Influences of different calcium sources on the early age cracks of self-healing cementitious mortar

Advances in microbial self-healing concrete: A critical review of mechanisms, developments, and future directions

The self-healing bioconcrete, or bioconcrete as concrete containing microorganisms with self-healing capacities, presents a transformative strategy to extend the service life of concrete structures. This technology harnesses the biological capabilities of specific microorganisms, such as bacteria and fungi, which are integral to the material's capacity to autonomously mend cracks, thereby maintaining structural integrity. This review highlights the complex biochemical pathways these organisms utilize to produce healing compounds like calcium carbonate, and how environmental parameters, such as pH, temperature, oxygen, and moisture critically affect the repair efficacy. A comprehensive analysis of recently published peer-reviewed literature, and contemporary experimental research forms the backbone of this review with a focus on microbiological aspects of the self-healing process. The review assesses the challenges facing self-healing bioconcrete, including the longevity of microbial spores and the cost implications for large-scale implementation. Further, attention is given to potential research directions, such as investigating alternative biological agents and optimizing the concrete environment to support microbial activity. The culmination of this investigation is a call to action for integrating self-healing bioconcrete in construction on a broader scale, thereby realizing its potential to fortify infrastructure resilience and sustainability.

Exploring a high-urease activity Bacillus cereus for self-healing concrete via induced CaCO3 precipitation

The structural integrity and esthetic appeal of concrete can be compromised by concrete cracks. Promise has been shown by microbe-induced calcium carbonate precipitation (MICP) as a solution for concrete cracking, with a focus on urease-producing microorganisms in research. Bacillus cereus was isolated from soil and employed for this purpose in this study due to its high urease activity. The strain exhibited strong tolerance for alkaline media and high salt levels, which grew at a pH of 13 and 4% salt concentration. The repair of concrete cracks with this strain was evaluated by assessing the effects of four different thickeners at varying concentrations. The most effective results were achieved with 10 g/L of sodium carboxymethyl cellulose (CMC-Na). The data showed that over 90% repair of cracks was achieved by this system with an initial water penetration time of 30 s. The study also assessed the quantity and sizes of crystals generated during the bacterial mineralization process over time to improve our understanding of the process. KEY POINTS: • MICP using Bacillus cereus shows potential for repairing concrete cracks. • Strain tolerates alkaline media and high salt levels, growing at pH 13 and 4% salt concentration. • Sodium carboxymethyl cellulose (CMC-Na) at 10 g/L achieved over 90% repair of cracks.

Strain Screening and Particle Formation: a Lysinibacillus boronitolerans for Self-Healing Concrete

Microbial-induced calcite precipitation is a promising technology to solve the problem of cracks in soil concrete. The most intensively investigated microorganisms are urease-producing bacteria. Lysinibacillus that is used as urease-producing bacteria in concrete repair has rarely been reported. In this study, Lysinibacillus boronitolerans with a high urease activity was isolated from soil samples. This strain is salt- and alkali-tolerance, and at pH 13, can grow to ~OD₆₀₀ 2.0 after 24 h. At a salt concentration of 6%, the strain can still grow to ~OD₆₀₀ 1.0 after 24 h. The feasibility of using this strain in self-healing concrete was explored. The data showed that cracks within ~0.6 mm could be repaired naturally with hydration when spores and substrates were added to the concrete in an appropriate proportion. Moreover, the number and morphology of CaCO₃ crystals that were produced by bacteria can be influenced by the concrete environment. An efficiency method to elucidate the process of microbial-induced calcium carbonate crystal formation was established with Particle Track G400. This study provides a template for future studies on the theory of mineralization based on microorganisms. IMPORTANCE The formation of calcium carbonate crystals in concrete by urease-producing bacteria is not understood fully. In this study, a Lysinibacillus boronitolerans strain with a high urease activity was isolated and used to analyze the counts and sizes of the crystals and the relationship with time. The data showed that the number of crystal particles increases exponentially in a short period with sufficient substrate, after which the crystals grow, precipitate or break. In concrete, the rate-limiting steps of calcium carbonate crystal accumulation are spore germination and urease production. These results provided data support for the rational design of urease-producing bacteria in concrete repair.