## 4 Performance of a NS RA-Modified Asphalt Mixture Based on Anti-Rutting Performance
### Anti-Rutting Performance  
To validate the anti-rutting performance of the modified asphalt mixtures of the optimum NS RA contents, rutting tests of the NS RA modified asphalt mixtures with different gradations were performed by using a rutting tester from China. The results are shown in Figure 6.  
It can be seen from Figure 6 that for five kinds of selected gradations, under the same experimental conditions, the dynamic stability values of the NS RA-modified asphalt mixtures were far higher those of the base asphalt mixtures. The dynamic stability values of NS RA-modified asphalt mixtures were at least 3-fold higher than those of the base asphalt mixtures, and their dynamic stability values were all far greater than the summer hot area requirement (no less than 2800 times/mm) of the technical Specifications for the construction of highway asphalt pavements (JTG F40-2004) in China. Therefore, for a NS RA content of 8%, the anti-rutting performances of their modified asphalt mixtures are excellent.  
To further validate the anti-rutting performances of the NS RA-modified asphalt mixtures, considering that the middle course is the anti-rutting key layer of the pavement [24], the rutting calculations of the pavement structure shown in Table 5 were carried out. Aggregate gradations of asphalt mixtures are shown in Figure 7. For asphalt mixture, the materials model of Burgers model was employed. The 15, 20, 35, 40, and 60 \({}^{\circ}\)C uniaxial creep tests of asphalt mixtures with the optimal asphalt aggregate ratios were done, and the results are shown in Table 6. According to the pavement temperature, the material parameters of the Burgers model were obtained by interpolation. According to the literature [25], other calculation parameters are shown in Table 7, and the axle load times of 4.2 \(\times\) 10\({}^{5}\) were adopted. The rutting calculation method from the literature [25] was used, where the error between the test data and the calculation result was 8.5%, as shown in Figure 8. The calculation results are shown in Figure 9.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  
Figure 8: Calculation and test results.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Material Type** & \begin{tabular}{c} **Thickness** \\ **(cm)** \\ \end{tabular} & \begin{tabular}{c} **Elastic Modulus** \\ **(MPa)** \\ \end{tabular} & \begin{tabular}{c} **Poisson** \\ **Ratio** \\ \end{tabular} & \begin{tabular}{c} **Friction** \\ **Angle (\({}^{\circ}\))** \\ \end{tabular} & \
\begin{tabular}{c} **Cohesive Force** \\ **(KPa)** \\ \end{tabular} &
\begin{tabular}{c} **Density** \\ **(kg/m\({}^{3}\))** \\ \end{tabular} \\ \hline Cement Stabilized aggregate & 19 & 1500 & 0.25 & - & - & 2400 \\ Lime soil & 20 & 550 & 0.35 & 22 & 55 & 1930 \\ subgrade & - & 48 & 0.40 & 16 & 30 & 1900 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Other calculation parameters.  
Figure 7: Aggregate gradations of the asphalt mixtures.  
It can be seen from Figure 9 that rut depths of structures A and B were 5.12 and 9.15 mm, respectively. The rutting depth of the pavement structure A was decreased by 44% over pavement structure B. However, the only difference between pavement structure A and B was the asphalt of the middle course. Therefore, the NS RA-modified asphalt mixtures used in the middle course of the pavement could obviously improve the anti-rutting performance of the asphalt pavement. Therefore, to enhance the anti-rutting ability of the pavement, it should be used in the middle course of the asphalt pavement.