Comparison of Dynamic and Steady Viscosity in High-Viscosity Modified Asphalt Binder and Analysis of Its Zero Shear Viscosity Test Methods

The purpose of this paper is to compare the dynamic viscosity and steady viscosity characteristics of high-viscosity modified asphalt binder (HVA) and to analyze the applicability of the Cox–Merz rule as well as of the different zero shear viscosity (ZSV) test methods for HVA. To this end, seven kinds of asphalt binders including base asphalt binder, traditional modified asphalt binder with 4.5% styrene-butadiene-styrene (SBS), commercial HVA, and four self-shearing HVAs were prepared. The frequency sweep test and shear rate sweep test were conducted to obtain dynamic viscosity and steady viscosity, and the Cross model, Carreau model, and Carreau–Yasuda model were used to calculate ZSV based on these two types of viscosity. The results show that both the dynamic and steady viscosity tests prove that asphalt binder exhibits shear-thinning and yield stress behavior. Besides, there is a critical shear rate in the shear rate sweep test and the critical shear rate decreases with the increase of modifier content. The empirical Cox–Merz rule has good applicability in the Newtonian plateau region of base asphalt binder, but it is only applicable to a partial shear-thinning range of modified asphalt binder. Noteworthily, it fails when applied to HVA-C. The frequency sweep test is only suitable for determining the ZSV of base asphalt binder but not applicable at all to the modified asphalt binder because there is no Newtonian plateau in the dynamic viscosity, and the fitting results based on model extrapolation have huge errors as well as vary with the number of iterations. However, the shear rate sweep test is suitable for testing ZSV for both base and modified asphalt binders. Furthermore, it should be pointed out that ZSV obtained by model fitting is not a steady viscosity at zero shear rate but a Newtonian viscosity at a low shear rate, so low shear viscosity (LSV) is a more accurate concept.