Dielectric and electrical properties of polycrystalline rocks at various hydration levels

The dielectric properties of low porosity natural polycrystalline rock material (marble) were investigated using broadband 10^-2 to 10⁶ Hz) dielectric relaxation spectroscopy at several hydration levels, from dry to fully hydrated samples, with the water content varying from 0 to 0.08% g water/g dry material. The measured dielectric response is characterized by large low frequency dispersions, which depend strongly on the water content. Upon varying the sample thickness, dielectric and water sorption measurements reveal that bulk rather than electrode/sample interface effects are responsible for the main part of the high values obtained for the complex permittivity ε*. Comparative analysis of the experimental data within the complex permittivity ε*, impedance Z* and modulus M*, allows a detailed investigation of the AC conductivity mechanisms existing in the rocks and of water content dependency. Concerning the rock-water interaction, a critical water content h_c, (h_c~0.04%, the water content for ambient humidity conditions) has been found