ABSTRACT
The viscosity of a liquid is the property that retards flow, so when a force is applied to a liquid, the higher the viscosity, the slower will be its movement. The viscosity of bitumen is dependent upon both its chemical make-up and its structure. Rutting of bituminous pavements is the most common type of failure in the UK. It is therefore important to be able to predict the permanent deformation for a bituminous mixture, and this depends on the low stiffness response, that is the stiffness at long loading times and high temperatures, as well as the balance between the viscous and elastic components of the mixture’s deformation. The wheel tracking test can be considered to be a simulative test. Since viscosity changes with temperature, different bitumens may have the same hardness at 25°C but different hardnesses at other temperatures. It is the varying elasticity of bitumens which prevents correlation between these empirical tests.
