## Materials
### Nano Hydrophobic Silane Silica  
Nanosilica is recognized as a modifier of asphalt for its superior stability, thixotropy, reinforcing, and thickening properties ([PERSON], China, 2018; [PERSON], China, 2018; [PERSON], China, 2018). [PERSON] et al. found that the antiaging property and rutting and fatigue cracking performance of nanosilica modified asphalt binders are enhanced, and the addition of nanosilica in the control asphalt asphalt mixture significantly improves the dynamic modulus, flow number, and rutting resistance of asphalt mixtures ([PERSON] et al., 2018). However, the presence of a large amount of hydroxyl groups on the surface of nanosilica particles causes the nanosilica to exhibit hydrophilicity, and the hydroxyl group of nanosilica has a high surface energy due to its strong polarity. Thus, the nanosilica particles are in a thermodynamic unstable state and are easily attracted to each other to form agglomerates, which makes it difficult to mix well in asphalt and asphalt mixture, leading to poor dispersion and compatibility with asphalt binder. In order to improve the compatibility of nanosilica in asphalt, the silane coupling agent was grafted onto the surface of nanosilica by chemical coupling to achieve surface modification of nanosilica. The surface modification method of nanosilica is detailed as follows: the X group in the silane coupling agent first undergoes hydrolysis by contacting with water, and then forms a temporary oligomer by dehydration condensation. The hydroxyl groups on the surface of nanosilica can react with the oligomeric structure to generate hydrogen bonds, then the nanosilica and the oligomer continue to undergo condensation and dehydration reaction by heating, drying, etc., and finally the silane coupling agent is successfully grafted onto the surface of the nanosilica by a covalent bond, as is shown in Figure 1.  
The nano hydrophobic silane silica (NHSS) is obtained by the surface modification of nanosilica by silane coupling agent, which can greatly improve the dispersibility of modified nanosilica in the organic polymer, so that the whole system has better stability, and the advantages of nanosilica and silane coupling agent can be fully utilized in the mixed system. NHSS was selected from Changtai Micro-Nano Chemical Co.,Ltd (Shouguang, Shandong, China) to be used in this study. The technical parameters of NHSS used in this study are summarized in Table 3. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Sieve (mm)** & **16** & **13.2** & **9.5** & **4.75** & **2.36** & **1.18** & **0.6** & **0.3** & **0.15** & **0.075** \\ \hline Apparent density & 2.78 & 2.78 & 2.78 & 2.74 & 2.74 & 2.75 & 2.70 & 2.70 & 2.69 & 2.67 \\ Bulk density & 2.77 & 2.76 & 2.75 & 2.68 & 2.64 & 2.59 & 2.60 & 2.59 & 2.57 & 2.55 \\ Gradation (\%) & 95 & 88 & 73 & 46 & 31 & 21.5 & 15.5 & 11.5 & 5.5 & 6 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Properties of aggregate and gradation of AC-16. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Technical** & \multicolumn{2}{c}{**Penetration**} & \multicolumn{2}{c}{**25 \({}^{\circ}\)C**} & \multicolumn{1}{c}{**Softening**} & \multicolumn{1}{c}{**Wax**} & \multicolumn{1}{c}{**Flash**} & \multicolumn{1}{c}{**Solubility**} & \multicolumn{1}{c}{**Density**} \\ \cline{2-9}
**Parameters** & **15 \({}^{\circ}\)C** & **25 \({}^{\circ}\)C** & **30 \({}^{\circ}\)C** & **Ductility** & **Point** & **Content** & **Point** & **Point** & **Solubility** & **Density** \\ \hline Units & & 0.1 mm & cm & \({}^{\circ}\)C & \({}^{\circ}\)C & \({}^{\circ}\)C & \({}^{\circ}\)C & \({}^{\circ}\)\(\geq\) & g\(\cdot\)cm\({}^{-3}\) \\ \hline Test results & 27.5 & 81.3 & 132.6 & \(>\)130 & 44.2 & 18 & 340 & 99. The microstructure of NHSS and nanosilica were examined by SU8000 electronic microscopy (Tianmei.co, Tokyo, Japan, 2008). The scanning electron micrographs of nanosilica and NHSS observed at magnifying power of \(\times\)10,000 are shown in Figure 2. (a and b).