Bond performance between FRP bars and geopolymer concrete after elevated temperature exposure

The use of geopolymer concrete structure reinforced with fiber reinforced polymer (FRP) bars is an effective approach to solve the problems of high energy consumption, large CO2 emission, and steel corrosion caused by traditional reinforced concrete structures. This paper presents an experimental study on the effect of elevated temperatures on bond performance between FRP bars and geopolymer concrete. The influence factors include exposure temperature, surface treatment of FRP bars, fiber type of FRP bars, geopolymer concrete strength and type of concrete. The test results indicate that the bond strength between FRP bar and geopolymer concrete increases first and then decreases gradually with the increase of exposure temperature. After exposure to 350 degrees C, the bond strength retention ranges from 56.0% to 83.3%, while after exposure to 400 degrees C, the residual bond strength retention is not more than 17.7%. The bond strength retention of FRP bars in geopolymer concrete is basically higher than that in ordinary concrete from 25 degrees C to 350 degrees C. Moreover, the ribbed FRP bars possess a higher bond strength retention than the sand-coated FRP bars after elevated temperature exposure. With the increase of the geopolymer concrete strength, the high temperature resistance of geopolymer concrete decreases, resulting in a corresponding decreasing in the bond strength retention. In addition, the fiber type of FRP bar has no significant effect on the interfacial bonding properties compared with surface treatment of FRP bar and concrete strength. Finally, the available equations for calculating the development length of FRP bar in geopolymer concrete after elevated temperature exposure was proposed, which may be used for the design of fire prevention and fire safety assessments.