The construction industry is increasingly seeking sustainable technologies capable of enhancing the performance and service life of cement-based materials while reducing maintenance costs and environmental impacts. One promising approach is Microbially Induced Calcium Carbonate Precipitation (MICP), a bio-mediated process whereby selected bacterial species precipitate calcium carbonate within the pore structure of cementitious matrices. This study investigates the influence of Bacillus coagulans and nutrient broth medium on the compressive strength, water absorption, and microstructural characteristics of cement mortar. Bacillus coagulans cultures were introduced into mortar mixtures at cell concentrations of 1.5 × 10^8, 6.0 × 10^8, and 1.2 × 10^9 cells/mL, while nutrient broth medium was incorporated as a partial replacement of mixing water at levels of 30%, 40%, and 50%. Mortar specimens were prepared using a cement-to-sand ratio of 1:3 and a water-cement ratio of 0.50. Compressive strength tests were conducted after 3, 7, 14, and 28 days of curing, while water absorption and microstructural analyses were performed to evaluate durability and calcite formation. Experimental results revealed that bacterial incorporation significantly improved mortar performance compared with conventional mortar. The optimum mixture containing 1.5 × 10^8 cells/mL Bacillus coagulans and 50% nutrient broth medium achieved a 28-day compressive strength of 28.02 MPa, compared with 24.08 MPa for the control specimen. Water absorption was reduced from 5.98% in the control mortar to 3.46% in the bio-treated mortar, indicating enhanced pore refinement and reduced permeability. Scanning Electron Microscopy (SEM) observations confirmed the formation of calcite crystals within pore spaces and microcracks, contributing to matrix densification and strength enhancement. The findings demonstrate that Bacillus coagulans-mediated bio-calcination represents an effective and environmentally sustainable strategy for improving the mechanical and durability properties of cement mortar. The technology offers significant potential for the development of self-healing and long-lasting construction materials suitable for modern infrastructure applications.
Keywords: Microbially Induced Calcium Carbonate Precipitation (MICP), Bacillus coagulans, Biocalcination, Cement Mortar, Compressive Strength, Durability, Calcite Precipitation, and SEM Analysis.