# Effect of Aggregate Crystalline Surface Anisotropy on
## 1 Introduction  
By the end of 2023, the total mileage of highways in China was recorded at 5,436,800 km, with 183,600 km of expressways, predominantly paved with asphalt. Asphalt mixtures, consisting of asphalt, aggregates, and mineral powders, are extensively used in road engineering [1]. Over time, fatigue cracking, rutting, water damage, and other defects are observed in asphalt pavements due to traffic loads and environmental factors. The interfacial properties of asphalt mixtures, comprising both asphalt and aggregates, are significantly influenced [2]. The adhesive properties between asphalt and aggregates are crucial in determining the performance of asphalt mixtures, affecting their structural strength, durability, and water stability. It is a recognized fact that alkaline aggregates adhere better to asphalt than acidic aggregates. The local separation of asphalt from aggregate surfaces under loads and water can be caused by poor adhesion, whereas strong adhesion can prevent early pavement defects, such as loosening, spalling, cracking, and potholes. Various factors, including the anisotropy of the aggregate crystalline surface, are known to influence the adhesion performance of asphalt mixtures [3, 4]. Therefore, the asphalt-aggregate interfacial mechanism and influencing factors must be studied in depth to improve the mixture performance. Studies on asphalt-aggregate interfacial interactions have largely focused on experimental methods. [PERSON] et al. [5] employed PeakForce Quantitative Nanomechanics andatomic force microscopy (PFQN-AFM) to characterize the nanostructure of the asphalt-aggregate interface, discovering that the adhesion at some interface regions was lower than in surrounding areas. [PERSON] et al. [6] investigated the shear damage characteristics of the asphalt-aggregate interface under various conditions using shear tests. Their findings indicated that increased surface roughness and loading rates produced higher interface shear strength. [PERSON] et al. [7] studied the effect of the asphalt film thickness on the shear mechanical properties of asphalt-aggregate interfaces through controlled shear tests, concluding that the film thickness was a key factor in the shear damage behavior. [PERSON] et al. [8] examined the effects of organic additives (Sasobit and RH) and water on adhesion at the asphalt-aggregate interface, finding that, while organic additives enhanced the adhesion under dry conditions, they significantly decreased the adhesion under wet conditions. To investigate asphalt-aggregate interfacial interactions at a microscopic level, molecular dynamics (MD) simulations provide an effective approach. [PERSON] et al. [9] found that silane coupling agent (SCA) modification enhanced the adhesion between asphalt and aggregates. [PERSON] et al. [10] studied the effect of water on the adhesion strength at the asphalt-aggregate interface using MD. [PERSON] et al. [11] determined that the adhesion and debonding behaviors depend on the chemical and mineralogical properties of the minerals. [PERSON] et al. [12] found that an asphalt anti-stripping agent (BHET) improved the cohesion and adhesion properties of asphalt mixtures. However, crystalline surface anisotropy leads to variations in properties like the modulus of elasticity, cracking strength, and surface physicochemical characteristics. Determining the crystal orientation and exposed surfaces remains a challenge in nanomaterials science. [PERSON] et al. [13] showed that polarized and unpolarized Raman spectroscopy can effectively determine the crystalline plane orientations and can be applied within the spatial limits of laser diffraction. [PERSON] et al. [14] used X-ray diffraction (XRD) to observe the mesoporous crystallographic planes and ordered structure of silicon dioxide. Most studies do not account for the crystallographic orientation of aggregates, with few providing detailed reasons. [PERSON] et al.