Microbial induced calcium carbonate precipitation study using Bacillus subtilis with application to self-healing concrete preparation and characterization

• A novel self-healing concrete is produced with Bacillus subtilis M9. • 0.3-mm-width crack gap can be sealed in 28 days. • About 14% flexural strength regain can be achieved. This study aimed to develop novel bacteria-based self-healing concrete by microbial induced calcium carbonate precipitation mechanism. A group of spore-forming bacterium related with gen Bacillus subtilis were selected for cultivation at elevated pH solution. The derived alkali-resistant Bacillus subtilis M9 was applied for biomineralization test whereas the precipitate mineral was calcium carbonate in calcite phase according to X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) results. With B. subtilis M9 as the healing agent, the self-healing concrete beam specimens were then prepared by incorporating polyvinyl alcohol fibers. Air-entraining agent was utilized to yield micro pores in cement paste mixture to provide ecological niches for microbe. 3-point-bending test was conducted to form 0.3-mm-width cracks on the beam bottom. After 28 days curing, the micro cracks were autonomously healed with calcium carbonate precipitation fillings due to the bacteria metabolic activity. The sequent SEM tests implied that calcite is the dominant mineral phase with some bacterial imprints on the crystal surface. Furthermore, flexural strength of the sealed beam subjected to repeated bending was enhanced by about 14% compared to residual flexural strength. The beam flexural strength recover was realized by remediation of the cracks in matrix as well as repairing of fiber–matrix interface bond.