Development of Biocementitious Grout Using a Silica Fume–Based Bacterial Agent for Remediation of Cracks in Concrete Structures

The self-healing of cracks via biomineralization in bacteria-based concrete has shown remarkable results in recent decades. This novel technique uses the ability of bacteria to precipitate ${\mathrm{CaCO}}_3$ for sealing cracks, and is termed microbially induced calcite precipitation (MICP). However, most previous studies focused on extensive laboratory-based procedures before incorporating them into concrete. This investigation developed a ready-to-use silica fume (SF) based bacterial agent that can be used directly to achieve ${\mathrm{CaCO}}_3$ precipitation. This will aid in the use of MICP for field-scale repair in concrete structures. Furthermore, most previous studies addressed crack remediation in the horizontal orientation of concrete structures. This study developed a remediation strategy to repair realistic cracks in existing concrete structures. The developed SF-based inoculum at an age of 180 days stored at 4°C was used to design biocementitious grouts. Various biogrouts were examined for fresh and hardened properties in order to develop the most effective biogrout. The effectiveness of the surface restored using biogrout was evaluated in terms of mechanical and watertightness properties. Microstructural analysis was conducted at the end of testing to evaluate its physicochemical attributes. The electromechanical impedance technique was used to quantify the microbial activity in the biorestored concrete during curing. The results suggested that precipitates led to the densification of pores, ultimately lowering the water permeability and the recovery of mechanical strength of the repaired specimens. Conclusively, the SF-based bacterial agent can increase MICP activity to seal cracks in actual concrete structures.