Axial compressive performance of sustainable BFRP-confined rectangular columns using recycled brick aggregates

This study examines the mechanical behavior of basalt FRP confined rectangular concrete columns using crushed brick aggregates, addressing a research gap. While previous work focused on circular and square columns, this is the first to explore rectangular ones. The use of waste brick aggregates promotes sustainability. The study aims to assess the mechanical properties, expecting improvements in strength and ductility, and could lead to broader applications of basalt FRP. A total of 32 rectangular specimens were tested to evaluate the influence of aggregate type, concrete grade, and number of BFRP layers (0, 2, 4, and 6) on axial compressive performance. Results showed that BFRP confinement significantly enhanced strength and ductility, with maximum gains of 81% in strength and 230% in strain observed in low-strength natural aggregate concrete. Although recycled brick aggregate concrete (RBAC) exhibited lower stiffness, BFRP still provided up to 23% strength improvement. The effectiveness of confinement reduced with increasing unconfined strength. Post-peak analysis revealed that additional BFRP layers delayed stiffness degradation, promoting more ductile failure. Experimental elastic modulus closely matched ACI predictions in natural aggregate (NA) specimens but was overestimated in RBAC due to its higher porosity. The findings demonstrate the viability of BFRP confinement for enhancing the structural performance of sustainable concrete, while emphasizing the need for aggregate-specific design considerations. Design-oriented modelling was adopted to predict the complete stress-strain response of BFRP-confined concrete incorporating both natural and recycled brick coarse aggregates. A two-branch idealization of the compressive response was performed. Several key points were identified and predicted by using nonlinear regression analysis. The proposed approach closely predicted the response of BFRP-confined concrete.