# Nano-Interaction Mechanism Between Crumb Rubber and Asphal Components: A Molecular Dynamic Study
## 1 Introduction  
With the rapid growth of vehicles in China, \"black pollution\" has occurred due to the increasing production of waste tires [1, 2]. How to effectively reuse these waste tires has become one of the essential issues in building a resource-saving and environmentally friendly society. In road engineering, crumb rubber (CR) modified asphalt (CRMA) can be prepared by grinding waste rubber tires into CR [3, 4, 5]. The addition of crumb rubber can improve the high-temperature, low-temperature, and fatigue performance of asphalt. At the same time, it can enhance the anti-skid performance and reduce the noise of the road surface. It has gradually been widely used in road engineering in recent years [6, 7, 8, 9, 10]. Asphalt, as a temperature-sensitive material, is greatly affected by the origin and preparation process. Its complex and variable composition makes it difficult to study the mechanism of rubber and other modifiers and their interaction. Traditionally, the investigation of the mechanism of rubber and asphalt is based on experimental methods. [PERSON] et al. [4] used physical, rheological, and fatigue properties tests to evaluate the performance enhancement effect of rubber powder on asphalt. [PERSON] et al. [11] enhanced the compatibility of CR by using physical and chemical surface-activation treatments. [PERSON] al. [2] evaluated the mechanism of the influence of the CR on the hydrophilicity of asphalt based on the surface energy theory. Through solvent elution and microscopic and microscopic tests, [PERSON] et al. [12] found that the action of CR with asphalt can be divided into three stages: solubilization, effective degradation, and excessive degradation. Other researchers [13; 14; 15; 16; 17] used infrared spectroscopy, gel chromatography, fluorescence microscopy, scanning electron microscopy, atomic force microscopy (AFM), and other micro-analysis techniques to explore the modification mechanism of rubber powder on asphalt systematically. However, regardless of the inverse mechanism of action analysis by asphalt performance testing or microanalytical methods based on functional group characterization, image testing, and other techniques, there are still significant limitations in the action mechanism of CR and asphalt [18; 19]. Molecular dynamics (MD), a simulation technique based on classical Newtonian mechanics, can analyze the research object action relationship and action process at the molecular and atomic level. This method can effectively compensate for the limitations of macroscopic test methods [20; 21; 22]. In recent years, MD has gradually been applied to asphalt modification research. For example, [PERSON] et al. [23] explored the effect of styrene-butadienestyrene triblock copolymer (SBS) structure on asphalt viscosity based on the MD method. It provided new insights for the optimization of SBS modification. [PERSON] et al. [24] analyzed the modification mechanism of polyphosphoric acid (PPA) on asphalt using the MD method. It revealed the change in the performance of PPA-modified asphalt. The above mechanism analysis provided an effective reference for the modification mechanism analysis of CRMA. There was also literature on the corresponding study of CRMA using MD. However, the relevant analysis did not involve the interaction between asphalt components and CR [13]. Also, the CRMA model used in existing studies varies significantly due to the differences in the source of CR and the preparation process. This led to unsystematic conclusions in different literature; some even had opposite conclusions [18]. Therefore, there is still a need for a systematic study of the interaction mechanism between CR and asphalt (especially the asphalt components). In this paper, base asphalt and CRMA models with different CR dosages will be constructed using MD simulation technology. Then, the validity of the model will be verified through multiple indicators.