CAIT project no.: FHWA-NJ-2009-011
Fiscal Year: 2006/2007
Principal investigator(s): Thomas Bennert, Ph.D.
Performing organization(s): Rutgers CAIT (CAIT #199 RU6619)
Managing organization: Rutgers CAIT
In cooperation with: New Jersey Department of Transportation, Bureau of Research
Partner project manager: Nazhat Aboobaker, Ph.D.
Supported by: New Jersey Department of Transportation, Bureau of Research
Supported by: USDOT-FHWA
One of the most critical parameters needed for the upcoming Mechanistic Empirical Pavement Design Guide (MEPDG) is the dynamic modulus (E*), which will be used for flexible pavement design. The dynamic modulus represents the stiffness of the asphalt material when tested in a compressive-type, repeated load test. The dynamic modulus is one of the key parameters used to evaluate both rutting and fatigue cracking distresses in the MEPDG. The computer software that accompanies the MEPDG also provides general default parameters for the dynamic modulus (i.e. – Level 2 and 3 inputs). However, caution has already been issued by the National Cooperative Highway Research Program (NCHRP) researchers as to the appropriateness of these parameters for regional areas. The major concern is that state agencies will use these default values blindly and sacrifice accuracy of the design. Hence, making the new mechanistic procedure no better than using a structural number (SN) with the old AASHTO method.
There were three primary objectives of the research study. First, the current version of the dynamic modulus test, AASHTO TP62-07, was evaluated to determine the relative precision of the test method, and if required, recommend a modified procedure with better precision. The second objective of the study was to develop a dynamic modulus catalog for use with the Mechanistic Empirical Pavement Design Guide (MEPDG) by testing plant-produced and laboratory-compacted samples of various asphalt mixtures. This would supersede Level 2 inputs currently in the MEPDG for New Jersey. The third primary objective of the research study was to assess the accuracy of two commonly utilized dynamic modulus prediction equations; 1) Witczak Prediction Equation and 2) Hirsch Model. The database developed during the study also led to the development of correlations between dynamic modulus and fatigue cracking and rutting performance of asphalt mixtures.