Advanced constitutive modelling of bituminous materials by energetic approach: formulation, calibration and experimental evaluation

This report introduces a generalized constitutive model for the characterization of stress-strain behaviour in asphalts, with particular reference to the problem of the rutting in the bituminous pavements. With the introduction of the function of density of Helmholtz free energy, for the description of the energy status of visco-elasto-plastic material, and using the concept of “internal variables”, it has been possible to express a law of plastic flow in mechanically rigorous terms, which can reliably quantify the permanent deformations. The three-dimensional formulation of the constitutive relationship has been developed in such a way as to verify the universal dissipation principle, expressed by the Clausius-Duhem dissipative inequality, and bound to the thermodynamic constraints that the system has to satisfy. The model has been calibrated and validated on the basis of the deformation behaviour of a particular Mastic Asphalt mix, through a specifically developed experimental-numerical procedure, based on the static creep test, both in the unconfined and confined configuration.