Mechanistic-Based Approach to Evaluate Rutting Susceptibility of Hot-Mix Asphalt Mixtures by Use of Dynamic Triaxial Testing

Designing appropriate asphalt mixture type and properties is an important task that pavement engineers perform routinely. For many years, this key decision has been made by relying on empirical procedures that might not be representative of the specific project condition. Therefore, there is a need to develop an advanced yet simplified approach to assessing, on the basis of closely simulated field conditions, the rutting susceptibility of hot-mix asphalt (HMA) mixtures under a given set of traffic loads and environmental conditions. This paper presents a new mechanistic-based approach that evaluates asphalt mixtures by using the repeated load triaxial (RLT) test at field-representative testing conditions to determine the critical temperature of the HMA. An HMA mixture was considered appropriate for a specific project location when the determined critical temperature was greater than the effective asphalt pavement temperature for rutting determined by using the Mechanistic–Empirical Pavement Design Guide software. Predictive equations that accounted for the actual project characteristics, such as climate conditions, material characteristics, operational speed, and traffic loading, were developed to estimate the effective asphalt pavement temperature. Nine HMA mixtures were characterized and analyzed for rutting behavior. The critical temperature for each HMA mixture was obtained with RLT results and actual field performance. Flow number criteria as a function of traffic level were also developed. The proposed approach was validated by using three additional mixtures from Nevada and two mixtures from the WesTrack accelerated test facility. Good agreement between laboratory results and field performance was achieved and supports the appropriateness of the proposed approach.