Effect of Calcium Organic Additives on the Self-Healing of Concrete Microcracks in the Presence of a New Isolate <i>Bacillus</i> sp. BY1

Abstract

Calcium carbonate–based biominerals are considered self-healing materials in concrete. The morphology and mineralogy of biominerals depend highly on the self-healing efficiency of concrete cracks. This study examined the morphology and mineralogy of biominerals with a new isolate, Bacillus sp. BY1, and various organic calcium compounds (i.e.,&nbsp;calcium formate, calcium acetate, and calcium lactate). In addition, compressive strength and crack self-healing efficiency were investigated under various other conditions. Biominerals formed in the presence of calcium formate and calcium lactate were mostly calcite (ca. 95% by weight) and contained more rhombohedral faces, whereas calcium acetate induced spherulite-shaped biominerals with a smaller fraction of calcite (ca. 61.5% by weight). With the addition of bacteria and organic calcium compounds, the compressive strengths decreased and increased, respectively; however, the loss of strength by the bacteria was compensated when both bacteria and organic calcium compounds were added together. Self-healing of cracks did not occur by the addition of bacteria alone and was more prominent when calcium lactate was used as a biomineral precursor.