The effects of using crushed waste concrete as coarse aggregates upon fresh and hardened properties of concrete were investigated through series of testing concrete cylinder specimens to failure. The coarse recycled concrete aggregate (RCA) used in this investigation was sourced from the tested concrete specimens like cubes, cylinders, prisms and beam specimens originally tested for various purposes in the concrete testing laboratory of IIT Roorkee. Total six numbers of concrete mixtures were prepared. These mixtures were differing only in amount of coarse RCA used. The mixture without any RCA was referred as control mixture. Considerable effect of replacement level on compressive strength was observed. Moreover increase in peak strain and significant decrease in static modulus was observed. Stress-strain curves generated during testing were utilized to evaluate normalized toughness and ductility index. Higher value of replacement level found decreasing normalized toughness and ductility index.

The experimentally observed behaviour of normal-strength recycled aggregate concrete made with varying amounts of coarse recycled concrete aggregate (RCA) in uniaxial compression was modelled using a single polynomial-based equation valid for both the ascending as well as the descending branches of the stress–strain relationship. The measured stress–strain relationships of companion cylindrical specimens were averaged using a simple procedure that was found to be effective. The proposed constitutive model reflected the experimental trend that, although the strain at peak stress increased with an increase in the replacement level of coarse RCA, the ultimate strain was not affected significantly whereas the compressive strength and the static modulus decreased. The predictions of the proposed model were found to be in good agreement with experimental results reported in the literature.

There is a growing demand of suitable substitute materials of concrete ingredients especially fine and coarse aggregates in order to achieve sustainable development in the era of rapid urbanisation. Therefore, the concrete making process by utilisation of aggregates that recycled from construction and demolition (C&D) debris has emerged as a primary objective for many government agencies. Consequently, the utilisation of recycled aggregate concrete (RAC) in structural applications become essential aspect. However, RAC can be employed in structural applications only if effective stress-strain relationship is available. The stress-strain models developed for natural aggregate concrete (NAC) are not fully suitable for RAC. Hence, the selection of good model which has precise prediction capacity plays a crucial role. Moreover, the stress-strain models provide the basis for the analysis and modern design procedures especially in FEA packages. In the present study, the stress-strain models for RAC have been selected from the literature and critically reviewed in order to evaluate their predictive efficacy. The test samples in the form of measured stress-strain relations-hips derived from literature have been compared with the predictions of each selected model. Besides the comparison of measured and predicted stress-strain profiles, the output of selected models in terms of normalized toughness and ductility index was assessed. The consistency of output of models are further evaluated by employing statistical tools such as coefficient of variance and root mean square error. The outcomes of the model in the form of polynomial expression was relatively more accurate to that of other counterparts.

This study presents the ATENA-3D simulation of natural aggregate concrete (NAC) and recycled aggregate concrete (RAC) beams subjected to pure torsion and the beam was validated by the experimental results with corresponding outputs. All the test specimens were 150 mm wide, 250 mm, deep and 1800 mm long. The natural coarse aggregate (NCA) were replaced by coarse recycled concrete aggregate (RCA) at three replacement ratios of 0 %, 50 %, and 100 % to prepare concrete. All the beam specimens were simulated and tested to assess the parameters like torque, twist, crack pattern, stiffness, and toughness in pure torsion. The comparison of ATENA-3D and experimental results showed that torque resistance capacity, stiffness, and toughness of beams decreased as the % of RCA increased in the concrete. A similar torque-twist curve pattern was observed in simulation and experimental studies. All the specimens failed due to torsional cracking. The torsional capacity of the beams in ATENA-3D software was higher by 9.80 %, 10.67 %, and 12.80 % than the experimental results. The results reveal that varying the quantity of RCA in RAC does not compromise the pure torsional behavior of the beam in both methods. Also, it can be concluded that the use of RCA in RAC is acceptable for structural concrete beams in pure torsion.

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