As more and more asphalt producers gain experience with running shingles, they are learning what it takes to do so effectively. While shingles offer a less expensive source of asphalt cement, they involve certain challenges.
One challenge is to accomplish the correct blend of virgin AC with your shingles and reclaimed asphalt pavement, if RAP is also in the mix. While some states may allow as much as 5 percent recycled asphalt shingles (RAS) in a mix, that percentage may not work the best.
A FINER GRIND
Most producers who run RAS use a traditional cold-feed bin and weigh-belt system to enter the shingles into the mix. And a typical state specification will call for the RAS to be ground to 3/8-in (9.525 mm) minus. But Ideker Construction Co., based in St. Joseph, Missouri, has a different idea. The company located and bought a shingle grinder that will produce RAS ground to 1/10-in (0.254 mm) minus. The fine grind will produce more effective liquid AC to coat the aggregates, said Jack Neel, asphalt division manager at Ideker.
Top image: Ideker’s plant near the southern city limit of Kansas City, Missouri, is equipped to run recycled asphalt roofing shingles.
“Chances are that 3/8-in (9.525 mm) chip is not getting melted down to be 100-percent effective oil,” said Neel. “The PG grade of those shingles is extremely high. It takes a lot of heat to melt them down. It’s much like sticking a frozen pie in the oven versus a tater tot.”
Last year, Ideker fitted up one plant with a special RAS bin not built by Astec, and did run the finer grind of shingles for a time. “With the fine grind, we could run up to probably 6 percent shingles and you don’t even know it’s there,” said Neel. But the bin failed, and that company is currently working on supplying Ideker with another RAS bin.
This year, Ideker is working with Astec to supply another RAS bin for the second plant, new control software, and an effective way to transfer the RAS to the mixing drum of the dual-drum plant. Both Astec and the other company are supplying Ideker with weigh-depletion RAS bins, which have load cells in them.
As the RAS is fed out to the plant, it gets weighed by the load cells. “Weigh depletion is a much more accurate way to know exactly what’s going into the mix than the traditional weigh-belt,” said Neel.
Earlier this year, Astec was writing software to enable Ideker’s controls to call the RAS the primary source of liquid AC in the mix. “By using these weigh depletion bins, we actually meter the amount of shingles or oil going into the mix,” said Neel. The virgin AC pumps do their job, but that AC enters as a secondary source of asphalt.
Recycled shingles don’t flow in like normal aggregates. They can form bridges, and not feed into a weigh-belt system. So with Ideker’s new weigh depletion system, if a blockage somehow occurs, the new software automatically knows that it’s feeding less RAS in, and the software will speed up the AC pump to enter more virgin asphalt. “So that way we always keep our AC binder as close to accurate as possible,” said Neel. “The other nice thing about the fine grind shingles is that you get a more homogeneous mix.”
Ideker will enter the finely-ground RAS into a chute between the drying drum and the mixing drum. “That way, your oil products are not exposed to any burner, but since they’re ground up fine enough, the heat of the virgin aggregates helps melt that fine shingle, and they get mixed in the mixing drum,” said Neel.
This system has its challenges. “It’s in transferring the material to the mixing drum where the biggest challenge is,” said Neel. “We’re still trying to get over that hump. So hopefully we can get the bin to do what we need it to do. We’re talking about stuff that nobody has done yet. Everybody is in kind of a race to do this. Because it only makes sense, that the finer you can grind the shingle, the more effective oil you will get out of it.”BACK TO ISSUE
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