February 2nd, 2012
ALL NATURALPreserve Infrastructure, by Catherine Higgins.
Pavement made from natural asphalt mined in Utah will be placed in Uintah County this spring.
The Uintah Transportation Special Services District’s Seep Ridge Road Project will use a newly formulated specification for Plant Mixed Oil Sand Asphalt – PMOSA. According to Kimball Young, the spec produces pavement that is reverse-engineered to live up to oil sands roads that are still in good shape 40 years after being placed.
Young is President of Natural Asphalt Solutions, Inc., a privately funded company focusing on research and development of products using oil sands.
Pavement made from oil sands has been shown to be flexible and durable in the field. 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 asphalt roads that carry similar loads. However the mix used on those roads differ – the Maeser pavement was placed using road-mix method and the Bonanza Highway pavement is a hot-mix design. Young’s challenge is to develop a mix design that is reproducible.
Just like a conventional HMA project, paving with PMOSA needs to be “reviewed, monitored and tested throughout the process,” says Young. The oil sand content of PMOSA varies from 33 to 40 percent with the average about 36 percent, Young explains. The variation allows for some field judgment when formulating the product, “depending on how it coats the aggregate.” Natural occurring asphalt contained in the oil sands acts as the binder – no additional binder is specified in the in the mix design.
Finding an effective way to introduce the oil sands to aggregate at the plant is an ongoing challenge. Oil sands particles can be anywhere from “pea sized to orange size” in the field, according to UDOT Engineer for Asphalt Materials Kevin VanFrank. Under laboratory conditions, tests of the PMOSA mix design meets UDOT standards for low volume roads. But, “it’s the scale up, the transition between the lab and the plant that has yet to be demonstrated.”
During the mixing process, the oil sands particles need to get hot enough to bond to the aggregate, and that bonding is not likely to occur with large particles. According to VanFrank “the problem is delivering the material uniformly…they face continued challenges.”
Problems aside, the technology along with the properties realized by using oil sands in pavement is promising. Van Frank believes the effort is worthwhile. Providing new products to the market is a function of the free enterprise system, and so far no other organizations have stepped forward to take on that role.
The Seep Ridge Road will be built south of US 40 and extend to the Uintah County line.