Characterization of linear viscoelastic properties of asphalt concrete subjected to confining pressure

This paper presents a triaxial storage modulus master curve model and a continuous relaxation spectrum model for characterizing the linear viscoelastic (LVE) properties of asphalt concrete subjected to confining pressure. The triaxial master curve model relates the reduced storage modulus to the reduced frequency by performing both horizontal and vertical shifting on storage modulus test results. The horizontal shifting is used to characterize the time- and temperature-dependent behavior of asphalt concrete, while the vertical shifting is to characterize the pressure-dependent behavior. The vertical shift factor has the form of a sigmoidal function and varies with the reduced frequency and confining pressure. A relaxation spectrum model as well as a long-time equilibrium modulus model has been derived from the triaxial master curve model via integral transforms of basic LVE equations and complex algebra. The model predictions agree well with the laboratory test results of three asphalt mixtures indicating the proposed models can accurately characterize the LVE behavior of asphalt concrete under confinement.