## 2 Materials
### Nano Hydrophobic Silane Silica  
Nanosilica is one of the nano-materials that have been extensively used in asphalt mixtures. However, nanosilica as a kind of inorganic non-metallic nanomaterial that is very prone to agglomeration. In addition, the asphalt binder is an organic cementitious material formed by high molecular hydrocarbons and non-metallic derivatives of these hydrocarbons, which makes nanosilica in asphalt binder have poor dispersibility and compatibility. In order to improve the dispersion of nanosilica in organic solvents and enhance their interaction with the medium, and to broaden the application field of nanosilica, the commonly used method is to physically or chemically react the surface of the nanosilica with the surface modifier through a certain process. The nano hydrophobic silane silica is obtained by grafting the silane coupling agent onto the surface of the nanosilica to carry out surface modification. The silane coupling agent has two groups with different properties, and the chemical formula is R-Si-X. X represents hydrolysable groups such as methoxy group (CH\({}_{3}\)O-) or ethoxy group (C\({}_{2}\)H\({}_{5}\)O-), which can be condensed with a hydroxyl group on the surface of nanosilica to form a siloxane bond and to be bonded to the R group. The R group can react strongly with different matrix resins or organic materials, such as vinyl, epoxy, sulfhydryl, amino, etc. [24; 25]. Nano hydrophobic silane silica remains amorphous and the crystal form does not change. The coupling agent grafts the organic group to the surface of the nanoparticle by chemical action, and the bonding ability is strong, and the modification effect more obvious. The nanosilica, after surface modification, have relatively uniform particle size and when the nanosilica changes from hydrophilic to hydrophobic, the oil absorption value of nanoparticles is increased, the agglomeration phenomenon between the nanoparticles is greatly improved, and the nanoparticles are more evenly dispersed in the organic system. The nano hydrophobic silane silica material was obtained from Changtai Weina Chemical Co., Ltd. (Shouguang, Shandong province, China). The technical properties of nano hydrophobic silane silica material have been presented in Table 2.  
The microstructure of nanosilica and NHSS were examined by SU8000 electronic microscopy (Tianmei.co, in Japan). The scanning electron micrographs of nanosilica and NHSS observed at magnifying power of \(\times\)1000, \(\times\)10,000 and \(\times\)100,000, which are shown in Figures 2-4. (a and b). \begin{table}
\begin{tabular}{c c c c c c} \hline
**Technical** & **Water** & **BET (m\({}^{2}\)/g)** & **Loss on Drying** & **Average Particle** & **pH Value** & **SiO\({}_{2}\)** \\
**Parameters** & **Characteristics** & **(105 °C, 2 h, wt\%)** & **Size (nm)** & **PHV Value** & **Content (\%)** \\ \hline Test results & Hydrophilia & 125 ± 20 & \(\leq\)0.5 & 12 & 5.0-8.0 & \(\geq\)99.8 \\ Standard values & — & 130 ± 30 & \(\leq\)3.0 & \(\leq\)20 & 3.7-6.5 & \(\geq\)99.8 \\ \hline \end{tabular}
\end{table} 
Table 2: Technical parameters of nano hydrophobic silane silica. Figure 2: SEM images of nanosilica and nano hydrophobic silane silica (NHSS) at magnifications of \(\times\)1000. (**a**) nanosilica; (**b**) NHSS. The shape of nanosilica and NHSS is evident from Figure 4, and the difference between nanosilica and NHSS is more obvious. From the physical structural characteristics, the NHSS particle can better connect to asphalt. From the chemical linking characteristics, the surface modified nanosilica can form a stable chemical bond with asphalt at the interface to enhance the overall strength and toughness of the modified asphalt system. After obtaining SEM images with different magnifications, the distribution of particle size of nanosilica and NHSS was statistically analyzed using Nano Measurer 1.2 software. The statistical results are shown in Figure 5.  
The diameters of 200 particles in the nanosilica and NHSS SEM images were randomly counted.