Viscoelastic Analysis of Diametral Compression of Asphalt Concrete

The diametral compression of short cylinders is generally accepted as the convenient and accurate test method for evaluating the mechanical properties of asphalt concrete mixtures. In particular, the test serves to determine the relation between the stresses and strains, with the assumption that it can be quantified by the elastic (resilient) modulus and Poisson's ratio. These parameters are used for both the asphalt concrete quality assessment and in elastic multilayer analytic or numerical predictions of pavement deflections. The elasticity-based test analysis used in practice accounts for viscous effects that asphalt concrete displays at moderate and elevated temperatures in a simplified fashion. The methodology presented in this paper incorporates the effect of viscosity in a rigorous manner, by deriving a linear viscoelasticity-based solution. The solution makes use of the elastic-viscoelastic correspondence principle and Laplace and Fourier transforms; it is valid for any load history. Specifically, expressions are derived, which relate the deformation of the cylinder and asphalt concrete viscoelastic properties, e.g., creep compliance, complex modulus, phase angle, and so on. Such properties are required for use with analytical or numerical viscoelastic models used for calculating stresses, strains, and displacements in a pavement system (e.g., in modeling rutting). The solution is illustrated with results of tests at room temperature carried out on one asphalt concrete mixture subjected to constant and pulse/rest load histories. A reasonable level of qualitative and quantitative agreement between the predictions and experiments was obtained.