Research on the bond performance between glass fiber reinforced polymer (GFRP) bars and Ultra-high performance concrete(UHPC)

In recent years, in order to overcome the problems that steel bars are prone to rust and the ductility of GFRP and ordinary concrete is insufficient, a new type of reinforced concrete structure with good durability and high ductility has been developed by combining glass fiber reinforced polymer (GFRP) bars with ultra-high performance concrete (UHPC). The bond performance between GFRP and UHPC is the guarantee for them to work together and achieve optimal performance, which is worthy of further research. In this paper, pull-out tests were performed on 75 center pull-out samples with a side length of 150 mm, taking into account factors such as GFRP bar diameter, surface treatment type, bond length, and fiber content. The failure modes and bond performance of GFRP bars and UHPC pull-out specimens were investigated. The results indicate that the bond-slip curves of GFRP bars in UHPC and ordinary concrete show similar bond-slip characteristics. Compared with ordinary concrete, UHPC pull-out specimens demonstrate superior mechanical properties, including better bond strength and ductility. The UHPC-GFRP bars and UHPC-steel bars (8 mm and 10 mm) underwent pull-out failure. However, the 12 mm steel bar in UHPC reached its ultimate tensile strength, causing pull-off failure. The bond strength of GFRP bars decreases with the increase of diameter. In addition, with the increase of bond anchorage length, the bond strength decreases. When GFRP bars of the same diameter are anchored in ultra-high-performance concrete, the GFRP bars with ribbed surfaces display superior bond performance compared to those with sandblasted surfaces. Based on the models proposed by previous researchers, this paper proposes a suitable formula for estimating the bond strength between GFRP bars and UHPC. The calculated results are in good agreement with the measured results.