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Transportation Technology e-Transfer |
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Yellowstone Greens Up with WMA
Not notable about the Yellowstone National Park seven-mile east Idaho, these were business as usual. What was notable was the absence of smoke and fumes during much of the road construction activity. The Federal Highway Administration (FHWA) Western Federal Lands Highway Division and the Office of Pavement Technology collaborated to construct two sections of warm-mix asphalt (WMA) using different materials and one hot-mix asphalt (HMA) section between Yellowstone National Park’s east entrance, about 52 miles (~84 km) west of Cody, Wyoming, and Sylvan Pass, a length of approximately seven miles (11.1 km). The key to hot-mix asphalt is providing enough heat to reduce asphalt viscosity enough to coat the aggregate. With WMA, viscosity is reduced and adequate coating is achieved by using additives and alternative processes. The lower production temperature substantially reduces asphalt fumes and plant emissions. Benefits include improved air quality, a healthier work site, and reduced costs for mix production. But does a “green” road necessarily qualify as a “good” road? While the benefits of WMA during construction are well-recognized, the long-term performance of WMA is not known. WRI participated with the FHWA Western Federal Lands Highway Division and the Office of Pavement Technology to construct a site in which different asphalt mixes were used in consecutive strips. The asphalt in the Yellowstone project was a PG 58-34 asphalt from Idaho Asphalt Supply. One section was constructed using traditional hot-mix asphalt paving methods. Synthetic zeolite is a crystalline hydrated aluminosilicate that holds about 20% water by mass. In the drum with the hot asphalt and aggregate, the zeolite releases its internal water, creating an extremely fine foam that improves mix workability. For the Yellowstone project, Advera, which is marketed by PQ Industries, allowed mix and compaction temperatures to be reduced by about 85 ºF (30 ºC). Sasobit, manufactured by Sasol Wax in South Africa, is produced using the Fischer-Tropsch (F-T) process of synthesizing hydrocarbons from hydrogen and carbon monoxide from the gasification of coal. With a melting point of about 212 ºF (100 ºC), it is soluble in asphalt above 285 ºF (140 ºC) and improves flow by reducing viscosity. With Sasobit, mixing and compaction temperatures can be reduced by 50-85 ºF (10 to 30 ºC). At service temperatures, Sasobit has a stiffening effect. WRI’s involvement began with Matthew Corrigan, Program Manager with the FHWA Office of Pavement Technology. He operates the FHWA Mobile Asphalt Pavement Mixture Laboratory (Mobile Asphalt Lab), which is used for gathering data, testing materials, and evaluating new technologies at the construction site. Corrigan worked with Brad Neitzke, a Materials Engineer with the FHWA Western Federal Lands Highway Division, the unit that is responsible for constructing roads in all western national parks. They designed the Yellowstone demonstration using hot mix, Advera and Sasobit and identified the testing to be conducted by Corrigan, using the Mobile Asphalt Lab. “Because the warm-mix technology is new, there was testing we wanted that went beyond the normal scope of the mobile lab,” says Corrigan. “We knew we could leverage our activities with those of the Asphalt Research Consortium.” Michael Harnsberger and Michael Farrar of WRI planned how to incorporate the Yellowstone site into the validation studies of the FHWA-sponsored Asphalt Research Consortium. WRI will monitor the road yearly to correlate chemical and rheological studies with the actual performance of the road over time. Harnsberger, Farrar and Mark Pooler, also of WRI, sampled all materials during construction, and these will be included in the Asphalt Research Consortium Materials Library. They will also be used in NCHRP Project 9-43, “Mix Designs for Warm Mix Asphalt Technologies,” which is being conducted with Advanced Asphalt Technologies of Sterling, Virginia. |
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