New unified viscoelastic constitutive equation for asphalt binders and asphalt aggregate mixtures

Constitutive equations for asphalt binders and mixtures are important for predicting pavement performance, characterizing their flow behaviors, and establishing databases. To choose a proper constitutive equation, material characteristics such as single-phase, multiphase, viscous, or viscoelastic fluid must be identified because each phenomena shows its unique equation. Past literature treated rheological behaviors of asphalt binders as a homogeneous single-phase fluid, and asphalt binders were classified differently from those of asphalt concrete mixtures. These generalizations are not always true. This paper presents a classification of material phases and definition of yield stress that are introduced for the first time on a scientific basis. In this classification, constitutive equations for certain modified asphalt binders holding yield stress can be identical to those of asphalt concrete mixtures, when both belong to multiphase fluids. Also, a unique constitutive equation for the linear viscoelastic fluids is proposed to illustrate differentiation from the one of viscous fluids. All constitutive equations suggested here are used in regression analysis of the measured data and their efficacy is proven in excellent curve fittings. Finally, temperature and aggregate concentration effects are added to propose the most versatile multiphase linear viscoelastic constitutive equation.