MINNESOTA RESEARCH
In Minnesota, the use of manufacturers’ recycled asphalt shingles in hot-mix asphalt began with laboratory research and field testing in 1991. The Minnesota Department of Transportation (Mn/DOT), the University of Minnesota, and the Minnesota Office of Environmental Assistance (OEA) collaborated on a research project that paved the way for the use of RAS in hot-mix asphalt. Since then Mn/DOT, the University of Minnesota, and the MPCA/OEA, along with the Solid Waste Management Coordinating Board (SWMCB), Ramsey County, Hennepin County, Dakota County and many other partners, have completed additional demonstration projects using both manufacturers’ and tear-off shingles.
Early Findings
An asphalt shingle contains the same basic ingredients as hot-mix asphalt - aggregate, asphalt cement, and mineral filler. Researchers wanted to study whether the similarities would result in an effective mix. The early research defined the characteristics and limitations of bituminous paving mixtures that contained RAS. The study investigated the influence of RAS on asphalt concrete properties. At the project's conclusion, researchers recommended development of a specification to allow up to 5 percent manufacturers’ RAS for use in hot-mix asphalt.
Field Testing
In 1991, field testing began in conjunction with the laboratory research. Mn/DOT chose a 3.6 mile section of Trunk Highway 25 for overlay. The project design consisted of a 1.5-inch Mn/DOT Type 31 leveling course followed by a one-inch Type 41 wear course. Using varying combinations, Mn/DOT added 5 percent and 7 percent manufacturers’ RAS to both the wear and non-wear course mixtures. Limited lab testing of tear-off shingles (post-consumer) was also conducted as a part of this earlier research. Mn/DOT tested post-construction cores, which showed the pavement that contained RAS performed at least as well as the pavement without RAS.
Additional Sites
Mn/DOT has conducted several demonstrations projects using RAS since 1991. Currently, Mn/DOT is working with Ramsey County to pave a bike trail using 5% tear-off shingles which will be completed in November 2007. For more information on the research and demonstration projects completed in Minnesota, stop by the MPCA Exhibitor Booth, or join us on Friday, November 2nd from 8:00 – 8:30 a.m. for an informational session on Minnesota’s Experience using RAS!
Specification Development
Through its research and field testing, Mn/DOT confirmed that mixtures containing RAS performed at least as well or better as those mixtures without shingle byproduct. As a result, in 1995 Mn/DOT formally issued specifications for the use of up to 5 percent (by weight of mixture) shingle byproduct in all courses for both Type 50 and type 60 Mixtures. The “permissive” specification allows RAS to be used as RAP,
5% shingles and 25% RAP, if the criteria is for 20% maximum RAP, then it could be 5% shingles, 15% RAP. Mn/DOT currently prepared a specification for Ramsey County to include 5% tear-off RAS of the total mix for a bike trail that will be completed in November 2007. The hot-mix asphalt for the bike trail does not include RAP,
Next Steps
As more contractors have gained access to shingle recycling equipment, the use of the manufactures waste shingles has grown in Minnesota so that the majority of all manufacturer’ shingle scrap is being used in HMA. Mn/DOT’s current efforts are to examine the feasibility of using tear-off (postconsumer) shingle scrap. Several test sections have been constructed and additional laboratory evaluations have been completed and are currently underway.