PSI - Issue 64

Marco Carlo Rampini et al. / Procedia Structural Integrity 64 (2024) 2141–2148 Author name / Structural Integrity Procedia 00 (2019) 000–000

2148

8

conditions and that the rebar corrosion conditions cannot be derived from the measurements taken in the central part. Some lower values were also recorded, indicating that water was penetrated likely from the points where welding was not continuous. It should, however, be noticed that the tests were performed after removing the tie rods from the natural exposure environment and that the inner moisture condition might have been altered from those in serviceability state. Conventional corrosion potential measurements were carried out, to detect the corrosion conditions of the bars. Although the electrical connection among the bars was assessed, the reliability of these measurements has still to be verified, due to presence of the paint and the possibility of its interference with the measurement itself. Most of the measured values were higher than -200 mV vs CSE, and, being in alkaline environment, this suggested that bars were in passive conditions, i.e. corrosion was not ongoing during the inspection. However, also lower values were detected (-300 mV vs CSE). This often occurred in correspondence of the ending parts of the tie rods, while in some cases in correspondence of the defects, where also corrosion products were observed. Such low values of corrosion potential usually indicate that bars are in active conditions, i.e. that corrosion process is taking place. In the case of the ending parts of the tie rods the corrosive phenomena may have been triggered after the removal of the structural elements from the bridge, therefore not being representative of the serviceability conditions, while in correspondence of defects of the cementitious composite, corrosion likely occurred while tie rods were still in place. The complexity of the system makes it difficult to establish the corrosion conditions of the bars, both due to the uncertainty of the measurement and the local environmental conditions in the inner cavities among the core bars. Destructive tests, during which the bars will be removed from the cementitious material, visually inspected, and cleaned from any corrosion products, will be needed to correctly interpret the detected values. 4. Conclusions and further development In this work, a series of reinforced concrete tie rods retrieved from a 70-years-old arch bridge were subjected to a laboratory mini-invasive diagnosis. These elements have been the object of a restoration intervention, as indicated by the current external diameter being higher than the original ones and by the presence of short plastic fibers non compatible with the age of the bridge. Then, it is possible to suppose that signs of degradation, probably related to corrosion, had occurred in the past and, consequently, the intervention was aimed at interrupting these phenomena. Based on the diagnosis carried out, which included electrochemical measurements and carbonation detection, it seems that corrosion was not ongoing during the inspection, probably thanks to the general adequacy of the restoration intervention made. The importance of its proper implementation also became clear; in fact, localized reductions of corrosion potential were found only in correspondence of the concrete voids or defects. Due to the complexity of the system under study, the effectiveness of the investigation technologies here presented have to be assessed. In particular, the effects of the protective paint and the absence of information regarding of the rehabilitation intervention to which the RC hangers were subjected in the past need to be investigated. More information can be obtained once the ties will be hydroscarificated and the state of corrosion of the steel bars, especially in the inner areas, will be observed. Therefore, in addition to extending the procedures already carried out for the first tie rods to all the available ones, tensile tests will also be performed on the smooth bars to assess the effects of corrosion deterioration on their mechanical response. References Bertolini, L., Elsener, B., Pedeferri, P., Redaelli, E., and Polder, R. B., 2013. Corrosion of steel in concrete: prevention, diagnosis, repair. John Wiley & Sons. Danciu, A. D., Guțiu, Ș. I., Moga, C., Dragomir, M. L., Ciotlăuș, M., Marusceac, V., 2023. A Review of the Network Arch Bridge. Appl. Sciences 13, 10966. https://doi.org/10.3390/app131910966 Elsener, B., Andrade, C., Gulikers, J., Polder, R., and Raupach, M., 2003. Half-cell potential measurements—Potential mapping on reinforced concrete structures. Materials and Structures, 36(7), 461-471. García-Guerrero, J.M., Jorquera-Lucerga, J.J., 2020. Improving the Structural Behavior of Tied-Arch Bridges by Doubling the Set of Hangers. Appl. Sciences, 10, 8711. https://doi.org/10.3390/app10238711 Tveit, P., 2019 "How to design economical network arches." IOP Conference Series: Materials Science and Engineering. Vol. 471. No. 5. IOP Publishing. https://doi.org/10.1088/1757-899X/471/5/052078 Bertolini, L., Carsana, M., Gastaldi, M., Lollini, F., and Redaelli, E., 2011. Corrosion assessment and restoration strategies of reinforced concrete buildings of the cultural heritage. Materials and corrosion, 62(2), 146-154.