Long-term performance of interlayer hybrid composites of polypropylene and glass fiber exposed to salt solution and deionized water at elevated temperatures

The research on hybrid fiber reinforced polymer (FRP) composites in civil engineering has emerged recently, but there is a lack of durability test data for common environmental conditions such as the marine and moist environments. Due to the presence of four failure modes in hybrid FRP composites, the applicability of durability findings from conventional FRP composites cannot be directly extrapolated to them. In the present study, the hybrid FRP composite composed of glass and polypropylene fiber was subjected to immersion in salt solution or deionized water at varying aging temperatures (20, 40, and 60 °C) for different durations of aging (30, 60, 90, and 120 days). The accelerated aging tests were primarily aimed to evaluate the tensile properties and microstructural changes of hybrid FRP composites. Test results demonstrated that both salt solution and deionized water exert a significant influence on the tensile properties of hybrid FRP composites, with the former exhibiting a more pronounced impact. The aging mechanism primarily involves degradation of the glass fiber and the epoxy matrix in hybrid FRP composites. The design recommendation for first limit stress of hybrid FRP composites aligns with that of glass FRP as specified in Chinese standard GB 50608–2010, while it recommends a retention rate of 0.7 for second limit stress. Other mechanical parameters (elastic modulus, second limit strain, and second modulus) can be considered independent of environmental factors. Furthermore, maintaining a glass fiber layer volume fraction below 12.3 % is beneficial for the long-term performance of hybrid FRP composites.