AN AC-IMPEDANCE SPECTROSCOPY STUDY OF HYDRATED CEMENT PASTES

In recent years there has been a growing trend to use AC impedance spe ctroscopy (ACIS) as an in situ and nondestructive method for monitorin g changes in the microstructure of cementitious materials. In this pap er we discuss experimental results aimed at testing an equivalent circ uit model that we have previously developed for interpreting AC impeda nce data for pore-reduced cement (PRCs). Impedance data for PRC cured in three different humidity environments at room temperature are repor ted as a function of hydration time. Z plots show the presence of two semicircular arcs. With lime, a decrease in cell conductance is obser ved and this is consistent with results of others. However, comparison of data from 'wet' and 'dry' cured samples show important differences 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 formali sms for analysing ACIS data.