Potential of cave isolated bacteria in self-healing of cement-based materials

Cementitious materials suffer from cracking, decreasing their durability. As a solution, crack self-healing materials using CaCO3 precipitating bacteria began to be studied worldwide. This research aimed to select the environmental bacterium with the most significant self-healing potential among samples isolated from a Brazilian cave in the Amazon region, besides providing a better understanding of the genome and its influence in crystal precipitation. For this purpose, 11 bacteria were tested in vitro for CaCO3 precipitation, using B4 medium (0.4% yeast extract, 0.5% glucose and 0.25% calcium acetate). The bacterium with the most significant precipitation potential was analyzed by SEM and EDS. Moreover, complete genome sequencing (CGS) was carried out for a better understanding of the precipitation mechanism. Afterward, a preliminary test was performed in mortars with cave-isolated bacteria to analyze self-healing ability and compressive strength. Besides that, the precipitated crystals were analyzed by XRD and SEM. The results showed that B. subtilis CV16 strain, isolated from a cave in the Oriental Amazon (Brazil), presented the most significant capacity of CaCO3 precipitation among the tested ones. Besides, the crystals analyzed by SEM presented typical calcite morphology. The CGS showed that CV16 is a Bacillus subtilis with several genes involved in CaCO3 precipitation. Moreover, the preliminary addition of this strain in mortars demonstrates their cracks self-healing ability and increased compressive strength after 63 days curing, without urea or calcium source. The precipitated crystals were identified by XRD as calcite and vaterite. This way, the strain CV16 has sustainable application potential in cementitious materials due to CaCO3 precipitation.