Evaluation of test methods for measurement of zero shear viscosity (ZSV) of asphalt binders

Zero shear viscosity (ZSV) is believed to be a good indicator of asphalt binder resistance to permanent deformation. It has widespread use in rutting characterization and is considered a good substitute for vacuum capillary viscosity. In the past many years, a number of test methods have been developed to measure the ZSV of asphalt binders. However, there is always a concern among researchers about reliable measurement of ZSV, especially of polymer modified asphalt binders. The objective of this study was to evaluate the applicability of three commonly used test methods, including the frequency sweep test, the shear rate sweep test, and the creep test, to different types of asphalt binders. A Discovery Hybrid Rheometer (DHR) was employed to perform the three tests on three neat asphalt binders and three SBS-modified asphalt binders with different performance grades at a temperature of 60 °C. After analyzing the test results, it was found that the ZSV of neat asphalt binders could be measured accurately and reliably using each of the three test methods. However, the shear rate sweep test was the only feasible approach to measure the ZSV of SBS-modified asphalt binders. The lack of viscosity plateau in the measured plot of complex viscosity versus angular frequency made it impossible to obtain a reliable prediction of ZSV from the frequency sweep test for SBS-modified asphalt binders. The creep test was not recommended for SBS-modified asphalt binders because it was difficult to ensure the shear viscosity was measured from the Newtonian plateau region. It can be concluded from this study that the selection of appropriate test methods depends on whether there is a viscosity plateau in the measured data.