Assessment of Aging at FHWA's Pavement Testing Facility (05-0925)**
Ghazi G. Al-Khateeb, Jordan University of Science and Technology
Xicheng Qi, Federal Highway Administration
Aroon Shenoy, Federal Highway Administration
Kevin D. Stuart, Federal Highway Administration
Terry M. Mitchell, Federal Highway Administration

Field cores were taken in 1995 and 2002 from 8 asphalt pavements constructed in 1993 at the Federal Highway Administration’s pavement testing facility to evaluate the in-situ pavement aging. Dynamic mechanical properties of these cores were evaluated using the Superpave Shear Tester. The moduli of aged pavements were also predicted from binder, aggregate, and mixture properties using available prediction models, and the aging severity levels of all pavements were compared between the lab-measured and model-predicted. Eight pavements with two polymer-modified and six unmodified binders were evaluated in this study. Polymer-modified asphalt pavements showed comparatively lower aging than unmodified asphalt pavements. For unmodified asphalt pavements, stiffer asphalts tended to have higher aging indices. The binder aging index was found to be inversely proportional to the loading frequency, and differences between the aging indices for different binders were higher at lower frequency. Comparison between lab-measured and model-predicted binder aging indices showed a good agreement in ranking for all binders. Low stiffness binders, e.g., AC-5, showed higher aging indices than high stiffness binders, e.g., Styrelf. Pavement depth significantly impacted binder aging. The aging index near the surface (6.35 mm) was found to be about 4 to 5 times the aging index at a depth of 139.7 mm in pavement. Comparison between lab-measured and model-predicted mixture aging indices showed large variations, from over-predicted to well under-predicted, depending on the binder type and nominal maximum aggregate size.