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Non-destructive testing methods for moisture determination

 
: Maierhofer, C.; Wolter, B.

Czech Society for Nondestructive Testing; Deutsche Gesellschaft für Zerstörungsfreie Prüfung e.V. -DGZfP-, Berlin:
NDT in Progress : Meeting of NDT-Experts; June 20 - 22, 2001, Castle Trest', Czech Republic ; proceedings
Prag, 2001
ISBN: 80-238-7263-X
S.41-54
NDT in Progress, Meeting of NDT-Experts <2001, Prag>
Englisch
Konferenzbeitrag
Fraunhofer IZFP ()
moisture; one-sided access NMR (OSA NMR); nondestructive testing; nuclear magnetic resonance (NMR)

Abstract
Damages in masonry and concrete structures can be related very often to an excess moisture and salt content which influences the physical properties of the materials. Hence, the knowledge about the content, the distribution and the transport mechanism of water in these building materials is of fundamental interest for durability and service life-time prediction.
Since three years BAM and IZFP have co-ordinated their activities regarding the non-destructive testing in civil engineering. An important field of research in both organisations is the development and the advancement of new non-destructive methods for moisture measurements in civil structures.
At the IZFP, One-Side Access Nuclear Magnetic Resonance (OSA NMR) is used to measure the one-dimensional water distribution (moisture profile) in building materials. With its aid, quantitative information about the water transport during capillary absorption and pressure driven permeation can be determined in-situ. Therefore, properties affecting durability of the material like water permeability and hydraulic diffusivity can be assessed with high accuracy.
Different methods based on electromagnetic wave penetration were developed and applied at BAM. From electromagnetic wave propagation velocity and/or absorption the dielectric properties are calculated and correlated to the moisture content. The mean moisture content along the sections of building structures can be determined with radar in the frequency range from 500 MHz to 1.5 GHz in transmission as well as in reflection configuration. Depth resolved moisture profiles can be performed by transmission measurement using two thin dipole antennae which can be moved in two thin boreholes with a diameter of 12 mm and a distance of 5 cm. For the calculation of the mean moisture and salt content in depths up to 30 cm, probes consisting of two metallic rods were designed for TDR (time domain reflectometry) measurements.

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