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Organisationseinheit der BAM
- 8 Zerstörungsfreie Prüfung (5)
- 8.2 Zerstörungsfreie Prüfmethoden für das Bauwesen (5)
- 7 Bauwerkssicherheit (1)
- 7.4 Baustofftechnologie (1)
- 8.0 Abteilungsleitung und andere (1)
- 8.1 Sensorik, mess- und prüftechnische Verfahren (1)
- 8.6 Faseroptische Sensorik (1)
- 9 Komponentensicherheit (1)
- 9.2 Versuchsanlagen und Prüftechnik (1)
This paper describes an innovation of a phased array using dry contact probes to test concrete components. Based on preceding work on pressure waves, a low-frequency ultrasonic phased array consisting of shear wave probes is used in the experiments. This configuration allows the variation and control of the sound field directivity during the measurement. The measurements are carried out on a concrete test block using a scanning laservibrometer and a scanner system in transmission mode. The laboratory measurements are compared to theoretical calculations to investigate the influence of the probes shape and dimension on the resulting sound field patterns. The comparison of the modelling and the measurements demonstrates the suitability of the point source synthesis as a tool for the optimization of probe array designs. Methods of coded are used to improve the signal to noise ratio.
Laser vibrometric contactless sound field measurements at a concrete test block are presented. Both excitation by an ultrasonic probe and by an impactor were used. The wave modes can be identified by their geometric wave forms and propagation velocities. Additionally, numerical simulation of the experimental situation is used to support this interpretation. Possible applications of the presented technique are discussed. ©2005 American Institute of Physics
Within the project SealWasteSafe, we advance construction materials and monitoring concepts of sealing structures applied for underground disposal of nuclear or toxic waste. As these engineered barriers have high demands concerning integrity, an innovative alkali-activated material (AAM) is improved and tested on various laboratory scales. This AAM has low reaction kinetics related to a preferential slow release of the heat of reaction in comparison to alternative salt concretes based on Portland cement or magnesium oxychloride cements. Hence, crack formation due to thermally induced strain is reduced. After successful laboratory scale analysis (Sturm et al., 2021), the AAM is characterised on a larger scale by manufacturing test specimens (100–300 L).
Conventional salt concrete (DBE, 2004) and the newly developed AAM are compared using two specimen geometries, i.e. cylindrical and cuboid. A comprehensive multisensor monitoring scheme is developed to compare the setting process of AAM and salt concrete for these manufactured specimens. The analysed parameters include temperature and humidity of the material, acoustic emissions, and strain variations. Passive sensor systems based on radiofrequency identification technology (RFID) embedded in the concrete, enable wireless access to temperature and humidity measurements and are compared to conventional cabled systems. Additionally, fibre-optic sensors (FOS) are embedded to record strain, but also have potential to record temperature and moisture conditions. Part of this project aims at demonstrating the high reliability of sensors and also their resistance to highly alkaline environments and to water intrusion along cables or at sensor locations. Further technical improvements were implemented so that first results clearly show the scalability of the setting process from previous small-scale AAM experiments and particularly the high potential of the newly developed approaches.
Furthermore, ultrasonic methods are used for quality assurance to detect obstacles, potential cracks and delamination. On the one hand, both active and passive ultrasonic measurements complement the results obtained from the multisensor monitoring scheme for the produced specimens. On the other hand, the unique large aperture ultrasonic system (LAUS) provides great depth penetration (up to nearly 10 m) and can thus be applied at in situ sealing structures built as a test site in Morsleben by the Federal Company for Radioactive Waste Disposal (Bundesgesellschaft für Endlagerung, BGE) as shown by Effner et al. (2021). An optimised field lay-out identified from forward modelling studies and advanced imaging techniques applied to the measured data will further improve the obtained results. To characterise the inside of the test engineered barrier and achieve a proof-of-concept, an ultrasonic borehole probe is developed to enable phased arrays that can further improve the detection of potential cracks. Modelling results and first analysis of semispherical specimens confirmed the reliability of the directional response caused by the phased arrays of the newly constructed ultrasonic borehole probe.
Overall, the project SealWasteSafe improves the construction material, multisensor monitoring concepts and ultrasonics for quality assurance. This will help to develop safe sealing structures for nuclear waste disposal. The outcomes are particularly valuable for salt as a host rock but partly also transferrable to alternative conditions.
Multi-sensory monitoring and ultrasound for quality assurance at underground sealing structures
(2023)
Within the safety concepts of underground disposal sites of nuclear waste, engineered barriers play an important role. As these sealing structures have high demands concerning integrity, we aim at advancing the available construction materials, monitoring, and inspection techniques within the project SealWasteSafe. A specifically developed alkali-activated material is compared to classical salt concrete. A comprehensive multi-sensory monitoring scheme is used at 150-340 l specimens to monitor setting and hardening of both materials. All sensors are demonstrated to resist the highly alkaline environments. Besides cabled and wireless temperature and humidity of the materials, strain variations using fibre optic sensors and acoustic emissions are recorded over periods of at least 28 days, partly for more than eight months. After hardening of the specimens, further nondestructive evaluations using ultrasonic echo and thermographic measurements are conducted.
Preliminary results proof the suitability of the tested sensors and clearly highlight differences between the tested materials. Particularly, the newly developed alkali-activated material shows lower acoustic emission activity indicating less cracking activity. Additionally, unique ultrasonic methods will enable better images of potential internal objects and cracks at in-situ sealing structures. A largescale ultrasonic system is optimised to reliably detect objects at a depth exceeding 9 m while still obtaining a good resolution. Modelling studies show the potential of further increasing the distance between individual transducer arrays. Additionally, a new ultrasonic borehole probe using phased arrays allowing for beam focussing is constructed and tested. Laboratory measurements at a halfcylindrical concrete specimen coincide well with the previous modelling. In total, the presented safe materials, detailed monitoring approaches and ultrasonic quality assurance methods will help to obtain safe sealing structures within salt as a host rock. The concepts can partly be transferred to sealing structures in alternative host rocks and will also be valuable for non-nuclear waste repositories.
Die Risstiefenbestimmung in Festen Fahrbahnen ist hinsichtlich der Dauerhaftigkeit der Konstruktion von wesentlichem Interesse. Im Rahmen eines gemeinsamen Forschungsvorhabens mit der DB AG wurden aus der Literatur bekannte Ansätze bewertet und darauf aufbauend ein Verfahren zur bildgebenden Rissdarstellung entwickelt. Rissüberbrückende Bewehrung sowie Kontaktstellen zwischen den Rissflanken wirken als Schallbrücken und erschweren die Risscharakterisierung, wie bei einem Einsatz an einer Betriebserprobungsstrecke festgestellt wurde. Ein aus der Literatur bekanntes Verfahren der einfachen Laufzeitmessung erwies sich für die Tiefenbestimmung von realen verunreinigten Rissen als ungeeignet.