Characterizations and quantification of freeze-thaw behaviors of recycled brick aggregate concrete

The use of recycled brick aggregates (RBAs) in concrete could provide sustainable solution in construction industry by reducing the consumption of natural resources and protecting the environment by saving landfill sites. However, the use of RBAs is uncommon due to limited available research studies investigating its mechanical and durability behavior, especially the freeze-thaw (FT) behavior. Despite a few studies on FT resistance of RBA concrete (RBAC), the FT deterioration mechanism in RBAC is not fully understood, particularly at the microscale. This lack of understanding hinders the widespread adoption of RBAC in sustainable construction practices, particularly in cold regions. Therefore, this study investigates the FT deterioration mechanism in RBAC using macro and microscale experiments and proposes a Weibull damage model to accurately describe the damage variation in RBAC. RBAC specimens with different water-cement (w/c) ratios of 0.65, 0.5 and 0.35 and RBA replacement levels of 0%, 25%, 50% and 100% were produced and tested under rapid FT cycles. Surface scaling, mass loss, relative dynamic modulus of elasticity, and compressive strength reduction were evaluated. X-ray computed tomography (XCT) was used to characterize pore structure and microcracking alterations during FT cycles. The results showed that the deterioration of RBAC increased with the increase in RBA replacement level. XCT revealed increased porosity and microcracking within the RBA particles, which was linked to the significant damage observed in RBAC compared to reference concrete. Quantitative analysis of pore size distribution before and after FT cycling revealed a substantial increase in small pores (<1 mm(3)) in RBAC. The proposed Weibull distribution damage model accurately described the damage variation in RBAC with different w/c ratios. This study provides new insights into multiscale FT deterioration mechanisms affecting RBAC, aiding in optimizing RBAC mix designs to balance sustainability and durability.