Influence of bacterial metabolic pathways on the microstructural evolution of bio-concrete

Abstract

This study explores the self-healing potential of bacterial concrete by employing Bacillus sphaericus and Bacillus pasteurii to improve crack closure and enhance mechanical durability. This study investigates the synergistic effect of steel fibres and calcite-producing bacteria (Bacillus sphaericus and Bacillus pasteurii) on the mechanical performance of concrete, including compressive, split tensile, and flexural strength characteristics. Concrete specimens were prepared with bacterial concentrations of 10³, 10⁵, and 10⁷ cells/ml, and artificial cracks were induced to simulate damage. Bacterial-induced calcite precipitation (biocalcification) was used as a mechanism to fill these cracks, assessing its effect on critical mechanical properties, including Compressive Strength (CS), Split Tensile Strength (STS), and Flexural Strength (FS). Microstructural analyses, including Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Energy-Dispersive X-ray Spectroscopy (EDAS), and Fourier Transform Infrared Spectroscopy (FTIR), were employed to confirm and characterize the formation and distribution of calcium carbonate crystals within the healed cracks. Additionally, the self-healing efficiency was quantified through water absorption tests and visual crack closure assessments. The results indicate that higher bacterial concentrations significantly improved the self-healing efficiency and enhanced both the compressive and tensile strength of the bio-concrete compared to the control specimens. Furthermore, the impact of each bacterial species on healing rates and calcite deposition was compared, highlighting Bacillus pasteurii as particularly effective in inducing rapid mineralization. These findings underscore the feasibility of utilizing bacteria as a sustainable means to improve concrete durability and longevity, offering potential applications in structural maintenance and repair. An analytical study was carried out on RC beams, including conventional and two optimized designs. The study primarily focuses on the crack patterns in these beams, and it proved helpful in predicting experimental outcomes.