## 3 Results and Discussion
### Morphological Analysis
[23], the changes in the dispersity of the asphalt particles with the curing time were determined by calculating \(D_{n}\), \(D_{w}\), and \(PDI\) of the asphalt particles using the following equations:  
\[D_{n}=\frac{\sum n_{i}D_{i}}{\sum n_{i}} \tag{4}\]  
\[D_{w}=\frac{\sum n_{i}D_{i}^{2}}{\sum n_{i}D_{i}} \tag{5}\]  
\[PDI=\frac{D_{w}}{D_{n}} \tag{6}\]  
where \(n_{i}\) is the number of particles with a diameter \(D_{i}\). The values of \(D_{n}\), \(D_{w}\), and \(PDI\) of the asphalt particles for different curing times are given in Table 6. In the initial curing stage, \(D_{n}\) of the asphalt particles increased with the curing reaction time. After 12 h, \(D_{n}\) gradually decreased and stabilized at approximately 18 \(\upmu\)m. The \(PDI\) first increased and then decreased, indicating relatively low uniformity of the epoxy asphalt dispersion in the initial curing stage. The formation of the crosslinked network resulted in the gradual division of large asphalt particles into small particles, increasing the dispersion uniformity. Figure 7: Diameter distribution of asphalt particles for different curing times. The evolution of the microscopic structural characteristics of the 3D epoxy resin crosslinked network during the curing process was investigated by performing SEM on epoxy asphalt samples (after asphalt etching) with different curing times. Figure 8 shows the SEM images of the epoxy resin for different curing times (12 h, 24 h, 36 h, 48 h, 72 h, and 96 h) at 300x magnification. The etched epoxy asphalt contained many pores of various sizes, indicating that the asphalt was wrapped by the epoxy resin network and that the epoxy resin network was filled with asphalt. As shown in Figure 8a, the crosslinked epoxy asphalt network did not form before 12 h. The crosslinked network gradually formed after 24 h, as shown in Figure 8b. The remaining pores had irregular shapes. In the earlier LSCM images, the pores were approximately round, showing that the pore shape depends on the curing degree of the epoxy resin. At the early curing stage, the epoxy resin had a low degree of crosslinking and was relatively soft; the sample pores after etching were large and deformed into irregular shapes at room temperature during drying. After 36 h (when \(\alpha\) reached approximately 0.36), the crosslink density of epoxy resin continuously increased, the pores became smaller and denser, and the epoxy resin formed a relatively stable and compact 3D network skeleton (Figure 8c-f), in agreement with the LSCM images. These phenomena reflect that in the early curing stage, the initially epoxy resin network was weak and easily deformable. As the curing reaction proceeded, the continuous increase in the crosslink density of the epoxy resin strengthened the 3D network structure, while also lowering the ductility of the epoxy asphalt. These results are consistent with the continuous increase in the tensile strength and the decrease in the elongation at break of the epoxy asphalt with increasing curing time. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & \(D_{n}\) (\(\mu\)m) & \(D_{w}\) (\(\mu\)m) & _PDI_ \\ \hline
0.5 h & 14.5 & 19.6 & 1.35 \\
3 h & 15.9 & 21.8 & 1.37 \\
5 h & 19.2 & 27.0 & 1.40 \\
12 h & 19.5 & 33.2 & 1.70 \\
24 h & 18.0 & 29.1 & 1.62 \\
48 h & 17.5 & 26.6 & 1.52 \\
72 h & 18.1 & 20.8 & 1.15 \\
96 h & 18.0 & 20.7 & 1.15 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: \(D_{n}\), \(D_{w}\), and _PDI_ of asphalt particles for different curing times. Figure 8: SEM images of epoxy resin with different curing times (60 \({}^{\circ}\)C): (**a**) 12 h, (**b**) 24 h, (**c**) 36 h, (**d**) 48 h, (**e**) 72 h, and (**f**) 96 h.  
A microscopic morphology analysis showed that the epoxy asphalt curing process is dominated by the reaction of the epoxy resin oligomer. In this process, heterogeneous microgels are first generated in the system, then gradually form large gels (Figure 8a), and finally form a gel-like polymer (Figure 8b).