Reinforced concrete is a widely used construction material in the building industry. With the increasing age of structures and higher loads there is an immense demand for structural health monitoring of built infrastructure. Coda wave interferometry is a possible candidate for damage detection in concrete whose applicability is demonstrated in this study. The technology is based on a correlation evaluation of two ultrasonic signals. In this study, two ways of processing the correlation data for damage detection are compared. The coda wave measurement data are obtained from a four-point bending test at a reinforced concrete specimen that is also instrumented with fibre optic strain measurements. The used ultrasonic signals have a central frequency of 60 kHz which is a significant difference to previous studies. The experiment shows that the coda wave interferometry has a high sensitivity for developing cracks and by solving an inverse problem even multiple cracks can be distinguished. A further specialty of this study is the use of finite elements for solving a diffusion problem which is needed to state the previously mentioned inverse problem for damage localization.
<p>Coda wave interferometry is an ultrasound-based possible candidate for structural health monitoring of concrete structures. It is based on a correlation evaluation of two ultrasonic signals. A perturbation, e.g., cracks in the medium are causing changes in the signal. The correlation development over the signal’s length is very characteristic for the position of the crack relative to source and receiver. This development can be modeled and allows to state an inverse problem whose solution localizes a new perturbation, e.g., crack in the medium.</p><p>An application at a four-point bending test of a reinforced concrete specimen with a span of 3.5 m and 25 ultrasonic transducers with a used central frequency of 60 kHz shows promising results for damage detection. The coda technology can successfully distinguish multiple developing cracks and results are compared to fiber optic sensor measurements. Some problems like cracks that develop into the installation position of the ultrasonic transducers are also found and solutions are proposed.</p>
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