Mechanical and microstructural evaluation of bacterial and two-component bacterial concretes

The serviceability and durability of concrete structures are often reduced by crack formation, which permits ingress of water and aggressive agents. This study presents an intrinsic self-healing approach using a two-component bacterial concrete system that combines Bacillus subtilis with a calcium source to promote in-situ biomineralization within the concrete matrix. The performance of this system was compared with bacterial concrete containing only micro-organisms and with normal concrete of grades M20, M25, and M30. Experimental evaluation included compressive, split tensile, flexural strength, modulus of elasticity, water absorption, and porosity tests. Scanning Electron Microscopy (SEM) confirmed calcite precipitation and microstructural densification in bacterial and two-component bacterial concretes. Statistical analysis using the Kruskal–Wallis test verified that the observed differences among the concrete types were highly significant (p < 0.001). Regression modelling further quantified the influence of concrete grade, age, and bacterial composition on strength parameters, achieving high predictive accuracy (R² = 0.65–0.96). The results demonstrate that the two-component bacterial system enhances both strength and durability, offering a sustainable and effective self-healing solution for extending the service life of concrete structures.