By: Prithvi S. (Ken) Kandhal, P.E.
Improving the quality of pavement performance Improving the quality of pavement performance
The National Center for Asphalt Technology (NCAT) has begun the construction of a 1.7-mile oval test track facility near the campus of Auburn University. Work on subgrade, subbase, permeable asphalt base and dense-graded hot-mix asphalt (HMA) base course has been completed. Test sections consisting of 50 mm HMA binder and wearing course are under construction.
Experimental sections on the test track are cooperatively funded by external sponsors, most commonly state DOT’s, with subsequent operation and research managed by NCAT. Forty-six different HMA test sections are being installed at the facility, each at a length of 200 ft. Materials and methods unique to section sponsors are imported during construction to maximize the applicability of results. After construction is completed in the spring, a design lifetime of truck traffic (10 million standard axle loads) will be applied over a two-year period of time. An array of surface parameters (smoothness, rutting, cracking) will be monitored regularly as truck traffic accumulates to facilitate objective performance analyses.
Besides the Federal Highway Administration, highway agencies from the following states are sponsoring test sections: Alabama, Florida, Georgia, Indiana, Mississippi, North Carolina, South Carolina and Tennessee. The proposed, specific HMA mix attributes whose performance will be compared on the test track are:
- Coarse-graded, fine-graded, and through the restricted zone gradation of Superpave mixes; neat versus modified asphalt binder at optimum content and optimum plus 0.5%;
- Stone-matrix asphalt (SMA) versus Superpave mix using granite aggregate;
- Gravel SMA versus Superpave gravel mix versus Superpave gravel/limestone blend mix;
- Gravel SMA versus Superpave gravel mix versus Superpave limestone mix;
- Fine-graded versus coarse-graded Superpave mixes (both containing limestone aggregate);
- 12.5 mm versus 9.5 mm Superpave mixes (both fine-graded and containing granite aggregate); and
- Coarse-graded versus fine-graded Superpave mixes (both containing granite aggregate).
Some other issues we expect covered based on the performance of various test sections include the meaningfulness of Superpave restricted zone for graduation, the cost effectiveness of modified asphalt binders and the worth of more expensive SMAs.
About The Author: Kandhal is the Associate Director at the National Center for Asphalt Technology at Auburn University. You may write him in care of the editor.
