Unlike typical asphalt that is finished when it is cold, the cold foam in-place material isn’t finished until it is compacted. As a subcontractor, FMG completed the cold foam in-place recycling while contractor Graniterock Pavex completed the finishing work. “We compacted the material with 15-ton steel drum rollers in 3 to 4 passes often achieving 98 to 105 percent density,” McElroy says. “Once we achieved compaction, we used pneumatic rollers to bring the fines up and knead it together to get the finished surface.” Crews were able to complete recycling at 20 to 30 feet per minute.
Within a few hours, the surface was dried and a 10-12 hundredths of fog seal was applied followed by sand. “It is imperative to put down sand and oil,” McElroy says. “The foam process leaves a crust on top, and that needs to be protected with a fog seal.”
A few steps away from a conventional process
When completing cold foam in-place recycling, contractors will recognize several challenges compared to the conventional overlay process. First, it is important to properly manage the material.
“Unlike paving, if you go a little too thick or thin you have to add or remove material,” McElroy says. “With what we’re doing we have a set amount of material. If we are grinding out 4 inches we have to put 4 inches back. If we start running out of material that means we’re going too thick and if we start gaining material that means we are going too thin.”
To manage the material, FMG uses a screed with an electronic grade control.
Another challenge FMG encountered was managing the traffic. Unlike other projects completed by FMG, the Monterey Road had freeway speeds, stop lights and turn lanes.
“The problem is you have stop lights in the middle of the job, and you have people driving 65 miles per hour to a stop, then accelerating out again,” McElroy says. “When you recycle, you are putting down a granular product. It takes four hours for it to get hard and cure out.” To manage the traffic, FMG would close down one lane, recycle the area, fog seal and sand it then temporarily stripe the lane opening it to traffic.
Prior to Monterey Road, FMG did not fog seal the surfaces. It was during this project that McElroy learned the importance of fog sealing.
“The other jobs we’ve completed have had light traffic volume so we didn’t fog seal them,” McElroy says. “We discovered on Monterey Road that you need the fog seal because we had slight raveling in the beginning. After the application of the fog seal, the raveling issue was eliminated.”
Contractors will notice several differences between the Wirtgen 3800RC and standard milling machines. “The machine we are running can be converted into a milling machine within a few hours,” McElroy says. “The drum that turns in a conventional milling machine is an upward cut system so the drum is spinning clockwise and will break the asphalt from underneath throwing it onto the conveyor. The drum of the Wirtgen 3800RC turns downward, in a counterclockwise rotation. If you go slowly you take small bites and if you go faster you take bigger bites.”
The change in cutting direction of the Wirtgen 3800RC allows contractors to manage the size of the aggregate being cut from the road.
Reasons to recycle
McElroy strongly believes in the cold foam in-place recycling process. With less money available to make the proper repairs on roads, cold foam in-place recycling is one solution that can complete repairs safer, faster and more economical.
“We’re a pretty small company. We went out on a limb, and we are taking a risk on it because recycling has to happen,” McElroy says. “The bottom line is cities, counties and states can’t afford to waste and throw away their resources anymore. They own these aggregates, and aggregates are a declining natural resource. We have to recycle not only for these reasons, but because it is the right thing to do.”