Synergistic effect of silica fume and hydrated lime on mechanical properties of re-cycled aggregate concrete

To improve the recycling efficiency of waste concrete, this study systematically investigated the effects of silica fume and hydrated lime modifications (both individual and in combination) on the mechanical properties of recycled aggregate concrete (RAC). The triple mixing technique was employed during concrete preparation. Compressive and splitting tensile tests were conducted to evaluate the fundamental mechanical properties of RAC, while scanning electron microscopy (SEM) was used to analyze its microstructural characteristics. The results demonstrated that the individual incorporation of either silica fume or hydrated lime yielded only marginal improvements in compressive strength and splitting tensile strength. In contrast, the composite modification combining both silica fume and hydrated lime significantly enhanced the mechanical performance of RAC. Microscopic analysis further revealed that the composite system substantially improved microstructural compactness and the interfical bonding between aggregates and cement paste. These findings provide valuable insights for the practical application of recycled coarse aggregates, demonstrating that optimized composite modification could effectively enhance the mechanical performance of recycled concrete while advancing sustainable resource utilization in construction.