Development of Bacterium for Crack Healing and Improving Properties of Concrete under Wet–Dry and Full-Wet Curing

Concrete cracking is inevitable, coupled with increased permeability, exacerbating the adverse impacts of atmospheric conditions and chemical attacks. Calcium carbonate precipitation resulting from certain microorganisms’ metabolism is a novel approach that can self-heal the cracks and improve concrete properties. In this study, the development and effect of bacteria Bacillus cohnii on crack healing, regained compressive strength after pre-cracking, sorptivity, water absorption, and concrete microstructures were investigated. For this purpose, a Bacillus cohnii bacterial concentration of 105 cells/mL was used as a water replacement in the concrete mixtures. Two methods subsequently cured the prepared concrete specimens: wet–dry (W-D) cycle and full-wet (F-W). In the wet–dry cycle, the cast specimens were immersed in water for 24 h and then kept at room temperature for 24 h, which was considered as one cycle; this process was repeated for 28 days. In the full-wet curing, specimens were immersed in water for 28 days. However, the curing water was changed every 24 h to facilitate the essential oxygen supply for bacterial activity to precipitate calcium carbonate. The results revealed that 90% and 88% surface healing was noticed in full-wet and full-dry pre-cracked specimens at 28 days.