King County is testing a program to recycle old asphalt roofing shingles into new pavement for roads. In September, the joint effort between the Solid Waste Division and the Road Services Division became a reality, as two miles of roadway near Enumclaw were repaved with the recycled material.
Every year, approximately 17,000 tons of tear-off asphalt shingles from re-roofing projects are generated in King County. It’s estimated that just one home re-roofing project sends one to three tons of shingles to a landfill.
“We have been working with the local recycling and paving community to develop a market for hot mix asphalt made with recycled asphalt shingles generated here in King County,” said Kevin Kiernan, director of the King County Solid Waste Division. “It has been done successfully in several other states, and it should be equally successful here in reducing waste and saving money.”
Asphalt roofing shingles are made from the same basic materials that make up the hot mix asphalt used to pave roads. The shingles can be ground up and mixed in small percentages with oil and rock to make new batches of HMA. About 3 percent of the HMA used for this demo is recycled asphalt shingles and 15 percent is recycled asphalt pavement.
“This could be a highly cost-effective technique for repaving,” said Linda Dougherty, director of the King County Road Services Division. “In recent years, escalating prices for petroleum-related materials have made our paving projects more and more expensive. We are always looking for ways to cut costs, yet still have a safe and long-lasting road surface.”
The shingle recycling project is part of LinkUp, a King County program that works to expand markets for selected recyclable and reusable materials by facilitating an interactive community of businesses, public agencies and other organizations.
According to Asphalt Contractor Magazine, recent data suggests that the equivalent of two barrels of oil can be recaptured from every ton of shingles recycled. Research cited by the Environmental Protection Agency indicates that using recycled asphalt shingles in HMA can improve the pavement’s performance by increasing its resistance to wear and moisture, and decreasing deformation, rutting, and weather-related fatigue and cracking.
The King County project has been under development for two years, and involved input from the Washington State Department of Transportation and an advisory group of public agency, recycling, and roofing and paving industry representatives.
For the demonstration project, the Road Services Division selected a 2-mile stretch of Southeast 416th Street north of Enumclaw. This arterial was already scheduled to be repaved this year, and provided a good mix of car and truck traffic for analysis of the durability of the recycled surface. Also, because there were other detour routes nearby, the road could be completely closed to give crews room to test and document the application of the recycled asphalt mix.
The Road Services Division will continue to monitor this stretch of road over the next three years to see how it stands up to traffic and the weather. The Solid Waste Division will produce a report to publish and share the results.
