1. Research Assistant Professor, Center for Earthworks Engineering Research, Dept. of Civil Construction and Environmental Engineering, 2711 South Loop Dr., Suite 4700, Iowa State Univ. of Science and Technology, Ames, IA 50010-8664 (corresponding author).
2. Associate Professor and holder of Richard L. Handy Professorship, Director of Earthworks Engineering Research Center, Dept. of Civil Construction and Environmental Engineering, Iowa State Univ. of Science and Technology, 422 Town Engineering, Ames, IA 50011-3232.
3. State Bituminous Engineer, Iowa Dept. of Transportation, Office of Materials, 800 Lincoln Way, Ames, IA 50010.