Molecular simulation on compatibility and mechanisms of SBS and PTW polymer modifiers in asphalt binder.

Context: Ultrathin overlays are preventive maintenance measures; the tensile and shear stresses generated inside a structural layer under vehicle load are greater than those of conventional thickness asphalt pavement. Therefore, asphalt binders must use high-viscosity and elasticity unique cementing materials to ensure stability. To investigate the modification mechanism of styrene-butadiene-styrene (SBS)/ethylene-butyl acrylate-glycidyl methacrylate copolymer (PTW) high-viscosity modified asphalt binder suitable for ultrathin overlays, the compatibility and molecular behavior of SBS/PTW high-viscosity modified asphalt binder were analyzed by the molecular dynamics (MD) method. These research results provide a reference for preparing ultrathin overlay high-performance composite modified asphalt binder.

Methods: SBS molecular models, PTW molecular models, asphalt binder molecular models, SBS/asphalt binder blend systems, and SBS/PTW/asphalt binder blend systems were sequentially constructed using Materials Studio (MS) software. The compatibility of SBS, PTW, and SBS/PTW with asphalt binder and the diffusion coefficients of SBS, PTW, and SBS/PTW in the asphalt binder were investigated separately using the MD method. The mechanical properties and molecular behavior of SBS, PTW, and SBS/PTW blended with asphalt binder were studied. The research results indicate that the compatibility of PTW with asphalt binder is better than that of SBS with asphalt binder. PTW can effectively decrease the solubility parameter of asphalt binder and improve the compatibility between SBS and asphalt binder. PTW effectively improves the diffusion coefficient and interaction energy of SBS in asphalt binder by up to 29% and 83%. In addition, SBS/PTW had a significant positive effect on the mechanical properties of the asphalt binders, increasing the elastic modulus (E), bulk modulus (K), and shear modulus (G) of the asphalt binder by 4.6%, 9.5%, and 3.5%, respectively, compared to SBS. The results indicate that the SBS/PTW modified asphalt binder composite can significantly improve the high-temperature shear resistance of asphalt binder. Meanwhile, SBS and PTW improve the self-aggregation behavior between asphalt binder component molecules. The distance between the center of mass of asphalt binder and resin system molecules is increased. PTW enhances the extensibility of the branched chains of asphalt binder component molecules and improves the interaction between asphalt binder components and the chains. This further enhances the density and stability of the asphalt binder molecular structure system, improving the physical properties of the asphalt binder.