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NDT.net Issue: 2022-09 International Symposium on Non-Destructive Testing in Civil Engineering (NDT-CE 2022), 16-18 August 2022, Zurich, Switzerland (NDTCE 2022) | Vol. 27(9) Special Issue of e-Journal of Nondestructive Testing (eJNDT) ISSN 1435-4934 Vol. 27(9) Session: Quality Assurance / Control Tue 17:00 Studio 3 | |
Ultrasonic quality assurance for underground salt shotcrete sealing structures in Teutschenthal mine, GermanyVera Lay17, Ute Effner19, Ernst Niederleithinger180, Jennifer Arendt2, Wolfram Kudla21BAM Federal Institute for Materials Research and Testing1480, Berlin, Germany 2Institute for Mining and Special Civil Engineering; TU Bergakademie Freiberg17, Freiberg, Germany Abstract: Underground sealing structures are necessary to seal radioactive or toxic waste in underground repositories. Particularly developed MgO concrete is used in the mine in Teutschenthal and applied at a large-scale test with the aim to provide concrete with low permeabilities. The test structures (up to 10 m long) were created with the help of a shotcrete procedure. Besides destructive tests, non-destructive ultrasonic measurements are used for quality assurance to monitor potential anomalies such as cracks, concrete inhomogeneities, and delamination. We show results of ultrasonic measurements with a multi-transducer system used at the front site of the concrete structure. Images are obtained by synthetic aperture focusing techniques. Concreting sections are not systematically imaged so that a successful concreting is assumed as also indicated by observed low permeabilities. Several reflectors up to a depth of 1.2 m are identified and interpreted as potential damages in the concrete. Phase analysis of prominent reflectors reveal a negative impedance contrast thus indicating air filled voids, cracks or delamination. Boreholes through some of the identified reflectors are used to verify the results from ultrasonic measurements. Additionally, an experiment with incorporated defects is undertaken to analyse the reliability of the applied methods. Overall, the conducted tests show the great potential of ultrasonic measurements to detect critical anomalies. Despite challenges at small-scale structures (cm-order), large-scale anomalies can be identified. Implementing ultrasonic monitoring during and after the construction of concrete sealing structures is recommended as a tool for quality assurance. Keywords: ultrasonic imaging (158), ultrasound (254), magnesia shotcrete, underground engineered barriers, Comments or Questions? Share:
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