The primary objective of this study is to develop estimates of the dynamic modulus of hot mix asphalt layers on Long-Term Pavement Performance (LTPP) test sections following the models used in the Mechanistic-Empirical Pavement Design Guide (MEPDG), for storage in the LTPP Pavement Performance Database. Other factors to be investigated include:

-What data elements, information, and computed parameters should be stored in a central location in the LTPP database to allow a user to either compute |E*| as a function of temperature and load duration following the MEPDG, compute |E*| at a set of reference conditions, or contain inputs a user would need to generate |E*| estimates using the MEPDG?

-Multiple estimates of the dynamic modulus master curve using different information sources. The hierarchical approach to estimating the dynamic modulus master curve can result in more than one estimate depending on the data sources used. Because LTPP data contains a mixture of data ranging from agency records to lab measurements it offers the opportunity to compare and contrast the results obtained from alternate estimation approaches for the same material.

-Aging effects. The MEPDG has models to address aging effects on the stiffness of the HMA mixture. On some sections LTPP laboratory measurement data related to estimation of the dynamic modulus are available that were obtained at different pavement ages. This allows investigation of mixture conditions at initial lay down to aged conditions using both estimation modeling and lab measured approaches.

-The LTPP pavement performance database does not include information on posted speed limits or measured speed of heavy trucks on LTPP test sections. The lack of this information will influence |E*| estimates and resulting use of this factor. Sites where vehicle speed data are available from sources external to the LTPP pavement performance database allow an evaluation of the sensitivity to the estimation process on the speed of heavy vehicle loads.

• DTFH61-02-D-00139

• Infrastructure

• FY 2002-2022 / Infrastructure / Long-Term Infrastructure Performance

• Long-Term Pavement Performance

The LTPP database was populated with |E*| values at five temperatures and six frequencies by using the prioritized artificial neural network models. More than 1,000 layers in the LTPP database now have |E*| estimate information available as a result of this study. These populated values will allow users of the LTPP database to develop a master curve for independent analysis or for input directly into the MEPDG. In addition, master curve sigmoidal parameters and temperature shift factors were computed and included in the population effort. These layers have binder data available at a combination of different aging conditions: unaged (original), rolling thin film oven aged, pressure aging vessel aged, or field aged. Additionally, user-friendly software was developed to facilitate dynamic modulus computations. The executable software can batch process data from a file to compute large quantities of dynamic modulus estimates in accordance with the model hierarchy. The program also has a feature that allows the user to manually input known parameters and select a model to use in computing dynamic modulus. The software can be obtained at no cost from the LTPP Customer Support Service Center at ltppinfo@dot.gov or at 202-493-3035.