PSI - Issue 84

Gianni Moor et al. / Procedia Structural Integrity 84 (2026) 1079–1086

1082

Fig. 6. Examples of grouting conditions and tendon corrosion inside post-tensioning ducts.

4. NDT methods for detecting grout voids Modern non-destructive testing methods such as ultrasonic pulse echo (UPE) and ground-penetrating radar (GPR) can reveal hidden details inside concrete without any invasive drilling or cutting. A handheld UPE instrument (Figure 7a) sends ultrasonic pulses into the concrete and can detect internal reflections that indicate the presence of voids in the grout. Meanwhile, a GPR scanner (Figure 7b) can be used in advance to trace the path of the tendon duct and to locate any crossing reinforcement bars (rebar) that might interfere with the UPE signals. Using these two methods in combination allows for efficient and accurate targeting of potential void areas.

Fig. 7. (a) An ultrasonic pulse echo device (Proceq Pundit PD8050) used to detect internal tendon duct voids; (b) A ground-penetrating radar device (Proceq GP8000) used to map the route of a post-tensioning duct and mark any intersecting rebar prior to UPE scanning. 5. Investigating possible voids in tendon ducts between anchorages To investigate the presence of voids along a tendon duct (between its end anchorages) and address any voids before corrosion can develop, the following procedure is recommended: • Map the tendon duct route: Use a GPR device (as in Figure 7b) to determine the path of the steel tendon within the concrete. Begin at a location where the tendon’s position is known (e.g. an anchorage or exposed segment) and scan perpendicular to the tendon at regular intervals (approximately every 300 mm). Mark the surface each time the tendon is detected. Connecting these marks on the concrete surface reveals the tendon’s profile throughout the span. • Mark crossing reinforcement: Using the GPR data, identify and mark any reinforcement bars crossing the tendon’s path. These locations, where rebar is directly above or below the duct, should be noted so that they can be avoided in the subsequent ultrasound scanning steps (rebar can attenuate or distort the UPE signal). • Scan the duct for voids: Deploy the ultrasonic pulse echo device along the mapped tendon route to scan for internal voids in the grout. Perform UPE measurements at regular intervals along the duct, taking care to avoid