Durability Study on the Bond Strength of Basalt Fiber-Reinforced Polymer (BFRP) Bars

Abstract

In the last few decades, Fiber-Reinforced Polymers (FRP) bars have emerged as alternatives to conventional steel reinforcing bars to overcome the corrosion problem found in reinforced concrete structures. Numerous studies have been conducted in order to evaluate the bond between FRP bars and concrete. Recently, a new type of FRP bars made of basalt fibers (BFRP) has emerged as an alternative to conventional glass-made FRP (GFRP) bars. BFRP bars have not yet been considered in international design codes due to lack of research on their structural performance. This research investigates the bond durability of BFRP bars to concrete. BFRP bars with two different surfaces were used in this study namely: sand-coated and indented surfaces. The bond durability for the GFRP bars was also investigated for comparison purpose. The test parameters included the FRP bar material, the surface coating, the environmental exposure, and the exposure duration. More than 100 pullout specimens were prepared and exposed to different environmental conditions over three durations: 30, 60, and 90 days. The accelerated harsh exposures included acid, alkaline, ocean water, tap water, high temperature, and high temperature followed by ocean or tap water environments. At the end of each exposure, pullout specimens were tested to study the bond performance of all specimens in terms of their bond strength, bond-slip curves, adhesion stress, and failure modes and mechanisms. Unconditioned (control) specimens were also tested to measure the bond between the bars and the concrete. Effects of each environmental exposure on the bond performance of the specimens were discussed. In general, BFRP bars showed bond behavior comparable to that of its GFRP counterparts. The well-known Eligehausen, Popov, and Bertero (BPE) model that describes the ascending branch of the bond-slip relationship of conventional steel was assessed and calibrated for the unconditioned and conditioned BFRP and GFRP bars. Design values of the bond coefficient α that defines the behavior of the ascending branch were recommended for the investigated exposures.