Development of autonomous-healing mortar using Geobacillus stearothermophilus

Autonomous healing by the microbially induced calcite precipitation (MICP) mechanism has garnered significant interest in the sustainable approach to concrete repair and maintenance. Previous research works have reported that Bacillus pasteurii and Bacillus sphaericus are the most commonly used in concrete associated with bacteria. However, there is limited information on other types of bacteria species. In this study, the vegetative cells of Geobacillus stearothermophilus were introduced and encapsulated into alginate-hydrogel before incorporation into the mortar. The urease activity, viability, swelling, and water retention properties of the bacterial Geobacillus stearothermophilus cell encapsulated in alginate-hydrogel were measured. The performance of alginate-encapsulated Geobacillus stearothermophilus (AE-GS) in the mortar mixture as a self-healing agent was measured by compressive strength, water absorption, and crack-healing efficiency. The precipitation of calcium carbonate of the AE-GS mortar was measured using thermogravimetric analysis (TGA). The highest level of crack healing was 63% (by the initial crack width) which was achieved by incorporating 15% AE-GS (replacement by total weight of the mortar). However, the lower result of compressive strength and the highest absorption rate were portrayed by the mortar specimens that contained 15% of AE-GS replacement compared with the control mortar (AE-R) and with those of AE-GS replacement level at 3 and 9%.