Dielectric and electrical properties of polycrystalline rocks at various hydration levels

The dielectric properties of low porosity natural polycrystalline rock mate rial (marble) were investigated using broadband 10(-2) to 10(6) Hz) dielect ric 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 lo w frequency dispersions, which depend strongly on the water content. Upon v arying the sample thickness, dielectric and water sorption measurements rev eal that bulk rather than electrode/sample interface effects are responsibl e for the main part of the high values obtained for the complex permittivit y epsilon*. Comparative analysis of the experimental data within the comple x permittivity epsilon*, impedance Z* and modulus M*, allows a detailed inv estigation of the ac conductivity mechanisms existing in the rocks and of w ater content dependency. Concerning the rock-water interaction, a critical water content h(Cl) (h(C) similar to 0.04%, the water content for ambient h umidity conditions) has been found.