Utilization of Bacillus Subtilis Bacteria for Improving Mechanical Properties of Concrete

Utilization of concrete as a building material is well-known worldwide and increasing continuously due to its sustainability, low maintenance cost, durability performance, etc. Ingredients of concrete, its constructional methodology, exposure conditions are moderating and improving day by day. However, this study covers a laboratory investigation of Bacterial Concrete. The bacterial concrete technology is based on the application of the mineral producing microbes. Some microbes like Bacillus subtilis which have the properties of bio-calcification can precipitate CaCO3 effectively inside concrete structures. This CaCO3 precipitation can fill the pores and therefore, the cracks internally and finally make the structure more compact. In this experimental study, Nutrient Broth (NB) media was employed for the growth and spore formation of Bacillus subtilis bacteria. Four different bacterial culture densities (0.107, 0.2, 0.637, and 1.221) were estimated at OD600 and directly added to concrete matrix maintaining previously fixed water to culture ratio (0.5:0.5). 100 mm cubical concrete specimens were cast, subjected to compressive and tensile strength tests for different curing ages and finally compared with Conventional Concrete (OD600=0). Significant increase in mechanical strengths was observed due to addition of Bacillus subtilis bacteria in concretes which have the culture density of 0.637. Soon cylindrical concrete specimens of 100 mm diameter and 200 mm height were prepared for Ultrasonic Pulse Velocity (UPV) analysis. The test results obtained from UPV analysis reveal that specimens prepared with culture density of 0.637 show higher pulse velocity than other microbial groups. Afterwards, this paper proposes a UPV vs. compressive strength relationship curve for different strengths of concrete.