Crack Bioremediation in Concrete by Photoautotrophic Cyanobacteria through Fly Ash-Based Cementitious Biogrout

Microbially induced calcium carbonate precipitation (MICCP) is widely employed in various engineering applications, including repairing cracks in cementitious materials. Many of these studies were performed using heterotrophic bacteria that utilize urea and releases harmful foul-smelling environmental pollutant. Cyanobacteria have emerged as potential substitutes for heterotrophic bacteria to overcome this concern. This study used photosynthetic cyanobacteria Synechocystis pevalekii to develop an ecofriendly and sustainable grout for crack remediation in concrete. To improve the fluidity characteristics of the grout, fly ash was incorporated as a partial cement replacement in the cementitious grout. The cementitious grouts were tested for fresh properties at different dosages of fly ash (0%-50%) by keeping water (or bacterial culture) to binder ratios of 0.45, 0.47, and 0.50. Based on flowability results, a 0.47 culture/binder ratio was selected to examine different FA dosages for hardened properties. A 40% FA substituted cementitious biogrout was selected for repairing cracks at the lab scale. Different cracked concrete specimens were repaired and cured using ponding and spray treatment for 28 days. At the end of the experiment, a significant improvement in strength and permeability was recorded in biogrout-remediated cracked specimens. The sample was collected from healed cracked region to confirm the healing mineral using field emission surface electron microscope (FESEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The developed fly ash incorporated biogrout will help as an economical and ecofriendly MICCP technology for the remediation of existing cracks in the concrete structures.