PSI - Issue 84

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

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However, as with any structural system, post-tensioning tendons must be inspected periodically as they age to verify their condition and fitness for service. Non-destructive testing (NDT) methods – such as ultrasonic pulse echo, see Figure 1a) – can provide detailed internal insights without causing damage to the structure (Terzioglu et al, 2018 & 2019; Mazzatura et al, 2023 & 2024).

Fig. 1. (a) Modern NDT techniques like ultrasonic pulse echo provide detailed internal insights without causing structural damage; (b) Installation of a post-tensioning duct and tendon in a concrete member before pouring the surrounding concrete.

Regular inspection is especially necessary to evaluate the extent of corrosion risk (FHWA, 2022), since corrosion is widely recognized as the greatest threat to post-tensioning systems worldwide. For example, the United Kingdom’s bridge management standard CS 465 “Management of post-tensioned concrete bridges” (Highways England, 2025) cautions that tendons have generally performed well but can suffer severe corrosion if their ducts are not fully grouted, as voids would permit moist air, water and contaminants to enter the system and attack the steel. Figures 1b shows the use of post-tensioning in a concrete structure, and Figures 2 and 3 illustrate its benefits.

Fig. 2. Typical crack locations in an under-reinforced concrete beam or slab (without adequate rebar or post-tensioning).

Fig. 3. A post-tensioning layout counteracts tensile zones in concrete, strengthening the areas where cracking would otherwise occur.

Grouting the tendon ducts in bonded post-tensioning provides a barrier against moisture ingress and thus helps prevent corrosion. An effective way to evaluate the corrosion risk in such systems is to investigate whether any voids exist in the grout that could allow water to collect around the tendon.