Electrochemical deposition method to repair leakage cracks in underground structures: Principle, laboratory experiment and field implementation

Abstract

Based on the service environment of underground structures, we proposed an electrochemical deposition method for repairing leakage cracks in underground structures and explained its basic principles. Experiments were conducted in the laboratory using electrochemical deposition methods to repair cracked concrete in asymmetric structures in groundwater environments. The macroscopic repair results confirmed that the electrochemical deposition method based on aluminum sulfate calcium acetate electrolyte solution can achieve a crack surface closure rate of 100% and a permeability decrease of 3–4 orders of magnitude after 7 d of repair in groundwater environment, achieving the effect of crack closure. The crack closure rate of the groundwater surface increased with groundwater concentration. Based on the microstructure analysis of X-ray diffraction, thermogravimetry and scanning electron microscope, the mechanism of electrochemical deposition method for repairing underground leakage cracks was revealed. It was confirmed that the main components of deposition products on the crack surface were compounds containing aluminum and calcium such as ettringite and gypsum while the main components on the groundwater side were magnesium calcium compounds such as magnesium hydroxide and calcium carbonate. And as the ion concentration in the groundwater increased, the amount of deposition products on the groundwater side has increased, which is consistent with the macroscopic results. The mercury intrusion porosimetry results showed that the electrochemical deposition method can increase the proportion of small pores in the matrix and optimize the pore size distribution of the matrix. Finally, on-site experiments were conducted on the electrochemical deposition method to repair leakage cracks on Nantong Metro Line 2, China. After repairing the cracks for 3 d, the leakage rate decreased from 6.06 to 1.95 mL/min, and the water seepage path changed, confirming that this method can be applied to the field work.