Novel high-temperature resistant GFRP bars with DOPO-modified vinyl ester: Design, performance, and application

Glass fiber-reinforced polymer (GFRP) bars are used in concrete structures to solve corrosion and durability concerns. While the rapid deterioration of the mechanical properties of GFRP bars at elevated temperatures hinders their widespread application. Thus, in this study, a modified vinyl ester resin with high glass transition temperature ( T g ) is developed and used as a matrix material for GFRP bars. The thermal stabilities of the vinyl ester (VE) resin with and without modification, and the tensile performance of the GFRP bars with modified VE at 20˚C, 150˚C, 300˚C, 400˚C, and 550˚C were investigated. The results showed that the modified VE had better thermal stabilities and flame-retardant properties; the failure modes of the GFRP bars changed from fiber fracture to hair-like form rupture when temperature increased from ambient temperature to 400˚C; at 150˚C, 300˚C, 400˚C, and 550˚C, the tensile strength retentions of GFRP bars were 90.6 %, 84.2 %, 68.0 % and 9.9 %, respectively. These findings highlighted the stability of GFRP bars at 400˚C, as they still retained a significant portion of their tensile strength at room temperature. This study implemented a real engineering application to demonstrate the practical utility of modified GFRP bars in addressing the fire resistance challenge. Preliminary parameters for GFRP reinforcement were first designed with a concrete cover thickness of 67 mm and a spacing of 500 mm between GFRP bars based on standard requirement. Finite element analysis was subsequently performed to simulate the behavior of the real structure under a 90-minute fire exposure, in compliance with the fire resistance rating requirements for concrete slabs . The results confirmed that GFRP bars retained ability to resist the fire load after steel reinforcement failed, and also highlighted the importance of maintaining adequate concrete cover thickness when using the modified GFRP bars. The study provides critical insights for the broader adoption of fire-resistance GFRP bars in structural engineering, particularly in fire-prone environments.