# Effect of Aggregate Crystalline Surface Anisotropy on
## 3 Results and Discussion
### Adhesion of Asphalt with Aggregates
Additionally, the average value of the adhesion energy of the asphalt-CaCO\({}_{3}\) system is larger than that of the asphalt-SiO\({}_{2}\) system, suggesting that alkaline aggregates with calcite minerals as the main component have a stronger bond with asphalt than acidic aggregates with silica as the main component. This finding is consistent with previous experimental studies [36]. For the asphalt-SiO\({}_{2}\) system, the interaction energy and adhesion energy of the three interfacial models are ranked as (1 0 1) \(>\) (0 0 1) \(>\) (1 0 0), as shown in Figure 13. The interaction energy of the three models is dominated by van der Waals energy, while  
Figure 11: The interaction energy and adhesion energy of the asphalt–aggregate interface system. Figure 12: The interaction energy of the asphalt–aggregate interface system. electrostatic energy has a smaller effect. On all three surfaces, the van der Waals energy exceeds 80% of the total energy. The SiO\({}_{2}\) (1 0 1) surface has the highest interaction energy and adhesion work, being 22.5 kcal/mol and 20.78 mJ/m\({}^{2}\) greater than the smallest (1 0 0) surface, which represent increases of 13.00% and 25.68%, respectively. This implies that the (1 0 1) surface of SiO\({}_{2}\) has stronger bonding strength to asphalt than the other two commonly exposed surfaces. Complex surface characteristics such as the surface roughness and matrix porosity of minerals profoundly affect the adsorption behavior between minerals and adsorbates [37]. The different surface topological features of the three asphalt-SiO\({}_{2}\) systems led to varying bonding strengths in the three exposed surfaces. The high bonding strength of the SiO\({}_{2}\) (1 0 1) surface with asphalt can be attributed to the smaller gaps between neighboring silicon atoms and the higher density of the surface atoms, resulting in stronger van der Waals forces. In contrast, the quartz (0 0 1) and (1 0 0) surfaces had larger gaps between neighboring silicon atoms, resulting in relatively weaker van der Waals forces. For the asphalt-CaCO\({}_{3}\) system, the interaction energy and adhesion energy of the three interfacial models are ranked as (0 1 8) \(>\) (1 0 4) \(>\) (2 1 4), as shown in Figure 13. Unlike the asphalt-SiO\({}_{2}\) system, van der Waals and electrostatic energies significantly impact the interaction energy in all three models. The (0 1 8) surface of CaCO\({}_{3}\) has the highest interaction energy and adhesion work, with differences of 80.99 kcal/mol and 37.11 mJ/m\({}^{2}\) compared to the lowest (2 1 4) surface, whose values are 38.28% and 37.22% higher, respectively. This implies that the (0 1 8) surface of CaCO\({}_{3}\) has higher bonding strength with asphalt than the other two commonly exposed surfaces. Unlike the relatively stable covalent bonding of Si-O in SiO\({}_{2}\), the ionic bonding of CaCO\({}_{3}\) in calcite mineral crystals breaks when cut, causing the mineral surfaces to charge due to the breakage of ionic bonds. This directly affects the electrostatic attraction of the mineral surfaces to asphalt. The more ionic bonds that are broken, the stronger the electrostatic attraction of the mineral surface to asphalt. The (0 1 8) surface has the most broken ionic bonds and possesses the most suspended bonds, suggesting its higher bonding strength to asphalt.