Enhancement mechanism of different recycled fine aggregates by microbial induced carbonate precipitation

The high water absorption and low strength of recycled fine aggregates limit its resource utilization in building materials. Microbial induced calcium carbonate precipitation (MICP) is an environmentally friendly method to improve recycled fine aggregates. However, the precipitation efficiency of MICP is also affected by the characteristics of various recycled fine aggregates, such as pH environment and pore structure. In this study, the effects of MICP on the properties of three recycled fine aggregates were studied, and enhancement mechanism was analyzed. The results show that the performance of biological calcium carbonate can effectively improve the performance of recycled aggregates. A large amount of calcium carbonate formed on the surface and some calcium carbonate formed in pores larger than 0.2 μm inside are the keys to enhance the performance of recycled aggregates. The modification effect on RBA was the best, that on RCA was next, while that on RMA was the worst. The crystal forms of calcium carbonate were different due to the pH environment in various recycled aggregates. A low pH environment is beneficial for the formation of Vaterite calcium carbonate, while high pH favors rhombic calcite.