Characterization of sulfate diffusion into cement paste by low frequency impedance spectroscopy

In this study, EIS was used to investigate sulfate diffusion process into cement paste. Cement paste samples with w/c ratio of 0.35 and 0.45 were immersed in 10wt% sodium sulfate solutions for different durations. An equivalent circuit model of cement paste exposed to sulfate attack was proposed, and some relevant parameters of the equivalent circuit were obtained by EIS analysis. The validations of the effectiveness of EIS on investigating the sulfate diffusion have been provided by SEM and XRD analysis. As the results shown, it is sensitive to use EIS to characterize the diffusion process of sulfate ions into cement paste. The relationship between ingress depth of sulfate obtained from EIS analysis and the square root of exposing time is approximately linear.