All initial warm mix testing was carried out on private sector and local municipality applications. Before Barrett could use the mix on N.Y. State Department of Transportation projects, the Terex® warm mix asphalt system had to be approved. “This approval process is one of the most in-depth in the country,” says McMaster.
During the review, State officials requested and tested warm mix asphalt samples of virgin and RAP designs using both PG 64-22 and PG 70-22 binders. The D.O.T. also required experience and feedback from other states where the system has been used to produce warm mix asphalt.
From calibration of the water pump to water injection rates to technical information covering how this warm mix technology operates, the N.Y. State D.O.T. left nothing to be questioned prior to approving the system to produce warm mix for State jobs. The review reached beyond the plant to include responses about lay down and compaction procedures.
Terex Roadbuilding partnered with Barrett to supply all the State-requested data covering the system. In the summer of 2010, the Terex® warm mix asphalt system became the first water-injection foamed warm mix asphalt technology to be approved for use on N.Y. State D.O.T. projects.
First Warm Mix Project
This fall, Barrett produced and paved asphalt for the first warm mix asphalt project specified by Region 3 of the N.Y. State D.O.T. The spec called for a mill-and-fill resurfacing job of Highway 481 straddling Fulton and Oswego Counties. Each direction of the divided highway consisted of two 12-ft lanes and 10- and 4-ft shoulders. In all, nearly 20 lane-miles were resurfaced along this 4.9-mile stretch of highway, requiring 22,000 tons of warm mix asphalt.
Barrett’s crews milled the top two inches of the oxidized asphalt surface of the highway. Compacted to a two-inch thickness, a fresh 9.5 mm top course mix with a PG 64-22 binder and 20 percent RAP content replaced the old surface.
Equipped with the Terex® foamed asphalt system, the Magnum E400 plant in Jamesville produced mix for the project. Even though the jobsite was more than 30 miles from the plant with a one-way transit time of approximately one hour, “mix temperatures were lowered to between 285° and 290° F,” says Lallier. Produced as hot mix asphalt, this design would have been mixed at temperatures ranging from 310° to 320° F.
Even with the long transit time, little temperature loss was experienced with the tarped loads. “We received the mix at about 280° F,” mentions Wesley Hood, construction manager for Barrett’s N.Y. Central Region.
As soon as the mix left the screed, the breakdown roller compacted the mat. “When the mix was at a steady 275° to 285° F behind the screed, the pavement laid great,” explains Donald Williamson II, project superintendent for Barrett’s N.Y. Central Region. “We also noticed improved compaction with our breakdown roller, since we did not have to vibrate as many passes to achieve our needed compaction.”
The finish roller followed closely behind and started its compaction passes in the 250° to 260° F range. Crews achieved specified density of 92 to 97 percent when the mat was approximately 230° F. Hood reports that the foamed asphalt stays workable longer than the hot mix version.
Fewer emissions associated with producing asphalt at lower temperatures also benefit the paving and work crews at the jobsite. “The biggest keys to warm mix are the emissions and better environment for the people working with the mix,” says Hood. “It’s not as hot, and you don’t smell it as much. It’s better to work with, better for the crews and better for the traveling public.”