When wheel loads are applied on the pavement surface, both tension and compression are developed in the asphalt concrete layer. Laboratory tests were conducted on asphalt concrete specimens under different dynamic loading and temperature conditions. Largely different tensile and compressive moduli were obtained, especially at high temperatures.

A nonlinear finite element multi-layer program that can account for the bimodular nature of asphalt concrete (BIMODPAV) was developed. The program applies traffic loads in increments, checks the stress state at each element, and selects the appropriate modulus accordingly using the modulus values obtained from the lab tests. The BIMODPAV program was further used to analyze stresses, strains and displacements in typical pavement sections under different conditions. The results indicate that pavement response parameters calculated by the bimodular analysis are significantly different from those calculated by assuming a single modulus value. Using single-modulus analyses erroneously over-predict fatigue and rutting pavement lives as compared to those obtained from the bimodular analysis. The effect of bimodularity is most significant for pavements with a thick asphalt layer and/or at high temperatures. The mechanistic analysis technique developed in this study allows pavement to be designed in a more scientifically-based manner.