Effect of bar diameter on bond performance of helically ribbed GFRP bar to UHPC

The bar diameter is one of the key factor affecting the bond performance between GFRP bar and ultra-high performance concrete (UHPC). However, there is no consensus regarding the effect of bar diameter on the corresponding bond strength in existing studies. An experimental study on centric pull-out test of helically ribbed GFRP bars with nine different diameters was conducted to investigate the effect of bar diameter on the bond strength between GFRP bars and UHPC. The parametric analysis regarding steel bars and UHPC was investigated in the comparative test. For GFRP bars with diameters ranging from 8 mm to 25 mm and an embedment length of 1-2 times the bar diameter, the bond strength between UHPC and GFRP bars varies between 26.5 MPa and 56.2 MPa. The bond strength initially increases with the bar diameter in the range from 8 mm to 18 mm, while it decreases in the range from 18 mm to 25 mm. The relative rib height Hrd is observed as the decisive factor among geometric parameters of the GFRP bar affecting the bond strength. In addition, a correction factor Kr obtained from the geometric parameters and experiments results was proposed to modify the existing prediction formula of bond strength. The prediction of the proposed formula shows a good agreement with the experimental results.