Synergetic effect of fly ash and ground-granulated blast slag on improving the chloride permeability and freeze–thaw resistance of recycled aggregate concrete

•Synergetic effects of FA and GGBS on enhancing the durability of RAC are analysed.•The combined addition of FA and GGBS is better than single addition of FA or GGBS.•Simultaneously incorporating FA and GGBS exists an optimum ratio to replace cement.•The combined addition of 15% FA and 15% GGBS effectively enhances the properties of RAC. In this study, the synergetic effects of fly ash (FA) and ground-granulated blast slag (GGBS) on the compressive behavior and durability of recycled aggregate concrete (RAC) were comprehensively investigated. FA and GGBS were incorporated separately or simultaneously into the RAC containing 0%, 35%, and 50% recycled coarse aggregate (RCA) to replace partial cement. Moreover, the frost resistance and chloride penetration resistance of RAC, respectively, were experimentally determined by the rapid freeze–thaw cycle test and rapid chloride permeability test (RCPT). Results showed that an optimum replacement ratio could exist for improving the properties of RAC by partially replacing cement with FA and GGBS. The optimum ratio of the simultaneous incorporation of FA and GGBS to replace partly cement for improving the 90-day-compressive strength and the chloride penetration resistance of RAC were 10% and 20%, respectively, but for enhancing the frost resistance of RAC were 15% and 15%. In addition, the synergetic effects of simultaneously incorporating FA and GGBS were more effective than the effects of separately incorporating FA or GGBS on enhancing the performance of RAC. When adopting the simultaneous incorporation of 15% FA and 15% GGBS, the 90-day-compressive strength, chloride penetration resistance, and frost resistance of RAC incorporating 50% RCA were better than those of ordinary concrete.