Utilization of Recycled Materials in Illinois Highway Construction
- Waste roofing shingles are generated during the demolition of existing roofs, and from scraps of trimmed asphalt shingles. Consumer aged waste shingles are referred to as tear-off shingles, whereas manufacturer waste is known as roofing shingle tabs or punch-outs, which includes "out-of-spec" and mis-colored or damaged shingles. Both materials are shredded in two to three stages to achieve the desired size (1, 18).
- Physical Properties:
- Roofing shingles are made of a supporting membrane of organic fibers, glass felt, or mat, a saturate of hot asphalt, and coating of mineral fines. These fines may include ceramic or lap granules, backsurfacer sand, and asphalt stabilizer. Different types of roofing shingles exhibit different material properties. Consequently, tear-off shingles are not as characteristically predictable as manufactured tabs and may contain asbestos (1, 18, 19).
- Engineering Value:
- Roofing shingle tabs are used as an asphalt cement modifier often resulting in a stiffer mix with improved temperature susceptibility and rut resistance. Tear-off shingles may be used in the same way, but are difficult to process due to the presence of foreign materials, and may also be in an irreversible age-hardened state. In general, both types may function as a fine aggregate or mineral filler depending on the size of the shredded material. Roofing shingles may be susceptible to moisture-related damage thus mix designs should include an anti-strip or retained stability test (18, 19, 20, 21).
- Potential Application:
- Waste roofing shingles in combination with bituminous concrete mixes have been investigated by many state DOTs, including Pennsylvania, Minnesota, and Iowa.
Pennsylvania has determined that a bituminous concrete modified with properly shredded fiberglass shingle tabs performs as well as a conventional bituminous pavement. Minnesota has had similar results with both felt and fiberglass shingle tabs. Both states were able to reduce the amount of virgin asphalt cement required a potential for cost savings. Both states have issued provisional specifications allowing limited amounts of processed shingle tabs in bituminous concrete mixes.
Iowa DOT inspected efforts in utilizing bitumen tear-off shingles. One year after construction, the roadway remained workable and virtually dust free. (18, 19, 20, 21)
- Department Concern:
- The Department has concerns regarding the presence of any asbestos in tear offs, glass felt tabs, and/or from storage cross-contamination. Also of concern, the presence of any foreign debris from nails, wood, and insulation, and the environmental impact of polynuclear aromatic hydrocarbons present in roofing tars on plant and paving site air emissions.