# Anti-Aging Performance and Action Mechanism of Asphalt Modified by Composite Modification
## 3 Results and Discussion
### Verification of asphalt model  
Density Verification  
At a temperature of 298 K, the NPT ensemble was selected for a 100 ps dynamic optimization, and the simulated asphalt density over time is shown in Figure 25. After the simulation, the density of the asphalt system was 0.986 g/cm\({}^{3}\), while the actual density of the asphalt material at 298 K was about 1.000 g/cm\({}^{3}\). The difference between the simulated density value and the experimental density value was controlled within 5%, indicating that the constructed matrix asphalt molecular model is applicable. Figure 23: Temperature and energy variations simulated under the NVT tether. Figure 24: Temperature and energy variations simulated under the NPT system combination. Figure 25: Variation in modeled density of asphalt. Glass Transition Temperature Verification  
Tg represents the temperature at which asphalt transitions from a high-elastic state to a glassy state. To predict the glass transition temperature, the relationship between specific volume and temperature is used. First, ten temperature points were selected: 130 K, 160 K, 190 K, 220 K, 250 K, 280 K, 310 K, 340 K, 370 K, and 400 K. The density of asphalt molecules at these temperatures was measured and used to calculate the specific volume at each temperature, as shown in Table 5. Linear fitting was performed for the data from the first five and the last five temperature points. The intersection of these two fitting lines represents Tg, which was found to be 256.7 K. This value is consistent with the range reported in existing literature (232 K-264.4 K) [26], indicating that the model is reliable. (5)  
Anti-aging agent model  
The UV-928 ultraviolet absorber has the molecular formula C\({}_{29}\)H\({}_{35}\)N\({}_{3}\)O. The model of the UV-928 ultraviolet absorber, constructed using the Visualizer module, is shown in Figure 3a. Hydrotalcite features a unique layered structure with the general formula \([M_{1}^{2+}x_{x}^{M}x_{x}^{+}(OH)_{2}](A^{n}\ \ )_{x/n}mH_{2}O\). The model of hydrotalcite is depicted in Figure 26. In Figure 26, white spheres represent hydrogen (H) atoms, gray spheres represent carbon (C) atoms, red spheres represent oxygen (O) atoms, blue spheres represent nitrogen (N) atoms, pink spheres represent aluminum (Al) atoms, and green spheres represent magnesium (Mg) atoms. (6)  
Anti-aging modified asphalt model  
Based on the previously established models for asphalt, UV absorbent, and layered double hydroxides (LDHs), models for UV absorbent-modified asphalt, LDH-modified asphalt, and UV absorbent-LDH composite-modified asphalt were developed. These models were analyzed from the perspective of molecular dynamics to study the properties  
Figure 26: Modifier molecular model. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Temperature (K)** & **Specific Volume (cm\({}^{3}\)/g)** & **Fit Curve** & **Intersection (K)** \\ \hline
130 & 0.9775 & & \\
160 & 0.9872 & y = 0.0002\(\times\) + 0.9509 & \\
190 & 0.9921 & R\({}^{2}\) = 0.9855 & \\
220 & 0.9990 & & \\
250 & 1.0040 & & \\
280 & 1.0132 & & 256.7 \\
310 & 1.0225 & y = 0.0006\(\times\) + 0.8482 & \\
340 & 1.0331 & R\({}^{2}\) = 0.9143 & \\
370 & 1.0493 & & \\
400 & 1.0846 & & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Specific volume of asphalt molecules at different temperatures. of the three types of asphalt and to compare and analyze the aging resistance of the composite-modified asphalt. The models for the modified asphalt are shown in Figure 27. In Figure 27, white spheres represent hydrogen (H) atoms, gray spheres represent carbon (C) atoms, red spheres represent oxygen (O) atoms, blue spheres represent nitrogen (N) atoms, pink spheres represent aluminum (Al) atoms, and green spheres represent magnesium (Mg) atoms. From the above analysis, it is concluded that the UV absorber has better compatibility with base asphalt compared to hydrotalcite. Therefore, it is preliminarily determined that the combination of UV absorber and hydrotalcite can improve the compatibility between hydrotalcite and asphalt.