Performance of GFRP-Reinforced Concrete Beams Subjected to High-Sustained Load and Natural Aging for 10 Years

The long-term performance of glass fiber-reinforced polymer (GFRP) bars under high levels of sustained load combined with real field conditioning has not yet been thoroughly investigated. Our experimental investigation examined the flexural behavior of concrete beams reinforced with GFRP bars subjected to a high sustained bending load after 10 years of natural aging. The experimental program consisted of eight rectangular concrete beams measuring 250 × 250 × 2,000 mm. All beams were reinforced with sand-coated GFRP bars. Four beams were subjected to a high sustained load of up to 40% of the ultimate tensile capacity of their GFRP bars with simultaneous exposure to aggressive natural weathering (temperatures ranging from −25°C to 35°C) for 10 years. The remaining four were stored in the laboratory and treated as control specimens without any loading. The conditioned beams were tested up to failure in a four-point bending setup. The results were compared in terms of load–displacement behavior, ultimate strength, displacement capacity, failure modes, and cracking patterns. In addition, the microstructure of the GFRP bars was studied to evaluate the physical changes of the bars, and their bond condition with surrounding concrete at different stress levels. The findings indicate a strength deterioration of only 16% for this early generation of GFRP bars under harsh natural conditioning and high sustained loads for 10 years. On the other hand, the bond between the concrete and GFRP bars, as well as the glass-transition temperature, infrared spectra, and interlaminar shear strength of the GFRP bars, remained unaffected. Finally, analytical approaches were implemented to predict the load–displacement behavior and crack widths of the tested beams.