Viscoelastic Asphalt Pavement Simulations and Simplified Elastic Pavement Models Based on an Equivalent Asphalt Modulus Concept

Asphalt pavements exhibit viscoelastic behavior resulting in deflections, strains, and stresses varying with both temperature and traffic speed. For structural thickness design against fatigue cracking, the material response is typically assumed to be linear elastic to simplify the calculation of the critical horizontal strain at the bottom of the asphalt layer. An asphalt modulus representing the response of the materials under average conditions for both temperature and traffic speed is generally adopted in the simplified pavement model. This paper presents a method to determine an equivalent asphalt modulus (EAM) for the asphalt layer. The EAM, when used in the linear elastic analysis of a pavement, will result in a resilient response in terms of the critical strain criterion that is equivalent to the response of that structure when calculated using viscoelastic modeling. The methodology of this paper included a qualitative comparison of the EAM approach with published field results. Two thick asphalt pavement configurations representative of typical French pavement designs were considered in this paper. Results showed expected trends of the equivalent asphalt modulus with changes in traffic speed and temperature. The application of time-temperature superposition principle allowed building pseudo-master curves for the EAM dataset. The effect of different asphalt temperature and different traffic speed on the viscoelastic strains was qualitatively validated against the trends observed under full-scale testing.