Performance of recycled aggregates subjected to pre-soaking, mechanical crushing, and carbonation processes

The use of recycled aggregates (RA) derived from construction and demolition waste (CDW) offers a viable alternative to natural aggregates (NA), with potential to reduce reliance on virgin resources. However, the effective utilization of RA requires integrated process design to mitigate the adverse effects of adhered mortar and interfacial heterogeneity. This study proposes an integrated multi-stage treatment framework for RA, combining mild chemical pre-soaking, controlled mechanical abrasion, and pressurized carbonation, with emphasis on process sequencing and threshold-based optimization. Raw RA was soaked in a mild acetic acid solution for 24 h, mechanically processed using a Los Angeles abrasion test machine (LAATM) at rotation levels ranging from 0 to 600, and subsequently subjected to 2 h of pressurized carbonation. The resulting combinedly treated recycled aggregates (CTRAs) were incorporated into M40-grade concrete at replacement levels of 0%, 20%, 40%, 60%, 80%, and 100%. Mechanical performance was evaluated through compressive and splitting tensile strength tests. The results indicate the existence of a critical mechanical processing window at approximately 500 LAATM rotations, beyond which further processing provides diminishing benefits. Concrete incorporating 60% CTRA processed at 500 rotations exhibited a reduction of 17.34% in compressive strength and approximately 16% in splitting tensile strength relative to natural aggregate concrete, while maintaining stable performance trends within the investigated scope. These findings demonstrate that coordinated treatment sequencing and processing intensity, rather than isolated treatment steps, govern the mechanical response of recycled aggregate concrete, supporting a concurrent engineering approach to recycled aggregate system design.