The influence of Calcite-Producing Bacteria on Cement Mortar Compressive Strength and Durability Characteristics

Background: The phenomenon of microbiologically induced calcite precipitation (MICP) is a part of the chemical process called biomineralization. Microorganisms form inorganic solids like calcite by such process. Bacillus spp. are common soil bacteria that may induce calcite precipitation. The microbial sealant properties of CaCO3 improve mortar and concrete's compressive strength. Methods: This study examined the impact of locally isolated Calcite-Producing bacteria on mortar characteristics. Eight isolates of Bacillus spp. have been prepared in suspensions adjusted to absorbance of 1 at 600 nm, that contain 2% urea and 25 mmoll-1 calcium chloride, and applied to prepare mortar cubes. The ratio of cement: sand: water mix was 1:3:0.5. Control cubes were prepared using the same mix ratio and containing water instead of bacterial suspension. Compressive strengths for all cubes on days 7 and 28 were measured. A durability tests and water absorption test for the cubes were performed. Results: Bacterial mortar cubes showed a compressive strength about 39 to 81% and 9.6 to 60.2% higher than the control on the 7th day and 28th day, respectively. Bacterial mortar cubes resist H2SO4 attack at pH ≥ 2, while control cubes couldn't resist at pH ≤ 6. After treatment with 5% MgSO4, all bacterial cubes showed higher compressive strengths. Water absorption of bacterial cubes ranged from 2.4-4.8%, while the control cubes absorbed water with a percentage of 7.2%. Conclusion: These species are promising contenders for MICP involved investments, and can be used in a many of construction applications.