## 3 Results and Analysis
### Bond-Slip Curves  
Based on Equation (1) and \(S_{F}\), the bond-slip curves of the specimens were plotted and are shown in Figure 8.  
Scholars have observed that there are four characteristic points on the bond-slip curves of rebar and NC, namely internal cracking, splitting, limit and residual, which were used to classify five stages [23] in this study. According to the bond-slip curves and the failure patterns of the SFRC specimens, the bond-slip curves of SFRC at different high temperatures were divided into five stages by considering the effects of steel fibers and the temperature. A typical bond-slip curve of SRFC is shown in Figure 9. \(\tau_{u}\) is the ultimate bond stress and \(s_{u}\) is the free-end slip corresponding to the ultimate bond strength in Figure 9. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Specimen ID** & \(P\) **(kN)** & \(\tau_{u}\) **(MPa)** & \(s_{u}\) **(mm)** & \(\beta_{T}\) & \(\beta_{V}\) & **Failure Patterns** \\ \hline SF0T20 & 74.155 & 24.08 & 0.38 & 1.000 & 1.000 & Splitting \\ SF0.5T20 & 82.58 & 26.82 & 0.59 & 1.000 & 1.114 & Split-pullout \\ SF1T20 & 90.02 & 29.235 & 0.805 & 1.000 & 1.214 & Split-pullout \\ SF1.5T20 & 98.31 & 31.925 & 1.015 & 1.000 & 1.326 & Split-pullout \\ SF0T200 & 62.92 & 20.43 & 0.445 & 0.848 & 1.000 & Splitting \\ SF0.5T200 & 74.315 & 24.13 & 0.665 & 0.900 & 1.181 & Split-pullout \\ SF1T200 & 82.37 & 26.75 & 0.91 & 0.915 & 1.309 & Split-pullout \\ SF1.5T200 & 91.67 & 29.77 & 1.1 & 0.932 & 1.457 & Split-pullout \\ SF0T400 & 39.50 & 12.825 & 0.625 & 0.533 & 1.000 & Splitting \\ SF0.5T400 & 67.11 & 21.795 & 0.865 & 0.813 & 1.699 & Split-pullout \\ SF1T400 & 74.375 & 24.155 & 1.08 & 0.826 & 1.883 & Split-pullout \\ SF1.5T400 & 80.31 & 26.08 & 1.49 & 0.817 & 2.034 & Split-pullout \\ SF0T600 & 24.09 & 7.82 & 0.735 & 0.325 & 1.000 & Split-pullout \\ SF0.5T600 & 35.855 & 11.64 & 0.965 & 0.434 & 1.488 & Split-pullout \\ SF1T600 & 46.56 & 15.12 & 1.37 & 0.517 & 1.934 & Split-pullout \\ SF1.5T600 & 54.77 & 17.785 & 1.84 & 0.557 & 2.274 & Split-pullout \\ \hline \end{tabular}
\end{table} 
Table 5: Experimental results of pull-out tests. (1) Initial micro-slide phase (OA)  
The concrete around the rebar near the loaded end of the specimen is elastically deformed at the beginning of central pull-out test. A small relative slip between rebar and concrete appears. At this stage, the bond between rebar and concrete is dominated by the chemical bond force and supplemented by the mechanical bite force caused by the small  
Figure 8: Bond–slip curves of specimens at (**a**) 20 \({}^{\circ}\)C, (**b**) 200 \({}^{\circ}\)C, (**c**) 400 \({}^{\circ}\)C, and (**d**) 600 \({}^{\circ}\)C.  
Figure 9: Bond–slip curves of SFRC. slip. The bond-slip curve at this stage is essentially linear. Steel fibers do not play a role in preventing cracking because the concrete around the rebar has not yet cracked. (2) Slip phase (AB)  
With the increase in pullout force, the chemical bond force disappears. The oblique squeezing force of the rebar rib on the concrete increases and its radial component causes the concrete around the rebar to produce radial cracks and relative slip from the loaded end. The bond force is mainly provided by the mechanical bite force of the rebar rib on the concrete and the frictional resistance between the surface of the rebar and the concrete. At this stage, the steel fibers, which are in the same direction as the main tensile stress, start to play a crack-arresting role. The development of cracks is thus greatly restricted. Therefore, the bond-slip curve enters a nonlinear growth phase. (3) Splitting failure phase (BC)  
As the oblique squeezing force increases, the ultimate tensile strength of concrete at the periphery of the rebar is reached. Cracks in the concrete appear along the direction perpendicular to the rebar ribs. The crack-bridging effect of steel fibers sharply increases, which effectively delays the development of cracks. There is a trend of slowly rising until the bond-slip curve reaches the peak point.