EFFECT OF CONCRETE COVER ON BOND OF GFRP BARS IN ULTRA-HIGH-PERFORMANCE FIBER-REINFORCED CONCRETE (UHPFRC)

This study aims at establishing the development length of sand-coated GFRP bars embedded into UHPFRC with a focus on the effect of concrete cover on bond strength. The study uses notched beam specimens tested in flexure where the bars are under realistic tensile stress as opposed to pull-out tests. The embedment length of the bars was varied in different beams to establish a correlation with the maximum tension force attained, thereby calculating the minimum embedment length required to enable the full tensile capacity of the bar, namely the development length. Concrete mixes containing 2% steel fibers were used for all specimens in the study. It was found that ACI440.11-22 code equation grossly overestimates GFRP bar development length in UHPFRC by a factor of 2.6-2.9. The Michaud et al. (2021) equation provided a much better prediction but was unable to account for varying concrete covers. As such, it overestimated development length by a factor of 1.3 for the thickest cover used in this study.