Tendon Duct Assessment Using Impact-Echo and Ultrasonic Pulse-Echo in Combination with an Automated Scanning System

An automated test frame was designed and built in which concrete blocks with artificial defects or testing problems can be tested by various NDT methods. The focus of the measurements carried out on a tendon duct block was to see how precisely the tendon ducts can be located in the block and if the different areas with different grouting states (empty, fully, or half-grouted) can be identified. Ultrasonic pulse-echo successfully located the ducts in their lateral position as well as in depth. Even the different sizes of the ducts can be estimated from the results. In the impact-echo data, the lateral positions of the ducts can be determined based on a shift of the measured thickness towards an apparently increased thickness at the location of the duct. However, this means that the duct cannot be located in depth. All four ducts were partly filled with grout to simulate voids in the grout. Although there are certain indications in the ultrasonic as well as in the impact-echo data that are correlated to the actual position of the voids, the indications are rather vague. Very likely this was due to a fabrication issue: the grout debonded from the wall of the duct thus making it impossible to distinguish between grouted and ungrouted parts of the duct.