Verteilte Rissbreitenmessung im Betonbau mittels faseroptischer Sensorik: Neue Anwendung von verteilten faseroptischen Messsystemen

Distributed crack width measurement in concrete structures using fibre-optic sensor technology – New application of distributed fibre optic sensing. Cracks and their changes are important indicators for concrete structures. Conventional crack sensors can only detect known cracks or determine their change in width. This paper presents a new crack measurement system that uses low-cost fibre optic sensors subsequently bonded to the concrete surface to detect cracks over long distances without knowing their location in advance. With distributed fibre optic sensing (DFOS), new cracks can be identified using fibre length of up to 70.0 m. The position of identified cracks can be located to 3.5 cm and their change in width determined. The achieved accuracies for the width are 0.035 mm (laboratory scale) and 0.15 mm (real applications). With DFOS, individual cracks can be measured at the usual crack distances of 15 cm in reinforced concrete construction, even without a possibility of visual inspection. Furthermore, a newly developed evaluation algorithm is presented with which the historical crack development is recorded. In the case of epoch measurements, this can be used to draw conclusions about the maximum crack width that has occurred in the meantime. Laboratory tests and real measurements in the course of a pilot application of more than one year show the methodology as well as the boundary conditions for the choice of fibre and adhesive. Comparisons of different measuring systems show an achieved accuracy in a similar order of magnitude as conventional crack sensors.