Microstructural analysis of the constitutive behavior of asphalt concretes

Asphalt concretes are composite materials consisting of interspersed aggregates, asphalt binder and air voids. Their constitutive behavior depends largely on the interaction of the aggregates and the binder, which have drastically different stiffnesses. This behavior is further complicated by the non-linear viscoelastic behavior of the binder. The paper at hand presents a fundamental methodology for describing the constitutive behavior of asphalt concretes. It involves three main steps. The first step involves the development of mechanistic binder models from rheological measurements and their implementation into stress-strain relationships suitable for FEM modeling. Binder non-linearity is treated in a piece-wise linear fashion, whereby the binder model constants are assigned as a function of strain level. The second step involves capturing the microstructure of asphalt concretes through imaging techniques and processing the images to translate them into FEM grids. The third step involves verification of these asphalt concrete models by comparing predictions of shear modulus and phase angle to the properties measured in the laboratory using a Simple Shear Test (SST).