## 3 Results and Discussion
### Quantitative Analysis of the Curing Process Using FTIR  
The curing of epoxy asphalt was analyzed by using FTIR spectroscopy to track the change in the characteristic peak (915 cm\({}^{-1}\)) of the epoxy group in epoxy asphalt at 60 \({}^{\circ}\)C with changes in the curing time [21]. FTIR tests were carried out on epoxy asphalt samples with different curing times. Figure 3 shows that the intensity of the epoxy group peak decreased as the curing time increased and stabilized after 69 h. The concentration of epoxy groups decreased as the curing time increased, reflecting the participation of the epoxy group in the curing reaction. Therefore, the curing process of epoxy asphalt can be quantitatively analyzed by tracking the change in the concentration of epoxy groups [20]. The two commonly used methods for FTIR quantitative analysis are peak height and peak area analyses. A vertical line is drawn between the peak vertex and the horizontal axis. The peak height is the distance between the vertex and the intersection of the vertical line and the baseline. The area  
Figure 3: Local FTIR spectra of epoxy asphalt. Figure 2: Comparison of the mechanical properties of fully cured epoxy asphalt and pure epoxy resin: (**a**) tensile strength and (**b**) elongation at break. enclosed by the curve of the absorbance peak and the baseline is the peak area. Peak area analysis was used in this study. To eliminate the influence of the coating thickness of the infrared samples on the absorbance peak area, an internal standard method was used to determine the variation in the concentration of characteristic groups with the curing time. The characteristic peak of a group that does not participate in the curing reaction (the benzene ring group at 830 cm\({}^{-1}\)) was selected as a reference peak. The ratio of the peak area of the epoxy group (915 cm\({}^{-1}\)) to that of the benzene ring group (830 cm\({}^{-1}\)), \(A_{915}\)/\(A_{830}\), was used to represent the variation in the epoxy group concentration [24]. FTIR was used to quantitatively analyze the epoxy group concentration at different curing times, and then the conversion rate of epoxy group with curing time was calculated based on the epoxy group concentration to indirectly evaluate the curing degree of epoxy asphalt. The conversion rate (\(\alpha\)) of the epoxy groups in the curing reaction was calculated as follows:  
\[\alpha=1-\frac{(A^{{}^{\prime}}{}_{915}/A^{{}^{\prime}}{}_{830})_{t}}{(A_{915 }/A_{830})_{0}} \tag{1}\]  
where \((A^{{}^{\prime}}{}_{915}/A^{{}^{\prime}}{}_{830})_{t}\) and \((A_{915}/A_{830})_{0}\) denote the aforementioned area ratio at curing times of \(t\) and before the start of the curing reaction, respectively. To accurately obtain the area of the absorbance peak of the chemical functional group, Peakfit (v4.12, Systat Software Inc, San Jose, CA, USA) was used in this study to fit the FTIR sample spectra [25]. The Peakfit software performed a baseline calibration on the selected wavenumber region and then initially fitted the approximate position and number of peaks based on the first derivative of each spectral line. Multiple fittings were achieved using Gaussian peaks. After the residual was minimized, the absorbance peak area of the subpeak was quantitatively obtained. The fitting results of the absorbance peaks are shown in Figure 4.  
The value of \(\alpha\) at each curing time was calculated using Equation (1). The curing reaction degree of epoxy asphalt, \(G_{\alpha}\), was defined as follows:  
\[G_{\alpha}=\frac{\alpha_{t}}{\alpha_{144}}\times 100\% \tag{2}\]  
where \(\alpha_{t}\) is the conversion rate of epoxy groups at a curing time t, and \(\alpha_{144}\) is the corresponding final stable conversion rate at a curing time of 144 h.  
The calculated \(\alpha\) and \(G_{\alpha}\) values are shown in Table 4. It can be seen that \(\alpha\) increased with time: at 69 h, \(\alpha\) reached 0.504, and the curing reaction degree exceeded 90%; \(\alpha\) eventually stabilized at 0.55.