ABSTRACT
The viscosity of a liquid is the property that retards flow so that when a force is applied to the liquid, the higher the viscosity, the slower will be the movement of the liquid. The viscosity of bitumen is dependent upon both its chemical make-up and its structure. To take account of the viscoelastic nature of bitumen, Van der Poel introduced the concept of stiffness modulus. Bitumens are thermoplastic materials so that they soften as the temperature rises but become hard again when the temperature falls. When a stress is applied to a bituminous material, both the aggregate particles and the bitumen will be subjected to the stress. Bituminous mixtures that utilise a continuously graded aggregate, such as asphalt concretes, rely mainly on aggregate particle interlock for their resistance to deformation. Thus, the grading and particle shape of the aggregate are major factors governing deformation.
