Effectiveness of FRP confinement for low strength recycled aggregate concrete compressive members having optimized combination of fibers

The quantity of recycled concrete aggregates is increasing day by day due to the enhanced demolition rate of old infrastructures, which is dangerous to the environment's sustainability. Therefore, it is essential to handle these recycled aggregates for sustainable development. Furthermore, due to the low compressive strength (COS) of recycled aggregate concrete (RAC), it has always remained an active research area to ameliorate the mechanical performance of such concrete by either adding fibers and/or laterally confining with carbon fiber reinforced polymer (carbon-FRP) wraps. The main objective of the current investigation is to improve the strength of hybrid fiber-reinforced recycled aggregate concrete (HFRAC) transversely wrapped with carbon-FRP wraps. The axial COS, axial strain, and compressive stress-strain graphs of the tested samples were assessed by manufacturing a total sum of 18 cylindrical samples wrapped with either one or two carbon-FRP wraps. Two different grades of HFRAC were fabricated that is, 15 and 20 MPa containing hybrid fibers (steel and polypropylene fibers). The results showed that the transverse wrapping effectively ameliorated the axial strain, COS, and axial stiffness of HFRAC samples. By using a single layer of carbon-FRP wraps, an enhancement of 115.7% was observed while using two layers of carbon-FRP wraps, an enhancement of 130.7% was observed in the COS of 15 MPa group HFRAC samples. Similarly, by using a single layer of carbon-FRP wraps, an enhancement of 37.4% occurred while using two layers of carbon-FRP wraps, an enhancement of 112.6% occurred in the COS of 20 MPa group HFRAC samples. Hence, the lateral wrapping of low-strength HFRAC is more efficient than the high-strength HFRAC. A theoretical investigation based on the analysis of 11 different models was also performed to predict the COS of carbon-FRP-wrapped HFRAC samples.