Abstract: Preparation of microbial self-healing concrete by direct internal mixing will affect the long-term activity of mineralized microorganisms due to factors such as squeezing friction and limited living environment. In this work, we select Bacillus pasteurii as a mineralized microorganism, and use expanded perlite and ceramsite as microbial carriers, and cement slurry and metakaolin slurry as carrier coating materials. An experiment is conducted to optimize the carrier and its reasonable particle size and coating materials that contribute to the release and protection of the microorganism; the effect of microbial immobilization on the self-healing effect of cracks is studied. The results show that quantitative expanded perlite, added to a hydraulic concrete specimen, increases the tensile crack ratio at its splitting crack; as a microbial immobilization material, it is more effective to release mineralized microorganisms than ceramsite. Metakaolin slurry is more suitable as a carrier coating material than cement slurry, and its encapsulation of the microorganism achieves a 14-day survival rate of 86.6%, effectively ensuring the long-term activity of the immobilized microorganism. The microorganism that are immobilized with expanded perlite and coated with metakaolin slurry can achieve a 90-day repair and maintenance effect of the cracks up to a width of 0.616 mm, wider than 0.453 mm of the direct addition method. Thus, our method effectively improves the crack self-healing effect of concrete specimens.

Key words: hydraulic concrete, mineralized microbial, immobilization, coating material, crack self-repairing