The hydration process of cement materials with coal metakaolin (CMK) was investigated byelectrochemical impedance spectroscopy (EIS) using a new equivalent circuit model in this study. Theresults suggested that the electrochemical impedance characteristics of blended cement materials varysignificantly with the content of CMK. The impedance parameters Rs and Rct1 associated with thechanges in the cement microstructure increased with increasing hydration time and CMK content acrossthe entire hydration process. Additionally, the fractal dimension d, which characterizes the complexityand density of the pore structure, showed a trend similar to those of the above impedance parameters,but the fractal dimension ds, which characterizes the surface properties of the pore structure, showed theopposite trend. In addition, there was a significant correlation between the impedance parameter Rct1 andthe compressive strength of the blended cements with different CMK contents and hydration times.
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