Biomineralization in self-healing cement-based materials: investigating the temporal evolution of microbial metabolic state and material porosity

The potential for self-healing of concrete via biomineralization processes in which microorganisms influence mineral precipitation is promising. To embed microorganisms within a cement-based material, key challenges are to find a microorganism that can tolerate the highly alkaline conditions, survive the mixing process, and remain viable with limited access to nutrients. The focus of this work is to determine the metabolic state of unencapsulated Sporosarcina pasteurii, inoculated vegetatively, in a cement-based matrix over time and to examine its ability to remediate internal cracks and reduce porosity. Viable S. pasteurii was found in hardened mortar samples that were as old as 330 days, and 48% of the viable cells detected were vegetative. A greater fraction of the inoculated cells remained viable in mortar as compared to cement paste, which is promising because mortar is a better representation of the composite nature of concrete than cement paste. Furthermore, as compared to neat paste and neat mortar, addition of the vegetative cell culture to bacterial paste and bacterial mortar resulted in reduced porosity. Bacterial mortar also demonstrated increased strength recovery as compared to neat mortar. The reduction in porosity and increase in mechanical regains demonstrated by the bacterial mortar suggest improved durability and service life for bioconcrete as compared to traditional concrete