Asphalt Recycling Section
Better Roads Staff
“In the pug mill, a consistent 1.6 percent emulsion was added by a computerized injection system. The flow of emulsion is automatically regulated according to the weight of the material crossing the belt scale. If needed, the operator can add a bit of water to help the movement of the material,” says Rogers. “Much of the time, we just go with the water that’s added at the milling cutter, which is around 1.5 to 2.0 percent,” he says.
Once the emulsion was mixed in with the RAP, the recycler deposited the recycled asphalt in a windrow. From there, Granite Construction used a Cedarapids windrow elevator to pick up the material and place it into a paver hopper. Working one lane wide, the paver spread the material and compaction followed.
Microsurfacing came next – over all the entire 9 miles. Pavement Coatings used three microsurfacing machines, all truck-mounted VSS Macropaver 12B units, to apply a Type II microsurface. The application rate was 18 pounds per square yard. The microsurfacing machine uses a pug mill to mix fine aggregates, emulsion, and 0.5 to 1.0 percent portland cement as a setting agent, to control the break of the liquid. The final microsurface is one-quarter to three-eighths of an inch thick.
“The project was completed in just eight days. The CIR process required very few trucks for material delivery during construction,” Ford notes. “Using hot mix would have been difficult, because the nearest hot mix plant was 55 miles away. Plus, access to the site was difficult.”
By using the CIR and microsurfacing, the county was able to save approximately 25 percent compared to a conventional cold mill and overlay with 1.5 inches of hot mix. Pavement Recycling Systems estimates the CIR process saved 334 offsite truck trips, eliminated more than 12,523 truck miles, saved 4,420 tons of virgin aggregates and almost 200 barrels of oil. The energy savings was at least 32 percent compared to a hot mix alternative.
“When we can fix the cause of the problem, but still save money and minimize the impact to the environment, that’s what I call a perfect green solution,” says Diaz.
“One of the things that made this project so fantastically successful was the teamwork between the county, the suppliers, and the contractors,” says Ford.
Rocky Mountain Hot
For Colorado’s State Highway 141, CDOT goes with HIR
by Daniel Brown, Contributing Editor
State Highway 141 south of Grand Junction, Colo., was in pretty rough shape. Sections had rutted, and there was both fatigue cracking and alligator cracking. The rural asphalt roadway had served for 25 to 30 years with only chip seals and some patching to maintain it.
To rehabilitate Highway 141 last summer, the Colorado Department of Transportation (CDOT) elected to use hot-in-place recycling on the top 2 inches followed by a 2-inch hot-mix asphalt overlay. By heating, remixing and repaving the top 2 inches of the existing roadway, CDOT figures it saved 38 percent – compared to cold milling the top 2 inches and replacing it with a new asphalt overlay.
“At the time we were looking at paying $600 to $700 per ton of PG 64-22 liquid asphalt cement,” says Devin Ray, CDOT project engineer. “That put our cost for new hot mix at $60 per ton. So it cost us $11.65 per square yard for the 2 inches of asphalt overlay. By comparison, the hot-in-place recycling – including the virgin mix that we added – cost $7.27 per square yard. So that’s a 38-percent savings right there. And we got a rehabilitated road that is structurally comparable to all-new asphalt.”