Bond Strength of GFRP Reinforcing Bars at High Temperatures with Implications for Performance in Fire

Abstract

The polymer matrices currently used for the fabrication of fiber reinforced polymer (FRP) reinforcing bars soften near their glass transition temperature Tg, resulting in a reduction of mechanical strength. This paper discusses the effect of high temperatures on the bond behavior of three types of glass FRP (GFRP) reinforcing bars using standard pullout tests. The bars were 16 mm in nominal diameter with different surface treatments, including sand-coated and ribbed surfaces. The tests were conducted under steady-state and transient temperature protocols for a temperature range of 25°C–36°C at the concrete-to-bar interface. In addition, the effect of embedment length was investigated for a limited number of specimens. The bond failure modes were assessed in detail for different bars. The results for temperatures below 8°C are relevant for elevated service temperatures, and higher temperatures have important implications for performance in fire. At temperatures such as those that would be experienced in a fire (i.e., above 2°C), bond strength dramatically deteriorated, and the retained strength was below 17%. The glass transition temperature of the matrix material was found to be critical for the bond performance of GFRP bars in fire scenarios. The results in this paper are needed to develop rational design guidelines for embedment and anchorage of GFRP bars to obtain the required fire endurance (e.g., 2–3 h) that has been demonstrated through separate full-scale fire tests.