The Study of Factors Affecting the Shape and Duration of Vertical Stress Pulses in Asphalt Layers

Due to the Viscoelastic nature of Asphalt Mixes, the stiffness of these materials in new mechanistic – empirical methods is expressed by a dynamic modulus Master Curve, which is a function of temperature and loading rate. Therefore, for accurate determination of the dynamic modulus by the Master Curve, it is essential to accurately determine the frequency or duration of loading in addition to temperature. After determination of the dynamic modulus of the asphalt mix, the pavement structure may be analyzed using a quasi-static method and critical responses can be computed. Previous studies into the shape and duration of vertical stress pulses in asphalt layers do not show a good agreement for factors that may affect the vertical stress pulse. Therefore, the objective of this paper is the parametric study of factors that affect the vertical stress pulses at different depths in the asphalt layers. Factors that have been studied in this paper are resilient modulus of subgrade soil, resilient modulus of asphalt concrete, base layer modulus to asphalt layer modulus ratio, thickness of base layer, thickness of asphalt layer and type of moving axle. For this purpose, multilayer elastic theory has been employed to study the effect of each parameter on the shape and duration of the vertical stress pulse. The study shows that the most important factors that affect the shape and duration of vertical stress pulses in asphalt layers are asphalt layer thickness, base layer modulus to asphalt layer modulus ratio and depth of the desired point in the asphalt layer. In addition to these parameters, the thickness of the base layer and axle type can affect the vertical stress pulse slightly, and the effect of subgrade soil modulus can be neglected.