Hydrothermal aging of carbon fiber reinforced polymer rods intended for cable applications in civil engineering

Carbon fiber reinforced polymer (CFRP) composites have become increasingly popular due to their high strength-to-weight ratio and excellent mechanical properties. However, CFRP composites are susceptible to hydrothermal aging when used as cable applications in civil engineering, which can cause irreversible damage to their service performance. In this study, the effects of water immersion (water@60 °C), constant temperature and humidity exposure (95%RH@60 °C), and alternating hydrothermal environment (12h_60 °C&12h_25 °C@95%RH) were investigated on the property degradation of the CFRP rods. In addition, the water absorption behavior, and thermal and mechanical properties of the CFRP rods were systematically analyzed and compared. We found that elevated temperature and humidity accelerated the water absorption process, resulting in to the higher equilibrium moisture content and diffusion coefficient. Hydrothermal exposure led to maximum degradation in the tensile strength, three-point bending strength and short-beam shear strength of CFRP rods, with values reaching 4.8%, 17.4% and 24.3% in the water@60 °C, 95%RH@60 °C, and 12h_60 °C&12h_25 °C@95%RH conditions, respectively. Among the three mechanical performance properties analyzed, the tensile strength degradation of the CFRP rods was least affected by the three environmental conditions, primarily due to the tensile direction along the carbon fibers. In addition, the three-point bending and short-beam shear strength values of the CFRP rods showed the greatest degradation in the 12h_60 °C&12h_25 °C@95%RH environment. The long-term effects of the water molecules against the CFRP rods in the hydrothermal environment caused resin hydrolysis and debonding of the fiber-matrix interface, leading to degradation in three-point bending and short-beam shear strength. Additionally, the temperature alternating factor accelerated the degradation of the mechanical properties of the CFRP rods, and the mechanical properties of the CFRP rods declined most noticeably with alternating temperatures under the same moisture content conditions