Abstract: The compressive strength and damage evolution of recycled coarse aggregate concrete under the influence of mineralization and precipitation of Bacillus Cohnii were examined via uniaxial compression test and acoustic emission test. The recycled coarse aggregates used in the present test were prepared from waste C30 concrete blocks through crushing and screening (particle size in the range of 20-50 mm), and then soaked in Bacillus Cohnii solutions of different pH values. In subsequence, the recycled coarse aggregates were used for preparing recycled concrete specimens with a replacement ratio of 20%. Test results demonstrated that the residual Ca²⁺ concentration in the used solution declined with the reduction of pH value, which implied that Bacillus Cohnii solution enhanced the compactness of recycled coarse aggregates, especially under acidic environment. Concrete made of the treated recycled aggregates witnessed a notable increment in peak strength. During compression, damage evolution alleviated and damage deterioration attenuated. The damage variable and cumulative damage of concrete specimens made of recycled aggregates soaked in solution of pH=8 were evidently smaller than those in solution of pH=8.

Key words: recycled aggregate concrete, microbial mineralization and precipitation, Bacillus Cohnii, compressive strength, acoustic emission