# Study of Basalt Fibers and Graphene Enriched Polymers on Bond Behavior of FRP Bars in Concrete
## 4 Results and Discussions
### Room Temperature Results
[32] also presented a similar peak slip \(s_{1}\) as the present cases. However, for the grooved case investigated by [PERSON] et al. [30], this slip was smaller. Figure 8: Bond stress-slip curves for GFRPg cases. (**a**) All experimental tests and corresponding numerical simulations; (**b**) average values; (**c**) average for diameter 8 and 12.5 mm and results by [PERSON] et al. [33]. Discussion  
Despite the changes in bond strength with concrete strength in all cases reported in this work, a statistical analysis of variance (ANOVA) indicates these variations are not significant. This conclusion is in agreement with the findings of [PERSON] and [PERSON] [1] and others, that concrete strength has a limited influence on bond because the bar surface will be damaged after certain level of bond, regardless the concrete. GFRP bars will be considered here benchmarks to compare with the two new materials tested in this work. In the former cases there is an increase of the bond strength with greater bar diameter, but the main reason for the increase seems linked to the height of ribs (rh). Figure 10 then compares GFRP with GFRPg and BFRP. First, in Figure 10a, a comparison of the average values for 8 and 12.5 mm bars between GFRPg and GFRP cases is shown. As already discussed, the main difference between the two is the polymer used. It is observed that there is an equivalence in terms of bond strength \(\tau_{1}\) for both cases, despite the tendency for GFRPg cases to have a slightly larger slip peak \(s_{1}\). Therefore, results indicate that the addition of GNP was able to overcome the trend of more unfavorable behavior usually associated to polyester polymers, keeping the cost of the addition competitive with standard GFRP. This preliminary study encourages future studies to further access the effect of GNP additions in FRP bars. Finally, in Figure 10b a comparison of the average values  
Figure 9: Bond stress-slip curves for BFRP cases. (**a**) All experimental tests and corresponding numerical simulations; (**b**) average values; (**c**) average for diameter 8 and 12.5 mm; (**d**) average for diameter 8 and 12.5 mm and results by [PERSON] et al. [32] and [PERSON] et al. [30]. for 8 and 12.5 mm bars between BFRP and GRFP cases is shown. For the 12.5 mm case, combination BFRP/helically-wounded presented a bond strength almost twice as much as the bond for combination GFRP/helically-wrapped. Considering that both surfaces have similar characteristics (e.g., \(m\) and roughness), results indicate a superior behavior of the first combination when compared to the second. However, for the 8 mm cases the behavior of the combination BFRP/smooth is inferior to GFRP/helically-wrapped. The comparison emphasizes again the importance of the surface treatment of FRP bars in general, i.e., the type of fiber alone cannot be considered the determinant factor defining bond. The parameters of the curves shown in Figure 10 are presented in Table 6. In general, \(s_{0}\) is smaller and \(\alpha\) is bigger for the GFRP bars, which showed higher initial stiffnesses in comparison to the other bars. Conversely, due to lower initial stiffness, GFRPg bars showed larger values of \(s_{0}\) and smaller \(\alpha\) values. The addition of GNP was unable to improve this typical characteristic of the polyester. Higher values of \(\tau_{0}\) are associated to 12.5 mm bars when compared to 8 mm bars of the same type, which can be linked to higher values of \(m\) in former cases