Effect of nano-calcium carbonate on resistance to calcium leaching and chloride penetration in recycled concrete

Recycled aggregate concrete (RAC) is an important material for promoting sustainable development in the construction industry. However, due to the inherent performance defects of recycled concrete aggregates, RAC often exhibits inferior mechanical and durability properties compared to conventional concrete. The effects of nano-CaCO3 (NC) on the resistance of RAC to calcium leaching and chloride penetration were evaluated in this study. The results indicate that the resistance of RAC to both calcium leaching and chloride penetration initially increases and then decreases with increasing NC content (0.0%∼2.0%), with the optimal NC content being 1.0%. For the recycled concrete with 1.0% NC, the leaching depth at 56 days and the apparent chloride diffusion coefficient at 60 days were reduced by 37.50% and 14.91%, respectively, compared to the control group. In addition, the strong correlation between ultrasonic pulse velocity (UPV) and compressive strength confirms that UPV can serve as a reliable non-destructive indicator for evaluating the mechanical properties of recycled concrete subjected to calcium leaching. The above research findings contribute to the improvement of the performance of recycled concrete and the expansion of its application in water-exposed concrete structures.