Numerical visco-elastoplastic constitutive modelization of creep recovery tests on hot mix asphalt

This paper presents and discusses a visco-elastoplastic constitutive model for the analysis of the creep deformability of asphalt concretes at high service temperature, finalized to improve the interpretation of the permanent deformation phenomenon and the performance design of the road pavements. A three dimensional constitutive visco-elastoplastic model has been introduced, in tensor as well as in numerical form. The associated uniaxial model has been obtained arranging a plastic element in series with a viscoelastic component, the latter defined by an elastic spring in parallel with three Maxwell elements. Three different hardening laws, namely isotropic, kinematic and mixed hardening, were considered in the constitutive model, in order to compare the different creep deformability. The proposed constitutive model has been calibrated and validated on the basis of uniaxial creep-recovery test results at 40°C, performed on a High Performance Hot Mix Asphalt concrete (HP-HMA), at different stress and loading times. The permanent deformation data predicted by the proposed model resulted reasonably consistent with the experimental creep-recovery data, depending on the hardening law considered. A rational constitutive model, physically congruent with the creep phenomenon of the asphalt concretes, has been developed and calibrated, in order to achieve a deeper understanding of the stress-strain response of such materials. It has been demonstrated the fundamental relevance of an appropriate modeling of the plastic response, in the study of the creep behavior of asphalt concretes for highway and road pavements.