Experimental and analytical investigations on enhancing compressive stress vs. strain response of square-section recycled brick aggregate concrete by steel clamps

In this study, a novel strengthening method using steel clamps to enhance the compressive stress vs. strain relation of recycled brick aggregate concrete (RBAC) in square sections is introduced. Experimental results demonstrated that steel clamp confinement significantly modified the compressive failure of concrete, transitioning from brittle to ductile failure. The stress vs. strain behavior of steel clamp-confined concrete consists of two branches: an initial ascending part until the peak strength (i.e., the peak compressive stress), followed by a descending branch. The stiffness of the descending part (Z) reduced as the confinement ratio increased (0.021-0.230). Notably, concrete made with natural aggregates (made from natural crushed stones) showed up to 81.2 % and 66.8 % improvement in peak strength for unconfined compressive strengths of 15.4 MPa and 25.8 MPa, respectively. RBAC exhibited up to 65.2 % and 79.1 % improvement in peak strength for RBAC made with fired-clay solid and hollow bricks, respectively, alongside an ultimate strain improvement of 192.9 % and 177.1 %, respectively. Comparatively, circular sections demonstrated superior compressive stress vs. strain relation improvements across all confinement ratios. A unified model was developed using nonlinear regression, incorporating the cross-sectional shape, confinement ratio, and coarse aggregate type, yielding R2 values greater than 0.90 for peak strength, the strain at peak strength, and Z, providing accurate predictions of steel clamp-confined concrete compressive stress vs. strain behavior.