Linear Visco-Elasticity of Asphalt in Terms of Proportion and Polarity of Sara Fractions

Abstract

Understanding the relationships between rheological properties and asphalt chemical compositions has long been interest of researchers. This paper explored the qualitative and quantitative correlation between linear viscoelasticity and asphalt chemistry in terms of proportion and polarity of the SARA (Saturates, Aromatics, Resins and Asphaltenes). A semi-quantitative evaluation on the polarity of SARA fractions was performed by identifying absorbance areas of notable functional groups, and new asphalt polarity indices were proposed on this basis. Sufficient SARA were collected to obtain the derived asphalt binders, and the 2S2P1D and Burgers models were used to describe dynamic and static viscoelasticity, respectively. The results showed that the polarity of the SARA fractions decreased in the order of asphaltenes, resins, aromatics, and saturates. Polarity played a dominant role in determining the linear viscoelasticity of asphalt. The effect of SARA fraction on linear viscoelasticity could be summarized that saturates and aromatics played a viscous role, while the asphaltenes significantly improved asphalt elasticity. The increase in the dispersion phases (saturates and aromatics) in the colloidal asphalt structure not only increases viscosity, but also decreases elasticity. The resins had viscoelasticity similar to asphalt, and certain decreasing in dynamic and static performance occurred as the resin content was increased to further disperse the asphaltenes. Statistically, the proposed asphalt polarity index (API) showed a higher correlation with viscoelasticity than [[EQUATION]] and [[EQUATION]] indices related to colloidal stability. The gained knowledge and proposed polarity indices will be of great benefit for further modeling of the linear viscoelasticity of asphalt.

Keywords: Asphalt chemistry, SARA fraction, polarity, linear viscoelasticity, creep compliance, 2S2P1D model