Abstract
Reinforced concrete strength (RCS) is one of the most important parameters in tunnel lining, which ensures a safe, reliable service life. Chloride and carbon penetration are the most common durability problems in tunnels and significantly affect the sustainability of RCS. Using experimental tests, a procedure was developed to evaluate the RCS of tunnel linings under corrosion conditions. The corrosion conditions were classified into three levels: light, medium and heavy, which represent the duration of the corrosion acceleration technique used for 4, 6 and 8days, respectively. The variables that were studied in the experiments were the corrosion rate, steel bar diameter, concrete cover and concrete strength. Axial loads and bending moments about the longitudinal axis of the specimens were applied. The purpose of the experimental design was to study stress conditions in tunnel linings. Cracks were observed during the time-based bending–compression test when loads were applied accordingly. The test results show that the overall metal loss, at a constant corrosion index, depends on the diameter of the steel bars. Furthermore, the effect of the concrete cover thickness on the loss of strength was found to be significant. The group of specimens, (35-mm and 50-mm concrete covers with 10-mm diameter bars) showed bearing capacity losses of 32% and 35% due to corrosion rates (Jr) of 24% and 28%, respectively. It was also found that a linear relationship exists between the corrosion rate and residual strength. At a constant corrosion index, the concrete strength C30 had a significant effect on the RCS compared with the concrete strength C25. Based on the theoretical and experimental results, the evaluation procedure includes three primary steps: bond strength, cracking and specimen performance. The test procedure is a simple method to evaluate the tunnel lining strength for corrosion resistance by designing specimens with similar tunnel lining conditions.
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