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Credit: Photo: National Asphalt Pavement Association

After three years, the 250 tons of warm-mix asphalt that Charlotte, N.C., placed on this section of Old Statesville Road showed no appreciable rutting or other deterioration. Core comparisons with a hot-mix section show that hot and warm mixes densify at about the same rate.
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Credit: Photo: National Asphalt Pavement Association

Produced and placed at lower temperatures than hot-mix asphalt, warm mixes eliminate fumes and increase worker comfort during paving operations.

The objective of Project 09-43, “Mix Design Practices for Warm Mix Asphalt Technologies,” is to develop a performance-based mix design procedure in the form of a manual of practice. The project began last March and is scheduled for completion in March 2010. The California, Minnesota, North Carolina, Ohio, and Pennsylvania transportation departments are on the oversight panel.

Project 09-47, “Engineering Properties, Emissions, and Field Performance of Warm-Mix Asphalt Technologies,” will compare production and installation costs between warm- and hot-mix pavements, and provide relative emissions measurements for warm-mix versus conventional hot-mix technologies. It's due to begin later this year and will run for about 3½ years. Its oversight panel includes representatives from the Arizona, California, Florida, Rhode Island, Texas, and Washington transportation departments.

— Kenneth A. Hooker is a freelance writer based in Oak Park, Ill.

Web extra: For more information on the Warm-Mix Asphalt Technical Working Group, jointly sponsored by FHWA and NAPA, visit the “article links” page under “resources” at www.pwmag.com.


Full speed ahead

Not bothering to wait for the results of field trials, managers move ahead with warm-mix paving projects.

Ohio and Illinois are just two states that are incorporating warm-mix asphalt (WMA) into their paving programs.

The material worked well in two trial projects constructed last year for the Illinois DOT.

In the first, 1,000 tons of WMA were placed as a 6-inch stabilized subbase under acontinuously reinforced concrete surface course on a section of the Dan Ryan Expressway in Chicago. In the second, 2,000 tons of warm surface mix were placed on a downstate township road west of Lawrenceville.

In both cases, the material was substantially cooler when placed and compacted than standard hot-mix asphalt, and didn't require additional equipment or new processes to place.

The agency doesn't plan to create new pavement specifications to accommodate warm mixes.

"That's part of the beauty of the material," says Hot Mix Asphalt (HMA) Operations Engineer Jim Trepanier. "If a contractor proposed substituting warm-mix on a project, we'd be willing to accept it as long as it represented the bid price."

In September 2006, Ohio built one of the early U.S. field trial pavements as an overlay on an existing road in Guernsey County. The trial included four test sections, each with a 3?4-inch layer of HMA and a 11?4-inch top layer. The top layers consisted of three types of warm mixes and a control section of a hot mix. The test pavements are considered successful demonstrations of warm-mix technology.

When James Beasley was hired as director of the Ohio DOT (ODOT) early last year, he was impressed enough to include WMA in the agency's 2008-2009 business plan.

"Our goal is to preserve Ohio's roadways with the least possible harmful impact on the environment," says ODOT Communications Director Scott Varner. "Especially in these tough financial times, the potential cost savings also is an important benefit."

The department will use WMA on six pavement projects slated for this summer. Each project will be a two-lane primary or secondary state road, and each will be done half with warm-mix and half with conventional hot-mix. The work will be contracted out, not performed by department crews.

Like Illinois, Ohio hasn't modified specifications to accommodate warm mixes, and plans to allow it as a substitution if the contractor can prove it would reduce the cost.