Exploring the potential application of microbial mineralization to achieve self-healing of cracks in cement-based sealing materials

Abstract

The gas extraction effect is restricted by the weakness of cement-based sealing materials that are prone to cracking, which can easily lead to a sudden drop in gas concentration. Microbial mineralization can achieve self-healing of cracks and is a potential solution. Unfortunately, the physicochemical characteristics of cracks determined by the hydration product system of Portland cement are relatively harsh and not suitable for microorganisms. A new strategy is proposed to regulate the formation of inorganic gel in cracks to reshape the environmental conditions and improve the activity of microorganisms. First, the deposition law of inorganic gel regulated by Ca, Si and Al sources in simulated crack solution was explored. When the Ca:Si:Al ratio is 3:1:5, the solution pH can be reduced to 10.5 and maintained for 24 h, and the volume expansion rate of the deposited gel is 643 %. This is primarily due to the formation of CaAl-LDHs phase gels, as they absorb a large number of H₂O into their molecular structure. Then, microorganisms were cultured and microbial powder was prepared, and the influence of typical ions of cement-based materials on microbial activity was tested. The suitable pH range for microorganisms is 9–10. A concentration of 0.025 mol/200 ml of [SiO₂]aq or 0.03 mol/200 ml of Al(OH)₄^- can increase the solution pH to around 13.0, significantly inhibiting microbial activity. Furthermore, the feasibility of the coexistence of gels and microorganisms in crack solutions was explored. When the Ca:Si:Al ratio is 3:1:5, the proportion of bio-CaCO₃ in the products can reach 31.82 %. Environmental parameters cannot be ignored for microbial mineralization, and the gel pre-deposition method is feasible. The system based on Ca/Si/Al sources and microorganisms has a stronger ability to generate solid phase products. The research results provide a reference for the development of efficient healing agents for sealing materials.