Abstract: Hydraulic concrete is prone to erosion and cracking in the wet-dry alternating zones under water level fluctuation. A mixture of aerobic and facultative anaerobic mineralized microorganisms can better adapt to the fluctuating oxygen content in concrete cracks. This study prepares a microbial self-healing agents using the microorganisms of aerobic Bacillus megaterium and facultative anaerobic Sporosarcina pasteurii for two cases－a single component and a mixture of both, and conducts the compressive strength test and permeability coefficient test on the concrete samples. For each case, we evaluate the influence on the performance and crack self-healing effect of hydraulic concrete through a quantitative index analysis of crack repair. An optimal mixing ratio of aerobic and facultative anaerobic has been obtained. A SEM analysis of the samples is used to reveal the microscopic mechanism of mixed microorganisms on concrete performance improvement. The results show that the mixing of mineralized microorganisms can effectively elevate the density of concrete pore structure, and the best effect of calcium carbonate precipitation occurs at the mix ratio 4:6 of Bacillus megaterium and Sporosarcina pasteurii. Under the synergistic influence of aerobic microbial respiration and facultative anaerobic microbial enzymatic action, the mixed microorganisms yield better improvement on the mechanical properties and crack self-healing efficiency of hydraulic concrete.

Key words: hydraulic concrete, crack self-healing, mixed microorganisms, MICP, microscopic analysis