Composite materials are mixtures of different components. In the case of asphalt, these components are bitumen, aggregates and air voids. Recent research advance is the modeling of nonlinear composite materials based on model parameters of the components.
For the modelling of asphalt as a composite material, the bitumen is regarded as the matrix and aggregates and air voids as the inclusions. The microscopic components of a composite material can have various different mechanical properties. Whereas it is possible to model each microscopic component separately by a constitutive law to describe its mechanical behaviour, this is not the case for the composite material, which cannot be described only by its single components but must also consider the interactions between them. With homogenisation techniques this problem can be overcome and it is possible to create a macroscopic uniform material, based on micromechanical theories.
The behaviour of the bitumen has a significant influence on the deformation and the time dependent performance of a pavement. The elasticity of bitumen is strongly temperature-dependent. At low temperatures, it becomes brittle with a very low tensile strength. During winter, this characteristic is the reason for crack propagation at the bottom side of a pavement. However, at high temperatures the bitumen has a very low viscosity. In summer, the formation of ruts and the bleeding of asphalt, the leaking of bitumen, are generated by high traffic loads. The temperature-dependence is strongly associated with the chemical compounds of the bitumen.
Example: Analysis of road pavement with surface courses made of AB 11 and SMA 11
During the course of a day, the deformations at the top side of the pavement are evolving dependent on the used material and the various temperatures.