The new Mechanistic-Empirical Pavement Design Guide (M-E PDG) utilizes several performance models to predict dominant distress types (cracking and rutting) for flexible pavements. For each distress, a unique distress mechanism controls its initiation and accumulation over time. However, severalcauses can be attributed to each distress mechanism. Axle repetitions andloads are the main cause of all load-related distress types. The M-E PDG incorporates axle load spectra to characterize the unique axle loadings for a site. These loading characteristics are employed to calculate pavementresponse and for subsequent damage accumulations. Generally, these axle load distributions exhibit a bimodal shape and a mixture of two continuous distributions can be used to model them. In this paper, closed-form solutions are developed to estimate the characteristics of a mixture bimodal axle load distribution. The observed axle load spectra from fourteen sites indifferent states were used to relate load distribution characteristics with predicted flexible pavement performance. It is found that the overall mean and other characteristics of a bimodal axle load distribution explained the variations in expected flexible pavement performance. More precisely, cracking, surface rutting, and ride quality performance are related to the fourth root of the 4th moment of the axle load distributions. However, rutting in the HMA layer is found to be strongly associated to the overallmean while in the base and subbase layers, rutting is related to the 95thpercentile load of the axle load spectra. These finding imply that more cracking, rutting, and roughness growth in flexible pavements is mainly caused by the axle load distributions having heavier tails with infrequent extreme loads. In general, heavier loads seem to cause more cracking while higher number of load repetitions are more critical in developing more surface rutting in flexible pavements.
Samenvatting