Crack Healing and Mechanical Properties of Bacteria-based Self-healing Cement Mortar

Abstract

In this study, the improvement of mechanical properties and crack healing as a result of the calcium carbonate precipitation due to bacterial activity have been investigated in two phases. First, the optimum mix design of self-healing cement mortar has been achieved considering different amounts and concentrations of the bacterial solution of bacterium Sporosarcina pasteurii (ATCC 11859) in non-pre-cracked specimens. Some of the mechanical properties, such as compressive strength, flexural strength, energy absorption capability, and weight change in bacteria added cement mortar specimens are compared with those of control specimens. Second, using the determined optimum mix design, mechanical properties of self-healing cement mortar specimens with initial cracks are compared with those of non-pre-cracked specimens to evaluate the recovery degree. 28-day compressive and flexural strengths of cement mortar specimens through direct addition of bacterial suspension with a concentration of 5.1 × 10⁷ cells/ml improved by 45% and 18%, respectively. These results for 7-day specimens were 78% and 24%, respectively. Experimental flexural strengths of pre-cracked specimens are higher than their theoretical values based on the reduced cross-sections, and in pre-cracks with smaller dimensions, higher recovery degrees are achieved.