Cracks that tend to be the starting point of deterioration of concrete structures can be repaired by concrete itself, repair cracks and maintain the sound of concrete structures, "self-healing concrete", which has been attracting attention. Self-healing concrete is broadly classified into three categories: inorganic, organic, and microbial. Microbial systems are characterized by their
ability of function to close cracks through biological metabolism. In this research project, we focused on the aerobic bacterium Bacillus subtilis var. natto and developed a high-function self-healing concrete that can not only fill cracks by the metabolism of organisms but can also use the bacterium's breathing to deprive the concrete of oxygen and thus suppress corrosion of the steel rebar inside, in addition, we implemented development of a microcapsule material that can be used to efficiently apply Bacillus subtilis var. natto to concrete. We selected shirasu balloon and shirasu pumice as microcapsule materials, which are both natural pozzolans, to which the Bacillus subtilis var. natto could be absorbed to achieve micro-encapsulation, it would be also expected a secondary benefit of this technique: further concrete precision resulting from the pozzolan reaction of the volcanic glass. The photos below show mortar test specimens in which cracks were induced after Bacillus subtilis var. natto had been applied, before they were exposed in water for a certain period to verify the efficacy of the bacterium Bacillus subtilis var. natto and microcapsules working in combination. While the mortar to which the bacterium Bacillus subtilis var. natto was not applied did not confirm any sign of its cracks being filled, in the specimens to which shirasu balloon and shirasu pumice had been absorbed the bacterium Bacillus subtilis var. natto, a calcium-derived substance was being deposited in their cracks closed them.