Abstract
Self-healing concrete has been widely researched to reduce the cost of repairing and maintaining concrete infrastructure. Microbially induced calcite precipitation (MICP) is a promising solution that uses bacteria to produce calcite within cracks and seal them, preventing further deterioration. However, protecting the self-healing agents, including calcium precursors, bacteria, and growth nutrients, from the concrete matrix can be challenging, and encapsulation methods can lead to strength loss, slowed cement hydration, and complicated manufacturing. Therefore, in this study, to reduce the need for protective shells and their negative impact, we investigated the role of aerobic non-ureolytic bacteria in the healing process and determine the feasibility of inducing calcite precipitation without extra added calcium precursor in the concrete matrix. This study investigated the self-healing efficiency of this novel bacteria-based self-healing cementitious composites (BBSHCC) via crack observation, permeability test and compositions’ analysis. Samples at different curing ages were prepared as well to clearly indicate the impact of minerals of cementitious composites on the microbial activities. The novel BBSHCC samples, consisting solely of bacteria and nutrients, demonstrated exceptional self-healing ratios in terms of crack closure and water tightness regain. These ratios exceeded 95% and 80%, respectively, after 28 days of healing, irrespective of the curing ages. This demonstrates the high potential of using calcium minerals naturally present in the cement matrix as a calcium source for aerobic non-ureolytic bacteria Bacillus cohnii to activate biomineralization and achieve healing. Notably, with increasing curing age of the novel BBSHCC, the rate of crack closure decreased, which was likely due to decreased accessibility of calcium for biomineralization. Additionally, healing products generated by biomineralization tended to initially form locally around cementitious composites, especially in mature samples. Further analysis of the cementitious composites near the healed crack revealed a large presence of portlandite, which was suggested to be a result of biomineralization.
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