"We remove all the debris that doesn't contain asphalt on a sorting line," Pahl explains. "Essentially the material is spread out on a conveyer belt and we have laborers that manually remove all non-asphalt containing materials as they move along the sort line. From there, the shingles are ready to be ground. Generally the grinder then directly feeds the material to a trommel screen to create the desired end product used for the asphalt hot mix."
Pahl uses a grinder designed specifically to process shingle material. The raw asphalt shingles are first ground to under a ½-inch (.6 cm) minus size, and that material is then fed to a trommel to reduce the ground shingle material to an even finer size. Dem-Con purchased a Wildcat 626 trommel unit built by Wildcat Manufacturing - a Vermeer owned company - to assist in streamlining the process. "Our spec at the hot mix plant varies across the country but ½-inch minus is fairly standard," Pahl explains. Some states, including Minnesota, require an even finer sizing and that's when the trommel screen is really the only way you can get a product down to the size they want cost effectively."
The trommel can be equipped with different screen sizes to achieve the desired end result. For example, Minnesota Department of Transportation (MDOT) requires the end material to be of a consistency that Pahl describes as similar to a coarsely ground coffee. As the material passes through the different screen, each screen setting gets smaller and reduces the material to the desired end consistency. Pahl explains the process.
"The number four sieve is somewhere in between a 1/8- and 3/16-inch (.3 and .5 cm)," he explains. "The spec calls for 90 percent of the material passing the number four sieve and 100 percent passing the 1/2-inch (1.3 cm). Some states spec a material that is a bit coarser; all are different. We have found that more and more states are requiring a finer material so the Wildcat trommel will play a more important role in the upcoming seasons. The Wildcat trommel with multiple sections of screen that we can adjust quickly helps us to create a lot of variables and flexibility on how we size our final product.
All of the overs (material that is too large to meet the specs) are recycled back through the grinder and end up getting ground down further, a closed-loop process that results in all the raw material being used and no waste - so no asphalt material ever ends up in the landfill. Everything gets used.
Expanding and streamlining the processes
Dem-Con has reached out to recyclers across the country and worked with state Departments of Transportation (DOT) to expand asphalt shingle recycling nationwide. This has required establishing an in-depth knowledge of the asphalt paving industry and the hot-mix process used for completing road construction and parking lot projects.
"When we were getting this started a lot of state DOTs didn't have a hot-mix spec using shingles, but more and more are coming online," Pahl says. "Whatever the DOT spec is, we are able to meet it. We're competing with virgin asphalt because that's what the asphalt recovered from the shingles replace. Using shingles in the mix allows the hot mix producer to lower the use of the high-price virgin asphalt. So it's really a cost savings to them and this is what enables this process to be economically viable."
Dem-Con works hard to pre-sell a majority of the final product, a necessary component of Pahl's business operation because of preparing product specifically for so many different state DOTs and asphalt suppliers. "We have quite a bit of money invested in the process and we make sure the product has a home before we process it," Pahl explains. "We are also working with local recyclers who are involved with collecting shingles throughout the country to help them as well. So there are times where we may assist the company, just trying to market the material, before we ever show up to process it. It benefits everyone to be as cost-effective as possible so we will assist in whatever way possible to try to drive the process."
Growth and expansion expected
According to Pahl, asphalt shingle recycling has been occurring for several years, but the process has just recently become more refined, mainstream and is gaining efficiencies. As more states adopt specs for hot-mix materials, he is optimistic that the industry will continue to grow.