Asphalt pavement aging and temperature dependent properties through a functionally graded viscoelastic model, Part-I: Development, implementation and verification

Asphalt concrete pavements are inherently graded viscoelastic structures. Oxidative aging of asphalt binder and temperature cycling due to climatic conditions are the major cause of such graded non-homogeneity. Current pavement analysis and simulation procedures either ignore or use a layered approach to account for non-homogeneities. For instance, the recently developed Mechanistic-Empirical Design Guide (MEPDG) [1], which was recently approved by the American Association of State Highway and Transportation Officials (AASHTO), employs a layered analysis approach to simulate the effects of material aging gradients through the depth of the pavement as a function of pavement age. In the current work, a graded viscoelastic model has been implemented within a numerical framework for the simulation of asphalt pavement responses under various loading conditions. A functionally graded generalized Maxwell model has been used in the development of a constitutive model for asphalt concrete to account for aging and temperature induced property gradients. The associated finite element implementation of the constitutive model incorporates the generalized iso-parametric formulation (GIF) proposed by Kim and Paulino [2], which leads to the graded viscoelastic elements proposed in this work. A solution, based on the correspondence principle, has been implemented in conjunction with the collocation method, which leads to an efficient inverse numerical transform procedure. This work is the first of a two-part paper and focuses on the development, implementation and verification of the aforementioned analysis approach for functionally graded viscoelastic systems. The follow-up paper focuses on the application of this approach.