## 3 Comparison of Mechanical Properties of HMAC and Conventional Asphalt Pavement  
The structure of the conventional asphalt pavement that was used in this study was identical to the structure of HMAC pavement, except for the middle surface layer. The high-modulus structural layer in HMAC pavement was located in the middle surface layer, while the middle surface layer in the conventional asphalt pavement was composed of the ordinary material, AC-20. The specific parameters of these materials were determined by referring to literature [32], as shown in Table 6.  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**The Middle** & **Thickness** & **Density** & **Resilient** & **Poisson’s** & **Damping** & **Damping** & **\(g_{1}\)** & **\(g_{2}\)** & \(\tau_{1}\)** & \(\tau_{2}\)** \\
**Surface Layer** & **(mm)** & **(kg-m\({}^{-3}\))** & **Modulus** & **Ratio** & **Coefficient** & **\(\alpha\)** & **\(g_{1}\)** & **\(g_{2}\)** & \(\tau_{1}\)** & \(\tau_{2}\)** \\ \hline AC-20 & 6 & 2 500 & 1 000 & 0.35 & 0.8 & 0.37 & 0.63 & 621.07 & 20.45 \\ HMAC-20 & 6 & 2 500 & 2 000 & 0.30 & 0.8 & 0.18 & 0.82 & 24 526.03 & 170.58 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Comparison of material parameters in the middle surface layer.  
Figure 1: Finite element model of pavement structure.  
Figure 2: Diagram of loading regions.  
The vertical stress, vertical strain, and vertical displacement at the upper surface layer were analyzed, as well as the shear stress and the shear strain at the middle surface layer. These measurements were taken underneath point B in Figure 2: that is, underneath the center of the leftmost tire of the vehicle. This data was compared to the conventional asphalt pavement. The dynamic response comparison results are shown in Figures 3-7.  
Figures 3-7 show the following results:  
Under the action of moving loads, the pattern variations of the five parameters were essentially the same between the two types of pavement. Compared to conventional asphalt pavement, the vertical stress and vertical shear stress in HMAC pavement were larger, while the vertical strain, vertical shear strain, and vertical displacement were smaller. This is consistent with the conclusion of reference [33; 34], which argued that the vertical stress of the upper surface layer of HMAC pavement is greater than that of conventional asphalt pavement.  
The difference in the mechanical properties of HMAC pavement compared to conventional asphalt pavement are summarized as follows: the maximum vertical stress increased 7.96% from 326.11 kPa to 352.07 kPa; the strain value decreased 24.5% from \(-\)25.02 \(\upmu\varepsilon\) to \(-\)18.89 \(\upmu\varepsilon\); and the vertical displacement decreased 18.8% from 0.16 mm to 0.13 mm. It can be seen that the HMAC pavement has good resistance to vertical deformation.  
Both the shear stress and the shear strain changed abruptly before and after the load passed the point of interest. Before the vehicle moved over the loading point, the maximum vertical shear stress of the middle surface layer compared to the conventional surface layer increased from 117.96 kPa to 132.51 kPa, while the vertical shear strain decreased from 45.81 \(\upmu\varepsilon\) to 30.80 \(\upmu\varepsilon\). These relationships show that HMAC can be used to reduce the strain deformation caused by shear stress and effectively prevent the shear damage of the pavement.  
Although the use of HMAC increased the stress in the surface layers, the strain decreased, which indicated that the rutting resistance ability of the asphalt pavement improved.  
Figure 3: Comparison of vertical stress in the upper surface layer.  
Figure 4: Comparison of vertical displacement in the upper surface layer.  
Figure 5: Comparison of vertical strain in the upper surface layer.  
Figure 6: Comparison of vertical shear stress in the middle surface layer.