PSI - Issue 64

A. Cagnoni et al. / Procedia Structural Integrity 64 (2024) 951–958 957 Alessandro Cagnoni, Pierluigi Colombi, Marco A. Pisani, Tommaso D’Antino / Structural Integrity Procedia 00 (2019) 000–000 7

not damaged by the cycles. Wang et al. (2007) and Zhou et al. (2019) studied the effect of exposure to fire temperatures on the behavior of CFRP rods. In both studies, a linear decrease in the tensile strength of the rods was observed with increasing temperature. Grace et al. (2021) performed tensile tests on CFCC strands exposed to fire temperatures and sustained loads. Results confirmed that an increase in temperature led to a proportional decrease of the tensile strength and a preload loss (relaxation). Relaxation was permanent and not recovered with a decrease of temperature, unlike tensile strength, which returned to its original level after a cooling period. Scott and Lees (2012) analyzed the mechanical behavior of CFRP rods exposed to water and salt water under different tests. The samples subjected to tensile tests exhibited a residual tensile strength of 91% after exposure to salt water. 5. Conclusions This paper provided a state of the art on open issues hindering the widespread use of carbon fiber-reinforced polymer (CFRP) tendons for external strengthening of reinforced concrete (RC) structures. After a deep analysis of the available literature, main open issues were identified, including the selection of anchorage system, the determination of prestress level, and the assessment of the effect of harsh environmental conditions on carbon composites. Concerning anchorage systems, the choice between mechanical anchors and bonded anchors represents a significant challenge. While bonded anchors generally offer higher anchorage efficiency, they necessitate longer installation and curing times, as well as increased embedded length compared to mechanical anchors. In term of prestress level of CFRP tendons, available American and Canadian standards limit the level of stress at jacking and at load transfer with the aim of avoiding sudden ruptures coming from creep and fatigue phenomena. However, these standards appear overly conservative. Finally, the exposure to alkaline solution, freeze-thaw cycles, high temperature, and salt water produced minimal deterioration of residual tensile strength of CFRP tendons. However, the direct exposure to fire temperatures produced significant damages to the composites. Thus, specific solutions are needed to protect the tendons from direct exposure to fire temperatures. References ACI Committee 440, 2004. 440.4R-04 - Prestressing Concrete Structures with FRP Tendons. Ali, A. H., Mohamed, H. M., Benmokrane, B., and ElSafty, A., 2019. Theory-based approaches and microstructural analysis to evaluate the service life-retention of stressed carbon fiber composite strands for concrete bridge applications, Composites Part B: Engineering, 165, 279– 92. Ali, D.-A., Mohamed, H., ElSafty, A., and Benmokrane, B., 2015. Long-term durability testing of tokyo rope carbon cables. Al-Mayah, A., Soudki, K., and Plumtree, A., 2006. Development and Assessment of a New CFRP Rod–Anchor System for Prestressed Concrete, Applied Composite Materials, 13, 321–34. Al-Mayah, A., Soudki, K., and Plumtree, A., 2013. Simplified Anchor System for CFRP Rods, Journal of Composites for Construction, 17(5), 584–90. Barron, V., 2001. Frequency effects on the fatigue behaviour on carbon fibre reinforced polymer laminates, Journal of Materials Science. Benmokrane, B., Ali, A. H., Mohamed, H. M., Robert, M., and ElSafty, A., 2016. Durability Performance and Service Life of CFCC Tendons Exposed to Elevated Temperature and Alkaline Environment, Journal of Composites for Construction, 20(1), 04015043. Burningham, C. A., Pantelides, C. P., and Reaveley, L. D., 2014. New unibody clamp anchors for post-tensioning carbon-fiber-reinforced polymer rods, PCI Journal, 59(1), 103–13. Burningham, C. A., Pantelides, C. P., and Reaveley, L. D., 2015. Repair of reinforced concrete deep beams using post-tensioned CFRP rods, Composite Structures, 125, 256–65. Cai, D., Yin, J., and Liu, R., 2015. Experimental and analytical investigation into the stress performance of composite anchors for CFRP tendons, Composites Part B: Engineering, 79, 530–4. Canadian Standards Association (CSA), 2002. S806-02. Chen, Y., Davalos, J. F., Ray, I., and Kim, H.-Y., 2007. Accelerated aging tests for evaluations of durability performance of FRP reinforcing bars for concrete structures, Composite Structures, 78(1), 101–11. D’Antino, T., and Pisani, M. A., 2019. Long-term behavior of GFRP reinforcing bars, Composite Structures, 227, 111283. Dyer, K. P., and Isaac, D. H., 1998. Fatigue behaviour of continuous glass fibre reinforced composites, Composites Part B: Engineering, 29(6), 725–33. Elrefai, A., West, J., and Soudki, K., 2012. Fatigue of reinforced concrete beams strengthened with externally post-tensioned CFRP tendons, Construction and Building Materials, 29, 246–56. Garner, P., 2024. Most Polluting Industries in 2024 Revealed, URL: https://heatable.co.uk/boiler-advice/most-polluting-industries. Grace, N. F., Mohamed, M. E., Chynoweth, M., Kose, N., and Bebawy, M., 2021. Effect of Elevated Temperatures on the Mechanical Properties and Relaxation of CFRP Strands, Journal of Composites for Construction, 25(3), 04021019. Grace, N. F., Mohamed, M. E., and Bebawy, M. R., 2023. Evaluating fatigue, relaxation, and creep rupture of carbon-fiber-reinforced polymer strands for highway bridge, 68(3), 36–61.