Effect of incorporation of Bacillus Subtilis bacteria and calcium lactate on properties of concrete – An experimental approach

This manuscript investigates the incorporation of Bacillus subtilis bacteria in concrete, using a nutrient source as calcium lactate (CL) to enhance the performance of concrete through the microbial-induced calcite precipitation (MICP) process. Bacterial culture was systematically prepared under controlled laboratory conditions to ensure the desired concentration of 1 × 10⁵ CFU/ml. Both control concrete (CC) and bacterial concrete (BC) samples were prepared with same water-cement (W/C) ratio to ensure consistency in evaluating their fresh and hardened properties. The experimental results demonstrated remarkable enhancement in the strength properties of BC. The compressive strength (CS) increased by approximately 22%, split tensile strength (STS) by 17%, and flexural strength (FS) by 19% compared to CC. Durability assessments further supported these outcomes as the ultrasonic pulse velocity (UPV) values exhibited a 4% increase, indicating improved internal integrity and homogeneity of the concrete matrix. Moreover, water absorption (WA) decreased by 21%, reflecting enhanced impermeability and higher resistance to the penetration of water and harmful agents. Microstructural investigations using Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive Spectroscopy (EDS), and X-Ray Diffraction (XRD) provided further evidence of bacterial activity within the concrete. FESEM images reported dense, compact microstructures with substantial calcite accumulation along microcracks, while EDS analysis indicated increased calcium and carbonate contents, confirming the formation of calcium carbonate. XRD patterns displayed intensified peaks of calcite and calcium silicate hydrates (CSH). This study illustrated that incorporating Bacillus subtilis and CL enhanced the properties of concrete, providing an eco-friendly solution for self-healing concrete.