MARCH 2012

Asphalt recycling pulls material from roads and roofs

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Asphalt is one of America’s most recycled materials, but the sticky black product admired for its weather resistance, its ability to bind together other materials, to pave roads and cover roofs also faces challenges in meeting its full recycling potential.

The brightest success in asphalt recycling is found in paving. Margaret Cervarich, vice president for communications and public affairs of the National Asphalt Pavement Association, a Lanham, Maryland trade group, said 99 percent of the asphalt covering the nation’s roads is recycled when it is removed for resurfacing or other purposes. “In 2010 we reclaimed 72.9 million tons of asphalt pavement,” Cervarich said.

Asphalt used for paving is easy to recycle, for several reasons. One is that it is mostly made up of rocks in the form of aggregate bound together by the sticky asphalt. Not only are the rocks highly durable and readily re-used for the same purposes, but asphalt itself can be recycled indefinitely, Cervarich said.

Perhaps most important is that the paving and recycling is done as part of the same process, often by the same company, and it uses processes that are time-tested and uncomplicated. “They just mill it up off the road,” Cervarich said. “It’s very simple and straightforward. It’s a technology we’ve been using since the seventies, and it’s done by asphalt contractors.”

Post-consumer products, on the other hand, are harder to recycle because consumers have to be recruited to gather and place materials into the recycling stream. Some of the same difficulties apply when businesses recycling materials aren’t the same ones collecting the recyclables. “The people who demolish a house aren’t necessarily going to take those same elements and put them into another house,” Cervarich said. “With asphalt pavement it’s very simple. You use a milling machine to chew it up off the pavement, take it back to the asphalt plant, grade it, sort it and store it until you’re ready to use it. The same people doing the reclaiming are also doing the construction and reuse.”

Recycling asphalt removed from road surfaces and then re-applying it saves transportation costs, as well as the costs of mining new asphalt from deposits or extracting it from petroleum. Recycling asphalt is more economical for paving companies than obtaining and employing virgin materials, so they are financially motivated to recycle all of it they can get.

In the process, recyclers divert many tons of material from landfills, while conserving energy that would be used for transportation and refining virgin asphalt. “We’re saving natural resources instead of filling in landfills,” Cervarich said. “It’s an extremely efficient thing to do.”

One recycling challenge is getting states’ road building agencies to agree to higher percentages of recycled materials in the asphalt mix applied to roads. Some states limit the amount of recycled asphalt that can be used in public roads below 50 percent, although private road builders are less demanding. Recycled material has been suspected of causing cracking when added to mixes in high concentrations. But recent research indicates recycled material can be used without affecting cracking, Cervarich said. 

Old asphalt is milled off of roads, and immediately recycled on-site into material for the replacement roadway. The challenge is convincing states to allow mixes with a higher percentage of recycled content.

“We think that reclaimed asphalt is a great resource of America,” Cervarich said. “We have 2 million miles of paved roads and about 94 percent of them have an asphalt surface. All of that pavement on the road is a resource we can mine and reuse.”

The other major use of asphalt is for roofing, in the form of asphalt shingles used in homes and other buildings and asphalt coverings for flat roofs. Here the situation is different. A large portion and perhaps the majority of asphalt shingles, which are the primary source of roofing asphalt entering the materials stream, are not recycled.

That’s not to say roofing companies don’t recycle any. “It’s hard to tell the total percentage, but the number I have is that if you don’t recycle asphalt shingles, there would be 11 million tons per year that would go into the landfills,” said John Ferraro, general manager of Asphalt Roofing Manufacturing Association, a Washington, D.C.-based trade group.

Just as several factors help to make pavement recycling relatively easy, convenient and practical, a constellation of issues prevent shingles from being more readily recycled. “One factor that would help increase recycling is the presence of an end market for the recycled material,” said Ferraro. “Right now the primary use for asphalt is turning it into pavement for roads. It goes into a hot mix and is used for pavement. There are a couple of other uses for it but that’s by far the primary use.”

With lower state road building budgets, demand for recycled asphalt shingles for paving has been slow. “They’re not paving as much as they would in a good economy,” Ferraro said. “As that picks up a little more the demand side will start to pick up as well.”

Another problem is that sometimes asbestos is mixed in the material, so that recyclers have to remove the hazardous substance. Other than that, most of the technology for recycling shingles is straightforward. “It’s still just the basic grinder that separates the asphalt from the rest of the construction debris,” Ferraro said. “It gets ground up into various stages of fine material. Certain hot mixes have to have different formulas of asphalt and everything else that go into it. But it’s just your typical grinder that’s used now.”

Asphalt is a regulated material already, and recycling it poses no additional problems for companies used to working with it. One thing Ferraro would like to see is a national standard for guidelines for recycling, however, because now each state regulates it differently.

To improve recycling rates, Ferraro said one focus is an education campaign to teach businesses that remove roofs that the shingles can be recycled rather than being dumped in landfills. “The future looks very promising,” he said. It’s certainly a growing piece and as technology gets better, the product will become better quality.”