## 4 Results and Discussion
### Analysis of Factors Affecting the Interaction Capability Between Asphalt and Mineral Filler  
4.1 Influence of Mineral Filler Chemical Composition on the Interaction Capacity Between Asphalt and Mineral Filler  
To examine the effect of mineral filler chemical composition on the interaction capacity between asphalt and mineral filler, asphalt mastics prepared with three different types of mineral fillers, each exhibiting distinct chemical compositions, were evaluated using 90\(\mu\) base asphalt under identical experimental conditions of temperature and loading frequency. For analytical consistency, the chemical composition of the mineral fillers was characterized by their SiO\({}_{2}\) content. Mineral filler acidity/alkalinity is a chemical property, whereas the thickness of the adsorbed asphalt film in asphalt mastic is also affected by the specific surface area of the mineral filler. Therefore, to exclusively analyze the relationship between the interaction capability of asphalt and mineral filler and the acidity/alkalinity of the mineral filler, this study introduced a coefficient \(d_{\text{S}}\), defined as the adsorbed asphalt film thickness per unit of specific surface area. Based on the specific surface area and the fitted adsorbed asphalt film thickness of the three mineral fillers, the \(d_{\text{S}}\) values of the three types of asphalt mastics were determined. A higher \(d_{\text{S}}\) value indicates a stronger interaction capability between asphalt and mineral filler. The relative content of chemical components in the three mineral fillers was determined via XRD analysis. The diffraction peak patterns of the XRD results were integrated, and the relative content of each compound was calculated by dividing the sum of the peak areas corresponding to each compound by the total peak area. The relative content of each compound is shown in Table 6. Figure 11 illustrates the relationship between the \(d_{\text{S}}\) value of asphalt mastic and the SiO\({}_{2}\) content of mineral filler. Table 6 presents the relative chemical composition of the three mineral fillers. Among them, limestone filler has the lowest SiO\({}_{2}\) content and the highest CaO content (51.48%), being an alkaline compound. Coal gangue filler contains 19.01% CaO and a relatively high amount of Al\({}_{2}\)O\({}_{3}\) (25.93%)--another alkaline component. In contrast, fly ash has a lower content of alkaline compounds and primarily consists of acidic SiO\({}_{2}\). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Filler Type**} & \multicolumn{8}{c}{**Chemical Component (\%)**} \\ \cline{2-7}  & **SiO\({}_{2}\)** & **Al\({}_{2}\)O\({}_{3}\)** & **Fe\({}_{2}\)O\({}_{3}\)** & **MgO** & **CaO** & **Na\({}_{2}\)O** & **K\({}_{2}\)O** \\ \hline Limestone filler & 2.13 & 0.53 & 0.25 & 9.48 & 51.48 & 0.11 & 0.2 \\ Fly ash & 45.01 & 16.52 & 17.1 & 1.2 & 2.8 & 0.5 & 0.6 \\ Coal gangue filler & 35.42 & 25.93 & 2.39 & 1.22 & 19.01 & 0.86 & 0.21 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Relative content of chemical components in fillers. \begin{table}
\begin{tabular}{c} **Correlation** \\ **Coefficient R\({}^{2}\)** \\ \end{tabular} \\ \hline
28 & 0.163 & 0.888 & 0.138 & 0.897 & 0.187 & 0.989 \\
40 & 0.175 & 0.844 & 0.135 & 0.899 & 0.179 & 0.989 \\
52 & 0.183 & 0.826 & 0.145 & 0.924 & 0.173 & 0.977 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Fitting results and goodness of fit for adsorbed film thickness for different types of asphalt mastic. As shown in Figure 11, within the critical volume fraction range of mineral filler, the interaction capability between asphalt and mineral filler decreases with increasing SiO\({}_{2}\) content. This is because asphalt contains a significant amount of asphaltenes and anhydrides, while SiO\({}_{2}\), an acidic component in mineral filler, negatively impacts the adhesion between asphalt and mineral filler [41].