An AC impedance spectroscopy study of hydrated cement pastes

In recent years there has been a growing trend to use AC impedance spectroscopy (ACIS) as an in situ and non-destructive method for monitoring changes in the microstructure of cementitious materials. In this paper we discuss experimental results aimed at testing an equivalent circuit model that we have previously developed for interpreting AC impedance data for pore-reduced cement (PRCs). Impedance data for PRC cured in three different humidity environments at room temperature are reported as a function of hydration time. Z* plots show the presence of two semicircular arcs. With time, a decrease in cell conductance is observed, and this is consistent with results of others. However, comparison of data from ‘wet’ and ‘dry’ cured samples show important diflerences in the characteristics of both the low- (LF) and high-frequency (HF) arcs. These differences, and their implications for ACIS measurements on cement systems, are discussed by the use of other immitance formalisms for analysing ACIS data.