Resumo:
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.
