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An effective compliance matrix Č is proposed to model the behavior of concrete based on phenomenological evidence and physical insight. Three parameters α, β, and γ are introduced in the effective compliance matrix Č. α and β are introduced to model the different behavior of concrete in tension and compression, while the third parameter γ is introduced to account for volumetric change. The predictive capability of the proposed elasto-damage model for uniaxial and multiaxial stress paths is investigated for uniaxial compression, biaxial compression, triaxial compression, uniaxial tension, and tension—compression— compression. The simulative capability of the model to capture the phenomenological behavior of concrete such as strain softening, stiffness degradation, biaxial strength envelope, volumetric dilatation, different behavior in tension and compression, and gain in strength under increasing confinement is reflected. The predicted results correlate well with the available experimental data.

The investigation herein focuses on studying the possibility of using recycled concrete aggregates in structural concrete. The study aims in investigating the uniaxial compressive, tensile and flexural strength of recycled aggregate concrete and behaviour of reinforced RAC beams by assessing several important aspects which may influence its behaviour. These aspects include the replacement percentage of recycled aggregates used in concrete and water to cement ratio. Concrete made with recycled concrete aggregates having replacement percentage of 0%, 30% 50%, 70% and 100% was used and were tested at 28 days curing. In general, it was found that increasing percentage of the recycled aggregates resulted in decrease in the concrete compressive, tensile and flexural strengths. However, the use of RAC as structural concrete can be justified by optimizing the replacement percentage of recycled concrete aggregates and water to cement ratio to get the desirable behaviour of reinforced concrete structures.

This study assesses the behaviour of self-compacting geopolymer concrete (SCGC) with and without recycled concrete aggregates (RCA) by studying the rheological, mechanical and durability properties and comparison with self-compacting concrete (SCC). The idea of using RCA in geopolymer is to attain sustainable development goals, i.e., with less carbon footprint and the use of waste materials such as fly ash and RCA. Two types of concretes were prepared, namely “self-compacting concrete (SCC)” and “self-compacting geopolymer concrete (SCGC)”. Using each concrete type, two design mixes were prepared. The first mix contained 100% natural coarse aggregates (NCA), whereas, in the second mix, 30% NCA were replaced with RCA. The result of rheological properties indicated that the viscosity, passing ability, and segregation results of SCC and SCGC mixes were higher when NCA was partially replaced with RCA. Results of mechanical properties indicated that the increase in the compressive strength of the control mix of SCC (denoted as SCC-30) and SCGC mix (denoted as SCGC-0) at 28 days was 38.3% and 33.1% higher than those containing 30% RCA (denoted as SCC-30 and SCGC-30), respectively. The percentage increase in the compressive strength of SCC-0 and SCC-30 mixes was 20.24% and 13.45% higher compared to SCGC-0 and SCGC-30 mixes. The increase in the split tensile strength of SCC-0 and SCC-30 mixes was 9% and 21.74% higher than SCGC-0 and SCGC-30 mixes. The split tensile strength of control mixes SCC-0 and SCGC-0 is 47.73% and 55% higher than SCC-30 and SCGC-30 at 28 days, respectively. Durability performance of SCC and SCGC mixes was investigated by performing hydraulic permeability, accelerated carbonation, half-cell potential and pull-out tests at 28, 90, 180, 365, and 720 days, and were found inferior for SCGC mixes. The water penetration depth of SCGC-0 and SCGC-30 mixes was 5.71% to 16.1% and 10% to 18.6% higher than SCC-0 and SCC-30 mixes at 28 to 720 days. The carbonation depth in SCGC-0 and SCGC-30 mixes was 8.11% to 20.83% and 7.89% to 13.73% higher than SCC-0 and SCC-30 mixes at 28 to 720 days. The half-cell potential difference results for SCGC-0 and SCGC-30 mixes were 27.5% to 50% and 8.3% to 16.41% higher than SCC-0 and SCC-30 mixes at 28 to 720 days. The pull-out strength of SCC-0 and SCC-30 mixes was 11.36% to 29.5% and 8.3% to 38.97% higher than SCGC-0 and SCGC-30 mixes at 28 to 720 days, respectively. Overall, the mechanical and durability properties of SCC mixes were better than SCGC at the same exposure period.

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