Durability of Concrete Reinforced with GFRP Bars Under Varying Alkalinity and Temperature Conditions

The application of glass fiber reinforced polymer (GFRP) bars offers a promising solution for enhancing the durability of reinforced concrete structures, potentially reducing maintenance costs and associated socioeconomic impacts. However, concerns persist regarding the durability of GFRP bars in the highly alkaline environment of concrete, which can lead to physical, chemical, and mechanical degradation. This study evaluates the durability of GFRP bars composed of isophthalic polyester, vinyl ester, and epoxy matrices (6.0 mm diameter) under accelerated aging conditions. The bars were exposed to non-carbonated concrete (with and without silica fume) and carbonated concrete at temperatures of 23 °C, 40 °C, and 60 °C for durations of 500, 1000, and 3000 h. Interlaminar shear strength (ISS) was measured before and after aging. SEM and FTIR analyses confirmed degradation in the polymer matrix and fiber–matrix interface. Results indicated that silica fume significantly mitigated alkalinity effects, limiting ISS loss to 11.3%. Similarly, carbonation reduced the concrete’s pH, thereby decreasing ISS degradation to 10.7% after 3000 h. Among the tested materials, GFRP bars with vinyl ester matrix exhibited superior durability, followed by those with epoxy and polyester matrices. These findings emphasize the critical role of matrix selection and concrete mix design in improving GFRP durability.