Application potential of Bacillus megaterium encapsulated by low alkaline sulphoaluminate cement in self-healing concrete

With the help of microbial mineralization to accelerate carbonate deposition, microbial self-healing concrete has developed into a promising technology because it is environmentally friendly. At the same time, how to assemble properly microorganisms and nutrients to reduce the negative impact on the performance of concrete itself has become a bottleneck of this technology. In this research, microbial spores of Bacillus megaterium, nutrients and low-alkaline carriers were assembled as a whole by extrusion. Low alkali calcium sulphoaluminate (CSA) cement was used as the carrier to protect spores from the high alkalinity environment caused by cement hydration. After studying the protective effect of this assembly method on spores, this integrated self-healing agent was applied in concrete, and then repairing efficiency of cracks was evaluated by area repairing ratio, recovery of water resistance, recovery of resistance to chloride ions and healing depth. Meanwhile, the repairing products were analyzed by XRD and SEM equipped with an EDS. Moreover, two different nutrients were used as precursors for microbial mineralization, and their negative effects have also been studied. The results showed that Bacillus megaterium could use glucose and calcium lactate as the precursors, and this new repairing system significantly improves the efficiency of self-healing. Compared to glucose, calcium lactate has a better repair effect when used as a precursor, and the average healing depth reached 4000 µm. At the same time, CSA cement was an excellent carrier for spores and could reduce the negative impact of nutrients on concrete when microorganisms and nutrients were assembled with CSA cement.