Experimental Study on Compressive Behavior and Constitutive Modeling of CFRP-Confined Recycled Aggregate Concrete with Initial Damage

This study investigates the axial compressive behavior of initially damaged recycled aggregate concrete (RAC) prisms confined with carbon fiber-reinforced polymer (CFRP). Monotonic compression tests evaluated the effects of the recycled aggregate replacement ratio, concrete strength, initial damage level, and the number of CFRP layers. Results indicate that CFRP confinement significantly enhances RAC load-bearing and deformation capacities. Conversely, increasing the replacement ratio reduces compressive strength, particularly in high-strength concrete. Initial damage negatively impacts axial performance by primarily reducing the turning point strength, an effect not fully mitigated by additional CFRP layers. Furthermore, a constitutive stress–strain model incorporating a damage evolution parameter was developed for 30 to 60 MPa structural-grade RAC. Although precise ultimate strain prediction remains intrinsically challenging due to stochastic premature CFRP rupture at square corners, the proposed model reasonably captures primary mechanical trends, providing an acceptable theoretical basis for structural rehabilitation.