Viscoelastic behaviour of bitumen

The knowledge of the viscoelastic behaviour and in general the mechanical behaviour of bitumen is of significant importance to the engineer. 

In the first element, the strain (e ) is analogous to the applied stress (o), is related to the elastic modulus ( ) of the spring and is always recoverable. The stress/strain relationship that exists is o = x e. This is a Newtonian behaviour and Hooke s law is applied. 

0 = stress, E = strain, t = loading time, = viscous (permanent) deformation 

When unloading (oi = 0), the elastic deformation is instantly recovered, while deformation that is attributed to the viscoelastic behaviour of bitumen is recovered slowly. After a period of 

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Many researchers have attempted to display the viscoelastic behaviour of bitumen with mathematical equations. The equations developed were based on the combination of two mechanical elements that represent the elastic and viscous behaviour. These elements are the spring and the dashpot (see Figure 4.15a and b, respectively). 

The second model (Figure 4.15d) describes the complicated viscoelastic behaviour of bitumen. Upon application of stress, the model immediately presents elastic deformation and continues to deform at a non-linear rate. Thus, for a given temperature, if a constant stress (oi) is applied, the strain (e) after time (t) could be calculated using the Burgers model by the following equation ... 

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