Synergistic Effects of Ternary Microbial Self-Healing Agent Comprising Bacillus pasteurii, Saccharomyces cerevisiae, and Bacillus mucilaginosus on Self-Healing Performance in Mortar

In order to prevent structural damage or high repair costs caused by concrete crack propagation, the use of microbial-induced CaCO₃ precipitation to repair concrete cracks has been a hot topic in recent years. However, due to environmental constraints such as oxygen concentration, the width and depth of repaired cracks are seriously insufficient, which affects the further development of microbial self-healing agents. In this paper, a ternary microbial self-healing agent composed of different proportions of <i>Bacillus pasteurii</i>, <i>Saccharomyces cerevisiae,</i> and <i>Bacillus mucilaginosus</i> was designed, and its crack repair ability was evaluated. When the mixing ratio was 7:1:2, the cell concentration was the highest, the precipitation amount of CaCO₃ was the highest, and the crystallinity of calcite crystal was the highest. Compared to the single microorganism, the mortar specimens with ternary microorganisms had the largest repair area (up to 100%) and the deepest repair depth (CaCO₃ presents at 9-12 mm from the crack surface). This is because when the concrete breaks, all three microorganisms are activated by water, O_2, and CO₂. <i>Saccharomyces cerevisiae</i> and <i>Bacillus mucilaginosus</i> accelerated the growth of <i>Bacillus pasteurii</i> and more mineralized products; CaCO₃ was rapidly formed and quickly filled on the crack surface. When CaCO₃ seals the surface of the crack, the internal <i>Saccharomyces cerevisiae</i> and <i>Bacillus mucilaginosus</i> continue to play a role. <i>Bacillus mucilaginosus</i> can accelerate the dissolution of CO₂ produced by the anaerobic fermentation of <i>Saccharomyces cerevisiae</i> and the hydrolysis of CO₃^2-, thereby improving the repair of the crack depth direction.