Active–passive confinement interaction and stress−strain model of prestressed FRP-confined recycled aggregate concrete

Recycled aggregate concrete (RAC) offers significant environmental benefits, yet its inferior mechanical properties limit its widespread structural application. To enhance its performance, this study investigates the compressive behavior of RAC confined by prestressed fiber-reinforced polymer (FRP), wherein both active and passive confinement effects are activated during loading. A total of 33 prestressed FRP-confined RAC cylinders were tested to evaluate the influences of aggregate size, normalized pre-confining stress, and FRP confinement stiffness. The results show that prestressing effectively suppresses crack development at early loading stages, leading to improved transition strength, while FRP stiffness dominates the enhancement of ultimate strength and deformation capacity. Aggregate size governs the dilation activation mechanism and significantly affects confinement efficiency. Based on the experimental observations, modified formulations for predicting the transition point and ultimate condition were proposed by incorporating the geometric effect of aggregate size and the stress-path effect of prestress. A continuous stress–strain model suitable for prestressed FRP-confined RAC was then developed. Comparisons between model predictions and test data demonstrate well agreement, confirming the accuracy and applicability of the proposed model for FRP confined RAC subjected to combined active–passive confinement. This study meanwhile offers theoretical support for promoting structural-scale utilization of recycled aggregates in sustainable construction.