## 3 Results and Discussion
### Dynamic Rheological Properties and Temperature Sensitivity  
The complex shear modulus G* can be considered the binder sample's total resistance to deformation when repeatedly sheared. The log G* values of the 2, 3, 4, or 5 wt% SBS-modified binders with different GF-WTB contents vs. temperatures from 40 \({}^{\circ}\)C to 76 \({}^{\circ}\)C are shown in Figure 5. Figure 5 shows that the log G* values lineally decrease with the increase in temperature for all the asphalt samples. For the same SBS content, the log G* value at the end temperature 76 \({}^{\circ}\)C increases obviously with the GF-WTB content. In addition,  
\begin{table}
\begin{tabular}{c c c c c} \hline \multicolumn{1}{c}{\multirow{2}{*}{**Technical Index**}} & **Specification** & \multirow{2}{*}{**Test Result**} & \multirow{2}{*}{**Experimental Method**[26]} \\  & & **Requirement** & & \\ \hline Rotational viscosity@135 \({}^{\circ}\)C (Pa-s) & - & 0.571 & T0625 \\  & Mass change (\%) & \(\leq\)\(\pm\)0.8 & 0.1 & T0610 \\ RTFOT residue & Residual penetration ratio (\%) & \(\geq\)61 & 65 & T0640 \\  & Residual ductility @15 \({}^{\circ}\)C (cm) & \(\geq\)15 & 21.8 & T0605 \\ \hline \end{tabular}
\end{table}
Table 1: \(Cont.\)  
Figure 4: Effect of GF-WTB content on rotational viscosity under certain SBS dosage.  
the sensitivity of log G* to temperature, i.e., the regression coefficient (regression line slope), decreases with the increase in GF-WTB dosage under certain SBS content. The DSR test result analysis indicates that the addition of silane coupling agent modified GF-WTB reduces G* temperature sensitivity of the SBS-modified asphalt and the increase in the G* value of binder will transmit to the increase in the stiffness of respective asphalt mixture.  
Figure 5: Cont.  
Under the same G* value, the smaller the phase angle \(\delta\), which means the large elastic component and the small viscous one, the stronger the anti-rutting ability of the asphalt material. Under high-temperature conditions, the larger G*/sin \(\delta\) indicates that G* is larger and \(\delta\) is smaller [29]. Therefore, the rutting factor G*/sin \(\delta\) is used to represent the anti-rutting ability in the SHRP specification. The G*/sin \(\delta\) values of the 2, 3, 4, or 5 wt% SBS-modified binders with different GF-WTB contents vs. high temperatures 64-76 \({}^{\circ}\)C are shown in Figure 6. The Figure 6 shows that the G*/sin \(\delta\) values decrease with the increase in high temperature for all the asphalt samples. Evidently, the rutting factor increases with the SBS dosage. The horizonal line in Figure 6 represents the minimum G*/sin \(\delta\) value 1.0 kPa for the unaged binder in the performance-graded DSR specifications. Under the same SBS content, the addition of silane coupling agent modified GF-WTB improves the high-temperature performance grade, e.g., for 4 wt% SBS-modified asphalt, incorporation of 2 or 4 wt% GF-WTB elevates the high-temperature PG from 70 \({}^{\circ}\)C to 76 \({}^{\circ}\)C. The DSR test results show that GF-WTB/SBS composite-modified binders are of better resistance to deformation, anti-rutting ability, and temperature-insensitivity. Among the  
Figure 5: The logarithm of the complex shear modulus of GF-WTB/SBS composite-modified asphalt: (**a**) SBS2 + WTBx; (**b**) SBS3 + WTBx; (**c**) SBS4 + WTBx; (**d**) SBS5 + WTBx.  
composite-modified binders with 2, 3, 4 wt% SBS, in comprehensively considering the high-temperature PG, temperature sensitivity, and GF-WTB dosage, SBS4 + WTB2 is the optimal one.  
Figure 6: _Cont._