Chloride ion permeation and electrochemical impedance response of red mud-coal metakaolin geopolymer concrete

Abstract

In geopolymer concrete, chloride ions largely contribute to the surface passivation of steel reinforcement and accelerate its corrosion. However, real-time nondestructive testing of chloride ion diffusion has not been widely conducted. Therefore, this study determined the distribution of chloride ions in red mud-coal metakaolin geopolymer concrete with different water-binding ratios under natural immersion conditions. The electrochemical properties of geopolymer concrete in a sodium chloride environment were examined by electrochemical impedance spectroscopy (EIS) and the relationship between these properties and the chloride ion diffusion coefficient was established. The experimental results showed that the contents of free chloride ions, total chloride ions, and bound chloride ions gradually decreased with increasing penetration depth; total chloride ions and free chloride ions increased at the same depth with increasing water-binder ratio; and bound chloride ions decreased with increasing ratio. In addition, the contents of free chloride ions, total chloride ions, and bound chloride ions gradually increased with the increase of the immersion age. The EIS results showed that there was a significant correlation between the diffusion coefficient and the electrochemical parameters. Therefore, EIS is suitable for detecting the diffusion of chloride ions in geopolymer concrete.