Geometrical effects on impact-echo testing of finite concrete specimens

Scanning impact-echo testing of concrete specimens represents a significant improvement compared to usual single point measurements. Imaging and interpretation of the results in the time-domain (B-Scan) as well as in the frequency-domain (impact-echogram) leads to much more significant and reliable results for thickness and defect location measurements. We present experimental as well as numerical results obtained at a concrete plate containing steel reinforcement and tendon ducts. It is shown that the used imaging techniques lead to new insights for impact-echo testing of finite concrete specimens. Due to reflections of surface and body waves at the lateral boundaries of the specimen geometrical patterns appear in the impact-echogram which turn out to have an important effect on the accuracy of thickness and wave speed measurements, respectively. It is demonstrated that these effects depend not only on the dimensions of the specimen, but also on the location of the actual measuring point and on the duration of the detected time-domain signal.