PSI - Issue 84

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

1083

the spots where crossing rebar was identified in the previous step. (Figure 8 shows an example of this scanning process in practice.) • Identify anomalies: Analyze the UPE scan results to locate any anomalies. A significantly stronger echo or reflection at a particular location compared to the surrounding areas typically indicates a void or loss of grout at that location. In contrast, well-grouted sections produce weaker, more uniform reflections. (Example UPE signals for well-grouted vs. voided ducts are shown in Figure 9.) • Investigate anomalies: To confirm the nature of the detected anomalies, drill small-diameter “confirmation” holes at a few key locations – preferably at the positions of the strongest reflection (suspected void) and at a section with a normal (weak) reflection for comparison. Using a borescope / endoscope inserted into these holes (Figure 10), visually inspect the inside of the duct to verify whether grout is missing or present. These minimally invasive checks help validate the NDT findings before any repair decisions are made.

Fig. 8. After mapping the tendon’s route and marking interference from rebar, UPE scans are performed along the duct. Small holes are then drilled at locations of interest (strongest and weakest signal reflections) to verify grout presence/presence using a borescope.

Fig. 9. Typical UPE scan results comparing a fully “grouted” tendon duct (consistent, low reflection) versus an “un-grouted” duct with internal voids (distinct strong reflections from the void areas).

Fig. 10. A post-tensioning duct opened at two selected spots to confirm the UPE findings: one location shows intact grout, while the other reveals a void as predicted by the scan.