| Summary: | The study of fiber-reinforced concrete (FRC) is associated with improving the mechanical properties of the material, but it will only be sufficiently efficient when there is an interaction between the fiber and the matrix, which depends on the characteristics of the paste, and mainly on the characteristics of the surface of the reinforcement material. In this way, this research sought to evaluate the surface treatment of polyester fibers (F) with graphene oxide (GO) and its contribution to the transition zone (fiber-matrix) in concrete mixtures. The surface deposition on the fiber was carried out using the ultrasonication method with temperature variation reaching two maximum temperatures (50 °C and 80 °C), then reinforced concrete mixtures were obtained using the untreated fiber (FRC), fiber with GO auxiliary coating (FRC/GO) and GO (GOC). To evaluate the quality of GO deposition, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) tests were carried out, the same technique was used to evaluate the fiber-matrix transition zone, and tests were also carried out in the fresh and hardened for concrete mixes. The SEM images and the C/O ratio identified in the EDS demonstrate greater deposition of GO in fibers treated at 80 °C, increasing the C/O ratio by 47 % when compared to samples without treatment and 44 % higher than the treatment at 50 °C. It is possible to identify in the SEM images the change in the fiber-matrix transition zone for the FRC/GO samples, and in them the formation of denser regions of cement hydration products, which did not represent gains in mechanical properties, but rather 19 % reduction in water absorption when compared to FRC samples.
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