September 27th, 2011
PMOSA MIX DESIGNPreserve Infrastructure, by Catherine Higgins.
A Utah product could be the answer to more durable asphalt roads.
Three thirty year old roads in Utah are aging remarkably well. While other asphalt roads in the area have been rebuilt, Randlett Road, the Bonanza Highway and SR-121, between Maeser to Lapoint near Vernal, Utah, show minimal wear and very few ruts and cracks compared to other roads that carry similar loads. What’s the difference? Pavement made from native asphalt excavated in Utah.
“It’s pretty stout,” says UDOT Engineer for Asphalt Materials Kevin VanFrank who has tested oil sands pavement with a Hamburg asphalt mix performance tester. After over 12,000 passes with the machine’s weighted wheel, the old pavement showed similar wear as compared to newer typical asphalt mix designs used on similar roads.
Old oil sands mix designs varied in the past. SR-121, Maeser to LaPoint was paved in road mix method using kerosene as a cutter to mobilize the oil sands. Randlett Highway and the Bonanza Highway were paved using a hot mix. To make use of oil sands today requires a standardized design that considers repeatability and durability.
Oil sands, mined in the Uintah basin, are a source of natural asphalt that have been used in pavement for 80 years, explains Kimball Young, who is overseeing a project to put the product to work for the Uintah Transportation Special Service District with support from USTAR. Young’s project team has developed a non-proprietary design and placed oil sand pavement in test areas in Uintah County. Plant Mixed Oil Sands Asphalt uses un-processed oil sands along with the usual pavement components – crushed aggregate and hydrated lime.
The mix development process started with testing the old pavement. VanFrank worked with University of Utah researcher Pedro Romero on initial testing. Young worked with Tim Biel of CME Transportation group to continue the testing and development of a mix design that produces a stable mix and can be reproduced. Romero has maintained his involvement throughout the process.
All testing showed that pavement made from oil sands can produce high quality, durable pavement for light to medium traffic loads. The durability of oil sand pavement may be due to slower oxidation rates in natural asphalt as compared to asphalt from refined petroleum, explains Biel.
The mix design developed by Young’s team is composed of 35 to 40 percent oil sand containing a minimum of 12 percent asphalt and 60 to 65 percent course aggregate. Young’s team is testing warm mix designs with and without hydrated lime.