Microstructural modifications in Portland cement concrete due to forced ionic migration tests. Study by impedance spectroscopy

The forced migration test has been used during the last decades as an accelerated and useful method for determining the resistance of concrete to chloride ingress. Furthermore it allows to determine transport parameters of chloride ions through porous materials. The application of electric fields seems to introduce variations in the microstructure of concrete. In this work these variations have been studied using the impedance spectroscopy technique in the high frequency region (1 kHz–1 MHz). The results show that the dielectric response of concrete is also strongly modified during the migration experiments. The variations of the dielectric parameters during the migration tests can be explained in terms of modifications of the microstructure of concrete. The observed modifications are in good agreement with the results of mercury porosimetry analysis.