Interfacial crack self-healing by <i>Sporosarcina pasteurii</i>: From medium optimization to spore encapsulation

Self-healing cement takes advantage of microbial induced carbonate precipitation (MICP), a meritorious biological process, to achieve automatic healing of cement cracks. In this study, two beneficial factors, optimization of the bacteria culture medium and encapsulation of bacterial spores, were used to improve the MICP efficiency of Sporosarcina pasteurii in self-healing cement. On the one hand, in medium optimization, we compared the growth of Sporosarcina pasteurii fed with two generally used nitrogen sources, e.g., urea and ammonium chloride, and found that ammonium chloride can promote biomineralization more efficiently than urea. It was also confirmed that nickel (0.1 mg/l) and manganese ions (10 mg/l) benefit the MICP process through enhancement of urease activity and promotion of spore production. On the other hand, spores encapsulated in sodium alginate-gelatin gel beads prepared by using a flow nozzle device can have excellent swelling performance triggered by water. As an application demonstration, self-healing of cement cracks with consideration of the above beneficial factors was successfully verified without substantial influence on the cement compressive strength.