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The use of glass fibre reinforced polymer (GFRP) bars as internal reinforcement of new and existing (for rehabilitation or retrofitting) concrete structures has been growing, mainly due to the advantages they present over traditional steel reinforcement, namely their low weight, high strength and corrosion resistance. However, at moderately elevated temperatures, especially when approaching the glass transition temperature (Tg) of the polymeric matrix (usually between 65-150 ºC), the stiffness, strength and bond properties of these rebars are known to be significantly degraded. The first part of this paper presents an experimental investigation comprising tensile and pull-out tests on sand coated GFRP rebars at elevated temperatures; the tensile tests were carried out up to 300 ºC, whereas the pullout tests were performed on GFRP rebars embedded in concrete cylinders at 20 ºC, 40 ºC, 60 ºC, 80 ºC, 100 ºC and 140 ºC; two embedment lengths of the rebars were considered, corresponding to 5 and 9 times their diameter. Specimens were first heated up to the predefined temperature (measured at the GFRP-concrete interface) and then loaded up to failure. The applied load and the slip of the rebars at both loaded and free ends were measured during the pull-out tests. The obtained results confirmed that the stiffness and strength of the GFRP-concrete interface are significantly reduced with temperature increase, especially when the Tg of the GFRP rebars is approached and exceeded. In the second part of the paper, analytical bond vs. slip relations for the GFRP-concrete interface are proposed for each of the tested temperatures; these relations were obtained based on a numerical strategy in which the experimental data from the pull-out tests were used to calibrate the defining parameters of the local bond vs. slip laws. Moreover, the accuracy of two empirical (relaxation) models, proposed by Gibson et al. and Correia et al. in predicting the GFRP-concrete bond strength reduction with temperature was also assessed.

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