Behaviour of recycled brick aggregate concrete-filled FRP tubes under axial compression

Recycled brick aggregates (RBAs) from construction waste present a sustainable alternative to natural aggregates (NAs) in concrete; however, recycled brick aggregate concrete (RBAC) typically exhibits lower stiffness and strength compared to normal concrete (NC). This study investigates the axial compression behaviour of RBAC-filled fibre-reinforced polymer (FRP) tubes (RBACFFTs) to evaluate the contribution of FRP confinement in improving mechanical performance. A total of 70 cylinders were tested to examine the effects of RBAs on concrete properties and FRP confinement effectiveness. The test results indicate that the incorporation of RBAs alters crack propagation patterns and compromises mechanical properties, while this reduction can be effectively mitigated by restricting the replacement ratio. FRP confinement significantly enhances both the load-bearing capacity and deformability of RBAC. However, the confinement effectiveness progressively diminishes as the replacement ratio increases. Within the tested diameter range (up to 300 mm), neither RBAC nor RBACFFTs exhibited notable size effect, thus eliminating the need for size correction factors in analytical models. The confinement effectiveness coefficient in Jiang and Teng’s model was modified to account for the effect of the RBA replacement ratio. The revised model accurately predicts the stress–strain responses of RBACFFTs. • 70 FRP-confined recycled brick aggregate concrete (RBAC) cylinders tested. • RBA alters crack mode and reduces concrete strength and stiffness. • FRP confinement improves strength and ductility of RBAC. • No size effect observed for specimen diameters up to 300 mm. • A modified model shows good predictive capability for RBAC-filled FRP tubes.