Characteristics of the carbonation resistance of recycled fine aggregate concrete

•Effect of RFA on the carbonation resistance of RFAC.•Fly ash addition favors the carbonation resistance of RFAC, especially at 20% cement replacement ratio.•The microstructure of RAF and RFAC.•The self-cementing ability of RFA was analyzed. This study investigates the effects of the minimum recycled fine aggregate (RFA) particle size, RFA amount, and fly ash addition on the carbonation resistance of RFA concrete (RFAC). The results reveal that the carbonation depth of RFAC increases with decreased minimum RFA particle size and increased RFA amount. At >40% RFA amount, water significantly affects RFAC carbonation. Fly ash addition favors the carbonation resistance of RFAC, especially at 20% cement replacement ratio. In this study, the self-cementing ability of RFA is proved by the microstructural analyses of RFA and RFAC but is found to have a negligible effect on RFAC carbonation for a few carbonizable hydrated products. The poor microstructure of RFAC and the interfacial zone between the new cement paste and RFA result in easier CO2 ingression for RFAC.