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- Englisch (2)
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- Spectral induced polarization (2)
- Evaporative drying (1)
- Holz (1)
- Low-frequency impedance spectroscopy (1)
- Nondestructive (1)
- SIP (1)
- Sandstones (1)
- Saturation (1)
- Spektroskopie (1)
- ZfP (1)
Organisationseinheit der BAM
Dehydration is a common process occurring in natural environments, rocks, and building materials. Suitable methods for monitoring the changing moisture content should be identified.
We have investigated the impact of dehydration of sandstones on complex conductivity spectra. Spectral induced polarization measurements were performed on five sandstone samples during evaporative drying. The complex conductivity spectra indicate considerable changes with decreasing saturation. The relationship between conductivity and saturation can be described by a power law known as the second empirical Archie equation. Separate saturation exponents have been determined for the real and imaginary parts of conductivity. The imaginary part of conductivity indicates higher saturation exponents for the investigated sandstones compared to the real part. Obviously, the saturation exponents depend on the method used for changing water saturation. Evaporative drying, which is used in our experiments, causes an increase of pore-water salinity and results in lower saturation exponents for the real part of conductivity but higher exponents for the imaginary part in comparison with the classical imbibition/Drainage technique. We evaluate a theoretical approach that considers the influence of pore water salinity on the saturation exponents of the real and imaginary parts of conductivity. The complex conductivity spectra are processed by a Debye decomposition procedure.
The resulting integrating parameters such as direct current resistivity, total chargeability, normalized chargeability, and mean relaxation time indicate a power law dependence on saturation. Our experiments indicate that the imaginary part of conductivity and normalized chargeability have a high sensitivity related to the drying process of rocks and might be suitable indicators to Monitor the changes of moisture content in sandstones.
The method of low-frequency impedance spectroscopy has been successfully applied in Earth sciences to characterize soils and rocks. The method uses the diagnosing power of complex electrical resistivity in a frequency range between 1 mHz and 1 kHz. In our study, the potential of this method has been explored for the investigation of wood. We observed remarkable differences in the resulting spectra of complex resistivity for different European and Tropical tree species. The data processing of the acquired low-frequency impedance spectra yields integrating parameters. The comparison of the integrating parameters with the mean pore diameter that has been separately determined for the tropical tree species indicates clear correlations. An additional investigation has revealed remarkable difference in the complex resistivity spectra between oil bearing and non-oil bearing sandal wood. This result and the relations between electrical parameters and structural parameters of wood indicate the prospective potential of low-frequency impedance spectroscopy.