Chapter 29: Mechanical models for simulating bitumen and asphalt behaviour

The objective of this chapter is to introduce some simple models that can be used to simulate the behaviour of bitumen and/or asphalt. Linear viscoelastic models are able to model deformation (both recoverable and irrecoverable). A linear spring and a linear dashpot are used to represent elastic (recoverable) and viscous (irrecoverable) behaviour respectively and a linear spring connected in parallel to a linear dashpot used to represent delayed (recoverable) elastic behaviour. The response to creep loading, where a load is suddenly applied and held constant, is investigated and a method is introduced to deal with more generalised loading. Linear Elastic Fracture Mechanics and the Paris law are introduced to model crack propagation from an initial crack or flaw. A simple laboratory test is discussed as a means for obtaining Paris law parameters and a simple method is developed for applying the results to crack propagation in a pavement structure. The first two approaches treat the asphalt as a continuum, whereas the third approach recognises its particulate nature. Discrete element modelling is used to simulate the behaviour of an asphalt at the scale of an aggregate particle. The method treats the asphalt as an agglomeration of particles bonded together. The bond stiffness is time dependent to give viscoelastic behaviour and bond breakage is allowed to simulate softening as the material is progressively damaged.