Impact of endospore-forming bacterial co-culture on the long-term self-healing efficiency and hardened properties of cement mortar

Bacterial self-sealing concrete emerges as a promising approach to enhance the durability of the concrete structures. However, existing literature lacks insights into the long-term behavior of bacteria and the potential benefits of co-culturing different bacterial strains. Therefore, this study investigates the impact of individual strains of Bacillus subtilis and Sporosarcina pasteurii, as well as the co-cultured bacteria, on compressive strength, flexural strength, water absorption, and crack healing efficiency of cement mortar over a curing period of up to 360 days. Bacterial strains are incorporated at 10⁵ and 10⁶ cells/ml. The optimum cell count for increased compressive strength is 10⁵ cells/ml, with co-cultured samples achieving highest compressive strength of 57.0 MPa at 56 days, a 50.4 % increase compared to control samples. The highest increase in strength properties is observed up to 56 days, followed by a decline in the rate of strength gain after this curing period. Co-cultured samples also demonstrated the highest increase of 46.4 % in flexural strength and a lower water absorption rate of 4.8 %. Microscopic examination confirms 99.8 % healing of 0.3 mm cracks through CaCO₃ precipitations inside the cracks. Therefore, this study highlights the impact of individual and co-cultured bacterial strains, as well as cell concentration, on improving self-healing efficiency under long-term curing conditions.