Effects of SARA fractions on the rheological properties and microscopic behavior of hard asphalt

The relationships between the chemical components of hard asphalt, the most commonly used in Enrobe<acute accent> a Module <acute accent>Eleve<acute accent> (EME) asphalt, and its macroscopic rheological properties remain unclear. Four chemical components: saturates, aromatics, resins, and asphaltenes (SARA), were extracted from the hard asphalt of the same source to prepare seven asphalt binder samples. The viscoelasticity, permanent deformation and fatigue performance of the binders were characterized by a dynamic shear rheometer (DSR), differential scanning calorimetry (DSC), atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopy to describe their microscopic behavior. The results showed that with increasing asphaltene and resin contents, the complex modulus increased rapidly, while the phase angle decreased, which improved the elastic recovery ability and resistance to permanent deformation of the asphalt. The stress sensitivity of the asphalt varied, declining initially and then increasing with decreasing content of aromatics and saturates. The fatigue life of the asphalt also exhibited a peak-and-trough pattern with increasing strain in the viscoelastic continuum damage (VECD) model. The correlational analysis revealed a good correlation between the fatigue life and stress sensitivity; when the strain was greater than 5 %, the correlation coefficient R2 was greater than 0.95. The roughness was correlated to the SARA content according to the AFM topographic images; the higher the asphaltene and resin contents were, the rougher the binder became. FTIR showed that IAr, IB and IB,a can represent the deformation vibrations of benzene ring C--C bonds and aliphatic chains, which may be related to the fatigue life. The gray relational analysis showed that saturates had the greatest effect on the rheological properties of the asphalt binders. This study reveals the effect and mechanisms of SARA on the rheological properties of hard asphalt binder, providing significant insights for improving the engineering performance of both hard asphalt and EME mixtures.