Novel approach to develop a performance based test for rutting of asphalt concrete

Asphalt concrete consists of compacted granular aggregates mixed with viscoelastic asphalt cement. The predictive phenomenological models had limited success in explaining the origin and propagation of pavement distresses like rutting and fatigue cracking. However, considerable movement and rotation of aggregates under repeated heavy traffic loads have been observed, but the effects of binding characteristics and overall behavior of asphalt concrete are not well understood. The current test methods to evaluate the suitability of asphalt concrete are not performance based, hence based on those test method asphalt concrete considered to be good may rut. This research describes the initial attempt to model the behavior of asphalt concrete under repeated loads using Discrete Element Method (DEM). The current use of DEM has been limited to modeling of dry contacts of particles and failure criterion is governed by Mohr-Coulomb type failure law. A microscopic model (TRUBAL), which is an example of the above models, is modified to incorporated the binder, asphalt cement. The rheological analog of viscoelastic asphalt cement is represented by a spring and a dashpot. Two sets of spring-dashpot combinations were placed in shear and normal directions, either before and after particles contact to simulate the shear and normal forces at different stages of contacts. A series of numerical simulations were conducted under different loading conditions to observe the stress-strain behavior and movement of particles. The results will then be compared with physical tests to select proper microscopic parameters and to determine the limitations for reliable predictions. In this paper simulation studies were performed to understand the behavior of actual pavements under real traffic conditions to observe the motion of particles and the stress-strain behavior. Then several different types of loads to different test specimens will be applied to mimic the observed particle motions and stress-strain behaviors to design a performance based test procedure for rutting.