A critical component in mechanistic-empirical flexible pavement design isthe accurate determination of loading duration from which load frequency and asphalt modulus can be computed. There are several approaches to theoretically determine the loading duration as a function of asphalt temperature, vehicle speed and depth that rely on simplifying assumptions. The Mechanistic-Empirical Pavement Design Guide (MEPDG) offers one such approach. The objective of this research was to evaluate this approach in the context of physical measurements made on a full-scale test pavement at the National Center for Asphalt Technology (NCAT) Test Track. Measurements of strain duration were made at various depths for a range of vehicle speeds and pavement temperatures. Laboratory testing was also conducted to determine the HMA modulus of each lift in the test section, thereby enabling the computation of load durations as prescribed by the MEPDG. Comparisons were drawn between field measured strain durations and those computed following the MEPDG method. Load duration was found to be a log-normal function of depth and a power function of vehicle speed and pavement temperature. The MEPDG was found to over predict the measured strain pulse durations byapproximately 80%. Further investigation is warranted into the definition of load duration and frequency and their application in the MEPDG framework.
Abstract