Thermal cycling effects on the durability of a pultruded GFRP material for off-shore civil engineering structures

This paper investigates the effects of thermal cycles on the structural integrity of a pultruded Glass Fibre Reinforced Polymer (GFRP). Through a critical review of current literature alongside a comprehensive experimental campaign, the material's response to cyclic thermal loading has been ascertained, defined by the rate of degradation of its physical, mechanical and visco-elastic properties. Matching sets of both dry and soaked samples conditioned in distilled water for 224 days. Freeze-thaw cycling of both dry and soaked samples was conducted between 20 °C and −10 °C for a total of 300 cycles. Computed Tomography scanning (CT-scan) was undertaken to assess the microstructural physical changes throughout freeze-thaw cycling. After exposure, GFRP samples exhibited a minor decrease in glass transition temperature (Tg) which indicated minor structural degradation. Dry GFRP sample's mechanical response exhibited negligible changes in both tensile and in-plane shear properties. However, as a result of the higher induced thermal stresses, soaked samples showed a significant degradation of their tensile and shear strengths. Yet, the soaked material's stiffness remained largely unaffected due to the potential reversible nature of plasticization, which acts to increase the material's molecular mobility when initially moisture-saturated, but is later recovered as the soaked samples lose moisture throughout freeze-thaw cycling.