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Mechanical and durability properties of recycled and repeated recycled coarse aggregate concrete Huda, Sumaiya Binte 2014

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MECHANICAL AND DURABILITY PROPERTIES OF RECYCLED AND REPEATED RECYCLED COARSE AGGREGATE CONCRETE  by  Sumaiya Binte Huda    A THESIS SUBMITTED IN PARTIAL FULFILLMENT  OF THE REQUIREMENTS FOR THE DEGREE OF  MASTER OF APPLIED SCIENCE in  The College of Graduate Studies (Civil Engineering)  THE UNIVERSITY OF BRITISH COLUMBIA (Okanagan)   February 2014  ? Sumaiya Binte Huda, 2014   ii ABSTRACT Disposal and treatment of construction and demolition (C&D) wastes are often costly and hazardous to the environment. Their recycling could lead to a greener solution to the environmental conservation and pave the way towards sustainability. This study utilizes demolished concrete as coarse aggregate often termed as recycled coarse aggregate (RCA) for producing industry quality concrete. Large scale recycling can substantially reduce the consumption of natural aggregate and help preserve the environment. However, in near future, it can raise new challenges. The use of ?repeated recycled coarse aggregate? in concrete production can be a viable solution to the growing problem regarding the C&D waste disposal. During the development of new generation product like recycled and repeated recycled coarse aggregate concrete, it is essential to investigate the fresh, hardened, and durability properties of concrete to promote and escalate its application in the construction industry. This research investigates the fresh, mechanical, and durability properties of 25 MPa recycled aggregate concrete (RAC) made with different RCA replacement levels. Durability performance of 25 MPa RAC was evaluated in terms of sulphate attack and cyclic wetting and drying along with chloride exposure. Chloride propagation was evaluated after 1, 4, 9, 16, 28, 90, and 120 cycles. This study reveals that the performance of RAC is decreasing with increasing RCA replacement levels but their overall performance is comparable to natural aggregate concrete (NAC).  Three different generations of repeated recycled coarse aggregate concrete were produced using 100% RCA as a replacement of natural coarse aggregate. Similar mix design was used for producing 32 MPa concrete. Along with this, their durability performance was examined under three different exposure conditions namely, freeze-thaw, sulphate, and chloride exposure. It was found that the compressive strength of different generations of repeated recycled concrete was    iii lower than the control concrete. However, all of the mixes exceeded the target strength at 120 days. The durability performance of the different generations of repeated recycled coarse aggregate concrete was negatively affected by using different generations of such aggregates but still these findings will add a new achievement towards sustainable world.        iv PREFACE Major portions of the work outlined in this thesis have been submitted (see list below) for possible publication in peer reviewed technical journals. The author carried out all experimental work, analyses of results, and writing of the initial draft of all papers listed below. The contributions of her research supervisor consisted of providing guidance and supervision, and helping in the development of the final versions of the publications.  Refereed Journal Publications Huda, S.B. and Alam, M.S. 2014. Mechanical and durability properties of recycled aggregate concrete (RAC) made with different replacement levels of recycled coarse aggregate (RCA). Submitted to Construction and Building Materials. Huda, S.B. and Alam, M.S. 2014. Mechanical behavior of three generations of 100% repeated recycled coarse aggregate concrete. Submitted to Cement and Concrete Research. Huda, S.B. and Alam, M.S. 2014. Durability properties of repeated recycled coarse aggregate concrete. Submitted to Construction and Building Materials.         v TABLE OF CONTENTS ABSTRACT?? ....................................................................................................................... ii PREFACE ................................................................................................................................. iv TABLE OF CONTENTS????????????????????????????v LIST OF TABLES .................................................................................................................... ix LIST OF FIGURES .................................................................................................................... x ACKNOWLEDGEMENTS ..................................................................................................... xiii DEDICATION???????????????????????????????...xv Chapter  1 : INTRODUCTION AND THESIS ORGANIZATION ............................................. 1 1.1 GENERAL ........................................................................................................................ 1 1.2 OBJECTIVE OF THE STUDY ......................................................................................... 2 1.3 RESEARCH SIGNIFICANCE .......................................................................................... 3 1.4 THESIS OUTLINE ........................................................................................................... 4 Chapter  2 : LITERATURE REVIEW ........................................................................................ 6 2.1 GENERAL ........................................................................................................................ 6 2.2 GREEN CONCRETE ....................................................................................................... 7 2.3 GREEN CONCRETE AND SUSTAINABILITY.............................................................. 8 2.4 DIFFERENT WAYS OF GREEN CONCRETE PRODUCTION ...................................... 9 2.5 RAC UTILIZATION ...................................................................................................... 10 2.6 PROPERTIES OF RECYCLED AGGREGATE ............................................................. 13 2.6.1 Gradation, Shape and Texture ................................................................................... 14 2.6.2 Specific Gravity ........................................................................................................ 15 2.6.3 Absorption ................................................................................................................ 15 2.6.4 Abrasion resistance ................................................................................................... 16 2.7 PROPERTIES OF RAC .................................................................................................. 18 2.7.1 Fresh Properties of RAC ........................................................................................... 18 2.7.1.1 Workability ........................................................................................................ 18 2.7.1.2 Slump ................................................................................................................. 19 2.7.1.3 Air content ......................................................................................................... 20 2.7.1.4 Initial and final setting time ................................................................................ 20    vi 2.7.2 Properties of Hardened RAC ..................................................................................... 20 2.7.2.1 Physical properties ............................................................................................. 21 2.7.2.1.1 Permeability ................................................................................................. 21 2.7.2.1.2 Porosity of concrete ..................................................................................... 21 2.7.2.1.3 Coefficient of thermal expansion .................................................................. 22 2.7.2.1.4 Ultra sound pulse velocity ............................................................................ 22 2.7.2.2 Mechanical properties ........................................................................................ 22 2.7.2.2.1 Compressive strength ................................................................................... 23 2.7.2.2.2 Hardness ...................................................................................................... 26 2.7.2.2.3 Flexural strength .......................................................................................... 26 2.7.2.2.4 Tensile strength ............................................................................................ 27 2.7.2.2.5 Modulus of elasticity .................................................................................... 27 2.7.2.2.6 Drying shrinkage.......................................................................................... 28 2.7.2.3 Durability of Recycled Concrete ......................................................................... 28 2.7.2.3.1 Freezing and thawing resistance ................................................................... 28 2.7.2.3.2 Carbonation ................................................................................................. 29 2.7.2.3.3 Corrosion ..................................................................................................... 29 2.7.2.3.4 Alkali-silica resistance (ASR) and alkali carbon resistance (ACR) ............... 30 2.7.2.3.5 Sulfate resistance ......................................................................................... 30 2.7.2.3.6 Chloride penetration resistance..................................................................... 30 2.7.2.3.7 Chloride content ........................................................................................... 30 2.7.2.3.8 Chloride conductivity ................................................................................... 30 2.8 MIX DESIGNS FOR RAC.............................................................................................. 32 2.9 CLOSURE ...................................................................................................................... 33 Chapter  3 : MECHANICAL BEHAVIOR OF RECYCLED AGGREGATE CONCRETE  (RAC) MADE WITH DIFFERENT REPLACEMENTLEVELS OF RECYCLED COARSE AGGREGATE (RCA) .............................................................................. 34 3.1 GENERAL ...................................................................................................................... 34 3.2 SOURCES OF AGGREGATES ...................................................................................... 35 3.3 PROPERTIES OF AGGREGATES ................................................................................ 36 3.3.1 Gradation .................................................................................................................. 36    vii 3.3.2 Bulk Density, Specific Gravity, and Moisture content of Aggregates ........................ 37 3.4 EXPERIMENTAL PROCEDURE .................................................................................. 38 3.5 RESULTS AND DISCUSSION ...................................................................................... 41 3.5.1 Results of fresh concrete properties ........................................................................... 41 3.5.2 Results of Compressive Strength ............................................................................... 41 3.5.3 Failure Pattern of Concrete ....................................................................................... 45 Chapter  4 : DURABILITY OF RAC MADE WITH DIFFERENT RCA REPLACEMENT LEVELS: SULPHATE AND CHLORIDE ATTACK ............................................... 46 4.1 GENERAL ...................................................................................................................... 46 4.2 TEST METHOD TO ASSESS THE SULPHATE RESISTANCE OF RAC .................... 47 4.3 TEST METHOD TOASSESS THE CHLORIDE ION INGRESSION INTORAC ........... 50 4.4 RESULT AND DISCUSSION ........................................................................................ 52 4.4.1 Results of Sulphate Resistance Test .......................................................................... 52 4.4.2 Results of Chloride Ion Ingression into RAC ............................................................ 58 Chapter  5 : INFLUENCE OF REPEATED RECYCLED COARSE AGGREGATE ON THE FRESH AND HARDENED PROPERTIES OF CONCRETE ................................... 61 5.1 GENERAL ...................................................................................................................... 61 5.2 SOURCES OF AGGREGATES ...................................................................................... 63 5.3 PRODUCTION OF REPEATED RECYCLED COARSE AGGREGATE ...................... 63 5.4 PROPERTIES OF AGGREGATES ................................................................................ 66 5.4.1 Gradation .................................................................................................................. 67 5.4.2 Bulk Density, Specific Gravity, and Moisture Content of Aggregates ....................... 68 5.5 EXPERIMENTAL PROGRAM ...................................................................................... 70 5.6 EXPERIMENTAL RESULTS ........................................................................................ 73 5.6.1 Results of Fresh Concrete Properties ......................................................................... 73 5.6.2 Results of Compressive Strength ............................................................................... 74 5.6.3 Stress-Strain Curve ................................................................................................... 76 5.6.3.1 Modulus of elasticity and poisson?s ratio ............................................................ 79 5.6.4 Results of Splitting Tensile Strength ......................................................................... 79 5.6.5 Failure Pattern of Concrete ....................................................................................... 80 Chapter  6 : Durability Properties of Repeated Recycled Coarse Aggregate Concrete ............... 82    viii 6.1 GENERAL ...................................................................................................................... 82 6.2 FREEZE-THAW DURABILITY TEST OF REPEATED RECYCLED COARSE AGGREGATE CONCRETE ............................................................................................. 83 6.3 TEST METHOD TO ASSESS THE SULPHATE RESISTANCE OF REPEATED RECYCLED COARSE AGGREGATE CONCRETE ........................................................ 84 6.4 TEST METHOD TO ASSESS THE CHLORIDE ION INGRESSION INTO    REPEATED RECYCLED COARSE AGGREGATE CONCRETE ................................... 85 6.5 RESULT AND DISCUSSION ........................................................................................ 85 6.5.1 Results of Freeze-Thaw Durability Test .................................................................... 85 6.5.2 Results of Sulphate Resistance Test .......................................................................... 92 6.5.3 Results of Chloride Ion Ingression into Recycled Concrete ....................................... 97 Chapter  7 : Conclusions and Recommendations ..................................................................... 101 7.1 SUMMARY .................................................................................................................. 101 7.2 CONCLUSIONS ........................................................................................................... 101 7.2.1 Recycled Concrete Made with Different RCA Replacement Levels ........................ 102 7.2.2 Repeated Recycled Coarse Aggregate Concrete ...................................................... 102 7.3 LIMITATIONS OF THIS STUDY ................................................................................ 103 7.4 RECOMMENDATIONS FOR FUTURE RESEARCH ................................................. 104 REFERENCES ....................................................................................................................... 106 APPENDIX-A : COMPRESSIVE STRENGTH AND CHLORIDE ION CONCENTRATION ............................................................................................................................... 121    ix LIST OF TABLES Table 2.1: Current condition of RAC ........................................................................................ 13 Table 2.2: Allowable maximum limits of different harmful substances in recycled aggregate   (after Oikonomou 2005) ........................................................................................... 14 Table 2.3: Variation of attached mortar contents with the particle size of recycled aggregate .... 15 Table 2.4: Specific gravity of aggregate .................................................................................... 16 Table 2.5: Absorption capacity of different types of aggregates ................................................ 17 Table 2.6: Abrasion resistance .................................................................................................. 17 Table 2.7: RAC specifications limit .......................................................................................... 19 Table 2.8: Pore radius of different concrete mixes at 90 days (after Gomez-Soberon 2002) ...... 22 Table 2.9: Variation in compressive strength of RCA concrete ................................................. 25 Table 2.10: Variation in flexural strength of RCA concrete ....................................................... 26 Table 2.11: Variation in tensile strength of RCA concrete......................................................... 27 Table 2.12: Comparative analysis of concrete properties made from recycled concrete    aggregate (after ACI Committee 555, 2001) ........................................................... 31  Table 3.1: Properties of aggregates ........................................................................................... 38 Table 3.2: Mix proportions ....................................................................................................... 39 Table 3.3: Properties of fresh concrete ...................................................................................... 41 Table 3.4: Compressive strength results of different concrete mixes ......................................... 43 Table 5.1: Properties of aggregates ........................................................................................... 70 Table 5.2: Mix proportions ....................................................................................................... 72 Table 5.3: Fresh concrete properties ......................................................................................... 74 Table 5.4: Mechanical properties of different concrete mixes at 120th day................................. 79 Table A1: Chemical composition (after Siddique 2003) .......................................................... 121 Table A2: Concentration of chloride ions per unit surface area of concrete cylinder................ 121 Table A3: Compressive strength of the natural coarse aggregate concrete and different generations repeated RCA concrete ........................................................................ 122 Table A4: Concentration of chloride ions per unit surface area of concrete cylinder................ 122    x LIST OF FIGURES Figure 2.1 Breakdown of construction and demolition waste stream in Ottawa (after City of Ottawa 2013) ............................................................................................................ 10 Figure 2.2 The effect of recycled concrete aggregate on concrete compressive strength (after Yang et al. 2008) ...................................................................................................... 24 Figure 3.1 Sieve analyses of (a) Natural fine aggregate, (b) Natural coarse aggregate, and (c) Recycled coarse aggregate (RCA) ............................................................................ 37 Figure 3.2 Compressive strength of concrete made with different replacement levels................ 43 Figure 3.3 Variation in compressive strength of different concrete mixes at the age of 7, 28,     56, and 148 days ....................................................................................................... 44 Figure 3.4 Failure pattern of different concrete mixes (a) Mix-1, (b) Mix-2, (c) Mix-3,              (d) Mix-4, (e) Mix-5, and (f) Mix-6 .......................................................................... 45 Figure 4.1 Sulphate bath used for sulphate exposure test ........................................................... 50 Figure 4.2 Sequence of one wet-dry cycle ................................................................................. 52 Figure 4.3 Sulphate Compressive strength of concrete made with different RCA replacement level under sulphate exposure ................................................................................... 53 Figure 4.4 The percent (%) change in compressive strength of concrete made with different  RCA replacement levels at the age of 148 days under sulphate exposure with respect to the compressive strength of moist cured specimens at the same respective age ..... 55 Figure 4.5 Compressive strength of various concrete mixes ...................................................... 55 Figure 4.6 (a) Height change (%)  (b) Volume change (%) of concrete cylinders under     sulphate exposure condition ...................................................................................... 56 Figure 4.7 Discoloring during exposed to sulphate .................................................................... 57 Figure 4.8 Compressive strength of concrete after being exposed to chloride solution (a) 28 cycles (at 56thday), (b) 90 cycles (at 118thday), and (c) 120 cycles (at 148thday) ........ 58 Figure 4.9 Compressive strength of concrete at the age of 148 days .......................................... 59 Figure 4.10 Concentration of chloride ions per unit surface area of concrete cylinder ............... 60 Figure 5.1 Flow diagram of evolution process of recycled concrete made with repeated    recycled coarse aggregate ......................................................................................... 65 Figure 5.2 The crushing setup used for producing repeated recycled coarse aggregate .............. 66    xi Figure 5.3 Gradation curves of (a) natural fine aggregate and (b) natural coarse aggregate........ 67 Figure 5.4 Sieve analyses of different generations repeated recycled coarse aggregates  where  (a) 1stgeneration recycled coarse aggregate (RCA1), (b) 2ndgeneration recycled    coarse    aggregate (RCA2), and (c) 3rd generation recycled coarse aggregate     (RCA3)..................................................................................................................... 68 Figure 5.5 Microscopic view (magnification 40x) of different types of coarse aggregate:           (a) Control (natural coarse aggregate), (b) 1stgeneration recycled coarse aggregate (RCA1), (c) 2ndgeneration recycled coarse aggregate (RCA2), and (d) 3rd generation recycled coarse aggregate (RCA3) ............................................................................ 71 Figure 5.6 Compressive strength of various concrete mixes ...................................................... 75 Figure 5.7 Variation in 3, 7, 28, 56 and 120-day compressive strength of various concrete batches ..................................................................................................................... 77 Figure 5.8 Stress-strain curves of various concrete mixes at the age of 120 days ....................... 78 Figure 5.9 Splitting tensile strength of various concrete mixes at the age of 28 days ................. 80 Figure 5.10 Failure pattern of various concrete mixes (a) Control (natural coarse aggregate concrete) at 56th day, (b) 1st generation repeated RCA concrete (RC1) at 56th day,     (c) 2nd generation repeated RCA concrete (RC2) at 56th day, (d) 3rd generation  repeated RCA     concrete (RC3) at 56th day, (e) Control (natural coarse aggregate concrete) at 120th day, (f) 1st generation repeated RCA concrete (RC1) at 120th day,  (g) 2nd generation repeated RCA   concrete (RC2) at 120th day, and (h) 3rd      generation repeated RCA concrete (RC3) at 120th day .............................................. 81 Figure 6.1 Relative dynamic modulus of elasticity of concrete .................................................. 87 Figure 6.2 Length change of concrete ....................................................................................... 88 Figure 6.3 Weight change of concrete ....................................................................................... 89 Figure 6.4 Durability factor of concrete .................................................................................... 90 Figure 6.5 Specimens for freeze-thaw durability test before being placed in freeze-thaw   chamber where (a) Control (natural coarse aggregate concrete), (b) 1st generation repeated    RCA concrete (RC1), (c) 2nd generation repeated RCA concrete (RC2),  and (d) 3rd generation repeated RCA concrete (RC3) ................................................ 91 Figure 6.6 Concrete specimens after being exposed to 300 freeze-thaw cycles where                 (a) Control (natural coarse aggregate concrete), (b) 1st generation repeated RCA    xii concrete    (RC1), (c) 2nd generation repeated RCA concrete (RC2), and (d) 3rd generation repeated RCA concrete (RC3) ................................................................. 91 Figure 6.7 The results of compressive strength test at the age of 7days (before being placed in 5% sodium sulphate solution) and 56 days (after 7 weeks of exposure) ..................... 93 Figure 6.8 The results of compressive strength test at the age of 56 days of standard moist    curing cylinders and sulphate exposed cylinders ....................................................... 93 Figure 6.9 Compressive strength of various concrete mixes at 56th day ..................................... 94 Figure 6.10 Height change (%) of concrete cylinders under sulphate exposure condition .......... 96 Figure 6.11 Volume change (%) of concrete cylinders under sulphate exposure condition ........ 97 Figure 6.12 Compressive strength of concrete at the age of 56 days .......................................... 98 Figure 6.13 Compressive strength of various concrete batches at 56th day ................................. 99 Figure 6.14 Concentration of chloride ions per unit surface area of concrete cylinder ............. 100 xiii  ACKNOWLEDGEMENTS I convey my profound gratitude to the almighty Allah for allowing me to bring this effort to fruition. I express my sincere gratitude to my advisor, Dr. M. Shahria Alam for providing me with an opportunity to work with him during my graduate studies at The University of British Columbia, Okanagan. I couldn?t have asked for a better mentor and guide for my MASc program and I really appreciate all the support, guidance, and motivation that he has provided me through my academic career. He has been instrumental with knowledge, support, and mentoring that made my graduate experience at UBC so impeccably productive and rewarding, and made a great contribution to the success of this research.  I would like to thank my master?s dissertation committee members, Dr. Rehan Sadiq and Dr. Ahmad Rteil for always supporting my research work and providing me with great feedback from time to time, helping me improve the quality of my work immensely. The assistance of Dr. Lukas Bichler is also noted in generating the microscopic image of recycled aggregate. Graduate school and experimental research facility at UBC?s Okanagan campus has provided an excellent educational experience, and I would like to acknowledge the support I have received for pursuing a graduate degree at this Institution from Natural Sciences and Engineering Research Council of Canada (NSERC). Additionally, OK Builders Ltd. has supported this research project and provided required materials and useful thoughts throughout. I feel privileged to get the opportunity to work with such an excellent group of graduate students in the research group especially Anant, Shahidul, Kader, and Muntasir who helped me during my experimental works, offered technical knowledge, and friendship. I would also like to acknowledge Dr. Nouroz Islam for his generous help in setting up the data acquisition system    xiv and strain gauges.  I offer my enduring gratitude to the lab technicians for their valuable and generous assistance during my experimental works.  Finally, It is particularly important to thank my husband, Muntasir, for his support throughout my graduate studies and my parents, whom I feel to be the key source of inspiration for all my achievements.                  xv        Dedicated to my parents         1 Chapter  1: INTRODUCTION AND THESIS ORGANIZATION  1.1 GENERAL Sustainable construction and infrastructure management largely depend on the recycling and reuse of construction and demolition (C&D) waste. In Canada, C&D waste constitutes almost 25% of the municipal solid waste (MSW) (Statistic Canada 2008). It is estimated that, in British Columbia, C&D waste is almost 27.5% of total MSW where in Ontario and Alberta it is 29% and 7.5%, respectively (Statistics Canada 2008).  Unfortunately, the amount of C&D waste is increasing every year. Among all the C&D wastes in Canada concrete waste occupies a significant portion. As their disposal is costly and occupies large amount of space in  landfills, it is critical to find a way to reuse them so that this huge amount of waste can be turned into a natural resource for construction industry. One possible way of utilizing this concrete is to use it as coarse aggregates in new concrete, which can lead to a greener environment and pave the way for sustainable construction. Recycled aggregate concrete (RAC) is a relatively new construction material which is produced by crushing old concrete and used as aggregate replacement in new concrete. On the other hand, as this concrete gets older and need to be demolished, it will regenerate further concrete waste, which has the potential for similar reuse. Therefore, repeated recycled coarse aggregate concrete is a completely innovative green product, which requires extensive experimental investigation as its utilization will lead us one step forward towards a more sustainable world. Repeated recycled coarse aggregate concrete is produced by sequential crushing of used concrete products. Its uses in construction industry will help minimize two major environmental problems. First, it will reduce the environment pollution and second it will    2 help in preserving limited natural resources. Although RAC is a promising construction material, before any large industrial application its strength and durability properties must be properly investigated since the prominent characteristics of recycled aggregates differ from the natural aggregates. The differences in mechanical properties of recycled aggregate significantly influence the quality of RAC, and considered as one of the major barriers related to the field application of RAC. The influence of repeated recycled aggregate cannot be fully understood without proper investigation as the aggregate properties might vary significantly with the number of repetitions. In order to provide a sustainable construction material a suitable balance is essential between the quality and cost of RAC. The use of RAC is a very cost effective option if the quality remains comparable to the conventional concrete. To enhance the use of RAC and its acceptance as a sustainable construction material, the investigation of mechanical and durability properties is necessary which will help gain confidence regarding its application and lead us significantly closer to an ideal safe and sustainable solution to our need for green infrastructure. 1.2 OBJECTIVE OF THE STUDY Although the properties of recycled and repeated recycled aggregates differ from natural aggregate, these aggregates can be considered as a potential replacement to natural aggregate. Throughout the world extensive research have already been conducted on RAC (Yang et al. 2008, Poon et al. 2004, Etxeberria et al. 2007, Alam et al. 2013, Huda et al. 2013). The performance of RAC can be significantly influenced by its source. The finding of this study will boost up the confidence level of local industries regarding the use of RAC. The overall objective of this study is to develop a sustainable solution for natural coarse aggregate replacement in concrete by introducing repeated recycled aggregate as raw materials for producing ready mix    3 Green Concrete. This study seeks to produce a durable concrete that is acceptable in its  fresh and hardened properties. This study is conducted to achieve the following objectives: 1. Compare the fresh and hardened properties of RAC made with different recycled coarse aggregate (RCA) replacement levels with those of natural aggregate concrete (NAC). 2. Evaluate the durability performance of RAC made with different RCA replacement levels 3. Investigate the potential of repeated recycled coarse aggregate 4. Investigate the aggregate properties of different generations? repeated recycled coarse aggregates  5. Study fresh and hardened properties of different generations of repeated recycled coarse aggregate concrete. 6. Durability performance of repeated recycled coarse aggregate concrete is examined in terms of freeze thaw durability test, sulphate attack, and cyclic wetting and drying along with sodium chloride solution.  1.3 RESEARCH SIGNIFICANCE The mechanical and durability properties of recycled aggregate have been investigated by several researchers all over the world (Poon et al. 2004, Etxeberria et al. 2007, Yang et al. 2008, Salem et al. 2003, Alam et al. 2013). The quality and mechanical properties of recycled aggregate can vary significantly due to the geographic location and environmental condition. Studies performed in Europe or Asia might not be applicable to North America. This study aims to provide important information on the mechanical and durability properties of RAC to the local    4 ready mix industry. The outcome of this study will provide local concrete industry and practitioners? necessary information regarding the application of RCA as a replacement of natural coarse aggregate for producing RAC. The results excerpted from this study will boost up the confidence level and allow various applications of RAC in aggressive environment such as cold climatic condition undergoing freeze-thaw cycles, sulphate attack, and chloride penetration. Repeated recycled coarse aggregate concrete is a potential sustainable construction material. Since its absorption and porosity can be higher than conventional concrete, durability could be an issue that needs to be addressed. Currently there is no published literature on the durability properties of repeated recycled coarse aggregate concrete. This research addresses information on the characteristics of the different generations recycled coarse aggregate concrete and encourages their application. Specifically, this study offers a new generation green concrete and its practical application can reduce the carbon emission, carbon footprint, and size of land fill. Most importantly, it will reduce the use of limited natural aggregate and it can provide a cost effective solution in terms of present and future concerns (Smith 2009, Donalson et al. 2011). 1.4 THESIS OUTLINE Chapter-1 covers the objectives and scope of this study including a general introduction on green concrete (RAC and repeated recycled coarse aggregate concrete). Chapter-2 provides a detailed literature review on green concrete using C&D waste.This chapter also covers the sustainability perspective of green concrete, provides statistical information about the utilization of RAC and synthesizes the properties of recycled aggregate and the fresh, hardened, and durability properties of RAC available in literature.    5 Chapter-3 describes the experimental procedure along with the results of aggregate property and the fresh and hardened properties of 25 MPa RAC made with RCA of different replacement levels. Chapter-4 provides the methodology and the results of durability of RAC made with different RCA replacement levels in terms of sulphate attack and chloride ion ingression under cyclic wetting and drying. Chapter-5 includes the experimental procedure and their results for investigating the fresh and hardened properties of 32 MPa repeated recycled coarse aggregate concrete. Chapter-6 describes the durability of different generations of repeated recycled coarse aggregate concrete.  Chapter-7 presents the conclusions derived from this study, discusses the limitations of this study and provides recommendations for future research directions.     6 Chapter  2: LITERATURE REVIEW  2.1 GENERAL A large portion of Canadian civil infrastructure is reaching the end of its life span and will soon need to be replaced. Although the replacement of this infrastructure will increase the amount of construction and demolition (C&D) waste already found in Canadian landfills, these C&D waste can be potentially used as an alternative aggregate (recycled aggregate) in construction industry (Yeheyis et al. 2013). C&D waste as recycled aggregates not only reduces the scarcity of landfill, but also provides a sustainable construction material. Currently concrete waste makes up about 12% of C&D waste found in Ottawa (City of Ottawa 2013). If this trend continues, Canadian landfills will be saturated and polluted. However, a huge amount of this waste can potentially be recycled.  With the use of recycled aggregate in concrete mixtures, it is possible to minimize the use of natural aggregate and scarcity of landfill significantly. As environmental preservation is becoming a primary societal concern, the use of sustainable materials in construction is gaining popularity all over the world. The use of construction wastes for the production of new sustainable concrete is, however, not a new research area. From history it was found that Romans often used C&D waste or debris for road construction (Tabsh and Abdelfatah 2009). RAC has been reported to provide environmental benefits through both its production and use, thus, providing a greener and more sustainable solution. By using concrete waste as aggregate for producing new concrete (recycled aggregate concrete), natural resources (e.g. gravel pits, rock quarries) can be preserved, which can eliminate other related manufacturing processes, e.g. excavation/blasting, transportation,    7 crushing etc. When an old structure is demolished, the demolition wastes also need to be sent to the landfills. This process involves the cost of material handling, dumping, and transportation cost. The use of C&D waste will substantially reduce the landfill use.  This chapter presents a detailed summary of the existing literature on RAC, in particular, various properties of RAC, comparative analyses on the fresh and hardened properties of NAC and RAC, and their durability aspects. This chapter presents the existing knowledge on the properties of RAC using useful graphs and tables, and discusses their advantages and disadvantages in a systematic manner.   2.2 GREEN CONCRETE Concrete is being used as a construction material for more than 2000 years. In construction industry concrete has become more acceptable for its dependable nature and long lasting property. Other than construction purpose, the contribution of concrete in economic growth, social progress, and environmental protection is often ignored. It was found that energy performances of concrete structure are superior to steel structures (Lemay 2011). Concrete structures are not only flexible in design but also affordable. Moreover, concrete structures are more environmentally friendly than aluminum or steel structures. To make the concrete industry more sustainable and environment friendly, researchers are working continuously and they came up with the idea of green concrete (recycled concrete).  Green concrete or recycled concrete is a sustainable type of concrete resulting from aggregate replacements such as RAC, rubber tire, ceramic waste, tile, glass aggregate etc. It could also be a result of portland cement replacements such as fly ash, silica fume and slag or it could result from waste material admixtures such as waste latex paint. As a result, RAC has less    8 environmental impact in terms of energy consumption and emission during its manufacturing process (Hameed 2009) and can reduce the cost associated with concrete production.  2.3 GREEN CONCRETE AND SUSTAINABILITY A sustainable material is often defined as a material that produces environmental benefits through both its production and use. However, environmental benefits are not the only aspect that defines a sustainable material. Social and economic benefits must also be considered before deeming a material sustainable. As a result, the green concrete should provide a sustainable solution for reducing industrial waste through the investigation of its environmental, economic and social benefits. The environmental benefits of using green concrete can be seen primarily in two ways.  Firstly, the benefit of using any amount of recycled concrete aggregate would help limit the amount of industrial waste heading to landfills.  Recycled concrete aggregates do not degrade easily and will, therefore, remain in our landfills for long periods of time. By reducing these waste materials it is possible to limit the size and increase the longevity of our landfills.  Secondly, the use of green concrete would contribute to a reduction in our carbon footprint. By using RAC in new concrete the number of gravel pits/rock quarries can be reduced which would eliminate the large amount greenhouse gases emitted through the natural aggregate excavation/extraction process (Marinkovic et al. 2010, Sjunnesson 2005). This reduction of gravel pits/rock quarries can also prevent the destruction of our carbon neutralizing ecosystems. Recently, Huda et al. (2013, 2014) conducted studies on the life cycle analysis of recycled concrete. They found that by using RCA in new concrete production, total impact of concrete production can be reduced by 1% to 7%.    9 The use of RAC has also significant economic gains. Tam (2008) concluded that the large costs associated with the extraction of natural aggregate (such as the stripping and blasting) are not present with waste aggregate. The use of recycled aggregate from local landfills will also contribute to a reduction in high transportation costs currently incurred through the use of natural aggregate. The social benefits of using the green concrete may not be as obvious as the environmental or the economic benefits in other regions. It is not desirable to have a landfill in a public community as soil contamination, odors, increased traffic, and land value depreciation can result.    By using recycled aggregate in concrete, the amount of landfill space being used could be reduced.  In addition, landfills are typically operated by local municipalities that generally carry the costs.  These savings could be redirected into social programs to benefit communities. The reduction in gravel pit sizes can also provide social benefits. Although gravel pits often provide jobs and economic benefits to communities, they come at a cost as gravel pits increase the number of truck volume in that particular area. The increase in truck traffic can make the roads dangerous for children; reduce the life span of roads not designed for the large traffic, impact privacy, and cause noise and air pollution that negatively affect communities. As a result, the reduction of gravel pits can also be seen to benefit communities.  2.4 DIFFERENT WAYS OF GREEN CONCRETE PRODUCTION Different ingredients used in concrete production include cement as a binder, sand as fine aggregate and crushed stone, gravel or brick chips as coarse aggregates. Green concrete is a sustainable type of concrete resulting from either aggregate replacements or cement replacements. Green concrete can be produced by three types of replacement:    10            1) Replacing coarse aggregate            2) Replacing fine aggregate and            3) Replacing cement Water replacement can be done using waste latex paint. In RAC, coarse aggregate replacement can be done with construction or demolition waste (C&D), ceramic waste, tile, rubber tire, glass waste etc. Figure 2.1 shows the breakdown of construction and demolition waste stream in recycled aggregate, where we can see that concrete represents 12% of total construction waste. As this study area is focused on RAC made with RCA, this chapter mainly covers the details on RAC.  Figure 2.1 Breakdown of construction and demolition waste stream in Ottawa (after City of Ottawa 2013) 2.5 RAC UTILIZATION Recycled aggregates have been successfully used in concrete production for more than half century. In Europe, recycling waste industries are well established. After the Second World War, European countries have been utilizing the C&D waste for concrete production. The European Concrete 12%Gypsum10%Wood26%Metal9%Oil17%Paper and Card board14%Other12%   11 Demolition Association calculated that, approximately 200 million tons of wastes are generated every year in Europe (Tabsh and Abdelfatah 2009). But currently, only 30% of the waste is being recycled. In Europe, recycling and reusing of C&D waste is a popular and well supported program by the European Commission on Management of Construction and Demolition Waste. The target levels of recycling C&D waste of different European Union members are varied from 50% to 90% (Tabsh and Abdelfatah 2009). On the other hand, some of the European Union countries are still struggling to achieve this high recycling rate such as the recycling rate of Spain and Greece is about less than 20% where Ireland, Germany, Netherland, and Denmark, effectively achieve recycling rate which is higher than 70% (Jeffrey 2011). Currently in USA, around 2.2 billion tons of virgin aggregates are being produced every year (USGS 2009) and about 10-15% of this quantity is used for pavements. In addition, other maintenance and construction works for roads are required further 20-30% of aggregate. The rest amount of aggregate is consumed for structural applications, which is about 60-70%. In USA, 50% of recycled aggregate is produced by natural aggregate producer, 14% by debris recycling center, and 36% by contractors. Many initiatives were taken to facilitate the application of recycled aggregate but initially the application was limited for road construction as base or filler material (Gilpin et al. 2004).  A geological survey carried out in 2000 revealed that every year almost 100 million tons of recycled concrete aggregate is produced in US. This huge amount of recycled concrete aggregate is utilized by various sectors such as asphalt pavement (9%), new concrete production (6%), riprap (14%), base materials (68%), and other (7%) (Li 2005). California, Michigan, Texas, Minnesota, and Virginia are taking the initiative regarding the utilization of recycled aggregate in new concrete (FHWA 2004). Minnesota Department of Transportation succeed to save $600,000 by using recycled aggregate to construct a 16 miles    12 plain concrete pavement in 1980 (Salem et al. 2003).  It is possible to save $11 in every 1000 kg by using recycled concrete aggregate instead of natural aggregate (Smith et al. 2008).   The use of RCA is very specific and limited in Canada. It is estimated that the utilization of RCA is only 3% in Ontario (Miller 2005). Previously, Ministry of transportation of Ontario (MTO) did not encourage the use of recycled aggregate in construction. Later they started to use blending aggregates (natural and recycled) for the sub base and base of concrete pavement (Gilbert 2005).  Among the Asian countries, Japan has a very fascinated and enriched research history regarding RAC. Due to the structural safety requirement very little amount of recycled aggregate is being used in the real case scenario/field. Never the less in 1991 recycling law was established by Japan government, to encourage the reuse of demolition waste specially the waste concrete. After this initiative the rate of application of recycled aggregate increased from 48% (1990) to 96% in 2000, though they were mostly as a sub-base materials for concrete pavement (Kawano 2003). Every year 14 million tons of wastes are generated in Hong Kong. Earlier, non-hazardous wastes were used for land reclamation process. Due to various difficulties this recycling process was hindered. SAR government of Hong Kong started a pilot project incorporating recycling facility of C&D waste where daily recycling capacity was 2400 tons. They successfully reused recycled aggregate in different appropriate government projects (Rao et al. 2007).  Like other countries, Taiwan introduced some comprehensive program to fascinate and promote the application of recycled aggregate in the production of new concrete. In 1999 they utilized RAC during the rehabilitation program of infrastructures after a devastating earthquake.    13 Almost 30 million tons of C&D waste was generated during rehabilitation program. This unexpected situation was overcome by successfully recycling 80% of those waste and 30% of those recycled material was used as pavement base (Rao et al. 2007). Table 2.1 presents a summary of the overall condition of waste management through recycling, reusing and incineration around the world. Table 2.1: Current condition of RAC Country Source Waste generation (million tons) Recycled or reused (%) Waste sent to landfills or incinerated (%) Canada (C&Dwaste) Yeheyis et al. 2013 9 22 78 USA EPA, 2009 243 33.8 66.2 Europe Tabsh and Abdelfatah2009 200 30 70 China Zhao and Rotter 2008  120 50 50 Japan Saotome 2007 79 98 2 Austria Hyder Consulting 2011 19 55 45 India WMW 2011 10-12 50 50  2.6 PROPERTIES OF RECYCLED AGGREGATE Aggregates occupy a large portion of concrete volume and its properties significantly influence the properties of concrete. In case of RAC it is very difficult to get clear and appropriate idea about its quality because the origin of the recycled aggregate is often unknown. The application of recycled aggregate in new concrete is not only fascinating but also challenging. Due to the variation in sources, recycled concrete aggregate may possess impurities along with the adhered mortar content. This significantly influences the properties of RAC and make it difficult to predict the properties of new concrete (Smith 2009).  German committee of reinforced concrete structure has specified maximum permissible limit of different harmful    14 ingredients that can be presented in recycled aggregate (Grubl and Ruhl 1998). Later Greek standard adopted this limit in their standard.Table 2.2 represents thepermissible maximum limit of different harmful ingredients that can present in recycled aggregate. Table 2.2: Allowable maximum limits of different harmful substances in recycled aggregate (after Oikonomou 2005) Substance Arsenic As Lead Pb Cadmium Cd Chromium Cr Copper Cu Nickel Ni Iodine I Zinc Zn Limit (?g/l) 50 100 5 100 200 100 2 400  Following section discusses the different properties of recycled aggregate. 2.6.1 Gradation, Shape and Texture The properties of RAC are significantly affected by the gradation, shape, and texture of the recycled aggregate used. Since recycled aggregates can be obtained from different sources, their shape and textures are likely to vary over a wide range. Salem et al. (2003) found that recycled aggregate possesses hundred percent crushed faces as aggregates are produced from primary and secondary crushing. Katz (2003) found that the gradation and attached mortar content of recycled aggregates are not influenced by the crushing strength and the age of parent concrete. According to Corinaldesi et al. (2002) the size of recycled aggregate is dropped down to 50mm by primary crushing process and all types of metal impurities are removed by using electromagnets while transferring from primary to secondary crusher. Then particle size is reduced to 14-20 mm during secondary crushing process. The adherent mortar contains of fine and coarse aggregate are 25% and 6.5%, respectively (Katz 2003). Table 2.3 presents the variation of attached mortar contents with the particle size of recycled aggregate.    15 Table 2.3: Variation of attached mortar contents with the particle size of recycled aggregate Particle size Attached mortar (by volume) Reference 20-30 mm 20% BCSJ 1978 16-32 mm 25%- 35% Hansen and Narud 1983 14-20mm 25%-6.5% Katz 2003 8-16 mm 40% Hansen and Narud 1983 5-25 mm 35.5% Hasaba et al. 1981 4-8 mm 60% Hansen and Narud 1983 2.6.2 Specific Gravity Natural aggregate has a specific gravity of around 2.7. On the other hand recycled aggregate?s specific gravity is less than natural aggregate. Salem et al. (2003) and Katz (2003) explained that the presence of attached mortar on the surface of recycled aggregate is responsible for this reduced specific gravity of recycled aggregate. Specific gravity of recycled fine aggregate is from 2 to 2.3 and its value increases with the increased size of RCA and it varies from 2.2 to 2.6 while in saturated surface dry conditions (ACPA 1993, Katz 2003). Specific gravity of different type of aggregates are shown in Table 2.4. 2.6.3 Absorption  A lower absorption capacity is observed by natural coarse aggregate which is around 0.3%. RCA has a higher absorption capacity than natural coarse aggregate due to the attached mortar. 3.2% to 12% range of water absorption is seen in the case of fine and coarse recycled aggregates (Katz 2003). The absorption capacity of recycled fine aggregate is higher than that of RCA (Katz 2003, Salem et al. 2003, Gomez-Soberon 2002, Rao 2005). The absorption capacities of different types of aggregates are given below in Table 2.5.     16 Table 2.4: Specific gravity of aggregate  Specific gravity Reference Natural coarse aggregate 2.11 Alam et al. 2013 Natural coarse aggregate 2.65 Nassar and Soroushian 2012 Natural coarse aggregate 2.67 Salem et al. 2003 Natural coarse aggregate (lime stone) 2.71 Fathifazl et al. 2009 Natural coarse aggregate (river gravel) 2.74 Fathifazl et al. 2009 Natural coarse aggregate 2.7 Katz 2003 RCA 2.59 Katz 2003 RCA 2.4 Nassar and Soroushian 2012 RCA 2.4 Salem et al. 2003 RCA 2.5 Fathifazl et al. 2009 RCA 2.42 Fathifazl et al. 2009 RCA 2.03 Alam et al. 2013 RCA 2.2 Oikonomou 2005 Natural fine aggregate 2.65 Nassar and Soroushian 2012 Natural fine aggregate 2.54 Leite et al. 2013 Natural fine aggregate 2.72 Fathifazl et al. 2009 Recycled fine aggregate 2.45 Leite et al.2013 Recycled fine aggregate 2.23 Katz 2003 2.6.4 Abrasion resistance Abrasion resistance of aggregate gives idea about the weathering resistance and the quality of aggregate. According to Sagoe- Crential et al. (2001) virgin aggregate abrasion resistance is 12% higher than that of recycled aggregate. Recycled aggregate has abrasion resistance of 20% to 45% and sometimes it can be as high as 50% (ACPA 1993). Abou- Zeid et al. (2005) found that replacement pattern of recycled aggregate (full or partial) does not influence the abrasion resistance of aggregate. Table 2.6 shows the abrasion resistance of natural and recycled aggregate.It reflects the difference between the initial mass and the final mass of the tested samples with respect to the percentage of the initial mass.     17 Table 2.5: Absorption capacity of different types of aggregates   Absorption Reference Natural coarse aggregate 2.28% Nassar and Soroushian 2012 Natural coarse aggregate 0.30% Salem et al. 2003 Natural coarse aggregate 0.9-1.1% Gomez-Soberon 2002 Natural coarse aggregate (lime stone) 0.34% Fathifazl et al. 2009 Natural coarse aggregate (river gravel) 0.89% Fathifazl et al. 2009 Natural coarse aggregate 0.4% Leite et al. 2013 Natural coarse aggregate 2.17% Alam et al. 2013 Natural coarse aggregate 1.24-1.25 Poon et al. 2004 RCA 4.35% Nassar and Soroushian 2012 RCA 4.70% Salem et al. 2003 RCA 5.8-6.8% Gomez-Soberon 2002 RCA 3.3-5.4% Fathifazl et al. 2009 RCA 5.23% Alam et al. 2013 RCA 3.2-3.4% Katz 2003 RCA 3% Oikonomou 2005 RCA 6.28-7.56 Poon et al. 2004 RCA 5.5% Leite et al. 2013 Natural fine aggregate 0.97% Nassar and Soroushian 2012 Natural fine aggregate 0.54% Fathifazl et al. 2009 Natural fine aggregate 0.8% Leite et al. 2013 Natural fine aggregate 1.49% Gomez-Soberon 2002 Recycled fine aggregate 5.5% Leite et al. 2013 Recycled fine aggregate 11.2-12.7% Katz 2003 Recycled fine aggregate 8.20% Gomez-Soberon 2002  Table 2.6: Abrasion resistance   Abrasion resistance Reference Natural  aggregate 22.80% Nassar and Soroushian 2012 Recycled aggregate 31.60% Nassar and Soroushian 2012 Recycled aggregate 20-50% ACPA 1993     18 2.7 PROPERTIES OF RAC Presently in new construction only a small portion of RAC is used as there is a lack of adequate technical specification and guidelines for producing good quality RAC.  As a result lots of research works are being conducted all over the world to investigate the properties of RAC. These results will intensify the industrial production of recycle concrete.  There are five existing specifications for recycled concrete made with used concrete (Oikonomou 2005, Kuroda 2005, Noguchi 2005, Li 2008). These five are Greek Specification Concrete technology (GSCT), Chinese technical code (DG/TJ07-008), RILEM (RILEM 1994a), BS8500 (2002), and Japanese Industrial Standards (JIS). Table 2.7 represents the specification limit for RAC of GSCT, JIS, DG/TJ07-008, and BS8500 and also another proposed specification limit for RAC for Egypt (Kamel and Abou-Zeid 2008, Kamel 2008). 2.7.1 Fresh Properties of RAC 2.7.1.1 Workability In 2001, it was found that commercially produced recycled aggregates are smoother and spherical than recycled aggregates which are usually produced for laboratory work (Sagoe- Crential et al. 2001). This type of shape increases the workability of commercially produced RAC than that of laboratory produced RAC. Due to the higher absorption capacity of recycled aggregate, the concrete mixes become stiffer and less workable compared to NAC (Salem et al. 2003). Some researchers observed that RAC requires 5-10% extra free water to achieve the same workability than that of NAC though it is significantly influenced by the quality of recycled aggregate (Hasan 1992, Leite et al. 2013).     19 Table 2.7: RAC specifications limit RAC specification GSCT* JIS* DG/TJ07-008** BS8500** Egypt* Coarse Fine Type I? Type II Specific gravity (kg/m3) 2.2 (min) 2.5 (min) 2.5 (min)        Water absorption (%) 3 (max) 3 (max) 3.5 (max) 7 (max) 10(max)  7 (max) Foreign ingredients (%) 1 (max) 1 (max) 1 (max) 1(max)  1(max)  Foreign ingredients (kg/m3)       2 to 10 Organic ingredients (%) 0.5 (max)   0.5 (max)    Sulphate ingredients (%) 1 (max)   1(max)  1(max)  Amount of sand (%) 5 (max)       Amount of filler (%) 2 (max)       Los Angeles abrasion (%) 40 (max) 35 (max)     40 to 50 Soft granules (%) 3 (max)       Soundness or loss (%) 10 (max)       Sand equivalent (%) 80 (min)       Solid volume (%)  55 (max) 53 (max)     Material passing 75 ?m (%)  1 (max) 7 (max)     10% fineness value (kN)       50 to 150 Chloride content  0.04 (max) 0.4 (max) 0.25(max)    ASR  Harmless Harmless     Flakiness index (%)             40 [?structural use,* Smith 2009, **Li 2008] 2.7.1.2 Slump Slump value represents the consistency and workability of fresh concrete. Topcu and Sengel (2004) showed that at a fixed water cement (w/c) ratio, the workability decreases with the increased amount of recycled aggregate replacement which consequently decreases the slump    20 value of RAC. The loss of slump is higher in case of over dry recycled aggregate at similar w/c ratio.  Yang et al. (2008) studied the mechanical and durability properties of RAC. In terms of the fresh concrete properties such as slump, they found that as the percentage (%) of recycled aggregate increased in the concrete, the concrete slump slightly decreased. However, since the reduction in slump was very small, it can be offset with the use of admixtures. Poon et al (2004) found that after adjusting the required amount of water content of air dry RCA as per its actual moisture state the slump value was 100 mm for RAC made with 50% RCA where it was 110-100mm for NAC.   2.7.1.3 Air content Salem et al. (2003) obtained that air content of RAC is higher than NAC. This means that RAC contains high amount of entrapped air compared to NAC. Similar observation was found by Katz (2003).  2.7.1.4 Initial and final setting time Hansen and Hedegkd (1984) found that admixtures of parent concrete does not influence the initial and final setting time of RAC.  2.7.2 Properties of Hardened RAC Hardened concrete properties reveal the strength and durability properties of concrete. In an experimental study Tavakoli and Soroushian (1996) showed that several factors are correlated with the strength of RAC. Original/parent concrete strength has a significant impact on the strength of RAC. RAC strength properties are also affected by coarse aggregate replacement level. They found that the values of flexural, compressive and splitting tensile strength of RAC    21 differed from conventional concrete.  Following section discusses about the different types of physical and mechanical properties of RAC. 2.7.2.1 Physical properties 2.7.2.1.1 Permeability Concrete made with recycled aggregate has higher permeability by 10-45%than that of NAC almost. Mainly the permeability property of RAC depends on aggregate source (Zaharieva et al. 2003,Abou-Zeid et al. 2005). The water absorption of recycled concrete aggregate is higher than virgin aggregate. During the harden stage of concrete this water evaporates and causes porosity. Extension of curing period can produce fine pore and thus help reducing the permeability of RAC by 50% (Zaharieva et al. 2003) 2.7.2.1.2 Porosity of concrete Gomez-Soberon (2002) examined the porosity of concrete made with recycled aggregate and investigated different properties of RAC such as, the threshold ratio, critical pore ratio, average pore ratio, and theoretical pore radius of concrete. These properties were examined mainly at the age of 7, 28, and 90 days. These test results indicated that replacing natural aggregates with recycled coarse aggregates yielded an increase in porosity. The tensile and compressive strengths of RAC are decreased with increased porosity. It was also found that the modulus of elasticity decreases with the increased porosity. It is difficult to find a proper relation between the total porosity and properties of RAC. It can be improved by distributing the pore radius. Table 2.8 represents the pore radius of concrete at 90 days.     22 Table 2.8: Pore radius of different concrete mixes at 90 days (after Gomez-Soberon 2002) Mix Pore radius (nm) Control 18.8 30% RCA 19.6 60% RCA 21 100% RCA 24.7  2.7.2.1.3 Coefficient of thermal expansion Smith and Tighe (2009) conducted an experimental study to find the impact of recycled concrete aggregate on the coefficient of thermal expansion (CTE) of RAC. They concluded that the concrete performance improves with the increasing percentages of recycled aggregate. They found that CTE values were 7.28?10-6/?C and 4.10?10-6/?C for virgin concrete and 50% RCA, respectively. On the other hand Yang et al. (2003) results conflict with Smith and Tighe (2009) findings. Yang et al. (2003) stated that the RCA concrete has higher CTE value. They found 8.9?10-6/?C and 11.6?10-6/?C   CTE values for cylinder and prism RCA specimens, respectively.  2.7.2.1.4 Ultra sound pulse velocity NAC ultra sound pulse velocity is around 69-70 ?s and this value increases for RAC which is approximately 92-93 ?s (Topcu 1997). 2.7.2.2 Mechanical properties Researchers have been exploring the possibility of using recycled aggregate especially C&D wastes since 1970. Several researchers (Yang et al. 2008, Poon et al. 2004, Etxeberria et al. 2007) found that similar/comparable strength can be achieved by concrete made with RCA instead of natural coarse aggregates. Best match was observed between RAC and conventional    23 concrete when recycled aggregate contained less amount of attached mortar (Yannas 1977). Following portion discusses the mechanical behavior of RAC.  2.7.2.2.1 Compressive strength The compressive strength of RAC is greatly influenced by the recycled aggregate replacement ratio and the effective w/c ratio (Ulloa et al. 2013). Higher variation in terms of the compressive strength is observed for 100% replacement where it is comparatively low for lower replacement levels such as 20% to 50%. Alam et al. (2013) found that almost 15% reduction in compressive strength as compared to control mix for 25% to 50% RCA concrete.    Test result by Hansen and Narud (1983) indicated that if all other factors are kept constant then RAC compressive strength is greatly influenced by the w/c ratio of original/parent concrete. The strength of RAC will be equivalent or better than NAC if its w/c ratio is lower or at least similar to that of original concrete.  Yannas (1977) conducted an experimental investigation to examine and compare the mechanical behavior of recycled and conventional concrete. It was found that the compressive strength and modulus of elasticity of concrete made with RCA were 76% and 60% to 80% of that of conventional concrete, respectively. Later, Crentsil and Brown (2001) found no major difference between the compressive strength of control concrete and RAC. High strength and high performance RAC mechanical behaviors were investigated by Ajdukiewicz and Kliszczewicz (2002). In their study, 40-70 MPa concrete were used for producing recycled aggregate. They concluded that for producing RAC with similar workability, a modification in water content is required in the mix design. This study reflected the conclusion drawn by Tavakoli and Soroushian (1996). Ajdukiewicz and Kliszczewicz (2002) reported a    24 reduction in the compressive strength of RAC by 10%, whereas Yannas (1977) found a reduction of 24%. Juan and Gutierrez (2006) suggested that for producing good quality of structural recycled concrete aggregates the attached mortar content should be below 44%. They found that the compressive strength of recycled concrete made using this quality recycled concrete aggregates are generally not lower than 25MPa.  Yang et al. (2008) used different recycled aggregate replacement levels (30%, 50%, and 100%) to produce 40 MPa concrete with recycled aggregate and a water-cement ratio of 50% by weight. They found that any replacement level of recycled concrete aggregate will produce concrete with the same compressive strength as what is normally found for NAC. Figure 2.2 shows the results of compressive strength of RAC with different RCA replacement levels found by Yang et al. (2008). From this figure, it is evident that irrespective of RCA replacement levels, the compressive strength remains almost constant.  Figure 2.2 The effect of recycled concrete aggregate on concrete compressive strength (after Yang et al. 2008) 051015202530354045500 25 50 75 100Compressive Strength (MPa)Curing Time (days)0% RCA30% RCA50% RCA100% RCA   25 Limited studies and experimental data are available regarding the use of RCA in high strength concrete. Acker (1996) produced high strength concrete using three different replacement percentages of RCA (5%, 10% and 12.5%). With 30% RCA, Limbachiya et al. (2000) achieved a compressive strength of 80 MPa at 28th day. Their aim was to produce high strength concrete (50 MPa or more) using RCA. They used rejected precast structural concrete elements as RCA. Their study showed that there was no significant effect in concrete strength up to 30% replacement of coarse aggregate by RCA. They suggested that if more than 30% RCA replacement levels are used, it can reduce the strength of RAC. Table 2.9 shows the variations of compressive strength of RAC with different RCA replacement levels compared to NAC. Table 2.9: Variation in compressive strength of RCA concrete Replacement Level Variation in Compressive Strength as compared to natural concrete Reference 25% 9% Increase Etxeberria et al. 2007 25% 15% Decrease Alam et al. 2013 30% 10% Decrease Yang et al. 2008 30% 9.5% Decrease Kwan et al. 2012 30% Similar Limbachiya et al. 2000 50% 11% Increase Etxeberria et al. 2007 50% 14.7% Decrease Alam et al. 2013 50% 5% Decrease Yang et al. 2008 50% 5% Decrease Limbachiya et al.  2000 60% 30% Decrease Kwan et al. 2012 100% 7.7% Increase Etxeberria et al. 2007 100% 11% Decrease Yang et al. 2008 100% 2.4% Increase Salem et al. 2003 100% 8.9% Decrease Limbachiya et al. 2000 100% 8% Decrease Ajdukiewicz and Kliszczewicz 2002       26 2.7.2.2.2 Hardness The hardness value depends on RAC?s compressive strength. If the compressive strength decreases, the hardness value also decreases. Very little information is available in the literature regarding the hardness of RAC. Topcu (1997) found the hardness value for natural concrete as 21.3 MPa, while it declines and becomes 11.6 MPa for 100% RAC. 2.7.2.2.3 Flexural strength Conflicting results are observed from the literature regarding the impact of recycled aggregate on the flexural strength of concrete. Table 2.10 provides a summary of the variation in flexural strength as a function of RAC replacement level obtained by different researchers. Several researchers concluded that use of recycled aggregates in concrete production decreases the flexural strength of RAC (Alamet al. 2013, Katz 2003). Zaharieva (2004) showed that concrete made with recycled concrete aggregate flexural strength was 10-20% less than virgin concrete. On the other hand, Poon et al. (2002) found that concrete made with 100% recycled concrete aggregate flexural strength was13% higher than virgin concrete.  Conversely, Alam et al. (2013) found a reduction of 16% in flexural strength of RAC made with 25% RCA. Table 2.10: Variation in flexural strength of RCA concrete Replacement Level Variation in Flexural Strength as compared to natural concrete Reference 25% 2.2% Increase Poon 2002 25% 16% Decrease Alam et al. 2013 50% 6.25% Increase Poon 2002 50% 32% Decrease Alam et al. 2013 75% 10.8% Increase Poon 2002 100% 13% Increase Poon 2002 100% 31% Decrease Katz 2003     27 2.7.2.2.4 Tensile strength Like flexural strength, researchers have come up with contradictory conclusions regarding the tensile strength of RAC. Table 2.11 shows the variation in tensile strength results of RAC found in different experimental studies. Tensile strength of RAC is decreased with the increased porosity (Gomez-Soberon 2002). Ajdukiewicz and Kliszczewicz (2002) found that the tensile strength value of RAC was 10% smaller than NAC. However, Etxeberria et al. (2007) and Alam et al. (2013) found higher tensile strength for RAC. Table 2.11: Variation in tensile strength of RCA concrete Replacement Level Variation in Tensile Strength as compared to natural concrete Reference 15% Similar Gomez-Soberon 2002 25% 6% Increase Etxeberria et al. 2007 25% 34%% Increase Alam et al. 2013 30% 2.7% Decrease Gomez-Soberon 2002 50% 18% Increase Etxeberria et al. 2007 50% 16% Increase Alam et al. 2013 60% 8% Decrease Gomez-Soberon 2002 100% 2% Decrease Etxeberria et al. 2007 100% 10.8% Decrease Gomez-Soberon 2002  2.7.2.2.5 Modulus of elasticity Depending on the RCA replacement level and water-cement ratio the modulus of elasticity of RAC is 50-70% of NAC (Rao 2005, Ajdukiewicz and Kliszczewicz 2002, Oliveira et al. 1996).To improve the quality of RAC a new technique was proposed by Qian et al. (2011). Their technique is known as shucking technique which was established as a secondary process for improving the performance of simply crushed recycled aggregate. Qian et al. (2011) investigated    28 the elastic modulus of shucking RAC made with RCA and reported improved strength and elastic modulus properties of shucking RAC compared to commonly used RAC. 2.7.2.2.6 Drying shrinkage Crentsil and Brown (2001) concluded that the drying shrinkage of RAC is higher than NAC. Replacement ratio significantly influences the drying shrinkage of RAC. The value of drying shrinkage increases with the increased recycled aggregate replacement ratio (Poon et al. 2002). They reported that the drying shrinkage of RAC increases by 5%, 10%, 15%, and 27.5% for RCA replacement levels of 25%, 50%, 75%, and 100%, respectively. 2.7.2.3 Durability of Recycled Concrete RAC properties can be better understood by investigating the durability properties. The durability properties of RAC were studied by several researchers (Olorunsogo and Padayachee 2002, Yang et al. 2008, Zaharieva 2004, Kwan et al. 2012). RAC with variable percentages of RCA (0%, 50% and 100%) were studied by Olorunsogo and Padayachee (2002). They found that if the RCA level is increased, the durability property of RAC decreases. The quality of RAC can be enhanced with the curing age. Following section discusses the durability properties of RAC.  2.7.2.3.1 Freezing and thawing resistance Different types of opinions are found about the freeze thaw resistance of RAC. Gokce et al. (2004) investigated the freeze thaw durability of RAC. They showed that it depends on the source of parent concrete. RAC made with air entrained recycled aggregate showed better performance than RAC made with non-air entrained recycled aggregate. Non-air entrained concrete has higher mass loss than air entrained concrete. The relative dynamic modulus of    29 elasticity of RAC originated from air entrained concrete was approximately 90% or above after exposed to 500 freeze thaw cycles. On the other hand only 60% of the relative dynamic modulus of elasticity observed after exposed to 500 freeze thaw cycles when RAC originated from non-air entrained concrete. Salem and Burdette (1998) and Zaharieva et al (2004) reported that recycled aggregate originated from concrete made with air entrained admixture produced high quality freeze thaw resistance concrete. Kasai et al. (1988) found that high replacement ratio of RAC declines the frost resistance of new concrete and also suggested that it is better not to use recycled concrete aggregate in sever freeze thaw exposure condition.  Yamato et al. (1988) examined the durability of RAC under freezing and thawing condition. They concluded that RAC resistance was less than NAC. For freeze thaw, small reduction in resistance was observed up to 30% replacement of recycled aggregate.    2.7.2.3.2 Carbonation Many researchers reported that the carbonation depth of RAC is 1.3 to 2.5 times higher than virgin concrete (Levy-Salomon and Paulo 2004, Katz 2003, Crentsil et al. 2001, Shayan  and Xu 2003). Otsuki et al. (2003) concluded that slightly higher carbonation depth was observed for RAC than the original concrete with similar water cementing ratio. Presence of attached mortar increases the permeability of RAC and thus increases the carbonation depth of concrete.  2.7.2.3.3 Corrosion Chloride, sulphate and carbonate exposure conditions are mainly responsible for the corrosion of concrete. Shayan and Xu (2003) observed less corrosion risk for RAC using half- cell potential test.    30 2.7.2.3.4 Alkali-silica resistance (ASR) and alkali carbon resistance (ACR) Fly ash can improve alkali-silica reactivity up to an acceptable limit but as per CSA guideline fly ash content should not be more than 25% of total cementing material. No significant improvement was observed for incorporating 15% fly ash (Li and Gress 2006). Shayan and Xu (2003) reported that recycled concrete aggregate has better alkali aggregate reactivity. 2.7.2.3.5 Sulfate resistance Shayan and Xu (2003) found that RCA concrete sulphate resistance was more than NAC, and after one year exposure the related expansion was less than 0.025%. 2.7.2.3.6 Chloride penetration resistance Chloride penetration is one of the major causes which generate corrosion in concrete. Shayan and Xu (2003) obtained almost 2.2 to 2.3 mm higher penetration depth for RAC than NAC after exposed to chloride solution. 2.7.2.3.7 Chloride content ACPA (1993) stated that Chloride contents of recycled coarse and fine aggregates were 0.7%-0.9% and 0.03%, respectively which are less than ACI acceptable limit. But Hansen and Hedegkd (1984) obtained 0.69% soluble chloride ion by weight of cement in concrete made with recycled concrete aggregate which was higher than ACI acceptable limit. 2.7.2.3.8 Chloride conductivity Chloride conductivity is the diffusion rate of chloride ions inside the concrete (Olorunsogo and Padayachee 2002, Smith 2009). It is possible to decrease the chloride conductivity of    31 concrete by increasing the curing of concrete. As the amount of recycled aggregate increases it automatically decreases the conductivity of RAC. The presence of cracks and fissures during the processing of recycled aggregates may influence this phenomenon. As a result RAC becomes more susceptible in terms of absorption, permeation, and diffusion of liquid substances (Olorunsogoand Padayachee 2002). Table 2.12 presents comparative performance of RAC produced by both fine and coarse aggregate replacement. The results are provided in terms of expected changes in concrete properties from similar mixes using natural aggregate.  Table 2.12: Comparative analysis of concrete properties made from recycled concrete aggregate (after ACI Committee 555, 2001) Property RAC made with coarse and fine recycled concrete aggregate RAC made with coarse recycled concrete aggregate Corrosion Rate May be faster May be faster Air Content Slightly higher Slightly higher Water Bleeding Less Slightly less Workability Slightly to significantly lower Similar to slightly lower Water Demand Much greater Greater Finishability More difficult Similar to more difficult Compressive Strength 15% - 40% less 0% - 24% less Carbonization Up to 65% more Up to 65% more Tensile Strength 10% - 20% less 0% - 10% less Permeability 0% - 500% more 0% - 500% more Strength Variation Slightly more Slightly more Creep  30% - 60% more 30% - 60% more Modulus of Elasticity 25% - 40% less 10% - 33% less Freeze-Thaw Durability Depends on air void system Depends on air void system Coefficient of thermal expansion 0% - 30% more 0% - 30% more ASR Less susceptible Less susceptible Drying Shrinkage 70% - 100% more 20% - 50% more Sulfate Resistance Depends on mix Depends on mix Specific Gravity 5% - 15% less 0% - 10% less     32 2.8 MIX DESIGNS FOR RAC Introduction of a proper guideline for RAC mix design could result in a dramatic increase in the application of the recycled concrete aggregate in concrete industry. ACI-555R provides some guidelines about the mix proportion of RAC. But these sources don?t provide the proper mix design method for gaining hardened and fresh characteristics of RAC. These guidelines were mainly based on conventional mix proportioning method. To give a new dimension in RAC mix design Fathifazl et al. (2009) proposed the equivalent mortar volume method for RAC. In the equivalent mortar volume method they predicted RAC as a two phase material cluster of cement paste and natural aggregate. Total mortar volume in RAC must be equal to the total mortar volume in NAC for their proposed method. A large number of mixes were made by them using their proposed and conventional method. By applying their equivalent mortar volume method they obtained higher slump for RAC. In RCA concrete, fine aggregate and cement amount can be significantly reduced by using this equivalent mortar volume method. By utilizing this method, they observed similar mechanical properties for both RAC and standard NAC.  Lin et al. (2005) used taguchi method to maintain the quality of recycled aggregate. Bairagi et al. (1990) found out the suitable mix design method for RAC from existing mix design methods. They suggested an empirical equation for modifying influencing factor. Their suggested modified procedure requires 10% extra cement but it improves the quality of RAC.  Kwan et al. (2012) found that the DoE (Department of Environment, UK, 1988) method is good for RAC?s mix design with up to 80% RCA replacement of the total coarse aggregate content of the mix. They observed that the level of RCA replacement is directly proportional to the water absorption of concrete. They concluded that up to 30% substitution of coarse    33 aggregate, no significant change was observed in compressive strength which was quite similar to the finding of Limbachiya et al. (2000). 2.9 CLOSURE This chapter has presented a detailed review of the state-of-the-art knowledge available on the mechanical and durability properties of RAC.  This review provides an insight into the current research activities and applications relating to development of RAC. Because of its wide variation in mechanical properties found from different experimental studies, the application of RAC in commercial projects is still limited.  Since its inception, researchers have investigated the properties of RAC by varying the replacement levels, mix proportions, and other factors. This study summarized the variation of different experimental studies found in different parts of the world along with their features and results. This study also identified the gaps in existing literature and the remainder of the thesis is outlined to fill up some of those research needs for commercial application of RAC.      34 Chapter  3: MECHANICAL BEHAVIOR OF RECYCLED AGGREGATE CONCRETE (RAC) MADE WITH DIFFERENT REPLACEMENTLEVELS OF RECYCLED COARSE AGGREGATE (RCA)  3.1 GENERAL Engineers and researchers are always striving and exploring different ideas to utilize various industrial wastes to produce concrete for construction. Determining the characteristics and behavior of these different types of concrete has become an important research stream in order to exploit them in mix design. Compressive strength is the most important characteristics of concrete that dictates its durability. Due to its worldwide availability, comparatively low cost, and ability to take any form and shape, concrete has emerged as the most widely used construction material all over the world. According to Cement Association of Canada, every year 15 billion tonnes of concrete is produced throughout the world (Cement Association of Canada 2012). This widely accepted construction material, however, has some disadvantages such as greenhouse gas emissions during the production, consumption of limited natural resources. The overall production process of concrete contributes approximately 5% of the greenhouse gas (GHG) emissions produced each year (Concrete Association of Canada 2012).  To help reducing the environmental impacts of concrete production, researchers and industries are continuously investigating to find new ways and come up with innovative idea of producing concrete with reduced environmental impact. Nowadays, RAC as a coarse aggregate has become a trade mark for sustainable design of concrete production that has potentials for construction projects to achieve LEED (Leadership in Energy and Environmental Design) certification (USGBC 2014). Before any mass application of a new concrete mix, it is important to investigate its mechanical    35 and durability properties. The main objective of this study is to investigate the mechanical and durability characteristics of concrete made with different replacement levels of recycled coarse aggregate (RCA) with an aim to escalate the commercial production of this new concrete and its application in the Okanagan Valley. This chapter focuses on the fresh and hardened properties of RAC and its comparison with NAC (control). This chapter also discusses the properties of different types of aggregate which were used in this study. 3.2 SOURCES OF AGGREGATES One of the main objectives of this study is to produce 25 MPa RAC with different replacement levels of RCA and compare it with NAC.  Natural aggregate and recycled concrete aggregate were used as coarse aggregate for the production of concrete. Natural sand was used as fine aggregate for production of both natural and recycled concrete. Recycled fine aggregate was not considered in this study due to high absorption of such aggregate. Moreover, many impurities associated with recycled fine aggregate can reduce concrete strength.  It is usually not recommended to use recycled fine aggregate for the production of concrete (BSI 2006, Hasan 1992, DIN 2002, Marinkovic et al. 2010,Rilem TC 121-DRG1994). High water absorption and high cohesion of recycled fine aggregate cause difficulties to control RAC production. Control mix was produced using 100% natural coarse aggregate. Natural aggregate with a maximum size of 20 mm was used in this study.  RCA source plays a vital role for achieving desired properties of concrete. Recycled coarse aggregate with a maximum size of 14 mm was used in this study. The source of recycled aggregate is often unknown. It is very beneficial for this study to represent the practical situation. If gross commercial production is taken into consideration then it is very difficult to track the    36 source of recycled aggregate. Recycled aggregates are usually produced from demolished concrete. Normally demolished concrete is collected from landfills and it is very hard to identify the sources because those concrete come from different sources like bridges, buildings, sidewalks, pavements, hydraulic structures, and other structures. Smaller size RCA (14mm) was obtained after several crushing stages to minimize the amount of adhered mortar content. RAC strength can be negatively affected by RCA over 19mm. Interfacial transition zone of RCA would increase for aggregate size over 19 mm which may have some negative impact on the strength of RAC made with RCA (Smith 2009). 3.3 PROPERTIES OF AGGREGATES Different types of aggregate testing were performed for the natural coarse aggregate, natural fine aggregate (sand), and RCA. The results of various aggregate property tests are discussed in the following sections. 3.3.1 Gradation Fresh and hardened properties of concrete can be affected by the gradation of aggregate. Improper gradation can affect the air content, slump, and result in excessive voids in the hardened concrete. Sieve analyses of coarse and fine aggregates were performed according to CSA A23.2-2A (CSA 2009). The upper and lower limits in CSA A23.2-2Awere used to check the gradation standard of different types of aggregates used in this study. The fine and coarse natural aggregate has a maximum nominal size of 5 mm and 20 mm, respectively. Figures 3.1a and 3.1b show the aggregate gradation curve of natural fine and coarse aggregates, respectively. These two graphs illustrate that both the fine and coarse natural aggregates are well graded and within the CSA limit.      37 0204060801001 10 100Passing (%)Sieve Opening (mm)CSA LowerCSA UpperCoarse NA(b)0204060801000.01 0.1 1 10Passing (%)Sieve Opening (mm)CSA LowerCSA UpperFine NA(a)0204060801001 10 100Passing (%)Sieve Opening (mm)CSA LowerCSA UpperRCA(c)                 Figure 3.1 Sieve analyses of (a) Natural fine aggregate, (b) Natural coarse aggregate, and (c) Recycled coarse aggregate (RCA) In this study, various percentages of RCA were used as a substitute of natural coarse aggregate. It was also critical to check whether its gradation falls within the CSA limits as their parent concrete source was unknown.  The gradation of RCA is illustrated in Figure 3.1c. This can be noted that RCA has a well gradation and has a nominal maximum size of 14 mm.   3.3.2 Bulk Density, Specific Gravity, and Moisture content of Aggregates The specific gravity (relative density) and absorption capacity of natural and recycled coarse aggregates were determined according to CSA A23.2-12A (CSA 2009). The results of different types of aggregate properties tests are shown in Table 3.1. The specific gravity of RCA    38 was 2.48 which was lower by 6% than that of natural coarse aggregate. It is due to the adhered mortar of RCA. The adhered mortar also increased the absorption capacity of RCA which was 3.75 times higher than that of natural coarse aggregate. The bulk density of natural and recycled coarse aggregates were 1576.8kg/m3 and 1374.8 kg/m3, respectively. The bulk density test was performed according to CSA A23.2-10A (CSA 2009).  Moisture content of RCA was calculated to be 1.9% which was higher than that of natural coarse aggregate (0.22%). Table 3.1: Properties of aggregates   Bulk dry specific gravity  Bulk SSD specific gravity  Apparent specific gravity Bulk density (kg/m3) Absorption capacity   (%) Moisture content (%) Natural coarse aggregate 2.62 2.65 2.71 1576.8 1.2 0.22 RCA 2.37 2.48 2.66 1374.8 4.5 1.9 Fine aggregate 2.54 2.64 2.77  - 1.99 4.14 Procedure outlined in CSA A23.2-6A (CSA 2009) was followed to determine the relative density and absorption capacity of fine aggregate. The bulk SSD specific gravity and moisture content of fine aggregate was 2.64 and4.14%, respectively. 3.4 EXPERIMENTAL PROCEDURE The concrete mix design used in this study was provided by OK Builders Supplies Ltd. In the case of 25 MPa ready mix concrete, the effective water-cement ratio of the mix was 0.56.  Coarse aggregate, fine aggregate, cementitious materials, water, water reducer, and air entraining admixture were used to produce different concrete mixes. The concrete mixes also utilized a 20% cement (GU cement) replacement with fly ash (Class F) that acts as a cementitious material thus decreasing the amount of cement required, in turn lowering the cost and CO2 embodied in the concrete. Siddique (2003) investigated the chemical composition of Class F fly ash. The    39 chemical composition of Class F is given in Table A1 (Appendix-A). The use of fly ash also aids in the sulphate and chloride resistance by forming a tighter concrete matrix thereby reducing the permeability and rate of chemical infiltration. Glenium 3030NS (BASF 2013) and Micro Air (BASF 2013) were used as water reducing admixture and air entraining admixture, respectively. Table3.2 shows the mix proportions for the various designs that were tested for this study. Table 3.2: Mix proportions Mix component Mix 1 Mix 2 Mix 3 Mix 4 Mix 5 Mix 6 (Control)          (30% RCA) (40% RCA) (50% RCA) (75% RCA) (100% RCA) Cementing materials GU cement 208 208 208 208 208 208 Fly ash 52 52 52 52 52 52 Fine aggregate Natural aggregate 807.6 807.6 807.6 807.6 807.6 807.6 Coarse aggregate Natural aggregate 1040.7 728.5 624.4 520.4 260.2 0 Recycled aggregate 0 312.2 416.3 520.4 780.5 1040.7 Water   150 150 150 150 150 150 Water reducer  Glenium 3030 468 ml 468 ml 468 ml 468 ml 468 ml 468 ml Air entraining admixture Micro air 120 ml 120 ml 120 ml 120 ml 120 ml 120 ml  As presented in Table 3.2, six different concrete mixes were designed with varying levels of RCA replacement. The RCA content used to replace a portion of the natural coarse aggregate varies from 30-100 % with a 0% RCA replacement as the control mix (Mix-1). Control mix made with conventional aggregate (NA) was required to facilitate the proper comparison between RCA concrete and NAC. The control specimens also facilitated as a reference for comparing the durability performance and quantify any change in the concrete specimen?s    40 degradation with increasing RCA content. All other mix components remained constant to ensure that the test results only reflect the effect of changing the RCA proportions. The mechanical properties of concrete are only discussed in this chapter and the next chapter (Chapter 4) covers the durability aspects of  RAC. To investigate the mechanical property of concrete, compressive strength test was done according to CSA A23.2-9C (CSA 2009). Moreover, fresh concrete properties were investigated by performing slump and air content test. For each concrete batch produced, it was decided that 12 cylinders were to be cast to allow for 7, 28, 56, and 148 days test for compressive strength test. As a result, a total of 72 concrete cylinder specimens were produced.  According to CSA A23.2-3C (Clause 7) (CSA 2009), ?100 x 200 mm cylinder specimens were cast. Concrete mixing was performed according to the requirements outlined in CSA A23.2-2C (CSA 2009). Mixer drum was used for mixing concrete ingredients. The water reducing admixture and air entraining admixture were added to water just before it was added to the mixer drum. At first, half of the mixing water was added with coarse aggregates into the mixer drum and then it was started for mixing. Fine aggregate, GU cement, fly ash along with rest of the water were added into the mixer and was allowed to run for further 3 minutes. After that, it was rested for another 3 minutes followed by an additional2 minutes of finial mixing.  Each mix?s fresh concrete slump was measured following the guideline mentioned in CSA A23.2-5C (CSA 2009) using a standard slump cone. Air content of fresh concrete was measured according to CSA A23.2-4C (CSA 2009).Fresh concrete samples for slump and air content tests were taken from the same batch to maintain the consistency of results of fresh concrete properties.     41 The compressive strength tests specimens were cured inside a moisture monitored curing chamber according to CSA A23.2-3C (Clause 7.3.1) (CSA 2009). Those concrete cylinders were demolded after 24 hours of casting and were then placed immediately in the automated humidity controlled curing chamber. The cylinders were taken out from the curing chamber and dried  before testing on the specified dates. 3.5 RESULTS AND DISCUSSION 3.5.1 Results of fresh concrete properties The 25 MPa concrete mix was designed for a 90 mm target slump. The results of the fresh concrete properties are provided in Table 3.3. This table shows that the slump value of different concrete mixes remained unaffected due to the utilization of different replacement levels of RCA. The CSA requirement of air content for the 14-20 mm nominal maximum sizes of aggregates is 5-8% for category-1. From Table 3.3it can be seen that the air content of Mix- 1 (control) and Mix-6 (100% RCA) were 5.7% and 5.5%, respectively.  Table 3.3: Properties of fresh concrete   Mix 1 Mix 2 Mix 3 Mix 4 Mix 5 Mix 6 Slump (mm) 110 110 110 100 100 95 Air content (%) 5.7 5.8 5.8 6 5.6 5.5 [Mix-1 = Control, Mix-2 = 30% RCA, Mix-3 = 40% RCA, Mix-4 =50% RCA, Mix-5 =75% RCA, and Mix-6 =100% RCA] 3.5.2 Results of Compressive Strength The cylinder compression tests were conducted after 7, 28, 56, and 148 days of curing and the results are presented in Figure 3.2 and Table 3.4. Compressive strength versus age graph is depicted in Figure 3.2 illustrating that as the percentage of RCA replacement increases the compressive strength decreases. Inadequate hydration and weak interfacial transition zone (ITZ)    42 between the components of concrete cluster caused by the high amount of attached mortar on the surface of recycled aggregate are the major reasons behind the strength degradation of RAC with the increased replacement level of RCA (Yang et al 2008, Tu et al. 2006). It is also influenced by the low bulk density and adhered mortar of RCA. On the other hand, 148 days? compressive strength of Mix-2 (30% RCA replacement) was higher than Mix-1 (control). Mix-1 compressive strength was 24.1 MPa at 148 days which was 5.5% less than the compressive strength of Mix-2 at the same age. This was due to the rough texture and higher absorption capacity of RCA. Presence of adhered mortar increases the absorption capacity of RCA and crushing of demolished concrete makes aggregate surface rough. Both of these properties of RCA lead to better interlocking and bonding between the RCA and cement paste as compared to natural aggregate concrete (Salem and Burdette 1998, Etxeberria et al. 2007). Within the considered time period the highest compressive strength was gained by Mix-2 (25.5MPa) and the lowest was found for Mix-4 (19.8 MPa). The strength gaining pattern of Mix-5 and Mix-6 were almost similar except at the age of 28 days the compressive strength of Mix-6 was 9.3% lower than that of Mix-5. Table 3.4 shows the results of compressive strength at different test days and their percent difference in strength gain with respect to NAC (Mix-1) at the same respective age. The percent difference in compressive strength between the Mix-1 (control mix) and Mix-6 (100% RCA replacement) at 148 days was 14.5 %. This illustrated the true loss in strength as a result of replacing RCA with NA.As the replacement level of natural aggregate by RCA increases, the percent difference also increases.     43  Figure 3.2 Compressive strength of concrete made with different replacement levels [Mix-1 = Control, Mix-2 = 30% RCA, Mix-3 = 40% RCA, Mix-4 =50% RCA, Mix-5 =75% RCA, and Mix-6 =100% RCA]  Table 3.4: Compressive strength results of different concrete mixes   Mix-1 Mix-2 Mix-3 Mix-4 Mix-5 Mix-6 (MPa) (MPa) (MPa) (MPa) (MPa) (MPa) 7 days 12 13.4(11.7%) 9.6(-19.6%) 10.1(-15.5%) 8.7(-27.8%) 8.9 (-25.4%) 28 days 17.1 16.5(-3.6%) 16.3(-4.8%) 14.7(-14.2%) 15.1(-11.6%) 13.7(-19.9%) 56 days 23 22(-4.2%) 18(-21.6%) 18.9(-17.9%) 17.7(-23%) 16.6(-27.8%) 148days 24.1 25.5(5.8%) 19.9(-17.4%) 19.8(-17.8%) 21(-12.9%) 20.6(-14.5%) [Mix-1 = Control, Mix-2 = 30% RCA, Mix-3 = 40% RCA, Mix-4 =50% RCA, Mix-5 =75% RCA, and Mix-6 =100% RCA] Note: the value in braces represents the percent difference in strength gain with respect to Mix-1 In contrast, the percent difference of different concrete mixes decreased at 148thday which indicates that the RCA aggregate concrete is more favorable than NAC while considering its long term strength development. This long term strength is contributed by the unhydrated cement paste on the exterior surface of RCA (Khatib 2005). Besides, it may be attributed by the absorbed water of RAC that may work as a source of water to complete the hydration process (Yang et al 2008).  01020300 30 60 90 120 150Compressive strength (MPa)Age (days)Mix-1 Mix-2 Mix-3Mix-4 Mix-5 Mix-6   44 Statistical analyses were carried out to evaluate the variation of the compressive strengths of six different mixes. Figure 3.3 presents the box plot of data found from the 7, 28, 56, and 148 day compressive strength of RAC made with different RCA replacement levels and its comparison with control mix (Mix-1). Figure 3.3 shows the variation of compressive strengths in individual mix proportion where the numerical range (maximum and minimum values) of data is represented by height. The boxes represent the 1st quartile through 3rd quartile. The horizontal line inside the box represents the 50th percentile (median value).It can be observed that the initial strength test results (7days) are almost symmetrically/normally distributed for all mixes. In the case of Mix-1, initially (7, 28, and 56 days) it  showed symmetrical distribution but later negative skewness was observed. On the other hand, Mix-3 experienced negative skewness for 28 and 56 days but later it experienced positive skewness.  Figure 3.3 Variation in compressive strength of different concrete mixes at the age of 7, 28, 56, and 148 days [Mix-1 = Control, Mix-2 = 30% RCA, Mix-3 = 40% RCA, Mix-4 =50% RCA, Mix-5 =75% RCA, and Mix-6 =100% RCA] 51015202530Mix-1 Mix-2 Mix-3 Mix-4 Mix-5 Mix-6Compressive strength (MPa)    45 3.5.3 Failure Pattern of Concrete Failure pattern of RAC made with different RCA were also investigated according to CSA A23.2-9C (CSA 2009) and compared with NAC. The concrete specimens after the compressive strength tests are shown in Figures 3.4a-f where different types of failure patterns were observed. Shearing type of failure was observed for Mix-1,2, and 3. As the RCA replacement level was increased beyound 40%, the failure pattern also changed. Mix- 4 and Mix-5 experienced cone and split  type failure. In these cases, the concrete was trying to split tangentially or radially and it coulde bedue to the weak interfacial transition zone of RACwith increased RCA replacement levels. In each case it was observed that the failure was mainly due to mortar failure.  Figure 3.4 Failure pattern of different concrete mixes (a) Mix-1, (b) Mix-2, (c) Mix-3, (d) Mix-4, (e) Mix-5, and (f) Mix-6 [Mix-1 = Control, Mix-2 = 30% RCA, Mix-3 = 40% RCA, Mix-4 =50% RCA, Mix-5 =75% RCA, and Mix-6 =100% RCA] (a) (b) (c)(e) (f)(d)   46 Chapter  4: DURABILITY OF RAC MADE WITH DIFFERENT RCA REPLACEMENT LEVELS: SULPHATE AND CHLORIDE ATTACK  4.1 GENERAL Durability of concrete was occasionally considered as a design criteria before 1970s. At that time government officials, design professionals, developers, and builders rarely considered durability property in a construction project. Later in 1980, ?concrete cancer? became a popular phrase in the society and media. This influenced peoples to grab their attention towards the durability performance of concrete. As a response, many countries reviewed and incorporated some changes in their code such as US (NIST 2013), Australia (QCL group 1999), and Europe (Foli? 2009). The deterioration of concrete structures, exposed to aggressive or harsh environments, is a vital fact that affects the durability of civil infrastructure. This reduces the life span of civil infrastructures which consequently increases the maintenance cost. Durability works as a key factor for enhancing the performance and life cycle of concrete structures. The use of RCA in concrete makes it more susceptible to degradation as these aggregates are more porous in nature than the natural coarse aggregate concrete. Porosity of RCA raises a concern about the durability performance of RAC. At this point there is little published material on the durability performance of RAC. However, before any commercial application, the ready mix industry would like to ensure that RAC can withstand the harsh environmental exposures. This chapter assesses the effects of sulphate attack and cyclic wetting and drying along with chloride exposure of 25MPa RAC made with different RCA replacement levels.    47 4.2 TEST METHOD TO ASSESS THE SULPHATE RESISTANCE OF RAC Groundwater, industrial effluents, sea water, soil and decaying organic matter are potential sources of sulphate and affect the performance of concrete. Moreover, RCA itself can work as a potential source of sulphate attack since these aggregates are usually collected from landfill where they can easily get contaminated. The cement paste?s composition and permeability are key factors in terms of resisting sulphate ions ingression into concrete. Once the dissolved sulphate ions enter into concrete, sulphate ions attack in the form of chemical reaction which causes strength degradation along with expansion, cracking, and spalling (Monteiro et al. 2000). The mechanism of sulphate attack involves the reaction of portlandite (CH), untreated C3A (Tri calcium aluminate), and monosulphate along with alkali sulphates such as sodium sulphate (Na2SO4) through the production of gypsum and ettringite causing disintegration and damage to the concrete. The formation of gypsum and ettringite cause expansion in concrete and cause strength loss. Calcium silicate hydrate (C-S-H) is the main contributing element to the strength of hardened concrete and the loss of C-S-H during long time sulphate exposure is one of the reasons behind the degradation of concrete strength (Monteiro et al. 2000, Bassuoni and Nehdi 2008). Currently there is no guideline or standard to assess the sulfate resistance of concrete. This is due to the fact that the delayed visual damage along with the expansion usually shows up after several years even when those are exposed to high concentrated sulphate solutions. Here, the sulphate resistance of RAC with different RCA replacement levels was assessed following an accelerated test method done by California Department of Transportation (Monteiro et al. 2000). Monteiro et al. (2000) used this method to investigate the sulphate resistance of five different types of cement. This accelerated test method used by Monteiro et al. (2000) can represent the    48 field conditions where their results obtained from this method could yield similar behavior as found in field conditions. Moreover, ASTM C1012 and C452 (ASTM 2012) cannot represent the real deterioration pattern of concrete (Mehta et al.1979) since these guidelines are for mortars. It is very important to investigate the sulphate resistance of RAC concrete due to the presence of interfacial transition zone which differentiate it from mortar. In this chapter, sulphate resistance of 25MPa RAC made with different RCA replacement levels (Mix-2 to Mix-6) was investigated and compared to NAC (Mix-1) following the accelerated test method. The fresh and hardened properties of these mixes have already been discussed in Chapter 3. Almost similar type of experimental approach was followed for evaluating the sulphate resistance of RAC by Shayan and Xu (2003). In accelerated test method, sulphate resistance of RAC was measured in terms of the strength loss (compressive strength loss) along with expansion during the sulphate exposure. Expansion only reveals the ettringite formation due to sulphate attack. However, loss in strength indicates that the cracking occurred due to the gypsum and ettringite formation during the sulphate exposure (Cohen and Mather 1991, Mehta and Gjorv 1974).  In this study, the sulphate resistance performance was evaluated using 75?150 mm cylinders. This size was chosen to maximize the surface area to volume ratio. The increased surface area to volume ratio helped accelerate the effects of the sulphate by increasing the exposure area. Prism and bar specimens can represent the length expansion more accurately due to their geometry compared to cylindrical specimens since it has more surface area compared to its volume. Due to unavailability of such molds we had to work with cylindrical specimens. Cylinders were cast along with the casting of previously mentioned specimens in Chapter 3. These cylinders were demolded and then moist cured for seven days in the same moist curing chamber as mentioned in Chapter 3before being placed in the sulphate bath. Moist curing was    49 done for 7 days to replicate the field condition. Before being placed in the sulphate bath the diameter and height of each cylinder were measured. Cylinders from each mix were broken under compression to measure the 7thday strength of that mix. Sulphate bath was prepared one day before the use with 5% sodium sulphate (Na2SO4) solution and stored at 23 ? 2?C. In the storage container the ratio of the volume of sulphate solution to the volume of concrete cylinder was 4? 0.5.The pH of sulphate solution was always maintained around 7 which is close to pH (7.2) of typical field condition. Sulfuric acid (H2SO4) was added into the sulphate bath to maintain the pH of sodium sulphate solution. During the testing period pH was monitored twice everyday with pH strips. As a result, the concentration of sulphate ion remained constant over the testing period. Every week all the specimens were taken out from the sulphate bath to measure the dimension and height of the cylinders. The volume and height changes were determined using the following equations % Volume change,                 ? ? 100% ????iitVVVV                     (4.1) where Vi = average initial volume of cylinder (mm3); and Vt = average  volume of cylinders after a prescribed exposure period (mm3). % Height change,                   ? ? 100% ????iitHHHH  (4.2) where, Hi = average initial height of the cylinder (mm); and  Ht = average height of the cylinder after a prescribed exposure period (mm).    50 Visual inspection was also done to determine any sign of deterioration on the specimen. Compressive strength test was done at the age of 28days, 56 days, and 148 days to evaluate the loss of strength during the sulphate exposure. The used sodium sulphate solution was discarded after taking the measurement of cylinders at certain intervals such as at 56 days, 90 days, and 148 days. All the specimens were kept inside the sulphate bath and the changes were monitored on a regular basis until just before the testing at specified dates. Figure 4.1 shows one of the storage containers used to soak the specimens in the sulphate solution.   Figure 4.1 Sulphate bath used for sulphate exposure test  4.3 TEST METHOD TOASSESS THE CHLORIDE ION INGRESSION INTORAC The durability of concrete is greatly affected by the ingress of fluid inside the concrete. Chloride ions ingress into RAC can significantly affect the durability of RAC as recycled aggregate porosity is higher than that of natural aggregate. In order to study the chloride ion ingression into 25 MPa RAC (Mix-2 to Mix-6) and NAC (Mix-1), cyclic wetting in sodium chloride (NaCl) solution and subsequent drying was considered. In North America NaCl is    51 widely used as a de-icing salt on a regular basis during winter. Therefore, a high concentration of sodium chloride solution forms on concrete surface and subsequently it penetrates through the concrete. It is well documented that cyclic wetting and drying increases the chloride ion ingression into concrete (Moukwa 1990) and thus accelerates the effects to yield faster test results (Yeomans 1994, Hong and Hooton 1999, Hong 1998). For chloride exposures the specimen size selected was 100x200mm cylinders. All the test specimens were cast during the casting of other specimens used for the fresh and hardened properties of 25MPa concrete. The specimens were demolded and cured inside the moist curing chamber (relative humidity 100%) for 28 days before being placed in 5% sodium chloride solution for six hours. After 6 hours of wetting those cylinders were taken out from chloride bath and placed on a shelf at normal room temperature (21?C) and relative humidity of 65% for drying. Those cylinders were left there for 18 hours for drying. That means one cycle took 24 hours as shown in Figure 4.2. McCarter and Watson (1997) found that the wetting rate is faster than drying rate and in some situations it is 3 to 7 times faster. Sodium chloride solution at a concentration of 5% was prepared using locally available table salt and it was oven dried at 110?C before being mixed with water. To investigate the chloride ion ingression concentration 1, 4, 9, 16, 28, 90, and 120 cycles were considered. After being subjected to these numbers of cycles, chloride concentration was measured using Ion Chromatography test. Ion Chromatography test is usually used for water chemistry analysis. In this method ion concentration is measured by separating them based on their interaction with resin. In this method small discs were cut from the surface of concrete cylinder using chisel and hammer. Then these small discs were pulverized using a pulverizer. The powdered concrete was then    52 analyzed using ?Ion Chromatography Test?. The chloride concentration was found in units of parts per million (ppm).   Figure 4.2 Sequence of one wet-dry cycle Compressive strength test was also done after being subjected to 1, 4, 9, 16, 28, 90, and 120 wetting and drying cycles with 5% sodium chloride solution. This was done to investigate whether chloride ion ingression has any effect on the strength properties of RAC. 4.4 RESULT AND DISCUSSION 4.4.1 Results of Sulphate Resistance Test The sulphate durability test was based on the strength loss as well as the changes in volume and height of the specimen which were measured over time. This indicated how reactive the specimens were to sulphate and whether one mix was more reactive than the other, thereby making it less durable. The compressive strengths of concrete with different RCA replacement levels at different interval of time under sulphate exposure condition are shown in Figure 4.3. The bar diagram reveals that even under sulphate exposure up to 56 days, the compressive strengths of all mixes were increasing and later a decreasing phenomenon was observed by all mixes. Strength increase does not indicate anything about sulphate attack. It only reveals that WettingDrying   53 cement continues to hydrate in sodium sulphate solution during that time and the pores get filled up with hydrated products along with gypsum and ettringite. Further formation of these products are responsible for the micro crack development and degradation of concrete strength in the later period as these products have a considerably greater volume than the compound they replace during the reaction in sulphate exposure (Neville 2011). The results also indicate that as the RCA replacement increases the compressive strength decreases. The compressive strength of Mix-1 at the age of 148 days under sulphate exposure was 14.5 MPa which was 9.8% higher than that of Mix-2 (13.2 MPa).   Figure 4.3 Sulphate Compressive strength of concrete made with different RCA replacement level under sulphate exposure  [Mix-1 = Control, Mix-2 = 30% RCA, Mix-3 = 40% RCA, Mix-4 =50% RCA, Mix-5 =75% RCA, and Mix-6 =100% RCA] The relative change in compressive strength (?Cs) found at the age of 148 days after 141 days of sulphate exposure is shown in Figure 4.4 . The change in compressive strength due to sulphate exposure was measured as a percentage of the strength of each cylinders found after 148 days of moist curing (C148m). The equation is given below: 0510152025307 28 56 148Compressive strength (MPa)Age (days)Mix-1 Mix-2 Mix-3Mix-4 Mix-5 Mix-6   54 ? ? 100%148148148 ????mmss CCCC         (4.3) where, C148s = average initial compressive strength of cylinders under sulphate exposure at the age of 148 days (141 days sulphate exposure) (MPa) and  C148m = average  compressive strength of moist cured cylinders at the age of 148 days (MPa) Figure 4.4 shows that after 141 days of sulphate exposure, Mix-6 showed the highest strength reduction (48%) among the six considered mixes. This is due to the formation of micro crack for the production of gypsum and ettringite. Presence of old interfacial transition zones also significantly influences this phenomenon. Mix-1 and Mix-3 performed almost in a similar fashion. Only exception was Mix-2 (48%) which showed the highest amount of percent strength reduction as found for Mix-6 though its RCA replacement level was less than the other different replacement levels of RCA.  Figure 4.5 presents the box plot of data found from the 148 days compressive strength of moist cured concrete specimens and its comparison with specimens exposed to sulphate for 141 days. It can be seen that after being exposed to sulphate for 141 days, substantial strength reduction was observed due to sulphate exposure. Mix-1, Mix-2, Mix-3, Mix-4 showed positive skewness for moist curing specimens where Mix-1, Mix-3 exhibited negative skewness while being exposed to sulphate. It can be also observed that the strength ranges for sulphate exposed RAC specimens substantially decreased compared to moist cured specimens, whereas there was no change in the case of Mix-1.      55  Figure 4.4 The percent (%) change in compressive strength of concrete made with different RCA replacement levels at the age of 148 days under sulphate exposure with respect to the compressive strength of moist cured specimens at the same respective age [Mix-1 = Control, Mix-2 = 30% RCA, Mix-3 = 40% RCA, Mix-4 =50% RCA, Mix-5 =75% RCA, and Mix-6 =100% RCA]   Figure 4.5 Compressive strength of various concrete mixes [ a = being exposed to sulphate for 141 days, b = moist curing cylinders at the age of 148 days] [Mix-1 = Control, Mix-2 = 30% RCA, Mix-3 = 40% RCA, Mix-4 =50% RCA, Mix-5 =75% RCA, and Mix-6 =100% RCA] -60 -50 -40 -30 -20 -10 0Mix -1Mix -2Mix -3Mix -4Mix -5Mix -6% Change in compressive strength0102030Mix-1 Mix-2 Mix-3 Mix-4 Mix-5 Mix-6Compressive strength (MPa)abaaaaabbbbb   56 As mentioned earlier the specimens used for sulphate testing were measured on a weekly basis to monitor the physical changes occurring over time.  The height change was increasing with the increased level of RCA replacement. The importance of the height change is that it is the larger dimension of the cylinder so it will experience more change than the diameter. Figure 4.6a shows the variation in terms of height change experienced by the specimens over time under sulphate exposure. The percent (%) height change of Mix-3 and Mix-4 were similar and lower than Mix-5 and Mix-6 at 56th day. The crumbling of concrete cylinders of Mix-4 was responsible for this similar value. At the age of 148 days, the highest change was observed for Mix-6 (0.2%) and it was 48%, 43%, 38%, 33%, and 18% higher than the percent height change of Mix-1, Mix-2, Mix-3, Mix-4, and Mix-5, respectively. This is due to increased porosity and old interfacial transition zone of RCA.  Figure 4.6 (a) Height change (%)  (b) Volume change (%) of concrete cylinders under sulphate exposure condition [Mix-1 = Control, Mix-2 = 30% RCA, Mix-3 = 40% RCA, Mix-4 =50% RCA, Mix-5 =75% RCA, and Mix-6 =100% RCA] 00.070.140.2128 56 148Height change (%)Age(days)Mix-1 Mix-2 Mix-3Mix-4 Mix-5 Mix-6(a)00.10.20.30.40.50.628 56 148Volume change (%)Age (days)Mix-1 Mix-2 Mix-3Mix-4 Mix-5 Mix-6(b)   57 Similar trend is observed for the results in terms of change in volume as seen in the height change where the volume change increases as the RCA content increases.  Figure 4.6b shows the average volume change for each mix over the considered time under 5% sodium sulphate solution. RAC made with different RCA replacement levels experienced higher volume expansion than the NAC (Mix-1). At the age of 28 days, Mix-6 showed the highest volume change which was 20% higher than that of Mix-5 (0.125%).From Figure 4.6b it can be observed that there was a significant expansion in the volume of concrete cylinders with increased period of time under sulphate exposure. Mix-2 experienced 3.8% higher volume change than Mix-1 and 1.2%, 2.4%, and 6.9% lower than that of Mix-3, Mix-4, and Mix-5, respectively at 148thday. Highest volume change of 0.495% was observed by Mix-6 at 148th day.  It was also observed during the sulphate testing that some of the cylinders started to experience some discoloration.  A faded yellow color was appearing on the top of the cylinders as shown in marked area in Figure 4.7.  This indicates that the aesthetics of concrete must also be taken into consideration while being exposed to sulphate attack.  Figure 4.7 Discoloring during exposed to sulphate    58 4.4.2 Results of Chloride Ion Ingression into RAC The compressive strength test results of RAC with different RCA replacement levels after exposed to cyclic wetting and drying with sodium chloride solution for 28, 90, and 120 cycles are shown in Figures 4.8a-c. Standard moist cured cylinders? compressive strength results are also shown in this figure for evaluating the change in strength over the test period. Results indicate that the strength remains unaffected by cyclic chloride exposure.  Figure 4.8 Compressive strength of concrete after being exposed to chloride solution (a) 28 cycles (at 56thday), (b) 90 cycles (at 118thday), and (c) 120 cycles (at 148thday) [Mix-1 = Control, Mix-2 = 30% RCA, Mix-3 = 40% RCA, Mix-4 =50% RCA, Mix-5 =75% RCA, and Mix-6 =100% RCA] 09182736Mix -1 Mix -2 Mix -3 Mix -4 Mix -5 Mix -6Compressive strength (MPa)Standardard moist curingCyclic wetting and drying with chloride solution09182736Mix -1 Mix -2 Mix -3 Mix -4 Mix -5 Mix -6Compressive strength (Mpa)Standardard moist curingCyclic wetting and drying with chloride solution09182736Mix -1 Mix -2 Mix -3 Mix -4 Mix -5 Mix -6Compressive Strength (MPa)Standardard moist curingCyclic wetting and drying with chloride solution(b)(c)(a)   59 Figure 4.9 shows the box plot of data found from the 148 day compressive strength of standard moist curing specimens and its comparison with chloride exposure specimens after being subjected to 120 wet-dry cycles. Positive skewness was observed for Mix-3 and Mix-4 after being exposed to 120 wet-dry cycles. The highest difference in terms of maximum and minimum values was observed for Mix-5 of standard moist curing condition.   The results obtained from the ion chromatography test were divided by the surface area of the cylinder to get the chloride ion concentration per unit area of concrete and are shown in Table A2 (Appendix-A) and Figure 4.10. This representation approach of chloride concentration is different from pervious researchers? approach. The results illustrate that the concentration of chloride ion increased with the increased number of RCA replacement levels. It was found that chloride ion concentration significantly increased with increased number of wetting and drying cycles. Table A2 indicates that no chloride concentration was found for moist curing samples. Initially chloride ion ingression rate was higher and for Mix-6 it was the highest.  Figure 4.9 Compressive strength of concrete at the age of 148 days [Mix-1 = Control, Mix-2 = 30% RCA, Mix-3 = 40% RCA, Mix-4 =50% RCA, Mix-5 =75% RCA, and Mix-6 =100% RCA] 15202530Mix-1 Mix-2 Mix-3 Mix-4 Mix-5 Mix-6Compressive strength (MPa)   60 From Figure  4.10 it can be observed that after being exposed to 90 wet dry cycles Mix-2?s chloride concentration is higher than Mix-1 (91.59 ppm/m2).  This can be attributed to the presence of attached mortar and pores of RAC.  The difference in chloride concentration between Mix-1 and Mix-2 after exposed to 90 wet dry cycles was 17.96 ppm/m2.It can be seen that the chloride ion concentration value of Mix-1 after being expose to 4 wet dry cycles was 1.56 times higher than that of first cycle and the value of chloride ion concentration gradually increased with the number of cycles which was 120.96 ppm/m2 after 120 cycles. Mix-2?s chloride ion concentration was 2.1% higher than Mix-1 after being subjected to 120 cycles. After 120 wet dry cycles the chloride ion concentration of Mix-6 was 0.8% and 6.8% higher than that of Mix-5 and Mix-4, respectively. This reveals that permeability of RAC increases with the increased amount of RCA replacement, which is due to the presence of old interfacial transition zone (ITZ) and attached mortar on the surface of recycled aggregate.  Figure 4.10 Concentration of chloride ions per unit surface area of concrete cylinder  [Mix-1 = Control, Mix-2 = 30% RCA, Mix-3 = 40% RCA, Mix-4 =50% RCA, Mix-5 =75% RCA, and Mix-6 =100% RCA 0701402101 cycle 4 cycles 9 cycles 16 cycles 28 cycles 90 cycles 120 cyclesChloride ion concentration (ppm/m2)Mix -1 Mix -2 Mix -3Mix -4 Mix -5 Mix -6   61 Chapter  5:INFLUENCE OF REPEATED RECYCLED COARSE AGGREGATE ON THE FRESH AND HARDENED PROPERTIES OF CONCRETE  5.1 GENERAL The consumption of natural aggregate is significantly increasing with the increased production and utilization of concrete in the construction sector. Construction industry is one of the largest consumers of the natural aggregate. Every year 15 billion tonnes of concrete are produced throughout the world which means 2tonnes of concrete per inhabitant per year (Barcelo 2013). In order to fulfill this huge demand, the sources of good quality natural aggregates are considerably declining all over the world. Each year ten to eleven billion tonnes of aggregate are being used all over the world (Smith 2009). Approximately three billion tonnes of aggregates are being produced and used in European Union countries per year (European Environment Agency 2008). Rapid and increased use of natural aggregate raise a huge concern regarding the possible unavailability of natural aggregate in the near future. On the other hand, a significant portion of infrastructures are now reaching or getting close to the end of their service life. A recent study (Mirza 2007) showed that about 30 percent of the municipal infrastructures in Canada are more than 85 years old and around 80percent of the infrastructures have passed their expected design life. An economic study revealed that a huge amount of investment is required for the repair and maintenance of the existing civil infrastructure in Canada which would cost almost $130 billion where most of those structures are aging and nearing the end of their life span (Canadian Sailings 2011).     62  New public infrastructure projects of $12-billion were announced by the federal government to replace the old and deficient infrastructure by new construction (CEAP-Budget 2009). This replacement will increase the amount of construction and demolition (C&D) waste already found in landfill. If this replacement process is constantly going on, soon there will be a scarcity of available land spaces to dump C&D waste material among which 52% is concrete waste (Michael et al. 2003). The replacement process of structure is not only raising a dumping issue but also becoming a threat to the environment. Many countries throughout the world have been suffering from lack of proper dumping place. Initiatives have been taken to minimize the use of natural aggregate and landfilling, for instance, heavy taxes have been introduced to discourage the disposal of C&D waste. Recycling or reusing of demolished concrete is a viable option which can significantly decrease the burden of landfill.  Large scale recycling can deplete the consumption of limited resources like natural aggregate as well as play a vital role in solving the waste disposal problem. Researchers can not only think about the current condition, they also need to envisage the future situation from their curious/intuitive perceptions because the wide application of RCA can result in new challenges. One has to think about the next generation of this recycled concrete, i.e. what happens when this recycled concrete structures need to be demolished and what about its disposal issue. Similar steps can be taken i.e. the idea of ?repeated recycled coarse aggregate? to be used in concrete production can be a viable solution to the growing problem regarding the C&D waste disposal and limited source of natural coarse aggregate. In this chapter, the fresh and hardened properties of sustainable recycled concrete made with repeated recycled coarse aggregates are discussed. Although previous research has been conducted for the use of RCA in concrete, the use of repeated recycled coarse aggregate is a new research area and has been found, in this study, to have exciting potential. Proper    63 investigation about this new generation concrete is very necessary to understand the behavior of its mechanical and durability properties. Moreover, this will pave the way for future research opportunities and new challenges to the researchers. Most importantly, repeated recycled coarse aggregate will reduce the load on the landfill and decrease the use of natural aggregate thus, offsetting related extraction, processing, transportation, and environmental loads. Different types of aggregate properties and mechanical behavior of recycled concrete made with three different generations of repeated recycled coarse aggregates are covered in this chapter. 5.2 SOURCES OF AGGREGATES This study considers the use of100% RCA to be used repeatedly in first, second and third generation (i.e. RCA was recycled 3 times over its life span) of concrete production and compares the mechanical behavior of produced concrete among them. The target was to produce 32 MPa concrete with different generations of repeated RCA. Aggregates were collected from the same source as already mentioned in Chapter 3.  This time recycled coarse aggregates were collected from a demolished bridge. Several screening, sieving, and washing were done to remove these impurities. Recycled coarse aggregate was sieved to discard particle size smaller than 5mm. 5.3 PRODUCTION OF REPEATED RECYCLED COARSE AGGREGATE This study evaluates the performance of first, second, and third generation of recycled concrete made with 100% RCA and compares them with that of NAC. 100% replacement level was considered to boost up the confidence level of construction industry for application of RCA in new concrete production. If the performance of concrete made with 100% replacement level is comparable to NAC, than definitely all other replacement levels will perform better and increase    64 the application of RCA. First (1st) generation recycled aggregate concrete (RC1) was produced using 100% RCA which were collected from OK Builders Winfield pit. After curing for 56 days, this concrete was crushed and went through several screening and crushing stages to produce second (2nd) generation repeated recycled aggregate. The second generation recycled aggregates were sieved and washed to eliminate the smaller sized particles (less than 5mm) from the stockpile. This second (2nd) generation repeated recycled coarse aggregate (RCA2) was used to produce recycled concrete which is described as second (2nd) generation repeated recycled concrete (RC2) in this study. Then RC2 was cured for another 56 days, and then crushed and recycled to produce the third (3rd) generation recycled concrete aggregate. The third (3rd) generation repeated recycled coarse aggregates (RCA3) were sieved to remove smaller particles (less than 5 mm). Then those coarse aggregates were washed out with water to remove other impurities. Third (3rd) generation repeated recycled coarse aggregate (RCA3) was used to produce third (3rd) generation repeated recycled concrete (RC3).  The flow diagram of production process of different generation recycled concrete is shown in Figure 5.1. Since different generations of repeated recycled concrete were produced using sequential crushing of different generations of concrete, it was very difficult to estimate the amount of recycled coarse aggregate for producing RC1. Almost 1m3of concrete (more than 480 cylinders and 29 beams) was cast using RCA1 to meet the aggregate requirement for the third generation where 100% natural aggregates were replaced by RCA in all generations. After curing, RC1 was taken to the crushing plant. Figures 5.2a-f show the sequence of crushing process used for recycling purpose.    65  Figure 5.1 Flow diagram of evolution process of recycled concrete made with repeated recycled coarse aggregate [RCA1 = 1st generation repeated recycled coarse aggregate, RC1 = 1st generation repeated recycled coarse aggregate concrete, RCA2 = 2nd generation repeated recycled coarse aggregate, RC2 = 2nd generation repeated recycled coarse aggregate concrete, RCA3 = 3rd generation repeated recycled coarse aggregate and RC3 = 3rd generation repeated recycled coarse aggregate concrete] In the beginning of recycling process the hardened recycled concrete is loaded into a hopper which is followed by crushing through jaw crusher. Small size of concrete specimens(cylinder of 100?200 mm and beam of 150?150?500 mm) caused difficulties during the loading into the hopper. Those specimens were loaded into a loader bucket (Figure 5.2a) and then manually dropped one by one inside the hopper as shown in Figure 5.2b. After crushing the concrete inside the hopper and jaw crusher, those were passed through a conveyer belt (Figure 5.2c). Then, different sizes of crushed repeated recycled aggregates were separated using sieve. Large sized particles were further processed into an impact crusher for secondary RCA3CastingRCA1RCA2LandfillCrushingRC1CastingCrushingCrushingCastingRC3RC2   66 crushing(Figure 5.2d-e). All those crushed aggregates were gathered together into a bucket of loader at the end of several crushing stages as shown in Figure 5.2f and then transported to the lab for mixing. In this investigation crushing was done twice and similar crushing procedure was followed in both cases.  Figure 5.2 The crushing setup used for producing repeated recycled coarse aggregate 5.4 PROPERTIES OF AGGREGATES The implementation of repeated recycled coarse aggregate is a new initiative toward the development of sustainable concrete and it is very important to examine their properties before use. This section will discuss the various aggregate properties investigated in this study. The aggregate testing was performed for the natural coarse aggregate, natural fine aggregate (sand), and three different generations of RCA. The procedure used to determine the different properties of aggregates was same as mentioned in Chapter 3. (a) (b) (c)(d) (e) (f)   67 5.4.1 Gradation The natural fine and coarse aggregates were donated by OK Builders and were supposed to have a good gradation as those are usually used for their ready mix production. Sieve analyses were performed according to CSA A23.2-2A (CSA 2009). The sieve analysis results for both the fine and coarse natural aggregates are presented in Figures 5.3a and 5.3b. From these graphs it can be observed that both the coarse and fine natural aggregates possess fairly good gradations as per CSA standard.    Figure 5.3 Gradation curves of (a) natural fine aggregate and (b) natural coarse aggregate In this study, natural coarse aggregates were replaced by 100% different generations of repeated RCA to produce repeated recycled coarse aggregate concrete. Recycled concrete was repeatedly used as a replacement of natural coarse aggregate. Figures 5.4a-c show the sieve analysis results of three different generations of repeated recycled aggregate. From these figures it can be observed that all the different generations of repeated recycled coarse aggregates fall within the CSA acceptable range. 0204060801001 10 100Passing (%)Sieve Opening (mm)CSA LowerCSA UpperCoarse NA(b)0204060801000.01 0.1 1 10Passing (%)Sieve Opening (mm)CSA LowerCSA UpperFine NA(a)   68  Figure 5.4 Sieve analyses of different generations repeated recycled coarse aggregates where (a) 1stgeneration recycled coarse aggregate (RCA1), (b) 2ndgeneration recycled coarse aggregate (RCA2), and (c) 3rd generation recycled coarse aggregate (RCA3) 5.4.2 Bulk Density, Specific Gravity, and Moisture Content of Aggregates Different aggregate property tests were performed to show a comparison among different generations of repeated recycled coarse aggregates and the natural coarse aggregate. Various physical property tests were conducted and the results are presented in Table 5.1. The bulk density, specific gravity, and absorption capacity of all five different types of aggregates were measured according to CSA standard as mentioned in Chapter 3. The bulk density of natural coarse aggregate was 1622.3 kg/m3, which was the highest among the considered coarse aggregates. On the other hand, the bulk density of repeated recycled coarse aggregate was 0204060801001 10 100Passing (%)Sieve Opening (mm)CSA LowerCSA Upper1st Generation(a)0204060801001 10 100Passing (%)Sieve Opening (mm)CSA LowerCSA Upper2nd Generation(b)0204060801001 10 100Passing (%)Sieve Opening (mm)CSA LowerCSA Upper3rd Generation(c)   69 relatively low and was decreasing with the number of repetitions. The reduced value of bulk density is due to the adhered cement paste which remains as the residues upon the top of natural aggregate after the recycling process. Since the amount of adhered mortar is increasing with the number of recycling, the bulk density of next generations of repeated recycled coarse aggregates are increasing compared to the previous one. The bulk density of RCA1, RCA2, and RCA3 were 1396.2 kg/m3, 1251.2 kg/m3, and 1195.9 kg/m3, respectively which were approximately 13.9%, 22.9%, and 26.3% smaller than that of natural coarse aggregate. The bulk SSD specific gravity of RCA1, RCA2, and RCA3 were 2.55, 2.33, and 2.23, respectively whereas the bulk SSD specific gravity of natural coarse aggregate was 2.69.The observed lower values of three different generations of repeated recycled coarse aggregate were due to the adhered mortar. This is why the bulk density subsequently gets lowered and is found the lowest in the case of RCA3. The absorption value of repeated recycled coarse aggregate is an expression of its porosity. The absorption capacities of RCA1, RCA2, and RCA3 were 5.2%, 7.1%, and 9.4%, respectively. Natural coarse aggregate?s absorption capacity was only 1.2%, which was much lower than any of the recycled aggregates. The high absorption values of repeated recycled coarse aggregate appear mostly due to the presence of the residue of cement paste that still remained on the surface of the parent coarse aggregate after crushing. Therefore, the absorption of the repeated recycled coarse aggregates increases considerably when the number of repetitions increases. The specific gravity, bulk density, and absorption are interrelated properties that are greatly influenced by the attached mortar quantity leading to porosity. The moisture content of natural coarse aggregate was 0.3%. Table 5.1 also illustrates that the moisture content of fine aggregate was higher than its absorption capacity which means extra moisture was present on the surface of the fine aggregate.    70 Table 5.1: Properties of aggregates  Bulk dry specific gravity  Bulk SSD specific gravity  Apparent specific gravity Bulk density (kg/m3) Absorption capacity   (%) Moisture content (%) Natural coarse aggregate 2.67 2.69 2.73 1622.3 1.2 0.3 1st generation RCA (RCA1) 2.32 2.55 2.63 1396.2 5.2 2.53 2nd generation RCA (RCA2) 2.17 2.33 2.57 1251.2 7.1 2.57 3rd generation RCA (RCA3) 2.03 2.23 2.52 1195.9 9.4 2.66 Fine aggregate 2.67 2.71 2.79   1.8 2.13  Figures 5.5a-d show the microscopic view of different types of coarse aggregate. These figures reveal that the crack and other damages increased with the number of repetitions. On the other hand, pore and crack was not found in the case of natural aggregate even under the microscope as shown in Figure 5.5a.The quality of coarse aggregate degraded with the number of repetitions which might influence the mechanical and durability properties of different generations of repeated recycled coarse aggregate concrete.   5.5 EXPERIMENTAL PROGRAM The main purpose of this study is to determine the potential of repeated recycled coarse aggregate to be utilized as construction material. When new and innovative technologies are being introduced to an industry there are always fears about adopting them due to unknown performance in various exposures and its long-term durability. There is a need/demand for sustainable products where concrete industry does support the idea, but fears that the new technology may not perform over time and therefore negatively impact their businesses.  This study offers a solution and hope by producing sustainable concrete which utilizes 100% RCA    71 and fly ash, while ensuring that concrete meets all the strength and durability requirements set forth by CSA.  Figure 5.5 Microscopic view (magnification 40x) of different types of coarse aggregate: (a) Control (natural coarse aggregate), (b) 1stgeneration recycled coarse aggregate (RCA1), (c) 2ndgeneration recycled coarse aggregate (RCA2), and (d) 3rd generation recycled coarse aggregate (RCA3)  This study also investigates the quality of the new generation concrete as compared to the conventional concrete. To investigate the generation effect of repeated recycled coarse aggregate, four different kinds of coarse aggregate were used to produce 32 MPa concrete. OK Builders? 32 MPa mix design for exposure class C2 was used in this study in order to provide a more realistic and comparable evidence to the concrete industry. The effective water-cement ratio of the mix was 0.41. Coarse aggregate, fine aggregate, cementitious materials, water, water (a) (b)(c) (d)   72 reducer, and air entraining admixture were used to produce different concrete mixes. Class F fly ash was used as a 20% replacement of ordinary Portland cement (GU cement). The fly ash aids in the durability performance of concrete by forming a tighter concrete matrix thereby reducing the permeability and rate of chemical infiltration. Glenium 3030 NS (BASF 2013) and Micro air (BASF 2013) were used as water reducing admixture and air entraining admixture, respectively. Table 5.2 shows the mix proportions for various generation of repeated recycled coarse aggregate concrete that were tested in this study. Table 5.2: Mix proportions Mix Component Control 1st generation recycled concrete (RC1) 2nd generation recycled concrete (RC2) 3rd generation recycled concrete (RC3) Cementing materials GU cement 280 280 280 280 Fly ash 70 70 70 70 Fine aggregate Natural fine aggregate 750 750 750 750 Coarse aggregate Natural coarse aggregate 1040 0 0 0 Repeated recycled coarse aggregate 0 1040 1040 1040 Water   150 150 150 150 Water reducer  Glenium 3030 630 ml 630 ml 630 ml 630 ml Air entraining admixture Micro air 120 ml 120 ml 120 ml 120 ml  The generation effect was examined by using four different types of coarse aggregate and those were natural coarse aggregate, RCA1, RCA2, and RCA3. In these four mixes all other components remained constant except the use of different generation of recycled aggregate in order to ensure that the test results only reflect the generation effect. Control concrete mix    73 worked as a base line for evaluating the behavior of different generation of repeated recycled coarse aggregate concrete. The hardened concrete properties were determined by conducting compressive strength test and splitting tensile strength test. Splitting tensile strength was performed according to CSA A23.2-13C (CSA 2009) and only three cylinders were cast for 28 days test. Compressive strength test was done according to CSA A23.2-9C (CSA 2009) at the ages of 3,7,28,  56, and 120 days. At least three cylinders of ?100?200 mm were cast to perform the specified date compressive and splitting tensile strength of the natural and different generations of repeated recycled coarse aggregate concrete. Concrete mixing and curing were done as mentioned in Chapter 3. The specimens remained in the curing chamber until they were removed for testing. Fresh concrete properties (slump and air content) were also investigated according to CSA Standard mentioned in Chapter 3. 5.6 EXPERIMENTAL RESULTS 5.6.1 Results of Fresh Concrete Properties The variations of concrete slump and air content are presented in Table 5.3.The slump value for the mix prepared with natural coarse aggregate was 100 mm which was little bit higher than the target slump of90 mm. This slump value was considered to represent a more realistic mix because in ready mix industry the usual slump is close to 90 mm. Table 5.3shows that the slump values of  RC1, RC2, and RC3 were 100mm, 94mm, and 85 mm, respectively, which were within a narrow range of the target slump. The workability of concrete remained unaffected due to application of different generations of repeated recycled coarse aggregate.      74 Table 5.3: Fresh concrete properties   Slump (mm) Air content (%) Control 100 3.4 1st generation repeated RCA concrete (RC1) 100 3.6 2nd generation repeated RCA concrete (RC2) 94 3.9 3rd generation repeated RCA concrete (RC3) 85 4.4  The results of the air content test of all the mixes are shown in Table 5.3, which shows an increasing trend with the increased number of repetitions. The concrete containing repeated RCA seemed to have slightly increased air content compared to that of the reference mix though every time the same amount of air entraining admixture was used. In a study by Katz (2003), it was also found that the effect of RCA replacement on air content was higher (approximately 4%-5.5% for recycled concrete).Similar phenomenon was found in the present study for different generations of repeated RCA concrete. Though, the reason of the increased air content is not properly understood, this is probably due to the fact that the amount of adhered mortar content is increasing with the number of repetitions. Light weight aggregate concrete also shows increased air content than the normal weight concrete (Wischers and Manns 1974, Katz 2003). The bulk density of the considered different types of recycled concrete aggregates is gradually decreasing with repetitions compared to that of natural coarse aggregate. This is another reason why 3rd generation repeated RCA concrete (RCA3) has the highest air content considering its lowest bulk density. 5.6.2 Results of Compressive Strength The compressive strength test results of different concrete mixes are presented in Table A3 (Appendix-A) and Figure 5.6 for ages of 3, 7, 28, 56 and 120 days. The subsequent use of 100%    75 repeated recycled coarse aggregates lead to a drop in the compressive strength of this new generation recycled concrete with repetitions. It can be observed that the compressive strengths of concrete containing RCA1 and RCA2 were 35.9 MPa and 36.8 MPa at 56th day which were slightly lower than the natural coarse aggregate concrete (43.1 MPa).   Figure 5.6 Compressive strength of various concrete mixes The compressive strength of RC2 was 2.5% higher at the age of 56th day than that of RC1 though the bulk density of RCA2 was lower. This was due to the rougher texture and more angular shape of RCA2 which subsequently improved the bonding and interlocking between the RCA2 and the cement paste. This may also be contributed by the higher absorption capacity of 2nd generation repeated RCA which latter may have worked as a source of water in the form of internal curing (Yang et al. 2008). It can be seen that all the considered concrete batches achieved their target compressive strength (32 MPa) at the age of 28 days except RC3. RC3 also failed to achieve the 32 MPa target strength even at the age of 56 days. The effect of repeated use on the compressive strength of RC3 was more than RC1 and RC2.Compressive strength at 56th day of RC3 was 32.7%, 19.2%, and 21.2% lower than that of natural coarse aggregate 01836540 40 80 120Compressive strength (MPa)Age (days)Control1st Generation2nd Generation3rd Generation   76 concrete, RC1, and RC2, respectively. The lower bulk density of RCA3, large amount of adhered mortar content, and weak interfacial transition zone are the main reasons behind the significant strength degradation of RC3 (Tu et al. 2006, Yang et al.2008). However, the compressive strength of RC3 could reach up to 44.3 MPa at the age of 120 days which was at  least 25% higher than the target strength. Figure 5.7 shows the box plot of compressive strength obtained from different concrete mixes. In this figure each individual mix has a diagram where the height represents the numerical range of data (maximum and minimum values) for compressive strength. The ?boxes? represent the 25th through the 75th percentile. The horizontal line inside the box is the median value (i.e.50th percentile). It can be observed that the later strength test results (56 and 120 days) are almost symmetrically/normally distributed for all mixes. In the case of RC1, it shows the highest ranges in all age groups and exhibited negative skewness for the 3, 7 and 28 days strength. In the case of RC3, it experienced the highest rate of late strength development compared to all other mixes. 5.6.3 Stress-Strain Curve The stress-strain curves at the age of 120 days of different generations of repeated recycled coarse aggregate concrete and control concrete are shown in Figures 5.8a-e. The average stress-strain curve is shown in Figure 5.8e. The tests were conducted according to CSA standard (CSA A23.2-9C) in a load controlled manner. A significant influence was found on the stress-strain curve of different concrete mixes due to the use of different generations of repeated recycled coarse aggregate. Similar pattern of the stress-strain curves was found for all the repeated    77 recycled concrete mixes. The peak stress for the control mix was 49.8MPa and its corresponding peak strain was 0.00211.   Figure 5.7 Variation in 3, 7, 28, 56 and 120-day compressive strength of various concrete batches  [ where a = 3 days, b = 7 days, c = 28 days, d = 56 days, and e = 120 days] [Control = Natural aggregate concrete, RC1 = 1st generation repeated recycled coarse aggregate concrete, RC2 = 2nd generation repeated recycled coarse aggregate concrete, and RC3 = 3rd generation repeated recycled coarse aggregate concrete]  The value of the strain corresponding to the peak stress was higher for repeated recycled coarse aggregate concrete compared to that of NAC. This is due to the lower modulus of elasticity of recycled concrete compared to NAC as shown in Table 5.4. The peak axial strain values of RC1, RC2, and RC3 were 0.00268, 0.00253, and 0.00239, respectively. The ultimate strain is considered as the axial strain beyond the peak stress at a stress level equal to 85% of the peak stress during the load control test (Gonzalez-Fonteboa et al. 2009). The ultimate axial strain of control mix was 0.0023 which was 14.8% and 11.5% lower than that of RC1 and RC2, respectively. The ultimate strain of RC3 was 0.0025. The transverse strains of different concrete mixes are also shown in the figure. Similar pattern is also observed in transverse strain response. 10152025303540455055Control RC1 RC2 RC3Compressive strength (MPa) a a a a e e e b e d d d d c c c c b b b    78  Figure 5.8 Stress-strain curves of various concrete mixes at the age of 120 days [where, a= Control, b = RC1, c = RC2, d = RC3, and e = average] [Control = Natural aggregate concrete, RC1 = 1st generation repeated recycled coarse aggregate concrete, RC2 = 2nd generation repeated recycled coarse aggregate concrete, and RC3 = 3rd generation repeated recycled coarse aggregate concrete]  0102030405060-0.001 0 0.001 0.002 0.003Stress (MPa)Control-AxialControl-Transverse(a)Axial  strainTransverse  strain0102030405060-0.001 0 0.001 0.002 0.003 0.004Stress (MPa)RC1(1)-AxialRC1(1)-TransverseRC1(2)-AxialRC1(2)-Transverse(b)Axial  strainTransverse  strain0102030405060-0.001 0 0.001 0.002 0.003Stress (MPa)RC2(1)-AxialRC2(1)-TransverseRC2(2)-AxialRC2(2)-Transverse(c)Axial  strainTransverse  strain0102030405060-0.001 0 0.001 0.002 0.003Stress (MPa)RC3(1)-AxialRC3(1)-TransverseRC3(2)-AxialRC3(2)-Transverse(d)Axial  strainTransverse  strain0102030405060-0.001 0 0.001 0.002 0.003Stress (MPa)Control-AxialControl-TransverseRC1-AxialRC1-TransverseRC2-AxialRC2-TransverseRC3-AxialRC3-Transverse(e)Axial  strainTransverse  strain   79 5.6.3.1 Modulus of elasticity and poisson?s ratio Table 5.4 shows the variations of modulus of elasticity and poisson?s ratio of different generations of repeated recycled coarse aggregate concrete and their comparison with control mix. The modulus of elasticity of different generations of repeated recycled coarse aggregate concretes decreased with the increased number of repetitions. The highest modulus of elasticity was found for control mix which was 27.9 GPa and it was 8.1% higher than that of RC3. This was due to the decreasing stiffness and bulk density of RCAs. This also indicates that the quality of repeated recycled coarse aggregates was decreasing with the increased number of repetitions. Poisson?s ratio of control mix was found as 0.23. The value of poisson?s ratios was increasing with the number of repetitions. The poisson?s ratio value of RC1 was 0.25 and it was 8.7% higher than the control mix. Table 5.4: Mechanical properties of different concrete mixes at 120th day Concrete mix Modulus of elasticity Peak stress Strain at peak  stress Ultimate strain Poisson?s ratio (GPa) (MPa) (mm/mm) (mm/mm)   Control 27.9 49.8 0.00211 0.0023 0.23 RC1 27.1 46.2 0.00268 0.0027 0.25 RC2 26.1 46.4 0.00253 0.0026 0.24 RC3 25.8 42.8 0.00239 0.0025 0.26  5.6.4 Results of Splitting Tensile Strength The splitting tensile strengths of various concrete mixes are shown in Figure 5.9for the age of 28 days. Here the splitting tensile strengths found for all new generation concrete can be compared directly to the splitting tensile strength of the control concrete. It can be seen from the data presented in the figure that the values of the splitting tensile strength of RC1 and RC2 were    80 higher than the control by almost 3-4%. This was attributed by the effectiveness of new interfacial transition zone and the absorption capacity of the attached mortar on the surface of repeated recycled coarse aggregate (Etxeberria 2007, Salem and Burdette 1998).This phenomenon was also found in few studies where it was discovered that the splitting tensile strength of concrete containing RCA was higher than the control mixture (Alam et al. 2013, Etxeberria 2007,Malesev 2010). The repeated recycled coarse aggregate concrete containing RCA3 experienced lower than the splitting tensile strength of control mix by approximately 33%. This was the consequence of large amount of old cement paste and lower bulk densityofRCA3 leading to a weaker interfacial transition zone.  Figure 5.9 Splitting tensile strength of various concrete mixes at the age of 28 days [Control = Natural aggregate concrete, RC1 = 1st generation repeated recycled coarse aggregate concrete, RC2 = 2nd generation repeated recycled coarse aggregate concrete, and RC3 = 3rd generation repeated recycled coarse aggregate concrete]  5.6.5 Failure Pattern of Concrete The failure patterns of various concrete mixes at the age of 56 days are shown in Figures 5.10a-d and Figures 5.10e-f represent the failure patterns of these mixes at 120th day. Those 9.7 10.010.16.504812Control RC1 RC2 RC3Splitting tensile strength (MPa)   81 failure patterns were observed when those specimens were subjected to compressive strength test. Cone and shear failure was observed by the control mix which is shown in Figure 5.10a. Shear failure pattern was shown by RC1. Again cone and shear failure pattern was observed for both RC2 and RC3. At the age of 120 days shear failure was observed for the control mix and RC1 as shown in Figures 5.10e-f.  Cone and shear failure was observed for RC2 at 120th day where RC3 showed shear failure at the same age as shown in Figure 5.10h.  Figure 5.10 Failure pattern of various concrete mixes (a) Control (natural coarse aggregate concrete) at 56th day, (b) 1st generation repeated RCA concrete (RC1) at 56th day, (c) 2nd generation repeated RCA concrete (RC2) at 56th day, (d) 3rd generation repeated RCA concrete (RC3) at 56th day, (e) Control (natural coarse aggregate concrete) at 120th day, (f) 1st generation repeated RCA concrete (RC1) at 120th day, (g) 2nd generation repeated RCA concrete (RC2) at 120th day, and (h) 3rd generation repeated RCA concrete (RC3) at 120th day   (b)(a) (c) (d)(e) (f)(g)(h)   82 Chapter  6: DURABILITY PROPERTIES OF REPEATED RECYCLED COARSE AGGREGATE CONCRETE  6.1 GENERAL The performance of concrete not only depends on its mechanical properties but also significantly affected by its durability properties. The service life of concrete structure is also strongly dependent on its durability characteristics. Durability is one of the major concerns associated with the application of new generation repeated recycled coarse aggregate concrete. Its absorption and drying shrinkage are higher than NAC as it is being produced by crushing different generations of repeated recycled coarse aggregate concrete. The production of repeated recycled coarse aggregate concrete will offer a green, sustainable, and environment friendly product to the concrete industry. Before any kind of practical application, the durability performance of this new generation concrete must be tested to ensure that it can handle different harsh exposure conditions. At present there is no published literature on the durability of repeated recycled coarse aggregate concrete and in order to advance the pursuit of a more sustainable concrete, the durability of this concrete must be determined. In this chapter the durability performance of 32 MPa repeated recycled coarse aggregate concrete is evaluated in terms of freeze-thaw cycles, sulphate attack, and wetting-drying cycles in chloride environment. The fresh and hardened properties of this new generation concrete are already discussed in Chapter 5. The required specimens for investigating the durability problems were cast along with the specimens used for testing the fresh and hardened properties of repeated recycled coarse aggregate concrete. These three durability related problems of different    83 generations of repeated recycled coarse aggregate concrete (RC1, RC2, and RC3) were examined by comparing their performance with control concrete (natural coarse aggregate concrete). 6.2 FREEZE-THAW DURABILITY TEST OF REPEATED RECYCLED COARSE AGGREGATE CONCRETE Freeze-thaw is one of the major durability concerns of this new generation concrete in cold regions since the absorption, porosity, and the attached mortar content are increasing with the increased number of repetitions with this new generation concrete. Extensive research is needed to understand the freeze-thaw durability performance of repeated recycled coarse aggregate concrete. ASTM C666 (ASTM 2012) Procedure A was followed to examine the durability performance of 32 MPa repeated recycled coarse aggregate concrete. 76?102?406 mm standard beam molds were used to cast specimens for this test. Two beams were cast for each generation of repeated recycled concrete. Two beam specimens were also cast with NAC (control) to compare the performance of repeated recycled coarse aggregate concrete. After the removal of mold, these specimens were moist cured for 14 days in the moist curing chamber. After 14 days of curing these specimens were brought to the target thaw temperature which is between 2?C to -1?Cusing the freeze-thaw cabinet. The length, weight and fundamental transverse frequency of those beam specimens were measured. Then the specimens were placed inside the containers of the freeze-thaw machine and the containers were completely filled with clean water to start the freeze-thaw test. After each 36 cycles specimens were removed from the machine, and the length, weight, and fundamental transverse frequency of the beam specimens were measured to monitor the changes as mentioned in ASTM C666 (ASTM 2012). Containers were rinsed out and filled with clean water before putting back the specimens each time. This test was continued    84 up to 300 cycles. According to ASTM C666 (ASTM 2012), the freeze-thaw testing should continue until the specimens passed 300 cycles or reached the failure criteria. It is specified that if the value of relative dynamic modulus reaches 60% of its initial value or the length expansion is 0.10%, then the specimen has reached the failure criteria and should be discarded.   6.3 TEST METHOD TO ASSESS THE SULPHATE RESISTANCE OF REPEATED RECYCLED COARSE AGGREGATE CONCRETE The sulphate resistance test of different generations repeated recycled coarse aggregate concrete was performed following the same procedure mentioned in Chapter 4.This time the specimen size selected was 100?200mm cylinders for sulphate exposures experiments. This size was chosen to eliminate the problems which occurred in case of small sized cylinder (75?150 mm) for recycled concrete made with different RCA replacement levels. During the 7 days strength test, the small size cylinder compressive strength was much lower than the 100?200 mm cylinders. Three cylinders were cast for each generation of repeated recycled coarse aggregate concrete and control concrete. The cylinders were moist cured for seven days before being placed in the sulphate bath. Sulfate bath preparation and the pH monitoring were done exactly the same way as discussed in Chapter4. The specimens used for sulphate testing were measured on a weekly basis to determine the physical changes occurring in the specimen over time. The used sodium sulphate solution was discarded after taking the measurement of cylinders at certain intervals such as at the age of 28 days and 56 days. Compressive strength test was performed at the age of 56 days after the sulphate exposure of 7 weeks to investigate the loss of strength during the sulphate exposure.     85 6.4 TEST METHOD TO ASSESS THE CHLORIDE ION INGRESSION INTO REPEATED RECYCLED COARSE AGGREGATE CONCRETE This study also investigated the durability of 32 MPa repeated recycled coarse aggregate concrete under chloride exposure condition along with wetting-drying cycles, and compared those results with the control mix. The repeated recycled coarse aggregate concrete is more porous than the control mix and any kind of fluid can penetrate into it. The aggressive ion ingression such as chloride can cause disintegration of concrete. Hence, it is very important to investigate the chloride durability performance of repeated recycled coarse aggregate concrete. The chloride concentration in concrete was measured using Ion Chromatography. Similar procedure was followed as discussed in Chapter 4. Only variation was the test period which was 56 days for each considered generation due to time restriction. As a result, chloride ion concentration was measured after 1, 4, 9, 16, and 28 cycles. Compression test was done on three specimens only at the age of 56 days after being exposed to 28 cycles to examine whether there is any degradation in strength due to propagation of chloride along with wet dry cycle.  6.5 RESULT AND DISCUSSION 6.5.1 Results of Freeze-Thaw Durability Test The freeze-thaw durability performance of different generations of repeated recycled coarse aggregate concrete was measured in terms of relative dynamic modulus of elasticity, percent change in length, and percent change in weight. The relative dynamic modulus of elasticity was estimated using the following equation suggested by ASTM C666 (ASTM 2012) 10022??onn nnP                                                                  (6.1)               86 where, n = number of cycles during the time of testing Pn =relative dynamic modulus of elasticity after n cycles of freezing-and-thawing no = initial fundamental transverse frequency , in Hz nn= fundamental transverse frequency after being exposed to n  freezing-and-thawing cycles, in Hz Figure 6.1 shows the results of relative dynamic modulus of elasticity at different number of cycles during the test period. Results show that as the number of repetitions increased, the value of relative dynamic modulus of elasticity decreased. Moreover, the values of relative dynamic modulus of elasticity also decreased with the increased number of freeze-thaw cycles.  Control concrete survived up to 288 freeze-thaw cycles without any reduction in the relative dynamic modulus of elasticity. It was found that after being subjected to 300 cycles the control concrete?s relative dynamic modulus of elasticity was 99.7%.As indicated in Figure 6.1, there was a drop at 144thcycle for the relative dynamic modulus of elasticity of RC1, RC2, and RC3 which were 0.89%, 1.35%, and 2.59%, lower than that of control concrete, respectively. After 300 cycles the relative dynamic modulus of elasticity of control mix was 1.95%, 3.32%, and 9.27% higher than that of RC1, RC2, and RC3, respectively. Lowest relative dynamic modulus of elasticity was found for RC3 which was 91.2%. This is due to the higher absorption and porosity of repeated recycled coarse aggregate concrete with the number of repetitions. Due to this increased porosity the absorbed water easily gets saturated and upon freezing, it develops internal stress. If this internal stress exceeds the tensile strength of aggregate then micro cracks    87 will generate inside the concrete and it will influence the relative dynamic modulus of elasticity of concrete (Salem et al. 2003).  Though slight reduction was observed in terms of relative dynamic modulus, three different generations of repeated recycled concrete performed quite well. Their relative dynamic modulus was higher than 90% after being exposed to 300 freeze-thaw cycles which was good as compared to ASTM failure criteria, which is around 60% of initial value.  Figure 6.1 Relative dynamic modulus of elasticity of concrete [Control = Natural aggregate concrete, RC1 = 1st generation repeated recycled coarse aggregate concrete, RC2 = 2nd generation repeated recycled coarse aggregate concrete, and RC3 = 3rd generation repeated recycled coarse aggregate concrete] As shown in Figure 6.2, the percent change in length of all considered types of concrete increased as the number of cycles increased. The lowest amount of percentage length change was observed for control mix after 300 cycles where the highest was observed for RC3. The length change of RC1 was 8.6% lower than that of RC2 after being exposed to 300 freeze-thaw cycles. 808590951000 36 72 108 144 180 216 252 288Relative dynamic modulus (%)No. of freeze-thaw cyclesControl RC1RC2 RC30     36     72     108    144    180    216   252  288 300      88  Figure 6.2 Length change of concrete [Control = Natural aggregate concrete, RC1 = 1st generation repeated recycled coarse aggregate concrete, RC2 = 2nd generation repeated recycled coarse aggregate concrete, and RC3 = 3rd generation repeated recycled coarse aggregate concrete] Figure 6.3 shows the weight change of concrete. In terms of the percentage weight change for all considered types, initially it showed an increasing pattern and later it was decreasing, then again little increased and decreased phenomenon were observed. As the weight gain indicated the presence of micro cracking and the weight loss meant the spalling of concrete (Kriesel et al. 1997). Both of these indicated the ongoing damage process. After 300 cycles the highest amount of weight change was observed for RC3 which was 66.2%, 15.8%, and 11.7% higher than that of control, RC1, and RC2, respectively. This was contributed by the attached mortar and the porosity of RCA3 which subsequently increased the ingression of water inside the concrete. Low absorption of natural aggregate helped demonstrate comparatively better resistance against the ingression of moisture.  00.030.060.090.120.150 36 72 108 144 180 216 252 288Length change (%)No. of cyclesControl RC1RC2 RC30     36     72     108   144   180   216   252   288 300      89  Figure 6.3 Weight change of concrete [Control = Natural aggregate concrete, RC1 = 1st generation repeated recycled coarse aggregate concrete, RC2 = 2nd generation repeated recycled coarse aggregate concrete, and RC3 = 3rd generation repeated recycled coarse aggregate concrete]  Figure 6.4 shows the durability factor of all considered concrete. The durability factor was calculated according to ASTM C666 (ASTM 2012) 100?? MPNDF                                                                   (6.4) where, DF = durability factor of the test specimen, P = relative dynamic modulus of elasticity at Ncycles, N = number of cycles at which P reaches the specified minimum value for discontinuing the test or the specified number of cycles at which the exposure is to be terminated, whichever is less, and M = specified number of cycles at which the exposure is to be terminated. As shown in Figure 6.4, better durability performance was observed for control than the repeated recycled concrete. Slight degradation in durability factor was observer for RC1 which 00.71.42.12.8Weight change (%)No. of freeze-thaw cyclesControl RC1RC2 RC30     36     72     108    144    180    216   252    288 300      90 was 97.8% while control achieved 99.7%.  Lowest durability factor was found for RC3 (91.2%) but still it survived up to 300 freeze-thaw cycles which indicates that even RC3 can perform well under harsh environmental condition. Results indicate that the freeze-thaw durability performance of repeated recycled concrete is comparable with NAC.  Figure 6.4 Durability factor of concrete [Control = Natural aggregate concrete, RC1 = 1st generation repeated recycled coarse aggregate concrete, RC2 = 2nd generation repeated recycled coarse aggregate concrete, and RC3 = 3rd generation repeated recycled coarse aggregate concrete] Along with these tests visual inspection was also done to investigate the damage due to freeze-thaw exposure. Figures 6.5a-d show the initial condition (before being placed in freeze-thaw chamber) of different generations repeated recycled coarse aggregate concrete specimens. On the other hand, Figures 6.6a-d reveal the condition of concrete specimens after being exposed to 300 freeze-thaw cycles. Concrete spalling was observed and marked with red colour in Figures 6.6a-d. Though all the considered concrete survived after exposed to 300 cycles, all of them showed some damages due to spalling. The extent of damage was higher for repeated recycled coarse aggregate concrete than that of control mix.   0255075100Control RC1 RC2 RC3Durability factor (%)   91  Figure 6.5 Specimens for freeze-thaw durability test before being placed in freeze-thaw chamber where (a) Control (natural coarse aggregate concrete), (b) 1st generation repeated RCA concrete (RC1), (c) 2nd generation repeated RCA concrete (RC2), and (d) 3rd generation repeated RCA concrete (RC3)   Figure 6.6 Concrete specimens after being exposed to 300 freeze-thaw cycles where (a) Control (natural coarse aggregate concrete), (b) 1st generation repeated RCA concrete (RC1), (c) 2nd generation repeated RCA concrete (RC2), and (d) 3rd generation repeated RCA concrete (RC3) (a)(b)(c)(d)(d)(b)(a)(c)   92 6.5.2 Results of Sulphate Resistance Test The durability performance against sulphate attack was examined based on the strength loss along with the changes of height and volume of the specimen which were measured over sulphate exposure time. Figure 6.7 shows the results of compressive strength test at the age of 7days and 56 days (after 7 weeks of exposure). It can be understood from Figure 6.7 that at the age of 56 days, after 7 weeks of sulphate exposure, the strength of all considered concrete batches were increasing as compared to 7 days strength (before being placed in 5% sodium sulphate solution). This increasing trend does not provide any indication regarding the sulfate resistance (Monteiro et al. 2000). It only reveals that cement continues to hydrate in sodium sulphate solution during that time and the pores get filled up with hydrated products along with gypsum and ettringite. If long term performances were evaluated these specimens will show the strength degradation as seen in Chapter 4 in the case of RAC made with different replacement levels. Long term performance could not be considered here due to time constraint. Figure 6.7also indicates that the compressive strength of RC3 was the lowest (35.1 MPa) among the different concrete mixes. This is due to the high amount of attached mortar and the weak interfacial transition zone of RC3. The presence of multi layers of interfacial transition zone significantly influenced this phenomenon. The strength of RC1 (37.5 MPa) under sulphate exposure at the age of 56 days was 19.5% and 5.1% lower than that of Control and RC2, respectively.  The compressive strengths of different concrete mixes at 56th day under different curing conditions are compared in Figure 6.8. From this figure, it can be observed that the compressive strengths at 56thday after 7 weeks of sulphate exposure were higher than those of standard moist cured specimens. This might be contributed by sulphate which acted as alkali activator at that    93 age under the sulphate exposure and influenced the pozzolanic reactivity of fly ash and thus increased the strength.  Figure 6.7 The results of compressive strength test at the age of 7days (before being placed in 5% sodium sulphate solution) and 56 days (after 7 weeks of exposure)  [Control = Natural aggregate concrete, RC1 = 1st generation repeated recycled coarse aggregate concrete, RC2 = 2nd generation repeated recycled coarse aggregate concrete, and RC3 = 3rd generation repeated recycled coarse aggregate concrete]   Figure 6.8The results of compressive strength test at the age of 56 days of standard moist curing cylinders and sulphate exposed cylinders [Control = Natural aggregate concrete, RC1 = 1st generation repeated recycled coarse aggregate concrete, RC2 = 2nd generation repeated recycled coarse aggregate concrete, and RC3 = 3rd generation repeated recycled coarse aggregate concrete] 29.746.625.337.527.639.517.935.1010203040507 days 56 DaysCompressive strength (MPa)Control RC1RC2 RC343.135.936.82946.637.539.535.1015304560Control RC1 RC2 RC3Compressive strength (MPa)Standard moist curingSulphate exposure   94 Statistical analyses were carried out to evaluate the variation of compressive strengths of four different mixes. Figure 6.9 presents the box plot of data found from the 56 day compressive strength of moist cured repeated recycled coarse aggregate concrete of different generations along with the compressive strength of specimens exposed to sulphate for 7 weeks. After being exposed to sulphate for 7 weeks symmetric distribution was observed for control mixes. RC3 exhibited positive skewness after being exposed to sulphate on the other hands it exhibited negative skewness for moist curing samples.    Figure 6.9 Compressive strength of various concrete mixes at 56th day [where a = moist curing and b = after 7 weeks of sulphate exposure] [Control = Natural aggregate concrete, RC1 = 1st generation repeated recycled coarse aggregate concrete, RC2 = 2nd generation repeated recycled coarse aggregate concrete, and RC3 = 3rd generation repeated recycled coarse aggregate concrete] The percent change in height and volume of different specimens are shown in Figures 6.10 and 6.11, respectively. Figures 6.10 and 6.11 show a similar trend where the number of repetitions increased the changes in the height and volume of cylinders also increased. This is due to the increasing porosity and decreasing bulk density of aggregates with the increased 253035404550Control RC1 RC2 RC3Compressive strength (MPa)aaaabbbb   95 number of repetitions. Micro cracking inside the aggregate could be another contributing factor. The height and volume changes were determined using equations 6.5 and 6.6where the results are depicted in Figures 6.10and 6.11. % Height change,                   ? ? 100% ????iitHHHH   (6.5) where, Hi = average initial volume of cylinder (mm); and Ht = average volume of cylinders after a prescribed exposure period (mm). % Volume change,                 ? ? 100% ????iitVVVV                     (6.6) where Vi = average initial volume of cylinder (mm3); and Vt = average volume of cylinders after a prescribed exposure period (mm3). It can be seen from Figure 6.10 that there was significant expansion in the height of concrete cylinders with increased period of time under sulphate exposure. The change in height of control concrete was 0.015% after being exposed to sulphate for one week and with time it was increasing. After 7 weeks of exposure (56 days) the change in height was 0.09% for control mix. The height change of RC1 was 7.7%, 25%, 66.7% lower than that of control, RC2, and RC3, respectively at the age of 28 days. The crumbling of concrete cylinders decreased the height change of RC1. The maximum height expansion was shown by RC3 (0.165%) at 56th day and it was 57.1% and 17.9% higher than the height expansion of RC1 and RC2, respectively. RC3 was more permeable in nature than RC1 and RC2 thus increased the sulphate ion ingression inside the concrete. Multiple layers of interfacial transition zone also worked as a contributing    96 factor. The height change of RC1 was 25% lower than RC2 at the age of 56 days under sulphate exposure. This was contributed by the porosity and adhered mortar, which were lower for RCA1 as compared to RCA2.     Figure 6.10 Height change (%) of concrete cylinders under sulphate exposure condition [Control = Natural aggregate concrete, RC1 = 1st generation repeated recycled coarse aggregate concrete, RC2 = 2nd generation repeated recycled coarse aggregate concrete, and RC3 = 3rd generation repeated recycled coarse aggregate concrete] Figure 6.11shows that volume change of RC3 was 94%, 50%, and 10% higher than that of control, RC1, and RC2, respectively at the age of 28 days under sulphate exposure. Control concrete volume expansion was lower than different generation repeated recycled coarse aggregate concrete over the test period under sulphate exposure. The volume change increased over time. The maximum volume change was observed for RC3 (0.45%) at 56thday after 7 weeks of sulphate exposure. These results indicate that as the number of repetitions increases the sulphate ion ingression inside the concrete increases which consequently affects the volume of concrete. 00.050.10.150.214 days 21 days 28 days 56 daysHeight change (%)Age (days)Control RC1RC2 RC3   97  Figure 6.11 Volume change (%) of concrete cylinders under sulphate exposure condition [Control = Natural aggregate concrete, RC1 = 1st generation repeated recycled coarse aggregate concrete, RC2 = 2nd generation repeated recycled coarse aggregate concrete, and RC3 = 3rd generation repeated recycled coarse aggregate concrete] 6.5.3 Results of Chloride Ion Ingression into Recycled Concrete The compressive strength results at the age of 56 days after being exposed to 28 wetting-drying cycles along with chloride solution for control and different generations of repeated recycled coarse aggregate concrete are shown in Figure 6.12. Their standard moist curing compressive strength test results are also shown in Figure 6.12 to examine the degradation of strength due to chloride propagation. It reveals that chloride propagation does not have any significant effect on the compressive strength of those considered concrete. 00.10.20.30.40.514 days 21 days 28 days 56 daysVolume change (%)Age (days)Control RC1RC2 RC3   98  Figure 6.12 Compressive strength of concrete at the age of 56 days  [Control = Natural aggregate concrete, RC1 = 1st generation repeated recycled coarse aggregate concrete, RC2 = 2nd generation repeated recycled coarse aggregate concrete, and RC3 = 3rd generation repeated recycled coarse aggregate concrete]  Figure 6.13 shows the box plot of compressive strength test results of moist curing and chloride exposed cylinders at 56th day. This figure shows that the distribution of moist curing and chloride exposure cylinders? compressive strength for RC1 and RC2 was normally distributed, whereas the distributions of compressive strength for RC3 and control concrete under moist curing and chloride exposure were negatively skewed. The concentrations of chloride ion per unit surface area of different generations of repeated recycled coarse aggregate concrete are given in Figure 6.14 and Table A4 (Appendix-A). Control concrete results are also shown to evaluate their chloride resistance performance. No chloride ion concentration was found in standard moist curing concrete mixes as presented in Table A4 (Appendix-A).It can be seen from Figure 6.14 that the chloride ion penetration increased as the number of repetitions increased. Moreover, the chloride concentration was also increasing with the increased number of cycles. Above mentioned phenomena were contributed by the adhered 01020304050Control RC1 RC2 RC3Compressive strength (MPa)Standardard moist curingCyclic wetting and drying with chloride solution   99 mortar and multi layers of old interfacial transition zone of repeated recycled coarse aggregate, causing repeated recycled coarse aggregate concrete more porous and permeable than the control mix (Otsuki et al. 2003).  Figure 6.13 Compressive strength of various concrete batches at 56th day [where a = after being exposed to 28 cycles along with chloride solution and b = moist curing] [Control = Natural aggregate concrete, RC1 = 1st generation repeated recycled coarse aggregate concrete, RC2 = 2nd generation repeated recycled coarse aggregate concrete, and RC3 = 3rd generation repeated recycled coarse aggregate concrete]  At 56th day, after being exposed to 28 wetting and drying cycles with sodium chloride solution, RC3 showed the highest concentration of chloride ion per unit surface area which was about 105.9 ppm/m2 and the control mix showed the lowest concentration. However, upto 4 cycles the chloride ion concentration values of RC1 and control were very close. Later, the chloride ion concentration rate increased gradually for RC1. After exposed to 16 cycles the chloride concentration of RC2 was 4.1% lower than RC3.    253035404550Control RC1 RC2 RC3Compressive strength (MPa)aabababb   100  Figure 6.14 Concentration of chloride ions per unit surface area of concrete cylinder [Control = Natural aggregate concrete, RC1 = 1st generation repeated recycled coarse aggregate concrete, RC2 = 2nd generation repeated recycled coarse aggregate concrete, and RC3 = 3rd generation repeated recycled coarse aggregate concrete] 0204060801001201 cycle 4 cycles 9 cycles 16 cycles 28 cyclesChloride ion concentration (ppm/m2)  Control RC1RC2 RC3   101 Chapter  7: CONCLUSIONS AND RECOMMENDATIONS  7.1 SUMMARY Concrete structures are integral parts of modern civil infrastructures constituting a large portion of national wealth of any country. Every year a huge amount of waste is generated due the construction and demolition of aging concrete structures, consequently increasing the environmental loads. Green concrete (recycled and repeated recycled coarse aggregate concrete) produced using C&D waste offers a sustainable construction material that can reduce overall impact of concrete production throughout its life cycle. This study was carried out to investigate the properties of green concrete. Two different target strengths were considered along with two different patterns of recycled aggregate utilization. One of these was 25 MPa recycled concrete made with different RCA replacement levels and anther one was 32MParepeated recycled concrete made with different generations of repeated recycled coarse aggregate. The performance of these concrete was compared with the control concrete mix. In this chapter the conclusions of this current study are discussed. In addition, limitations and recommendations for future study are also outlined here. 7.2 CONCLUSIONS The fresh, mechanical, and durability properties of the recycled concrete and repeated recycled coarse aggregate concrete were investigated. The following conclusions are drawn from this study.    102 7.2.1 Recycled Concrete Made with Different RCA Replacement Levels ? The absorption capacity of recycled coarse aggregate was 3.75 times higher than that of natural coarse aggregate. ? As the RCA replacement level increases the compressive strength decreases. Only exception was Mix-2 (30% RCA) which achieved 5.8% higher strength than that of Mix-1 (control) at 148th day. This can be attributed to the rough texture and better interlocking properties RCA. Therefore, upto 30% RCA replacement level, it is possible to achieve similar or higher compressive strength than the natural coarse aggregate concrete. ? The long term strength development of recycled coarse aggregate concrete is more favorable than natural aggregate concrete. ? The durability performance of recycled concrete is affected by the higher absorption and porosity of RCA. ? The result of sulphate resistance of recycled concrete was quite comparable to NAC. This study showed that the chloride ion ingression of RAC increased with the increased RCA replacement level. Repeated Recycled Coarse Aggregate Concrete 7.2.2 Repeated Recycled Coarse Aggregate Concrete  ? The bulk density, specific gravity, and absorption capacity of different generations of repeated recycled coarse aggregate decreased with the increased number of repetitions.  The findings of this study show that the CSA A23.2-12A can be used for investigating the absorption of repeated recycled coarse aggregates..  ? The values of the splitting tensile strength of RC1 and RC2were 3.1% and 4.1% higher than the control mix, respectively.    103 ? The application of different generations of repeated recycled coarse aggregate concrete exhibited reduction in terms of their strength properties but all of them achieved their target strength at 120thday. The compressive strengths of RC1 and RC2 were quite comparable to the control mix.  ? Three generations of repeated recycled coarse aggregate concrete successfully passed the freeze-thaw durability test. The durability performance of repeated recycled coarse aggregate concrete was satisfactory and for all the considered generations it was above 90% whereas the passing criteria is only 60% initial value. Due to the presence of the adhered mortar and multi layers of old interfacial transition zone of repeated recycled coarse aggregates, the chloride ion propagation increased with the increased number of repetitions. After being exposed to 28 wetting and drying cycles with sodium chloride solution the values of chloride ion concentration of control, RC1, RC2 and RC3 were 72.9 ppm/m2, 84.5 ppm/m2, 98.5 ppm/m2, and 105.9 ppm/m2, respectively. 7.3 LIMITATIONS OF THIS STUDY This study has the following limitations mainly due the unavailability of proper equipment and time constraint.   ? Height and volume changes of specimens would be more accurate if length comparator could be used. ? For sulphate durability test, prism or bar type specimens are better options rather than cylinder. Due to unavailability of mold we had to work with cylindrical specimens. ? During the production of different generation repeated recycled coarse aggregate  concrete crusher did not have similar sieve/mesh. This was due to the shortage of large    104 capacity crushers in the region, which was also associated with high amount of cost for this operation.  ? Strength loss due to sulphate attack of different generations repeated recycled coarse aggregate concrete was not observed over a long period of time due to time constraint. Long testing period is required to investigate the sulphate durability performance of both repeated recycled coarse aggregate concrete and recycled concrete made with different RCA replacement levels. 7.4 RECOMMENDATIONS FOR FUTURE RESEARCH Repeated recycled coarse aggregate concrete is a new generation concrete which can be a sustainable and cost effective solution for construction industry. The results of this study will surely grow interest among researchers towards new generation concrete. Potential improvements to the methods and results presented in this study include: ? Long time exposure should be considered to evaluate the durability performance of green concrete. ? Combination of NA and different generations of repeated recycled coarse aggregate with different replacement levels need to be investigated. ? The splitting tensile strength and flexural strength of recycled and repeated recycled concrete under different harsh exposure conditions need to be investigated to get more accurate idea about their durability performance. ? Investigate the fire resistance of both recycled and repeated recycled concrete. ? Design guideline should be formulated for recycled concrete mix design.    105 ?  Investigation of the attached mortar content of different generations of repeated recycled coarse aggregate should be carried out. ? Detailed lifecycle analysis should be conducted for recycled concrete.  ? It is also critical to determine the performance of structural elements (e.g. beams, columns, walls) made of recycled and repeated recycled concrete. ? 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Zhao, W. and Rotter, S. 2008. ?The current situation of construction & demolition waste management in China.? 2nd International Conference on Bioinformatics and Biomedical Engineering, ICBBE 2008, pp. 4747-4750.    121 APPENDIX-A: COMPRESSIVE STRENGTH AND CHLORIDE ION CONCENTRATION Table A1: Chemical composition (after Siddique 2003) Chemical composition Class F fly ash (%) ASTM C618 (%) Silicon dioxide, SiO2 55.3  Aluminum oxide, Al2O3 25.7  Ferric oxide, Fe2O3 5.3  SiO2+ Al2O3+Fe2O3 85.9 70 min Calcium oxide 5.6  Magnesim oxide 2.1 5 max Titanium oxide 1.3  Potassium oxide 0.6  Sodium oxide 0.4 1.5 max Sulfure trioxide 1.4 5 max LOI (1000?C) 1.9 6 max Moisture 0.3 3 max  Table A2: Concentration of chloride ions per unit surface area of concrete cylinder   Concentration of chloride ions per unit surface area of cylinder (ppm/m2)   Mix -1 Mix -2 Mix -3 Mix -4 Mix -5 Mix -6 Standard moist Curing 0.00 0.00 0.00 0.00 0.00 0.00 1 cycle (29th day) 19.15 26.39 34.42 34.26 36.69 39.25 4 cycles (32nd day) 30.06 33.60 36.39 43.41 46.91 49.05 9 cycles (37th day) 31.06 35.73 46.80 48.63 56.73 77.62 16 cycles (44th day) 43.25 46.54 63.78 70.17 78.60 82.74 28 cycles (56th day) 60.91 62.93 77.87 79.80 95.63 99.63 90 cycles (118th day) 91.59 109.55 121.17 144.00 163.08 166.15 120 cycles (148th day) 120.96 123.53 131.25 185.61 196.57 198.19 [Mix-1 = Control, Mix-2 = 30% RCA, Mix-3 = 40% RCA, Mix-4 =50% RCA, Mix-5 =75% RCA, and Mix-6 =100% RCA]     122  Table A3: Compressive strength of the natural coarse aggregate concrete and different generations repeated RCA concrete   Age (days) Compressive strength (MPa) Control 3 24.0 7 29.7 28 40.3 56 43.1 1st generation repeated RCA Concrete (RC1) 3 20.9 7 25.3 28 33.7 56 35.9 2nd generation repeated RCA Concrete (RC2) 3 22.8 7 27.6 28 34.5 56 36.8 3rd generation repeated RCA Concrete (RC3) 3 14.4 7 17.9 28 23.6 56 29.0  Table A4: Concentration of chloride ions per unit surface area of concrete cylinder   Concentration of chloride ions per unit surface area of cylinder (ppm/m2)   Control RC1 RC2 RC3 Standard moist Curing 0 0 0 0 1 cycle (29th day) 45.43 46.06 56.64 66.25 4 cycles (32nd day) 47.22 49.62 67.60 72.28 9 cycles (37th day)  56.48 63.77 79.35 84.36 16 cycles (44th day) 64.05 76.39 96.74 100.83 28 cycles (56th day) 72.90 84.54 98.49 105.88 [Control = Natural aggregate concrete, RC1 = 1st generation repeated recycled coarse aggregate concrete, RC2 = 2nd generation repeated recycled coarse aggregate concrete, and RC3 = 3rd generation repeated recycled coarse aggregate concrete]  

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