An approach of repairing concrete vertical cracks using microbially induced carbonate precipitation driven by ion diffusion

Abstract

Microbially induced carbonate precipitation (MICP) is an eco-friendly method of repairing cracks in concrete. However, for vertical cracks appeared in concrete components, the microbial mineralization solution injected into cracks tends to flow out due to gravity, resulting in incomplete crack repair. To address this obstacle, this study presents a novel approach in repairing vertical cracks using MICP with the ingression of calcium and urea driven by ion diffusion. For this purpose, a combined injection and diffusion method (CIDM) is proposed, in which the bacterial solution (ureolytic bacterium Sporosarcina Pasteurii) was first injected into crack and then the crack surface was adhered with a sponge containing the saturated cementation solution (urea and calcium acetate) for continuous ion diffusion. In comparison, the traditional injection method (TIM) is also conducted on the test cylindrical specimens. In addition to the pre-cracked concrete cylinders, four transversely load-induced cracked concrete beams were also utilized in this study and their vertical cracks were treated with CIDM under both loading and unloading conditions. The crack repair effects are evaluated by means of surface observations, microanalysis, water absorption tests and chloride penetration tests. Test results indicate that the proposed CIDM, whereby the calcium and urea are supplied through an ion diffusion approach, is a more effective method to repair vertical cracks than TIM. The generated white precipitations in cracks are confirmed to be calcium carbonate crystals existed in form of vaterite through energy dispersive spectrum (EDS) and X-ray diffraction (XRD) examinations, which also indicate that the CIDM method tends to produce a denser calcium carbonate cluster structure. After crack repairing with CIDM, the improvement coefficients of waterproof performance for the pre-cracked cylinders with widths of 0.1, 0.2 and 0.4 mm are 84.2%, 81.2% and 73.6%, respectively, which is 6%–12% higher than those got from TIM method. Furthermore, the average improvement coefficients of resistance to chloride penetration for vertical cracks with widths from 0.085 mm to 0.162 mm are about 76.9% and 88.5% for the sustain-loaded beams and unloaded beams, respectively.