Recycled concrete aggregates: Performance, enhancement strategies, and circular construction pathways

The broad utilization of recycled concrete aggregates (RCA) in structural construction is limited by the variability in mechanical properties, high processing costs, and disjointed regulations in various regions, such as Southeast Asia. Generally, the use of RCA leads to a reduction of compressive strength from 10 to 25%, while the reduction of elastic modulus ranges from 10 to 45% compared to natural aggregates due to an insufficient interface transition zone and residual mortar. In terms of various treatments, CO 2 carbonation and mechanical abrasion are the most economically feasible options that guarantee the recovery of 15–25% of the lost mechanical properties without high equipment requirements. Additionally, the inclusion of RCA into the geopolymer matrix from local sources results in the structural compressive strength increasing from 35 to 52 MPa at a 50% replacement level. In order to solve the mentioned issues, the current paper investigates the literature regarding the mechanical behaviour, methods of enhancement, and circular economy in relation to recycled aggregate concrete. Based on the synthesized evidence, a three-stage performance-based pathway is proposed for RCA integration, ranging from untreated RCA in non-structural applications to conditionally treated RCA in conventional structural concrete and pre-treated RCA in structural geopolymer concrete, with application decisions governed by mechanical and durability performance criteria and aligned with ISO/TS 21056:2025.