## 2 Materials and Methods  
### Materials  
The base asphalt and SBS modified asphalt were used in this study, and their physical properties are presented in Table 1. The content of SBS in asphalt is 4%. The crumb rubber particles come from Binzhou City Shangdong Province, with the particle size of 1-3 mm, and the content of the crumb rubber particles in asphalt mixtures is 3% (mass ratio of mineral aggregate) [13]. Considering the convenience of practical application in engineering, the mixing method of rubber particles adopts the external mixing method. That is, the original mineral material gradation of the asphalt mixture is not changed, and rubber particles are mixed in the mixing process. The physical properties of rubber particles are shown in Table 2. The diatomic with a size below 0.075 mm was utilized to enhance the asphalt mixtures, whose composition is presented in Table 3. According to the standard (JTG E20-2011 T0736-2011), eight types of asphalt mixtures included suspended dense gradation and framework dense gradation were prepared in this study [23]. The grading curve is shown in Figure 1. In subsequent tests, the rutting plate specimens were fabricated by wheel rolling method, and the cylindrical specimens (100 mm in diameter and 63.5 mm in height) for freeze-thaw splitting tests and creep tests were fabricated by the Superpave Gyratory Compactor (SGC). The specific grouping number and the optimum asphalt-aggregate ratio are shown in Table 4. The optimum asphalt-aggregate ratio was determined according to the standard (JTG F40-2004) [24]. According to the standard, the design volume of air voids of suspended dense graded asphalt mixture and skeleton dense graded asphalt mixture are 4% and 3.5%, respectively. The basalt aggregate was used, and all performance indexes meet the specification requirements, as shown in Table 5. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Properties**} & \multicolumn{2}{c}{**Base Asphalt**} & \multicolumn{2}{c}{**SBS Modified Asphalt**} \\ \cline{2-5}  & **Standard** & **Value** & **Standard** & **Value** \\ \hline Density (15 \({}^{\circ}\)C, g/cm\({}^{3}\)) & — & 1.017 & — & 1.014 \\ Penetration (25 \({}^{\circ}\)C, 0.1 mm) & 80–100 & 91.6 & 60–80 & 65.1 \\ Softening point T\({}_{\text{R}\&\text{B}}\) (\({}^{\circ}\)C) & \(\geq\)45 & 46.9 & \(\geq\)55 & 61.0 \\ Ductility (cm) & \(\geq\)100 (25 \({}^{\circ}\)C) & \(>\)150 & \(\geq\)30 (5 \({}^{\circ}\)C) & 68.5 (5 \({}^{\circ}\)C) \\ Elastic recovery & — & — & \(\geq\)65 & 88 \\ \hline \multicolumn{5}{c}{After TFOT} \\ \hline Mass loss (\%) & \(\leq\pm\) 0.8 & 0.38 & \(\leq\pm\) 1.0 & 0.22 \\ Residual penetration ratio (25 \({}^{\circ}\)C, \%) & \(\geq\)57 & 73.3 & \(\geq\)60 & 66.9 \\ Ductility (cm) & \(\geq\)20 (15 \({}^{\circ}\)C) & \(>\)120 (15 \({}^{\circ}\)C) & \(\geq\)20 (5 \({}^{\circ}\)C) & 33.2 (5 \({}^{\circ}\)C) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physical properties of asphalt. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Properties**} & **Density** & **Water** & **Metal** & **Fiber** & **Ash** & **Carbon Black** \\  & **(g/cm\({}^{3}\))** & **Content (\%)** & **Content (\%)** & **Content (\%)** & **Content (\%)** & **Content (\%)** \\ \hline Value & 1.21 & 0.62 & 0.031 & 0.63 & 5.2 & 47 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Properties of rubber particles. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Correlation**} & \multicolumn{5}{c}{**Asphalt Types**} \\ \cline{2-7}  & **Base Asphalt** & **Diatomite and Crumb** & **SBS Modified** & **Diatomite and Crumb** \\  & **Buse Asphalt** & **+ Base Asphalt** & **Asphalt** & **+ SBS Modified Asphalt** \\ \hline AC-13 & AC (4.8\%) & DRAC (5.4\%) & SAC (4.9\%) & SDRAC (5.5\%) & SDRAC (5.5\%) \\ SMA-13 & SMA (5.3\%) & DRSMA (5.9\%) & SSMA (5.5\%) & SDRSMA (6.1\%) \\ \hline \hline \end{tabular} Note: The content in brackets in the table is the asphalt-aggregate ratio.  
\end{table} 
Table 4: Group number and asphalt-aggregate ratios.