Application of Koch's postulates in self-healing concrete

Concrete is a well-known construction material that is a homogeneous mixture of various materials like aggregates, binders, admixtures, water, etc. Based on the current requirements, modifications are being made to its composition, and various special types of concrete mixes are being developed. Self-compacting concrete is a rapidly growing special concrete due to its advantages, but there is a major chance of getting shrinkage cracks due to the high amount of fines. To fix the problem, Bacillus subtilis bacteria with a count of 1.3×10 ⁸ per ml is introduced into the concrete during the mixing process, and self-healing concrete is developed. Concrete cube specimens are cast with and without bacteria and tested for self-healing. Studies show that Bacillus subtilis can heal the cracks in concrete, but there is no confirmation for that. There is a need to confirm that Bacillus subtilis is causing the healing of cracks in concrete. In the present study, microbes are developed from both conventional and bacterial concrete. In bacterial concrete mix, 7% increment in compressive strength and 1.2 mm crack healing are confirmed as the self-healing activity. Koch's postulates confirmed that Bacillus subtilis can survive and is able to maintain the self-healing mechanism. The material produced in the crack is collected from the specimen and tested for microstructure; it is confirmed that the precipitation is CaCO ₃ formed by MICP. FESEM-EDS results give strong support to utilize Koch's postulates in finding out the relationship between the microbe and self-healing in concrete.