Microbial Calcite Precipitation by Marine-Derived Rhodococcus Strain RK-15: Characterization and Application in Concrete

This study investigates the impact of ureolytic bacteria isolated from sea surface water on the compressive strength and water absorption characteristics of concrete. In this context, the strain RK-15 was selected in the preliminary screening with Stuart's broth and used in further experiments. Phylogenetic analysis of the 16S rRNA gene sequence identified the isolate as Rhodococcus erythropolis. This strain demonstrated the highest urease activity on the 5th day at 30 degrees C and pH 8. The isolate accumulated spherical crystals in a solid Urea-CaCl2 medium. Energy-dispersive X-ray spectroscopy (EDS) analysis revealed the presence of calcium, carbon, and oxygen in the precipitated minerals. In concrete production, 0.5% of the cement weight (2 x 109 cells/ml) bacterial culture was used. Compressive strength and water absorption measurements were performed on the 3rd, 7th, and 28th days. Results showed that the addition of Rhodococcus strain RK-15 led to a 13.61% increase in compressive strength and a 23.33% reduction in water absorption by weight compared to the control group. These findings suggest that the addition of strain RK-15 offers a sustainable and environmentally friendly method to enhance the mechanical and physical properties of concrete.