Stress-strain behavior of spirally confined recycled aggregate concrete: An approach towards sustainable design

Application of recycled aggregate concrete (RAC) in the concrete structures is very limited due to inferior performance. Moreover, design of concrete structures ignores the role of transverse reinforcement in the strength enhancement of compression members. This study aims to utilize pre-existing transverse reinforcement to improve the performance of RAC. For this purpose, spirally confined concrete specimens were examined under axial compression, with the variation of three recycled aggregates (RA) replacement ratios (i.e., 0, 50 and 100%) and three pitches of spiral reinforcement (i.e., 20, 30 and 40 mm). The results show that increase of RA will cause a reduction of peak strength and peak strain. However, improved strength and ductility of RAC are observed with the increase in confinement pressure. A comparative study of the existing models for stress-strain behavior of steel confined normal aggregate concrete (NAC) with the test results indicates that the stress-strain characteristics of steel confined RAC cannot be well predicted using these existing models. Based on the test results, a model is developed in this work by modifying the parameters of best performing stress-strain model for steel confined NAC to incorporate the influence of RA replacement ratio. The proposed model can estimate the stress-strain characteristics of both NAC and RAC confined by steel spiral, which may be helpful in designing the sustainable RAC compression members. Moreover, an equation is presented to estimate the amount of RA for the given confinement level which can be recycled without compromising the design strength of spirally confined concrete compression members