LTPP Computed Parameter: Dynamic Modulus

1.0 INTRODUCTION

|E*| is a fundamental property that defines the stiffness characteristics of HMA mixtures as a function of loading rate and temperature. The significance of this material property is threefold. First, it is one of the primary material property inputs in the Mechanistic Empirical Pavement Design Guide (MEPDG) and software developed by NCHRP Project 1-37A.⁽²⁾ MEPDG uses a mastercurve and time-temperature (t-T) shift factors in its internal computations. The mastercurve is constructed using a hierarchical structure of inputs ranging from laboratory tests on HMA mixtures and binders to estimates based on properties of the HMA mixtures. Second, |E*| is one of the primary HMA properties measured in the Superior PERforming Asphalt PAVEment (Superpave™) simple performance TP that complements the volumetric mix design. Third, |E*| is one of the fundamental linear viscoelastic (LVE) material properties that can be used in advanced HMA and pavement models that are based on viscoelasticity.

Despite the demonstrated significance of |E*|, it is not included in the current LTPP materials tables because the database structure was established long before |E*| was identified as the main HMA property in the MEPDG. It is not practical to perform MEPDG level 1 laboratory |E*| tests on material samples from LTPP test sections at this time due to a lack of materials, budget limitations, and the absence of a suitable test method that is applicable to field samples obtained from relatively thin pavement structures. However, the LTPP database does contain other data that can be used to estimate the |E*| mastercurve and associated shift factors, estimate |E*| at specific load durations and temperatures, or develop inputs to the models contained in the MEPDG.

The primary objective of this project, as stated in the task order proposal request, was to “…develop estimates of the dynamic modulus of HMA layers on LTPP test sections following the models used in the MEPDG….” The team evaluated existing models used to estimate |E*| values and additional models that are developed based on the use of ANNs.