IntroductionThe Indiana Department of Transportation (INDOT) adopted the Superpave hot-mix asphalt (HMA) mixture design method and specifications during the 1990's and although long-term performance benefits were expected, long term data were not available. The INDOT therefore decided to participate in the full-scale test track experiment conducted at the National Center for Asphalt Technology (NCAT) in Alabama as a way to validate the Superpave design method and specifications. Additionally, INDOT was interested in establishing rutting performance relationships between the Accelerated Pavement Tester (APT), the Purdue Laboratory Wheel Tracker (PURWheel), and the NCAT test track (in-service) pavement sections.The objectives of the project were fulfilled using a coordinated effort between the INDOT, the Alabama Department of Transportation (ALDOT), and the Federal Highway Administration (FHWA). Ten HMA mixtures were placed on the NCAT test track that included three binder types (one neat (unmodified) and two modified), two gradations (fine-and coarse-graded), and two binder contents (optimum and optimum plus one-half percent). Ten million Equivalent Single Axle Loads (ESAL) were applied to these test sections over a twoyear period. In addition, eight of the ten track mixtures were duplicated in the APT using the same materials as used for the track mixtures. Slab specimens were cut from both the APT and the test track before the application of traffic and these were tested in the PURWheel.The volumetric properties of each of the ten mixtures was computed and statistically related to HMA rutting performance at the test track. Efforts to establish rutting performance relationships among the APT, PURWheel, and NCAT test track consisted of two approaches. The first directly related HMA mixture rutting performance from the PURWheel, APT, and test track. The second used finite element modeling to predict test track rutting based on PURWheel and APT test results. This latter approach first determined creep material parameters using APT and PURWheel data and used these as inputs into a finite element model of the NCAT test track. The track rutting predicted by this approach was then compared to the actual rutting experienced at the test track.
FindingsThe validation portion of the study found that the Superpave mixture design method and specifications provide well-performing HMA mixtures with respect to permanent deformation. As with all HMA projects, quality materials should be used and sound construction practices followed. Additionally, the data indicate that the use of modified binders can provide higher rutting resistance than neat binders and that modified binders allow for larger binder content variation without compromising rutting performance. Finally, the fine-graded Superpave mixtures used in this study show good performance under the heavy traffic applications at the test track.The direct rutting performance relationship between the APT and the PURWheel is very strong when the PURWheel specimens are taken dir...