Effect of ureolytic bacteria Bacillus sp. from local landfill for crack healing on flexural tensile strength of high-strength concrete

Abstract High-strength concrete made with large amount of cement augmented with additives causing high hydration heat and large shrinkage during hardening process, making it susceptible to cracks at early age due to its still low tensile capacity. These cracks must be mitigated early. Self-healing method using ureolytic bacteria Bacillus sp. as concrete crack-healing can be smart solution to overcome this problem. Urease enzyme produced by ureolytic bacteria can hydrolyze urea and Ca 2+ (derived from CaCl 2 ) added as precursors to precipitate CaCO 3 as concrete cracks closure biologically. This study aims to analyze effect of ureolytic bacteria Bacillus sp. cultivated from local landfill Gampong Jawa, Banda Aceh as crack self-healing on flexural tensile strength of high-strength concrete. Bacteria were immobilized into diatomaceous earth to increase viability during casting and after residing in harsh environment of concrete which used as 10% substitution for fine aggregates. Concentration of bacteria and growth media used were varied by 0%; 0.5%; 0.6%; and 0.7% of cement weight. Specimens were beams measuring 100×100×400mm which was given 1D10 mm tensile reinforcement to prevent brittle failure during testing. First, an initial crack load of 60% of 7 days concrete flexural tensile strength was given, then treatment was carried out for 28 days in water to observe crack healing for 7, 14, 21 and 28 days. After completing crack healing phase, flexural tensile capacity testing was carried out until the specimens collapsed. The results showed that flexural tensile capacity of high-strength concretes was 5.49 ton, 5.69 ton, 5.89 ton and 5.86 ton respectively and the percentage of concrete crack closure after healing phase for 28 days after being initially cracked was 4.76%; 77.90%; 87.09%; and 89.09% each, at variations of Bacillus sp. 0.0%; 0.5%; 0.6%; and 0.7%. Optimum value was obtained at bacterial percentage of 0.7% resulting in an increase both in flexural tensile capacity of 6.74% and in crack healing efficacy of 84.27% compared to non-bacteria concrete.