Efficiencies of carbonation and nano silica treatment methods in enhancing the performance of recycled aggregate concrete

•Effects of five recycled aggregate treatments on properties of RAC were compared.•Pressurized carbonation (PC) had higher efficiency than flowthrough/wet carbonation.•Nano silica (NS) spraying had larger increase in strength than carbonation methods.•Combined PC and NS spraying (PCNS) method caused highest enhancements.•PC and NS spraying method had synergistic effect in enhancing performance of RAC. This study compared the efficiencies of five recycled aggregate treatment methods (pressurized gas–solid carbonation (PC), flow-through gas–solid carbonation (FC), wet carbonation (WC), nano-silica (NS) spraying and combined PC with NS spraying (PCNS)) in enhancing the performance of recycled aggregate concrete (RAC). Mechanical properties, durability and microhardness of RACs were evaluated. The results showed that PC method recorded higher enhancing efficiency than both FC and WC method. NS spraying method caused higher improvement in mechanical properties of RAC than three carbonation methods. Because of the synergistic effect of enhanced old mortar and new ITZ, PCNS method recorded the highest efficiency.