Applied Science, Faculty of
Engineering, School of (Okanagan)
DSpace
UBCO
Hossain, F M Zahid
Doctor of Philosophy - PhD
University of British Columbia
This research examined the impact of using recycled coarse aggregate (RCA), crumb rubber (CR), and polypropylene fibre (PPF) as partial replacements for traditional concrete coarse and fine aggregates. Through a series of experiments, the study assessed the compressive strength, tensile strength, and flexural response of recycled aggregate concrete with CR and PPF in comparison to natural aggregate concrete. Further tests examined the bond strength of concrete with steel reinforcement, aiming to optimise resource use, and investigated the shear behaviour of concrete beams containing RCA, CR, and PPF. The findings contributed insights into the potential of these recycled materials to create more sustainable concrete solutions. The study found that increasing crumb rubber (CR) content resulted in reduced compressive, tensile, and flexural strength while adding polypropylene fibre (PPF) improved these properties. For toughness and ductility, PPF had the most significant positive effect, with both RCA and CR enhancing these aspects when added incrementally. In bond analysis, combining CR and PPF reduced concreteâs bond with steel reinforcement, though using either material alone in certain RCA mixtures improved bond strength. Shear strength tests showed that CR reduced shear strength, post-diagonal cracking resistance, toughness, and deformability in concrete beams, but adding PPF enhanced these effects at up to 30% RCA replacement. The optimal composition (30% RCA, 5% CR, and 1% PPF) showed the best shear resistance, deformability, and toughness, with minor rubber additions (up to 5%) enhancing beam deformability and fibre increasing post-crack resistance. The research concluded that the optimal mix for sustainable concrete applications of recycled materials includes up to 30% recycled coarse aggregate (RCA), 5% crumb rubber (CR), and up to 2% polypropylene fibre (PPF). This combination demonstrated the best balance of mechanical and structural performance, making it a viable option for integrating recycled materials into concrete in future.
MECHANICAL AND STRUCTURAL BEHAVIOUR OF RUBBERISED RECYCLED AGGREGATE CONCRETE by F M Zahid Hossain M.Sc., Bangladesh University of Engineering and Technology, 2005 B.Sc., Bangladesh University of Engineering and Technology, 1997 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in The College of Graduate Studies (Civil Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Okanagan) December 2024 © F M Zahid Hossain, 2024 ii The following individuals certify that they have read and recommended to the College of Graduate Studies for acceptance the dissertation entitled: MECHANICAL AND STRUCTURAL BEHAVIOUR OF RUBBERISED RECYCLED AGGREGATE CONCRETE submitted by F M Zahid Hossain in partial fulfillment of the requirements for the degree of Doctor of Philosophy. Dr. M. Shahria Alam, School of Engineering Supervisor Dr. Ahmad Rteil, School of Engineering Supervisory Committee Member Dr. Kasun Hewage, School of Engineering Supervisory Committee Member Dr. Thomas Johnson, School of Engineering University Examiner Dr. Sreekanta Das, Faculty of Engineering, University of Windsor External Examiner iii Abstract This research examined the impact of using recycled coarse aggregate (RCA), crumb rubber (CR), and polypropylene fibre (PPF) as partial replacements for traditional concrete coarse and fine aggregates. Through a series of experiments, the study assessed the compressive strength, tensile strength, and flexural response of recycled aggregate concrete with CR and PPF in comparison to natural aggregate concrete. Further tests examined the bond strength of concrete with steel reinforcement, aiming to optimise resource use, and investigated the shear behaviour of concrete beams containing RCA, CR, and PPF. The findings contributed insights into the potential of these recycled materials to create more sustainable concrete solutions. The study found that increasing crumb rubber (CR) content resulted in reduced compressive, tensile, and flexural strength while adding polypropylene fibre (PPF) improved these properties. For toughness and ductility, PPF had the most significant positive effect, with both RCA and CR enhancing these aspects when added incrementally. In bond analysis, combining CR and PPF reduced concreteâs bond with steel reinforcement, though using either material alone in certain RCA mixtures improved bond strength. Shear strength tests showed that CR reduced shear strength, post-diagonal cracking resistance, toughness, and deformability in concrete beams, but adding PPF enhanced these effects at up to 30% RCA replacement. The optimal composition (30% RCA, 5% CR, and 1% PPF) showed the best shear resistance, deformability, and toughness, with minor rubber additions (up to 5%) enhancing beam deformability and fibre increasing post-crack resistance. The research concluded that the optimal mix for sustainable concrete applications of recycled materials includes up to 30% recycled coarse aggregate (RCA), 5% crumb rubber (CR), and up to 2% polypropylene fibre (PPF). This combination demonstrated the best balance of mechanical and structural performance, making it a viable option for integrating recycled materials into concrete in future. iv Lay Summary Concrete as a fundamental material in construction, has significantly impacts on the environment. With the increasing demand for construction and the need for a sustainable green environment, it has become imperative to think about the reuse and recycling of concrete and other wastes. Both concrete and rubber pose a serious burden on the planet Earth. A lot of research has been done on recycled concrete aggregate and crumb rubber as to how to use these in the construction industries, especially on their replacement quantities and use. This thesis will try to address if both can be used as an element in a structure so that the replacement of a certain percentage of RCA and CR can be done. A guideline on the use of such material in a proportionate way is the key objective. So far, research has found that 20-30% replacement of RCA and 5-10% replacement of CR do not significantly reduce its strength and qualities. However, this study investigates the mechanical and structural behaviour of the combined use of RCA and CR in the construction industry for its practical application. v Preface This dissertation is based on original experimental investigations carried out by the author in the Applied Laboratory for Advanced Materials & Structures (ALAMS), School of Engineering at the University of British Columbia (UBC)âs Okanagan campus and Concrete and Structural Materials Laboratory, Military Institute of Science & Technology (MIST), Bangladesh. The author was responsible for the design and identification of tests & full research program, materials selection, data acquisition & collection, modeling, result analysis and thesis writing, assisted by some research assistants of UBCO and MIST with test setups. Guidance and supervision throughout the work were provided by Dr. M. Shahria Alam, Dr. Ahmad Rteil, and Dr. Kasun Hewage from UBC and Dr. Khondaker Sakil Ahmed from MIST. The author carried out a number of investigations related to Recycled Concrete Aggregate (RCA) and Crumb Rubber (CR) with Polypropylene Fibre (PPF) and published the following papers. Generative AI was not used for any aspects of this research, including data acquisition and result analysis. Some chapters and parts of this dissertation have already been presented in journals and conference proceedings, as shown below. 1. Most parts of Chapter 3 were published in HOSSAIN, F. M. Z., SHAHJALAL, M., ISLAM, K., TIZNOBAIK, M. & ALAM, M. S. 2019. âMechanical properties of recycled aggregate concrete containing crumb rubber and polypropylene fibre.â Construction and Building Materials, 225: 983-996. The author conceived the original idea for investigating for the first time with RCA, CR, and PPF in such a test scenario while getting guidance from Dr. M. Shahria Alam. They conducted a detailed study and published the paper. 2. Some parts of Chapter 4 are in the process of publication and submitted in Construction and Building Materials, Elsevier in HOSSAIN, F. M. Z., K.S., AHMED, RUKIYA, Q. U., TAMANNA, K., ALAM, M. S. as âInfluence of crumb rubber and polypropylene fibre on the bond strength of recycled aggregate concrete.â The author conceived the original idea for experiments with RCA, CR and PPF with pull-out tests in three phases, and taken guidance from Dr. M. Shahria Alam and conducted a detailed analysis. 3. Most parts of the Chapter 5 were published in HOSSAIN, F. M. Z., PAL, A, AHMED, K.S., BEDIWY,A., M. & ALAM, M. S. 2023. âShear behaviour of polypropylene fibre-reinforced concrete beams containing recycled aggregate and crumb rubber.â Journal of Cleaner Production, 412: 137370. The author first conceived the idea for the investigation of the structural shear behaviour of recycled concrete with RCA, CR and PPF and took vi guidance from Dr. M. Shahria Alam. Dr. Khondaker Sakil Ahmed played an important role by providing valuable recommendations with data and result analysis. 4. The author contributed in some parts with data collection and assessment in SHAHJALAL, M., ISLAM, K., BATOOL, F., TIZNOBAIK, M., HOSSAIN, F. M. Z., AHMED, K. S., , ALAM, M. S. AND AHSAN, R., 2023. âFibre-reinforced recycled aggregate concrete with crumb rubber; a state-of-the-art review.â Construction and Building Materials, 404: 133233. 5. The author contributed some parts included in Chapter 2 with data collection, data curation and writing in PAL, A, AHMED, K.S., HOSSAIN, F. M. Z., & ALAM, M. S. 2023. âMachine learning models for predicting compressive strength of fibre-reinforced concrete containing waste rubber and recycled aggregate.â Journal of Cleaner Production, Volume 423, 138673. Dr. Khondaker Sakil Ahmed played a pivotal role by providing valuable ideas on the formulation of machine learning models, statistical tests, and data analysis. 6. The author contributed to most parts of the design of experiment, data collection, result analysis & writing, as mentioned in some parts of the thesis from HOSSAIN, F. M. Z., ALAM, M. S., Islam, M. Z. 2020. âEnergy absorption behaviour of reinforced concrete column consisting recycled aggregate, crumb rubber and polypropylene fibre under lateral impact.â IABSE-JSCE Conference on Advances in Bridge Engineering-IV. https://iabse-bd.org/2020/ 7. The author contributed in most parts as co-author in the paper included in Chapter 3 of the thesis with the design of experiment, test set up, data collection and result analysis from SHAHJALAL, M., HOSSAIN, F. M. Z., TIZNOBAIK, M., & ALAM, M. S., 2019. âExperimental study on the mechanical properties of recycled aggregate concrete using crumb rubber and polypropylene fibre.â CSCE Annual Conference. vii Table of Contents Abstract ......................................................................................................................................... iii Lay Summary ............................................................................................................................... iv Preface ............................................................................................................................................ v Table of Contents ........................................................................................................................ vii List of Abbreviations and Acronyms ..................................................................................... xviii Acknowledgments ...................................................................................................................... xix Dedication .................................................................................................................................... xx Chapter 1: Introduction ............................................................................................................... 1 1.1 Motivation and Problem Statement ...................................................................................... 1 1.2 Background ........................................................................................................................... 1 1.3 Source and Production of RCA............................................................................................. 3 1.4 Source and Production of Crumb Rubber ............................................................................. 3 1.5 Source and Different Types of Fibre .................................................................................... 5 1.6 Research Objectives .............................................................................................................. 7 1.7 Thesis Organization .............................................................................................................. 7 Chapter 2: Literature Review .................................................................................................... 10 2.1 Introduction ......................................................................................................................... 10 2.1.1 RCA in Concrete .......................................................................................................... 10 2.1.2 CR in Concrete ............................................................................................................. 12 2.1.3 PPF in Concrete ........................................................................................................... 14 2.1.4 RCA, CR and PPF in Concrete .................................................................................... 15 2.1.5 Bond Behaviour ........................................................................................................... 18 2.1.6 Shear Behaviour ........................................................................................................... 19 2.1.7 Machine Learning Models for Material ....................................................................... 19 viii 2.1.7.1 Analysing Database .................................................................................................. 20 2.1.7.2 Statistical Overview of the Used Data ...................................................................... 20 2.1.7.3 Sensitivity Analysis .................................................................................................. 22 2.1.7.4 Data Analysis ............................................................................................................ 25 2.2 Research Gap ...................................................................................................................... 25 2.3 Significance of experiments on recycled aggregate concrete with CR and PPF ................ 26 2.3.1 Mechanical Behaviour ................................................................................................. 26 2.3.2 Shear Strength .............................................................................................................. 27 2.3.3 Bond Strength .............................................................................................................. 27 2.4 Summary ............................................................................................................................. 27 Chapter 3: Mechanical Behaviour of Recycled Aggregate Concrete Containing CR and PPF....................................................................................................................................................... 29 3.1 General ................................................................................................................................ 29 3.2 Materials Properties ............................................................................................................ 29 3.2.1 Cement ......................................................................................................................... 29 3.2.2 Properties of Natural Fine Aggregate (NFA)............................................................... 29 3.2.3 Properties of Natural Coarse Aggregate (NCA) .......................................................... 29 3.2.4 Properties of Recycled Coarse Aggregate (RCA) ....................................................... 30 3.2.5 Properties of Crumb Rubber (CR) ............................................................................... 30 3.2.6 Properties of Polypropylene Fibre (PPF) ..................................................................... 30 3.3 Test Matrix and Variables ................................................................................................... 31 3.4 Properties of Variables ........................................................................................................ 34 3.5 Test Specimens ................................................................................................................... 34 3.6 Sample Preparation ............................................................................................................. 34 3.7 Testing Procedure ............................................................................................................... 35 ix 3.8 Result Analysis ................................................................................................................... 36 3.8.1 Fresh concrete properties ........................................................................................ 36 3.8.2 Compressive strength .............................................................................................. 37 3.8.3 Splitting tensile strength ........................................................................................... 40 3.8.4 Assessment with standard code of practices ............................................................... 46 3.8.5 Hardened concrete density ........................................................................................ 49 3.9 Failure Pattern ..................................................................................................................... 50 3.10 Summary ........................................................................................................................... 53 Chapter 4: Bond Behaviour of Recycled Aggregate Concrete with Rebar Containing CR and PPF ............................................................................................................................................... 54 4.1 General ................................................................................................................................ 54 4.2 Test Matrix and Variables ................................................................................................... 54 4.3 Properties of Materials ........................................................................................................ 56 4.4 Test Specimen ..................................................................................................................... 57 4.5 Specimen Preparation ......................................................................................................... 58 4.6 Testing Procedure ............................................................................................................... 59 4.7 Result Analysis ................................................................................................................... 62 4.7.1 Phase I: Bond Strength of Concrete with RCA, CR and PPF ...................................... 62 4.7.1.1 Crumb rubber effect on bond strength ...................................................................... 63 4.7.1.2 Comparative study of CR and PPF ............................................................................ 65 4.7.1.3 Combined analysis .................................................................................................... 67 4.7.1.4 Relation of bond strength with compressive strength (Normalized) ........................ 69 4.7.1.5 Load-extension behaviour ........................................................................................ 71 4.7.1.6 Slip analysis .............................................................................................................. 73 4.7.1.7 Failure pattern ........................................................................................................... 74 x 4.7.2 Phase II: Comparative Study of Recycled Concrete Aggregate and Crumb Rubber .. 75 4.7.3 Phase III: Study on the combined effect of RCA, CR and PPF on bond strength with variable bar diameter............................................................................................................. 76 4.7.3.1 Comment on the overall outcome of bond strength in phase III............................... 79 4.8 Comparison with existing Models and Codes .................................................................... 81 4.9. Regression Analysis ....................................................................................................... 84 4.10 Summary ........................................................................................................................... 86 Chapter 5: Shear Behaviour of Recycled Aggregate Concrete Containing CR and PPF .... 87 5.1 General ................................................................................................................................ 87 5.2 Shear Behaviour of Rubberised Concrete Beams Containing RCA, CR and PPF ............. 87 5.3 Test Matrix and Variables ................................................................................................... 87 5.4 Physical Properties of the Materials ................................................................................... 89 5.5 Test Specimens ................................................................................................................... 91 5.6 Sample Preparation ............................................................................................................. 91 5.7 Testing Procedure ............................................................................................................... 92 5.8 Experimental Data .............................................................................................................. 94 5.9 Result Analysis ................................................................................................................... 95 5.9.1 Fresh Characteristics .................................................................................................... 95 5.9.2 Compressive Strength .................................................................................................. 96 5.9.3 Load-deflection Response ............................................................................................ 98 5.9.4 Post-diagonal Cracking Resistance ............................................................................ 102 5.9.5 Failure Mode and Crack Pattern ................................................................................ 103 5.9.6 Digital Image Correlation (DIC) ................................................................................ 107 5.9.7 Beam Deformation and Load-strain Relation ............................................................ 109 5.9.8 Shear Capacity Comparison with Codes.................................................................... 113 xi 5.10 Summary ......................................................................................................................... 116 Chapter 6: Conclusion .............................................................................................................. 118 6.1 Summary ......................................................................................................................... 118 6.1.1 Mechanical Properties of Concrete with RCA, CR and PPF ................................ 119 6.1.2 Bond Strength of Concrete Containing RCA with CR and PPF ........................... 120 6.1.3 Shear Strength of Concrete Containing RCA with CR and PPF .......................... 121 6.2 Conclusions and Future Guidelines.............................................................................. 122 6.2.1 Overall Conclusions .............................................................................................. 122 6.2.2 Guidelines for Use ................................................................................................ 123 6.3 Limitations of the Study ............................................................................................... 124 6.4 Novelty of this Study.................................................................................................... 125 6.5 Recommendations for Future Research ....................................................................... 126 Bibliography .............................................................................................................................. 127 Appendices ................................................................................................................................. 136 Appendix A Allowable limits of deleterious elements in RCA .............................................. 136 Appendix B Classifications of rubber aggregate. ................................................................... 137 Appendix C Chemical composition of CR by different researchers....................................... 138 Appendix D Different properties of fibre ............................................................................... 139 Appendix E Summary of compressive strength of RRAC and FRRAC by different researchers................................................................................................................................................. 139 Appendix F Summary of modulus of elasticity by different researchers. .............................. 142 Appendix G Summary of tensile strength by different researchers. ....................................... 143 Appendix H Summary of flexural strength of RRAC and FRRAC by different researchers. 144 Appendix I Comprehensive reference table of different research related to RCA ................. 145 xii List of Tables Table 2.1 Statistical distribution of database features (Pal et al., 2023). ...................................... 22 Table 2.2 Correlation matrix of the input variables (Pal et al., 2023). ......................................... 24 Table 3.1 Properties of Portland Composite Cement (PCC) ........................................................ 31 Table 3.2 Specifications for PPF .................................................................................................. 31 Table 3.3 Specimen identification description.............................................................................. 33 Table 3.4 The proportion of aggregates for concrete mixtures per cubic metre (Hossain et al., 2019)....................................................................................................................................................... 33 Table 3.5 Physical properties of aggregates ................................................................................. 34 Table 3.6 Mechanical properties of different concrete mixtures (56 days) .................................. 40 Table 3.7 Summary of flexural response (for 10% RCA) (Hossain et al., 2019) ......................... 43 Table 3.8 Summary of flexural response (for 30% RCA) (Hossain et al., 2019) ......................... 43 Table 3.9. Ductility value of various batches (Hossain et al., 2019) ............................................ 46 Table 4.1 Designations and description of different materials used in the study (RxCyFz) ........ 54 Table 4.2 Mix proportions of different materials (RCA+CR+PPF) in Phase I ............................ 55 Table 4.3 Mix proportions of different materials (RCA+CR) in phase II ................................... 55 Table 4.4 Mix proportions of different materials (RCA+CR+PPF) in phase III .......................... 56 Table 4.5. Physical properties of PPF ........................................................................................... 57 Table 4.6 Physical properties of aggregates ................................................................................. 57 Table 4.7 Designations and interpretation of length-diameter variations symbols (DxLyCz) of reinforcing steel ............................................................................................................................ 58 Table 4.8 All Pull-out test data recorded in 14 days and 28 days ................................................. 63 Table 4.9 Slip analysis data of different specimens ...................................................................... 73 Table 4.10 All Compressive and Pull-out test data recorded in 28 days ...................................... 76 Table 4.11 Parameters and experimental bond strength for regression analysis .......................... 81 Table 4.12 Comparison of experimental and code-based bond strength (t) of FRRAC ............... 82 Table 4.13 Parameters and experimental bond strength for regression analysis .......................... 85 Table 5.1. Aggregate proportions in concrete mixes (Hossain et al., 2023) ................................. 88 Table 5.2 Aggregates Physical characteristics (Hossain et al., 2023). ........................................ 89 Table 5.3 Chemical and physical properties of OPC (Hossain et al., 2023) ................................. 90 Table 5.4 PPF specifications ......................................................................................................... 90 xiii Table 5.5 Mechanical properties of reinforcing steel. .................................................................. 90 Table 5.6 Test Result Summary .................................................................................................... 94 Table 5.7 Value of and compressive strength of concrete (Hossain et al., 2023) ......................... 97 Table 5.8 Test results showing crack numbers and pattern (Hossain et al., 2023) ..................... 102 Table 5.9 Vtest/Vcode for rubberised concrete made with RCA and PPF (Hossain et al., 2023) . 115 xiv List of Figures Figure 1.1 Process of RCA Production, images from sources (Shahjalal et al., 2023) ..... 3 Figure. 1.2 Production of RCA and stage-wise process of tire-shredding, image from sources (Li et al., 2022; Roychand et al., 2020; M. Valente and A. Sibai, 2019; Gupta et al., 2014) ............... 4 Figure 1.3 Types of fibres used in concrete (Hossain et al., 2019; Ganjian et al., 2009; Mhaya et al., 2020; Islam et al., 2022; Micelli et al., 2020; Emon et al., 2017; Sadrolodabaee et al., 2021; Shadheer et al., 2021) images are not in scale. ............................................................................... 6 Figure 1.4 Research Overview ........................................................................................................ 9 Figure 2.1 Concrete replaced with RCA & CR particles: (a-b) interface of rubber-cement paste, and (c-d) interface of recycled aggregates-cement paste (Su, 2015; Ahmed et al., 2019; Meherier, 2016) ............................................................................................................................................. 13 Figure 2.2 Variation of strength of FRRAC considering (a) compressive strength, (b) tensile strength, (c) modulus of elasticity, (d) flexural strength ............................................................... 16 Figure 2.3 Graphical representation of the outcome of RCA, CR and PPF on mechanical behaviour of concrete (Shahjalal et al., 2023) ............................................................................................... 17 Figure 2.4 Distribution of input variables of fibre-reinforced concrete made with rubber and recycled concrete aggregate database (Pal et al., 2023) ................................................................ 21 Figure 2.5 Difference in compressive strength of concrete with respect to (a) nominal coarse aggregate size (mm), (b) RCA (%), (c) Rubber (%), (d) W/C, (e) Fibre (%), (f) Fibre Type (Pal et al., 2023) ....................................................................................................................................... 23 Figure 2.6 Correlation matrix heat map of the input variables (Pal et al., 2023). ........................ 24 Figure 3.1 Aggregate used in concrete: (a) Recycle Coarse Aggregate (b) Crumb Rubber (c) Polypropylene Fibre (Hossain et al., 2019) .................................................................................. 30 Figure 3.2 Gradation curve of (a) natural coarse aggregate (NCA) and RCA; (b) sand and CR (Hossain et al., 2019) .................................................................................................................... 31 Figure 3.3 Test setup (a) compression test (b) quasi-static flexural test ....................................... 35 Figure 3.4 Slump value and air content of different concrete mixtures ........................................ 37 Figure 3.5 Variation in compressive strength of different concrete mixtures for (a) 10%, and (b) 30% RCA combinations (Hossain et al., 2019) ............................................................................ 37 Figure 3.6 Splitting tensile strength of various concrete mixtures for (a) 10%, and (b) 30% RCA combinations (Hossain et al., 2019) .............................................................................................. 40 xv Figure 3.7 Flexural strength variation in different concrete mixtures for (a) 10%, and (b) 30% RCA combinations(Hossain et al., 2019) ............................................................................................... 41 Figure 3.8 Load vs deflection response of beams under various replacement levels of RCA (for 5% CR & 2% Fibre) ...................................................................................................................... 44 Figure 3.9 Load vs deflection of beams under various replacement of CR for (a) 30% RCA and 1% fibre, and (b) 30% RCA and 2% fibre combinations (Hossain et al., 2019) .......................... 44 Figure 3.10 Load vs deflection of beams under various fibre content for (a) 30% RCA and 0% CR, (b) 30% RCA and 5% CR, and (c) 30% RCA and 10% CR combinations (Hossain et al., 2019) 45 Figure 3.11 Comparison of splitting tensile strength with different codes ................................... 47 Figure 3.12 The ratio between the experimental and the calculated values (ξ) of splitting tensile strength using available guidelines for concrete ........................................................................... 48 Figure 3.13 Comparison of flexural strength with different codes ............................................... 48 Figure 3.14 The ratio between the experimental and the calculated values (ξ) of flexural strength using available guidelines for concrete ......................................................................................... 49 Figure 3.15 Harden density of concrete specimens ...................................................................... 50 Figure 3.16 Failure pattern of concrete cylinder under compressive strength test: (a) control, (b) only 30% RCA, (c) RCA, CR and fibre combination................................................................... 51 Figure 3.17 Concrete specimen after splitting tensile strength test: (a) only for RCA and (b) RCA, rubber and fibre combination ........................................................................................................ 51 Figure 3.18 Failure pattern of the concrete beam under flexural strength test: (a) control, (b) only 10% RCA, (c) RCA 30%, CR 10% and fibre 2% ......................................................................... 52 Figure 3.19 Beam specimen after flexural strength test (a) R10C0F0, (b) R30C0F2, (c) R30C5F2 ... 52 Figure 4.1 Pull-out test specimens ................................................................................................ 59 Figure 4.2 Cross-section of the specimen ...................................................................................... 60 Figure 4.3 Pull-out test â Phase I (a) Special apparatus, (b) Apparatus setup in UTM, (c) Complete test setup........................................................................................................................................ 61 Figure 4.4 Pull-out test â Phase II (a) Cross section of the specimen, (b) Complete test setup ... 61 Figure 4.5 Phase III (a) Compressive test setup, (b) Pull out test setup ....................................... 62 Figure 4.6 (a) Crumb rubber effect in 14 days bond strength with various bar diameter-length variations for variable RCA content ............................................................................................. 64 xvi Figure 4.6 (b) Crumb rubber effect in 14 days bond strength with various bar diameter-length variations for variable RCA content rubber effect in 28 days ...................................................... 65 Figure 4.7 Crumb rubber effect in bond strength with various bar diameter- length variations .. 65 Figure 4.8 (a) Bond strength variation for CR and PPF ................................................................. 67 Figure 4.8 (b) Comparative study between CR and PPF with 30% RCA .................................... 67 Figure 4.9 (a) Bond strength of concrete with RCA, CR, and PPF for three length-diameter combinations at 28 days ................................................................................................................ 68 Figure 4.9 (b) Compressive and Bond strength of concrete with RCA, CR, and PPF for three length-diameter combinations at 28 days ..................................................................................... 69 Figure 4.10 (a) Normalized relation between Compressive and Bond strength of FRRAC with Rebar for D12L100 at 28 days ...................................................................................................... 70 Figure 4.10 (b) Normalized relation between Compressive and Bond strength of FRRAC with Rebar for D12L150 at 28 days ...................................................................................................... 70 Figure 4.10 (c) Normalized relation between Compressive and Bond strength of FRRAC with Rebar for D10L100 at 28 days ...................................................................................................... 71 Figure 4.11 Load-extension graph of (a) D12L100C1, (b) D12L100C2, (c) D12L100C3, (d) D12L100C4, (e) D12L100C5, (f) D12L100C6 and (g) D12L100C7 ............................................ 72 Figure 4.12 Cracking and splitting failure â (a) front view and (b) top view; (c)Radial failure by pull-out bar lug; Abrupt failure of the control specimen â (d) front view and (e) exploded specimen....................................................................................................................................................... 74 Figure 4.13 Phase II - Comparative analysis of concrete bond strength with RCA and CR ........ 75 Figure 4.14 Phase III - Comparative analysis of concrete compressive and bond strength with RCA, CR and PPF......................................................................................................................... 77 Figure 4.15 (a) Normalized relation between Compressive and Bond strength of FRRAC for 12 mm rebar at 28 days ...................................................................................................................... 78 Figure 4.15 (b) Normalized relation between Compressive and Bond strength of FRRAC for 16 mm rebar at 28 days ...................................................................................................................... 78 Figure 4.15 (c) Normalized relation between Compressive and Bond strength of FRRAC for 20 mm rebar at 28 days ...................................................................................................................... 79 Figure 4.16 Phase III - Comparative analysis of bond strength with RCA, CR and PPF with 10 and 30 % RCA replacements ............................................................................................................... 80 xvii Figure 4.17 A comparison of bond strength between experimental results and existing models for (a) 12mm, (b) 16mm, (c) 20mm rebar .......................................................................................... 83 Figure 4.18 A comparison between experimental and predicted bond strength of FRRAC ........ 86 Figure 5.1 Gradation curve of (a) crumb rubber (CR) and natural fine aggregate (NFA); (b) recycled concrete aggregate (RCA) and natural coarse aggregate (NCA) ................................... 90 Figure 5.2 Diagram of four-point shear test, (b) cross-section of beams (Hossain et al., 2023) .. 91 Figure 5.3 Different stages of the experiment .............................................................................. 93 Figure 5.4 Graph for load versus mid-span deflection of the tested beams (a) different RCA replacement levels, (b) different CR replacement levels, (c) different CR replacement with 30% RCA, (d) different CR replacement with 50% RCA, (e) influence of PPF (f) influence of PPF with replacement 30% RCA, and (g) influence of PPF with replacement 50% RCA (Hossain et al., 2023) ........................................................................................................................................... 101 Figure 5.5 Observed patterns and failure modes of the tested beams (Hossain et al., 2023) .... 105 Figure 5.6 Graphic crack patterns of the tested beams (Hossain et al., 2023) ............................ 106 Figure 5.7 Computed longitudinal strains obtained from the surface of the beam using DIC (Hossain et al., 2023) .................................................................................................................. 108 Figure 5.8 Deflected concrete beams at various load stages (Hossain et al., 2023) ................... 110 Figure 5.9 Load-strain response of the concrete beam (Hossain et al., 2023) ............................ 112 Figure 5.10 The ratio between the experimental and the theoretical values of ultimate shear capacity utilizing existing design codes (Hossain et al., 2023) .................................................. 116 xviii List of Abbreviations and Acronyms ACI American Concrete Institute ASTM American Standards for Testing and Materials BS British Standards c/d cover to rebar diameter ratio CSA Canadian Standards Association CR crumb rubber DAQ Data Acquisition System DIC Digital Image Correlation db nominal diameter of rebar EN European Norms fâc Concrete compressive strength fib The International Federation for Structural Concrete FRRAC Fibre-Reinforced Rubberised Recycled Aggregate Concrete ITZ Interfacial Transition Zone LVDT Linear Variable Displacement Transducer MoE Modulus of Elasticity ML Machine Learning NAC Natural Aggregate Concrete NCA Natural Coarse Aggregates NFA Natural Fine Aggregate PPF polypropylene fibre RCA recycled coarse aggregate ROI Region of Interest RRAC rubberised recycled aggregate concrete SD standard deviation SEM Scanning Electron Microscopy SSD Saturated Surface Dry t bond strength UTM Universal Testing Machine xix Acknowledgments I would like to mention my supervisor, Dr. M Shahria Alam, who not only supported me with his valuable suggestions but also kept my spirit alive to do this long and arduous task. I would like to thank other members of the committee, Dr. Ahmad Rteil and Dr. Kasun Hewage, for guiding me in completing the thesis. This research was conducted in the Applied Laboratory for Advanced Materials & Structures (ALAMS) at UBCâs Okanagan campus with assistance from KON KAST and facilities of the concrete and structural laboratory of MIST. The author would like to mention all the staff and members of these institutions, especially Ms. Kishoare Tamanna, M.S. Meherier and many others, for their support. Finally, I would like to thank the following people who supported this work in diverse ways, providing valuable assistance and physical work during experiments, especially Dr. Khondaker Sakil Ahmed, Lecturer Md. Shahjalal, Avijit Pal, Quazi Umme Rukiya, Md. Moinul Islam, Md. Mohinul Islam and a few students of MIST. Particular thanks to all the past and present students of ALAMS for helping me with various suggestions and technical support. xx Dedication To the Creator Almighty for keeping me physically fit and resolute to complete this research despite covid 19 and many other struggles since I started the program. I would like to mention my wife, Shahida Nasreen, and my children (Anika and Tahmid) in this thesis since they inspired me all the way to achieve it. Finally, I would like to dedicate this outcome to all staff of the UBC School of Engineering, especially Professor Dr. M Shahria Alam, Dr. Ahmed Rteil, and Dr. Kasun Hewage, for their valuable guidance during my work. 1 Chapter 1: Introduction 1.1 Motivation and Problem Statement For the last decade or so, there have been extensive studies on recycled materials for construction industries to find out means to reduce the use of natural resources and decrease environmental pollution. One of the alternatives was to use the old demolished concrete for natural fine and coarse aggregate in the concrete mix and supplementary cementitious materials that provide the same properties as cement. Discarded rubber tires, which are put in landfills, are a source of pollution and depletion of resources. Vast amounts of toxic gas and materials are spread all over the world due to the production of cement and the disposal of tires and wastes. Much research has been carried out so far to investigate the effect of using recycled concrete aggregate as a replacement for natural aggregate that we get from the mining of rocks and stones that come from mountains and rocky areas. The replacement of these natural aggregates by demolished concrete aggregate has been the focus of material and structural engineering for many years, and a reasonable portion of that has been proposed to be replaced with natural aggregate in concrete production. However, specific tests for the structural use of recycled materials like demolished aggregate after recycling and scrap tires after shredding have not been thoroughly studied to propose definite quantities or proportions in the concrete mix. This certainly needs some essential tests such as mechanical, bond, tensile and shear strength of those in concrete. There is a cost and additional energy requirement of reusing and preparing these recycled materials in the concrete, but that cost and energy loss may be much less than mother nature, which is compromising or exhausting its resources. So, the primary endeavour of this study will be to understand the recycled materials and how they interact in the concrete mix in terms of their mechanical and structural behaviours like compressive, flexural, tensile, bond and shear strength in structural concrete elements so that they can be widely used in concrete industries as structural elements. 1.2 Background With the growing demand for concrete as a civil engineering construction material, the concerns related to its production are also rising. One such issue that has grabbed the attention of 2 researchers in this field is the decline in sources of natural aggregate. The gravel for these aggregates is generally collected by excavating mountains, mining, and extracting stones from streams and river beds. These non-renewable natural resources will soon be exhausted, which is a significant concern for the construction industry (Alam et al., 2013). Again, modernization and rapid population growth have resulted in a need for rehabilitation and reconstruction of structures. Construction activities around the world have expanded dramatically in recent decades, as has the number of nonfunctioning/out-of-service structures, resulting in a large volume of construction and demolition (C&D) wastes. In 2014, concrete made up 70% of total construction and demolition (C&D) waste in the United States, with 15.9% coming from buildings, 29.5% from roads and bridges, and 24.9% from other structures. (Hossain et al., 2019). Many countries, including Canada, are having difficulty disposing of and reusing structural debris due to the requirement to create a healthy environment, keep it pollution-free, and minimise carbon emissions (Alam et al., 2013). The waste from demolished concrete buildings and structures is recycled into aggregates (Huda & Alam 2014, Behera et al. 2014). This waste is used as recycled aggregates in concrete after undergoing several phases of crushing, removing impurities, shedding, grinding, cleaning, sorting, and sizing (ACI Committee 555, ACI PRC-555-01, 2010). According to Silva et al. (2014), recycled aggregates are classified into four types: recycled concrete aggregates, recycled masonry aggregates, mixed recycled aggregates, and construction and demolition recycled aggregates. The use of recycled aggregates in concrete provides a promising solution to the problem of C&D waste management (Rao et al., 2007). The authors further state that research by concrete engineers has clearly suggested the possibility of appropriately treating and reusing such waste as aggregate in new concrete, especially in lower-level applications. According to Aslani et al. (2018), crumb rubber comprises 40% carbon, 45% polymer, and 15% organic components, which contribute to pollution, fires, and hazardous leachates in landfills. Consequently, the critical importance of repurposing RCA and waste tire-derived CR for construction applications cannot be overstated, highlighting its role in environmental sustainability and waste management. As such, sources and production of RCA, CR, and PPF are discussed in subsequent paragraphs to give an idea of their sources and preparation process. 3 1.3 Source and Production of RCA Impurities are added to recycled aggregates during the recycling process. Harmful elements like zinc (Zn) and copper (Cu) are limited to fewer than 400 and 200 μg/l, respectively (listed at Appendix A). This was done to make the usage of RCA more environmentally friendly (Oikonomou, 2005). In 2001, the ACI Committee 555 (2002) approved the use of RCA in concrete. Furthermore, ASTM C33 (2018) and CSA A23.1 (2014) standards and specifications are widely used in different nations. The diagram in Figure 1.1 shows the process of crushing and sorting the RCA from demolished structures. Figure 1.1 Process of RCA Production, images from sources (Shahjalal et al., 2023) 1.4 Source and Production of Crumb Rubber It is anticipated that by 2030, there will be 1.2 billion tons of tires that have reached the end of their usable lives, up from over 1 billion tons annually (Thomas et al. 2014; Alwesabi et al., 2021). By repurposing used tires in civil engineering applications, this urgent problem may be 4 resolved. Prior to being used in the concrete mixture, these discarded tires are cut into various pieces. Crumb rubber (CR) is the most often utilised type of rubber as aggregate (Hossain et al. 2019, Tamanna 2018, Meherier 2016, Shahjalal et al. 2019, Alfayez 2018). Natural fine aggregates (NFA) can be partially replaced by these CR, which typically have a diameter of 0.425 to 4.75 mm (Ganjian et al., 2009). Additionally, rubber aggregates that pass through filter No. 40 (0.425mm) are categorized as fine-grained rubber (Boshan et al., 2004; Emiroglu et al., 2007; Ganjian et al., 2009). Figure 1.2 shows the rubber aggregate's step-by-step processing. According to Aslani et al. (2018), crumb rubbers contain 40% carbon, 45% polymer, and 15% organic components. Figure. 1.2 Production of RCA and stage-wise process of tire-shredding, image from sources (Li et al., 2022; Roychand et al., 2020; M. Valente and A. Sibai, 2019; Gupta et al., 2014) 5 1.5 Source and Different Types of Fibre The fibres commonly used are steel fibre (Guo et al., 2014; Lau & Anson, 2006; Noaman et al., 2017); polypropylene fibre (Hossain et al., 2019; Ahmed et al., 2019; Islam et al., 2022); glass fibre; carbon fibre (Micelli et al., 2020); galvanized iron fibre (Emon et al., 2017); basalt fibre (Chen et al., 2020); textile fibre (Sadrolodabaee et al., 2021); recycled steel-wires (Alfayez, 2018); macro synthetic fibre (Islam et al., 2022); and natural fibres such as jute, bamboo, sugarcane, coconut coir, wood, hast, sisal, bagasse, palm, kenaf, banana leaf, pine, seed, banana leaf, pine, banana leaf, seed, and wool (Micelli, 2020, Shadheer et al., 2021; Sethunarayanan et al., 2008; Torgal & Jalali, 2011). Steel fibres are the most often utilised fibres in the manufacturing of concrete. It has a tensile strength of over 1000 MPa and is more effective at preventing cracks from spreading (Islam et al., 2022). Additionally, they can lessen the need for shear reinforcement in concrete constructions (Hanai & Holanda, 2008). In terms of reducing segregation and boosting cohesiveness amongst the constituents, synthetic fibres like polypropylene fibres (PPF) performed better (Tamanna, 2018). According to N. Banthia and S.M. Soleimani's 2005 study, concrete's lower specific gravity means that it requires less PPF than steel fibres. Furthermore, polypropylene fibre-reinforced concrete performs better in terms of durability because PPF does not corrode like steel fibre (Wang et al., 2019). Furthermore, PPF generates less CO2 during production (Shen et al., 2010) and has comparatively lower labour and production costs (Ochi et al., 2015). According to published research, from the workability standpoint, the highest amount of fibre that can be used is up to 2% (Hossain et al., 2019; Islam et al., 2022). Figure 3 shows an overview of the various types of fibres. Due to the universal availability of RCA and CR, the use of these two materials is presumably easy and less costly than PPF. PPF is not widely available in all countries, and its cost varies from region to region. However, the present research will not take the cost into consideration because the life cycle cost may need separate research altogether. 6 (a) Steel fibre (b) Polypropylene fibre (c) Glass fibre (d) Carbon fibre (e) Galvanized iron fibre (f) Basalt fibre (g) Textile fibre (h) Recycled steel-wires (i) Macro synthetic fibre (j) Natural fibre (Jute) Figure 1.3 Types of fibres used in concrete (Hossain et al., 2019; Ganjian et al., 2009; Mhaya et al., 2020; Islam et al., 2022; Micelli et al., 2020; Emon et al., 2017; Sadrolodabaee et al., 2021; Shadheer et al., 2021) images are not in scale. 7 1.6 Research Objectives Over the years, many studies have been undertaken to utilise recycled materials in concrete to mitigate pollution, create a sustainable concrete industry, and make energy efficient structures. As such, the use of demolished concrete aggregate, recycled crumb rubber from tires and other materials were under study. There is no definite guideline as to how much percentage and proportion of original constituents should be replaced by recycled materials. This study aims to cover the use of RCA as a replacement for natural aggregate along with the use of CR and PPF. There is a requirement to assess the combined applicability of all these three replacements as materials in structural concrete. As such, the following objectives are set for this research: â¢ To assess the properties and performance of concrete by integrating RCA, CR, and polypropylene fibres (PPF), focusing on both its fresh and mechanical properties. â¢ To analyse the bond strength behaviour of rubberised fibre-reinforced recycled aggregate concrete with reinforcement to determine its combined effect. â¢ To assess the shear beheviour of reinforced concrete beams integrating Recycled Concrete Aggregate (RCA), Crumb Rubber (CR), and Polypropylene Fibres (PPF), determining the efficacy of these combined materials in concrete structures. 1.7 Thesis Organization This thesis is organized into six chapters. Chapter 1 provides the background and introduction, outlining the research objectives and the organizations involved. The chapter also presents the methodology and experimental processes, with an overview of the experimental setups depicted in Figure 1.4. Chapter 2 reviews the available literature on the mechanical behaviour, bond strength, and shear resistance of concrete incorporating Recycled Concrete Aggregate (RCA), Crumb Rubber (CR), and Polypropylene Fibres (PPF). This chapter highlights the test methods employed by various researchers to analyse the properties and sources of RCA and CR, the proportions of aggregates, and the conclusions drawn from different testing approaches. Additionally, it addresses the state of the art in producing quality recycled aggregates, with a particular focus on their use in concrete. 8 Chapter 3 investigates the mechanical behaviour of concrete when RCA, CR, and PPF are used in combination. In this chapter, all test methods are detailed and discussed, along with a summary of the experimental matrix to show the various compositions tested. Chapter 4 focuses on the bond behaviour of recycled aggregate concrete with rebar, integrating both polypropylene fibres and crumb rubber. It examines the effects of RCA and CR, as well as PPF, using different test methods and presenting the results in the context of various mix compositions. Chapter 5 explores the shear behaviour of recycled aggregate concrete, utilising polypropylene fibre-reinforced concrete cylinders and beams that incorporate RCA and CR. The chapter analyses the effects of RCA and CR, in combination with PPF, based on various tests and results using different compositions. Chapter 6 summarizes the study, discusses the limitations of the research, and its novel contributions, and finally provides guidelines and suggestions for future work. 9 Figure 1.4 Research Overview Thesis Writing End Start Literature Review â¢ Recycled Coarse Aggregate â¢ Crumb Rubber â¢ Polypropylene Fibre Data Acquisition for â¢ Mechanical Properties Analysis â¢ Analysis of Bond Behaviour â¢ Investigating Structural Behaviour Mechanical Property Tests Pullout Test Four Point Static Loading Test Effect of RCA, PPF and CR on bond strength between concrete and rebar Joint impact of RCA, CR and PPF on shear capacity of concrete beam and its failure pattern Impact of RCA, CR and PPF on compressive strength, tensile strength and flexural strength of concrete Material Collection and Testing Mix Design and Sample Preparation Mechanical Property Structural Behaviour Shear Strength Bond Strength â¢ Workability and Hardened Density â¢ Compressive Strength â¢ Flexural Strength 10 Chapter 2: Literature Review 2.1 Introduction The literature review explores the potential of Recycled Concrete Aggregate (RCA) and Crumb Rubber (CR) as sustainable materials in construction while also addressing their limitations. RCA, derived from demolished concrete, is a promising alternative to Natural Concrete Aggregate (NCA), but it exhibits lower density, higher water absorption, and increased porosity due to the presence of old mortar. These characteristics can reduce the compressive strength and permeability of concrete. However, replacing 25%-50% of NCA with RCA has shown minimal impact on critical mechanical properties, including compressive and bond strength, as per research. CR, sourced from recycled scrap tires, also presents both opportunities and challenges in concrete applications. While CR enhances impact resistance, toughness, and energy absorption, it has been found to reduce workability and strength in high quantities. Research into the combined use of RCA and CR reveals mixed outcomes, especially for tensile and flexural strength. For instance, a 50% RCA and 10% CR combination increased tensile strength by 11%-16% in some studies, though other studies show tensile strength reductions with higher replacement ratios. Fibre reinforcement, particularly with steel and polypropylene fibres (PPF), shows promise in enhancing tensile strength by bridging cracks, though the beneficial effect of fibres lessens with increased RCA and CR contents. These findings underscore the need for balanced proportions in RCA and CR use to optimise both mechanical integrity and sustainability in concrete applications. Therefore, the individual materials are discussed in this chapter along with the mechanical, bond, and shear behaviours as found in existing literature and various findings. 2.1.1 RCA in Concrete Although recycled concrete aggregate (RCA) is a promising building material, its mechanical and structural behaviour needs to be understood before it can be produced and used on a large scale. This is because RCA has lower density, a higher Los Angeles abrasion capacity, and a higher absorption capacity than NCA (De Juan & Gutiérrez, 2009). However, studies suggest that replacing 25%-50% NCA with RCA causes no significant change in the mechanical properties 11 of concrete (Wen et al., 2015; Huda & Alam, 2015; Limbachiya et al., 2000). A similar observation was made by (Alam et al., 2013), and the study concluded that partially replacing NCA with RCA does not cause any significant change in concrete strength. Xiao and Falkner reached the conclusion that RCA replacement has no direct influence on the bond strength of the deformed bar (Xiao et al., 2007). Rockson (2020) found that the bond strength of commercially produced Recycled Aggregate Concrete did not fluctuate much from the data of ACI 408 (Rockson et al., 2020). However, the shear strength of concrete reduces with increasing replacement of RCA (Sogo et al., 2004; Al Mahmoud et al., 2020). NCA and accompanying old mortar on the surface of the aggregates make up the RCA, which is made from construction and demolition wastes (CDW). Because of this, recycled aggregate concrete has two interfacial transition zones (ITZs): one between old mortar and natural aggregate concrete (NAC) (old ITZ) and another between RCA and new mortar (new ITZ). However, NAC only has one new ITZ (Wang et al., 2021). As a result, the recycled aggregate concrete has a higher volume of ITZ than NAC, which results in porosity, increased permeability, and worse mechanical qualities. Previous researchers found that adding recycled aggregate decreased compressive strength and increased the tendency to absorb water (Martín-Morales et al., 2011; Tamanna et al., 2020; Duan and Poon, 2014; Bai et al., 2020). Due to the associated mortar, RCA has an absorption capability ranging from 3.2% to 12% (Katz, 2003). Compared to NCA, the concrete is less workable because of the increased absorption capacity of RCA (Salem et al., 2003; Topçu & Åengel, 2004). Using RCA from medium and high-strength concrete minimized performance losses in recycled aggregate concrete (Bogas et al., 2015). Again, research shows the replacement of up to 45% NCA with RCA had no significant influence on concrete parameters like compressive strength, Modulus of Elasticity and flexural strength, indicating that RCA may be utilised for structural concrete (Wen et al., 2015). (Alam et al., 2013) discovered that RCA concrete had a 15% drop in compressive strength for a 25% replacement. Meanwhile, RCA-built concrete reduced flexural strength by 15.8% for 25% RCA replacement and increased tensile strength by 34% for 25% RCA replacement and 16% for 50% RCA replacement. Up to 30% replacement, the compressive strength of RCA concrete did not change much, but RCA replacement above 30% reduced the strength, according to (Limbachiya 12 et al., 2000). More research is required to determine the unknown variability of RCA replacement above 30%. 2.1.2 CR in Concrete It has been reported that every year, approximately 1 billion scrap tires are being generated worldwide, almost 150000 tons of which are produced in Bangladesh (Chowdhury, 2017) and 350,000 to 450,000 tons of scrap tires are produced in Canada (Canadian Association of Tire Recycling Agencies, (CATRA) 2022). This large amount of disposed of tires is creating waste management problems. However, these discarded scrap tires can be proven as valuable construction materials through proper research. In fact, in 2017, approximately 315 thousand tons of scrap tires had been used for civil engineering projects (Chowdhury, 2017). Because of its improved mechanical qualities, such as its ability to absorb energy and withstand impacts, rubberised concrete has gained preference among researchers (Naito et al., 2014). When used in place of some fine aggregate, CR enhances fatigue performance, toughness, and shock absorption capability. A study concluded that replacing NFA by 20% of CR improved the resistance against abrasion better than the control (Kumar et al., 2016). Moreover, CR has been found to have lower density, higher toughness and higher impact resistance compared to natural aggregates, which makes it acceptable as a building material (Gerges et al., 2018). Gesoglu et al. (2015) found rubberised concrete has a lower bond strength than plain concrete as the soft skeleton of CR fails to produce the necessary friction between concrete and reinforcement bars (Gesoglu et al., 2015). Moreover, the shear strength of concrete negatively impacts the use of CR alone (Furlan & de Hanai, 1997, Ataria & Wang, 2019). Higher ductility, high energy dissipation capacity, improved resistance to cracking and spalling, and improved freeze-thaw durability were all reported in previous studies (Mohamed & Assem, 2016; Sgobba et al., 2015; Zheng et al., 2008; Khaloo et al., 2008; Ismail & Hassan, 2017; Mendis et al., 2018; Ayman & Mohamed, 2017) that used CR in concrete. In addition, because rubber particles have a lower specific gravity, CR can be used to create similar lightweight concrete (Hossain et al., 2019). Classifications of rubber aggregate including CR used in construction and their chemical compositions are shown at Appendix B and Appendix C respectively (Shahjalal et al., 2023). Despite these advantages, the CR tends to increase water absorption and permeability (Thomas et al., 2016) and decrease compressive strength, modulus of elasticity, and splitting 13 tensile strength (Meherier, 2016). According to Meherier (2016), concrete's compressive strength significantly decreased when the proportion of CR exceeded 20%; yet, the concrete specimens demonstrated superior strain tolerance when compared to the control sample. In order to achieve results equivalent to those of the control concrete specimens, the study also recommended a maximum replacement of 10% CR. In order to comprehend how the ITZ forms in the presence of CR, fibre, and recycled concrete aggregates, previous researchers (Su, 2015; Meherier, 2016; Copetti et al., 2020) used the scanning electron microscopy (SEM) approach. These investigations also discovered that the CR particles had rough surfaces and irregular forms (Figure 2.1 a-d). It is presumed that air entrapment is caused by the mixing of the RRAC for its irregular form. Figure 2.1 Concrete replaced with RCA & CR particles: (a-b) interface of rubber-cement paste, and (c-d) interface of recycled aggregates-cement paste (Su, 2015; Ahmed et al., 2019; Meherier, 2016) (a) (b) (c) (d) 14 2.1.3 PPF in Concrete Fibre-reinforced concrete has become of interest to researchers owing to its ductile property, crack resistance capability, and improved mechanical properties. Plain concrete acts as a brittle material under tensile stress. Hence, the concrete fails without any warning, and the cracks that form propagate rapidly. In addition, concrete with a certain amount of fibres has a higher impact on abrasion and shatter resistance. Moreover, fibres decrease the permeability of concrete, which results in reduced bleeding. PPF is mainly introduced to the concrete mix to prevent cracking caused by plastic and drying shrinkage (Najimi, 2009). Some researchers reported an increase in the compressive strength, tensile strength and flexural strength of concrete after incorporating PPF (Mohod, 2015; Alsadey & Salem, 2016; Ramujee, 2013). A comparative analysis of mechanical characteristics and structural behaviour integrating RCA, CR, and fibre has been the subject of little research (Xie et al., 2015; Guo et al., 2014b; Xie et al., 2019b). Researchers employed steel fibre in those trials and discovered that while adding more CR considerably decreased the concrete's compressive strength and fracture toughness, the coupling impact of CR and silica fume improved the concrete's ductility, toughness, and compressive strength. They came to the conclusion that the mechanical characteristics of rubberised fibre-based concrete are significantly impacted by the addition of silica fume. However, when a study on bond strength was done after adding PPF, it revealed that PPF has smooth surfaces, which prevent the generation of enough friction, leading to a reduced bond strength (Singh et al., 2004), but the inclusion of fibre had improved concreteâs shear strength carrying capacity (Jadhav & Koli, 2013). Since the concrete tends to encounter brittle failure mechanisms, using fibre in concrete mixtures enhances ductility while decreasing workability (Najimi, 2009). The fibres usually used in the concrete industry are steel fibre, PPF, glass fibre, carbon fibre, galvanized iron fibre, basalt fibre, textile fibre, recycled steel wires and macro synthetic fibre all of which have different influences on concrete behaviour. Properties of different types of fibres commonly used are shown at Appendix D (Shahjalal et al., 2023). According to research by Banthia and Soleimani (2005), because concrete has a lower specific gravity than steel fibres, it requires less PPF. Furthermore, PPF concrete performs better in terms of durability since it does not corrode like steel fibre (Wang et al., 2019). Hossain et al. (2019) and Islam et al. (2022) suggested that the highest amount of fibre that can be used is up to 15 2%. As per previous research, a 1% volume substitution of PPF increased compressive strength by 23% and flexural strength by 21%. Meanwhile, Najimi et al. (2009) found that adding fibres to concrete mixes improves tensile strength and ductility while decreasing the occurrence of spalling (Zeiml et al., 2006). 2.1.4 RCA, CR and PPF in Concrete According to Ahmed et al. (2019), samples with RCA ranging from 0% to 100% and CR ranging from 0% to 20% had a 38% reduction in tensile strength. Tamanna et al. (2020) observed that RCA (50%) and CR (10%) could enhance tensile strength by 11% to 16% in contrast to a specimen that had neither RCA nor CR. To increase tensile strength, the researchers decided to include fibres in addition to RCA and CR. According to the majority of research, steel and PPF both increase tensile strength; however, the effect of fibre is negligible when the RCA and CR levels are increased for the same fibre ratio. Due to their bridging qualities and ability to distribute tensile stresses along fractures, fibres primarily contribute to this improvement in tensile capacity (Ding et al., 2012; Ning et al., 2015; Tahenni et al., 2016). Flexural strength was often decreased when CR was added to RRAC and FRRAC combinations. Furthermore, Su (2015) found that when particle size increased, flexural strength decreased. For 3 mm, 0.5 mm, and 0.3 mm of CR particles, this reduction reached 13%, 11%, and 10%, respectively. Li et al. (2016), on the other hand, showed an increase in flexural strength when CR particle size rose while being unaffected by greater CR concentration. Flexural strength was found to decrease with the addition of RCA and CR, and to worsen with increasing replacement content (Chen et al., 2020; Alfayez et al., 2020; Xie et al., 2015). However, the addition of fibres greatly increased flexural strength (Hossain et al., 2019; Alfayez et al., 2020; Chen et al., 2020). Prior studies employing RRAC have demonstrated enhanced toughness, ductility, and energy absorption capacity after CR was added (Liu et al., 2015; Li et al., 2016). Excessive CR content in RRAC, on the other hand, would have a detrimental influence on the capacity of concrete (Khaloo et al., 2008). Guo et al. (2014a) stated that adding CR up to 4% is the best choice if toughness is a significant concern. Additionally, higher fibre inclusion results in improved ductility and toughness. This is because, when fibres are present, aggregate and cement establish a strong bond. In the same way, Xie et al. (2018) found that 1% steel fibres enhanced the hardness of recycled aggregate concrete and NAC by about 14% and 9%, respectively. However, experts recommend 16 restricting the usage of CR in FRRAC to a particular amount to improve toughness value. Figure 2.2 contains a comparison between the mechanical properties of FRRAC derived from various studies (Tamanna et al., 2020; Ahmed et al., 2019; Alfayez et al., 2020; Shahjalal et al., 2021; Guo et al., 2014a). Improvement of various physical, mechanical, and durability qualities of concrete is still being researched (Li et al., 2022; Gillani et al., 2017; Hassan et al., 2019) and as part of that process, studies on the effects of RCA, CR, or PPF on concrete properties are being conducted. In general, studies have revealed that the replacement of CR and RCA, to a certain extent, does not Figure 2.2 Variation of strength of FRRAC considering (a) compressive strength, (b) tensile strength, (c) modulus of elasticity, (d) flexural strength 02468101214Hossain etal., 2019Shahjalal,2022Jian-he etal., 2015Ahmed etal., 2019Alfayez,2018Flexural Strength (MPa)(d)ControlMaximumMinimum01234567Hossain etal., 2019Shahjalalet al.,2021Shahjalal,2022Tamanna,2018Ahmed etal., 2019Alfayez,2018Tensile Strength (MPa)(b) ControlMaximumMinimum0102030405060Shahjalal,2022Tamanna,2018Xie et al.,2018Jian-he etal., 2015Alfayez,2018Guo et al.2014MoE (GPa)(c)ControlMaximumMinimum01020304050607080Compressive Strength (MPa) (a) ControlMaximumMinimum17 influence the properties of concrete significantly. Beyond a certain limit, the inclusion of these materials causes concrete properties to deteriorate. On the other hand, fibre-reinforced concrete has more enhanced properties than plain concrete. The figure below contains a graphical representation of the few mechanical properties of Rubberised Recycled Aggregate Concrete (RRAC) and Fibre Reinforced Rubberised Recycled Aggregate Concrete (FRRAC) (Shahjalal et al., 2023). Figure 2.3 Graphical representation of the outcome of RCA, CR and PPF on mechanical behaviour of concrete (Shahjalal et al., 2023) According to previous studies, adding RCA, CR, and fibres to concrete mixtures deteriorates their workability (Bravo & De Brito, 2012; Marie, 2017). The control mixture's slump value was 75.3 mm, while the RRAC mixtures blended with 20% RCA and 20% CR showed a 42% decrease. During their investigations, various researchers noted a decrease in modulus of elasticity (MoE) values for recycled aggregate concrete, RRAC, and FRRAC. They came to the conclusion that both RCA and CR content did not significantly alter the MoE results (Bompa et al., 2017; Tamanna et al., 2020), and this demands a separate investigation. However, Gupta et al. (2017) found that the MoE values for rubberised concrete (RC) and RRAC samples decreased by 27% and 28%, respectively. In a novel approach, Tamanna et al. (2020) investigated how RCA and CR content affected MoE in RRAC samples. According to the author, 50% RCA produced 18 better outcomes than 100% RCA, particularly when combined with 10% CR, which raised MoE by 7.4%. The RC's ductility, toughness, and tensile qualities were found to be improved by the addition of fibres, but the MoE properties were left unchanged (Tamanna et al., 2020; Hesami et al., 2016. The majority of earlier studies (Gesoglu et al., 2015; Raffoul et al., 2016; Bompa et al., 2017) found that adding CR and RCA decreased compressive strength. Additionally, Liu et al. (2015) found that the strength of the concrete with 10%, 20%, and 30% CR and 100% recycled aggregates decreased significantly by 27%, 39%, and 47%. To increase the compressive strength and other toughened qualities, some researchers experimented with employing different fibres in conjunction with CR and RCA. Chen et al. (2020) found that samples containing 40% RCA and 10% CR had a lower compressive strength at first, but this trend improved after adding 4 kg/m3 of basalt fibre. According to Ahmed et al. (2019), the compressive strength of the sample was up to 31% higher than that of the fibre-free equivalent. The author utilised 0.1% steel wire in FRRAC with 100% RCA and 20% CR. Similarly, FRRAC showed an increase in strength of about 26.0% when PPF was introduced (Hossain et al., 2019). Aslani and Klein (2018) noted that the compressive strength of lightweight self-compacting rubberised concrete may be increased by 22% and 47%, respectively, by adding 0.1% PPF and 0.75% steel fibre. Furthermore, Chen et al. (2020) noted a slight variation in the Modulus of Elasticity (MoE) values between recycled aggregate concrete and NAC. Silva et al. (2016) found that the inherent characteristics of recycled concrete aggregate (RCA), such as its size, type, and original material quality, have a significant impact on the extent of Modulus of Elasticity (MoE) reduction in RCA. Furthermore, it is anticipated that the MoE and Poisson's ratio will vary greatly for varying proportions of CR and PPF. Appendices F, G and H display a summary of the modulus of elasticity, tensile and flexural strength with various parameters of RRAC and FRRAC determined by several researchers (Shahjalal et al., 2023). 2.1.5 Bond Behaviour To find out how steel bar length and diameter affected the strength of the concrete bond, pull-out tests using a variety of reinforcing bar length-diameter variations were carried out. Xiao et al. (2007) used pull-out experiments to assess the bonding capacity of recycled aggregate concrete (RCA replacements of 0, 50, and 100%) with rebar that had both plain and deformed surfaces. The authors discovered that an increase in the RCA replacement percentage of 50% and 19 100% reduces the bond strength between the recycled aggregate concrete and plain rebar by 12% and 6%, respectively, under equivalent mix proportions (i.e., the mix proportions are the same, except for different RCA replacement percentages), whereas the bond strength between the recycled aggregate concrete and the deformed rebar had no obvious relationship with the RCA replacement percentage. Butler et al. (2011) compared the bond strength of steel reinforcing bars to concrete using beam end specimens and discovered that the bond strengths of natural aggregate concrete specimens were 9% to 19% greater than those of identical RCA counterparts (100% replacement) gathered from two independent sources. Gesoglu et al. (2015) investigated the steel-concrete bond strength (via Pull-out test) while maintaining a consistent reinforcing steel surface area (16mm diameter and 150mm embedment length) by replacing NFA and NCA with total aggregate volume (0, 5, 10, 15, 20, 25, and 30%). Furthermore, the study discovered that the bonding strength of concrete and reinforcing steel with rubberised concrete was lower than with plain concrete. Because of its flat surface, PPF has a poor bond with the cementitious matrix, making it difficult for sufficient friction to form between the two. Singh et al. (2004) investigated the pull-out behaviour of concrete using a cementitious matrix and discovered that adding fibre weakens the bond between the concrete and the embedded reinforcing bar. 2.1.6 Shear Behaviour Numerous tests have already been conducted on the shear behaviour of concrete that solely contains RCA, CR, or PPF. It was shown by Sogo et al. (2004) and Sato et al. (2007) that beam shear strength is reduced when NCA is substituted with RCA. Additionally, as the RCA replacement level increased, the concrete beams' shear strength reduced due to a decrease in elastic stiffness and the production of many cracks at an early loading level (Al Mahmoud et al., 2020; Alrajfi et al., 2021; IgnjatoviÄ et al., 2017). Additionally, the concrete's shear strength is decreased when just rubber particles are included in the mix (Ataria & Wang, 2019; Xie et al., 2019a). However, when compared to a beam without any fibres, Jadhav et al. (2013) found that the integration of the PPF significantly increased the beam's load-carrying performance. 2.1.7 Machine Learning Models for Material There are very few machine learning (ML)-based models available for forecasting concrete's compressive strength. The authors (Pal et al., 2023) collaborated to investigate a wide range of machine learning methods using an extensive database in order to accurately assess the 20 compressive strength of FRRAC concrete. In addition to other standard parameters like the water-cement ratio and natural aggregate content, the study assembled the largest database (with two of the authors' publications) of concrete strength and its corresponding proportions of recycled concrete aggregate, crumb rubber, and various fibres (Pal et al., 2023). A greater understanding of the mix design and the performance of different constituents in FRRAC may result from this investigation, which might then be applied in the concrete industry for environmental and construction sustainability. 2.1.7.1 Analysing Database From the literature, a thorough dataset containing several input parameters influencing the compressive strength of concrete was gathered (Pal et al., 2023). In addition to two experimental data from ongoing studies, the dataset included 905 experimental results from 71 peer-reviewed scientific publications (journal articles and conference proceedings). The information came from experimental testing conducted on concrete that had various RCA, rubber, and fibre combinations. A variety of inputs were used to forecast the compressive strength of concrete, such as the water/cement ratio (W/C), rubber as a fine aggregate substitute, NCA and RCA replacement, fibre addition, and fibre type. It should be noted that compressive strength is also influenced by a number of other elements. In this study (Pal et al., 2023), only significant factors with sufficient experimental data were regarded as input variables. Throughout the data collection procedure, a number of difficulties were faced, such as missing and incomplete data. Either the information supplied was used to calculate the missing values, or the standards most frequently applied in commercial applications were used to infer the values. 2.1.7.2 Statistical Overview of the Used Data Pal et al. (2023), including the author, published a journal examining the statistical distribution of input characteristics representing the database, and those results are displayed in Figure 2.4. As can be observed, 429 specimens, or approximately 48% of the total database, had nominal aggregate sizes in the range of 10 and 20mm. RCA is present in 391 out of the 905 specimens. 0â25% and 75â100% are the two most commonly utilised RCA percentage ranges. Rubber was used in place of NFA in over 77% of the data, falling between 2 and 25%. Approximately 87% of the specimens had steel or PPF, while 637 specimens were fibre-free. Moreover, the W/C ratio most commonly used in the concrete industry to guarantee the required 21 compressive strength was between 0.3 and 0.6 in over 88% of the specimens. These findings imply that a great deal of research has been done on fibre-based concrete with RCA, and CR. Figure 2.4 Distribution of input variables of fibre-reinforced concrete made with rubber and recycled concrete aggregate database (Pal et al., 2023) The statistical measurements of the database's features with continuous values are listed in Table 2.1. It is inferred that 25% of the data had aggregates smaller than 25 mm, while the nominal aggregate size ranged from 8 to 40 mm (SD=6.96). Table 2.1 shows that the mean RCA used is 27.02% with an SD of 38.19% and that CR was absent in more than 75% of the data, despite the fact that the range for RCA and CR was 0â100%. Additionally, fibre's mean value was 0.25%, which is the 75th percentile value for the parameter. 50% of the data had a W/C ratio between 0.25 and 0.45, as indicated in Table 2.1. This indicates that the mean W/C ratio is 0.46, with an SD of 0.09. With output parameters ranging from 0.37 to 101.32 MPa, the database contains a wide variety of data. With an SD of 17.69 MPa, the statistics indicate that 50% of the data had compressive values between 27 and 47 MPa. A comprehensive reference table of different research related to RCA with and without CR and PPF is displayed at Appendix I (Pal et al., 2023). 22 Table 2.1 Statistical distribution of database features (Pal et al., 2023). Statistical Parameters Nominal Coarse Aggregate Size (mm) RCA% Rubber (%) Fibre (%) W/C Compressive Strength (MPa) Min 8 0 0 0 0.25 0.37 Max 40 100 100 3.43 0.77 101.32 25th percentile 12.5 0 0 0 0.4 27.33 50th percentile 20 0 0 0 0.45 36.82 75th percentile 25 50 0 0.25 0.53 47.07 Mean 19.35 27.02 4.32 0.25 0.46 39.46 SD 6.96 38.19 12.47 0.51 0.09 17.69 2.1.7.3 Sensitivity Analysis In order to illustrate the variables in the data set, Figure 2.5 shows the concrete's compressive strength (fâc, MPa) as a function of the six input variables. Analysis of Figure 2.5 (a to d) shows that the nominal coarse aggregate size, RCA (%), rubber (%), and W/C ratio have a substantial impact on the compressive strength of FRRAC. Rubber (%) and nominal coarse aggregate size have more noticeable effects than RCA (%). As the percentage of RCA increases, the compressive strength progressively decreases. As expected, there is an inverse connection between w/c and compressive strength. Nonetheless, the addition of fibre improved the concrete's strength, as seen in Figure 2.5e. Additionally, compared to polypropylene or other types of fibre, steel fibre has been shown to increase compressive strength more (Figure 2.5 f). The prospect of a perfectly linear relationship between the input and output variables is eliminated, though, because the range of recorded compressive strengths for a particular input variable is still somewhat large. 23 Figure 2.5 Difference in compressive strength of concrete with respect to (a) nominal coarse aggregate size (mm), (b) RCA (%), (c) Rubber (%), (d) W/C, (e) Fibre (%), (f) Fibre Type (Pal et al., 2023) 24 It is possible that some of the particular variables are interrelated. Consequently, correlation coefficients for all possible variables have been established. They are shown in Figure 2.6 and Table 2.2. Excessive correlation coefficients between the input components may result in inefficiencies and make it difficult to understand how these factors impact the outcome. The findings show that there are no discernible correlations between the independent input variables. Concretesâ compressive strength has been demonstrated to be significantly correlated with the input parameters rubber (%) and W/C. Figure 2.6 Correlation matrix heat map of the input variables (Pal et al., 2023). Table 2.2 Correlation matrix of the input variables (Pal et al., 2023). Variables Input Output Parameter Nominal Coarse Aggregate size (mm) RCA% Rubber (%) Fibre (%) W/C Compressive Strength (MPa) Input Nominal Coarse Aggregate size (mm) 1 - - - - - RCA% 0.40 1 - - - - Rubber (%) -0.21 -0.22 1 - - - Fibre (%) -0.21 -0.21 -0.09 1 - - W/C 0.09 0.12 -0.15 -0.08 1 - Output Compressive Strength (MPa) -0.23 -0.14 -0.30 0.25 -0.51 1 25 2.1.7.4 Data Analysis One method for turning unclean data into clean data is data preparation. To put it another way, whenever data is gathered from different sources, it is done in its unprocessed state, which makes analysis difficult or even impossible. For machine learning projects to get better results from the applied model, the data format needs to be in the right order. Data in a specified format is needed for a given machine learning model. The organization of the data set is another crucial aspect to take into account in order to use different machine learning and deep learning algorithms and select the most effective one. As a result, numerical representations of the dataset's categorical properties are required. Dataset standardization, which puts all numerical data inside a certain range, is a requirement of many machine learning methods. To obtain a unit variance, the mean was subtracted and scaled in the program. 2.2 Research Gap To promote the structural use of polypropylene fibre-reinforced recycled aggregate concrete containing CR, its mechanical properties need evaluation. So far, several studies have been conducted on the influence of the said materials on concrete individually or on the influence of CR or PPF on recycled aggregate concrete. However, no research has been done to look into how PPF and CR work together in concrete with recycled aggregate. Concrete's mechanical qualities, such as its compressive, split tensile, or flexural strengths, are determined by the mortar's quality, which is influenced by its component parts. As previous literature suggests, CR causes an adverse impact on the mechanical properties, which, on the contrary, improves after the addition of fibre. Again, a certain percentage of RCA has been found to be a suitable replacement for NCA. However, to produce environmentally friendly and sustainable high-strength concrete, the proportion of these materials needs to be studied. Both bond and shear strength play crucial roles in the structural response of materials like concrete. The bond ensures the effective transfer of forces between concrete and reinforcement, contributing to structural integrity and durability. Shear forces, on the other hand, can cause structural instability and failure if not adequately addressed in design and construction, highlighting the importance of shear reinforcement and proper detailing in structural elements. 26 The bond between concrete and rebar depends on friction and adhesion between these two components, which are highly affected by the presence of CR and PPF. On the other hand, though RCA and CR adversely affect the shear strength of concrete, PPF enhances it. However, how these three materials work together in terms of their effect on structural strength is yet to be understood. In order to determine the structural applicability of RCA, CR, and PPF in the concrete industry, a few experiments on properties and structural applications have been carried out. An optimum or definite proportion of recycled materials like RCA, CR, and PPF may give the researchers a chance to reach a common understanding of this new subject of interest while helping the academia establish design codes and specifications for the application. 2.3 Significance of experiments on recycled aggregate concrete with CR and PPF Since a lot of isolated experiments and studies have been carried out on the RCA mixed with CR, PPF and various additives, the proportions of individual constituents are still not fully certain or determined in the concrete industry. Flexure, shear and bond behaviour of recycled aggregate concrete with rubber and fibre have enough scope for in-depth investigation. However, this paper has tried to combine the experimental results so far carried out by the researcher to conclude what amount of RCA, CR. and PPF can be used in a concrete element using recycled material after ascertaining its shear, bond, flexure and mechanical behaviour for structural use. Mechanical properties, shear behaviour of RCA beam element, and bond strength of recycled aggregate concrete with rebar made with CR have been carefully studied. 2.3.1 Mechanical Behaviour Researchers have studied recycled aggregate concrete's durability and mechanical qualities throughout the past few decades. In contrast to the control concrete, they typically fell short of achieving improved mechanical qualities in terms of toughness, ductility, flexural strength, and compressive strength. Fibres and rubber particles are added to concrete mixtures to increase its properties like ductility and energy-absorbing capability. To the researcher's knowledge, not much study has been done to date to examine the mechanical characteristics of concrete that combine fibre, RCA, and CR. In order to facilitate sustainable construction, the current study carefully examines the mechanical characteristics of recycled aggregate concrete that contains CR and PPF. Furthermore, it's critical to determine whether or not recycled aggregate concrete with CR and PPF 27 can be designed using the same design criteria as regular aggregate concrete. A summary of compressive strength with different design parameters of RRAC and FRRAC examined previously by different researchers is shown at Appendix E (Shahjalal et al., 2023). 2.3.2 Shear Strength Few studies have previously been conducted on the use of recycled materials in structural components where shear, which is relatively brittle and can happen suddenly, is the dominant mechanism of failure. Furthermore, adding a modest amount of non-metallic fibres can successfully negate the common belief that adding CR/RCA lowers the cementitious composite's mechanical qualities. In order to evaluate the shear behaviour of concrete beams reinforced with steel reinforcement bars, this study program aims to determine how well RCA, CR, and PPF work together. 2.3.3 Bond Strength Many researchers have investigated the effects of either CR or PPF on the bond strength of recycled aggregate concrete with reinforcing steel bars. This research examines the performance of recycled aggregate concrete with both CR and PPF in terms of bond strength with reinforcing steel bars. The interaction between RCA, CR, and PPF with respect to bond strength has been thoroughly examined in this study to determine their optimum replacement levels. The surface area of reinforcing steel plays a vital role in concrete bond strength. In order to examine the impact of differences in steel surface area on the bond strength of recycled aggregate concrete including CR and PPF, this study has included steel reinforcement in varying lengths and diameters. In addition, customized pullout tests of cylinders in the laboratory are also used to examine the viability of using these recycled materials in concrete and the ideal replacement levels for maximising the bond strength of concrete. 2.4 Summary This review explored the mechanical properties of concrete incorporating Recycled Concrete Aggregate (RCA), Crumb Rubber (CR), and Polypropylene Fibre (PPF), focusing on whether these sustainable materials could enhance concrete's performance. Previous research 28 indicated that while RCA-based concrete often showed no significant improvements in properties like compressive strength and ductility compared to conventional concrete, the addition of fibres and CR can boost energy absorption and ductility. There is a gap in research on the combined effects of RCA, CR, and PPF, particularly on bond strength, shear strength, and overall mechanical performance. Key findings from earlier studies suggest that RCA and CR tend to decrease bond strength, especially with plain rebar, and that PPF may further weaken this bond due to its smooth surface. Additionally, RCA and CR are known to reduce shear strength, partly due to CR's low rigidity. However, PPF has been shown to improve the load-carrying capacity of concrete beams, indicating that fibre reinforcement may mitigate the negative effects of RCA and CR on shear strength. Overall, the study underscores the potential of combining these materials to create more sustainable concrete mixtures, though it calls for further research on their combined effects, particularly for structural applications. The findings could influence future design guidelines for concrete made with recycled materials, promoting more eco-friendly construction practices. 29 Chapter 3: Mechanical Behaviour of Recycled Aggregate Concrete Containing CR and PPF 3.1 General In order to examine the compressive strength, splitting tensile strength, and flexural bahaviour under various situations, this study focuses on the experimental investigation of concrete that combines RCA, CR, and PPF. The applicability of current design guidelines created for regular aggregate concrete was confirmed using the measured experimental parameters of fibre-based rubberised concrete. 3.2 Materials Properties 3.2.1 Cement Portland Composite Cement (PCC) is used in this study. PCC is the most widely used cement around the world. The chemical compositions and properties of PCC are shown in Table 3.1. The normal consistency of cement is measured using ASTM C187-16, and setting time is measured using ASTM C191-18. 3.2.2 Properties of Natural Fine Aggregate (NFA) This study uses well-graded natural sand that is readily available in the area and has a nominal maximum grain size of 4.75 mm. ASTM C128-15 is used to measure the sand's specific gravity and water absorption capacity, while ASTM C29-17 is used to measure the unit weight. The ASTM C136-14 standard is used for sieve analysis and grading of sand. Table 3.5 provides a summary of the physical characteristics of sand. The gradation curve of NFA is shown in Figure 3.2(b), and it is within the range specified by ASTM. 3.2.3 Properties of Natural Coarse Aggregate (NCA) In this investigation, the NCA is set at a maximum aggregate size of 19 mm. While ASTM C29-17 is used to test the unit weight, ASTM C127-15 is used to measure the NCA's specific gravity and water absorption capacity. Additionally, the abrasion test is carried out in accordance with ASTM C131-14. The ASTM C136-14 standard is used for sieve analysis and NCA grading. The NCA gradation curve, shown in Figure 3.2(a), makes it abundantly evident that the coarse aggregate falls between the ASTM upper and lower bound range. 30 3.2.4 Properties of Recycled Coarse Aggregate (RCA) The study's recycled concrete was gathered from a building that had been demolished and physically crushed to a maximum aggregate size of 19 mm. Many undesired items were mixed with recycled concrete when it was gathered from an old building that had been demolished. To get rid of these contaminants, a number of screens, sifting, and washing procedures were carried out. To remove particles smaller than 4.75 mm, the aggregate was sieved. The same process used for the NCA is used for the material characterization of the RCA. Figure 3.2 (a) displays the RCA's gradation curve. 3.2.5 Properties of Crumb Rubber (CR) As a fine aggregate, a maximum CR size of 4.75 mm is employed. Figure 3.2 (b) displays the CR and NFA gradation curves. It is evident from the chart that while CR does not fit inside the ASTM range, NFA does. A local business provides the commercially made CR for this study. However, the combined gradation of both materials is considered to adhere to the stipulated standard because CR is used in place of NFA. Table 3.5 lists the specific gravity, absorption capacity, and fineness modulus for CR. 3.2.6 Properties of Polypropylene Fibre (PPF) The PPF for this investigation was supplied by a private Japanese company. The PPF specifications are shown in Table 3.2. Figure 3.1 Aggregate used in concrete: (a) Recycle Coarse Aggregate (b) Crumb Rubber (c) Polypropylene Fibre (Hossain et al., 2019) (a) (b) (c) 31 Table 3.1 Properties of Portland Composite Cement (PCC) Compound (%Mass) Normal Consistency (%) Setting Time (min) Initial Final SiO2 Al2O3 Fe2O3 CaO MgO SO3 Na2O K2O LOI 26.7 130 180 20.60 4.74 3.28 64.82 1.84 2.4 0.21 0.38 1.73 Table 3.2 Specifications for PPF Variables PPF No. of Denier 03 Specific gravity (g/cm3) 0.91 Fibre Length (mm) Diameter (µm) Aspect ratio 12 18 667 Tensile Strength (MPa) 480 Elastic Modulus (GPa) 7.0 Figure 3.2 Gradation curve of (a) natural coarse aggregate (NCA) and RCA; (b) sand and CR (Hossain et al., 2019) 3.3 Test Matrix and Variables The test matrices and variables that were employed in various combinations are shown in the Tables 3.3 below. In order to allow comparative analysis, fifteen different concrete mixtures were cast for this investigation. In most regions of the world, depending on the category and kind of construction, reinforced concrete structures are designed with a target compressive strength of 0204060801001 10 100Percent Fine (%)Sieve Opening (mm)ASTMUpperNCARCAASTMLower(a)01020304050607080901000.1 1 10Percent Fine (%)Sieve Opening (mm)ASTM UpperNFACRASTM Lower(b)32 25â35 MPa, or 28 days concrete strength. To provide the concrete industry with more credible and comparable evidence, the planned compressive strength was set at 30 MPa. In different scenarios, when working with high strength concrete or concreting in cold and hot weather, different durability parameters should be studied, which is not in the scope of this research. The effective water-to-cement ratio and cement content were maintained at 0.38 and 427.1 kg/m3, respectively. The percentages of natural coarse aggregate, RCA, sand, CR, cement, and PPF therefore varied. The concrete's coarse and fine aggregates are in a saturated surface dry (SSD) state. 10% and 30% of RCAs are changed, with replacements determined by weight. According to the earlier study, concrete strength was not significantly affected by RCA replacement up to 30%; however, when the RCA content rose, strength gradually decreased (Alam et al., 2013; Huda et al., 2015; Limbachiya et al., 2000; Meherier, 2016). According to Etxeberria et al. (2007), some researchers have suggested that in order to meet standard requirements for a 5% absorption capacity of aggregates, the replacement level should not exceed 30%. For this reason, 10% and 30% are regarded as the RCA replacement levels. They are proportioned on a volume basis because CR has a very low specific gravity in comparison to sand. PPF is added to the concrete mixture at 1% and 2% by volume of concrete mixed with cement due to its finer texture and very light weight, whereas CR is utilised to replace sand at 5% and 10% amounts. These ratios are taken into account because Meherier (2016) recommended that in order to get a comparable outcome with the control of concrete specimens, the CR content should not be increased by more than 10%. In the case of polypropylene fibre, K. Ravi and A.V. Karvekar (2014) worked with various fibre combinations like polypropylene fibre, galvanized iron fibre, steel fibre, and high-density polyethylene fibre at 1.5% volume fraction and reported that in all cases the compressive strength compares to control mixture. In the current study, 1% and 2% fibre content are added to provide some variance from this percentage. The mix design does not include any water-reducing admixtures. The proportions of various elements in the concrete mix for 15 possible combinations are presented in Table 3.4. 33 Table 3.3 Specimen identification description Batch identifying name: RxCyFz Description R RCA X % of NCA replaced with RCA C CR Y % of FA replaced with CR F PPF Z % of PPF replaced with concrete in the mix The specimen identification description is shown in Table 3.3. For example, Batch 6 (R10C5F2) means 10% RCA replacement, 5% CR replacement along with 2% fibre and Batch 10 (R30C0F1) means 30% RCA replacement, 0% CR replacement along with 1% fibre. Table 3.4 The proportion of aggregates for concrete mixtures per cubic metre (Hossain et al., 2019) Batch No. Batch Code Natural Coarse Aggregate (kg/m3) Fine Aggregate (kg/m3) RCA (kg/m3) CR (kg/m3) Cement (kg/m3) PPF (kg/m3) 1 R0C0F0 990.2 678.7 00.0 00.0 427.1 0 2 R10C0F0 891.2 678.7 99.0 00.0 427.1 0 3 R10C0F1 891.2 678.7 99.0 00.0 425.8 1.3 4 R10C0F2 891.2 678.7 99.0 00.0 424.5 2.6 5 R10C5F1 891.2 662.1 99.0 16.6 425.8 1.3 6 R10C5F2 891.2 662.1 99.0 16.6 424.5 2.6 7 R10C10F1 891.2 645.5 99.0 33.2 425.8 1.3 8 R10C10F2 891.2 645.5 99.0 33.2 424.5 2.6 9 R30C0F0 693.2 678.7 297.0 00.0 425.8 1.3 10 R30C0F1 693.2 678.7 297.0 00.0 425.8 1.3 11 R30C0F2 693.2 678.7 297.0 00.0 424.5 2.6 12 R30C5F1 693.2 662.1 297.0 16.6 425.8 1.3 13 R30C5F2 693.2 662.1 297.0 16.6 424.5 2.6 14 R30C10F1 693.2 645.5 297.0 33.2 425.8 1.3 15 R30C10F2 693.2 645.5 297.0 33.2 424.5 2.6 Note: a) Mix Proportion In the mix design, natural coarse aggregate (NCA) was replaced by recycled coarse aggregate (RCA) by weight. Natural fine aggregate (NFA) was substituted with crumb rubber (CR) by volume. Polypropylene fibre (PPF) was incorporated into the concrete by volume basis and was also added to the cement by weight. b) PPF 1% Calculation for Batch 14 Total Volume of concrete = (L x H x B) = (1.5x0.3x0.2) cubic metre = 0.09 cubic metre (for sample beam) So, 1% PPF of concrete volume = 0.09 * 1% = 0.0009 cubic metre Now, conversion as per cement weight basis = 0.0009 cubic metre x 1440 kg/ cubic metre = 1.3 kg/ cubic metre 34 c) CR 10% Calculation for Batch 14 Mass of Sand (Fine aggregate) in R0C0F0 is 678.7 Kg Specific Gravity of Sand is = 2.41 Volume of Sand = Mass Ã· Sp. Gravity = 678.7 Ã· 2.41 = 281.62 cubic metre 10% Volume Replacement of Sand is = 281.62 x 10% = 28.162 cubic metre Specific Gravity of Sand is = 1.18 Now, Conversion for CR with sand by volume basis = 28.162 x 1.18 = 33.23 Kg 3.4 Properties of Variables Table 3.5 below presents the properties of various constituents tested in accordance with ASTM standards for mix design and result analysis. Table 3.5 Physical properties of aggregates Variables Natural Coarse Aggregate RCA Sand CR Apparent Specific Gravity 2.73 2.64 2.47 - Bulk Specific Gravity (SSD) 2.71 2.51 2.41 1.18 Bulk Specific Gravity (OD) 2.70 2.44 2.36 - Absorption Capacity (%) 0.48 3.23 1.8 1.3 Fineness Modulus (FM) 2.51 2.45 2.39 3.49 Unit Weight (Loose) (kg/m3) 1477.02 1557.54 1455.44 - Unit Weight (Compact) (kg/m3) 1525.57 1658.71 1579.25 - % of Voids (Loose) 45.1 35.9 38.3 - % of Voids (Compact) 43.3 31.7 33.0 - Abrasion value (%) 14.58 40.5 - - 3.5 Test Specimens A total of 270 concrete cylinders are cast for the tests of compressive strength at 7, 28, and 56 days, splitting tensile strength at 28 and 56 days, and the unit weight of hardened concrete cylinders at 28 days. The mould for the cylinders is 100 mm in diameter and 200 mm high. In order to assess the flexural strength at 28 days, 60 small-size beams with mould sizes of 150 mm x 150 mm x 500 mm (ASTM C1609/ASTM C78) are cast for 15 different concrete mixtures. 3.6 Sample Preparation In this study, the concrete and sand were partially replaced by PPF and CR by volume basis whereas NCA was replaced by RCA by weight basis. PPF was added to cement for ease of mixing by converting it to weight from volume proportions to cater from small amount of PPF that needed to be placed in the mixer. A mixture machine was used to make the concrete in accordance with ASTM-C192/C specifications. While the CR was manually mixed with the sand, the PPF was 35 uniformly blended with cement before the ingredients were poured into the mixture machine. To prevent the materials from sticking to the hands, a glove was worn. After that, the machine was filled with the NCA and RCA. Sand, cement, and water were then added, in that order. The air content and slump tests were conducted on freshly prepared concrete. The air content of fresh concrete samples was measured using ASTM C231-17, and the slump value of concrete mixes was measured using ASTM C143-15. Before being removed for testing, the specimens were first cured for 24 hours in a damp room with the mould. After that, they were demoulded and maintained in a continuous state under fresh water at a regulated laboratory temperature. 3.7 Testing Procedure In accordance with ASTM C39-18, the compressive strength test was conducted (Hossain et al., 2019). The load was applied at a rate of 0.25 ± 0.05 MPa/s. Two strain gauges are fastened to the middle of the concrete cylinders for a duration of 56 days, and the longitudinal and transverse strain was measured using a data logger. The cylinder's surfaces were leveled with sulfur capping before to testing in order to remove loading eccentricity. The ASTM C496-14 were followed when performing the splitting tensile strength test. ASTM C78 and ASTM C1609 were used to test the concrete prisms' flexural strength. The displacement rate used for the flexural strength test was 0.15 mm/min. ASTM C642-13 standard was adopted to determine the unit weight of hardened concrete cylinders. The tests set up for the compressive strength test and flexural strength test are shown in Figure 3.3 below. Figure 3.3 Test setup (a) compression test (b) quasi-static flexural test (a) (b) 36 3.8 Result Analysis 3.8.1 Fresh concrete properties The slump values, i.e., the workability indicator of different fresh concrete mixes, are shown in Figure 3.4. In comparison to the other 14 combinations, the control concrete mixture is found to have a higher slump value of 110 mm. This suggests that the control mixture offers the best workability for the studied specimens. Because Batch-15 (R30C10F2) is composed of the maximum replacement level of RCA, rubber, and fibre, it exhibits the lowest slump value. The slump value was found to decrease as the incremental replacement level of CR increased for a fixed RCA replacement. The slump value drops by 40% for 5% CR and by 54% for 10% CR for 10% RCA substitution with 1% fibre. Both the 30% RCA combinations and the fixed 10% RCA replacement with 2% fibre show the same pattern. CR needs extra water to overcome inter-particle friction because it is a porous material that does not blend well when mixed. Additionally, it was noted that when the fibre content rose, the slump value sharply fell significantly. Fibre lowers the workability of aggregates by increasing interlocking between them. The slump value dropped by 20% for 1% fibre and 58% for 2% fibre for 10% RCA replacement when CR is 0%. Additionally, 10% RCA and 5% CR, 10% RCA and 10% CR, and 30% RCA combinations showed a similar pattern. It was found during the test that fibre had a greater impact on slump value than CR and RCA. As the amount of fibre increased, the slump value sharply declined. However, due of its higher absorption capacity and increased surface roughness, the slump value dropped as the percentage of RCA increased. Figure 3.4 illustrates that when the degree of RCA in concrete increases, so does the air content. In the case of CR, the air content rises in tandem with the CR level. The air content is 1.54%, 2.69%, and 3.05% for 0%, 5%, and 10% replacement levels of CR, respectively, for 10% RCA with 1% fibre. This pattern was also seen for 30% RCA combinations and 10% RCA and 2% fibre. Higher air content is the result of air bubbles and air entrapment in the concrete mixture caused by adhered mortar containing RCA and CR combined. Alam et al. (2013) and Huda et al. (2017), earlier concluded the similar outcome on recycled concrete with their comparable findings. Additionally, batch 3 and batch 4, batch 5 and batch 6, batch 7 and batch 8, batch 10 and batch 11, batch 12 and batch 13, and batch 14 and batch 15 showed that the air content reduced as the fibre content increased incrementally. In terms of concrete's fresh density, it can be observed that the 37 mixture's with RCA, rubber, and fibre content lowered the samples' fresh densities compared to the control mix (Figure 3.15). The weight of the concrete is slightly decreased by the addition of CR and fibre to the mixture because they have low specific gravity. Due to the greater RCA and rubber levels in this combination, batch 14 (R30C10F1) had the lowest density. Figure 3.4 Slump value and air content of different concrete mixtures 3.8.2 Compressive strength Figures 3.5 to 3.7 below explain how compressive strength, split tensile strength and flexural strength of concrete increased with fibre amount yet showed a decline with the increase in RCA and CR amount. Figure 3.5 Variation in compressive strength of different concrete mixtures for (a) 10%, and (b) 30% RCA combinations (Hossain et al., 2019) 0.01.02.03.04.0020406080100120Air content (%)Slump (mm)Slump Air content01020304050Compressive strength (MPa) 7 days 28 days 56 days (a)01020304050Compressive strength (MPa) 7 days 28 days 56 days (b)38 Figure 3.5 summarizes the compressive strength test results for hardened concrete after 7, 28, and 56 days. With the exception of batches 7 and 9, all batches of concrete had a higher 7-day compressive strength than the control concrete mix. After seven days, the control specimen's concrete compressive strength is about 61% of the intended value. It was evident from the control batches, R10C0F0 and R30C0F0, that the compressive strength rises with 10% RCA replacement but falls with 30% RCA. A lower water-to-cement ratio at the ITZ may be the result of better/optimal internal curing brought about by the greater amount of water absorbed by RCA, which also contributes to the higher compressive strength for R10C0F0. As a result, the new cement paste and the mortar that is connected to the RCA's surface form a stronger bond. However, because RCA in R30C0F0 introduces a greater degree of porosity into the system, this effect disappears at 30% RCA. The several layers of ITZ may be the cause of this decrease in strength. Huda and Alam (2015) also found that the compressive strength for RCA replacement drops by at least 30% as the fraction of RCA replacement rises. It is evident from Batches 3 (R10C0F1), 5 (R10C5F1), 7 (R10C10F1), 4 (R10C0F2), 6 (R10C5F2), and 8 (R10C10F2) that the compressive strength dropped at a fixed RCA and fibre with the incremental replacement of CR. A similar pattern was also discovered by other studies (Xie et al., 2018; Meherier, 2016). The cement paste and aggregate have a poorer bond as a result of CR. Because of its extremely poor capacity to absorb water, the concrete mixture contains more free water, which weakens the transition zone. Furthermore, because CR is far weaker than NFA, it affects the concrete in a manner similar to that of porosity. Because CR is hydrophobic and has a lower elastic modulus, it increases porosity, which makes concrete less strong (Xie et al., 2018). Additionally, the CR has a low bonding capacity due to the presence of certain contaminants, such as zinc and sulfur (Meherier, 2016). For 30% RCA combinations (Batch-10, Batch-12, Batch-14 and Batch-11, Batch-13, Batch-15), the same phenomenon is also observed. When comparing the results between Batch-3 (R10C0F1) & Batch-4 (R10C0F2), Batch-5 (R10C5F1) & Batch-6 (R10C5F2), Batch-7 (R10C10F1) & Batch-8 (R10C10F2), Batch-10 (R30C0F1) & Batch-11 (R30C0F2), and Batch-12 (R30C5F1) & Batch-13 (R30C5F2), it is evident that the compressive strength increases as the proportion of fibre increases for a fixed RCA and CR replacement level. 39 Concrete's compressive strength can be increased by fibre creating a bridging effect between the aggregate and cement paste. Batches 14 and 15 (R30C10F1 and R30C10F2, respectively) deviated from this pattern. This was because, for a large amount of rubber replacement level, the influence of fibre was less significant, and the RCA and CR replacement levels were both reasonably high in these combinations. As a result, of the batches examined, Batch-15 exhibited the lowest compressive strength. It was evident from Batches 6 (R10C5F2) and 7 (R10C10F1) that the compressive strength of Batch 7 declined more than that of Batch 6 because the proportion of rubber in Batch 7 rose while the fibre content fell. Batches 4 (R10C0F2), 5 (R10C5F1), 11 (R30C0F2), 12 (R30C5F1) & 13 (R30C5F2), and 14 (R30C10F1) exhibit the same pattern. Because batch 11 (R30C0F2) does not contain CR and has a larger amount of fibre, it exhibited the maximum compressive strength at 56 days, 27% more than the control mixture. Rubber-based concrete exhibited high Poisson's ratios because of its soft texture and improved energy absorption capacity, as seen in Table 3.6. Better deformability and energy absorption capability were shown by a growing Poisson's ratio as the replacement level of rubber increased. Conversely, it was observed that as the fraction of fibre increases, Poisson's ratio falls, indicating that the fibre resists deformation. It was discovered that for R10C0F0 and R30C0F0, the Poisson's ratio rises with the increasing RCA replacement level. Concrete cylinders containing CR and fibre did not break easily like control specimens did. Because of its intrinsic mechanical characteristics, the CR distort more than sand under compressive loading conditions. Because it forges a solid link between the aggregate and cement paste and keeps the aggregate particles together to prevent cracking, fibre effectively prevents cracking. Therefore, future research using a combination of rubber and fibre can concentrate on larger deformation, higher energy absorption, and more impact resistant construction requirements. 40 Table 3.6 Mechanical properties of different concrete mixtures (56 days) Batch No. Batch ID Peak Stress (MPa) Axial Strain at Peak Stress Transverse Strain at Peak Stress Ultimate strain Poissonâs Ratio 1 R0C0F0 35.02 0.00278 0.000684 0.00294 0.246 2 R10C0F0 36.23 0.00201 0.000386 0.00305 0.181 3 R10C0F1 37.12 0.00340 0.000670 0.00370 0.197 4 R10C0F2 37.94 0.00561 0.000976 0.00581 0.174 5 R10C5F1 32.70 0.00011 0.000032 0.00021 0.291 6 R10C5F2 36.02 0.00439 0.001070 0.00552 0.244 7 R10C10F1 31.17 0.00267 0.000839 0.00323 0.314 8 R10C10F2 35.91 0.00101 0.000266 0.00120 0.263 9 R30C0F0 33.31 0.00264 0.000660 0.00310 0.250 10 R30C0F1 36.38 0.00585 0.001825 0.00619 0.312 11 R30C0F2 44.56 0.00238 0.000508 0.00270 0.213 12 R30C5F1 35.21 0.00408 0.001340 0.00427 0.328 13 R30C5F2 35.70 0.00444 0.001010 0.00463 0.227 14 R30C10F1 32.11 0.00340 0.001140 0.00382 0.335 15 R30C10F2 30.95 0.00518 0.001242 0.00542 0.240 3.8.3 Splitting tensile strength The test results associated with spitting tensile strength is shown in Figure 3.6 for both 28 and 56 days tests and with different variations of recycled materials. Figure 3.6 Splitting tensile strength of various concrete mixtures for (a) 10%, and (b) 30% RCA combinations (Hossain et al., 2019) The splitting tensile strength data for various concrete mixes at 28 and 56 days is in Figure 3.6. At 28 and 56 days, Batch-4 (R10C0F2) exhibited the highest result, which was about 21% 012345Splitting tensile strength (MPa)28 days 56 days (a)012345Splitting tensile strength (MPa)28 days 56 days (b)41 and 18% higher than the control, respectively. At 28 and 56 days, Batch-14 (R30C10F1) has the lowest tensile strength, which is 22% and 10% lower than the control, respectively. It was evident from Batch-2 (R10C0F0) and Batch-9 (R30C0F0) that the splitting tensile strength drops as the amount of RCA increased from 10% to 30%; it was about 2.5% and 3.5% lower, respectively, than the control mixture. When it comes to CR, the splitting tensile strength of concrete dropped as CR levels rose. The tensile strength values for 10% RCA at 1% fibre content are 3.16 MPa, 2.82 MPa, and 2.79 MPa for 0%, 5%, and 10% replacement levels of CR. At 28 and 56 days, this pattern was also seen for 10% RCA and 2% fibre, as well as for 30% RCA combinations. CR is weak in tensile strength and has a lower elastic modulus. As a result, the bond between CR and cement paste is vulnerable to abrupt separation, resulting in a weak ITZ. However, because fibre has a high tensile capacity, the splitting tensile strength rises as the amount of fibre in the concrete mixture increases. This could be explained by the high amount of fibre that forms a strong link between the cement paste and aggregate along the fracture plane prior to splitting. Flexural strength Figure 3.7 Flexural strength variation in different concrete mixtures for (a) 10%, and (b) 30% RCA combinations(Hossain et al., 2019) The quasi-static flexural strength data is displayed in Figure 3.7. Compared to the control mix, the majority of the concrete mixes exhibited reduced flexural strength. As the amount of RCA increased, the flexural strength fell (Batch-2 & Batch-9). Flexural strength declined with increasing CR replacement level at a fixed fibre content. CR weakened the ITZ, produced a 01234Flexural strength (MPa) (a)01234Flexural strength (MPa) (b)42 weaker link between the aggregate and cement paste, and reacted unevenly with the matrix. Therefore, it may be said that when the replacement amount of CR grows incrementally, the flexural strength falls. On the other hand, it was observed that increasing the proportion of fibre inclusion in the concrete mixture results in an increase in flexural strength at a certain CR replacement level. Fibre builds a strong bridge between the cement paste and aggregate, which is why this happens. The bridging fibres are visible, extending outward and perpendicular to the cross-section following the break in the beam. Regarding Batches 6 (R10C5F2) and 7 (R10C10F1), it was seen that the flexural strength of Batch-7 was lower than that of Batch-6 due to an increase in the percentage of rubber and a drop in the fibre content. Batches 4 (R10C0F2), 5 (R10C5F1), 11 (R30C0F2), 12 (R30C5F1), 13 (R30C5F2), and 14 (R30C10F1) exhibited the same pattern. The highest flexural strength was displayed by Batch-11 (R30C0F2), which was 8.5% greater than the control. There was no CR in this mixture because of the high fibre content, which created a solid bond between the aggregate and cement paste. The lowest result, 16% below the control, was displayed by batch 7 (R10C10F1). This combination had a smaller percentage of fibre and a larger percentage of CR. The load versus deflection curve was used to calculate the toughness of a particular batch. The area under the load versus deflection curve up to a deflection of L/150 (= 3 mm, when the effective span of the beam is 450 mm) was indicated by the toughness, TD150, in accordance with ASTM C1609. It was evident from Tables 3.7 and 3.8 that the hardness value for each batch was higher than that of the control concrete batch. Because fibre can create a bridge inside the densified concrete matrix on either side of the fracture and can withstand load against a greater deflection once it has reached its ultimate failure point, the toughness rating rises as the percentage of fibre in the concrete mixes increases. Therefore, the load versus deflection graph is much larger than what is depicted in Figures 3.8, 3.9, and 3.10. Additionally, fibre serves as a barrier to stop cracks from spreading and forges a solid link between aggregate and cement paste. The toughness value, on the other hand, was observed to rise as the replacement level of CR increased up to 5% and then fell at 10% CR (Batch-3, Batch-5, Batch-7; Batch-4, Batch-6, Batch-8; Batch-10, Batch-12, Batch-14 & Batch-11, Batch-13, Batch-15). The toughness value was highest for batch 13 (R30C5F2). 43 Table 3.7 Summary of flexural response (for 10% RCA) (Hossain et al., 2019) Batch R0C0F0 (Control) R10C0F0 (B-2) R10C0F1 (B-3) R10C0F2 (B-4) R10C5F1 (B-5) R10C5F2 (B-6) R10C10F1 (B-7) R10C10F2 (B-8) Toughness, TD150 (N-mm) 1827 2387 (30.6%) 3553 (94.5%) 5207 (185%) 3828 (109.5%) 5337 (192%) 3178 (74%) 5134 (181%) Flexural Toughness Factor (FTF) (MPa) 0.27 0.36 0.53 0.78 0.57 0.80 0.48 0.77 Equivalent Flexural Strength ratio, RD150 (%) 7.79 10.29 15.17 21.88 19.16 25.67 16.16 25.16 Table 3.8 Summary of flexural response (for 30% RCA) (Hossain et al., 2019) Batch R0C0F0 (Control) R30C0F0 (B-9) R30C0F1 (B-10) R30C0F2 (B-11) R30C5F1 (B-12) R30C5F2 (B-13) R30C10F1 (B-14) R30C10F2 (B-15) Toughness, TD150 (N-mm) 1827 3477 (90.3%) 5689 (211.3%) 9688 (430%) 6277 (243.5%) 10179 (457%) 5242 (186.9%) 5640 (208.7%) Flexural Toughness Factor (FTF) (MPa) 0.27 0.52 0.85 1.45 0.94 1.53 0.79 0.85 Equivalent Flexural Strength ratio, RD150 (%) 7.79 16.29 25.24 38.00 28.13 40.22 23.61 24.25 44 Figure 3.8 Load vs deflection response of beams under various replacement levels of RCA (for 5% CR & 2% Fibre) Figure 3.9 Load vs deflection of beams under various replacement of CR for (a) 30% RCA and 1% fibre, and (b) 30% RCA and 2% fibre combinations (Hossain et al., 2019) 024680 0.5 1 1.5 2 2.5 3 3.5Load (kN)Deflection (mm)024680 0.5 1Load (kN)Deflection (mm)ControlRââCâ FâRââCâ Fâ024680 0.5 1 1.5 2 2.5 3 3.5Load (kN)Deflection (mm)(a)024680 0.5 1Load (kN)Deflection (mm)ControlRââCâFâ024680 0.5 1 1.5 2 2.5 3 3.5Load (kN)Deflection (mm)(b)024680 0.5 1Load (kN)Deflection (mm)Control RââCâFâRââCâ Fâ RââCââFâ45 Figure 3.10 Load vs deflection of beams under various fibre content for (a) 30% RCA and 0% CR, (b) 30% RCA and 5% CR, and (c) 30% RCA and 10% CR combinations (Hossain et al., 2019) 024680 0.5 1 1.5 2 2.5 3 3.5Load (kN)Deflection (mm)Control(c)024680 0.5 1Load (kN)Deflection (mm)ControlRââCââFâRââCââFâ024680 0.5 1 1.5 2 2.5 3 3.5Load (kN)Deflection (mm)(a)024680 0.5 1Load (kN)Deflection (mm)Control RââCâFâRââCâFâ RââCâFâ024680 0.5 1 1.5 2 2.5 3 3.5Load (kN)Deflection (mm)(b)024680 0.5 1Load (kN)Deflection (mm)ControlRââCâ FâRââCâ Fâ46 From the load versus deflection figures (Figure 3.8 to 3.10) above, the ductility of various batches was calculated according to the following equation: µ = δUδY where, δU = deflection at ultimate strength (i.e., deflection value when the failure crack forms and applied load starts to drop), and δY = deflection up to the linear portion of the load-displacement curve (i.e., deflection when the first crack forms in the beam). The ductility values of the different batches are displayed in Table 3.9. The ductility or deformation capacity of the beam was found to increase with increasing fibre levels, suggesting that rubberised concrete with fibre will provide a sufficient warning prior to failure. Up to 5% CR, ductility rose as the replacement level of CR rose, after which it dropped to 10% CR. Table 3.9. Ductility value of various batches (Hossain et al., 2019) Batch R0C0F0 (Control) R10C0F0 (B-2) R10C0F1 (B-3) R10C0F2 (B-4) R10C5F1 (B-5) R10C5F2 (B-6) R10C10F1 (B-7) R10C10F2 (B-8) Ductility 2.30 1.31 1.62 1.75 1.78 2.00 1.73 1.87 Batch R0C0F0 (Control) R30C0F0 (B-9) R30C0F1 (B-10) R30C0F2 (B-11) R30C5F1 (B-12) R30C5F2 (B-13) R30C10F1 (B-14) R30C10F2 (B-15) Ductility 2.30 1.15 1.21 1.29 2.43 2.80 1.27 1.31 3.8.4 Assessment with standard code of practices There are several design recommendations that use compressive strength to estimate the mechanical response of concrete. The current investigation predicts the various responses of the concrete specimens using design recommendations from the ACI, fib, and Euro-code (EC2), CSA (Figure 3.11 and Figure 3.13). The outcomes of the experiment are compared with these anticipated behaviours. As shown in Figures 3.12 and 3.14, according to Hossain et al. (2019), the ratio (ξ) between the experimental and anticipated values was computed for comparison purposes. A value of ξ greater than 1 denotes an overprediction of the outcome, whereas a value less than 1 denotes an underprediction. 47 Splitting tensile strength ACI 318-14 [58] fctm,sp = 0.556âfCâ² ; where fctm,sp is mean splitting tensile strength in MPa fib2010[59] fctm = 0.3(fCm)23 ; where fctm is mean tensile strength in MPa and fcm is mean compressive strength in MPa EC2[60] fctm = αspfctm,sp ; where EC2 recommends the value of αsp as 0.9 Modulus of rapture ACI 318-14 [58] fâr= 0.62âfcâ² ; where fâc is concrete compressive strength in MPa ACI 209-92 [61] fâr= 0.013âÏ. fcâ² ; where Ï is the density of concrete in kg/m3 and fâc is in MPa fib2010 [59] fâr= 0.3((fCâ² )23)αfl ; where, αfl = 0.06hb0â 71+0.06hb0â 7 and hb = depth of beam(mm); fâc is in MPa CSA A23.3-14 [62] fâr= 0.6Î»âfcâ² ; where λ=1.0 for normal density concrete and fâc is in MPa Figure 3.11 Comparison of splitting tensile strength with different codes 024Splitting tensile strength (MPa) ACI 318-14 fib2010 EC248 Figure 3.12 The ratio between the experimental and the calculated values (ξ) of splitting tensile strength using available guidelines for concrete Figure 3.13 Comparison of flexural strength with different codes 0.00.51.01.5Ratio between experimental and calculated values ACI 318-14 fib2010 EC202468Flexural strength (MPa)ACI 318-14 ACI 209-92fib2010 CSA A23.3-1449 Figure 3.14 The ratio between the experimental and the calculated values (ξ) of flexural strength using available guidelines for concrete 3.8.5 Hardened concrete density Figure 3.15 displays the hardened concrete density data for the different concrete combinations. It was evident from the figure that the concrete examples from various batches differed significantly in weight. In comparison to the recycled rubberised fibre-based concrete, the control concrete specimens exhibit a marginally higher density. Despite being nearly identical to the control, the density of the 10% RCA was observed to drop by 3.6% for the 30% RCA. Additionally, R10C10F2 and R30C10F2 showed that, when rubber and fibre contents were fixed, the density dropped by 2.7% and 6.2%, respectively, when RCA levels rose in comparison to control. It could be seen from Batches 3 (R10C0F1), 4 (R10C0F2), 14 (R30C10F1), and 15 (R30C10F2) that density likewise dropped as the amount of fibre increased. It appeared from Batches 4 (R10C0F2), 6 (R10C5F2), 8 (R10C10F2), and 11 (R30C0F2) that the density of 0% and 5% CR replacement were nearly the same when the RCA and fibre were fixed. However, because rubber particles have a lower specific gravity and produce low-density concrete, it dropped significantly for 10% rubber. Concrete with this density decrease, however, cannot be categorized as lightweight. As a result, recycled rubberised fibre-based concrete will weigh less and have a lower dead load. 0.00.51.01.5Ratio between experimental and calculated values ACI 318-14 ACI 209-92fib2010 CSA A23.3-1450 Figure 3.15 Harden density of concrete specimens Batches 6 (10% RCA, 5% CR, and 2% fibre) and 13 (30% RCA, 5% CR, and 2% fibre) outperformed the control concrete mix in terms of compressive strength, split tensile strength, flexural strength, and toughness, according to mechanical property tests conducted when both recycled materials were used. 3.9 Failure Pattern The failure pattern of the tested concrete cylinders under the compressive strength test is presented in Figure 3.16. Most of the cylinders experienced cone and shear failure under compressive load. Due to CR's excellent deformability and fibre's ability to hold cracks, concrete cylinders reinforced with fibre and CR failed more slowly than the control. Since CR is a softer substance than sand, it is extremely deformable when subjected to compressive force. PPF forms a solid link between aggregate and cement paste and keeps the aggregate particles together to prevent cracking. It was observed that concrete cracked along well-defined failure planes for both the control and solely RCA replacement concrete under the splitting tensile strength test. Conversely, because the fibre keeps the aggregate and cement paste together to prevent cracks, rubberised fibre-based concrete cylinders had uneven failure planes (Figure 3.17). Figure 3.18 shows the concrete beam's failure pattern during the flexural strength test. Specimens without fibre 22002300240025002600Unit Weight (Kg/m3)51 were easily broken into two pieces during flexural strength tests, and their load-deflection curve suddenly dropped. In contrast to the control and just RCA specimens, which had well defined failure planes, the specimens with CR and fibre shattered along uneven failure planes during split tensile tests. However, after reaching their maximum load-bearing capacity, fibre-containing specimens showed delayed, gradual, ductile failure and did not completely break. As seen in Figure 3.19, such beams are then physically fractured to inspect the failure surfaces. It was clear that the fibre created a bridge on either side of the crack in the concrete matrix at the plane of failure. Figure 3.16 Failure pattern of concrete cylinder under compressive strength test: (a) control, (b) only 30% RCA, (c) RCA, CR and fibre combination Figure 3.17 Concrete specimen after splitting tensile strength test: (a) only for RCA and (b) RCA, rubber and fibre combination (a) (b) (c) 52 Figure 3.19 Beam specimen after flexural strength test (a) R10C0F0, (b) R30C0F2, (c) R30C5F2 Figure 3.18 Failure pattern of the concrete beam under flexural strength test: (a) control, (b) only 10% RCA, (c) RCA 30%, CR 10% and fibre 2% P/2 P/2 Control (Flexural Failure) P/2 P/2 R10C0F0 (Flexural Failure) P/2 P/2 R30C10F2 (Flexural Failure) Bridging (c) (b) (a) 53 3.10 Summary The study suggested that while RCA, CR, and PPF present challenges (e.g., reduced compressive strength and workability), they offer valuable benefits in terms of energy absorption, impact resistance, and deformability. By using polypropylene fibres, these mixtures can be enhanced for applications where flexibility and resistance to cracking are more important than high compressive strength. Future studies should explore the potential of fibre-reinforced concrete made with recycled materials like RCA and CR in applications such as pavements, industrial floors, and earthquake-resistant structures where flexibility, energy absorption, and impact resistance are prioritized over traditional strength issues. 54 Chapter 4: Bond Behaviour of Recycled Aggregate Concrete with Rebar Containing CR and PPF 4.1 General This chapter focuses on elucidating the influence of CR and PPF on bond strength in concrete elements using recycled concrete aggregates (RCA). Since the last chapter explains the mechanical aspects of RCA and CR made concrete, it is essential to understand the structural behaviour of the same to find out its practical application. The experimental studies are enumerated subsequently in this chapter. 4.2 Test Matrix and Variables This study was conducted in three phases. In phase I, a mix design with fewer (seven) combinations of RCA, CR, and PPF was used to analyse their effects on the bond strength of concrete. In phase II, another twelve combinations of concrete with varying RCA and CR contents were produced to observe the behaviour of concrete bond strength with rebar further when only CR and RCA are present. NCA was replaced by only 10 and 30% RCA by weight. In phase III, thirteen combinations of concrete with varying RCA, CR, and PPF contents were produced to observe the combined effect of RCA, CR, and PPF and conclude on the behaviour of concrete bond strength with rebar. The designations and interpretation of the symbol used (RxCyFz) for different materials in the study are tabulated in Table 4.1. Table 4.1 Designations and description of different materials used in the study (RxCyFz) R x C y F Z Recycled Coarse Aggregate (RCA) % of RCA replaced for NCA by weight Crumb Rubber (CR) % of CR used as the replacement for NFA by volume PPF % of PPF used as the replacement for concrete by volume For example, R10C5F2 represents a concrete mix with 10% RCA, 5% CR, and 2% PPF replacement levels. 55 The combination of specimens with their mix proportions for phase I, phase II and phase III of this study are tabulated in Table 4.2, Table 4.3 and Table 4.4, respectively. Table 4.2 Mix proportions of different materials (RCA+CR+PPF) in Phase I Serial Combination NCA (kg/m3) RCA (kg/m3) NFA (kg/m3) CR (kg/m3) PPF (kg/m3) Cement (kg/m3) C1 R0C0F0 990 0 679 0 0 427 C2 R10C5F2 891 99 662 17 3 424 C3 R10C10F2 891 99 645 33 3 424 C4 R30C0F2 693 297 679 0 3 424 C5 R30C5F0 693 297 662 17 0 427 C6 R30C5F2 693 297 662 17 3 424 C7 R30C10F2 693 297 645 33 3 424 Table 4.3 Mix proportions of different materials (RCA+CR) in phase II Serial Combination NCA (kg/m3) RCA (kg/m3) NFA (kg/m3) CR (kg/m3) Cement (kg/m3) M1 R0C0 990 0 679 0 427 M2 R10C0 891 99 679 0 427 M3 R30C0 693 297 679 0 427 M4 R50C0 495 495 679 0 427 M5 R0C5 990 0 645 17 427 M6 R10C5 891 99 645 17 427 M7 R30C5 693 297 645 17 427 M8 R50C5 495 495 645 17 427 M9 R0C10 990 0 611 33 427 M10 R10C10 891 99 611 33 427 M11 R30C10 693 297 611 33 427 M12 R50C10 495 495 611 33 427 56 Table 4.4 Mix proportions of different materials (RCA+CR+PPF) in phase III Serial No Combination NCA (kg/m3) RCA (kg/m3) NFA (kg/m3) CR (kg/m3) Cement (kg/m3) PPF (kg/m3) 1 R0C0F0 990.16 0.00 678.70 0.00 427.08 0.00 2 R10C0F0 891.14 99.02 678.70 0.00 427.08 0.00 3 R10C0F2 891.14 99.02 678.70 0.00 424.45 2.63 4 R10C5F0 891.14 99.02 662.08 16.62 427.08 0.00 5 R10C5F2 891.14 99.02 662.08 16.62 424.45 2.63 6 R10C10F0 891.14 99.02 645.47 33.23 427.08 0.00 7 R10C10F2 891.14 99.02 645.47 33.23 424.45 2.63 8 R30C0F0 693.11 297.05 678.70 0.00 427.08 0.00 9 R30C0F2 693.11 297.05 678.70 0.00 424.45 2.63 10 R30C5F0 693.11 297.05 662.08 16.62 427.08 0.00 11 R30C5F2 693.11 297.05 662.08 16.62 424.45 2.63 12 R30C10F0 693.11 297.05 645.47 33.23 427.08 0.00 13 R30C10F2 693.11 297.05 645.47 33.23 424.45 2.63 4.3 Properties of Materials The following table depicts the physical properties of PPF and aggregates. As per Table 4.5, the specific gravity of PPF is only 0.9, which is much less than other constituents which was replaced in concrete on a volume basis. According to Table 4.6, it was found that RCA has 5~7 times higher water absorption than NCA because of its attached mortar and rough surface. Whereas CR is a hydrophobic material having 1~1.5 times lower absorption capacity of water. This indicated that an adjustment for the water-cement ratio and improvement of workability were necessary for tests with RCA and CR. 57 Table 4.5. Physical properties of PPF Properties Values Specific gravity 0.9 Fibre length (mm) 12.0 Fibre diameter (µm) 18 Aspect ratio 667 Tensile strength (MPa) 480.0 Elastic Modulus (GPa) 7.0 Table 4.6 Physical properties of aggregates 4.4 Test Specimen Deformed steel bars of two different diameters of 10mm and 12mm in phase I, and later in phase III, rebars of 12mm, 16mm and 20mm with a tensile strength of 420 MPa or grade 60 were used. Since the main focus of the experiment was to examine the variation of bond stress of different combinations and control specimens, the diameter variation was not an important factor, but its effect was observed. Research has shown that smaller bar sizes result in a larger bond stress and vice versa when larger rebars are used (CSA A23.3 and ACI 318-11). The steel bars were collected from a local company and then cut to suitable sizes for casting the specimens. Table 4.7 below depicts the designations of reinforcing steel used to distinguish different lengths and diameters. Apparent specific gravity Specific gravity Water Absorption capacity (%) Fineness Modulus Unit weight (kg/m3) % Voids SSD OD Loose Compact Loose Compact NCA 2.73 2.71 2.70 0.48 2.51 1477 1526 47.1 45.3 RCA 2.64 2.51 2.44 3.23 2.71 1558 1659 35.9 31.7 NFA 2.47 2.41 2.36 1.8 2.39 1455 1579 38.7 33.5 CR - 1.18 - 1.3 3.49 - - - - 58 Table 4.7 Designations and interpretation of length-diameter variations symbols (DxLyCz) of reinforcing steel D x L y C Z Diameter Diameter used in a particular specimen Embedded Length of steel bar Embedded length used in a particular specimen Concrete mix (Phase I) Serial of combination ( C1,C2, â¦C7) A total of 126 specimens were cast for 7 different concrete combinations for the pull-out test in phase I of this study for 14 and 28 days. In phase II, another 36 cylinders with 12 different combinations were made. In phase III, 156 specimens were cast for 13 different combinations with three different higher diameter rebar variations. The compressive and pull-out tests were done for the specimens. Formwork with 200mm height and 100mm diameter cylinder was used. In phase I, only 10 and 12mm diameter steel bars were used, and embedment lengths of 100 and 150mm were maintained. Then, in phase II, only one diameter (12mm) and one embedment length of 5db (60mm) were used to observe the trend of bond characteristics of concrete containing RCA and CR only with steel reinforcement. Furthermore, in phase III, three different higher diameters (12mm, 16mm & 20mm) with different embedment lengths (5db) of steel were used to observe the bond behaviours of the concrete containing RCA, CR and PPF. In phases II and III, the specimens had an unbonded length near the loading end of the specimen, which was achieved using a PVC pipe as a bond breaker. Initially, in phase I, only seven combinations were cast with three variables (RCA, CR & PPF) with fewer variations. In the second phase, only recycled materials (RCA and CR) were used to see their interdependent behaviour. Finally, in phase III, 15 different combinations were used to ascertain the effect of diameter variation, compressive and bond strength relationship and combined effect of all the variables with regard to concrete bond with rebar to get a better understanding of the subject. 4.5 Specimen Preparation The concrete mixes were prepared in a concrete mixer according to the different mix proportions, as previously stated in Table 4.2, Table 4.3 and Table 4.4. The concrete was then poured into moulds to cast the cylinders. After that, different diameter steel bars with different embedment lengths were placed. For instance, a 10mm diameter steel bar was embedded by 59 100mm into the concrete-filled cylinder at its center (whereas for phase III, an embedment length of 5db is maintained, such as for 16mm rebar embedment length was 80mm). For all the specimens, the exposed length or the grip length was kept constant at 250mm. A wood sheet with a hole in the center and a support system to hold it in place was used to ensure the non-eccentricity of the embedded rebar. The steel bar was inserted carefully at the center of the cylinder. After casting, all the specimens were kept in moulds for 24 hours. Figure 4.1 Pull-out test specimens 4.6 Testing Procedure In phase I, a simplified formwork and testing setup was used to investigate the bond strength of conventional concrete against recycled aggregate concrete with PPF. For this, an additional apparatus was used to hold the concrete cylinder with an embedded steel bar in the âUniversal Testing Machineâ (UTM). The apparatus was made in the laboratory, as shown in Figure 4.3. The pull-out test was conducted using the UTM using code ASTM C900-15 standard. The embedded lengths were 100 and 150mm for 10mm and 12mm diameter steel bars. The 250mm grip length was fixed for all specimens. At first, the apparatus was set on the UTM, and the cylinder was placed upside down. The steel bar was set onto the moveable lower portion of the UTM. The upper grip was holding the pull-out device and was kept fixed. A uniform stroke of 1mm/min was applied on the lower grip, holding the steel bar throughout the test. The lower portion of the UTM provided the tensile force. Pull-out load and elongation of steel bar data were recorded throughout the test duration. The dimensions and embedment length are shown in Figure 4.2. From the pull-out load, the bond strength between the concrete and steel bar was calculated by dividing the pull-out force by the surface area of the embedded steel bar. Here, it was assumed that the non-uniform 60 distribution of stress at the bottom of the test cylinder due to the gap for pulling rebar did not have any direct effect on the bond stress at the opposite end of the cylinder, as observed in the failure specimen. Figure 4.2 Cross-section of the specimen In phase II, only 12mm diameter steel reinforcement was used with 60mm (5db) embedment length, and the steel was de-bonded from concrete using PVC pipe. In phase III, 12mm,16mm and 20mm rebar was used with 60mm, 80mm and 100mm embedment lengths. The bond between concrete and steel was broken near the loading end of the specimen. Figures 4.3 and 4.4 illustrate the mechanism for the bonded-unbonded pull-out test setup. The test process was the same as before, except LVDT was used to record the displacement values over time. An illustration showing the specimen and test setup for phase II is shown in Figure 4.4 (a). 61 Figure 4.3 Pull-out test â Phase I (a) Special apparatus, (b) Apparatus setup in UTM, (c) Complete test setup LVDT Bonded Segment (5db) PVC Pipe Unbonded Segment Counter Force db UTM Gripping Segment P= Pull-out force (KN) Figure 4.4 Pull-out test â Phase II (a) Cross section of the specimen, (b) Complete test setup (a) (b) (c) (b) (a) 62 Figure 4.5 Phase III (a) Compressive test setup, (b) Pull out test setup 4.7 Result Analysis 4.7.1 Phase I: Bond Strength of Concrete with RCA, CR and PPF The phase I, bond strength tests were done with only seven combinations to see the influence of CR and PPF in RCA made concrete in general. Variations of bar diameter and length were done within these few combinations as well. The compressive and bond strengths of all combinations are shown in Table 4.8. 63 Table 4.8 All Pull-out test data recorded in 14 days and 28 days Combinations Compressive Strength 14 days 28 days D12L100 (MPa) D12L150 (MPa) D10L100 (MPa) D12L100 (MPa) D12L150 (MPa) D10L100 (MPa) R0C0F0 24.4 6.5 6.7 6.10 6.6 7.7 8.1 R10C5F2 31.7 7.6 8.2 10.1 8.3 10.0 11.4 R10C10F2 25.8 5.8 8.3 6.3 7.2 8.7 7.4 R30C5F2 28.9 8.0 8.4 9.0 8.5 9.2 10.3 R30C10F2 27.0 5.1 5.8 6.8 6.5 6.7 7.9 R30C0F2 31.5 4.5 6.1 7.1 12.4 10.4 12.7 R30C5F0 33.8 5.4 5.2 8.2 13.5 14.6 15.1 4.7.1.1 Crumb rubber effect on bond strength For 0%, 10% and 30% RCA, the effect of CR is shown in Figure 4.6 (a, b) for five combinations (R0C0F0, R10C5F2, R10C10F2, R30C5F2, and R30C10F2) in 14 and 28-days analysis with a constant 2% PPF inclusion. In all cases, 5% CR exerts greater bond strength than 10% CR, which means that up to 5% CR can be used as a replacement of NFA, which will increase the bond strength capacity as well. However, it will decrease the bond strength of concrete if more than 5% CR is used. Figure 4.6 (a, b) shows that combinations containing 10% CR have lesser bond strength than the control sample. This is because earlier researchers found that a high amount of CR lessens the compressive strength of concrete (Hossain et al., 2019) and thus reduces the bond strength as well. 64 Figure 4.6 (a) Crumb rubber effect in 14 days bond strength with various bar diameter-length variations for variable RCA content As there exists a significant number of pores in CR, using it at a high percentage on concrete mix reduces the workability and thus weakens the bond since less workability affects the compressive and bond strength of concrete. 10% CR inclusion exhibited a reduction in the bond strength of concrete of at most 13% from the parent sample. Figures 4.6 (a, b) and Figure 4.7 show that 10% RCA with 5% CR shows the highest bond strength of concrete, which is 27% greater than the control sample. D10L100 (D= diameter of steel bar 10mm, L= Embedded length of steel bar 100mm) showed the best performance on bond strength of concrete (11.14 MPa) with 10% RCA and 5% CR, while D12L100 displayed the lowest strength. The usual phenomenon of embedded length variations was observed on bond strength in D12L100 and D12L150 (D= diameter of steel bar 12mm, L= Embedded length of steel bar) samples, where, with a fixed diameter of steel bar, a higher length showed better performance. D12L100 (5%) D12L100 (10%) D12L150 (5%) 6 D12L150 (10%) 4 D10L100 (5%) D10L100 (10%) 2 0 R0 R10 Fibre=2% R30 8 10 12 Bond strength (MPa) 65 Figure 4.6 (b) Crumb rubber effect in 14 days bond strength with various bar diameter-length variations for variable RCA content rubber effect in 28 days Figure 4.7 Crumb rubber effect in bond strength with various bar diameter- length variations 4.7.1.2 Comparative study of CR and PPF A further study was carried out with another two new combinations (R30C0F2, R30C5F0) to examine the interaction between CR and PPF with 30% RCA for different length-diameter variations, as depicted in Figure 4.8 (a, b). Only 30% RCA was used here because 30% RCA is the amount where no significant change in concrete bond strength can be observed; instead, an 024681012RâCâFâ RââCâ Fâ RââCâ FâBond Strength-(MPa)28 daysDââLâââ (5%CR) DââLâââ (10%CR)DââLââ â (5%CR) DââLââ â (10%CR)DââLâââ (5%CR) DââLâââ (10%CR)Crumb Rubber Effect (28 days) 14 D10L100 (5%) 12 D10L100 (10%) 10 D12L100 (5%) 8 D12L100 (10%) D12L150 (5%) 6 D12L150 (10%) 4 2 0 R0 R10 Fibre= 2% R30 Bond strength (MPa) 66 increase in bond strength was noted, and only 5% CR was used this time as 10% CR decreased the bond strength of concrete in all cases. It was also observed from the figure that for all length-diameter variations, R30C5F0 showed a higher value than R30C0F2. Both R30C5F0 and R30C0F2 had 46% and 36% higher bond strength than of the control sample, respectively. Overall, D10L100 showed higher bond strength than the other length-diameter variations, and with 5% CR and no PPF, it had the highest bond strength. Changing the diameter to D12L100, the bond strength decreased. So, the lower diameter has a positive effect on the bond strength of concrete. Again, increasing the length and keeping the diameter fixed in the D12L150 sample displayed higher bond strength. Overall, the lower diameter and higher length of the steel bar showed greater bond strength between concrete and steel bar, and the bond of 30% RCA with 5% CR without PPF was higher than 2% PPF without CR. 67 Figure 4.8 (a) Bond strength variation for CR and PPF Figure 4.8 (b) Comparative study between CR and PPF with 30% RCA 4.7.1.3 Combined analysis Figure 4.9 (a) presents the bond strength of the seven concrete mixes â C1, C2, C3, C4, C5, C6, and C7 together for three length-diameter combinations of steel (D12L100, D12L150, D10L100) at 28 days to assess the behaviour of CR and PPF within recycled aggregate concrete. D12L100 D12L150 D10L100R0C0F0 6.55 7.74 8.1R30C0F2 12.42 10.37 12.68R30C5F0 13.52 14.58 15.10246810121416Bond Strength (MPa)Comparative Data Between CR & PPF with 30 RCA16 14 12 10 8 6 4 R0C0F0 R30C0F2 R30C5F0 D12L100 D12L150 RCA= 0%, 30% D10L100 Bond strength (MPa) 68 Figure 4.9 (a) Bond strength of concrete with RCA, CR, and PPF for three length-diameter combinations at 28 days Variable RCA (0,10 and 30 percent) and constant fibre content (2%) with 5% CR showed higher strength compared to that of 10% CR. In fact, the inclusion of 10% CR reduced the bond strength by 10% compared to the control. Moreover, 5% CR increased the bond strength the most when mixed with 10% RCA. Here, the D10L100 bar exhibited the strongest bond composed of 10% RCA, 5% CR and 2% PPF with a bond strength of 11.0 MPa (3.0 MPa increased). Similar to the effect of CR, implementing a higher percentage of PPF lowered the bond strength. Consequently, R30C5F0 had increased the average bond strength by 45%, while the increase by R30C0F2 was only 30%. As such, it can be said that CR is better than PPF when separately mixed with RCA in concrete. Considering the effects of bar diameter and embedment length on bond strength, when the steel diameter increased from 10 to 12mm, the bond strength of the concrete decreased. However, for the same diameter, increasing the embedment length from 100 to 150mm resulted in an increase in bond strength for the D12L150 specimens in all cases except when both CR and PPF were present. Thus, a lower diameter of the steel bar renders a higher bond strength. Also, a higher embedment length of the steel bar further increases the bond strength of the concrete. But when both PPF and CR were present, the trend was unpredictable, with higher embedment length showing less bond strength due to adding an additional smooth surface of PPF with the matrix, 0246810121416R0C0F0 R10C5F2 R10C10F2 R30C0F2 R30C5F0 R30C5F2 R30C10F2Bond Strength (MPa)D12L100D12L150D10L10069 reducing bond with rebar, mortar and RCA. The compressive strength and the bond strength measured from the laboratory test are shown in Table 4.8 and Figure 4.9 (b). The normalized graphs between compressive and bond strength are shown subsequently in Figures 4.10 (a,b,c). Figure 4.9 (b) Compressive and Bond strength of concrete with RCA, CR, and PPF for three length-diameter combinations at 28 days 4.7.1.4 Relation of bond strength with compressive strength (Normalized) The following normalizations in Figure 4.7 (a,b,c) for D12L100, D12L150 and D10L100 through the regression analysis observed the differential characteristics of the bond strength in relation to the square root of compressive strength. As the length increased and diameter decreased, the bond increased. A linear regression equation is established for the bond strength relationship with compressive strength, and the regression equation displays that the equation is the best fit and values are 0.7-0.87 in all the cases. Bond strength is a critical behaviour because of the variability due to length, diameter, surface conditions and properties in this research. As such, the R2 value, which was very close to 1.0, was not desired and was difficult to attain. 0510152025303540R0C0F0 R10C5F2 R10C10F2 R30C5F2 R30C10F2 R30C0F2 R30C5F0Strength (Mpa)CombinationCompressive strength Bond Strength (D12L100) Bond Strength (D12L150) Bond Strength (D10L100)70 Figure 4.10 (a) Normalized relation between Compressive and Bond strength of FRRAC with Rebar for D12L100 at 28 days Figure 4.10 (b) Normalized relation between Compressive and Bond strength of FRRAC with Rebar for D12L150 at 28 days y = 7.4399x - 31.002R² = 0.72060.002.004.006.008.0010.0012.0014.0016.004.80 4.90 5.00 5.10 5.20 5.30 5.40 5.50 5.60 5.70 5.80 5.90Bond Strength, MPaCompressive Strength (Sq Root), MPa1/2Normalization Graph for D12L100y = 6.5021x - 25.325R² = 0.6960.002.004.006.008.0010.0012.0014.0016.004.80 4.90 5.00 5.10 5.20 5.30 5.40 5.50 5.60 5.70 5.80 5.90Bond Strength, MPaCompressive Strength (Sq Root), MPa1/2Normalization Graph for D12L15071 Figure 4.10 (c) Normalized relation between Compressive and Bond strength of FRRAC with Rebar for D10L100 at 28 days 4.7.1.5 Load-extension behaviour From UTM, load and extension data were recorded. From the recorded values of load, the bond strength of the concrete was calculated by dividing the load by the contact area of the steel bar with the concrete. The load vs extension graphs for different combinations in different length-diameter variations on the 28th day are shown in Figure 4.11 (a-g). From the load-extension graph, slip analysis is done afterwards. y = 8.2302x - 33.897R² = 0.8740.002.004.006.008.0010.0012.0014.0016.004.80 4.90 5.00 5.10 5.20 5.30 5.40 5.50 5.60 5.70 5.80 5.90Bond Strength, MPaCompressive Strength (Sq Root), MPa1/2Normalization Graph for D10L10072 (a) D12L100C1 (R0C0F0) (b) D12L100C2 (R10C5F2) (c) D12L100C3 (R10C10F2) (d) D12L100C4 (R30C5F2) (e) D12L100C5 (R30C10F2) (f) D12L100C6 (R30C0F2) (g) D12L100C7 (R30C5F0) Figure 4.11 Load-extension graph of (a) D12L100C1, (b) D12L100C2, (c) D12L100C3, (d) D12L100C4, (e) D12L100C5, (f) D12L100C6 and (g) D12L100C7 73 4.7.1.6 Slip analysis A slip analysis was done using the load-extension graph. Bond-slip reinforcement models are valid when it is assumed that a perfect bond no longer exists between the concrete and the reinforcement bars. This results in a slip, or relative displacement, between the concrete and the reinforcement. This slip causes interface tractions along the reinforcement bars. From the increasing force in UTM, the load also increases continuously, and the first load where a discontinuity occurs on the increase in load, that load value is considered as slip load. The slip load values are given in Table 4.9. The table shows that, as discussed before with regard to bond strength, combination R30C5F0 or C7 has the highest slip value, implying that a better bond exists between concrete and reinforcement for a longer time than other combinations when it is 5% CR and 30% RCA. Control had a higher slip load, and R10C5F2 was also close to control, but R30C5F0 has 50% higher slip load than control because of the absence of PPF. Table 4.9 Slip analysis data of different specimens Samples Load at first Slip (KN) Samples Load at first Slip (KN) Samples Load at first Slip (KN) D12L100C1 4.598 D12L150C2 3.54 D10L100C2 1.971 D12L100C2 4.302 D12L150C2 3.733 D10L100C2 1.187 D12L100C3 2.921 D12L150C3 0.702 D10L100C3 1.169 D12L100C4 1.605 D12L150C4 2.953 D10L100C4 2.7134 D12L100C5 3.348 D12L150C5 1.718 D10L100C5 1.739 D12L100C6 3.534 D12L150C6 3.649 D10L100C6 1.192 D12L100C7 6.959 D12L150C7 3.666 D10L100C7 4.07 Where, C1=R0C0F0, C2=R10C5F2, C3=R10C10F2, C4=R30C5F2, C5=R30C10F2, C6=R30C0F2, C7=R30C5F0 D= Diameter of reinforcing steel bar L= Embedment length of reinforcing steel bar It is observed from Table 4.9 that combination 7 (R30C5F0) reached the highest value, which was better than the control, which was without PPF. Again, Combination 2 & 3, having both CR and PPF attained the minimum strength from the slip point of view. As such, it can be said that CR and PPF adversely affect the bond and slip in concrete. 74 4.7.1.7 Failure pattern As per Figure 4.12, two types of failures were predominantly noticed: cracking as well as splitting of concrete and radial failure of concrete around the concrete steel interface, where the latter was the governing type of failure. The control specimens, without RCA, CR or PPF, split into two parts after a single stroke of loading, while the specimens containing RCA, CR and PPF did not break even after hitting the ground multiple times. (a) (b) (c) (e) (d) Figure 4.12 Cracking and splitting failure â (a) front view and (b) top view; (c)Radial failure by pull-out bar lug; Abrupt failure of the control specimen â (d) front view and (e) exploded specimen 75 4.7.2 Phase II: Comparative Study of Recycled Concrete Aggregate and Crumb Rubber A comparison was made to assess how RCA and CR affect bond strength to determine the optimal percentages of Recycled Concrete Aggregate (RCA) and Crumb Rubber (CR) without compromising the minimum strength requirements of concrete. For concrete with 0% and 5% CR replacement, the bond strength decreased as the percentage of RCA increased. However, when the CR replacement is increased to 10%, the bond strength shows a slight improvement with increasing RCA. Despite this, an overall trend of decreasing bond strength was observed as both RCA and CR percentages increased. A comparative analysis of the effects of RCA and CR replacements on bond strength is illustrated in Figure 4.13. It was observed that for 10% RCA replacement, 14% bond strength decreased, and it went up to a 30% decrease with 50% RCA. Alternatively, when only 5% CR was replaced with NFA, the strength was reduced to 16% only from the control specimen. After that, any addition of CR of more than 5% and RCA of more than 30% kept on decreasing the bond strength. This trend established that both RCA and CR increase beyond 10% and 5% will have a significant negative impact on concrete bond strength with RCA and CR. Therefore, recycled aggregate concrete with 10% to 30% RCA and up to 5% CR can be used in construction as long as the reduced bond strength with rebar is acceptable. Figure 4.13 Phase II - Comparative analysis of concrete bond strength with RCA and CR y = -0.7126x + 23.57R² = 0.6683051015202530RâCâ RââCâ RââCâ Râ âCâ RâCâ RââCâ RââCâ Râ âCâ RâCââ RââCââ RââCââ Râ âCââBond Strength (MPa)76 4.7.3 Phase III: Study on the combined effect of RCA, CR and PPF on bond strength with variable bar diameter. Phase III evaluated the combined effects of compressive and bond strength, and the study incorporated all the materials (RCA, CR, and PPF) together in different combinations. Compressive strength was assessed through a series of tests conducted on specimens without rebar. For the bond strength assessments, steel reinforcements with larger diameter rebars from the previous experiments and a 5db embedment length were utilised, with the steel being de-bonded from the concrete via a PVC pipe. Consistent with the observations from Phase II, the bond between the concrete and steel was found to fail near the specimen's loading end, which indicated the effect of non-uniform stress distribution at the lower end of specimens was negligible. The results of phase III are listed in Table 4.10 and Figure 4.14, respectively. Table 4.10 All Compressive and Pull-out test data recorded in 28 days Combinations Compressive Strength (MPa) for 28 Days Bond Strength (MPa) for 28 Days 12mm 16mm 20mm R0C0F0 36.92 22.04 13.41 10.79 R10C0F0 44.40 22.40 13.56 8.98 R10C0F2 41.57 22.82 14.21 6.45 R10C5F0 38.53 19.81 15.60 8.98 R10C5F2 32.63 18.05 11.52 7.11 R10C10F0 32.23 18.85 11.84 7.20 R10C10F2 33.60 12.09 10.21 7.69 R30C0F0 40.87 24.63 18.86 13.21 R30C0F2 39.63 21.65 17.23 9.40 R30C5F0 38.03 19.71 13.04 8.21 R30C5F2 34.67 18.23 16.28 9.35 R30C10F0 27.30 16.33 13.04 6.21 R30C10F2 30.27 15.72 10.31 6.64 SD 4.9 3.4 2.6 2.0 COV (With Compressive Strength) - 12.9 7.2 5.2 77 Figure 4.14 Phase III - Comparative analysis of concrete compressive and bond strength with RCA, CR and PPF The normalization graph at Figure 4.15 (a,b,c) shows that bond strength behaviour with regard to various bar diameters becomes unpredictable as the normalization includes various parameters and combinations. The R2 value from the linear regression analysis with bond strength and square root of compressive strength is 0.8, 0.5 and 0,7, respectively, for 12mm, 16mm and 20 mm bar diameter samples with different combinations. It indicates that linear graphs fit optimally in the case of normalization, and the margin of error is a little higher due to the unpredictable nature of combinations because of the presence of mostly CR and PPF. 0.005.0010.0015.0020.0025.0030.0035.0040.0045.0050.00R0C0F0 R10C0F0 R10C0F2 R10C5F0 R10C5F2 R10C10F0 R10C10F2 R30C0F0 R30C0F2 R30C5F0 R30C5F2 R30C10F0 R30C10F2Bond Strength (MPa)Compressive & Bond Strength data for 12, 16 & 20 mm diameter rebarCompressive StrengthBond Strength for 12mmBond Strength for 16mmBond Strength for 20mm78 Figure 4.15 (a) Normalized relation between Compressive and Bond strength of FRRAC for 12 mm rebar at 28 days Figure 4.15 (b) Normalized relation between Compressive and Bond strength of FRRAC for 16 mm rebar at 28 days y = 5.6756x - 13.937R² = 0.805910.0012.0014.0016.0018.0020.0022.0024.0026.005.00 5.50 6.00 6.50 7.00Bond Strength, MPaCompressive Strength (Sq Root) MPa1/2y = 5.2841x - 18.521R² = 0.50358.0010.0012.0014.0016.0018.0020.005.20 5.40 5.60 5.80 6.00 6.20 6.40 6.60 6.80 7.00Bond Strength, MPaCompressive Strength (Sq Root) MPa1/279 Figure 4.15 (c) Normalized relation between Compressive and Bond strength of FRRAC for 20 mm rebar at 28 days 4.7.3.1 Comment on the overall outcome of bond strength in phase III It is seen from these series of experiments related to Figure 4.16 and Table 4.10 that initially, the increment of RCA or both RCA and CR increases the compressive strength by 20% (10% RCA) and 4% (10% RCA, 5% CR) and again by 10% (30% RCA) and 3% (30%RCA, 5% CR). Again, the compressive strength decreased between 9% and 18% when both 10% RCA and 30% RCA were used in combination with 2% fibre. Again, it showed a slight decrease of 5% & 11% bond strength when using only 5% CR with 10 or 30% RCA, respectively. The relationship between compressive and bond strength is always positive from the normalized graph, as shown in Figure 4.15 (a,b,c). y = 2.3398x - 5.8588R² = 0.71614.005.006.007.008.009.0010.0011.005.00 5.20 5.40 5.60 5.80 6.00 6.20 6.40 6.60 6.80 7.00Bond Strength, MPaCompressive Strength (Sq Root) MPa1/280 Figure 4.16 Phase III - Comparative analysis of bond strength with RCA, CR and PPF with 10 and 30 % RCA replacements In the case of bond strength, the behaviour of 10 and 30% RCA without CR or PPF was similar to control or a little higher. As fibre was added, the bond strength started decreasing. The decreasing trend of bond stress was noticed with the increase in bar diameter. While using both CR and PPF in combinations, R10C10F0 and R30C10F0 were better combinations than R10C10F2 or R30C10F2 because of the effect of PPF. As PPF was added to the matrix, it helped maintain good compressive strength but did not have a positive effect in terms of bond. CR and PPF did not interact positively since the interface between the two had a very bad interlocking and 0.005.0010.0015.0020.0025.00R0 C0 F0 R10 C0 F0 R10 C0 F2 R10 C5 F0 R10 C5 F2 R10 C10 F0 R10 C10 F2Bond Strength of Different Rebar Diameter with R1012mm 16mm 20mm0.005.0010.0015.0020.0025.0030.00R0 C0 F0 R30 C0 F0 R30 C0 F2 R30 C5 F0 R30 C5 F2 R30 C10 F0 R30 C10 F2Bond Strength of Different Rebar Diameter with R3012mm 16mm 20mm81 bond since the surface of PPF was smooth. It is ascertained that the results of both R10C5F0 and R30C5F0 were very close to control since fibre was not used. Lower diameter and higher length of steel bars always depict higher bond strength in concrete. It was observed that approximately 20-30% bond strength decreased for 12mm to 16mm and 16mm to 20mm diameter changes, confirming the earlier tests done in this experimental program on lower to higher diameter rebars. 4.8 Comparison with existing Models and Codes In this study, the experimental bond strength was compared with the existing models and code-based equations. The equations used in this study are presented in Table 4.11. The comparisons of the bond strength ratios between experimental and model prediction values are presented in Table 4.12 and Figure 4.17 for 12mm, 16mm and 20mm diameter deformed rebar. Table 4.11 Parameters and experimental bond strength for regression analysis Existing equations Bond Strength Equation CEB-FIP MC90 MacGregor Orangun et.al 82 Table 4.12 Comparison of experimental and code-based bond strength (t) of FRRAC Ser Combination texp / tcode (Standard) MacGregor (1997) Orangun, Jirsa and Breen(1975,1977) CEB-FIP MC90 Batch Name 12mm 16mm 20mm 12mm 16mm 20mm 12mm 16mm 20mm 1 R0C0F0 1.68 1.43 1.50 1.84 1.29 1.14 1.81 1.10 0.89 2 R10C0F0 1.55 1.31 1.14 1.70 1.19 0.87 1.68 1.02 0.67 3 R10C0F2 1.64 1.42 0.85 1.80 1.29 0.64 1.77 1.10 0.50 4 R10C5F0 1.48 1.62 1.23 1.62 1.47 0.93 1.60 1.26 0.72 5 R10C5F2 1.46 1.30 1.06 1.60 1.18 0.80 1.58 1.01 0.62 6 R10C10F0 1.53 1.35 1.07 1.68 1.22 0.82 1.66 1.04 0.63 7 R10C10F2 0.96 1.14 1.12 1.06 1.03 0.85 1.04 0.88 0.66 8 R30C0F0 1.78 1.90 1.75 1.95 1.72 1.33 1.93 1.48 1.03 9 R30C0F2 1.59 1.77 1.27 1.74 1.60 0.96 1.72 1.37 0.75 10 R30C5F0 1.48 1.36 1.13 1.62 1.24 0.86 1.60 1.06 0.67 11 R30C5F2 1.43 1.78 1.35 1.57 1.62 1.02 1.55 1.38 0.79 12 R30C10F0 1.44 1.61 1.01 1.59 1.46 0.76 1.56 1.25 0.59 13 R30C10F2 1.32 1.21 1.02 1.45 1.10 0.78 1.43 0.94 0.60 It can be seen from Table 4.11 and Figure 4.17 that the ratio of experimental to model varies in the range of 1.95â0.96, 1.90-0.88, and 1.75-0.5 for 12mm, 16mm, and 20mm diameter rebars, respectively. The results showed that the smaller diameter rebars yielded a higher ratio compared to that of the larger diameter rebars. It is interesting to highlight that the combination containing only 30% RCA showed the highest bond strength ratio, whereas a combination containing both 10% CR and 2% PPF showed the minimum bond strength ratio. This phenomenon can be attributed to the fact that excessive amounts of CR and PPF yielded poor bonding with rebars due to smoother surfaces. 83 Figure 4.17 A comparison of bond strength between experimental results and existing models for (a) 12mm, (b) 16mm, (c) 20mm rebar 0.001.002.003.00Bond Strength (Exp) / Bond Strength (model)MacGregor (1997) Orangun,Jirsa and Breen (1975,1977) CEB-FIP MC900.000.501.001.502.002.50Bond Strength (Exp) / Bond Strength (model)MacGregor (1997) Orangun,Jirsa and Breen (1975,1977) CEB-FIP MC900.000.200.400.600.801.001.201.401.601.802.00Bond Strength (Exp) / Bond Strength (model)MacGregor (1997) Orangun,Jirsa and Breen (1975,1977) CEB-FIP MC9084 4.9. Regression Analysis Bond strength in concrete is largely influenced by its compressive strength, length-to-diameter ratio, cover-to-diameter ratio, etc. Since this study incorporates the inclusion of RCA, CR, and PPF, they can be the factors that influence bond strength in FRRAC. Therefore, in this regression analysis, the bond strength will be the function of all these parameters as follows: t = f ( âððâ², %RCA, %CR, %PPF , c/d )â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦ (4.1) where, fâc is the concrete compressive strength c/d is cover to rebar diameter ratio db is the rebar diameter % shows the percentages of individual variables All test data for regression analysis of different experiments, including all their parameters are presented in Table 4.13. The equations derived from the regression analysis is given below: t= (1.06 ð ð¶ð´% â 4.79 ð¶ð % â 10.6ððð¹% + 1.07ð¶ðð)âððâ² â¦â¦â¦â¦â¦â¦â¦ (4.2) It can be observed that the bond strength is positively affected by the RCA and concrete strength, while the inclusion of CR and PPF negatively influences its behaviour. In addition, the c/d ratio increases the bond strength linearly. A comparison of the experimental and predicted bond strength from regression analysis is shown in Figure 4.18. It is evident from the regression analysis that there is a strong correlation between the experimental and predicted bond strength, with an excellent value of 0.90. Therefore, the proposed model can be conveniently used for deformed rebars in concrete containing RCA, CR, and PPF. 85 Table 4.13 Parameters and experimental bond strength for regression analysis Specimen ID RCA CR Fibre Rebar Dia fâc sqrt(fâc) ld/db c/db Bond Strength (MPa) R0C0F0 0 0 0 12 36.92 6.076 5 3.667 22.04 R10C0F0 0.1 0 0 12 44.40 6.663 5 3.667 22.40 R10C0F2 0.1 0 0.02 12 41.57 6.447 5 3.667 22.82 R10C5F0 0.1 0.05 0 12 38.53 6.208 5 3.667 19.81 R10C5F2 0.1 0.05 0.02 12 32.63 5.713 5 3.667 18.05 R10C10F0 0.1 0.1 0 12 32.23 5.677 5 3.667 18.85 R10C10F2 0.1 0.1 0.02 12 33.60 5.797 5 3.667 12.09 R30C0F0 0.3 0 0 12 40.87 6.393 5 3.667 24.63 R30C0F2 0.3 0 0.02 12 39.63 6.296 5 3.667 21.65 R30C5F0 0.3 0.05 0 12 38.03 6.167 5 3.667 19.71 R30C5F2 0.3 0.05 0.02 12 34.67 5.888 5 3.667 18.23 R30C10F0 0.3 0.1 0 12 27.30 5.225 5 3.667 16.33 R30C10F2 0.3 0.1 0.02 12 30.27 5.502 5 3.667 15.72 R0C0F0 0 0 0 16 36.92 6.076 5 2.625 13.41 R10C0F0 0.1 0 0 16 44.40 6.663 5 2.625 13.56 R10C0F2 0.1 0 0.02 16 41.57 6.447 5 2.625 14.21 R10C5F0 0.1 0.05 0 16 38.53 6.208 5 2.625 15.60 R10C5F2 0.1 0.05 0.02 16 32.63 5.713 5 2.625 11.52 R10C10F0 0.1 0.1 0 16 32.23 5.677 5 2.625 11.84 R10C10F2 0.1 0.1 0.02 16 33.60 5.797 5 2.625 10.21 R30C0F0 0.3 0 0 16 40.87 6.393 5 2.625 18.86 R30C0F2 0.3 0 0.02 16 39.63 6.296 5 2.625 17.23 R30C5F0 0.3 0.05 0 16 38.03 6.167 5 2.625 13.04 R30C5F2 0.3 0.05 0.02 16 34.67 5.888 5 2.625 16.28 R30C10F0 0.3 0.1 0 16 27.30 5.225 5 2.625 13.04 R30C10F2 0.3 0.1 0.02 16 30.27 5.502 5 2.625 10.31 R0C0F0 0 0 0 20 36.92 6.076 5 2.000 10.79 R10C0F0 0.1 0 0 20 44.40 6.663 5 2.000 8.98 R10C0F2 0.1 0 0.02 20 41.57 6.447 5 2.000 6.45 R10C5F0 0.1 0.05 0 20 38.53 6.208 5 2.000 8.98 R10C5F2 0.1 0.05 0.02 20 32.63 5.713 5 2.000 7.11 R10C10F0 0.1 0.1 0 20 32.23 5.677 5 2.000 7.20 R10C10F2 0.1 0.1 0.02 20 33.60 5.797 5 2.000 7.69 R30C0F0 0.3 0 0 20 40.87 6.393 5 2.000 13.21 R30C0F2 0.3 0 0.02 20 39.63 6.296 5 2.000 9.40 R30C5F0 0.3 0.05 0 20 38.03 6.167 5 2.000 8.21 R30C5F2 0.3 0.05 0.02 20 34.67 5.888 5 2.000 9.35 R30C10F0 0.3 0.1 0 20 27.30 5.225 5 2.000 6.21 R30C10F2 0.3 0.1 0.02 20 30.27 5.502 5 2.000 6.64 86 Figure 4.18 A comparison between experimental and predicted bond strength of FRRAC 4.10 Summary The combination of 5% CR and no PPF (R30C5F0) produced the highest bond strength in concrete with 30% RCA, followed by R30C0F2. The inclusion of fibres (especially at higher percentages) and larger steel bar diameters had a tendency to reduce bond strength due to poor interaction with the matrix or the smooth surface of fibres. Smaller diameter bars (10 mm) and longer embedment lengths (150 mm) enhanced bond strength, and combining these factors with 5% CR provided the best results for improved concrete-steel bonding. The experimental bond strength was compared to the existing code-based equations and well-established models. A regression-based model was developed considering all influencing parameters capable of predicting bond strength quite accurately with a coefficient of determination (R2= 0.90). R² = 0.89490.005.0010.0015.0020.0025.0030.005 10 15 20 25 30Predicted Bond Strength (MPa)Experimental Bond Strength (MPa)87 Chapter 5: Shear Behaviour of Recycled Aggregate Concrete Containing CR and PPF 5.1 General The purpose of this study is to evaluate the shear behaviour of reinforced concrete beams without transverse reinforcement that are constructed with RCA, CR, and PPF. In Chapter 3, a quasi-static flexural test (four-point bending) was used to examine the flexure, rupture, and deformation properties of RCA's mechanical behaviour. Studying the same concrete's shear behaviour became crucial as a consequence. Apart from flexural failure, short or deep beams are typically more likely to experience shear failure. Therefore, the chapter's main goal is to examine the concrete's shear behaviour. 5.2 Shear Behaviour of Rubberised Concrete Beams Containing RCA, CR and PPF This work focuses on assessing the shear behaviour of reinforced concrete beams made with RCA, CR, and PPF without transverse reinforcement while also assessing the compressive strength and workability. In the mechanical behaviour of RCA, the flexure, crack and deformation properties were investigated with a quasi-static flexural test (four-point bending) in Chapter 3. Therefore, the need to study the shear behaviour of the same concrete became essential. In most cases, short beams or deep beams fail early in shear, and some columns and beams fail to bend as well. As such, the focus of the chapter is to examine the shear behaviour of concrete. 5.3 Test Matrix and Variables Natural coarse aggregate (NCA), recycled concrete aggregate (RCA), natural fine aggregate (NFA), crumb rubber (CR), ordinary Portland cement (OPC), and polypropylene fibre (PPF) were the six types of materials used to cast the concrete mixtures. Table 5.2 displays the characteristics of NCA and RCA, which were established in accordance with ASTM C127-15 and ASTM C29-17, respectively. ASTM C131-20 was used to assess the coarse aggregate's abrasion resistance. The proportions of the concrete mix are displayed in Table 5.1. The various factors used in this investigation were used to determine the labels for the test beams. For instance, specimen R50C10F0 has no PPF content and was cast with 50% RCA and 10% CR. In a comparable way, the R30C5F1 specimen shows that the concrete mix contains 30% RCA, 5% CR, 88 and 1% PPF. In this investigation, RCA was utilised to replace up to 50% of the weight of NCA. Prior research has shown that when coarse aggregates are substituted with RCA by more than 50% by weight, the mechanical qualities of recycled aggregate concrete gradually decrease (Limbachiya et al., 2000; Alam et al., 2013; Huda & Alam, 2015; Etxeberria et al., 2007). Furthermore, CR was used in place of sand at two distinct volumetric replacement levels (5% and 10%). These values are consistent with a prior study (Islam et al., 2016) that suggested limiting the CR content to less than 10% in order to mitigate any poor results. The recommended amount of steel fibre in concrete is between 1% and 1.5%, as per Xie et al. (2018). As such, one percent of PPF was chosen as the replacement for concrete by volume in this study. Table 5.1 lists the proportions of the concrete mix. On the day of testing, standard cylinders measuring 100 mm by 200 mm at 28 days of casting were tested to measure the concrete's actual compressive strength in accordance with ASTM C192/192M. Table 5.1. Aggregate proportions in concrete mixes (Hossain et al., 2023) Serial No Specimen Code Water (kg/m3) Coarse Aggregate Fine Aggregate Binder NCA (kg/m3) RCA (kg/m3) NFA (kg/m3) CR (kg/m3) Cement (kg/m3) PPF (kg/m3) 1 Control 163.8 990.2 0 678.7 0 427.1 0 2 R0C5F0 163.8 990.2 0 662.1 16.6 427.1 0 3 R0C10F0 163.8 990.2 0 645.5 33.2 427.1 0 4 R0C5F1 163.8 990.2 0 662.1 16.6 425.8 1.3 5 R0C10F1 163.8 990.2 0 645.5 33.2 425.8 1.3 6 R30C0F0 163.8 693.1 297.1 678.7 0.0 427.1 0 7 R30C5F0 163.8 693.1 297.1 662.1 16.6 427.1 0 8 R30C10F0 163.8 693.1 297.1 645.5 33.2 427.1 0 9 R30C5F1 163.8 693.1 297.1 662.1 16.6 425.8 1.3 10 R30C10F1 163.8 693.1 297.1 645.5 33.2 425.8 1.3 11 R50C0F0 163.8 495.1 495.1 678.7 0.0 427.1 0 12 R50C5F0 163.8 495.1 495.1 662.1 16.6 427.1 0 13 R50C10F0 163.8 495.1 495.1 645.5 33.2 427.1 0 14 R50C5F1 163.8 495.1 495.1 662.1 16.6 425.8 1.3 15 R50C10F1 163.8 495.1 495.1 645.5 33.2 425.8 1.3 89 5.4 Physical Properties of the Materials The characteristics of NCA and RCA were determined according to ASTM C127-15 and ASTM C29-17, respectively, as shown in the table below. Table 5.2 Aggregates Physical characteristics (Hossain et al., 2023). Variables NCA RCA NFA CR Apparent specific gravity 2.68 2.69 2.62 1.18 Bulk specific gravity (SSD) 2.64 2.58 2.54 1.18 Bulk specific gravity (OD) 2.61 2.52 - - Absorption capacity (%) 1.02 2.49 2.00 1.20 Fineness modulus 2.57 2.48 2.68 2.78 Unit weight (kg/m3) Loose condition 1498 1495 1473 421 Compact condition 1535 1526 1561 489 % Voids Loose condition 48.2 32.1 43.6 64.2 Compact condition 44.1 29.2 40.2 58.5 According to ASTM C136-14, the grading curves of the NFA, NCA, and RCA were established using sieve analysis; these curves are shown in Figure 5.1 and fall comfortably within the ASTM range. Furthermore, as shown in Figure 5.1 (b), NCA and RCA were also graded and compared with ASTM limitations. As shown in Table 5.2, the physical characteristics of the NFA were experimentally determined in accordance with ASTM C128-15 and ASTM C29-17 specifications. After being gathered from an old building that had been demolished, RCA was carefully crinkled, filtered, sieved, and cleaned to produce high-quality material with a maximum size of 19 mm. Table 5.2 also lists the physiochemical characteristics of the CR. A local business or dealer provided the CR utilised in this experiment. It is important to note that the collected CR was further shredded in order to satisfy the maximum and lower gradation limits specified by the ASTM. The physical and chemical characteristics of the cement utilised in this investigation are given in Table 5.3. Table 5.4 lists the characteristics of the PPF. The concrete beams in this study were longitudinally and transversely reinforced with 72-grade mild steel rebars. The characteristics of the steel reinforcement are listed in Table 5.5. 90 Figure 5.1 Gradation curve of (a) crumb rubber (CR) and natural fine aggregate (NFA); (b) recycled concrete aggregate (RCA) and natural coarse aggregate (NCA) Table 5.3 Chemical and physical properties of OPC (Hossain et al., 2023) Chemical composition (%) Setting Time (min) Normal Consistency (%) Initial Final SiO2 Al2O3 Fe2O3 CaO MgO SO3 122 174 27.20 22.13 5.32 3.34 63.73 1.80 2.42 Table 5.4 PPF specifications Variables Polypropylene fibre Fibre diameter (µm) 18 Fibre length (mm) 12 Specific gravity (g/cm3) 0.91 Tensile strength (MPa) 400 Elongation at failure (%) 26.8 Elastic modulus (GPa) 4.01 Melting point (oC) 170 Table 5.5 Mechanical properties of reinforcing steel. Serial No. Diameter (mm) Yield strength (MPa) Ultimate strength (MPa) Elongation (%) 1 8 641 775 19 2 10 519 715 24 3 16 496 694 29 91 5.5 Test Specimens In accordance with ACI 318-19, fifteen simply supported reinforced concrete (RC) beams were designed, built, and tested with a target 28-day compressive strength of 30 MPa. With an overall length of 1500 mm and an effective span of 1140 mm, the beams had a 200 x 300 mm rectangular section. Figure 6.2 displays a schematic depiction of the beam, test setup, and equipment. To preserve a 25mm transparent concrete cover, the reinforcing cage was supported by plastic chairs. To support the stirrups, the beams were strengthened with two 10-M longitudinal bars at the top and two 16-M longitudinal bars on the tension side. To guarantee that the beam would fail in shear, the amount and spacing of transverse reinforcement were planned. Consequently, only the loading span and the support zones were equipped with 2-branch, 8-M stirrups spaced 50 mm apart. In this experiment, the shear span to depth ratio ranged from 1 to 2.5, allowing the beam to function as a short shear span and fail in diagonal shear mode. (ACI 318-08 and MacGregor and Bartlett's Reinforced Concrete Mechanics and Design, 2000). Figure 5.3 depicts the preparation of the test specimen. Figure 5.2 Diagram of four-point shear test, (b) cross-section of beams (Hossain et al., 2023) 5.6 Sample Preparation All beams were cast and cured in accordance with ASTM C31-19 specifications. To ensure that CR and PPF were evenly distributed throughout the concrete, a particular mixing method was LVDT LVDT LVDT LVDT 92 used conforming ASTM. To attain the required workability, concrete's coarse and fine aggregates were in a saturated surface dry (SSD) state. To reduce any source of variability that might result from various additives influencing the workability of new concrete and the mechanical qualities of hardened concrete, superplasticizers and extra water were not used. The mixer was filled with NCA and RCA first, then CR and sand, then cement and PPF, and lastly, the mixing water. The slump of fresh concrete was measured using ASTM C143-15. In the lab, wet burlap and plastic sheets were used to cover the beam samples in order to cure them. In accordance with ASTM C39-18, standard cylinders measuring 100mm Ã 200mm were tested on the day of testing to determine the concrete's true compressive strength. In accordance with ASTM C642-13, the unit weight of specimens of hardened concrete was measured. 5.7 Testing Procedure All beams were tested under a four-point static load configuration until failure following a 28-day curing period. Figure 5.2 shows the test setup in general, as well as the instruments, data gathering system, and specimen preparation. The load was applied using a 1000 kN Universal Testing Machine (UTM) at a displacement-controlled rate of 0.5 mm/min. Three concrete strain gauges were affixed to the concrete surface of each specimen: two at the bottom of the mid-shear span and one at the top of the mid-span. Furthermore, the UTM was installed with four linear variable displacement transducers (LVDTs) to examine the deflection behaviour along the beam: two at the center of the shear span, one in the mid-span, and one at the support. To capture the values during the test, primarily load-displacement response, strain response, deflection, and fractured surface, all of the equipment were connected to a computerized data acquisition system (DAQ) and three high-definition cameras. The cracks were identified during the test, and the associated loads were noted. The shear zones were spackled by spraying black paint dots on a white base because they were regarded as an area of interest (ROI). To record the ROI for digital image correlation (DIC) analysis, two cameras were positioned parallel to the beam's side plane. In order to comprehend the field of strains and displacements of the concrete surface in the shear zones of each beam specimen, discussed in more detail in the next sections, the recorded video of ROI was analysed using commercial software, Ncorr (Blaber et al., 2015). 93 Figure 5.3 Different stages of the experiment 94 5.8 Experimental Data Table 5.6 contains the first diagonal crack load, failure load, deflection at failure, and ultimate shear load derived from the flexural test of the beams. Table 5.6 Test Result Summary Specimen name 1st Diagonal cracking load (kN) Failure load (kN) Deflection (mm) at failure Ultimate shear load, Vu (kN) Post-diagonal cracking resistance % Failure mode R0C0F0 101.4 195.3 3.0 97.6 48.1 Shear R0C5F0 104.2 169.9 3.3 85.0 38.7 Shear R0C10F0 110.8 158.8 1.7 79.4 30.2 Shear R0C5F1 100.7 173.4 3.7 86.7 41.9 Flexure-shear R0C10F1 122.8 210.2 3.9 105 41.6 Flexure-shear R30C0F0 105.6 193.5 2.7 96.7 45.4 Shear R30C5F0 95.30 159.4 2.8 79.7 40.3 Shear R30C10F0 75.65 119.1 1.5 59.6 36.5 Shear R30C5F1 110.1 201.1 4.9 100.5 45.2 Flexure-shear R30C10F1 70.10 132.7 2.4 66.4 47.2 Shear R50C0F0 95.20 170.5 3.7 85.3 44.2 Shear R50C5F0 99.20 157.2 1.8 78.6 36.9 Shear R50C10F0 103.2 151.5 1.8 75.8 31.9 Shear R50C5F1 90.30 143.7 2.2 71.8 37.2 Shear R50C10F1 80.70 130.8 3.1 65.4 38.3 Shear The table shows that ultimate shear resistance and deformability both dropped when RCA was used in place of NCA. At RCA replacement of 30% and 50%, the shear capacity was reduced by 1% and 13%, respectively, with respect to the control specimen (R0C0F0). However, when the RCA quantity was raised to 30% with 10% CR, the decrease became more noticeable. The shear 95 capacity of R30C5F0 and R30C10F0 had decreased by 17% and 38%, respectively, in comparison to R30C0F0, whereas the shear capacity of R50C5F0 and R50C10F0 had decreased by 8% and 11%, respectively, in comparison to R50C0F0. However, in the case of deformability, the introduction of CR decreased the shear capacity without showing any noticeable trend. In the absence of RCA or PPF, the shear capacity decreased by 13% and 18%, respectively, for adding CR by 5% and 10%. Adding PPF to the mixture had a different kind of effect. In spite of the existence of CR or RCA, PPF's bridging impact enhanced the beam's ultimate shear and deformation capacities. Only when the RCA quantity was maintained between 0 and 30% with the addition of PPF, shear strength increase significantly. Shear strength increased by 2%, 32%, 26%, and 11% for R0C5F1, R0C10F1, R30C5F1, and R30C10F1 for 1% fibre usage, respectively, in comparison to samples with no fibre but similar amounts of RCA and CR. Because CR creates a poorer interface between cement paste and RCA, the introduction of both RCA and CR had a negative impact on the post-diagonal crack resistance. As a result, the formation of cracks was facilitated through this preferential location. Following the inclusion of 5% and 10% CR, respectively, crack resistance was reduced by 15% and 28%. However, even in the presence of CR, adding 1% fibres to the concrete mix increased the post-diagonal crack resistance by an average of 7% and 29% since fibres efficiently transfer stress across cracks. 5.9 Result Analysis 5.9.1 Fresh Characteristics The fresh properties of concrete are its rheological parameters like flowability, workability, and ease of casting. The slump test, the most widely used fresh concrete workability test, is represented in Table 5.7. Overall, the fresh concrete slump was negatively impacted by the inclusion of RCA. The control mixture (R0C0F0) had a slump of 82 mm, for instance. However, the addition of RCA at replacement levels of 30% and 50% (R30C0F0 and R50C0F0) reduced the slump by 29% and 63%, respectively. This is because RCA has a greater capacity to absorb water than NCA and because attached mortar caused surface roughness and increased angularity, which raised inter-particle friction (Butler et al., 2011). No water reducing admixture was applied to compensate for this. The addition of CR to the cementitious matrix seems to have the same impact on reducing slump. The addition of CR to R0C5F0 and R0C10F0 resulted in a decrease in slump to 60mm and 41mm, respectively, in comparison to the control mixture (R0C0F0), which had a 96 slump of 82mm. The addition of fibre to these mixes likewise had the same detrimental effect on the concrete slump. The specimen with the lowest slump, 10 mm, was found with all of the ingredients (R50C10F1). The workability of any concrete will be significantly reduced because more water will be absorbed or consumed due to the porous nature of CR and the hydrophilic behaviour of PPF once they are used. CR and PPF also introduce more inter-particle friction and interlocking action. For concrete with CR and RCA, comparable experimental results have been previously published (Hossain et al., 2019; Shahjalal et al., 2021). 5.9.2 Compressive Strength The average compressive strength for each mixture derived from cylinders tested on the day the beams were tested and displayed in Table 5.7. Regardless of the replacement level or the presence of RCA in the matrix, the table indicates a decreasing trend when the NFA was replaced with CR particles. For instance, compared to the control specimens (R0C0F0), the cementitious matrix's compressive strength dropped by 10% and 15%, respectively, when 5% (R0C5F0) and 10% (R0C10F0) CR were added. This decrease can be attributed to CR's inherent physical characteristics. In other words, CR is a porous substance that has a lower specific gravity and a greater absorption capacity than NFA (see Table 5.2). As a result, the cementitious matrix and the CR particles had a poor link, resulting in a weak/porous ITZ that reduced the matrix's strength (Ganjian et al., 2009; Gupta et al., 2014). Nevertheless, the findings demonstrated that, with the exception of the maximum replacement level of 50%, the gradual addition of RCA was associated with a modest increase in compressive strength. The prior trend should be evident when comparing the compressive strengths of specimens R0C0F0, R30C0F0, R50C0F0; R0C5F0, R30C5F0, R50C5F0 and R0C10F0, R30C10F0, R50C10F0. Smith (2009) and Shahria et al. (2013) had reported identical findings. When RCA is added, the cement content increases and the ITZ becomes weaker. When RCA is employed up to 30%, it appears that the extra cementitious material takes precedence over the weaker ITZ. The weaker ITZ takes over and reduces the concrete's mechanical strength beyond this replacement level. Regardless of the dose of CR, the addition of fibre to the concrete mix enhanced compressive strength when the replacement level of RCA was maintained between 0 and 30%. For example, comparing the results of the mixtures (R0C5F0 vs R0C5F1), (R0C10F0 vs R0C10F1), (R30C5F0 vs R30C5F1), and (R30C10F0 vs R30C10F1), the compressive strength showed an 97 increase with 0.7%, 58%, 19% and 3%, respectively. The capacity of the fibres to fill in cracks has been credited with increasing the compressive strength. The mixture R0C10F1 has the highest compressive strength. Though the mix contains fibres that can bridge cracks and increase strength, it seems unusually high since it contains CR. This high compressive strength may be attributed to the unwanted error caused by additional compaction during casting, considering its lower slump. For the same reason, its compressive strength was higher, with wide variability (SD = 2.48). However, this trend was invalid when the NCA was replaced by 50% RCA, where the addition of fibre had very little effect on the compressive strength of concrete. The former neutral effect from the PPF on the compressive strength might be ascribed to the poor bonding between the fibre and the mortar surrounding the RCA due to the presence of existing air voids between the RCA and fibre (Grzesiak et al., 2021). Table 5.7 Value of and compressive strength of concrete (Hossain et al., 2023) Serial Specimen name Slump (mm) Compressive strength (MPa) Mean (SD)* 1 R0C0F0 82 31.3 1.08 2 R0C5F0 60 28.1 1.28 3 R0C10F0 41 26.6 2.23 4 R0C5F1 58 28.3 1.59 5 R0C10F1 37 41.9 2.48 6 R30C0F0 58 33.4 1.45 7 R30C5F0 45 32.1 2.37 8 R30C10F0 30 29.0 1.42 9 R30C5F1 40 38.2 1.52 10 R30C10F1 20 29.9 0.61 11 R50C0F0 30 35.0 2.55 12 R50C5F0 22 34.4 0.59 13 R50C10F0 18 32.4 0.74 14 R50C5F1 19 29.1 1.37 15 R50C10F1 10 28.6 1.58 *SD = Standard Deviation 98 5.9.3 Load-deflection Response The load-deflection relationship of the tested beams at mid-span is shown in Figure 5.4. Up to the ultimate load, the load-deflection response of every beam was nearly bilinear. This behaviour was characterized by a steep slope that first ascended until the first flexural crack formed. As the cracking took place, due to the reduction in the stiffness, moderate slopes were observed with different tendencies, which were attributed to the different constituents used to cast each beam. The effect of using different concretes on ultimate shear capacity can be seen in Figure 5.4 and Table 5.8. As seen in Figure 5.4 (a), substituting RCA for NCA resulted in a drop in ultimate shear resistance and a decrease in deformability at the same load level as the control beam. The shear capacity of both beams (R30C0F0 and R50C0F0) was reduced by 1% and 13%, respectively, in comparison to the control beam that was completely cast with NCA (R0C0F0), even though the compressive strength was found to increase when RCA was added at 30% and 50% replacement levels (see Table 5.7). This might be explained by the shear resistance mechanism, which was more effective for the NCA-cast beams than the RCA included ones. It was mostly caused by the aggregate interlock. It's also noteworthy that the beams with RCA had a much higher initial stiffness and that the stiffness decreased more sharply after the initial crack. This occurred as a result of RCA and other materials interacting more strongly when mortar was used. However, following the initial crack, the cracks spread farther along the RCA's attached mortar, which eventually led to noticeably less stiffness. As shown in Figure 5.4 (b), the addition of CR to concrete beams consistently resulted in a decrease in the ultimate shear capacity without exhibiting a consistent pattern or trend in the beam deformability. In comparison to R0C0F0, the shear capacity of the R0C5F0 and R0C10F0 specimens decreased by 13% and 18%, respectively, when CR was added at 5% and 10%. Overall capacity was decreased due to rubber particles' lower modulus of elasticity and stiffness as compared to NFA (Tamanna et al., 2020). In contrast to the control and R0C5F0, Figure 5.4 indicated that R0C10F0 has a larger starting stiffness but had a comparatively smaller ultimate shear resistance. Although CR influences inelastic deformation and ultimate shear resistance, it is not anticipated to have a significant impact on initial stiffness. Because of its low slump, R0C10F0 concrete may have higher compaction during casting, leading to fewer voids. In addition, this concrete's SD for compressive strength was greater. In comparison to the other specimens, all of these might have contributed to the initial stiffness being higher. Using 30% and 50% RCA replacement levels in 99 addition to the CR particles produced a similar result, as shown in Figure 5.4 (c) and Figure 5.4 (d), respectively. As anticipated, when the RCA content increased to 30% or 50% replacement levels, the shear capacity decrease became more noticeable for the reasons mentioned above. For example, adding 5% and 10% CR in the beams R30C5F0 and R30C10F0 decreased the shear strength by 17% and 38%, respectively, with respect to the control specimen cast without CR. Moreover, using 50% RCA along with the CR particles, an 8% and 11% drop in shear strength was observed for R50C5F0 and R50C10F0 specimens, respectively, as compared to R50C0F0. When CR is present with 50% RCA, the deformability of the beams is significantly reduced, as observed in Figure 5.3 (d). The observation of concrete beams can be explained by the fact that the shear capacity was weakened because the frictional force and aggregate interlocking were significantly lower in CR than in NFA because CR is softer, not stiffer. Furthermore, fracture propagation was made worse by the poor link between the cementitious matrix and the CR, which limited or prevented the beams from withstanding increased shear stresses. Conversely, even with the presence of CR particles, the addition of PPF to the concrete mix had a more significant impact on enhancing the beams' ultimate shear and deformation capacities due to the fibres' capacity to bridge concrete fractures. Table 5.8, Figure 5.4 (e), and Figure 5.4 (f) demonstrate that PPF-containing beams (R0C5F1, R0C10F1, R30C5F1, R30C10F1, R50C5F1, and R50C10F1) exhibited significantly more deformation than fibre-free beams (R0C5F0, R0C10F0, R30C5F0, R30C10F0, R50C5F0, and R50C10F0). It is important to note that when the replacement level of RCA was maintained between 0 and 30%, the use of PPF in concrete increased the shear strength. When compared to R0C5F0, R0C10F0, R30C5F0, and R30C10F0 beams, the shear strength of R0C5F1, R0C10F1, R30C5F1, and R30C10F1 beams increased by 2%, 32%, 26%, and 11%, respectively. The fracture pattern and DIC data covered later in the text provided evidence that PPF regulated the development of diagonal cracks, which explains the increase in ultimate shear strength. The fibres' effectiveness and crack-bridging properties, which enhance ductility and ultimate shear resistance, have been established by this observation. Nevertheless, it is also clear that the fibres' presence does not increase the beams' initial stiffness. This can be explained by the fact that fibre has a far lower stiffness than concrete aggregate and becomes very important once cracks start to develop. The shear strength of concrete beams was negatively impacted by the use of PPF in conjunction with a high replacement level of RCA (50%). For instance, the R50C5F1 and R50C10F1 specimens showed shear strength reductions of about 100 9% and 13%, respectively, when compared to the R50C5F0 and R50C10F0 beams. Such behaviour may be attributed to bigger air spaces between the RCA and fibre in a higher percentage of RCA (Grzesiak et al., 2021). Because of the weaker ITZ between RCA and mortar caused by this concrete mix, premature failure happens at a comparatively lower load. In general, it can be stated that the addition of CR and/or RCA to the beam specimens lowers their ultimate strength and deformability. This is easily overcome by adding PPF, making the trio-recycled materials a feasible and sustainable choice for a variety of structural applications. 101 Figure 5.4 Graph for load versus mid-span deflection of the tested beams (a) different RCA replacement levels, (b) different CR replacement levels, (c) different CR replacement with 30% RCA, (d) different CR replacement with 50% RCA, (e) influence of PPF (f) influence of PPF with replacement 30% RCA, and (g) influence of PPF with replacement 50% RCA (Hossain et al., 2023) 102 Table 5.8 Test results showing crack numbers and pattern (Hossain et al., 2023) Specimen name 1st Diagonal cracking load (kN) Failure load (kN) Deflection (mm) at failure Ultimate shear load, Vu (kN) Post-diagonal cracking resistance % Failure mode At failure No. of cracks Max. crack width (mm) Failure angle (deg.) R0C0F0 101.4 195.3 3.0 97.6 48.1 Shear 7 2.9 41 R0C5F0 104.2 169.9 3.3 85.0 38.7 Shear 6 3.4 42 R0C10F0 110.8 158.8 1.7 79.4 30.2 Shear 8 4.2 30 R0C5F1 100.7 173.4 3.7 86.7 41.9 Flexure-shear 12 2.2 53 R0C10F1 122.8 210.2 3.9 105 41.6 Flexure-shear 13 2.6 33 R30C0F0 105.6 193.5 2.7 96.7 45.4 Shear 7 2.5 38 R30C5F0 95.30 159.4 2.8 79.7 40.3 Shear 5 2.7 30 R30C10F0 75.65 119.1 1.5 59.6 36.5 Shear 7 2.9 34 R30C5F1 110.1 201.1 4.9 100.5 45.2 Flexure-shear 7 4.5 50 R30C10F1 70.10 132.7 2.4 66.4 47.2 Shear 9 2.9 46 R50C0F0 95.20 170.5 3.7 85.3 44.2 Shear 6 3.0 35 R50C5F0 99.20 157.2 1.8 78.6 36.9 Shear 5 3.2 48 R50C10F0 103.2 151.5 1.8 75.8 31.9 Shear 8 2.1 33 R50C5F1 90.30 143.7 2.2 71.8 37.2 Shear 10 1.8 44 R50C10F1 80.70 130.8 3.1 65.4 38.3 Shear 5 1.5 40 5.9.4 Post-diagonal Cracking Resistance The maximum resistance that the beam can sustain following the creation of the initial diagonal crack is represented by the post-diagonal cracking resistance (Ismail & Hassan, 2017). Table 5.8 also presents the values of the post-diagonal cracking resistance for all tested beams, which were computed using a simple formula as (ððð¥ððð¢ð ððððð¢ðð ððððâ1ð ð¡ ðððððððð ðððððððð ððððððð¥ððð¢ð ððððð¢ðð ðððð). Table 5.8 illustrates the impact of RCA, CR, and PPF. First, increasing the amount of RCA added to the cementitious matrix decreased the post-diagonal cracking resistance. This behaviour supports the authors' theory that the post-diagonal cracking resistance decreased as a result of preferential locations for crack propagation during loading, which is caused by the weak bond between the aggregate particles and surrounding paste, which ultimately resulted in lower tensile strength. Additionally, when the CR particles were added, the same decline in post-diagonal cracking resistance was observed. The average post-diagonal cracking resistance for non-fibrous 103 beams decreased by 16% and 28%, respectively, with the addition of 5% and 10% CR. Because of the weaker interface between CR and hydrated cement paste, the addition of more CR particles to the cementitious particles implicitly facilitated the crack growth at higher rates after the formation of the first large crack (Ganjian et al., 2009; Gupta et al., 2014). However, as PPF was essential in preventing fractures from spreading and acting as a bridge to transfer stress between crack faces, the latter behaviour improved when it was added to the concrete. When comparing the post-diagonal cracking resistance results for two sets of specimens (R0C5F0, R30C5F0, and R50C5F0 vs. R0C5F1, R30C5F1, and R50C5F1) and (R0C10F0, R30C10F0, and R50C10F0 vs. R0C10F1, R30C10F1, and R50C10F1), for example, adding 1% of PPF to the concrete with 5% and 10% CR caused an average increase of 7% and 29%. Even if CR was used to replace fine aggregate, this still shows the significance of fibres. 5.9.5 Failure Mode and Crack Pattern The concrete surface's crack pattern was carefully marked and observed in Figure 5.5 and 5.6. The modes of failure and crack patterns for every beam at failure are displayed in Figures 5.6 and 5.7, respectively. Shear was the primary cause of failure for all PPF-free beams (R0C0F0, R0C5F0, R0C10F0, R30C0F0, R30C5F0, R30C10F0, R50C0F0, R50C5F0, and R50C10F0). As expected, the former mode of failure occurred after one of the large diagonal cracks spread within the shear zone due to the absence of shear reinforcement. The first fine flexural fractures occurred at the soffit of the beams in the mid-span between the two loading points, and the internal forces followed the elastic distribution in the very early phases of loading, which were between 70.10 kN and 122.8 kN. Shear cracks began to form in the beam's shear zone and spread diagonally towards the center zones as a result of shear in these regions when the load increased further. At this point, existing cracks deepened and widened before failing in shear. It is important to note that when the full shear capacity was reached, all non-fibre beams underwent brittle failure, which was abrupt and accompanied by abrupt sound. In contrast, greater diagonal crack patterns were observed in the shear zone of PPF beams (R0C5F1, R0C10F1, R30C5F1, and R30C10F1), where flexural-shear cracking caused all fibre-supported beams to fail. Following the flexural crack's development, the concrete's shear stress increased, which prompted the start of flexural-shear cracks, in which the major tensile stresses caused by the combined shear and flexural stresses were greater than the concrete's tensile strength. The load-deflection response from Figure 5.4 (e-g) 104 confirms this behaviour/failure because the PPF greatly enhanced the beams' ductility (post-peak response) and load-carrying capacity. The PPF reduced the width of cracks and increased the number of cracks at higher load levels (See Table 5.8), which distributed the tensile stresses along the shear zone. Additionally, Table 5.8 provides a summary of the principal shear cracks' width, number, and angle. As the CR percentage increased, so did the cracks' width and quantity. For instance, in specimens, R0C0F0, R0C5F0, R0C10F0; R30C0F0, R30C5F0, R30C10F0; R50C0F0, R50C5F0, and R50C10F0, increasing the CR particles from 0 to 5% and then to 10% resulted in an increase in crack width of 0.2-1.3 mm. The weaker interfacial bond between CR and the cementitious matrix than NFA may be the cause of the increase in crack width and number of cracks. This, in turn, reduced the beams' ability to support loads and widened the cracks. Furthermore, the CR particles' low modulus of elasticity and high Poisson's ratio caused differential movement at the CR-paste interface. As a result, the number of cracks that propagated along the shear zone of the beams increased. 105 Figure 5.5 Observed patterns and failure modes of the tested beams (Hossain et al., 2023) 106 Figure 5.6 Graphic crack patterns of the tested beams (Hossain et al., 2023) 107 5.9.6 Digital Image Correlation (DIC) The initiation and gradual propagation of cracks at various load levels taken from DIC are shown in Figure 5.7. As the specimens R0C10F1 and R30C5F1 showed improved performance compared to the control specimen (R0C0F0), due to the space limitations, the DIC results for these three specimens were presented in Figure 5.7. In order to describe the longitudinal strain fields along the broken surface of the beam, seven pictures were taken at various loading levels. For all beams, the initial loading level was set at 140 kN, which corresponded to the control beam's first crack appearance. Until the failure load had been reached for every beam, additional pictures were observed at 10-kN intervals. The control beam (R0C0F0) began to exhibit mild strain localization (the cyan color at the bottom) at a load level of 140 kN. The beams R30C5F1 displayed significant diagonal cracks (colored yellow and red) in contrast to specimen R0C10F1, which was undamaged and showed no strain fields (mainly dark blue). 108 Figure 5.7 Computed longitudinal strains obtained from the surface of the beam using DIC (Hossain et al., 2023) 109 At stress values of 160 kN and 170 kN, respectively, the specimens R0C0F0 and R0C10F1 began to exhibit the significant diagonal crack. The crack continued to spread for all beams after the major diagonal crack formed and as the load increased. As can be seen, the specimens R0C10F1 and R0C0F0 had cracks with angles of inclination of 33o and 41o, respectively, whilst the beam R30C5F1 had a steeper crack with an average crack inclination of 50o. The importance of the RCA, CR, and PPF in maintaining the integrity of the beam was highlighted by steep cracking angles, which are often a sign of flexural damage (Zaborac et al., 2019). This resulted in more flexural failure rather than pure shear failure. However, even though there was 10% CR in the matrix, the greater performance of the beam R0C10F1 may be attributed to the lack of the RCA and the use of PPF, which improved the crack propagation resistance. In comparison to the control beam R0C0F0, the presence of PPF also enhanced the load-carrying capacity and crack growth resistance of both beams R0C10F1 and R30C5F1, as per the fibre bridging mechanism phenomena. 5.9.7 Beam Deformation and Load-strain Relation The deflection for each of the fifteen beams during the test at various load levels is displayed in Figure 5.8. A large diagonal crack formed, resulting in higher deflection values close to the maximum load. In beams cast without RCA, increasing the CR percentage was associated with a decrease in the beam's deformation capacity, but the addition of PPF had the opposite impact (Figure 5.8 (a-e)). This is explained by the fact that the introduction of CR particles increases deformability by decreasing beam stiffness. However, for the beams cast without fibres and with higher CR replacement levels, the shear cracks started very early, and as a result, the failure occurred when the ultimate stress and deflection were small. On the other hand, as shown in Figure 5.8 (d) and Figure 5.8 (e), the addition of PPF improved the tensile strength because of the bridging mechanism, which in turn increased the ultimate load and, as a result, improved the specimen's deformability with fibre. As shown in Figure 5.8 (f-o), a comparable pattern was also observed for beams cast with RCA. It is worth mentioning that the beam deformation/deflection increased as the RCA replacement level increased, except for 50% RCA replacement, where the beams showed lower deformability and brittle response. 110 Figure 5.8 Deflected concrete beams at various load stages (Hossain et al., 2023)111 The load versus measured strains in concrete for the tested beams are shown in Figure 5.9. For the strains measured at the top surface of the compression zone at mid-span and the bottom face of the shear zones, tensile and compressive strains were indicated. Figure 5.9 (a-e) demonstrated that the control specimen had greater compression and tensile strains than the beams with 5% or 10% CR particles. It is evident that the fibre-containing beams exhibited greater strain levels than their fibre-free counterparts (for both tensile and compression faces). The load-strain responses for the beams with 30% RCA are displayed in Figure 5.9 (f-j). With the exception of the combination containing 10% CR without fibre (R30C10F0), it was clear from the results that the load strain behaviour was similar to and near the control specimen for both tension and compression. Even when 5% CR was present (R30C5F0), the ultimate strain was relatively low. PPF has a major impact on the load-strain responses shown in Figure 5.9 (d and e). For the fibre-containing, well-performing beams, there was no abrupt decline. Additionally, 30% RCA by itself was able to provide outstanding bonding with other components. R30C10F0, on the other hand, exhibited poor strain responses, with strain gauge breaks occurring before the inelastic stage is reached. Figure 5.9 (k-o) shows the load strain responses of the beam specimens with 50% RCA. In specimens with 50% RCA, increasing the CR particles had the negative consequence of making the beams more brittle prior to failure, and sudden cracks damaged the strain gauges as depicted in Figure 5.9(m). However, the addition of fibres showed a slight enhancement in the ductile response, and the overall beam capacity was reduced significantly. This behaviour can be attributed to the fact that in the case of 50% RCA, excess fine contents arising from RCA in the combined NFA, CR, and fibres resulted in an imbalance in the mix. Consequently, at a comparatively lower ultimate load and deformation, the cracks spread through the weaker ITZ. Despite the fibres' ability to withstand brittle failure, cracks in those beams showed somewhat earlier. Additionally, the beams with 50% RCA exhibited a lower shear resistance and a low improvement in deformability in the load-deformation response. 112 Figure 5.9 Load-strain response of the concrete beam (Hossain et al., 2023) 113 5.9.8 Shear Capacity Comparison with Codes The purpose of this study was to determine whether the shear strength equations used by the Canadian Standards Association (CSA) in 2014, the ACI Committee in 2019, the European Committee for Standardization (ECS) in 2004, the CSA in 2014, and CEB-FIP (2010) could be used to predict the ultimate shear capacity of polypropylene fibre-reinforced rubberised concrete. The shear strength was calculated for each code using the following equations. â¢ CSA A23.3-14 ' (1)c c w vV f b dï¬ï¢= Where, Vc is the shear capacity (kN), λ is the strength reduction factor to account for low density concrete. For normal density concrete, its value is 1. fâc is the concrete compressive strength (MPa), β is the factor for accounting for the shear resistance of cracked concrete, for maximum sized coarse aggregate less than 20 mm and no transverse reinforcement is provided, β is taken as 2301000 zesï¢ =+, where350.8515ze z zgs s sa= ï³+, sz is the crack spacing parameter and conservatively taken as equal to dv, ag is the maximum nominal aggregate size, dv is the effective shear depth and can be calculated by dv= max[0.9d,0.72h], bw is the beam width (mm), d is the distance from the extreme compression fibre and h is the overall depth of the beam (mm). â¢ ACI 318M-19 - 22.5.5.1 (c) 1' '30.66 ( ) 0.42 (2)6uc s w c w c wgNV f b d f b dAï¬ ï¬ ï² ï¬ï© ï¹= + ï£ïª ïºïª ïºï« ï» Where λs is the size effect modification factor, shall be determined by Î»s=â(2/(1+0.004d) â¤ 1, λ=1 for normal weight concrete, Ïw is the longitudinal reinforcement ratio, shall be determined by Ïw=As/bwd, fâc is the concrete compressive strength (MPa), bw is the width of the beam (mm), d is the effective depth of the beam (mm). 114 â¢ Eurocode 2, ( )1' 32000.18 1 100 (3)c c wV f b ddï²ï¦ ï¶= +ï§ ï·ï§ ï·ï¨ ï¸ Where fâc is the concrete compressive strength (MPa), bw is the width of the bam (mm), d is the effective depth of the beam (mm), Ï is the longitudinal reinforcement ratio of the beam and shall be calculated by swAb dï² = , As is the area of tensile reinforcement (mm2). â¢ CEB-FIP, ( )113' 3200 30.15 1 100 (4)c c wdV f b dd aï²ï¦ ï¶ï¦ ï¶= +ï§ ï·ï§ ï·ï§ ï·ï¨ ï¸ï¨ ï¸ Where d is the effective depth of the beam (mm), É is the length of the shear span of the beam (mm), fâc is compressive strength (MPa), bw is the width of the bam (mm), Ï is the longitudinal reinforcement ratio of the beam and shall be calculated by swAb dï² = , As is the area of tensile reinforcement (mm2). Table 5.9 and Figure 5.10 show comparisons between the experimental shear capacity (Vtest) and the code estimated shear capacity (Vcode) of the tested beams. It is worth mentioning that if the ratio between Vtest and Vcode (Vtest/Vcode) was greater than 1.0, this indicates a conservative shear capacity prediction by such design code, whereas a value less than 1 indicates unsafe shear capacity predictions. The ratio of experimental-to-predicted, (Vtest /Vcode) calculated for all codes was in the range of 1.12 to 1.85. All codes have significantly underestimated the shear capacity with a mean value of Vtest /Vcode ratio of 1.58, 1.52, 1.56, and 1.57 for the CSA A23.3, ACI 318M, Eurocode 2, and CEB-FIP, respectively. The higher values of Vtest /Vcode (above 1.70) were observed for the beams R0C0F0, R0C10F1, R30C0F0, and R30C5F1. Relatively, lower values of the ratio were found for the beams containing CR and 50% RCA without PPF. Though the compressive strength was comparatively higher for R50 mixes, the ultimate shear resistance was smaller due to excessive fine content and premature crack propagation through weaker ITZ. As a result, the concrete compressive strength-based equations (by different codes) predicted relatively 115 high ultimate shear resistance that yields smaller values of Vtest / Vcode for 50% RCA. It can be noticed that CSA A23.3-14, ACI 318M-19, Eurocode 2, and CEB-FIP code showed conservative estimations of the shear capacity of rubberised RCA beams with fibre, similar to the prediction obtained from the control beam. In addition, no estimated values were found to be below 1, which means that all the above-mentioned codes can safely predict the shear capacity of beams made with RCA, CR, and PPF. However, provisions of shear capacity available in such current codes need to be revised to predict better the capacity of beams containing recycled materials. Table 5.9 Vtest/Vcode for rubberised concrete made with RCA and PPF (Hossain et al., 2023) Specimen name Vtest/Vcode CSA A23.3-14 ACI 318M-19 EC-02 CEB-FIP R0C0F0 1.84 2.22 1.83 1.83 R0C5F0 1.75 2.07 1.68 1.70 R0C10F0 1.64 1.96 1.58 1.58 R0C5F1 1.73 2.08 1.68 1.69 R0C10F1 1.76 2.09 1.81 1.83 R30C0F0 1.80 2.15 1.79 1.81 R30C5F0 1.47 1.78 1.47 1.47 R30C10F0 1.16 1.40 1.14 1.15 R30C5F1 1.72 2.07 1.76 1.76 R30C10F1 1.32 1.57 1.28 1.30 R50C0F0 1.53 1.84 1.54 1.55 R50C5F0 1.42 1.71 1.43 1.44 R50C10F0 1.44 1.72 1.42 1.44 R50C5F1 1.43 1.71 1.39 1.40 Average 1.32 1.57 1.28 1.29 (CoV) 1.57 1.88 1.56 1.57 116 Figure 5.10 The ratio between the experimental and the theoretical values of ultimate shear capacity utilizing existing design codes (Hossain et al., 2023) 5.10 Summary This study investigated the impact of recycled concrete aggregates (RCA), crumb rubber (CR), and polypropylene fibre (PPF) on the shear and deformability behaviour of concrete beams. The key findings were: 1. Replacing natural coarse aggregates with RCA decreased both shear strength and deformability. For instance, a 30% RCA replacement reduced shear by 1%, while 50% RCA resulted in a 13% reduction. When combined with CR, shear strength dropped even more. 2. Adding CR also reduced shear strength and deformability. CRâs lower modulus of elasticity and higher water absorption reduced the concreteâs stiffness. The effect was variable, with mixtures containing 10% CR showing initial higher stiffness, possibly due to casting effects. 117 3. The addition of 1% PPF enhanced shear strength and deformability, particularly with lower RCA levels. For example, PPF improved shear strength by up to 32% with 30% RCA and 5% CR. However, the benefit diminished with higher RCA content due to poor bonding between fibres and RCA particles. 4. CR reduced compressive strength due to its porous nature. Up to 30% of RCA slightly increased compressive strength, while fibres enhanced compressive strength at lower RCA levels, though the effect was less significant with higher RCA content. 5. Beams with higher RCA content showed increased deflections, but PPF improved crack resistance and ductility, leading to higher deflections before failure. The crack patterns shifted from shear to flexural failure, aided by the fibres. In conclusion, while RCA and CR reduced shear strength and deformability, the addition of PPF helped counter these effects, especially when RCA content was kept below 30%. This combination of materials offered a sustainable solution for concrete applications, although high RCA content (over 50%) required careful consideration due to its negative impact on mechanical properties. 118 Chapter 6: Conclusion 6.1 Summary This thesis presents the findings from a comprehensive, three-year experimental investigations into the mechanical and structural performance of concrete incorporating recycled concrete aggregate (RCA), crumb rubber (CR), and polypropylene fibre (PPF). The research focused on using these recycled materials to reduce reliance on natural aggregates, thus promoting sustainability by reusing waste materials and reducing environmental impacts. Over 270 concrete cylinders were tested for compressive, flexural, splitting tensile strength, workability and unit weight across various RCA, CR, and PPF mix proportions. Additionally, 60 small beams were tested for flexural strength. A structured database containing over 600 datasets of concrete compressive strength with RCA, CR, and PPF from the literature was developed to support machine learning-based predictive analysis, exploring parametric relationships in concrete mixes. The bond strength was assessed in three phases, varying RCA, CR, and PPF mix proportions and bar diameters. A total of 39 cylinders and 117 bond strength samples were cast to observe how bar length, diameter, and recycled additives affect bond behaviour in rubberised RCA based concrete. A total of 15 reinforced concrete beams, designed to fail in shear and constructed according to ACI 318-19 standards, were tested under four-point loading. The beams (200 mm x 300mm in section, with an effective span of 1140 mm) featured various combinations of RCA and CR to explore the shear behaviour with other parameters. The study provided valuable insights into the feasibility of RCA and CR as partial replacements for natural aggregates, with PPF as a reinforcing additive in concrete. The results demonstrated that RCA and CR can achieve sufficient mechanical performance, bond strength, and shear behaviour when proportioned correctly, offering a promising alternative for sustainable construction practices as predicted. The structured dataset and machine learning analysis highlighted predictive potential, supporting further optimization of recycled aggregate mixes. Based on the test results, the key findings of this research are described in the following subsections. 119 6.1.1 Mechanical Properties of Concrete with RCA, CR and PPF Research on the mechanical behaviour of concrete highlights the effects of varying levels of RCA, CR, and PPF on the properties of concrete mixes on workability, compressive strength, stress-strain behaviour, toughness, flexural and splitting tensile strength. Key findings from the experiments include: 1. Slump value decreases with higher replacement levels of RCA, CR, and fibre; with fibre having the most significant impact. The mix with 30% RCA, 10% CR, and 2% fibre showed the lowest slump, a 76% reduction from the control mix. 2. Compressive strength initially improved with 10% RCA replacement but declined at 30% RCA. Adding CR reduces compressive strength while increasing fibre content enhances it. The mix R30C0F2 (30% RCA, 2% fibre, no CR) achieved the highest compressive strength, 26% above the control at 28 days. 3. The mix with 30% RCA and 2% fibre (no CR) reached the highest peak stress (44.5 MPa) at 56 days, with peak strain and ultimate strain values slightly lower than the control mix. 4. Poissonâs ratio rose with increasing CR but decreased with higher fibre content. 5. Splitting tensile strength decreased with higher RCA and CR levels but increased with more fibre. 6. Flexural strength decreased with more RCA and CR but improved with added fibre. The mix combination of R30C0F2 showed the highest flexural strength, 8% above the control mix. 7. The mix R30C5F2 (30% RCA, 5% CR, 2% fibre) displayed the highest toughness and ductility. 8. Based on mechanical behaviour tests, mixes R10C5F2 (10% RCA, 5% CR, 2% fibre) and R30C5F2 demonstrated enhanced performance across compressive, split tensile, and flexural strength properties compared to the control. The findings showed that while higher levels of RCA and CR generally reduce certain strengths, adding fibre can offset these reductions and improve ductility and toughness, with specific mixes showing positive results for sustainable concrete applications. 120 6.1.2 Bond Strength of Concrete Containing RCA with CR and PPF The study evaluated the bond strength behaviour of recycled aggregate concrete containing RCA, CR, and PPF under different combinations. The findings provide insights into the interactions between RCA, CR, and PPF, as well as the influence of steel bar diameter and embedment length on bond strength. Key findings are: 1. In Phase I, concrete with 30% RCA and 5% CR (R10C5) showed the best bond strength among recycled material combinations. Increasing CR to 10% significantly reduced bond strength. 2. For concrete with fixed CR (5%) and PPF (2%), specimens with 10% RCA had 8% higher pull-out strength than those with 30% RCA, indicating that higher RCA levels weaken bonding, particularly with CR and PPF. 3. The phase II study suggested that 10% RCA and 5% CR (R10C5) can be used separately or together as replacements for natural coarse and fine aggregates due to their minimal impact on bond strength. 4. In Phase II, testing RCA and CR without PPF showed a progressive decrease in bond strength with higher RCA and CR percentages. Bond strength reductions ranged from 10% (R10C0) to 45% (R50C10) compared to the control. 5. Bond strength was higher with a 10mm diameter steel bar compared to a 12mm bar, and with a 150mm embedment length over 100mm for the same bar diameter. This established that reduced bar diameter and increased embedment improve bond strength. 6. In Phase III, increasing RCA and CR levels in the presence of PPF reduced bond strength. The weakest bond strength was observed in mixes R10C10F2 and R30C10F2, confirming that higher CR and PPF levels degrade bond performance. 7. Across all combinations in phase III, bond strength decreased when bar diameter increases from 12mm to 16mm and from 16mm to 20mm, confirming that larger bar diameters reduces bonding. 8. The combination of RCA, CR, and PPF had an adverse impact on concrete bonding with reinforcing steel. Optimal bonding was achieved when RCA was used with either CR or PPF alone. 121 The study concludes that bond strength is maximized when recycled aggregate concrete includes 10â30% RCA and a maximum of 5% CR without PPF. Additionally, reducing steel bar diameter while increasing embedment length enhances bond performance. This suggests that recycled aggregate concrete with these proportions can be effectively used in construction applications where bond strength becomes a primary focus. 6.1.3 Shear Strength of Concrete Containing RCA with CR and PPF The study examined the structural behaviour of concrete containing RCA, CR, and PPF, focusing on compressive strength, shear capacity, toughness, and overall ductility. Key findings from the study on compressive strength, ultimate shear capacity, toughness and crack behaviour, elastic and inelastic strain, and code comparisons are summarized as follows: 1. Compressive strength increased with RCA replacement up to 30% but declined with higher CR content. PPF improved compressive strength when paired with RCA up to 30%, while the mix with 10% CR alone (R0C10F0) showed the lowest strength. 2. Shear capacity decreased with higher CR content but increased with PPF addition when RCA was at or below 30%. Beyond 30% RCA, adding PPF reduced shear capacity. 3. Higher CR levels reduced toughness in beams with up to 30% RCA. PPF enhanced toughness by limiting crack propagation, increasing deformation and energy absorption. Lower CR content improved beam deformability, but higher CR led to brittle failure. PPF increased initial stiffness, reducing elastic deformation while enhancing inelastic and post-failure responses. 4. Control specimens showed higher compression and tensile elastic strain than beams with CR (5% or 10%). CR presence caused inelastic strain to initiate at lower loads, leading to earlier failure compared to beams with fibres, which showed a more integrated, ductile response. Beams with 50% RCA displayed more brittle behaviour before failure. 5. Shear strengths of beams with RCA, CR, and PPF were close to control beams and exceeded values recommended by codes (ACI 318, CSA A23.3, BS 8110, EN 2004). Ratios of Vtest to Vcode (Vtest/Vcode above 1.70) indicated that shear resistance was relatively high in mixes like R0C0F0, R0C10F1, R30C0F0, and R30C5F1, suggesting these combinations are structurally reliable. 122 6. Based on shear resistance performance, R0C10F1 is recommended for regions with surplus CR, R30C0F0 for areas concerned with RCA waste, and R30C5F1 where both RCA and CR as well as PPF are available. 6.2 Conclusions and Future Guidelines The overall research shows that rubberised recycled aggregate concrete is viable for both structural and non-structural applications. The next steps may include life cycle cost analysis for CR-based concrete to evaluate long-term sustainability and economic outcome. The research highlights the potential for cost reduction by substituting natural resources with recycled materials like RCA and CR, provided they are impurity-free and properly graded. Using RCA from high-strength parent concrete may be suggested for optimal performance. This study advances the scope to develop sustainable rubberised recycled aggregate concrete, aligning with environmental goals and reducing construction costs when cost-benefit is evaluated through waste material utilisation. 6.2.1 Overall Conclusions The key findings and recommendations of the study on the mechanical, bond, and shear performance of recycled aggregate concrete containing various proportions of RCA, CR, and PPF, aiming to optimise their use in structural concrete, are as follows: 1. Mechanical behaviour Mixes with 10â30% RCA, 5% CR, and up to 2% PPF (specifically R10C5F2 and R30C5F2) showed improvements in compressive strength, split tensile strength, and flexural strength compared to the control mix. These combinations are feasible for concrete structures, provided careful selection of materials and mix design are done. Exceeding the combination R30C10F2 (30% RCA, 10% CR, 2% PPF) can negatively impact the workability of RRAC (rubberised recycled aggregate concrete), thus limiting higher CR or RCA levels. 123 2. Bond behaviour with reinforcing steel Combining RCA, CR, and PPF reduced bond strength with reinforcing steel. However, RCA (up to 30%) combined with either 5% CR or 1% PPF was found to improve bond strength, indicating that using CR or PPF individually with RCA yields better bonding than combining all three. 3. Shear strength performance The combination R0C10F1 is suitable for regions with abundant CR, providing acceptable shear strength with only CR and minimal PPF. R30C0F0 is a viable option when managing RCA waste is an environmental concern, using RCA alone without additional CR or PPF. The R30C5F1 combination seems suitable for areas with surplus RCA and CR and sufficient PPF availability, offering balanced shear resistance with all three components. Thus, this study on shear strength proposes a maximum of 30% RCA with 5% CR and 1% PPF for concrete applications where recycled materials are utilised with high quality and performance. This research supports the use of recycled aggregate concrete with RCA, CR, and PPF in structural members under specific proportions. The results also indicated that 10-30% RCA with 5% CR and up to 2% PPF can enhance mechanical and structural performance while maintaining workability and acceptable bond strength with rebar. Future research is recommended to assess the long-term durability, energy absorption behaviour and cost-benefit of these materials for sustainable construction. 6.2.2 Guidelines for Use The study offers practical guidelines and recommendations for using RCA, CR, and PPF in construction, focusing on design considerations, application needs, and material limitations: 1. Design considerations. Designers should prioritize well-graded RCA and CR, ensuring a balanced replacement of coarse and fine aggregates to improve aggregate interlock, reduce voids, and enhance workability, strength, and durability. Moreover, 124 selecting fibres that can be uniformly dispersed is crucial for effective crack control and improving ductility. 2. Suitability based on structure. The study suggests that RCA, CR, and fibre-based concrete be used according to the structural importance, location, and durability requirements of each project. Ensuring the durability of recycled aggregate concrete (with CR and optionally with PPF) is essential before application in critical structures. 3. Optimum application. An initial mix recommendation includes up to 30% RCA, 5% CR, and up to 2% PPF. Given that CR may reduce compressive and bond strength, it can be used in higher proportions in applications with less stringent strength requirements, such as pavements and secondary roads. These recommendations aim to ensure structural integrity and durability by tailoring the use of RCA, CR, and PPF according to specific project requirements, while promoting sustainable construction practices by integrating recycled materials effectively. 6.3 Limitations of the Study This research acknowledges several contextual and practical considerations for using RCA, CR, and PPF in concrete, emphasizing the following points: 1. Regional variability and material selection. Characteristics of RCA, CR, and PPF can vary significantly in terms of raw ingredients, composition, dimensions, production processes, etc. Besides, regional factors such as climate, environmental conditions, and local construction practices will affect the concrete properties and their performance. This research used materials from different sources, ensuring they met all physical and quality requirements before testing to account for variability. 2. Durability assessment. The study did not examine the long-term durability of these recycled materials due to scope and other constraints. Key durability factors like permeability, chloride ion penetration, hot weather, fire and freeze-thaw resistance require extended testing periods, which were beyond the studyâs scope. 125 3. Application in high-strength concrete. High-performance or high-strength concrete was not explored, as analyzing these would involve extensive data and complex variables. The study suggests that within a defined replacement range, recycled aggregate concrete made with RCA, CR, and PPF would likely exhibit similar behaviour, which aligns with its focus on standard concrete applications rather than high-strength variants. While demonstrating the structural viability of RCA, CR, and PPF in standard concrete applications, the study recognizes regional material variability and leaves room for future research on durability and high-performance applications. These factors underscore the need for tailored material selection and rigorous durability testing when implementing recycled materials in different regions or high-strength concrete projects. 6.4 Novelty of this Study This whole research stands out for its novel approach and contributions to sustainable concrete design, as highlighted by the following key points: 1. Innovation in material combination. The study is groundbreaking in its combined use of RCA, CR, and PPF in concrete, marking the first time this specific mix has been explored in the concrete industry. 2. Structural application and behavioural analysis. This research uniquely investigated the effects of RCA, CR, and PPF on actual structural elements, examining their impact on critical aspects like mechanical properties, shear behaviour, and bond strength - an area previously unstudied with these material combinations. 3. Practical application in mix design. With findings showing that up to 30% RCA, 5% CR, and 1-2% PPF can be effectively integrated into structural concrete, the study paves the way for a practical mix design approach for recycled aggregate concrete, learnt by these tested proportions. This research establishes a pioneering framework for incorporating RCA, CR, and PPF into structural concrete, providing valuable insights into mechanical and structural performance and a guideline for sustainable mix design for the future in the construction industry. 126 6.5 Recommendations for Future Research The research suggests several avenues for further research to fully explore the potential and performance of recycled aggregate concrete incorporating CR and PPF. These proposed studies include: 1. Energy absorption behaviour. A dedicated study on the energy absorption properties of RRAC could provide insights into the potential of crumb rubber and polypropylene fibre to enhance the deformation and shock absorption capacity of concrete, particularly in structures that need to withstand dynamic loads. 2. Durability assessment. A long-term durability study, spanning three to five years, would be beneficial to assess the behaviour of CR and PPF within RRAC under various environmental conditions (hot, cold, and normal climates), along with different concrete strengths. This would help determine the longevity and resilience of these recycled materials in practical conditions. 3. Tests on bending and axial loads. Conducting pure bending tests, with and without axial load, on concrete columns made with RCA, CR, and PPF would allow for the examination of key properties such as flexural strength, tensile behaviour, deflection, buckling, and modulus of elasticity (MoE). This would provide a deeper understanding of the structural performance of RRAC under different loading conditions. These proposed studies would further enhance the understanding of RRACâs performance in various applications, addressing energy absorption, long-term durability, and structural behaviour under different loads, thus paving the way for more widespread adoption of these materials sustainably in concrete construction. 127 Bibliography ACI 209, Prediction of Creep, Shrinkage and Temperature effects in Concrete Structures, ed: American Concrete Institute, 2008, ACI 318-14, Building Code Requirements for Structural Concrete and Commentary, ed: American Concrete Institute, 2014. ACI Committee, 2019. ACI 318-19: Building Code Requirements for Structural Concrete and Commentary. In: A.C, 318M-19: Building Code Requirements for Structural Concrete and Commentary. American Concrete Institute, Farmington Hills, MI, USA, p. 628, 318. ACI COMMITTEE 555, ACI PRC-555-01, 2002. Removal and Reuse of Hardened Concrete, American Concrete Institute, Farmington Hills, MI. AHMED, H., TIZNOBAIK, M. & ALAM, M. S. 2019. Mechanical and durability properties of rubberized recycled aggregate concrete. AL MAHMOUD, F., BOISSIERE, R., MERCIER, C. & KHELIL, A. 2020. Shear behaviour of reinforced concrete beams made from recycled coarse and fine aggregates. Structures, 25, 660-669. ALAM, M. S., SLATER, E. & BILLAH, M. 2013. Green Concrete made with RCA and FRP Scrap Aggregate: Fresh and Hardened Properties. Green Concrete made with RCA and FRP Scrap Aggregate: Fresh and Hardened Properties, 25, 1783-1794. ALFAYEZ, S., OMAR, T. & NEHDI, M. 2020. Eco-efficient Preplaced Recycled Aggregate Concrete Incorporating Recycled Tire Rubber Granules and Steel Wire Fibre. Engineering Sustainability, 173, 1-12. ALFAYEZ, S. F. 2018. Eco-Effifficient Preplaced Recycled Aggregate Concrete Incorporating Recycled Tire Waste Rubber Granules and Steel Wire Fibre Reinforcement. Master of Engineering Science, The University of Western Ontario. ALWESABI E.A.H., BAKAR B.H.A., ALSHAIKH I.M.H., ZEYAD A.M., ALTHEEB A., AND ALGHAMDI H. 2021. Experimental investigation on fracture characteristics of plain and rubberized concrete containing hybrid steel-polypropylene fibre, Structures, 33 4421â4432. ALRAJFI, E., ASHTEYAT, A. & MURAD, Y. 2021. Shear behaviour of RC beams made with natural, recycled aggregate concrete and reclaimed asphalt aggregates under normal and elevated temperature. Journal of Building Engineering, 40, 102681. ALSADEY, S. & SALEM, M. 2016. Influence of Polypropylene Fibre on Strength of Concrete. ASLANI, F. & KELIN, J. 2018. Assessment and development of high-performance fibre-reinforced lightweight self-compacting concrete including recycled crumb rubber aggregates exposed to elevated temperatures. Journal of Cleaner Production, 200, 1009-1025. ASLANI, F., G. MA, D.L.Y. WAN, & G. MUSELIN, Development of high-performance self-compacting concrete using waste recycled concrete aggregates and rubber granules, Journal of Cleaner Production, 182 (2018) 553-566. ASTM C29, Standard Test Method for Bulk Density (Unit Weight) and Voids in Aggregate," ed. West Conshohocken, PA, 2017. ASTM C31 / C31M - 21a Standard Practice for Making and Curing Concrete Test Specimens in the Field. 128 ASTM C33/C33M-18, Standard Specification for Concrete Aggregates, ASTM International, West Conshohocken, PA (2018). ASTM C39, Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens," ed. ASTM International, West Conshohocken, PA, 2018. ASTM C78 / C78M - 16, Standard Test Method for Flexural Strength of Concrete (Using Simple Beam with Third-Point Loading)," ed. ASTM International, West Conshohocken, PA, 2016. ASTM C127, Standard Test Method for Relative Density (Specific Gravity) and Absorption of Coarse Aggregate," ed. West Conshohocken, PA, 2015. ASTM C 128, Standard Test Method for Relative Density (Specific Gravity) and Absorption of Fine Aggregate," ed. ASTM International,West Conshohocken, PA,2015. ASTM C131, Standard Test Method for Resistance to Degradation of Small-Size Coarse Aggregate by Abrasion and Impact in the Los Angeles Machine," ed. ASTM International, West Conshohocken, PA, 2014. ASTM C136, Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates," ed. ASTM International, West Conshohocken, PA, 2014. ASTM C143, Standard Test Method for Slump of Hydraulic-Cement Concrete," ed. ASTM International, West Conshohocken, PA, 2015. ASTM C187-04, Standard Test Method for Normal Consistency of Hydraulic Cement, ASTM International, West Conshohocken, PA, 2004 ASTM C191, Standard Test Methods for Time of Setting of Hydraulic Cement by Vicat Needle," ed. ASTM International,West Conshohocken, PA, 2018. ASTM C192/C192M - 16 - Making and Curing Concrete Test Specimens in the Laboratory - Docsity ASTM C191-04, Standard Test Method for Time of Setting of Hydraulic Cement by Vicat Needle, ASTM International, West Conshohocken, PA, 2004. ASTM C231, Standard Test Method for Air Content of Freshly Mixed Concrete by the Pressure Method," ed. ASTM International, West Conshohocken, PA, 2017. . ASTM C496, Standard Test Method for Splitting Tensile Strength of Cylindrical Concrete Specimens," ed. ASTM International, West Conshohocken, PA, 2014. ASTM C642, Standard Test Method for Density, Absorption, and Voids in Hardened Concrete," ed. ASTM International, West Conshohocken, PA, 2013. ASTM C900-15, Standard Test Method for Pull-out Strength of Hardened Concrete, ASTM International, West Conshohocken, PA, 2015. ASTM C1609, Standard Test Method for Flexural Performance of Fibre-Reinforced Concrete (Using Beam with Third-Point Loading)," ed. ASTM International, West Conshohocken, PA, 2013. ATARIA, R. B. & WANG, Y. C. 2019. Bending and shear behaviour of two layer beams with one layer of rubber recycled aggregate concrete in tension. Structures, 20, 214-225. AYMAN, M. & MOHAMED, A. E. 2017. Dynamic Properties of High Strength Rubberized Concrete. ACI Symposium Publication, 314. BAI, G., ZHU, C., LIU, C. & LIU, B. 2020. An evaluation of the recycled aggregate characteristics and the recycled aggregate concrete mechanical properties. Construction and Building Materials, 240, 117978. BANTHIA N. AND SOLEIMANI S.M. 2005. Flexural response of hybrid fibre-reinforced cementitious composites, ACI Materials Journal, 102(6) 382. 129 BAOSHAN H., GUOQIANG L., SU-SENG P., AND JOHN E. 2004. Investigation into Waste Tire Rubber-Filled Concrete, Journal of Materials in Civil Engineering, 16(3) 187â94. BATAYNEH, M. K., MARIE, I. & ASI, I. 2008. Promoting the use of crumb rubber concrete in developing countries. Waste Management, 28, 2171-2176. BEHERA M., BHATTACHARYYA S.K., MINOCHA A.K., DEOLIYA R., & MAITI S. 2014, Recycled aggregate from C&D waste & its use in concreteâA breakthrough towards sustainability in construction sector: A review, Construction and building materials, 68 501-516. BLABER, J., B. ADAIR, AND A. ANTONIOU, 2015. Ncorr: Open-Source 2D Digital Image Correlation Matlab Software. BOGAS, J. A., DE BRITO, J. & FIGUEIREDO, J. M. 2015. Mechanical characterization of concrete produced with recycled lightweight expanded clay aggregate concrete. Journal of Cleaner Production, 89, 187-195. BOMPA, D. V., ELGHAZOULI, A. Y., XU, B., STAFFORD, P. J. & RUIZ-TERAN, A. M. 2017. Experimental assessment and constitutive modeling of rubberized concrete materials. Construction and Building Materials, 137, 246-260. BRAVO, M. & DE BRITO, J. 2012. Concrete made with used tyre aggregate: durability-related performance. Journal of Cleaner Production, 25, 42-50. BUTLER, L., WEST, J. S. & TIGHE, S. L. 2011. The effect of recycled concrete aggregate properties on the bond strength between RCA concrete and steel reinforcement. Cement and Concrete Research, 41, 1037-1049. CHEN, A., HAN, X., CHEN, M., WANG, X., WANG, Z. & GUO, T. 2020. Mechanical and stress-strain behaviour of basalt fibre reinforced rubberized recycled coarse aggregate concrete. Construction and Building Materials, 260, 119888. CHOWDHURY, A. T. A. 2017. Turning waste tires into energy. Financial Express, October 19,2017. COPETTI, C. M., BORGES, P. M., SQUIAVON, J. Z., DA SILVA, S. R. & DE OLIVEIRA ANDRADE, J. J. 2020. Evaluation of tire rubber surface pre-treatment and silica fume on physical-mechanical behaviour and microstructural properties of concrete. Journal of Cleaner Production, 256, 120670. CSA A23.3-14, Design of Concrete Structures," ed: Canadian Standards Association, 2014. DE JUAN, M. S. & GUTIÃRREZ, P. A. 2009. Study on the influence of attached mortar content on the properties of recycled concrete aggregate. Construction and Building Materials, 23, 872-877. DING, Y., ZHANG, F., TORGAL, F. & ZHANG, Y. 2012. Shear behaviour of steel fibre reinforced self-consolidating concrete beams based on the modified compression field theory. Composite Structures, 94, 2440-2449. DUAN, Z. H. & POON, C. S. 2014. Properties of recycled aggregate concrete made with recycled aggregates with different amounts of old adhered mortars. Materials & Design, 58, 19-29. EMIROGLU M., KELESTEMUR M.H., AND YILDIZ S. 2007. An investigation on ITZ microstructure of the concrete containing waste vehicles tire, Proceedings of 8th International Fracture Conference, Istanbul/TURKEY. EMON M.A.B., MANZUR T., AND SHARIF M.S. 2017. Suitability of locally manufactured galvanized iron (GI) wire fibre as reinforcing fibre in brick chip concrete, Case Studies in Construction Materials, 7, 217â227. EN1992-1-1, Design of concrete structures General rules and rules for buildings, 1992. 130 ETXEBERRIA, M., MARI, A. & VÃZQUEZ, E. 2007. âRecycled Aggregate Concrete as Structural Materialâ. Materials and Structures, 40, 529-541. ETXEBERRIA, M., VÃZQUEZ, E., MARÃ, A., AND BARRA, M. 2007. "Influence of amount of recycled coarse aggregates and production process on properties of recycled aggregate concrete," Cement and Concrete Research, vol. 37, pp. 735 - 742. European Committee for Standardization, 2004. Eurocode 2: Design of concrete structures - Part 1-1: General rules and rules for buildings. European Committee for Standardization, Brussels, Belgium. fib Model Code for Concrete Structures, International Federation for Structural Concrete, 2010, ed FURLAN, S. & DE HANAI, J. B. 1997. Shear behaviour of fibre reinforced concrete beams. Cement and Concrete Composites, 19, 359-366. GANJIAN E., KHORAMI M., AND MAGHSOUDI A.A. 2009. Scrap-tyre-rubber replacement for aggregate and filler in concrete, Construction and building materials, 23(5) 1828-1836. GERGES, N. N., ISSA, C. A. & FAWAZ, S. A. 2018. Rubber concrete: Mechanical and dynamical properties. Case Studies in Construction Materials, 9, e00184. GESOGLU, M., GÃNEYISI, E., HANSU, O., İPEK, S., ASAAD, D. S. J. C. & MATERIALS, B. 2015. Influence of waste rubber utilization on the fracture and steelâconcrete bond strength properties of concrete. 101, 1113-1121. GRZESIAK, S., PAHN M., SCHULTZ-CORNELIUS, M., HARENBERG S., AND HAHN C. 2021. Influence of Fibre Addition on the Properties of High-Performance Concrete. GILLANI, S. S.-U.-H., KHITAB, A., AHMAD, S., KHUSHNOOD, R. A., FERRO, G. A., SALEEM KAZMI, S. M., QURESHI, L. A. & RESTUCCIA, L. 2017. Improving the mechanical performance of cement composites by carbon nanotube addition. Procedia Structural Integrity, 3, 11-17. GUO, Y.-C., ZHANG, J.-H., CHEN, G.-M. & XIE, Z.-H. 2014a. Compressive behaviour of concrete structures incorporating recycled concrete aggregates, rubber crumb and reinforced with steel fibre, subjected to elevated temperatures. Journal of Cleaner Production, 72, 193-203. GUO, Y. C., ZHANG, J. H., CHEN, G., CHEN, G. M. & XIE, Z. H. 2014b. Fracture behaviours of a new steel fibre reinforced recycled aggregate concrete with crumb rubber. Construction and Building Materials, 53, 32-39. GUPTA, T., SIDDIQUE, S., SHARMA, R. K. & CHAUDHARY, S. 2017. Effect of elevated temperature and cooling regimes on mechanical and durability properties of concrete containing waste rubber fibre. Construction and Building Materials, 137, 35-45. GUPTA T., CHAUDHARY S., AND SHARMA R.K. 2014. Assessment of mechanical and durability properties of concrete containing waste rubber tire as fine aggregate, Construction and building Materials, 73 562-574. HANAI J.B. AND HOLANDA K.M.A. 2008. Similarities between punching and shear strength of steel fibre reinforced concrete (SFRC) slabs and beams, RIEM-IBRACON Structures and Materials Journal, 1(1). HASSAN, A., ELKADY, H. & SHAABAN, I. G. 2019. Effect of Adding Carbon Nanotubes on Corrosion Rates and Steel-Concrete Bond. Scientific Reports, 9, 6285. HESAMI, S., HIKOUEI, I. & EMADI, S. 2016. Mechanical behaviour of self-compacting concrete pavements incorporating recycled tire rubber crumb and reinforced with polypropylene fibre. Journal of Cleaner Production, 133. 131 HOSSAIN, F. M., SHAHJALAL, M., ISLAM, K., TIZNOBAIK, M. & ALAM, M. S. 2019. Mechanical properties of recycled aggregate concrete containing crumb rubber and polypropylene fibre. Construction and Building Materials, 225, 983-996. HOSSAIN, F. M. Z., PAL, A, AHMED, K.S., BEDIWY,A., M. & ALAM, M. S. 2023. Shear behaviour of polypropylene fibre-reinforced concrete beams containing recycled aggregate and crumb rubber. Journal of Cleaner Production, Volume 412, 2016 137370. HOSSAIN M.U., POON C.S., LO I.M.C., AND CHENG J.C.P., Comparative environmental evaluation of aggregate production from recycled waste materials and virgin sources by LCA, Resources, Conservation and Recycling, 109 (2016) 67-77. HUDA, S. & ALAM, M. S. 2015. Mechanical and Freeze-Thaw Durability Properties of Recycled Aggregate Concrete Made with Recycled Coarse Aggregate. Journal of Materials in Civil Engineering, 27, 04015003. HUDA, S. B. & ALAM, M. S. 2014. Mechanical behaviour of three generations of 100% repeated recycled coarse aggregate concrete. Construction and Building Materials, 65, 574-582. IGNJATOVIÄ, I. S., MARINKOVIÄ, S. B. & TOÅ IÄ, N. 2017. Shear behaviour of recycled aggregate concrete beams with and without shear reinforcement. Engineering Structures, 141, 386-401. ISLAM, M. J., ISLAM, K., SHAHJALAL, M., KHATUN, E., ISLAM, S. & RAZZAQUE, A. B. 2022. Influence of different types of fibres on the mechanical properties of recycled waste aggregate concrete. Construction and Building Materials, 337, 127577. ISLAM, M. J., MEHERIER, M. S. & ISLAM, A. K. M. R. 2016. Effects of waste PET as coarse aggregate on the fresh and harden properties of concrete. Construction and Building Materials, 125, 946-951. ISMAIL, M. & HASSAN, A. 2017. Shear behaviour of large-scale rubberized concrete beams reinforced with steel fibres. Construction and Building Materials, 140, 43-57. JADHAV, H. & KOLI, M. J. I. J. S. C. E. R. 2013. Flexural behaviour of hybrid fibre reinforced concrete beams. 2, 210-218. KATZ, A. 2003. Properties of Concrete Made With Recycled Aggregate from Partially Hydrated Old Concrete. Cement and Concrete Research - CEM CONCR RES, 33, 703-711. KHALOO, A. R., DEHESTANI, M. & RAHMATABADI, P. 2008. Mechanical properties of concrete containing a high volume of tireârubber particles. Waste Management, 28, 2472-2482. KUMAR, S., MEHRA, P., GUPTA, R., JOSEPH, M. & CSETENYI, L. 2016. Abrasion resistance of sustainable green concrete containing waste tire rubber particles. Construction and Building Materials, 124, 906-909. LAU A. AND ANSON M. 2006. Effect of high temperatures on high performance steel fibre reinforced concrete, Cement and Concrete Research, 36(9) 1698-1707. LI, L.-J., TU, G.-R., LAN, C. & LIU, F. 2016. Mechanical characterization of waste-rubber-modified recycled-aggregate concrete. Journal of Cleaner Production, 124, 325-338. LI, Y., ZHOU, Y., WANG, R., LI, Y., WU, X. & SI, Z. 2022. Experimental investigation on the properties of the interface between RCC layers subjected to early-age frost damage. Cement and Concrete Composites, 134, 104745. LIMBACHIYA, M., LEELAWAT, T. & DHIR, R. 2000. Use of recycled concrete aggregate in high-strength concrete. Materials and Structures/Materiaux et Constructions, 33, 574-580. 132 LIU, F., MENG, L.-Y., NING, G.-F. & LI, L.-J. 2015. Fatigue performance of rubber-modified recycled aggregate concrete (RRAC) for pavement. Construction and Building Materials, 95, 207-217. MacGregor J.G. and WIGHT J.K., Book on Reinforced Concrete Mechanics and Design (6E) 2000. MARIE, I. 2017. Thermal conductivity of hybrid recycled aggregate â Rubberized concrete. Construction and Building Materials, 133, 516-524. MARTÃN-MORALES, M., ZAMORANO, M., RUIZ-MOYANO, A. & VALVERDE-ESPINOSA, I. 2011. Characterization of recycled aggregates construction and demolition waste for concrete production following the Spanish Structural Concrete Code EHE-08. Construction and Building Materials, 25, 742-748. MEHERIER, M. S. 2016. Investigation of mechanical and durability properties of cement mortar and concrete with varying replacement levels of crumb rubber as fine aggregate. Text. MEHERIER M.S. 2016. Investigation of mechanical and durability properties of cement mortar and concrete with varying replacement levels of crumb rubber as fine aggregate, Master of Applied Science, Department of Civil Engineering, University of British Columbia, Canada. MENDIS, A. S. M., AL-DEEN, S. & ASHRAF, M. 2018. Flexural shear behaviour of reinforced Crumbed Rubber Concrete beam. Construction and Building Materials, 166, 779-791. MHAYA A.M., HUSEIEN G.F., ABIDIN A.R.Z., & ISMAIL M., Long-term mechanical and durable properties of waste tires rubber crumbs replaced GBFS modified concretes, Construction and Building Materials, 256 (2020) 119505. Micelli F., Renni A., Kandalaft A.G., and Moro S. 2020. Fibre-reinforced concrete and ultrahigh-performance fibre-reinforced concrete materials, New Materials in Civil Engineering, 7 273-314. MOHAMED, K. I. & ASSEM, A. A. H. 2016. Performance of Full-Scale Self-Consolidating Rubberized Concrete Beams in Flexure. ACI Materials Journal, 113. MOHOD, M. 2015. Performance of Polypropylene Fibre Reinforced Concrete. MOHSENI, E., SAADATI, R., KORDBACHEH, N., PARPINCHI, Z. S. & TANG, W. 2017. Engineering and microstructural assessment of fibre-reinforced self-compacting concrete containing recycled coarse aggregate. Journal of Cleaner Production, 168, 605-613. NAITO, C., STATES, J., JACKSON, C. & BEWICK, B. 2014. Assessment of Crumb Rubber Concrete for Flexural Structural Members. Journal of Materials in Civil Engineering, 26. NAJIM, K. B. & HALL, M. R. 2010. A review of the fresh/hardened properties and applications for plain- (PRC) and self-compacting rubberised concrete (SCRC). Construction and Building Materials, 24, 2043-2051. NAJIMI, F. F. A. R. P. M. 2009. Effects of polypropylene fibres on physical and mechanical properties of concrete. Third International Conference on Concrete and Development. Tehran, Iran. NEMKUMAR, B. & SAYED MOHAMAD, S. 2005. Flexural Response of Hybrid Fibre-Reinforced Cementitious Composites. ACI Materials Journal, 102. NING, X., DING, Y., ZHANG, F. & ZHANG, Y. 2015. Experimental study and prediction model for flexural behaviour of reinforced SCC beam containing steel fibres. Construction and Building Materials, 93, 644-653. 133 NOAMAN, A. T., BAKAR, B. H. A. & AKIL, H. M. 2017. Investigation on the mechanical properties of rubberized steel fibre concrete. Engineering Structures and Technologies, 9, 79-92. OCHI T., OKUBO S., AND FUKUI K. 2007, Development of recycled PET fibre and its application as concrete-reinforcing fibre, Cement and Concrete Composites, 29(6) 448-55. ONUAGULUCHI O. AND BANTHIA N., Plant-based natural fibre reinforced cement composites: A review, Cement and Concrete Composites, 68 (2016) 96-108. OIKONOMOU N.D., Recycled concrete aggregates, Cement and concrete composites, 27(2) (2005) 315-318. PAL, A, AHMED, K.S., HOSSAIN, F. M. Z., & ALAM, M. S. 2023. Machine learning models for predicting compressive strength of fibre-reinforced concrete containing waste rubber and recycled aggregate. Journal of Cleaner Production, Volume 423, 138673. RAFFOUL, S., GARCIA, R., PILAKOUTAS, K., GUADAGNINI, M. & MEDINA, N. F. 2016. Optimisation of rubberised concrete with high rubber content: An experimental investigation. Construction and Building Materials, 124, 391-404. RAMUJEE, K. J. I. J. O. I. R. I. S., ENGINEERING & TECHNOLOGY 2013. Strength properties of polypropylene fibre reinforced concrete. 2, 3409-3413. RAO, A., JHA, K. N. & MISRA, S. 2007. Use of aggregates from recycled construction and demolition waste in concrete. Resources, Conservation and Recycling, 50, 71-81. RASHAD, A. M. 2016. A comprehensive overview about recycling rubber as fine aggregate replacement in traditional cementitious materials. International Journal of Sustainable Built Environment, 5, 46-82. RAVI, K. AND KARVEKAR A. V. 2014. "Performance Evaluation of Hybrid Fibre Reinforced Concrete Subjected to Freezing and Thawing Effect," International Journal of Research in Engineering and Technology, vol. 3. ROCKSON, C., TAMANNA, K., ALAM, M. S. & RTEIL, A. 2020. Effect of cover on bond strength of structural concrete using commercially produced recycled coarse and fine aggregates. Construction and Building Materials, 255, 119275. ROYCHAND, R., GRAVINA, R.J., ZHUGE, Y., MA, X., YOUSSF, O., & MILLS, J.E., A comprehensive review on the mechanical properties of waste tire rubber concrete, Construction and Building Materials, 237 (2020) 117651. SADROLODABAEE, P., CLARAMUNT, J., ARDANUY, M. & DE LA FUENTE, A. 2021. Mechanical and durability characterization of a new textile waste micro-fibre reinforced cement composite for building applications. Case Studies in Construction Materials, 14, e00492. SALEM, R., BURDETTE, E. & JACKSON, N. 2003. Resistance to freezing and thawing of recycled aggregate concrete. ACI Materials Journal, 100, 216-221. SATO, R., MARUYAMA, I., SOGABE, T. & SOGO, M. J. J. O. A. C. T. 2007. Flexural behaviour of reinforced recycled concrete beams. 5, 43-61. SETHUNARAYANAN R., CHOCKALINGAM S., ANDRAMANATHAN R. 2008. Natural Fibre Reinforced Concrete, Transportation Research Record, 1226, 57-60. SGOBBA, S., BORSA, M., MOLFETTA, M. & MARANO, G. C. 2015. Mechanical performance and medium-term degradation of rubberised concrete. Construction and Building Materials, 98, 820-831. 134 SHAHJALAL, M., ISLAM, K., RAHMAN, J., AHMED, K. S., KARIM, M. R. & BILLAH, A. H. M. M. 2021. Flexural response of fibre reinforced concrete beams with waste tires rubber and recycled aggregate. Journal of Cleaner Production, 278, 123842. SHAHJALAL M., HOSSAIN F.M.Z., ISLAM K., TIZNOBAIK M., AND ALAM M.S. 2019. Experimental Study on Mechanical Properties of Recycled Aggregate Concrete using Crumb Rubber and Polypropylene Fibre, CSCE Annual Conference: Canada. SHAHJALAL, M., ISLAM, K., BATOOL, F., TIZNOBAIK, M., HOSSAIN, F.M.Z., AHMED, K.S., ALAM, M.S., AHSAN, R. 2023. Fibre-reinforced recycled aggregate concrete with crumb rubber: A state-of-the-art review, Construction and Building Materials. 404, 133233 SHADHEER A.M., RAVICHANDRAN P., AND KRISHNARAJA A.R. 2021. Natural Fibres in Concrete â A Review, IOP Conference Series: Materials Science and Engineering, 1055, 012038. SHEN L., WORRELL E., AND PATEL M.K., 2010. Open-loop recycling: A LCA case study of PET bottle-to-fibre recycling, Resources Conservation and Recycling, 55(1) 34â52. SINGH, S., SHUKLA, A., BROWN, R. J. C. & RESEARCH, C. 2004. Pullout behaviour of polypropylene fibres from cementitious matrix. 34, 1919-1925. SILVA. R.V., BRITO. J. de, DHIR. R. K. 2016. Establishing a relationship between modulus of elasticity and compressive strength of recycled aggregate concrete, J. Clean. Prod. 112, 2171-2186 SILVA. R.V., BRITO. J. de, DHIR. R. K., 2014. Properties and composition of recycled aggregates from construction and demolition waste suitable for concrete production, Construction and Building Materials, 65, 201â217. SOGO, M., SOGABE, T., MARUYAMA, I., SATO, R. & KAWAI, K. Shear behaviour of reinforced recycled concrete beams. Proceedings of the International RILEM Conference on the use of recycled materials in building and structures, 2004. 610-618. SU, H. 2015. Properties of concrete with recycled aggregates as coarse aggregate and as-received/surface-modified rubber particles as fine aggregate. Ph.D, University of Birmingham. TAHENNI, T., CHEMROUK, M. & LECOMPTE, T. 2016. Effect of steel fibres on the shear behaviour of high strength concrete beams. Construction and Building Materials, 105, 14-28. TAMANNA, K., TIZNOBAIK, M., BANTHIA, N. & ALAM, M. S. 2020. Mechanical Properties of Rubberized Concrete Containing Recycled Concrete Aggregate. ACI Materials Journal, 117, 169-180. TAMANNA K., Mechanical properties of rubberized concrete containing recycled concrete aggregate and polypropylene fibre, Master of Applied Science, Department of Civil Engineering, University of British Columbia, Canada (2018). THOMAS, B. S., GUPTA, R. C. & PANICKER, V. J. 2016. Recycling of waste tire rubber as aggregate in concrete: durability-related performance. Journal of Cleaner Production, 112, 504-513. THOMAS B.S., GUPTA R.C., KALLA P., AND CSETENEYI L., Strength, abrasion and permeation characteristics of cement concrete containing discarded rubber fine aggregates, Construction and Building Materials, 59 (2014) 204-212. TOPÃU, Ä°. B. & ÅENGEL, S. 2004. Properties of concrete produced with waste concrete aggregate. Cement and Concrete Research, 34, 1307-1312. 135 TORGAL, F. P. & JALALI, S. 2011. 5 - Natural fibre reinforced concrete. Woodhead Publishing Series in Textiles, 154-167. WANG, B., YAN, L., FU, Q. & KASAL, B. 2021. A Comprehensive Review on Recycled Aggregate and Recycled Aggregate Concrete. Resources, Conservation and Recycling, 171, 105565. WANG, J., DAI, Q., SI, R. & GUO, S. 2019. Mechanical, durability, and microstructural properties of macro synthetic polypropylene (PP) fibre-reinforced rubber concrete. Journal of Cleaner Production, 234, 1351-1364. WEN, H., MCLEAN, D. & WILLOUGHBY, K. 2015. Evaluation of Recycled Concrete as Aggregates in New Concrete Pavements. Transportation Research Record: Journal of the Transportation Research Board, 2508, 73-78. VALENTE M. AND SIBAI A., Rubber/crete: Mechanical properties of scrap to reuse tire-derived rubber in concrete; A review, Journal of Applied Biomaterials & Functional Materials, (2019) 1-8. XIAO, J., FALKNER, H. J. C. & MATERIALS, B. 2007. Bond behaviour between recycled aggregate concrete and steel rebars. 21, 395-401. XIE, J.-H., GUO, Y.-C., LIU, L.-S. & XIE, Z.-H. 2015. Compressive and flexural behaviours of a new steel-fibre-reinforced recycled aggregate concrete with crumb rubber. Construction and Building Materials, 79, 263-272. XIE, J., FANG, C., LU, Z., LI, Z. & LI, L. 2018. Effects of the addition of silica fume and rubber particles on the compressive behaviour of recycled aggregate concrete with steel fibres. Journal of Cleaner Production, 197, 656-667. XIE, J., ZHENG, Y., GUO, Y., OU, R., XIE, Z. & HUANG, L. 2019a. Effects of crumb rubber aggregate on the static and fatigue performance of reinforced concrete slabs. Composite Structures, 228, 111371. XIE, J. H., LI, J., LI, Z., FANG, C., HUANG, L. & LI, L. 2019b. Combination effects of rubber and silica fume on the fracture behaviour of steel-fibre recycled aggregate concrete. Construction and Building Materials, 203, 164-173. ZEIML, M., LEITHNER, D., LACKNER, R. & MANG, H. A. 2006. How do polypropylene fibres improve the spalling behaviour of in-situ concrete? Cement and Concrete Research, 36, 929-942. ZHENG, L., HUO, X. & YUAN, Y. 2008. Strength, Modulus of Elasticity, & Brittleness Index of Rubberized Concrete. Journal of Materials in Civil Engineering - J MATER CIVIL ENG, 20. USTMA, 2017 U.S. Scrap Tire Management Summary, U.S Tire Manufactures Association (USTMA), Washington DC, U.S.A (2018). WANG J., DAI Q., SI R., AND GUO S., 2019. Mechanical, durability, and microstructural properties of macro synthetic polypropylene (PP) fibre-reinforced rubber concrete, Journal of Cleaner Production, 234, 1351-1364. ZABORAC, J., ATHANASIOU, A., SALAMONE, S., BAYRAK, O., HRYNYK, T. 2019. Evaluation of structural cracking in concrete. 2019, Texas. Dept. of Transportation. Research and Technology Implementation Office, Texas. 136 Appendices Appendix A Allowable limits of deleterious elements in RCA Element-substance Limit (μg/l) Zinc (Zn) 400 Copper (Cu) 200 Lead (Pb) 100 Nickel (Ni) 100 Chromium (Cr) 100 Arsenic (As) 50 Cadmium (Cd) 5 Iodine (I) 2 Note: Table from (N.D. Oikonomou, 2005) as per (Shahjalal et al., 2023). 137 Appendix B Classifications of rubber aggregate. Types of Rubber Aggregate References Shredded/Chipped Rubber Crumb Rubber Ground/Powdered Rubber Fibre Rubber/Buffing Diameter (mm) Specific Gravity Diameter (mm) Specific Gravity Diameter (mm) Specific Gravity Length (mm) Specific Gravity 13â76 1.3 0.425â4.75 - <0.425 0.8 - Ganjian et al. 13â76 - 0.5-5 - 0.15â19 - 8.5â21.5 - Siddique and Cachim 25â30 - 3-10 0.64â0.72 <1 - - Gerges et al. 10-300 - 1-10 - <1 - 0â40 Mohajerani et al. - - - <8 0.95 Emiroglu et al. - 0.15â4.75 1.15-1.25 - - Hossain et al., Shahjalal et al., Meherier, Tamanna et al., Chen et al. 138 Appendix C Chemical composition of CR by different researchers Elements (Symbol) Weight (%) Untreated Treated 20% NaOH 10% NaOH 20% NaOH 40% NaOH 10% NaOH Water Soaking 5% KMnO4/ 5% NaHSO4 10% H2O2 10% CaCl2 35% H2SO4 1% Silane Meherier Gupta et al. Mhaya et al. Angelin et al. Tamanna et al. Chen et al. Copetti et al. Muñoz-Sánchez et al. Ahmed et al. Tamanna et al. Copetti et al. Youssf et al. Carbon (C) 69.95 87.51 14 91.50 88.60 81.16-85.19 44.30 30-38 88.88 44.70 19.70 60.14 95.7 92.1 87.9 85.4 84.1 86 84 Oxygen (O) 20.93 9.23 3.30 9.40 1.72-2.07 6.54 8.65 29.60 57.2 5.36 4.3 6.3 9.5 11.9 8.1 8.8 10.2 Sodium (Na) 0.38 0.20 0.49 0.44 Magnesium (Mg) 0.23 0.14 0.06 0.08 Aluminum (Al) 0.71 0.08 0.95 - Silicon (Si) 1.53 0.20 0.20 1.32 0.09 22.70 22.90 0.21 Sulfur (S) 1.42 1.08 1.20 1.52-1.64 0.48 â¤5 1.08 1.70 Potassium (K) 0.12 0.03 Calcium (Ca) 0.22 0.10 0.70 0.39 0.26 3.00 0.20 0.26 Iron (Fe) 2.43 16.42 - 0.27 Copper (Cu) 0.15 3.58 - Zinc (Zn) 1.91 1.76 3.50 1.10 15.04 0.46 0.00 0.00 4.04 Hydrogen (H) 0.20 7.22-7.42 Nitrogen (N) 0.31-0.47 Acetone Extract 10 Ketonic Extract 10-20 Ash Content 24 3.84-7.44 3-7 Rubber Hydrocarbon 52 Polymers 40-55 Natural Rubber 21-42 Miscellaneous* 10.98 27.5 1.6 2.6 2.7 7.8 5.2 5.8 *Note: If the sum of all available elements in CR is less than 100%, then the rest percentage is reported as miscellaneous data. 139 Appendix D Different properties of fibreTypes of Fibre Specific Gravity Fibre Length (mm) Diameter (μm) No. of Denier Yield Strength (MPa) Tensile Strength (MPa) Elastic Modulus (GPa) Elongation at Ultimate Stress (%) Elongation at Rupture (%) Reference Steel Fibre 7.70â7.82 ~50 750â32000 â â 600â1030 â â 5 - 20 Jian-he et al., Guo et al., Xie et al., Mohseni et al. Polymeric Fibre (Polypropylene) 0.90â0.91 6â12 20â50000 03 â 130â689 3.4â7.0 â 15 Hossain et al., Micelli et al., Ismail et al., Mohseni et al. Glass Fibre 2.54â2.78 â 10 â â 2500â3500 70â73 â 3.6â4.8 Micelli et al. Carbon Fibre (PAN) 1.95 â 7.0â9.7 â â 2200 390 â 0.5 Micelli et al. Galvanized Iron Fibre â â 500â1000 â 214â455 315â621 17.5 18.0â40.03 â Emon et al., Islam et al. Basalt Fibre 2.60 20 15 â â 3800â4840 93â110 â 2.7â3.1 Chen et al. Textile Fibre â â 3.6 â 32.1 â â â â â â Sadrolodabaee et al. Recycled Steel Wires â 20-35 200 â â 2000 â â â Alfayez Jute Fibre 1.80 â 0.1 - 0.2 â â 250 -350 26 - 32 â 1.5 - 1.9 Micelli et al. Coconut Fibre 1.177 â â â â 95â118 2.8 â â Torgal and Jalali Bamboo Fibre 1.158 â â â â 73â505 10â40 â â Torgal and Jalali Sisal Fibre 1370 â â â â 347â378 15.2 â â Torgal and Jalali Appendix E Summary of compressive strength of RRAC and FRRAC by different researchers 140 RA Size (mm) Rubber Size (mm) Treatment Method w/c or w/b ratio Control Mixture Strength (MPa) RRAC FRRAC Reference Recycled Aggregate Rubber Strength Relative to Control (%) Fibre Strength Relative to Control (%) Replacement Level (%) Replacement Type Replacement Level (%) Replacement Type Fibre Type Fibre % (Total Volume) 5-20 & 20-40 0.25 No Treatment 0.38 50 100 Weight Basis of NCA 0, 10, 20,30 Volume Basis of NFA 110.6, 79.8, 67.2, 58.4 - - - Feng et al. 5-10 0.221 No Treatment - 60 100 Weight Basis of NCA 10, 20, 30, 40 Volume Basis of NFA 62.5, 52.5, 45.8, 43.3 - - - Li et al. 0.864 10, 20, 30, 40 72.5, 63.3, 56.6, 45.8 4.04 10, 20, 30, 40 79.3, 71.6, 66.7, 51.7 â¤10 0.3, 0.5 & 3 Un-treated 0.37 42.5 50 Weight Basis of NCA 20 Volume Basis of NFA 86.1 - - - Su NaOH (2hr) 84.2 NaOH (24hr) 86.8 SCA 92 4-14 5-10 No Treatment 0.45 50.39 0, 10, 20, 30, 40 Volume Basis of NCA+NFA 20 Volume Basis of NCA 44.1, 56.8, 55.6, 47.7, 53.8 - - - Aslani et al. â¤ 20 â¤ 3 No Treatment 0.30 43.0 100 Weight Basis of NCA 0, 25, 50 Volume Basis of NFA 139.5, 95.3, 69.8 - - - Henry et al. 5-20 0.075-4.75 No Treatment 0.56 27.33 0, 5, 10, 15, 20 Weight Basis of NCA 10 Volume Basis of NFA 80.5, 75.0, 73.2, 71.1, 69.5 - - - Marie 4.75-20 4.74-0.08 20% NaOH Solution (30 Min) 0.34 51.8 0 Weight Basis of NCA 0, 10, 20 Volume Basis of NFA 100.0, 93.0, 62.0 PPF 0.5 70.7, ** , 47.5 Tamanna 50 117.0, 73.4, 68.5 ** , 45.9, 45.2 100 90.0, 67.8, 56.8 77.2, ** , 59.1 â¤10 0.3, 0.5 & 3 No Treatment 0.37 50.9 0 Weight Basis of NCA 0, 10, 20, 30, 40 Volume Basis of NFA - PPF 1 kg/m3 100, 96.9, 91.9, 83.7, 70.9 Su 25 98.4, 95.5, 90.4, 81.7, 69.5 50 96.5, 93.3, 89.2, 80.4, 68.4 75 93.9, 91.4, 86.6, 78.2, 66.6 100 90.8, 88.0, 83.5, 75.2, 64.4 4.75-19 0.15-4.75 No Treatment 0.38 32 10 Weight Basis of NCA 0, 5, 10 Volume Basis of NFA - PPF 1 117.2, 104.7, 93.8 Hossain et al. 2 117.2, 109.4, 100 141 30 1 104.8, 103.1, 98.4 2 125.0, 105.0, 93.1 4.75-19 0.15-4.75 No Treatment 0.38 33.97 30 Weight Basis of NCA 0, 5, 10 Volume Basis of NFA - PPF 0.5 108.1, 88.4, 80.9 Shahjalal et al. 4.75-12.5 0.85-1.40 No Treatment 0.35 73.5 100 Weight Basis of NCA 0, 4, 8, 12, 16 Volume Basis of NFA - Steel Fibre 1 72.2, 71.8, 67.8, 61.0, 57.8 Jian-he et al. 4.75-19 0.075-10 20% NaOH Solution (30 Min) 0.31 40 0, 50,100 Weight Basis of NCA 0, 10,20 Volume Basis of NFA 100, 75, 87.5 Steel Tire Wires 0.1 150.0, 80.0, 115.0 Ahmed et al. 19-38 6-12 No Treatment 0.45 34.05 90, 80, 70, 60, 50 Weight Basis of NCA 10, 20, 30, 40, 50 Weight Basis of NCA 90.7, 86.8, 82.8, 78.9, 71.5 Tire Steel Wire Fibres 0.25 84.1, 81.1, 78.0, 73.2, 67.0 Alfayez 0.5 79.9, 76.7, 74.9, 68.5, 61.1 1 76.8, 74.8, 71.7, 67.6, 57.8 4.75-12.5 0.85-1.40 Unheated (25 â°C) 0.35 56.52 100 Volume Basis of NCA 0, 4, 8, 12, 16 Volume Basis of NFA - Steel Fibre 1 91.0, 86.8, 69.7, 66.5, 63.5 Guo et al. 200â°C 77.1, 71.5, 61.1, 56.9, 55.2 400 â°C 50.7, 46.4, 34.8, 31.2, 30.4 600 â°C 19.4, 22.6, 18.1, 14.7, 14.6 5-20 0.85-1.40 Untreated 0.48 45.65 100 Weight Basis of NCA 0, 5, 10, 15, 20 Volume Basis of NFA - Steel Fibre 1 79.1, 74.2, 62.3, 54.2 Xie et al. 5% Silica Fume 88.5, 74.9, 65.1, 59.1, 56.8 10% Silica Fume 104.8, 93.8, 73.6, 69.4, 67.8 Note: RA = Recycled Aggregate; SCA = Silane Coupling Agent; w/c = water/cement; w/b = water/binder; NFA = Natural Fine Aggregate; RRAC = Rubberised Recycled Aggregate Concrete; FRRAC = Fibre Reinforced Rubberised Recycled Aggregate Concrete; PP= Polypropylene; ** = Data not found. 142 Appendix F Summary of modulus of elasticity by different researchers. RA Size (mm) Rubber Size (mm) Treatment Method w/c or w/b ratio Control Mixture MoE (GPa) RRAC FRRAC Reference Recycled Aggregate Rubber Strength Relative to Control (%) Fibre Strength Relative to Control (%) Replacement Level (%) Replacement Type Replacement Level (%) Replacement Type Fibre Type Fibre % (Total Volume) â¤10 0.3, 0.5 & 3 Un-Treated 0.37 25.1 50 Weight Basis of NCA 20 Volume Basis of NFA 88.0 - - - Su NaOH (2hr) 88.8 NaOH (24hr) 89.2 SCA 94.8 â¤ 20 â¤ 3 No Treatment 0.30 35.0 100 Weight Basis of NCA 0, 25, 50 Volume Basis of NFA 92.9, 77.1, 62.9 - - - Henry et al. 4.75-20 4.74-0.08 20% NaOH Solution (30 Min) 0.34 29.6 0 Weight Basis of NCA 0, 10, 20 Volume Basis of NFA 100, 91.9, 79.7 PPF 0.5 98, ** , 93.2 Tamanna 50 119.6, 107.4, 79.1 ** , 66.9, 82.4 100 91.9, 77.7, 83.8 81.1, ** , 70.9 4.75-12.5 0.85-1.40 No Treatment 0.35 55.4 100 Weight Basis of NCA 0, 4, 8, 12, 16 Volume Basis of NFA - Steel Fibre 1 51.6, 51.3, 50.5, 46.9, 43.7 Jian-he et al. 19-38 6-12 No Treatment 0.45 41.01 90, 80, 70, 60, 50 Weight Basis of NCA 10, 20, 30, 40, 50 Weight Basis of NCA 95.8,94.4, 93.1, 84.7, 80.5 Tire Steel Wire Fibres 0.25 92.5, 88.7, 85.4, 77.0, 75.5 Alfayez 0.5 87.8, 81.3, 78.9, 75.5, 67.7 1 79.1, 76.6, 74.5, 73.2, 61.0 4.75-12.5 0.85-1.40 Unheated (25 â°C) 0.35 34.91 100 Volume Basis of NCA 0, 4, 8, 12, 16 Volume Basis of NFA - Steel Fibre 1 76.1, 72.2, 60.9, 59.8, 54.9 Guo et al. 200â°C 38.2, 39.1, 36.7, 33.2, 32.1 400 â°C 15.5, 12.9, 11.4, 10.3, 9.5 600 â°C 2.95, 3.70, 3.18, 2.66, 2.61 5-20 0.85-1.40 Untreated 0.48 46.63 100 Weight Basis of NCA 0, 5, 10, 15, 20 Volume Basis of NFA - Steel Fibre 1 79.8, 77.1, 75.4, 67.4 Xie et al. 5% Silica Fume 90.2, 80.9, 79.0, 76.0, 67.2 10% Silica Fume 84.1, 77.0, 72.3, 67.1, 64.7 143 Appendix G Summary of tensile strength by different researchers. RA Size (mm) Rubber Size (mm) Treatment Method w/c or w/b ratio Control Mixture Strength (MPa) RRAC FRRAC Reference Recycled Aggregate Rubber Strength Relative to Control (%) Fibre Strength Relative to Control (%) Replacement Level (%) Replacement Type Replacement Level (%) Replacement Type Fibre Type Fibre % (Total Volume) 4 10 No Treatment 0.45 3.70 0, 10, 20, 30, 40 Volume Basis of NCA+ NFA 20 Volume Basis of NCA 73.2, 81.6, 74.3, 80.3, 83.0 - - - Aslani et al. 4.75-20 4.74-0.08 20% NaOH Solution (30 Min) 0.34 6.52 0 Weight Basis of NCA 0, 10, 20 Volume Basis of NFA 100, 72.5, 56.9 PPF 0.5 73.3, ** , 50.2 Tamanna 50 69.8, 80.8, 53.7 ** , 52.1, 54.4 100 61.2, 52.6, 70.9 60.9, ** , 51.2 4.75-19 0.15-4.75 No Treatment 0.38 2.52 30 Weight Basis of NCA 0, 5, 10 Volume Basis of NFA - PPF 0.5 102.8, 98.0, 90.9 Shahjalal et al. 4.75-19.0 0.15-4.75 No Treatment 0.38 3.20 10 Weight Basis of NCA 0, 5, 10 Volume Basis of NFA - PPF 1 98.8, 88.1, 87.2 Hossain et al. 2 120.7, 112.5, 90.6 30 1 103.1, 85.9, 78 2 109.4, 93.8, 82.8 4.75-19 0.075-10 20% NaOH Solution (30 Min) 0.31 4.00 0, 50,100 Weight Basis of NCA 0, 10,20 Volume Basis of NFA 100, 75, 61.3 Steel Tire Wires 0.1 112.5, 112.5, 97.5 Ahmed et al. 19-38 6-12 No Treatment 0.45 5.12 90, 80, 70, 60, 50 Weight Basis of NCA 10, 20, 30, 40, 50 Weight Basis of NCA 92.8, 62.9, 57.4, 50.4, 43.8 Tire Steel Wire Fibres 0.25 105.5, 68.0, 64.3, 57.0, 51.6 Alfayez 0.5 108.0, 72.3, 69.3, 63.1, 58.0 1 111.7, 75.8, 71.9, 69.9, 66.4 144 Appendix H Summary of flexural strength of RRAC and FRRAC by different researchers. RA Size (mm) Rubber Size (mm) Treatment Method w/c or w/b ratio Control Mixture Strength (MPa) RRAC FRRAC Reference Recycled Aggregate Rubber Strength Relative to Control (%) Fibre Strength Relative to Control (%) Replacement Level (%) Replacement Level (%) Replacement Type Fibre Type Fibre % (Total Volume) 5-20 & 20-40 0.25 No Treatment 0.38 5.74 100 0, 10, 20,30 Volume Basis of NFA 89.7, 83.6, 78.9, 71.4 - - - Feng et al. 5-10 0.221 No Treatment - 5.25 100 10, 20, 30, 40 Volume Basis of NFA 87.6, 78.1, 73.3, 70.5 - - - Li et al. 0.864 93.3, 85.7, 82.9, 72.4 4.04 94.3, 90.5, 86.7, 77.1 4.75-20 4.74-0.08 20% NaOH Solution (30 Min) 0.34 4.7 0 0, 10, 20 Volume Basis of NFA 100, 91.5, 80.9 - - - Tamanna et al. 50 105.3, 80.9, 80.9 100 101.1, 75.5, 68.1 â¤10 0.3, 0.5 & 3 Un-Treated 0.37 5.1 50 20 Volume Basis of NFA 68.6 - - - Su NaOH (2hr) 72.5 NaOH (24hr) 72.5 SCA 80.4 4.75-19.0 0.15-4.75 No Treatment 0.38 3.52 10 0, 5, 10 Volume Basis of NFA - PPF 1 99.7, 85,2, 83.8 Hossain et al. 2 101.4, 88.6, 86.9 30 1 96.0, 95.2, 94.6 2 108.5, 108.0, 99.1 4.75-12.5 0.85-1.40 No Treatment 0.35 8.5 100 0, 4, 8, 12, 16 Volume Basis of NFA - Steel Fibre 1 91.8, 81.2, 69.4, 71.8, 67.1 Jian-he et al. 4.75-19 0.075-10 20% NaOH Solution (30 Min) 0.31 3.80 0, 50,100 0, 10,20 Volume Basis of NFA 100, 68, 94 Steel Tire Wires 0.1 115.8, 109.7, 89.5 Ahmed et al. 19-38 6-12 No Treatment 0.45 10.61 90, 80, 70, 60, 50 10, 20, 30, 40, 50 Weight Basis of NCA 95.6, 73.0, 67.3, 59.6, 42.0 Tire Steel Wire Fibres 0.25 102.4, 77.9, 74.0, 62.6, 48.3 Alfayez 0.5 108.3, 86.7, 76.0, 65.8, 51.6 1 110.5, 88.2, 82.8, 69.8, 58.6 Note: Replacement of NCA by Recycled Aggregate by weight 145 Appendix I Comprehensive reference table of different research related to RCA Ref # of Nominal Coarse aggregate RCA Rubber Fibre W/C Compressive Strength Fibre Type Tests Size (mm) (%) (%) (%) (MPa) Arezoumandi et al. (2014) 12 25 0â100 None None 0.4 30â37.2 None Gupta et al. (2014) 15 12 None 0â20 None 0.35â0.55 33â59.5 None Youssf et al. (2016) 15 20 None 0â20 None 0.5 35â56.1 None Krishna Rao et al. (2010) 9 20 None None 0â1 0.59â0.75 20.81â37.02 None, Polypropylene Al-quraishi et al. (2021) 8 10 None 0â50 0â1.5 0.36â0.51 25.2â35.3 None, Steel Gupta et al. (2019) 11 12 None 0â25 None 0.45 28.37â50.43 None Thirumurugan and 8 12.5 None None 0â0.3 0.3 39.6â48.4 None, Polypropylene Sivakumar (2013) Wen et al. (2015) 20 37.5 0â45 None None 0.39â0.44 29.92â38.54 None Choi et al. (2010) 24 25 0â100 None None 0.5 22.56â24.66 None Hossain et al., 2023 7 19 0â30 0â10 0â0.5 0.44 25.93â36.71 None, Polypropylene Qian and Piet (2012) 10 16 None None 0â0.95 0.4 68â80.8 None, Steel, Other Shahria Alam et al. (2013) 3 20 0â50 None None 0.4 42.6â50.03 None Sallam et al. 2008 8 14 None 0â30 None 0.34 30â38.44 None Khalil et al. (2019) 5 20 None 0â40 None 0.5625 15â26 None Liu et al. (2013) 4 40 None 0â15 None 0.313 26.9â43.3 None Huda and Shahria Alam 4 20 0â50 None None 0.41 30.4â35.6 None (2015) Khaloo et al. (2008) 9 20 None 0â100 None 0.45 0.37â30.77 None Matias et al. (2013) 14 25.4 0â100 None None 0.51â0.53 48â52 None Hossain et al. (2019) 15 19 0â30 0â10 0â2 0.38 30â40 None, Polypropylene Tamanna et al. (2020) 9 20 0â20 0â100 None 0.34 28â61 None Al-Tayeb et al. (2012) 4 20 None 0â20 None 0.48 29.64â37.15 None Li et al. (1998) 4 12.5 None 0â33 None 0.5 16.5â57.7 None Sukontasukkul and Chaikaew 7 9.525 None 0â20 None 0.33â0.47 5.4â36 None (2006) Topçu and Sengel (2004) 10 31.5 0â100 None None 0.54â0.64 11.9â18.8 None Akça et al. (2015) 12 25 0â55 None 0â1.5 0.53 32.3â53.5 None, Polypropylene Z. A et al. 6 20 0â100 None None 0.43â0.66 31.5â54.8 None Tam and Tam (2008) 6 20 5â30 None None 0.45 52.31â58.98 None Butler et al. (2013) 8 ** 0â100 None None 0.3â0.64 38.1â62.8 None Ait Mohamed Amer et al. 34 10 0â100 None None 0.4â0.6 29.53â56.98 None Ref # of Nominal Coarse aggregate RCA Rubber Fibre W/C Compressive Strength Fibre Type 146 Tests Size (mm) (%) (%) (%) (MPa) (2016) Khatib (2005) 9 20 0â100 None None 0.5 30â46.7 None Go´mez-Sobero´n 6 20 0â100 None None 0.44â0.52 34.5â39 None Xiao et al. (2005) 5 31.5 0â100 None None 0.43 23.8â236 None Rahal (2007) 10 19 0â100 None None 0.4â0.65 20.3â53.5 None Gao et al. (2017) 10 20 0â100 None 0â2 0.31â0.54 28.8â44.2 None, Steel Kurda et al. (2017) 19 22.4 0â100 None None 0.36â0.64 22â74 None Poon et al. (2004) 12 20 0â100 None None 0.58â0.77 38.1â48.3 None Kou et al. 24 20 0â100 None None 0.45â0.55 25.2â66.8 None Afroughsabet et al. (2017) 20 19 0â100 None 0â1 0.3 75.6â97.8 None, Steel Etxeberria et al. (2007) 14 25 0â100 None None 0.4â0.55 28â60 None Katkhuda and Shatarat 18 20 0â20 None 0â1.5 0.66 21.3â23.9 None, Other (2017) Pedro et al. (2017) 6 22.4 0â100 None None 0.37â0.4 66.22â82.86 None Ling et al. (2009) 21 10 None 5â40 None 0.45â0.55 10.47â35.81 None Schubert et al. (2012) 8 25â32 0â100 None None 0.39â0.59 25.12â38.36 None Mohammed et al. (2015) 72 25 0â100 None None 0.45â0.55 14.28â31.44 None Ganjian et al. (2009) 7 25 None 0â10 None 0.5 20.12â33.18 None Ashour et al. 18 10 None None 0.5â1.5 0.25 92â101.32 Steel Liu et al. (2020) 10 31.5 0â100 None None 0.43 28.03â45.45 None Dinh (2009) 16 9.525 None None 0â1.5 0.39â0.48 28.76â50.83 None, Steel Chaboki et al. (2019) 9 40 0â100 None 0â2 0.4125 35â37.4 None, Steel Jr and Hana (1997) 7 ** None None 0â2 0.45 43.8â54.8 None, Polypropylene, Ismail and Hassan (2017) 12 10 None 0â35 0â1 0.4 29.73â65.61 Steel None, Steel Marinkovic et al. (2017) 3 31.5 0â100 None None 0.58â0.6 24.5â28 None Rahal and Alrefaei (2017) 13 19 0â100 None None 0.5â0.54 31â39 None Mohammed et al. (2019) 4 25 0â100 None None 0.5 23.7â28.7 None Ceia et al. (2016) 4 22.4 0â100 None None 0.52 42.7â50 None Majdzadeh et al. (2006) 24 10 None None 0â1.5 0.6 37.8â47.1 None, Steel, Other Sharma, 1986 7 ** None None 0â3 0.45â0.49 42.3â48.6 None, Steel Mirsayah and Banthia 11 19 None None 0â2 0.49 46.6â47.53 None, Steel Adebar et al. 8 14 None None 0â1.5 ** 40.8â60 None, Steel Tan and Mansur (1991) 18 10 None None 0â1.5 0.6 23.6â33.2 None, Steel Son et al. (2011) 6 25 None 0â5.4 None 0.5â0.54 19â27.9 None Thomas et al. (2014) 27 20 None 0â20 None 0.4â0.5 17â42.5 None Ref # of Nominal Coarse aggregate RCA Rubber Fibre W/C Compressive Strength Fibre Type 147 Tests Size (mm) (%) (%) (%) (MPa) Song et al. (2005) 3 25.4 None None 0â0.027 0.65 23.02â25.88 None, Polypropylene, Ramujee (2015) 5 ** None None 0â2 0.5 33.7â45.25 Other None, Polypropylene Nili and Afroughsabet (2010) 16 19 None None 0â0.5 0.36â0.46 41.3â66.33 None, Polypropylene Karahan and Atis ¸(2011) 12 16 None None 0â0.2 0.35 42.4â64.9 None, Polypropylene Limbachiya et al. (2000) 12 20 0â100 None None 0.29â0.45 49.58â71.19 None Xu et al. (2018) 15 10 None 0â60 None 0.35 6.6â72.9 None Murahari (2013) 36 20 None None 0.15â0.3 0.35â0.5 22.23â77.63 Polypropylene Zhang et al. 10 8â10 None None 0â1 0.34â0.58 42.6â86.6 None, Steel Gencel et al. (2011) 10 15 None None 0â3.43 0.4 36.41â62.93 None, Polypropylene Hossain et al., 2023 15 19 0â50 0â10 0â1 0.38 26.6â41.9 None, Polypropylene Project 12 19 0â50 0â10 None 0.38 19.37â34.81 None
Thesis/Dissertation
eng
Civil Engineering
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Alam, M. Shahria
Mechanical and structural behaviour of rubberised recycled aggregate concrete
Text