Stress strain performance of steel spiral confined recycled aggregate concrete

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). The stress strain performance of steel spiral confined concrete specimens with different confinement pressure, recycled aggregates (RA) replacement ratio and target strength is studied. The results show a decrease in compressive strength of concrete with the rise in RA replacement ratio. Around 43, 37 and 33% drop in the strength is observed for 100% RA replacement ratio having different target strengths of NAC (i.e., 25, 40 and 60 MPa). However, steel confinement has a positive role to offset the negative effect of RA on strength. The rise in the confinement pressure results in improved ductility and stress strain behaviour of RAC. 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 and RAC, which provides guidelines for the design of RAC members. Furthermore, a relationship is also developed to determine the allowable content of RA for given confinement without affecting the concrete strength, which may be used to decide the allowable content of RA in designing the RAC compression members.