Thermal and Mechanical Fatigue Effects on GFRP Rebar-concrete Bond

This report summarizes an experimental program conducted to investigate the thermal and mechanical fatigue effects on the bond between Glass Fiber-Reinforced Plastic (GFRP) rebars and concrete. Variables included in the study were rebar diameter (No. 6 and No. 4 GFRP, No. 6 steel), material (steel and GFRP) and manufacturer (two different manufactures for the GFRP rebar). For comparison, specimens were also fabricated using steel rebar as a control. The embedment lengths were chosen so that a splitting failure was assured in all specimens.

A total of 30 inverted half-beam specimens were cast in 15 beams. Six specimens were mechanically tension-tension cycled, twelve specimens were thermally cycled and twelve were used as control specimens (no thermal or mechanical fatigue). During thermal fatigue, the rebars were also subjected to a constant tensile load to simulate dead load.

During the bond tests, specimens were loaded continuously until failure while monitoring load, free-end slip, and loaded end slip. The results were evaluated to compare the bond performance of GFRP rebar to steel rebar, and to determine the effects of thermal and mechanical fatigue on bond.

It was found that mechanical fatigue has more detrimental effect on steel that on GFRP specimens while thermal fatigue has more effect on GFRP than on steel specimens. The effect of thermal fatigue was more in GFRP M2 than in Ml specimens. The difference in bond performance between No. 6 and No. 4 GFRP Ml cannot be determined form this study due to inferior product quality of the No. 4 M bars.