## 4 Results and Discussion  
### Contribution of Shear Strength and Tensile Strength to Aggregate-Bitumen Interface Bond Strength  
The load applied to the asphalt binder can be decomposed into tensile and shear loads. In order to study the bond strength of aggregate-bitumen interface under different load effects in the spring-thaw season, the aggregate-bitumen interface shear and tensile strength test for BA and NHSSMA were carried out in -20\(\sim\)20 \({}^{\circ}\)C based on the spring temperature. The tensile strength and shear strength of aggregate-bitumen interface for BA and NHSSMA at different temperature are given in Figure 7. It is can be seen from this figure that the aggregate-bitumen interface bond strength was greatly affected following the addition of modifier. From Figure 7, it was observed that addition of nano hydrophobic silane silica improved the shear strength of aggregate-bitumen interface at the temperature above -10 \({}^{\circ}\)C, and the increase range is 16.8%-47.1%. The reason for the improvement in shear strength values of nano hydrophobic silane silica modified binder sample is that nano hydrophobic silane silica contribute to the viscosity of asphalt. When the temperature is high, NHSSMA can exert the advantage of high-viscosity property. Therefore, the aggregate-bitumen interface shear strength of NHSSMA is higher than that of BA. However, the asphalt exhibits more elastic characteristics at low temperature. NHSSMA becomes more brittle, so the aggregate-bitumen interface shear strength of BA is slightly larger than that of NHSSMA at -20 \({}^{\circ}\)C. It also can be seen from Figure 7 that the aggregate-bitumen interface tensile strength of NHSSMA is slightly larger than that of BA when the temperature is above 0 \({}^{\circ}\)C.  
From Figure 7, it was also observed that the aggregate-bitumen interface tensile strength was significantly higher than shear strength when the temperature is above -10 \({}^{\circ}\)C, but the aggregate-bitumen interface tensile strength was lower than shear strength at -20 \({}^{\circ}\)C. Thus, it can be concluded that the aggregate-bitumen interface shear failure is more likely to occur in the pavement when the temperature is above -10 \({}^{\circ}\)C, and the aggregate-bitumen interface is prone to tensile failure when the temperature is below -15 \({}^{\circ}\)C. This conclusion is also consistent with the fact that the pavement is prone to rutting at high temperatures and cracking is likely to occur at low temperatures. Since the shear failure dominates the aggregate-bitumen interface bonding failure in the spring temperature range, the following study focused on the aggregate-bitumen interface shear failure. In addition, it is interesting to note that the tensile strength of BA and NHSSMA has a peak at -10 \({}^{\circ}\)C, which may be related to the glass transition temperature of the asphalt. The glass temperature of asphalt is between -10 and -20 \({}^{\circ}\)C. Asphalt will change from glassy state to a viscoelastic state with increasing temperature. When the test temperature is higher than the glass temperature of the asphalt, the asphalt exhibits stronger viscoelasticity, and the adhesion between the asphalt and aggregate increases, resulting in an increase in tensile strength. As the temperature continues to increase, the viscosity of the asphalt gradually decreases, and the tensile strength gradually decreases.