The utilization rate of reclaimed asphalt pavement is significantly low in the sustainable design process of asphalt roads. Numerous researchers have extensively investigated the recycling and utilization of reclaimed asphalt pavements from various perspectives. Molecular dynamics simulations could elucidate the diffusion phenomenon occurring at the molecular scale between virgin and aged asphalt interfaces. This review provides a comprehensive summary of the simulation methods and applications of molecular dynamics simulation in the interface diffusion problem between virgin and aged asphalt. Diffusion theory and model testing methods are discussed. The review proposes the basic steps of molecular dynamics simulation and summarizes the molecular models with the corresponding parameter settings of virgin asphalt and aged asphalt. Moreover, the current influencing factors on the interfacial diffusion problem of virgin and aged asphalt are discussed. The paper explores the validation parameters including density, viscosity, radial distribution function (RDF), glass transition temperature, and solubility parameters based on the existing research. Molecular dynamics simulation could simulate interface diffusion at a micro-scale and clarify the diffusion depth and influence range of different asphalts. The purpose of the study of molecular dynamics is to solve interface issues and advance optimization of reclaimed materials.

To address the issue of inefficient interfacial diffusion between virgin asphalt and the aged asphalt in Reclaimed Asphalt Pavement (RAP), this study investigates how a rejuvenator improves the interfacial blending behavior and restores the functional properties of aged asphalt. Molecular dynamics (MD) simulations were employed to construct aged asphalt–rejuvenator models with varying rejuvenator contents and to establish a bilayer dynamic model of the virgin-aged asphalt–rejuvenator diffusion system. The kinetic characteristics of the diffusion process were analyzed based on system density and relative concentration profiles, while the mean square displacement (MSD) and diffusion coefficients were calculated to elucidate the diffusion mechanism. The accuracy of the MD simulation results was validated using Fourier Transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC), and the regulatory mechanism of the rejuvenator on the interfacial diffusion between virgin and aged asphalt was revealed at the microscopic scale. The results demonstrated that the addition of the rejuvenator effectively promotes the blending and diffusion at the virgin-aged asphalt interface. Specifically, a 6% rejuvenator significantly improved the diffusion efficiency at elevated temperatures, optimized system density toward virgin asphalt properties, and achieved the most uniform molecular distribution, thereby facilitating balanced intermolecular interactions. Meanwhile, the regenerant effectively restored the aromatic fraction content, reduced polar functional groups such as sulfoxide, and significantly lowered the glass transition temperature (Tg), thereby enhancing the low-temperature crack resistance and overall mechanical performance of RAP.

Cold recycled mixtures with asphalt emulsion (CRME) suffer the majority of damage from freezing and thawing cycles in seasonal freezing regions. However, an effective model for describing the internal damage evolution behavior of the CRME is still lacking. The objective of this study is to explore the performance of the destroy and damage model of the CRME subjected to freezing and thawing cycles with various water contents. The damage degree of performance at 60 °C and −10 °C, as well as the mechanical properties, were first analyzed in the laboratory. Then, the damage evolution models were established based on macroscopic properties, reliability, and damage theory. The results showed that the performance of the CRME decreased obviously as the number of freezing and thawing cycles increased; after 20 freezing and thawing cycles, the damage degree of 60 °C shear strength and 15 °C and −10 °C indirect tensile strength were 21.5%, 20.6%, and 19.8% at dry condition, but they were 34.9%, 31.8%, and 44.8% at half water saturation condition and 51.5%, 49.1%, and 56.1% at complete water saturation condition; the existence of water and the phase transition of water changed the failure characteristics of the CRME; the correlation coefficient of the damage model parameters was more than 0.98, so the damage evolution model could reveal the internal damage evolution law. Clearly, the freezing and thawing cycles accelerated the damage caused by CRME.