South Carolina’s First FDR Makes Royal Rehab
BY Wirtgen Group
The four-lane Highway 123 in Pickens County was the scene of the first full-depth reclamation (FDR) operation on the roads maintained by the South Carolina Department of Transportation (SCDOT). Up to 20,000 vehicles a day, 15 percent of which were trucks, had made structural rehabilitation of the 7-mile section of road unavoidable.
The construction project simultaneously widened the roadway to 14 feet, 5 inches.
“To this end, we initially milled off 2 feet along the inner edge of the roadway that borders the passing lane,” Mike Crenshaw said. He’s the president of King Asphalt Inc., Liberty, South Carolina, which served as the contractor for the project. Once King Asphalt had prepared the road, the cold recycling train, led by the W 380 CRi, could get rolling. The tracked cold recycler milled the damaged pavement at a width of 12 feet, 6 inches and a depth of 8 inches in a single pass. In the process, it simultaneously granulated the material while mixing in 2.3 percent foamed bitumen, 1 percent pre-spread cement and 3-4 percent water.
“In FDR, stabilizing the layers recycled with foamed bitumen gives the sub-base the structural strength it needs to withstand recurring loads over decades of use,” explained Mark Stahl, director of recycling products for the Wirtgen Group in North America.
The mix design plays a critical role in this process. This means determining the appropriate amount of biding agent to use. To do so, Wirtgen laboratory equipment—the WLB 10 S laboratory-scale foamed bitumen plant and the WLM 30 laboratory-scale mixer—was used to test six different material samples in advance.
At the end of the structural rehabilitation project, the W 380 CRi had recycled more than 100,000 tons of asphalt in an environmentally friendly and high-quality manner using the perfect formula. Crenshaw said he was delighted with the machine’s output of 420 U.S. tons of recycled material per hour: “It worked like a charm. I’ve never seen another machine that can even come close. More than 7 tons rolled over the discharge conveyor every minute.”
The W 380 CRi is also designed to rehabilitate road surfaces that exceed the available working widths of 10 feet, 6 inches; 11 feet, 6 inches; and 12 feet, 6 inches. In this case, the recycler scoops up the material on the side that was pre-milled by a cold milling machine and adds it to the mixing process. Thanks to a mixing capacity of 787 TPH in combination with rear loading onto a road paver with the appropriate buffer and paving screed, even very wide road surfaces can be rehabilitated in a single pass.