NCAT Report 09-06 MECHANISTIC CHARACTERIZATION OF RESILIENT MODULI FOR UNBOUND PAVEMENT LAYER MATERIALS

" The contents of this report reflect the views of the authors who are solely responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official view and policies of the National Center for Asphalt Technology of Auburn University. This report does not constitute a standard, specification, or regulation. " Taylor and Timm i ACKNOWLEDGEMENTS On behalf of the entire NCAT Test Track team, the authors wish to thank the Alabama, Florida, Missouri and Oklahoma state departments of transportation for their support and cooperation in this study. The Federal Highway Administration was also an integral part of this study and deserves special recognition. Finally, special recognition is given to Burns, Cooley, Dennis, Inc., for providing the laboratory test results integral to this research. ABSTRACT In recent years, there has been an industry shift in pavement design methodology from purely empirically based methods (e.g. The AASHTO Guide for the Design of Pavement Structures) to design methods that combine both mechanistic and empirical elements (e.g. the new Mechanistic-Empirical Pavement Design Guide). One of the critical inputs for accurate mechanistic-empirical (ME) pavement design is accurate characterization of the stiffness of the unbound pavement material layers. This stiffness is quantified as resilient modulus, and this value can be determined either through laboratory testing with the triaxial apparatus or though non-destructive testing in the field with the falling weight deflectometer (FWD). Resilient modulus is typically expressed as a function of unbound material stress-state using a non-linear stress-sensitivity model. For this project, five unbound materials utilized in the construction of eleven instrumented pavement test sections at the NCAT Test Track were characterized through both triaxial and FWD testing. Additionally, multiple non-linear stress-sensitivity models were evaluated for both testing methods with each material to determine which model provided the best fit to the respective data sets. For the materials tested in the laboratory, stress-sensitivity models that account for both the effects of shear and confining pressure provided a better fit to the triaxial data than models that only accounted for the effects of only one of these variables. The same held true for base layer materials tested with the FWD at the Test Track. Generally, poor agreement was seen between the stress-sensitivity models and moduli generated by different methods for the base layer materials. Reasonable agreement between the data sets was seen for the subgrade material utilized at …