Development of field applicable remediation procedure using bio-cementitious grout for concrete cracks in variable orientations

Microbially induced carbonate precipitation (MICP) has emerged as a promising solution in enhancing the durability of concrete structures in the recent decade. Bio-grout is generally developed by incorporating bacterial culture which further requires extensive bio-based labora-tory facilities which limits its practical implementation for civil engineers. In this study, a ready -to-use fly ash (FA) based bacterial inoculum with shelf life of 180 days was prepared that could be directly used to prepare bio-grout. This would help in executing MICP for field scale repair of concrete elements. The prepared bio-grouts were tested in terms of flowability, mini-slump, bleeding, setting time, mechanical strength and drying shrinkage to design the best-performing cementitious bio-grout. The best cementitious bio-grout was used to repair cracks in concrete structures. An attempt was made to develop a procedure for the remediation of cracks in three varying orientations, i.e. horizontal, vertical and inverted, to target actual cracks that might exist in the structures. The performance of the repaired surface was assessed in terms of recovery in flexural strength and water tightness. The mineral composition of the healing product was examined by FESEM-EDX and XRD; results clearly indicated the presence of calcite crystals inside the pores. Also, to quantify the calcium carbonate precipitation in the bio-repaired specimens during curing, electromechanical impedance technique was employed. Overall, it can be concluded that FA-based inoculum can effectively promote MICP activity to seal the fractured crack of any orientation in existing concrete structures.