# Study of Basalt Fibers and Graphene Enriched Polymers on Bond Behavior of FRP Bars in Concrete
## 4 Results and Discussions
### Thermal Effects  
Table 7 presents the values of \(\tau_{1}\), \(s_{1}\) and the rupture mode developed in the pull-out tests after exposing specimens to 60 and 120 \({}^{\circ}\)C. The average maximum stress value \(\tau_{1}\) and the corresponding standard deviation are also presented. Only C30 concrete and 12.5 mm bars are considered. Rupture always occurred by pullout without significant differences regarding room temperature ruptures. However, for 120-degree cases, in general, the polymer color changed and the degradation of the outer surfaces was more intense than lower temperature cases. Adjusted numerical parameters used in the numerical simulations are presented in the Appendix A. Results of average bond stress versus slip for all GRFP cases are shown in Figure 11a and average values per temperature are shown in Figure 11b (the figures also include room temperature results). From Figure 11b is observed that bond strength after heating process at 60 and 120 \({}^{\circ}\)C decays by 16.21% and 38.08% respectively, when compared to room temperature results. Also in Figure 11b, temperature effects on GFRP bars are presented as tested by [PERSON] et al. [33] and [PERSON] et al. [34]. In the former case, test conditions were fairly similar to the present work. However, tested temperatures were different (130 and 205 \({}^{\circ}\)C) but interpolating data to temperatures tested in this work, a bond strength decayed by 13.89% and 31.62% is observed, respectively. In [PERSON] et al. [34] grooved surface, 8 mm bars and test temperatures ranging from 80 and 165 \({}^{\circ}\)C were considered. Interpolating to temperatures tested in this work, these cases showed a decrease in bond strength of 23% for 60 \({}^{\circ}\)C case and 40% for 120 \({}^{\circ}\)C case. Therefore, thermal effects here presented for GRFP bars are on par with results of the literature. Interesting to note that all heated cases present a bond strength smaller than 12 MPa (minimal required by GOST 31938-2012 Standard [57]). Finally, Figure 12 shows temperature degradation curve according to the model by [PERSON] et al. [55] for the analysis done in the present work, as well as the \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline \multirow{2}{*}{**Combinations**} & \multirow{2}{*}{**Specimens**} & \multirow{2}{*}{\(\tau_{1}\) (MPa)} & \multirow{2}{*}{\(\text{s}_{1}\) (mm)} & \multirow{2}{*}{**Rupture**} & \multirow{2}{*}{\(\overline{\tau}_{1}\) (MPa)} & \multirow{2}{*}{\(\overline{\tau}_{1}\) (MPa)} \\  & & & & & & \\ \hline \multicolumn{6}{c}{GFRP bars} \\ \hline \multirow{3}{*}{C30-12G-60} & SP1 & 10.05 & 2.97 & pull-out & & \\  & SP2 & 11.35 & 1.93 & pull-out & 10.65 & 0.65 \\  & SP3 & 10.55 & 2.05 & pull-out & & \\ \hline \multirow{3}{*}{C30-12G-120} & SP1 & 8.59 & 2.24 & pull-out & & \\  & SP2 & 7.98 & 2.10 & pull-out & 7.87 & 0.79 \\  & SP3 & 7.03 & 2.28 & pull-out & & \\ \hline \multicolumn{6}{c}{GFRP bars} \\ \hline \multirow{3}{*}{C30-12G-60} & SP1 & 8.46 & 2.41 & pull-out & & \\  & SP2 & 8.32 & 3.54 & pull-out & 8.30 & 0.18 \\  & SP3 & 8.11 & 2.67 & pull-out & & \\ \hline \multirow{3}{*}{C30-12G-120} & SP1 & 6.48 & 2.95 & pull-out & & \\  & SP2 & 5.64 & 3.26 & pull-out & 6.32 & 0.62 \\  & SP3 & 6.85 & 2.74 & pull-out & & \\ \hline \multicolumn{6}{c}{GFRP bars} \\ \hline \multirow{3}{*}{C30-12B-60} & SP1 & 23.70 & 2.53 & pull-out & & \\  & SP2 & 17.45 & 2.65 & pull-out & 20.11 & 3.23 \\  & SP3 & 19.19 & 3.04 & pull-out & & \\ \hline \multirow{3}{*}{C30-12B-120} & SP1 & 17.72 & 2.55 & pull-out & & \\  & SP2 & 13.87 & 2.73 & pull-out & 15.90 & 1.94 \\ \cline{1-1}  & SP3 & 16.12 & 2.63 & pull-out & & \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Experimental results for specimens heated at 60 and 120 \({}^{\circ}\)C.  
interpolated results obtained from [PERSON] et al. [33] and [PERSON] et al. [34]. It is possible to see that results of the present work shows an intermediate behavior.