## 4 Results and Discussion
### Establishment of Moisture Damage Model of Aggregate-Bitumen Interface Shear Strength  
The aggregate-bitumen interface bond strength plays an important role in the pavement performance of bituminous pavement. Generally speaking, the stone is more hydrophilic compared with asphalt. In the spring-thaw season, after the moisture penetrates into the aggregate-bitumen interface, the moisture tends to wet more stone surface, which causes the bond failure between stone and asphalt, forcing the asphalt film to peel off from the stone surface. In order to evaluate the influence of interfacial moisture content on aggregate-bitumen interface shear strength of NHSSMA, a research method combining numerical calculations and laboratory tests was proposed. First, the relation between aggregate-bitumen interface shear strength and immersion time was established through laboratory tests. Secondly, the relationship between immersion time and interfacial moisture content was determined by Abaqus finite element software. Finally, the relationship between the interfacial moisture content and aggregate-bitumen interface shear strength was established by the intermediate indicator of the immersion time. The laboratory test refers to the aggregate-bitumen interface bond strength test of Section 3, the test shear sample was immersed in water at 10 \({}^{\circ}\)C and the immersion height was half the thickness  
Figure 10: The 10 \({}^{\circ}\)C aggregate-bitumen interface shear strength of BA and NHSSMA at different immersion times. of the lower test mold, approximately 5 mm. After 4, 24, 48, 96, and 144 h of water immersion, the damaged test shear sample was collected for shear test immediately. When the test temperature of shear test was \(-10\)\({}^{\circ}\)C, the damaged test shear sample needed to be packaged with plastic wrap and placed in a temperature control box at \(-10\)\({}^{\circ}\)C for 2 h. The shear test was carried out after the temperature of the test shear sample was stabilized at \(-10\)\({}^{\circ}\)C. The test results are shown in Figure 11.  
It can be seen from Figure 11 that the short-dated immersion can greatly reduce the aggregate-bitumen interface shear strength. After 48 h of water immersion, the interfacial moisture content tends to be stable, the 10 \({}^{\circ}\)C aggregate-bitumen interface shear strength of modified and unmodified asphalt are reduced by 48.3% and 50.3%, and the \(-10\)\({}^{\circ}\)C aggregate-bitumen interface shear strength of modified and unmodified asphalt are reduced by 44.5% and 47%, respectively. Thereafter, as the immersion time increases, the aggregate-bitumen interface shear strength of modified and unmodified asphalt enters a stage of steady decline. When the immersion time reached 144 h, 10 \({}^{\circ}\)C aggregate-bitumen interface shear strength of BA and NHSA asphalt are reduced by 59.9% and 59.3%, and \(-10\)\({}^{\circ}\)C aggregate-bitumen interface shear strength of modified and unmodified asphalt is reduced by 59.7% and 61.6%, respectively. The 10 or \(-10\)\({}^{\circ}\)C aggregate-bitumen interface shear strength of nano hydrophobic silane silica modified asphalt is higher than that of base asphalt by nearly 80% at any immersion time, and the modification effect is remarkable. Through the above tests, the relationship between aggregate-bitumen interface shear strength of modified and unmodified asphalt and immersion time was obtained. In order to further explore the effect of interfacial moisture content on aggregate-bitumen interface shear strength, it is necessary to quantify interfacial moisture content. In this paper, the Mass Diffusion module of Abaqus finite element software was applied for interfacial moisture content calculation. Abaqus/Standard provides transient and steady-state models for calculating the diffusion of one material to another. The control equation used in the calculation was an extended form of Fick diffusion law, which can be used to calculate the diffusion of a non-uniform solubility material in the base material.