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Organisationseinheit der BAM
The water-transport characteristics of concrete have a major impact on its resistance to damaging chemical processes such as Alkali-Silica-Reaction (ASR). Water transport in samples of damaged and undamaged concrete was measured using in-situ CT. The resulting measurements of water-front movement relative to time and the change in 3D-moisture distribution within the samples, are needed for calibration and validation of water-transport numerical models.
The use of high-performance concretes holds great promise for many structural applications. This paper investigates the performance of these materials when used in combination with traditional reinforcing bars. An improved understanding of failure during reinforcing bar pull-out from high-performance concretes is needed in order to better predict the embedment length required to develop full reinforcing bar pull-out strength and the required thickness of reinforcing bar cover for adequate corrosion protection. The cracking structures surrounding the reinforcing bars were analyzed using x-ray computed tomography (CT) in order to determine the stress states causing failure. This was accomplished by conducting in-situ reinforcing bar pull-out experiments during CT scanning. A conventional concrete, a high-strength concrete, and a high-strength fiber reinforced concrete were all tested during the experiments. The results of these experiments showed that the levels of brittleness of the different concrete materials had a major impact on the failure mechanisms that they experienced during reinforcing bar pull-out. It was also clear that the specimen geometry and the casting method had a major impact on fiber orientation. The inclusion of fibers within concrete was also found to significantly improve strength and corrosion protection during reinforcing bar pull-out.
The proposed BAM project SealWasteSafe will advance the state of the art for the construction and monitoring of safe sealing systems for underground repositories of radioactive or toxic waste. During this project, a novel salt concrete exhibiting neither significant cracking nor shrinkage will be optimized for use in the sealing systems. The composition of this material will be based on alkali-activated materials, which are characterized by particularly small thermal deformations during the hardening reaction. Quality assurance and continuous monitoring systems developed during this project will be demonstrated not only for high reliability, but also for resistance to highly alkaline environments and to water intrusion along cables or at sensor locations. A variety of sensors will be used in combination with wireless Radio Frequency Identification (RFID) technology to record moisture, temperature, and, if necessary, corrosion activity within the sealing system. Distributed Fibre Optic Sensor (FOS) technology will also be used for strain, temperature, and moisture content measurement. Ultrasound-based measuring methods will be utilized for the detection of cracks and delaminations. Additionally, digital image correlation and acoustic emission analysis will be used for deformation measurements and crack detection. A novel borehole probe and advanced ultrasound imaging techniques will be further developed to track cracks and delaminations within the host rock in 3D. The surface-based Large Aperture Ultrasound System (LAUS) will also be utilized to detect cracks and delaminations deep below the exterior surface of the sealing system. Although the focus of this project will be on the host rock salt, the resulting technologies will be intentionally developed in a way that facilitates their adaptation to other host rocks.
This poster provides an overview of ultrasonic investigations of an engineered test barrier at ERAM Morsleben, which were completed as part of contractual work with the Bundesgesellschaft für Endlagerung mbH (BGE). This includes both experiments with the Large Aperture Ultrasound System (LAUS) and the ultrasonic borehole array. Also included in the poster is a description of the planned BAM thematic project “SealWasteSafe”. In particular, the proposed geopolymer materials are described and future research requirements are detailed.