Hygrothermal resistance of pultruded carbon, glass and carbon/glass hybrid fiber reinforced epoxy composites

Abstract

The hygrothermal resistance of pultruded fiber reinforced polymer (FRP) composites is the key concern when applying in the reinforcement or strengthening of concrete structures in civil engineering. In the present study, the hygrothermal properties of pultruded carbon, glass and carbon/glass hybrid fiber reinforced polymer (CFRP, GFRP, C/GFRP) composite plates were investigated experimentally through the immersion in deionized water at 40 °C, 60 °C and 80 °C as long as 135 days. Water absorption, thermal properties, mechanical properties and microstructure analysis were conducted to evaluate the long-term hygrothermal evolution. It was found that the water absorption response of three kinds of composite plates represented the initial Fick’s diffusion response and a followed long-term deterioration response. Immersed in deionized water led to an obvious degradation of thermal and mechanical properties up to 29.5% for short beam shear strength (SBSS) of C/GFRP, 25.8% for three point bending strength (TPBS) of GFRP and 43.1% for glass transition temperature (Tg) of C/GFRP, respectively. The diffusion of water molecule in the plate brought about the reversible effect of resin plasticization and irreversible effect of resin relaxation. Furthermore, the irreversible interface debonding of fiber/resin aggravated the degradation of SBSS. Based on the Arrhenius accelerating theory, the long-term life of SBSS decreased to stable level of 87.90% (CFRP), 76.64% (GFRP) and 72.43% (C/GFRP), respectively. Meanwhile, the stable retentions of TPBS were 85.99% (CFRP), 77.32% (GFRP) and 81.40% (C/GFRP), respectively.