Summary

The Washington State Department of Transportation (WSDOT) paved about 5,000 tons of warm mix asphalt (WMA) as part of their I-90 West of George Paving project (MP 137.82 to 148.45).

Description

The project, titled "I-90 - West of George Paving", paved about 10.6 miles of the right lane of eastbound Interstate 90 between Vantage and George, WA. HMA and WMA paving took place in mid-June 2008. The project paved about 8,000 tons of HMA and about 5,000 tons of WMA on the project. The same contractor, production plant, trucks and paving equipment were used for both mixes. Two inches of the existing pavement was milled and the milled material was recovered and brought to the plant for recycling. Both mixes were placed in one lift and contained 20 percent reclaimed asphalt pavement (RAP), the maximum allowed by WSDOT without additional mix design requirements. The mix design was 1/2-inch Superpave with 5.2 percent PG 76-28 binder. Sasobit® was added at 2.0 percent by weight of the binder to create the WMA. Paving progressed west to east. The contractor used a paving train consisting of one IR windrow pickup device, one IR Blaw-Knox PF 5510 paver, two steel-wheel breakdown rollers (IR DD-130HF and DD-138) operated in vibratory mode, and a steel-wheel finish roller operated in static mode. Trucks traveled from the job to the HMA drum plant in Moses Lake, WA, a trip that averaged 35 miles one-way, including a required turn around because of the divided highway. End dump trucks were used with pup trailers, all of which were unloaded onto the milled surface with a windrow spreader. Compaction for the HMA averaged 93.6% of maximum theoretical density (range: 90.4 to 97.4%), while compaction for the WMA averaged 93.7% of maximum theoretical density (range: 90.6 to 96.4%).Fuel usage data was collected at the drum plant in the field and was reported in terms of gallons of diesel fuel per ton of mix produced. On average, the HMA mix (leaving the plant at 350°F) used 1.4 gallons of No. 2 diesel fuel, while the WMA mix (300°F) used 1.07 gallons. This 23.5 percent reduction is a result of the lower plant mix temperature as no other processes at the plant were changed to accommodate the warm mix.A life cycle assessment (LCA) of both processes showed the HMA process generally used about 11% more fuel. Emissions data was not available and thus conclusions on emissions reduction were limited.

Features

Warm Mix Asphalt (WMA)

Recycled Content (20% in HMA)

Pavement Reuse (mill-and-fill project)