Effect of polypropylene and brass‐coated steel fibers on bond behavior of <scp>GFRP</scp> bars in normal and high‐strength geopolymer concrete

Abstract In the current study, the effect of two types of fibers, polypropylene (PP) and brass‐coated steel (BS) fibers, on the bond performance of glass fiber‐reinforced polymer bars with geopolymer concrete is investigated. Additionally, the impact of embedment length, bar diameter, and compressive strength of the concrete on the bond behavior was considered. The result shows that inclusion of BS fibers considerably improves the pullout capacity and the curve's initial stiffness, as the BS fibers have a superior tensile strength than PP fibers. In the case of PP specimens, few samples demonstrated a change in failure mode from split to pullout. However, in the case of BS specimens, including those that showed split failure in PP specimens, failed in a pullout fashion. The crack width seen on the exterior concrete surface is considerably reduced with the addition of fibers. To assess the post‐peak response of the bond stress versus slip curves, energy‐based bond toughness parameters were proposed, and the results indicate that the post‐peak response was enhanced by the addition of BS fibers. Increasing the embedment length and bar diameter has a negative impact on the bond characteristics, whereas the concrete strength has the opposite effect. Experimental results compared with analytical models, and Cosenza‐Manfredi‐Realfonzo model outperformed the modified Eligehausen, Popov, and Bertero model. Overall, BS fibers produce superior outcomes.