Uniaxial Compression Constitutive Behavior of Mixed Recycled Brick-Aggregate Concrete After Carbonation

Mixed recycled brick-aggregate concrete (MRBAC), produced by substituting natural coarse aggregates with crushed waste bricks and waste concrete, serves as a promising approach for the resource utilization of construction solid waste and boasts broad engineering application prospects. At present, few studies have established uniaxial compressive constitutive models for MRBAC after accelerated carbonation, which restricts its structural application. In this study, 16 groups of specimens were fabricated with four replacement ratios of recycled brick aggregate (RBA)—0%, 10%, 20%, and 30%—as well as four accelerated carbonation durations—0 d, 40 d, 80 d, and 120 d. Accelerated carbonation tests were carried out to measure carbonation depth, cubic compressive strength, elastic modulus, and uniaxial compressive constitutive curves of MRBAC. Test results show that full 120-day carbonation increases cubic compressive strength and elastic modulus of MRBAC by 16.07–32.13% and 28.3–50.1%, respectively. Carbonation depth imposes a stronger effect on peak stress than RBA content, whereas strength-growth rate decreases with carbonation progress. Peak strain decreases with increasing carbonation depth but rises with higher RBA replacement ratios, and RBA addition improves concrete ductility. Based on experimental data, a constitutive model for MRBAC is proposed, which simultaneously accounts for the coupled effects of carbonation depth and RBA replacement ratio. This study provides a theoretical basis for the structural design and popularization of MRBAC under carbonation-service environments.