When wheel loads are applied on the pavement surface, bothtension and compression are developed in the asphalt concretelayer. Laboratory tests were conducted on asphalt concrete specimensunder different dynamic loading and temperature conditions. Largelydifferent tensile and compressive moduli were obtained, especiallyat high temperatures.

A nonlinear finite element multi-layer program that can accountfor the bimodular nature of asphalt concrete (BIMODPAV) was developed.The program applies traffic loads in increments, checks the stressstate at each element, and selects the appropriate modulus accordinglyusing the modulus values obtained from the lab tests. The BIMODPAVprogram was further used to analyze stresses, strains and displacementsin typical pavement sections under different conditions. The resultsindicate that pavement response parameters calculated by the bimodularanalysis are significantly different from those calculated byassuming a single modulus value. Using single-modulus analyseserroneously over-predict fatigue and rutting pavement lives ascompared to those obtained from the bimodular analysis. The effectof bimodularity is most significant for pavements with a thickasphalt layer and/or at high temperatures. The mechanistic analysistechnique developed in this study allows pavement to be designedin a more scientifically-based manner.