An investigation on mechanical properties and durability of metakaolin reinforced modified recycled concrete

This study examined the impact of various combinations of metakaolin and 15% fly ash mix (M) on the mechanical properties and durability of recycled fine aggregate concrete (RFAC), aiming to enhance the properties, cost-effectiveness, and sustainability of concrete, while also determining the optimal metakaolin admixture. And the effect of 0%, 30%, 60%, and 90% recycled fine aggregate replaced natural fine aggregate on the compressive strength, splitting tensile strength, flexural strength, and carbonation resistance of RFAC was investigated, and the functional relationship equation of the compressive strength and the model of carbonation depth were established. The results showed that the change rule in mechanical strength and carbonation depth of the recycled concrete with metakaolin were the same as those of the concrete with metakaolin natural aggregate. When metakaolin is mixed in amounts less than 15%, it has a positive effect on the mechanical properties of RFAC, particularly its compressive strength. And the increase in the dosage of metakaolin is obviously advantageous for the improvement of the carbonation resistance of RFAC. Recycled fine aggregates acted negatively on the various properties of concrete and the extent of effect increased with the increase in substitution rate. When 15% fly ash is used as cementitious material, it can be compounded with 15% metakaolin to formulate RFAC with excellent performance, and the recycled fine aggregate can be replaced by 60%.