others. The difference in cracks number and size depending on the pigments is likely due to the difference in the specific surface area decided by the particle size and/or shape.

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(2) The experiments where the ambient air temperature was cyclically changed were carried out using paint layer samples of Bengal red, red lead, lapis lazuli (coarse, fine), verdigris (coarse, fine), cinnabar, and organic pigments (safflower and dark red). Cracks were found in the verdigris (fine), red lead, and lapis lazuli (fine) paint layers. Verdigris (fine) and lapis lazuli (fine) paints are regarded as being sensitive to temperature. As for the organic pigments, the safflower showed discoloration. (3) In the salt experiment, white crystals appeared in all paint layers when mixed with salt, and a herpetiform pattern was formed in the talc substrate to which the saturated NaCl solution was added. Therefore, the same sort of herpetiform pattern found in the white substrate on the east ceiling of cave 285 seems to have been influenced by salt crystallization. (4) After UV irradiation for more than a year, all of the paint layers except for Bengal red and Taisha showed chroma saturation changes. The degree of the discoloration and fading differed depending on the pigment, showing a significant change in the case of the organic pigments (safflower and dark red) and red lead. Their chroma saturation changed in a few months. The orpiment, a pigment that has faded in cave 285, also showed a chroma saturation change. The red lead, which has discolored in the cave, changed color from orange to black. (5) An acrylic box, in which simulated paint layers made using Bengal red, red lead, cinnabar (coarse and fine), verdigris (coarse and fine), lapis lazuli (coarse and fine), safflower, and dark red were placed, was exposed to the sun on the roof. The cracks increased with time and were found in all paint layers after three months. These seem to have been caused by drying shrinkage of the glue due to the surface temperature being increased by solar radiation. To examine the influence of sunlight on the deterioration of the mural paintings, the simulation of illuminance under natural lighting during the period when the entrance hall had collapsed was conducted, and the following results were obtained. (1) In the upper area of the west wall, the northern part deteriorates faster than the southern part. This corresponds with the larger annual integrated illuminance in the northern part than the southern part. (2) Regarding to the grappers at the lower part of the north wall, the color of the two eastern grappers remains better than that of the three western grappers, which corresponds to the larger AII on the western part. (3) On the side wall of the doorway, the upper part on the main room side is better conserved than the lower part on the entrance hall side, which corresponds well with the distribution of AII. The same situation can be seen in caves other than cave 285. (4) The deteriorated state of red-colored, “Unkimon” on the ceilings are well correlated with the AII distribution in the following respect: the color on the eastern part of the ceiling remains better than that on the western part, and the color on

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the southern part is more significant than that on the northern part, and the color on the northern part remains less than any other part on the eastern part. Furthermore, we have investigated the effects of detachment and flaking due to the adhesion of windblown sand onto the eastern wall of cave 285 where solar radiation had little influence, using CFD simulation of airflow and sand movement around Mogao caves and in cave 285 using a high-Reynolds number k-ε turbulence model. In the simulation, we assumed the south wind had high velocity. As the influence of thermal condition was minimal when the outside wind had moderate to high velocity, the simulation was set to be an isothermal analysis. In order to calculate the airflow in cave 285 in detail than around the Mogao caves, nesting domain was set around cave 285. The followings are the two main conclusions: (1) The most severe deterioration caused by detachment and flaking is likely the result of windblown sand. (2) Sand adhesion has caused paintings to fade on walls which are inclined upwards. To examine the effects of hygrothermal environment on the deterioration of the mural paintings in cave 285, the simulations of heat, moisture, and salt transfer were conducted for both periods with and without entrance hall. The main results are as follows. (1) The cracks caused by drying shrinkage were mainly generated soon after the production of the paintings, and the shrinkage rarely increased after that. The cracks caused by thermal expansion are likely to continue to increase, and the exfoliation due to the cracks may be occurring. The cracks caused by thermal expansion were more generated at the east wall than at the west wall. (2) The exfoliation due to decrease in adhesive force of the glue, biodegradation, and destruction due to freeze-thaw are progressing very slowly at present, but they probably occurred more frequently when the entrance hall collapsed. (3) The deterioration of the paintings of the west wall caused by salt is likely due to the crystallization of the salt contained in the paintings (or the soil wall) just after their production. The current crystallization process of the salt contained in the background water is considered very slow. Regarding the relationship between temperature in the cave and insect excrement or secretion, the following results were obtained. (1) The black-spotted soiling spread over the entire walls and the brown deposit seen in the cracks or peeled parts on the ceiling is considered to be the results of the insects attaching the excrement or secretion to the wall paintings. (2) The inside of the main chamber where temperature is stable throughout the year provides the insects a suitable space to live in. Particularly, the temperature at the upper part of the main chamber is higher than that at the lower part throughout the year. By integrating the results in sections from 3 to 7, the deteriorating process of the mural paintings from the production period to the present was estimated, which can provide basic information to estimate the initial state of cave 285.

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Acknowledgments We thank The Dunhuang Academy and the National Research Institute for Cultural Properties, Tokyo. Funding This research received no specific grant from any funding agency in the public, commercial, or not-profit sectors.

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