# Study of Basalt Fibers and Graphene Enriched Polymers on Bond Behavior of FRP Bars in Concrete
## 4 Results and Discussions
### Room Temperature Results
(MPa)** \\ \hline \multicolumn{6}{c}{GFR bars} \\ \hline \multirow{3}{*}{C20-8G} & SP1 & 8.42 & 2.40 & pull-out & \multirow{3}{*}{7.58} & \multirow{3}{*}{0.73} \\  & SP2 & 7.26 & 1.75 & pull-out & & \\  & SP3 & 7.10 & 2.94 & pull-out & & \\ \hline \multirow{3}{*}{C20-12G} & SP1 & 10.16 & 2.59 & pull-out & \multirow{3}{*}{9.88} & \multirow{3}{*}{0.74} \\  & SP2 & 10.45 & 1.66 & pull-out & & \\  & SP3 & 9.04 & 1.88 & pull-out & & \\ \hline \multirow{3}{*}{C30-8G} & SP1 & 7.83 & 3.09 & pull-out & \multirow{3}{*}{6.69} & \multirow{3}{*}{1.41} \\  & SP2 & 7.12 & 1.87 & pull-out & & \\  & SP3 & 5.111 & 1.83 & pull-out & & \\ \hline \multirow{3}{*}{C30-12G} & SP1 & 12.76 & 2.59 & pull-out & \multirow{3}{*}{12.71} & \multirow{3}{*}{1.35} \\  & SP2 & 11.34 & 2.23 & pull-out & & \\  & SP3 & 14.04 & 2.25 & pull-out & & \\ \hline \multicolumn{6}{c}{GFRg bars} \\ \hline \multirow{3}{*}{C20-8 Gg} & SP1 & 6.02 & 2.80 & pull-out & \multirow{3}{*}{6.16} & \multirow{3}{*}{1.53} \\  & SP2 & 7.75 & 3.77 & pull-out & & \\  & SP3 & 4.70 & 3.07 & pull-out & & \\ \hline \multirow{3}{*}{C20-12 Gg} & SP1 & 12.81 & 2.88 & pull-out & \multirow{3}{*}{12.91} & \multirow{3}{it is still not possible to compare the present results with others. However, in the figure is included results obtained by [PERSON] et al. [33] diameter 12.7 mm, polyester polymer and other conditions fairly similar to the present experiments. The better behavior observed in the present cases in terms of \(\tau_{1}\) and \(s_{1}\) may indicate a positive effect of the GNP, with an increase of 49% in the bond strength. Further analysis of GFRPg cases is done in the discussion section below. Finally, in Figure 9a, the average bond stress vs slip relations for BRFP cases are shown, considering all experimental and numerical results. Again an excellent fit is obtained. The average for each case considered is presented in Figure 9b. The observed effect of the increase in concrete strength on bond strength is on the same direction as observed for GFRP bars: for 8-mm bars bond increased substantially and for 12.5-mm bars the bond presented a slight decreased. Figure 9c shows the average bond-slip relation for the two diameters tested. As in previous cases, the greater the diameter the greater the bond. However, in BRFP cases the substantial diameter effect on bond is believed to be related mostly to surface treatment. In the case of 12.5 mm bars, the presence of deformations increased the efficiency of the bar-concrete bond due to the better mechanical interlock they promote. In the 8.0 mm bar case, because of the smooth surface (see values of rib height, \(\dot{m}\), Table 1), the bond behavior depends basically on friction and adhesion. Also 12.5 mm bars  
Figure 7: Average bond stress-slip curves for GFRP cases. (**a**) All experimental tests and corresponding numerical simulations; (**b**) average values per case; (**c**) average for 8 and 12.5 mm bars; (**d**) average for 12.5 mm bar and results by [PERSON] et al. [53], [PERSON] et al. [2] and [PERSON] et al. [33]. have greater roughness (Table 1), which increases friction. As [PERSON] and [PERSON] [1] and others emphasize, mechanical interlock associated to surface treatment is a key factor to bond strength. It is already possible to find other bond studies in the literature regarding BFRP bars, but not exactly the same combinations tested in the present study. Figure 9d shows a comparison of C30-XXB results with such cases. [PERSON] et al. [32] analyzed the bond behavior for 8.0 mm diameter bars with sand coated surface treatment, obtaining a bond strength of 10.3 MPa or 33.6% higher value than current experiments. [PERSON] et al. [30], on the other hand, investigated the bond between 12.0 mm bars with grooved surface treatment and C30 concrete, finding a bond strength of 15.8 MPa, which is 41.7% smaller than current experiments. Such comparisons suggest again that the surface conformation of the bars has a fundamental role governing bond behavior. The sand coated case of [PERSON] et al.