There is no ceiling to how far down the highway C&D recycling can go. But there is a roof—and that roof is shingled.
Many states are moving to use of recycled asphalt shingles (RAS) in highway material, especially in hot mix asphalt (HMA). The big hurdle for RAS today is the low oil prices, which can make RAS in HMA an economic nonstarter.
RAS is gaining acceptance in asphalt road construction. Many states allow up to five percent manufacturer’s scrap in HMA. Several states, including Kansas and Ohio, allow tear-off shingles in the mix, too (see sidebar “State by state”).
The U.S. Environmental Protection Agency (EPA) estimates that 11 million tons of shingle tear-offs are generated annually in the United States. The fact is, EPA says, very little is recycled.
One of the foremost reasons currently is cheap oil prices. “With oil prices so low, it does not make economic sense,” says Grant Wollenhaupt, director of Research to Roads (R2R), Kansas City, Missouri. R2R is a majority-owned subsidiary of Superior Bowen, an asphalt pavement construction company.
While state transportation departments are more open to RAS in mixes, the near-term economic picture is gloomy.
“If we stabilized the oil market at $50-55 a barrel, we’d see asphalt in the $450 to $500 range. That would be enough to make someone think it worthwhile to go to the trouble of using shingles,” Wollenhaupt says.
Shingles typically run between 20 percent and 35 percent asphalt cement. Figuring 20 percent liquid and a value of $500 per ton for the asphalt content, under optimal market conditions that is $1.1 billion worth of asphalt from shingles available annually to highway departments.
South Carolina allows both manufacturing waste and tear-off shingles in its mix. “The majority of what we see is post-consumer tear-off,” says Cliff Selkinghaus, asphalt materials manager in the South Carolina Department of Transportation’s (SCDOT) office of materials and research.
Since the nearest shingle manufacturer is in Savannah, Georgia, the shingles tend to come from C&D debris.
SCDOT does not allow RAS on Interstates or high-volume primary roads. Its standard SC-M-407 does specify RAS for everyday road surfaces and for base mixtures. Selkinghaus indicates that, with further experience, approved uses could be expanded.
Nebraska also allows both manufacturing scrap and tear-off shingles in its specifications. State guidelines say HMA shall not contain “objectionable materials” greater than 1.5 percent by weight.
The goal, says Matt Beran P.E., assistant flexible pavements engineer with the Nebraska Department of Roads, is to allow shingles as a possibility. “We do not want to push out shingles if they make economic sense, but leave them as a fair option.”
Most RAS use in Nebraska is confined to the large urban centers in the Southeast. Omaha and Lincoln generate a lot of shingles and a Tamko Building Products manufacturing facility is located near the Kansas border in the south central part of the state. The goal is not to quash RAS if projects work. About half the projects containing RAS have been from manufacturing scrap and half from tear-offs.
Almost every state that has taken up RAS has a concept similar to Iowa’s Department of Natural Resources (DNR). Its policy says reducing reliance on landfills for the management of solid waste will remain a central objective. At the time that Iowa’s principal solid waste authority (Iowa Code Chapter 455B, Division IV “Solid Waste Disposal”, Part 1 “Solid Waste”) was passed it was recognized that environmentally preferable options for the management of solid waste were available other than landfilling. This remains the case today.
In short, keeping shingles out of landfills is a good idea.
To that end, Nebraska allows up to 10 percent on shoulders and 5 percent on the mainlines of its roadways.
“You can spec 5 percent or 10 percent shingles but you need to look at your dust-to-binder content and voids in mineral aggregate, too,” Beran says. “Those are the biggest hindrance.”
He notes that many state specifications, once set, are not revisited. “If you open the spec up by a half-percent or one-tenth percent, you can squeeze in shingles,” Beran says. “You need to know why you have the specs at a certain limit.”
In most states which approve use of recycled shingles in asphalt, cutbacks from shingle factories can be ground up and immediately added to the HMA process.
Wollenhaupt points to a trend away from percentage requirements to performance specifications in RAS. Although the specifications remain on the book, transportation departments in states like Texas no longer look at percentages but the effectiveness of the mix.
Manufactured shingles have a sizable percentage of asphalt, so use of RAS gives states both a cost-effective alternative to virgin asphalt and aggregate used in highways and a way to remove a common fraction of C&D material from the waste stream.
SCDOT, for example, tracks both RAS and recycled asphalt pavement (RAP). “We do allow the combination of the two,” Selkinghaus says. The state’s standard permits roughly 30 percent aged binder in paving. Since shingles are about 20 percent asphalt, the additional can be made up by RAP.
According to the Milwaukee-based Construction & Demolition Recycling Association (CDRA), several field studies were conducted in Minnesota, North Carolina and Pennsylvania, where portions of highways were paved with asphalt containing recycled shingles.
In each of those studies, the asphalt was checked and rechecked for quality, according to CDRA. The studies showed increased stiffness of the asphalt, decreased cracking, decreased susceptibility to rutting.
Moisture sensitivity was not affected. Keep in mind that Minnesota and Pennsylvania both experience harsh winters.
On top of that, CDRA says use of RAS in HMA applications can reduce the overall cost of paving a road.
Keeping shingles out of landfills, while nice, is not the economic driver some would think. “Tipping fees are not the problem,” Wollenhaupt says. “You literally can give shingles away for free and people won’t take them.”
The road to using RAS in HMA is not Easy Street. One of the challenges with shingles from tear-offs is handling roofing felt, shingle wrap and flashing.
SCDOT’s standards require use of shredded shingles that are produced primarily from a shingle manufacturer, a processing facility or are recycled from the construction of residential or commercial roofing sites.
Shingles must be sufficiently dry to be free flowing and to prevent foaming when blended with the hot binder.
COLD PATCH APPLICATION
There are several states that have used RAS as cold patch. This is not new. California, New Jersey and Washington state all have used RAS in cold patch for years. Chicago also is on the cold patch bandwagon.
Cold patch comprised of RAS has a longer life than other patch materials. Researchers say this probably can be credited to the fibers found in the felts and fiberglass in shingles.
Out on the highway, workers have found RAS patch easy to apply. A pothole is filled approximately one inch over grade. There is no need for a steam roller or heavy equipment. The daily vehicle traffic is usually sufficient to compress the patch.
Nebraska has found the big limitation on RAS is not shingles but the state’s RAP (recycled asphalt pavement) incentive. Contractors get an incentive if they use road millings on their projects.
Where on-site recycling is not done, other states find shingle-based material is easier to haul since it is less dense than other materials commonly used. It stores better, too, researchers have found, since it does not clump as quickly as some other patching products.
SORTING OUT ISSUES
EPA says one of the biggest concerns with RAS from tear-offs is the possibility of asbestos in old shingles. Although asbestos was phased out of shingle making in the early 1980s, roofing that lasted beyond the typical 20-to-25-year lifespan still could be reaching recyclers. In fact, SCDOT requires that shingles be free of all chemicals, oils or any other hazardous materials, citing particularly asbestos.
Sometimes, shingles get unfairly blamed for other engineering problems.
In Nebraska, Beran says they have seen no construction problems with shingles in their mix.
“Sometimes, shingles get a stigma,” he says. “Our thing is to find out whether we know shingles are the problem.”
He notes that mix design, material placement and other factors might be more at fault than the fact that the mix contained shingles. “Ask questions,” Beran says. “Shingles get blamed for more than what is the fault of the shingles.”
The key to success, Selkinghaus says, is to have C&D recyclers take the time to make a finer grind.
“If processors take the time to make a minus quarter-inch grind, we don’t see the pitting,” he says. “It creates more surface area and it gets mixed better.”
Still, Wollenhaupt says, the million dollar question remains when and where oil prices will stabilize. “If oil goes up (to $55 a barrel) and asphalt stabilizes around $450 a ton, the shingle market will be okay,” he says.
Beyond the cost of asphalt, engineers need to figure in the economics of mitigating technology that available to deal with issues like cracking, stiffening in the binder, and similar workability challenges. There are solutions to each of those challenges—but each solution costs money.