Optimization of bacterial sporulation using economic nutrient for self-healing concrete

The use of heat- and alkali-resistant bacteria is essential for the biological repair of damaged concrete. Lysinibacillus boronitolerans YS11 was isolated from the rhizosphere of Miscanthus sacchariflorus. The increased pH in the urea-minus condition during the growth of the YS11 strain promoted calcium carbonate (CaCO₃) formation. To identify the optimum medium that promoted the growth of the YS11 strain, a Plackett-Burman design was conducted for the screening process. Consequently, malt powder, rice bran, (NH₄)₂SO₄, and corn syrup were chosen to enhance YS11 growth. The optimization of these four useful factors was carried out using a central composite design. To obtain higher survivability in mortar, the sporulation process is essential, and additional factors such as Mn²⁺, Fe²⁺, and Ca²⁺ were found to contribute to sporulation. A mixture of L. boronitolerans YS11 spore powder, cement, paste, sand, yeast extract, calcium lactate, and water showed a healing effect on a 0.3 mm mortar crack in 7 days. Furthermore, calcium carbonate precipitation was observed over the crack surface. Thus, we confirmed that mortar treated with YS11 spore powder was effective in healing micro-cracks in concrete.