Uniqueness of the Viscoelastic Time-Function for Asphalt-Aggregate Mixes

In general mechanical terms asphalt-aggregate mixes are both viscoelastic and
viscoplastic at service temperatures and loading conditions. The focus of this paper is on the viscoelastic component-response under small-strains. This research is part of an ongoing effort by the authors to develop a 3-D constitutive model for asphalt mixes. The paper presents laboratory tests consisting of creep and recovery cycles under uniaxial and isotropic stress conditions. Using a special load-transfer device and employing advanced triaxial testing procedures it was possible to obtain fast unloading after each creep period and insure true zero-stress during recovery times. These features enabled a reliable and straightforward isolation of the viscoelastic response from the total deformation. Analysis of the test data shows that one unique creep-compliance function may be used to describe the viscoelastic response of the material under multiaxial stress conditions. This finding will greatly simplify any future development and calibration of a 3-D material-model.