| In very cold climates, thermal cracking is the main distress that affects asphalt pavements. At these temperatures, asphalt materials become very stiff and reach stress values higher than their strength, and cracks form and propagate. Asphalt pavements are built with asphalt mixtures, which are composite materials that contain coarse and fine aggregates of specific sizes bound together with asphalt binder, a highly temperature susceptible viscoelastic material.;In past years, micromechanical composite material models were used to explain the relationship between asphalt binder and asphalt mixture stiffness properties. Asphalt mixtures were assumed as two-phase materials or as three-phase material. Due to low order microstructural information (volume fractions) used in these models, the asphalt mixture stiffness was significantly under predicted. Recently, a semi-empirical model called Hirsch model and a transformation based on mechanically analog models, called ENTPE (École Nationale des Travaux Publics de l'État) transformation, were successfully used to predict asphalt mixture creep stiffness from asphalt binders creep stiffness and vice-versa, at low temperatures. In this thesis, these two models are further investigated to understand the physical meaning of the models parameters and to establish a link between the microstructure of mixtures and these parameters. This will be accomplished by analyzing digital images of the mixtures to obtain extensive information on their aggregate structure and by performing extensive three point bending creep tests on asphalt mixtures and their component asphalt binders. It is expected these results will significantly improve the design of asphalt mixture with good thermal cracking resistance. |
