South Dakota’s Department of Transportation has designed a flexible, high rock-content asphalt mix called Class S that’s well suited to the state’s heat and cold extremes. Class S eliminates rutting, extends surface life and provides skid resistance in winter driving conditions. The mix design includes a large volume of rock, and high polymer binder to bond the rock together. SDDOT Asphalt Mix Design Engineer Jim Costello says his department first used Class S about 25 years ago in the western part of South Dakota.
“Because of the high rock content of Class S, oil tends to drain right through the mix unless something is used to stop that drain down. In western South Dakota, we used limestone, which is plentiful in that part of the state,” Costello notes. “We began using Class S there in the late 1980s and early 90s. Rock in the mix is sized between ¾-inch and ¼-inch. The basis for the mix came out of Germany in the 1980s. They called it SMA, Stone Matrix Asphalt, which basically uses stone-on-stone content, which means the aggregate itself carries the traffic load.”
Because Class S was performing so well on high traffic areas in western South Dakota, SDDOT began considering how they could use it on high traffic roadways in the east where limestone wasn’t readily available. Eastern South Dakota quarries hold quartzite and granite, both high quality aggregates suitable for Class S. However, both quartzite and granite would require high binder contents and result in high drain down of the binder. In order to use quartzite and granite in the mix, SDDOT determined something was needed to prevent drain down from occurring.
“The resource we identified that was economic and effective is cellulose fiber,” Costello explains. “It’s like insulation you’d blow into your home. It’s recycled paper, grey in color. The fiber is blown into the drum while the mix heats. It’s been used in asphalt mix outside South Dakota for a number of years.”
The company who supplied cellulose fiber for the Highway 81 project was Hi-Tech Asphalt Solutions, based in Virginia. The cellulose fiber their company produces is made of recycled newspaper that’s ground and mixed with lime and other additives. Once ingredients are combined, the fiber is dried, baled and shipped to consumers.
Highway 81 project
SDDOT’s most recent project using Class S in eastern South Dakota was an overlay of 10 miles of US Highway 81 north of Yankton. The project, NH 0081(84)6, PCN 01BX Yankton County, began in June 2011 and was completed September 30, 2011. The project objective was to resurface the section of the roadway that was rutted, had faulted joints and areas of oxidation.
“Highway 81 was established in 1954 with a 4.5-inch gravel base and 8-inch concrete mesh PCC pavement,” Kevin Heiman, PE, Yankton Area DOT says. “In 1980, SDDOT completed a 1/2-inch Class D overlay in this same area, and in 1995, two lifts of recycled hot asphalt pavement were put down. The first lift was 2.5 inches; second was 1.5 inches. In 1996 the roadway was crack sealed. In 1997 a 3/8-inch asphalt treatment was laid. In 2003 a 3/8-inch asphalt surface treatment was applied.”
In preparing the roadway for the Class S overlay, 1.5-inches of the existing surface was cold milled. A total of 15,075 tons of Q3R in a 1.5-inch mat were laid under 8,075 tons of Class S 1.25-inch mat.
Commercial Asphalt, based in Mitchell, SD, used a Caterpillar AP1055 to lay both mats in the project. Two of their four rollers are Caterpillar CB64s, one is a Caterpillar CB634C and one a Caterpillar PS360C. Their haul trucks are all Freightliners pulling belly dumps. The asphalt plant they used is an Astec double barrel 400-tph system.
Neil Waldera, commercial asphalt division manager, says use of Class S was a new experience for their business, which is owned by Spencer Quarries Inc.