Bond-slip behavior and model of sand-coated deformed GFRP bars in ultra-high-performance concrete

The aim of this paper is to investigate the bond-slip behavior and model of sand-coated deformed glass fiber-reinforced polymer (GFRP) bars embedded in ultra-high-performance concrete (UHPC). For this purpose, a total of 24 pull-out specimens were tested to failure, varying embedded lengths (2 d b ,3 d b ,4 d b and 5 d b , where d b represents the diameter of the bar) and steel fiber volume fractions (1% and 2%). It was observed that as the embedded length or fiber volume fraction increased, the failure mode changed from progressive pull out of GFRP bars (pullout failure) to rupture of GFRP bars (rupture failure). Both modes of bond failure experienced damage at GFRP-UHPC interface due to the delamination of the outside layer of GFRP bars. The bond-slip response of GFRP bars exhibited four stages: micro slip stage, ascending stage, descending stage, and residual stage. The bond strength of GFRP bars embedded in UHPC exhibited an increasing trend with the fiber volume fraction, while it demonstrated a declining trend with the increasing embedded length. For specimens with fiber volume fraction of 1% and 2%, the bond strength decreased by 24.4% and 8.0%, respectively, as the embedded length increased from 2 d b to 4 d b . In addition, a database consisting of 200 bond specimens including 24 test specimens from this study was established to statistically derive a bond strength equation for GFRP bars embedded in UHPC. Furthermore, a bond-slip model was proposed to describe the bond-slip behavior of sand-coated deformed GFRP bars embedded in UHPC.