Comparative Investigation of Water Uptake and Interfacial Shear Property Aging of Pultruded Carbon Fiber Reinforced Polymer and Aramid Fiber Reinforced Polymer Bars

ABSTRACT To assess the long‐term durability of aramid fiber reinforced polymer (AFRP) bars in civil engineering applications, this study systematically compared the water absorption characteristics of pultruded carbon fiber reinforced polymer (CFRP) and AFRP bars under immersion at 20°C, 40°C, and 60°C, based on water absorption tests and the Fick diffusion model. Furthermore, the degradation of interlaminar shear strength (ILSS) for both CFRP and AFRP bars over 2000 h was investigated through short beam shear tests, complemented by microstructural analysis (SEM) to identify the degradation mechanisms. The results indicated that CFRP and AFRP bars exhibited time–temperature dependent moisture absorption behavior, with higher temperatures accelerating moisture diffusion. AFRP bars, due to the moisture‐absorbing properties of aramid fibers, demonstrated higher water absorption rates and diffusion coefficients compared to CFRP bars. Increased temperatures also exacerbated the degradation of ILSS in both materials under hydrothermal aging. The failure of CFRP bars was primarily influenced by the moisture‐induced expansion of the resin matrix, leading to continuous degradation of ILSS over time. In contrast, AFRP bars experienced more complex degradation at the fiber–resin interface due to the hygroscopic and highly water‐absorptive nature of aramid fibers. This resulted in varying degrees of compressive stress at the interface under different immersion times and temperatures, which could either enhance or impair ILSS. Although the degradation procession of AFRP bars exhibits fluctuations due to concurrent enhancing and weakening effects, the net effect is a more substantial reduction in ILSS compared to CFRP bars.