- Pavement Terminology
- Out-of-State Specifications
- California Specifications
- Local Government Testing
- Private Markets and Testing
A roadway is built in several layers: pavement, base, and sometimes subbase. The pavement is the surface layer. Asphalt pavement is usually referred to as asphalt concrete, or AC. The base is made of a layer of aggregate base over a layer of aggregate subbase.
In addition to saving landfill space, the benefits to recycling asphalt shingles in AC include possible economic savings and improved pavement performance.
There may be an immediate economic benefit due to asphalt reclamation. California plants produce fiberglass-based shingles, which are approximately 20 percent asphalt. AC is approximately 6 percent asphalt. So a small percentage of shingles (e.g., 5 percent by weight of aggregate) can displace a large percentage of asphalt binder (approximately 20 percent). Other economic factors include recyclers' tipping fees, costs to grind the shingles, price of virgin asphalt, and transportation costs.
Another benefit may be improved pavement performance. Because the asphalt used in shingles is harder than pavement asphalt, the pavement benefits may include improved resistance to rutting, increased stability, decrease in temperature susceptibility, improved compaction, and improved "rideability" index.
Hot-mix asphalt (HMA) is the most common process to which shingles can be added. Waste shingles are ground and screened to produce 1/2"-minus-size pieces for batch plants, or 1/4"-minus-size pieces for continuous feed plants. The ground shingles are usually fed into and mixed with the aggregate before adding the virgin asphalt binder.
A number of laboratory and field projects in North America have tested shingles in AC. Some of these projects have led to specifications from state departments of transportation (DOT).
State DOTs that allow asphalt roofing shingles in asphalt pavement include:
- Georgia (5 percent, manufacturing scrap only).
- Maryland (5 percent, manufacturing scrap only).
- Michigan (50 percent recycled asphalt spec routinely allows old and new shingles, though shingles are not specifically mentioned).
- Minnesota (5 percent, manufacturing scrap only).
- New Jersey (5 percent in "supplemental" spec, manufacturing scrap only).
- North Carolina (5 percent, manufacturing scrap only).
- Ohio (allows "certain percentage of recycled material").
- Indiana DOT (5 percent, manufacturing scrap only).
- Florida DOT began a test project to develop specifications. It was not finished, for reasons unrelated to technology. According to Mr. Gayle Paige of the State Materials Office, research indicates that shingles can comprise 5 percent of pavement, and even 15 percent if engineered properly.
The City of Brampton, Ontario allows 3 percent new and old asphalt roofing shingles in AC.
The key to opening large California markets for asphalt shingles in asphalt pavement is to allow the shingles in California's construction specifications. The specifications most widely used in California are Caltrans specifications and the Greenbook.
Caltrans specifications are used by Caltrans projects, most local government public works departments in Northern California, and many private projects. Caltrans testing of new road products adds a high level of confidence to a product or method. Caltrans specifications for shingle-content AC would significantly improve marketing prospects for recycled shingles. Caltrans specifications currently do not allow asphalt shingles in AC.
If Caltrans were to write specifications for shingles in AC, the process might include the following steps:
- Test in the laboratory.
- Write draft specifications, which are called Special Provisions (SP).
- Test in the field, perhaps on a heavily trafficked road such as a truck weigh station.
- Monitor for several years.
- Write specifications called Standard Special Provisions (SSP). These SSPs would then be available for routine use in Caltrans and local government projects.
The Greenbook is officially titled Standard Specifications for Public Works Construction.
It is used by the City and County of Los Angeles and 200 other local governments and agencies in the Los Angeles area. Greenbook specifications currently do not allow asphalt shingles in AC.
If the Greenbook were to include specifications for shingles in AC, the process may include the following steps:
- A local government tests the method in the field.
- The local government submits test results to the Greenbook Committee.
- The Greenbook Committee assigns it to a specialized Greenbook committee, perhaps the Surface Committee, which looks at test results, and recommends approval or rejection of the specification.
- The Greenbook Committee votes to approve or reject the specification.
CalRecycle Proposal to Caltrans
Proposal. In January 1997, CalRecycle submitted a proposal to Caltrans Pavement Design and Rehabilitation Committee (PDRC). The proposal suggested that Caltrans (1) write an SSP allowing 5 percent ground factory scrap asphalt shingles in hot mix asphalt pavement, and (2) conduct any tests needed to accomplish this. The proposal included a draft specification modeled after existing DOT specifications from other states.
Cost/Benefit Analysis. In February 1997, CalRecycle submitted to Caltrans a cost/benefit analysis investigating the use of ground shingles in AB and in AC. The analysis was favorable for AC.
Response. Caltrans responded to the proposal in a letter dated May 5, 1997, which indicated that Caltrans is not interested in evaluating shingles in AC at this time.
Local Government Testing
The most promising market at this time may be local government public works. Although local governments usually use Caltrans or Greenbook specifications, they are free to use any specifications of their choosing, or develop their own, for projects using local funds. Local governments could start with existing specifications from other state departments of transportation, and adapt them to local needs; test projects could begin with parking lots and low impact roads. Areas near shingle manufacturing plants may be particularly interested, such as the counties of Los Angeles, Orange, Contra Costa, San Bernardino, and Kern.
Alameda County Project
Alameda County Waste Management Authority gave Raisch Products a grant to research and develop (1) processing equipment to grind shingles, and (2) markets, including but not limited to AC. Findings will be made public through Alameda County and are expected in 1998.
Private Markets and Testing
Private markets include private roads, parking lots, driveways, and farm roads. Although many private owners also depend on Caltrans, Greenbook, or local public works specifications, some may be willing to accept shingles in asphalt, especially if the asphalt is tested for certain quality standards. There are approximately eight private laboratories in California that test asphalt products.
CalRecycle has published a series of fact sheets, case studies, and resource lists on construction and demolition recycling. The are available on line via CalRecycle's online publications catalog, which includes a C&D section. From the catalog you may also order hard copies by e-mail or phone.
The CalRecycle does not publish the following reports, but they are available by contacting the cited sources.
- Evaluation of the Benefits of Adding Waste Fiberglass Roofing Shingles to Hot-Mix Asphalt, July 1997, Ohio DOT, Office of Materials Management, by CTL Engineering, Columbus, Ohio.
- Minnesota's Experience Using Shingle Scrap in Bituminous Pavements, October 1996, Minn. DOT, David Janisch of Office of Minnesota Road Research and Curt Turgeon, Metropolitan Division.
- Influence of Roofing Shingles on Asphalt Concrete Mixture Properties, June 1993, University of Minnesota, Dept. of Civil and Mineral Engineering.
- Mechanistic Evaluation of Asphalt Concrete Mixtures Containing Reclaimed Roofing Materials, N. Ali, Dept. of Civil Engineering, Technical University of Nova Scotia, Canada, Transportation Research Record 1515.
- Evaluation of the Benefits of Adding Waste Asphalt Roofing Shingles to Hot Mix Asphalt, Ohio State University, Transportation Technology Transfer Center, Department of Civil Engineering, sponsored by Ohio Department of Transportation and Federal Highway Administration. Ohio Department of Transportation and Federal Highway Administration.
- Recovery and Reuse of Asphalt Roofing Waste--Incorporation of Roofing Waste in Asphalt Paving, Vol. I (Lab Investigation) & Vol. II (Analysis), Sept. 1986, University of Nevada, Reno, Nevada and Manville Sales Corp., Denver, Colorado for U.S. Department of Energy.