Compressive behaviour of GFRP tubes with concrete protection after exposure in elevated temperatures

Enhancing the fire resistance of the pultruded glass fiber reinforced polymer (GFRP) composites is critical for their safe and reliable use in engineering applications. The study experimentally evaluates the influence of concrete cover on the compressive behaviour of GFRP tubes after exposure to elevated temperatures. A total of 92 GFRP tubes were tested with three types of concrete protection, namely internal concrete, external concrete and dual-side concrete, under exposure to elevated temperatures of 250 ℃, 300 ℃, and 350 ℃ for duration of 30, 60, and 90 min. The post-heat bond-slip behaviour between the infilled concrete and GFRP tubes was investigated using push-out tests, revealing improved bonding due to surface roughening from resin decomposition. Subsequently, compression tests were performed after exposure, demonstrating that concrete protection is an effective and practical method for safeguarding GFRP tubes against elevated temperatures. Owing to effective oxygen isolation, the GFRP tubes with dual-side and external protection exhibited more than 88 % of their original strength even after exposure to 350 °C for 60 min. Additionally, a thin concrete cover (approximately 25 mm) provided sufficient protection, and when GFRP tubes were well protected, exposure duration had a negligible effect on the compressive behaviour.