Bond Durability of Near-Surface-Mounted BFRP and GFRP Bars in Aggressive Environments

Abstract

An experimental and analytical study on the bond durability of near-surface-mounted fiber-reinforced polymer bars is reported in this paper. C-shaped pullout specimens reinforced with either glass fiber–reinforced polymer (GFRP) or basalt fiber–reinforced polymer (BFRP) bars were tested after being exposed to aggressive environments, namely (1) immersion in salted water (SW) at 50°C for 30, 60, and 120 days; (2) exposure to 120 wet–dry cycles (WD) at 50°C during the wet duration and at 30°C during the dry duration; and (3) exposure to 120 freeze–thaw cycles (FT). Beside the environmental exposures, the examined parameters comprised the bar texture (either sand-coated or deformed) and the epoxy adhesive used (two epoxy–based adhesives). The effect of each parameter on the bond–slip curves, the adhesion to the surrounding epoxy adhesive, the bond strength of the bars, and the mode of failure are reported and discussed. The test results revealed that the unconditioned NSM-BFRP and GFRP specimens exhibited almost identical average bond strengths. The unconditioned deformed BFRP and GFRP bars exhibited higher adhesion stress than their sand-coated counterparts. The unconditioned specimens with SD (Sikadur-30) epoxy adhesive exhibited less bond strength than those with NG (NSM-Gel) epoxy adhesive whereas those with SD epoxy demonstrated excellent bond durability after being immersed in SW at 50°C for 120 days. Specimens exposed to wet–dry cycles showed slight variation in their bond strength after conditioning. However, specimens immersed in SW solutions for 30 and 60 days and those subjected to FT cycles showed significant losses in their bond strengths. The obtained scanning electron microscope data confirmed the modes of failure observed during testing. The Eligehausen, Popov, and Bertero analytical model was calibrated to model the bond–slip relationships of the NSM-BFRP bars.