Dielectric Relaxation of Iron Corrosion Products in Limestone under Saline Environment

Limestone is selected as test material to study the influence of corrosion on dielectric relaxations because of its high porosity (40-50%) that quickens the observation of the corrosion diffusion. The corrosion process is launched by an iron plate on the surface of the limestone imbibed in the brine. The complex dielectric properties from 50 MHz to 1.5 GHz have been measured since most ground penetrating radar (GPR) applications cover this frequency band. To analyse the dielectric relaxation associated with the corrosion products (mainly Fe rust, mixture of hematite and magnetite), the dielectric modulus has been used as a tool to suppress the influence of an apparent direct current conductivity ( $\sigma_{dc}$ ) brought by the imbibition in the brine. By finding out the feature relaxation peak of the Fe rust at a certain frequency, the content of Fe rust in the limestone can be estimated by the application of the complex refractive index model (CRIM). We hope that this study on the dielectric relaxation of Fe rust in limestone under saline environment can serve as a model which can eventually adapt for concrete structures in our future works.