Análise da durabilidade de armaduras poliméricas reforçadas com fibras de vidro submetidas ao ambiente alcalino e a elevadas temperaturas

Abstract

Glass fiber reinforced polymer (GFRP) rebar has been considered an alternative to minimize the degradation of reinforced concrete structures and reduce the economic impact resulting from the maintenance and rehabilitation activities of these structures. However, these rebars may have their service life reduced by physical, chemical, and mechanical changes that can occur when exposed to alkaline environment or elevated temperatures. In this context, seeking a better understanding of degradation mechanisms in highly aggressive environments, this study evaluated the durability of GFRP rebars, manufactured with polymeric isophthalic polyester, vinyl ester, and epoxy, with nominal diameters of 6.0 and 13.0 mm. Thus, accelerated aging tests were performed in the GFRP rebars exposed to the alkaline solution (pH 8.5, 12.6, and 13.5), at temperatures of 23 ˚C, 40 ˚C, and 60 ˚C and with different exposure periods (500 h, 1000 h, and 3000 h). In addition to the isolated rebars, samples embedded in concrete, with or without the addition of silica fume, and carbonated concrete were evaluated. Tensile strength and interlaminar shear tests were performed in rebar, isolated, or embedded in concrete, subjected to elevated temperatures (23 ˚C, 150 ˚C, 300 ˚C, and 350 ˚C). The degradation of glass fibers, polymeric matrices and fiber-matrix and rebar-concrete interfaces was evaluated before, and after accelerated aging, using the techniques of thermogravimetric analysis (TGA), differential exploratory calorimetry (DSC), differential thermal analysis (DTA), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The results showed that the degradation of GFRP rebars embedded in concrete and aged was lower than those directly aged in alkaline solution. The degradable effects were attenuated by the addition of silica fume, with a loss in interlaminar shear strength of 11.3%. It was observed that the carbonation of the concrete resulted in an environment less harmful to GFRP rebars, with a 10.7% reduction in interlaminar shear strength after 3,000 h of exposure. When exposed to elevated temperatures, the tensile strength behavior of GFRP rebars has a significant influence on the polymer matrix. In addition, the use of silica fume improved the performance of concrete covering and, consequently, the protection of GFRP rebars, making it difficult to diffuse oxygen and heat. The rebar/concrete adhesion was compromised by the thermal degradation of the ribs of the GFRP rebar. After analyzing a combination of degradation factors, GFRP rebars with epoxy matrix, among the rebars studied, presented the best performance in environments with exposure to elevated temperatures, and in an alkaline environment, the GFRP rebars with vinyl ester matrix presented better performance.