PSI - Issue 84

Luca Ranedda et al. / Procedia Structural Integrity 84 (2026) 1191–1197

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4.2. Comparison between Ultrasonic Tomography and Endoscopic Inspections

Endoscopic inspections were carried out with the dual purpose of accurately assessing the condition of the duct, the grouting, and the prestressing reinforcement, as well as verifying the reliability of the tomographic data. The surveys were performed using macro-photography in the hole , with a digital camera equipped with an eccentric lens and illuminating the hole with an inspection lamp mounted on a small- diameter stem (≈ 3 mm). This procedure produces images with sharpness and resolution superior to those obtainable with a video endoscope. 4.3. Results Endoscopic inspections were carried out at locations corresponding to tomographic anomalies that, based on the analysis of the tomograms, were attributed to possible defects in the cable grouting. In general, the tomographic survey did not reveal extensive anomalies along the cable layout; in most cases, the anomalies were local and well-defined. The endoscopic investigations showed that the prestressing cables were generally in good condition at the surveyed points. Out of the 39 endoscopic inspections performed, 11 cases (28.2%) showed insufficient grouting, and only 5 cases (12.8%) showed a complete absence of grouting. Comparison between the ultrasonic anomalies and the direct inspection results revealed a low correspondence: in approximately 70% of the anomalies detected by tomography, no defects related to cable grouting were observed.

Figure 8 – Example of a tomographic survey output along the layout of prestressing cable.

5. Conclusions The use of indirect survey techniques in the field of structural diagnostics has significantly improved the investigation capabilities on structures while reducing the need for destructive tests, which are highly disruptive both in terms of structural disturbance and in terms of time and cost. Ground-penetrating radar (GPR) is an indispensable investigation method for reconstructing both passive reinforcement and prestressing cables. The two techniques employed allowed the achievement of the same results; the