Performance enhancement of recycled aggregate concrete through spiral confinement

Due to the demolishing of old structures, a large amount of concrete waste is produced every year. Furthermore, the demand for natural coarse aggregates to manufacture concrete is increasing day by day and will be increased to double in the next few years. These natural coarse aggregates are obtained either through crushing natural rocks or through the river bed and thus increasing demand has significant environmental, energy and economic concerns. In the current scenario, the best possible solution is to utilize concrete waste as coarse aggregates (commonly known as recycled aggregates (RA)). After utilizing RA, concrete with inferior properties is produced as compared to concrete with natural coarse aggregates. Therefore, in the present world, the utilization of RA is limited to non-structural applications such as subbase material for roads. Improvement of concrete strength owing to confinement by lateral reinforcement is disregarded in the current concrete design practice. The focus of this study is to use the pre-existing lateral reinforcement to enhance the behaviour of recycled aggregate concrete (RAC). For this purpose, the effect of different variables such as RA replacement ratios, confinement pressures, target strengths and sources of RA on the performance of spirally confined RAC is considered. Stress-strain behaviour of spirally confined RAC is studied considering all these variables. Due to scant research work related to steel spiral confined RAC, existing models cannot estimate the stress strain performance of steel spiral confined RAC effectively. Therefore, a new model is developed in this study, considering a large experimental program. The newly developed model can be effectively used to predict the stress strain performance of both steel spiral confined normal aggregate concrete (NAC) and RAC, which provides guidelines for the design of RAC members. Due to the variation of sources of RA, prediction of the stress-strain behaviour of RAC is a challenging task. In this study, a general stress-strain model is developed that can be applied to steel spiral confined NAC, RAC and treated recycled aggregate concrete (TRAC) regardless of RA sources. Compared with other models that are RA source dependent, the unified model includes one additional variable, the water absorption rate of RA, which effectively quantifies and differentiates the effect of RA source. Moreover, a relationship is provided to calculate the permissible content of RA to achieve the compressive strength of steel spiral confined RAC or TRAC similar to NAC, which may be used to decide the allowable content of RA in designing the RAC compression members.