Influence of electrochemical parameters on chloride extraction efficiency

In order to determine the optimal parameters of electrochemical chloride extraction (ECE) treatment on the concrete structure contaminated by chloride, ECE treatment was applied to the cylindrical concrete specimens containing NaCl of 3% cement mass. The variation of chloride extraction content with time was studied at three different current densities of 1, 2 and 3 A/m² as well as in three different electrolyte solutions including tap water, saturated Ca(OH)₂ solution and 0.1 mol/L Na₃BO₃ solution. The results show that with increasing the current density, the chloride extraction speed within first 6 days increases, and the total chloride content extracted from the concrete becomes much more after ECE treating for 28 days. However, the deterioration of microstructure and accumulation of alkaline substance in the concrete near reinforcing steel bars is attributed to a higher current density. Therefore, it is suggested that the optimal current density should be 2 A/m² for the ECE treatment on the concrete. After ECE treating for 28 days with the same current density, the total chloride extraction content in tap water is about 50% of that in other two electrolyte solutions. It is recommended that the 0.1mol/L Na₃BO₃ solution or saturated Ca(OH)₂ solution with a high alkalinity should be used as the electrolyte solution for the ECE treatment.