Bond strength of sand-coated deformed GFRP bars in UHPC, HPC, and NC

Abstract

This paper focuses on evaluating the bond strength of sand-coated deformed Glass Fiber-Reinforced Composite (GFRP) bars in cement-based materials: Ultra-High Performance Concrete (UHPC), and High-Performance Concrete (HPC) and Normal Concrete (NC). A total of 48 pullout tests were conducted to examine the impact of parameters such as bond length (2.5db, 5db and 10db) and cover thickness (1db, 2db and 4.5db). Three common failure modes comprising bar pullout, rupture, and cover splitting were outlined, in which, pullout of GFRP rebars was controlled by shear damage between the resin and glass fibers, and UHPC splitting behaved with greater ductility than HPC or NC. The bond-slip curve of GFRP rebars involved the micro-slippage branch, the slippage branch, the exponentially descending branch, and the residual branch with oscillation characteristics. In comparison with HPC and NC, GFRP bars in UHPC showed 27.9%-72.6% and 130.5%-164.2% increases in bond strengths, respectively. Moreover, the higher bond strength was achieved in specimens with a smaller bond length or greater cover thickness. Specifically, bond strengths in samples having covers of 4.5db and 2db were enhanced by 30.8%-53.4% and 16.2%-26.8% to those with a cover of 1db. Furthermore, the bond strength calculation formula for GFRP rebars in UHPC was established and validated using the existing tests, and some design recommendations were presented.