Diffusion behavior of phase change materials at the interface of aged asphalt binder based on molecular dynamics simulation and experimental analysis

To investigate the diffusion behavior of phase change materials (PCMs) in differently aged asphalts during leakage and their impact on asphalt performance, this study focuses on three PCMs: paraffin, lauric acid, and tetradecanol. The diffusion coefficients of these materials at various temperatures were predicted using molecular dynamics (MD) simulations, and their practical implications were evaluated through diffusion experiments and rheological property analysis. The results indicated that the diffusion coefficients of PCMs increased progressively with rising temperatures. Additionally, at mixing temperatures (160 °C), PCMs diffused more rapidly in older asphalt. However, this trend reversed at medium and low temperatures. Furthermore, the proximity of the material layer to the PCMs correlated with higher concentrations of PCMs in the asphalt and a greater impact on its performance. Dynamic shear rheometer (DSR) tests revealed that PCM diffusion into asphalt reduced its resistance to high-temperature deformation while enhancing its resistance to low-temperature cracking. The impact of PCMs on the rheological properties of asphalt increased with the degree of aging. Lauric acid, due to its attraction to the strongly polar asphaltenes and resins in asphalt, exerted a more pronounced effect on the rheological properties of long-term aged asphalt. In contrast, paraffin, with its longer molecular chain, had the least impact. Although diffusion was a long-term and slow process, the high temperatures during asphalt mixing were sufficient to modify asphalt properties to a depth of 10 mm. Thus, preventing PCM leakage during the mixing process should have been prioritized.