The work on Old Alabama Road in Roswell, Ga., seems like any standard highway job. But under the surface, there is something much bigger — the future of asphalt paving.
By using the relatively new foamed asphalt process, Atlanta Paving & Concrete Construction has provided more evidence that this method is the next wave for the industry.
“Old timers don’t want to give this stuff a chance,” said Jeff Smith, foam foreman of the project. “If you get a company that does it wrong, it hurts the reputation. The process works, we just have to convince people to believe in it. The people of Roswell are convinced. If we do this right, and the state sees a couple good projects using foamed asphalt, this will really take off.”
Using a Wirtgen WR 2500 S recycler/soil stabilizer purchased from Cowin Equipment Company, Atlanta Paving crews are rejuvenating the road base and using cold water to mix with liquid hot asphalt. The mixture bubbles and the water causes the asphalt to expand 15 to 30 times its original volume.
“In essence, we’re gluing the road back together,” said Smith. “We blow bubbles through the asphalt, and the bubble is coated with the fine material. Once it goes back into the ground, you can keep doing what you need to do.”
According to Smith, foamed asphalt is popular in second and third world countries because it cuts down on cost and manpower. He estimates that it will take approximately a week-and-a-half to two weeks to finish the half-mile long, 26 ft. wide Old Alabama Road.
“We save so much time doing it this way,” said Smith. “There’s a lot more involved with stabilizing, then laying the base. Here, it’s one shot and you’re finished. We could probably do it faster if we didn’t have to worry about traffic and weather. We can only do a certain section at a time.”
The WR 2500 S starts out by digging up the existing road and pulverizing it through the machine. It can dig up to 20 in. down and refine the material to a specific size.
The foamed asphalt is kept in an expansion chamber on the WR 2500 S and heated to 350 F.
“It can’t get much hotter than that,” said Smith. “At 400 degrees, you won’t be able to spray it. The plant is nearby, so we don’t have to wait long to fill the machine, which holds approximately 20 tons. We start heating up the tank to 320 degrees 45 minutes before it gets here.”
The cold water is sprayed into the asphalt from a 130 gal. tank carried behind the WR 2500 S.
The foamed asphalt is then injected into the reclaimed asphalt pavement (RAP) and laid behind the stabilizer. Atlanta Concrete then uses Hamm rollers to compact the material. The crew makes seven passes with the mill and another seven with the rubber tire.
“We’ve got prepaving compaction density right around 99 percent,” said Smith. “It doesn’t get much better than that. We grade it own and smooth everything out.”
Finally, the road is stabilized properly for the asphalt overlay, a top layer 1.5 to 2 in. thick.
Smith has been working with foamed asphalt since 1999, attending seminars held by Wirtgen in Tennessee and helping companies understand the new technology. He joined Atlanta approximately two years ago to help prepare the staff for working with the WR 2500 S.
“They’re one of the first to try it in Georgia,” said Smith. “I showed how much control they can have over the materials. This road goes from 8 feet to 12 feet wide, but the nozzles can be adjusted for that, so we don’t have to overlap the same areas. It’s all computer controlled precisely. With other machines, it can be a bit of a guessing game.”
Donnie Varnell, general superintendent of Atlanta Paving, appreciates the attentiveness they have received from Cowin, from which they have purchased equipment for approximately five years.
“The service has been great,” Varnell said. “Any problems and they are out on the job site right away. We’re very pleased with them.” CEG