# Study of Basalt Fibers and Graphene Enriched Polymers on Bond Behavior of FRP Bars in Concrete
## 1 Introduction
Among the studies already done, it was found that they have higher tensile strength and elasticity modulus and better chemical stability than GFRP bars, besides being cheaper than CFRP bars [27; 28]. Another important advantage considering environmental and ecological issues is the fact that basalt fibers are produced by natural volcanic rocks. Regarding bond studies, helically wrapped surface were tested by [PERSON] et al. [29] and [PERSON] et al. [13], while grooved surfaces were studied by [PERSON] et al. [3] and [PERSON] et al. [30]. Finally, [PERSON] et al. [31] and [PERSON] et al. [32] considered sand coated surfaces. In all cases concrete ranged from C30 to C50 strength grade. Not all types of surfaces, bar diameters, concrete strengths have been tested and bond behavior of cases such as helically wounded, smooth, among other types have not been addressed, as far as these authors know. Therefore there is still an insufficient knowledge about BFRP bars, which have prevented them to be included in design standards for reinforced concrete structures so far, which is another motivational aspect for the present work. The low thermal resistance associated to FRP bars is another critical aspect. One of the pioneer studies in this regard was done by [PERSON] et al. [33] considering GFRP bars. It was shown that, for temperatures of \(250\,^{\circ}\mathrm{C}\), bond strength could drop up to \(90\%\) compared to room temperature strength. Surface treatment was a factor that changed thermal degradation. Another studies of thermal degradation can be found in [PERSON] et al. [34], [PERSON] et al. [35] and [PERSON] et al. [36]. The first focused on GFRP rebars while the others compared the behavior between GFRP and BFRP rebars. Thermal damage was slightly smaller for BFRP bars until certain temperature. For higher temperatures behavior was similar in both cases. Again surface treatment was considered an important factor for thermal degradation. Due to significant number of variables involved in FRP bond-slip behavior, the use of machine-learning techniques can be appropriate in order to provide a reliable estimation of bond strength in these cases. It may reduce the extensive testing required for assessing variables influence, reducing time and costs significantly. The use of the technique will not be pursued in the present work, but applications to FRP can be found for instance in [PERSON] et al. [37], [PERSON] et al. [38], among others. This work proposes an experimental/numerical analysis of the bond behavior by pull-out tests for BRFP bars and bars where GNP is added as an additive. In the first case, helically wounded and smooth surfaces are considered, which are cases still not fully investigated in the literature. In the second case, an exploratory study of the GNP addition on GFRP rebars with polyester matrix is proposed. Only helically wrapped surfaces are considered in the latter cases. Standard GFRP/helically wrapped bars are also tested in this work as a benchmark. At room temperature the effect of bar diameter and concrete strength on bond are studied. Thermal degradation is also studied for one particular combination of diameter and concrete. The tests are also reproduced by Finite Element (FE) simulations in order to validate experiments, explore stresses in the concrete and obtain parameters for an analytical model. In Section 2 the experimental study and materials are described. Numerical simulation details are shown in Section 3. Results and discussions are presented in Section 4. Finally, final remarks are stated.