Abstract
Both construction and demolition (C&D) activity and the production of concrete rely on huge amounts of natural sand and gravel. The use of Recycled Aggregate Concrete (RAC) with Recycled Aggregate (RA) from C&D waste could provide a pathway to addressing both pressures simultaneously. This review gathers and aggregates the latest scientific studies (2020-2026) published in the four fields of RAC: mechanical, durability, microstructural and environmental performance aspects. In general, the RAC has lower compressive strength, tensile strength, flexural strength, and bond strength than natural aggregate concrete (NAC), and this strength decrease becomes larger as the RAC replacement ratio rises, as indicated in many studies; about 20-30 percent replacement is considered a practical optimum level between strength retention and utilization of waste, in many reviews. The main reason for this lack is the interfacial transition zone (ITZ) that is present around recycled particles that is more porous and prone to crack because of the presence of the old mortar adhered to it. Also, permeability to chloride, sulfate ions and carbonates can differ, with RAC generally being slightly more permeable than NAC, although treatments of the aggregates like carbonation curing, nano-silica impregnation, and mechanical pre-treatment can significantly reduce the differences. Life-cycle assessment (LCA) studies have always shown that recycled aggregate generates significantly less (typically 50 to 65 percent less) greenhouse gas and requires significantly less (typically 50 to 65 percent less) non-renewable energy than quarrying virgin aggregate, depending on the transport distance and processing method. Limited use of RCA is now incorporated into regulations like BS8500-2, RILEM recommendations, ACI guidance, and a number of national standards, which are conservative, and harmonized quality-classification systems are still being worked out. The review concludes that RAC is a technically possible and environmentally acceptable material at moderate replacement rates, depending on the quality of the aggregates used and the correct treatment or mix-design compensation if necessary.