Physical and mechanical properties of recycled aggregates modified by microbially induced calcium carbonate precipitation

Microbially induced calcium carbonate precipitation (MICP) technology has a great potential for improving the engineering properties of recycled aggregates, but the major limitation is the inhomogeneous distribution of calcium carbonate precipitation resulting in the nonuniform modification of recycled aggregates. This paper proposed a spraying method to equally distribute the calcium carbonate, and discussed the influence of the new treatment on the physical and mechanical properties of the MICP modified recycled aggregates. The results showed that the water absorption of the coarse, medium and fine aggregates after seven cycles of treatment was greatly reduced by 58%, 26% and 46%, respectively. The shear strength, crushing value and California bearing ratio (CBR) were increased by the treatments, while the improvement was limited by the strength of the generated calcium carbonate precipitation. A significant decrease in the porosity and total pore volume was found after treatments, and the cubic and spherical calcium carbonate crystals were generated on the surface of the recycled aggregates. This indicated that the improvement of the physical and mechanical properties of the recycled aggregates was mainly attributed to the generated calcium carbonate filling the pores and reinforcing the surface. The MICP technology facilitates the high-value utilization of the recycled aggregates in pavement engineering.