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Warm Mix Asphalt

Case Studies

The FHWA is helping Yellowstone National Park stay green. Using warm mix asphalt in road construction can help provide long lasting pavements with an additional benefit of reduced fuel consumption and reduced smoke, odors, and other air emissions.

Yellowstone Gives a Warm Welcome to Warm Mix Asphalt

Workers paving road in Yellowstone with WMAWorkers paving road in Yellowstone with WMA

Campers and tourists who visited the Yellowstone National Park during road construction may have noticed something missing. Instead of the smoke and sharp smells that typically accompany newly placed asphalt, the air was clear. Asphalt odors were barely noticeable.

Only a transportation specialist might have guessed the reason. The clear air was just one positive result of a technology championed by the Federal Highway Administration: Warm Mix Asphalt (WMA).

To ensure that this environmentally friendly technology would meet Federal needs, the FHWA's Federal Lands Highway (FLH) Division partnered with State and local transportation agencies, contractors, the National Park Service, and other organizations to test WMA. The East Entrance Road to Yellowstone National Park was chosen as a test site, and three sections of road were placed for comparison.

Three variations of asphalt mixes were chosen. Two were warm asphalt mixes: Advera WMA and Sasobit WMA. As a control, the third was the traditional hot mix asphalt. Each mix was placed over a period of approximately 4 days per mix in similar stretches of the highway.

Yellowstone's Examination of Asphalt Factors

Reducing the consumption of natural resources was an important consideration for Yellowstone and the FHWA, but other factors were also examined. The durability, cost, ease of handling, and moisture sensitivity of each mix were evaluated. The truck haul distance from the mix production facility in Cody, WY to the Park paving site was 50-60 miles uphill. WMA was used to ensure the mixture placement and compaction were successful after the long haul.

Placement of the Advera WMA began on August 26, 2007. The workers noticed no differences in handling the new mixture and it was easy to manipulate. According to roller operators, the mix seemed less "tender" and was easy to compact.

The Sasobit mix was placed next. Again, workers saw no differences in handling the mix and even at the lowest temperatures, it was easily leveled. Workers also found it easy to achieve the required density.

For workers and observers, the major difference was reduced visible smoke and odors. WMA is reported to reduce visible smoke and odors by as much as 60percent. Air emissions are also reported lower. This made working conditions more pleasant for the contractor's employees.

Easy Asphalt Compaction Due to Lack of Moisture Sensitivity

Moisture sensitivity was not an issue on this project with the WMA. Compaction was easy to achieve after the long haul. There was good rut resistance for all of the mixtures.

The WMA also offered an impressive reduction in energy expenditures. Mix production for warm-mix asphalt is typically done at 10 °C (50 °F) to 37 ;°C (100 °F) below the standard hot-mix temperatures of 149 °C (300 °F) to 176 °C (350 °F). As a result, fossil fuel consumption was reported by the contractor as 20percent lower for the WMA mixtures.

In terms of cost, WMA can be economical. The overall cost of the warm-mix asphalt was a little higher than a conventional mix, but increased usage nationwide would reduce those costs. Lower fuel consumption also contributes to a more attractive bottom line.

Compaction Leads to Long–Term Performance

Using less fuel is also important in reducing greenhouse gas emissions and preserving natural resources. In addition, researchers believe that WMA's improved, less variable levels of compaction will lead to better long-term pavement performance.

"This was the first time warm-mix asphalt had been used in Yellowstone, and the process went very well," says Brad Neitzke, FLH Materials Engineer at FHWA. "Both the contractor and Federal Lands were very pleased with the outcome." As a result, Yellowstone has committed to using warm mix asphalt for future maintenance work.

Completed WMA road in Yellowstone Completed WMA road in Yellowstone

Warm mix is becoming more common in Western Europe as well as much of the United States. WMA has been demonstrated in 43 States, and is expected to grow in popularity.

Additional studies have reported even more impressive results. In 2009, the Transportation Research Board reported that WMA uses 30percent less fuel and emits about a third less dust and carbon dioxide than the mainstream process does.

Upgrading highways, roads, and other essential parts of the Nation's infrastructure is an important part of stimulating the U.S. economy. With warm-mix asphalt, building and maintaining those roads can also be environmentally friendly.

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Page last modified on August 12, 2013.
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