Degradation of GFRP bars in alkaline environments: An experimental and molecular dynamics study

Abstract

Glass fibre reinforced polymer (GFRP) bars are widely used as a replacement for reinforced bars due to their high strength-to-weight ratio, whereas they also show a high safety risk for corrosion potential from alkaline ions attack in concrete. In this study, the mechanical property evolution and degradation mechanism of GFRP bars in alkaline environments was studied by using experimental and molecular dynamics simulations. The results show that the decreased strength of the GFRP was mainly associated with the increase in the hydroxide concentration (COH-) in the corrosive solution rather than other ions. The tensile strength of the GFRP bars declined by approximately 10% after 300 days of exposure when the pH of the corrosion solution approached 13. When the pH barely reached 10, the resin-fibre interlaminar shear strength slumped by approximately 29%. The favorable hydrogen bonding network was disrupted by alkaline ions, resulting in a lower interaction energy between water molecules and epoxy resin chain segments. In addition, OH− was distributed around the ester bond and attacked the ester group, and finally, the ester bond was hydrolysed to form carboxylate and alcohol. Free sodium ions combine rapidly with oxygen lone electrons (Na-Ow), thereby accelerating water-resin debonding aging by breaking hydrogen bonds within the polymer network. The hydroxyl radicals further invade the fibres through the microcracks formed inside the resin, causing localized etching of the fibres. The study will provide a theoretical basis for the design of anti-corrosion modification of GFRP bars.