Experimental Investigation of Bond-Slip Response of GFRP Bars in Concrete Exposed to High Temperature in Alkaline Solution

This study presents an experimental and analytical investigation on the bond-slip behavior of glass fiber-reinforced polymer (GFRP) bars embedded in concrete and exposed to alkaline environments at different temperatures. GFRP bars are increasingly adopted in structural applications due to their corrosion resistance; however, their durability in high-pH environments remains a critical issue, especially at the bar-concrete interface. To address this, a database comprising 114 experimental bond tests from the literature has been defined, considering as key parameters the bar surface configuration, exposure duration, and temperature. The database analysis shows that surface condition significantly influences bond degradation. To supplement the dataset and investigate short-term exposure effects, additional bond tests were conducted on sand-coated GFRP bars embedded in concrete and conditioned in alkaline solution (with pH = 12) for 1.5 months at both ambient temperature and 60 °C. The average bond strength decreased by 12.7% and 17%, respectively, compared to the non-degraded reference specimen. Moreover, the shape of the bond-slip curves changed, especially in the softening branch. These findings emphasize the needing of accounting for environmental degradation in durability assessments and design processes for GFRP-reinforced structures.