In the field of reinforced-concrete (RC) structures, the use of fiber reinforced plastic rebars (FRP rebars) as an alternative to the steel reinforcements appears very promising, especially if such structures are exposed to corrosive environments. However, a better understanding of the mechanical behavior of FRP reinforcements - in particular bond behavior - is needed in order to use them for practical purposes. For this reason, in the last few years a number of tests on several types of FRP rebars has been conducted in order to evaluate the interaction phenomena between FRP rebars and the concrete matrix and to evidence behavioral differences with respect to the deformed steel rods. In this paper a state-of-the-art report on the bond of FRP bars to concrete is presented. Numerous tests are analyzed to better understand bond mechanisms and the influence of type of fiber, outer surface (shape and type of matrix), and other significant parameters (ie., confining pressure, bar diameter, compressive concrete strength) on bond performances. Furthermore, some analytical models of bond-slip behavior are examined to assess their adequacy to reproduce the experimental bond behavior. In particular, the investigation focuses on the reliability of the well-known model by Malvar (the first one dedicated to FRP reinforcements) as well as on the model by Eligehausen, Popov, and Bertero, developed for steel reinforcements but successfully applied to FRP ones. In addition, the effectiveness of two analytical formulations proposed by the authors, the first one representing the ascending branch of the bond-slip curve and the second the entire curve, is demonstrated.
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