Effect of surface configurations on the bond performance of GFRP bars in geopolymer concrete

Unlike steel bars, there are currently no standards for surface preparation of Glass Fibre Reinforced Polymer (GFRP) bars. As a result, a variety of GFRP bars are commercially available, such as sand coated (SC), helically wrapped (HW), grooved, ribbed, and helically wrapped-sand coated (HW-SC) bars, among others. On the other hand, the load transfer mechanism is sensitive to the surface configuration employed. Therefore, in order to examine the impact of surface configurations on the bond performance of GFRP bar in geopolymer concrete (GPC), two different surface configuration types such as grooves and HW ribs were taken into account in the present investigation. At the same time, an examination was conducted to determine the optimum groove configuration. When comparing HW bond specimens, the pullout capacity of 16 mm grooved specimens was the same, while that of 12 mm grooved specimens was significantly reduced. As the depth of the groove increases, a tendency to increasing and decreasing bond strength was observed for the grooved specimens. Increased groove spacing resulted in a slight increase in bond strength and stiffness. The failure mode for 12 mm specimens remains unchanged even for deeper depths and larger groove spacing, but split failure was observed for 16 mm specimens even for the lowest groove depth and spacing. The post-peak measurements showed that the bond stress-slip response of grooved specimens exhibited ductility due to successive breaking of groove segments, which the HW specimens did not show. Additionally, there were slight improvements in bond strength and stiffness with an increase in concrete grade for HW and grooved specimens. Analytical models and results from experiments compared; the CMR model performed better than the mBPE model. The study recommends using a groove depth of 9% and groove spacing equal to the diameter of the bar since they produced better results.