# Study of Basalt Fibers and Graphene Enriched Polymers on Bond Behavior of FRP Bars in Concrete
## 4 Results and Discussions
### Thermal Effects
It is evident the superior behavior overall of the combination BRFP/helically-wounded bars when compared to the others regarding bond strength \(\tau_{1}\) in all temperatures considered, being this case the only where residual strength after the 120 \({}^{\circ}\)C heating cycle is above 12 MPa. Interestingly peak slip \(s_{1}\) is very similar in all tests and ranges between 2-2.5 mm. Figure 16: Temperature degradation for BRFP cases compared to [PERSON] et al. [35]. [PERSON] et al. [55] model used. Figure 15: **(a)** All experimental tests and corresponding numerical simulations for BRFP at 60 and 120 \({}^{\circ}\)C (corresponding cases at room temperature included for comparison). **(b)** Average values compared to [PERSON] et al. [35]. Comparing curve parameter in all cases, see Table A4 in Appendix A, there is a consistent drop in the initial slope (\(\tau_{0}/s_{0}\)) of the bond curve with temperature, driven by a consistent drop in \(\tau_{0}\). Combination GFRP/helically-wrapped remained the case with greater initial bond stiffness among all, in all temperatures. GFRP cases showed the greatest initial slope (\(\tau_{0}/s_{0}\)) ranging from 37 to 12 with temperature, while GFRPg had always the smallest initial slope ranging from 6.7 to 5.9 with temperature. Considering the same conditions, \(\tau_{0}\) is always prone to be greater for greater diameters. Finally, GFRP cases tended to have the most negative \(\tau_{\infty}\) values, or the drop of bond after peak was more severe. Figure 17b compares thermal degradation of the three cases tested using the model by [PERSON] et al. [55]. It is observed again a superior behavior of BRFP cases when comparing with glass fiber cases. This is a conclusion also obtained in comparative studies done by [PERSON] et al. [36] and [PERSON] et al. [35], despite considering other types of polymers, concrete and diameter. The particular comparison between GRFP and GRFPg shows the latter with an equivalent thermal degradation or a slightly superior behavior, in particular for 120 \({}^{\circ}\)C case. Considering that polyester in general has a greater degradation than vinyl-ester with temperature, it is possible that the enhanced behavior of GRFPg is due to the addition of GNP. The better behavior overall at all temperatures associated to BRFP seems to be linked to combination basalt+helically wounded surface. The far better behavior of this combination at room temperature is the distinguishing factor. Regarding GRFPg results, they are equivalent to GRFP+vinyl-ester but far superior than GRFP+polyester. Therefore results are encouraging but more studies are necessary in this regard. Finally, Figure 18 shows normal Cauchy stress in \(y\) direction for case C30-12B (a) and case C30-12B120 (b) at the peak of the bond for both cases. These are the cases with maximal bond at room temperature and at 120 \({}^{\circ}\)C, respectively. It is observed that concrete strength is not attained in any case, assuring that concrete cover was sufficient and splitting rupture was not an issue. Also, the hypothesis of considering concrete as elastic in the simulations is correct. It is observed that concrete stresses near the adherent zone was mostly uniform, except near the ends of this zone. This is an expected result because in these regions rebars stop sharing stresses with concrete. Other cases showed a similar stress distribution and  
Figure 17: (**a**) Average of all experimental tests and corresponding numerical simulations for GFRP, GFRPg and BFRP at 60 and 120 \({}^{\circ}\)C (corresponding cases at room temperature included for comparison). (**b**) Temperature degradation according to model by [PERSON] et al. [55]. for this reason are not depicted. Finally, as expected, stresses in concrete are much smaller for the 120 \({}^{\circ}\)C case due to bond and elastic properties degradation.