PSI - Issue 62

Eleonora Bruschi et al. / Procedia Structural Integrity 62 (2024) 299–306 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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The preliminary analysis is completed by performing tests on the concrete in order to determine the occurrence probability of corrosion in the rebars and other metallic elements, such as metal ducts (in accordance with what is provided by CS 465). Therefore, other measurements are carried out regarding: • the thickness of the concrete layer covering the ducts, which is done concurrently with and where UST or Bor tests are performed; • the corrosion potential test according to the standards UNI 10174 or ASTM C 876. One measurement must be taken for beam 4 of span 3, beam 1 of span 5 and beam 4 of span 6 at the bottom of the beams, near the mid-span section. The measurement should be made by detecting, with a high- impedance voltmeter (> 10 MΩ), the potential with respect to a reference electrode (generally Cu/CuSO4) placed in contact with the concrete surface using a sponge soaked in water. The measurement must be carried out at an appropriate distance of about 50 cm from the area in which the rebars or ducts are exposed, and the covering concrete is expelled. The test involves mapping the corrosion potential, creating a grid of points with a mesh size of 200 mm and detecting the potential along the nodes. The measurements allow the identification of corroded areas, which are the most negative areas in the potential range and according to the American Standard ASTM C 876 which identifies three potential ranges, it is possible to estimate the probability of corrosion; • the concrete resistivity, which is measured according to RILEM Technical Recommendation TC 154, at the same locations where the corrosion potential test is performed; • the carbonation depth that is measured using a solution of phenolphthalein on the powder extracted from drill holes, so the test must be performed concurrently with Bor tests and on the edge beams (beam 4 of span 3, beam 1 of span 5 and beam 4 of span 6) and according to the standards (UNI EN 12504-1, UNI EN 14630, UNI EN 13295). The results are interpreted based on the combination of the chosen investigations. In this case study, non destructive test (UST) and semi-destructive tests (Bor) were chosen; therefore, the defects identified by UST are considered to be effectively present if confirmed by a significant percentage of Bor tests. In areas where only semi destructive tests can be performed, a defect is considered present if detected. All large defects must be investigated through UST tests, and at least half of medium-sized defects should be investigated through Bor tests, while small sized defects should be randomly investigated. Regarding the classification of void sizes, it is recommended to follow the summary in Table 16 of IGSI. Voids are considered significant when they are equal to or larger than "medium" (50-300 mm in length) and when the presence of corroded ducts with evident breaks, corroded wires, or moisture inside the duct is detected. Therefore, it is recommended to cross-reference the results obtained from the detection of significant voids with those obtained from the preliminary analysis of corrosion probability. 3. Conclusion In the present contribution, the procedure proposed by the Italian Guidelines for Special Inspection on PT bridges is applied to a seven-span bridge chosen as case study and characterized by various cable families. The aim of the work is to validate the Italian Guidelines procedure and provide specific instructions for conducting accurate assessments of PT bridges and viaducts. This application shows that by following the steps recommended by the Italian Guidelines, it is possible to investigate the structure through consecutive levels of depth and refinement, without neglecting elements that exhibit clear defects. However, this evaluation needs to be completed by carrying out the tests described in this paper in order to obtain specific feedback, particularly regarding the on-site practicality and feasibility of the proposed tests. Acknowledgements This study was supported by FABRE – “Research consortium for the evaluation and monitoring of bridges, viaducts and other structures” (www.consorziofabre.it/en). Any opinion expressed in the paper does not necessarily reflect the view of the funder.