Comparative Assessment of Thermal Conditioning Effects on Concrete–GFRP Bond Resistance Across Diverse Bar Diameters

Abstract

Cracking in concrete structures can result from excessive loading, long-term creep, construction defects, shrinkage, reinforcement corrosion, and exposure to elevated temperatures. Cracks may also develop because of differences in the coefficients of thermal expansion between concrete and glass fibre-reinforced polymer (GFRP) bars when used as an alternative to steel reinforcement. The transverse coefficient of thermal expansion of GFRP bars is approximately three times that of concrete. When GFRP-reinforced concrete members are exposed to elevated temperatures, thermal stresses develop around the bars, potentially causing cracks that reduce the bond strength between the concrete and GFRP and compromise structural durability. Steel fibres, 3–8 cm in length and randomly distributed throughout the concrete, are used to mitigate thermal cracking and enhance concrete tensile strength.

This study evaluated the effects of elevated temperatures on concrete reinforced with GFRP bars and incorporating steel fibres. Specimens were subjected to laboratory heating at 40, 80, and 120 °C. Compressive strength tests were performed on 100 mm concrete cubes, which were also tested for ultrasonic pulse velocity and density. Splitting tensile strength was measured using cylindrical specimens measuring 100 mm in diameter and 200 mm in height. Push-out tests were also conducted to assess the bond strength between GFRP bars and concrete using 100 mm concrete cubes, each containing a centrally embedded GFRP bar with a diameter of either 12 or 16 mm. Compared with the reference specimen, the test results demonstrated the effects of temperature on concrete tensile strength, compressive strength, and bond strength between concrete and GFRP bars of different diameters.