Laboratory study of the electrical properties of Lutetian limestones in the [100 Hz-10 MHz] frequency range
Résumé
Lutetian limestones have been widely used in historical monuments in the Paris Basin in the course of medieval and modern periods. Among the physical properties that can be used to assess the evolution of the limestones in situ in the buildings and their present health, the complex effective permittivity in the 10 kHz-100 kHz frequency range is easy to measure and reflects the stone internal structure with also the dependence on the water content. To improve the knowledge about this property, a laboratory study on four samples collected in the relevant quarries has been undertaken along the 100 Hz-10 MHz frequency range. Except close to zero water content, the observed results exhibit a quasi-absence of variation of the real effective permittivity with the water content. The frequency variation fairly fits with a model taking into account a Jonscher's decrease, a direct current conductivity, a high frequency dielectric permittivity and losses, and a relaxation phenomenon. When fitted by a Cole-Cole model, the magnitude of the corresponding relative permittivity change always stays close to 30 but the time constant varies from 1 to 0.1 µs as the water content increases.
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