Experimental study of FRP tube encased concrete cylinders exposed to fire

In recent years, fiber-reinforced polymer (FRP) tube encased concrete cylinders have been widely studied for their use in civil infrastructure. However, the performance of these FRP/concrete systems exposed to fire is a serious concern due to the combustibility of FRPs. This paper presents test results of temperature distributions and residual strength of three groups of FRP tube encased concrete cylinders (Groups 1, 2, and 3) exposed to a jet fire of 982 °C for a time period of 4 min, 8 min, and 12 min, respectively. The temperature distribution of the confined concrete cylinders under fire was recorded by the embedded thermocouples. After fire test, uniaxial compression tests were conducted to evaluate the residual strength. The results were compared with that from a group of FRP tube encased concrete cylinders without fire exposure (Group 4). To improve the fire resistance of the confined concrete cylinders, a fireproof additive was also applied to three other groups of specimens (Groups 5, 6, and 7) and these specimens were also fire tested for 4 min, 8 min, and 12 min, respectively. SEM was used to examine the burn-out of resin by fire. The test results show that the fire exposure has a significant effect on reducing the residual strength of the confined concrete cylinders. The resin has been fully burned-out and carbonized after 8 min of fire exposure. After 12 min of burning, the FRP tube basically loses its capacity to provide any meaningful confinement. The fireproof additive used is effective in minimizing the effect of the fire hazard.