Low alkali sulpho-aluminate cement encapsulated microbial spores for self-healing cement-based materials

Microbial self-healing cement-based materials have developed into a novel technology in recent years. It has the promising potential to improve self-healing capacity of cracks by microbial induced calcium carbonate precipitation (MICP). In this paper, low alkali sulpho-aluminate cement (SC) was used as the carrier to protect spores from the high alkalinity environment inside the cement-based materials. The protective effect of SC on spores was studied in the simulated pore solution of cement-based materials, and then area repair ratio, recovery ratio of water permeability, repair ratio of anti-chloride ion penetration and healing depth were used to evaluate the self-healing efficiency of cracks. Moreover, the precipitates formed at the crack mouth of specimens were analyzed by XRD and SEM equipped with an EDS. The results showed that sulpho-aluminate cement had an excellent protective effect for spores and the addition of microbial self-healing agent would slightly affect the early mechanical properties of cement-based materials, but could improve them in later ages. In addition, the cracks of microbial group with a width of 0.25 - 0.35 mm were completely filled by CaCO3, the area repair ratio, recovery ratio of water permeability and repair ratio of anti-chloride ion penetration were 99.2%, 97% and 63.2%, respectively. Meanwhile, the average healing depth of cracks was 2895 mu m, which had not been reported in self-healing cement-based materials researches.