Properties of ethanol-based foamed asphalt binders using the molecular dynamics (MD) method

The molecular structure models of asphalt binder, ethanol additive, and ethanol-based foamed asphalt were constructed through the Molecular Dynamics (MD) method. The standard ethanol-based foamed asphalt model was employed to describe the modifier with its different compositions, including 10%, 20%, and 30% ethanol. The simulation calculations were done for the ethanol-based foamed asphalt molecular models under the NPT and NVT ensembles. The density, glass transition temperature, and radial distribution function of ethanol-based foamed asphalt molecular models were obtained to verify the rationalization of asphalt models and analyze the variation of density parameters with temperature and ethanol content for ethanol-based foamed asphalt molecular models. The results show that the simulated densities of the asphalt binder and three ethanol-based foamed asphalt molecular models remained constant with the increase of simulation steps. The simulated density values of basic and 10%-ethanol-based foamed asphalt molecular models are close to 0.9 g cm ^−3 . The simulated densities of 20%-ethanol-based and 30%-ethanol-based foamed asphalt molecular models were 0.8 g cm ^−3 and 0.75 g cm ^−3 . Meanwhile, the simulated density values of both asphalt binder and all ethanol-based foamed asphalt decreased with the increase in temperature and ethanol additive dosage. The glass transition temperatures of basic asphalt binder, 10%-ethanol-based, 20%-ethanol-based, and 30%-ethanol-based foamed asphalt occurred in the range of 275–295 K, 330–350 K, 330–350 K, and 320–340 K, respectively. In contrast, the glass transition temperature of ethanol-based foamed asphalt increased with the increase of ethanol additive dosage, indicating that adding ethanol additive significantly improved the high-temperature resistance of matrix asphalt. In the radial distribution function diagrams of all samples, the first strong peak appeared at 0.85–1.3 Å, and the second strong peak appeared at 1.95–2.35 Å. Moreover, both peaks increased with the increase of ethanol additive dosage, suggesting that the contact between ethanol molecules and asphalt molecules was closer with the rise of ethanol additive dosage.