Optimization Design of Microbial Concrete Self-Healing Agent Mix Proportion and Research on Crack Repairing Effect

The application of microbe-induced carbonate precipitation (MICP) to self-healing concrete cracks has broad prospects, where the mix design of a microbial self-healing agent (MSHA) is the key to smooth concrete crack repair. In this study, expanded perlite was used as a microbial carrier to investigate the immobilization capacity of microorganisms under different pressure conditions. The optimum mix proportion of sugar coating layer material and protective layer material used to wrap microbial carriers to prepare MSHA were determined. Moreover, the repair effects of different wrapping layers on concrete cracks were investigated. Results showed that the immobilization capacity of small-pore expanded perlite (EP) was the greatest when the adsorption pressure was 0.05 MPa and the immobilization time was 20 min. The optimum ratio of water to cement (W/C) of sulphoaluminate cement for the sugar coating material was 0.52, and the optimum spraying ratio was 4.0. The best W/C of ordinary portland cement for the protective layer was 0.46, the best waterproofing material content was 7.5%, and the best spraying ratio was 3.5. The wrapping of a sugar coating layer and a protective layer around the carrier surface significantly improved MSHA performance and had excellent compatibility with concrete materials. When the crack width was 0.9 mm, the MSHA with this proportion completely repaired cracks after 14 days.