Comprehensive microbiological studies on screening bacteria for self-healing concrete

Abstract

The present study majorly focused on the selection of suitable bacteria through microbiological studies for concrete crack healing. However, Bacillus species of non-pathogenic type bacteria's Viz., Bacillus subtilis, Bacillus cereus, Bacillus licheniformis, and Bacillus halodurans were used as self-healing agents. Also conducted various microbiological studies such as gram staining process, biofilm, Exopolysaccharide, Endospores, Urease Enzyme, and Calcium Carbonate formations. Similarly, the growth pattern of bacteria was measured in different temperatures (25 °C, 30 °C, 35 °C, 37 °C, and 60 °C), environments (such as pH of 3,7,8,9,10,11,12,13, and 14), and concrete composition medium. The gram staining process has identified that the above four bacteria have gram-positive strains and a rod-like shape. The B.halodurans and B.licheniformis have shown more spore formation, urease enzyme production, Exopolysaccharide production, biofilm formation, and calcium carbonate formation than other cultures. The B.licheniformis has shown the highest growth rate at various temperatures and environmental conditions. However, in the case of concrete composition medium B.halodurans has shown the highest growth rate. To determine the above four bacteria's crack healing ability, 40 MPa strengthened concrete samples are prepared and, then 65% and 75% of stress level concentration were applied to form cracks. However, Ultra-sonic pulse velocity values and water absorption values are taken for the concrete specimens to assess the healing capability. From the obtained results, B.halodurans has shown an ultrasonic pulse velocity value of 4.6 km/s and with 1.71% of water absorption, which is optimum among other bacterial cultures. The present study strongly recommends using B.halodurans as self-healing agents in concrete repair works.