Influence of the migration of chloride ions on the electrochemical impedance spectroscopy of mortar paste

During the last decade, electrochemical impedance spectroscopy (EIS) started to be effectively exploited to investigate the electrical properties of hydrated cement pastes.This paper is devoted to the study of the high- and medium-frequency regions of the impedance spectrum and focused on determining the relationship between chloride migration and impedance spectroscopy in accelerated diffusion tests carried out on samples of mortar.After introducing an experimental protocol based on a four-electrode arrangement, we present the results of a parametric study which is related to the thickness and water-cement ratio (W/C) of the samples.Firstly, all our measurements show that the presence of chloride ions modifies the impedance response of mortar and reveals a small loop as of modification of the composition of the upstream solution. This loop is probably due to the development of interfacial phenomena between material and the solution.Secondly, as the migration of chloride process progresses, an increase followed by a decrease of the bulk electrical resistance is observed, whereas the second loop, due to the presence of chlorides, remains constant.An equivalent electrical circuit is then proposed to fit the different experimental data.