Effects of relative humidity, alkaline concentration and temperature on the degradation of plain/coated glass fibers: Experimental investigation and empirical degradation model

Abstract

Glass fiber reinforced polymer (GFRP) rebars are commonly considered as a substitute for conventional steel reinforcements in concrete structures to avoid possible steel corrosion. However, the tensile strength of GFRP rebars may degrade with time due to the degradation of glass fibers under H2O/OH– attack in a moist concrete with a high pH level (∼13.6). The purpose of this study is to investigate the degradation of glass fibers under exposure to various temperatures (23, 40 and 60 ℃), relative humidities (45%, 75%, 95%) and pH levels (i.e., pH = 7, 11, 12 and 13), and then build up a comprehensive database incorporating the information on physical, chemical and mechanical properties of conditioned fibers. Experimental results show that direct exposure to an alkaline solution is highly aggressive to plain glass fibers, resulting in violent chemical reactions (i.e., leaching and dissolution) and a significant reduction in the fiber radius and tensile strength. In contrast, the matrix coating (thickness of ∼ 1.5 μm) on the fiber surface can effectively delay the penetration of H2O/OH–, protecting fibers from radius reduction, chemical reaction and tensile strength degradation. The degradation of GFRP rebar with the same fiber and matrix is also analyzed to illustrate the inherent relationship between the macroscopic tensile strength performance of conditioned rebars and the degradation of local glass fibers at the microscopic level. The findings in this study yield useful information on the degradation of local glass fibers in the GFRP rebar, supplying engineers with a better understanding of GFRP degradation mechanism in an alkaline environment.