Bond strength of glass fiber-reinforced polymer bars in concrete after exposure to elevated temperatures

This paper presents the test results of an experimental study to investigate the effect of elevated temperatures on the bond properties of glass fiber-reinforced polymer bars in concrete. For this purpose, a total of 39 pullout specimens with glass fiber-reinforced polymer bars were cast for bond strength tests. In addition to the laboratory temperature, specimens were exposed to heating regimes of 100, 200, 300 and 350° for a period of 1, 2 or 3 h. The test results are presented in terms of bond strength, bond-slip relationship, and mode of failure. All specimens failed by shearing of the concrete corbels surrounding the bars and almost no damage was seen in the glass fiber-reinforced polymer bars. The results showed that the bond strength decreased as the temperature or exposure period increased. Reductions of about 20% of the original bond strength were recorded after exposure to 100 and 200° for 3 h. Significant reductions of about 50% in the bond strength were recorded after exposure to 350° for periods of 2 and 3 h. A modification to the ACI (American Concrete Institute) and CEB-FIP (Comité Euro-International du Béton-Fédération Internationale de la Précontrainte) equations was developed to consider the effect of elevated temperatures and it showed good agreement with test results.