PSI - Issue 84

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

1084

6. Inspection of anchorage zones for voids It is also important to examine the tendon anchorage zones at each end of the duct for voids or “grout blowouts” around the anchorage hardware. These regions are typically very congested with steel (anchor plates, bursting reinforcement, etc.) and are prone to voids forming during the grouting process. The following steps are recommended for inspecting each anchor zone (see Figure 11). • Obtain anchorage design details : Since the configuration of post-tensioning anchorages can vary by system and manufacturer, first review any available design drawings or documentation to understand the anchorage layout (duct size, anchor plate, local rebar configuration). Having this information beforehand will guide the inspection and interpretation of results. • Scan for reinforcement in the anchor zone : Use a GPR device (as in Figure 7b) to scan the concrete in the anchorage region. Mark the positions of reinforcement bars and other embedments near the tendon end. This mapping will help in planning the UPE scan to minimize interference (the dense rebar in these zones can strongly affect ultrasonic signals). • Perform UPE scanning of the anchor zone : Use a suitable UPE device such as that shown in Figure 7a to scan the anchorage zones (taking care to avoid any rebar located in the previous step above). The goal is to produce comparable images that can be used to deduce the likelihood of voids being present based on relative signal strength. If it is not possible to completely avoid the reinforcement, try – while creating the UPE scans – to have the reinforcement in the same location relative to the PT, in order to reduce variables. • Identify anomalies in anchor zone scans: Compare the UPE scan results from the anchor zone to identify any unusual reflections or echo patterns. A pronounced reflection in these scans is an indicator of a possible void or poor grout condition in the anchorage pocket. (Figure 12 shows an example, with differences in the UPE images used to judge where voids might exist.) • Investigate anomalies via targeted drilling : As with the tendon duct inspection, carefully drill a few small holes into the anchorage zone concrete at locations corresponding to the strongest UPE reflections (potential voids) and perhaps at a location with a normal baseline reading. Use a borescope to directly observe whether grout is present or if a void exists at those points. This confirmation step in the anchor zone is often more challenging due to steel congestion, but it is invaluable for verifying the scan interpretation before any repair or re-grouting is undertaken.

Fig. 11. Congested anchorage zone at the end of a tendon, which is susceptible to grout voids.

Fig. 12. Examples of UPE scan images in an anchor zone: variations in signal intensity are analyzed to evaluate the likelihood of voids.