By John Davis
The use of recycled asphalt shingles (RAS) in asphalt pavement throughout the U.S. is steadily increasing. Using RAS saves money, conserves resources and can produce good quality pavements.
According to the U.S. Environmental Protection Agency, approximately 11 million tons of asphalt roofing shingles are disposed of each year. About one million tons is waste produced by the roofing manufacturers and about 10 million tons is waste produced by residential tear-off shingles. The 11 million tons amounts to about 8 percent of the nation’s total building-related waste. Recycling this waste stream makes economical and environmental sense.
The composition of shingles makes them an especially appropriate material for use in asphalt pavements. Shingles are typically composed of 25 to 30 percent asphalt cement, 40 to 60 percent hard aggregate contained on the 30 and 60 sieves and 3 to 12 percent fiber. All of these ingredients are routinely used in hot mix asphalt (HMA) pavements.
The economic benefits of using RAS are several. Recycling them can save the cost of the shingle manufacturer transporting them to an available landfill and paying the tipping fees. Depending on the quality of the shingles, RAS can reduce the amount and the cost of the virgin asphalt and fine aggregate used in the HMA mix.
The environmental benefits of using RAS in pavement are twofold. Recycling shingles conserves space in crowded landfills and reuses valuable resources —asphalt binder and fine aggregate.
States and local agencies around the U.S. are using RAS on county, city and state roads. They are using RAS in aggregate base courses and for granular base stabilization on local roads. Paving contractors in many states are using RAS for parking lots, private driveways and in HMA mixes for varied purposes such as patching and temporary roads. Commercial Paving of Scarborough in Maine has been routinely using RAS as a base and subbase material on private and city projects for several years. One Florida contractor has been using recycled shingles for eight years on city streets and county roads.
The most promising future market may be local governments. Over the last ten years, Minnesota DOT (MnDOT) has been doing laboratory and field tests with RAS on hiking and biking trails and on town and county road sections. The tests have shown positive results.
Georgia DOT has experienced good results using RAS on local roads. They have modified their specifications to allow for 5 percent factory scrap shingles and tear-off shingles in the total mix.
Issues with RAS
Of course, there are some economic and material issues with using RAS that contractors must address. Shingle scrap from the roofing manufacturer is usually clean, and requires a minimum of handling before it is processed. But tear-off shingles are another story. The tear-offs must be sorted and all waste materials, such as wood, metal and nails, removed before they can be processed. Consequently, the cost of using tear-offs is higher than manufacturer’s scrap shingles.
“There are more costs involved,” says Todd Genovese of Lafarge North America in Westminster, Colorado. “Handling and cleaning the tear-offs makes the cost higher, but we are some distance from a shingle manufacturer so it is economical for us to use tear-offs rather than manufacturer’s scrap.”
“We have found,” adds Genovese, “that even clean shingles are not always clean. They must be cleaned again. We subcontract the first handling and cleaning, and the second, if necessary.” He says that asbestos monitoring in tear-offs is also “a cost that we have to consider.”
Oxidation is more extreme in tear-off shingles than manufacturer’s scrap shingles, which means the addition of a softer binder to met agency mix design specs.
After cleaning and sorting the load of manufacturer’s scrap or tear-offs, the processor must grind the RAS particles to state and local agency specifications—or to the contractor’s specifications, if RAS are being used on a private project.
The size of the processed shingle particles is important. The processor will grind RAS in a range of ¼-inch to 2-inch particles, depending upon the use of the material. If the RAS is being used in base stabilization, it will be a larger particle. If the RAS is being used in an asphalt surface course, it will be ground to between a ¼-inch and ½-inch size. Five percent by weight of mix is a typical application rate for using shingles in HMA.
Another issue that the hot mix producer must address is the hardness of the asphalt cement in the shingles. The asphalt cement in the shingles is usually air-blown and is substantially harder than the normal asphalt binder used in a standard HMA mix. So the HMA plant operator may use softer asphalt, such as a PG58-28 versus a PG64-22, to offset the harder asphalt contained in the shingles. In several states where RAS are being used, the state or local agency requires the HMA producer to use PG blending charts to properly design the mix.
Hot mix producers must also be aware that they need to keep the shingles in the plant long enough to melt the hard asphalt. This is called “dwell time.” Plant operators may raise the mixing temperature to 310 or 315 degrees to properly melt the shingle asphalt.
Finally, there is the asbestos issue. Because some shingles last 20 years or more and some roofs are covered with double layer roofing, re-roofing waste may contain asbestos until for the foreseeable future. Although there is only a miniscule quantity each year, government laboratory tests are required to quantify asbestos content. OSHA regulates asbestos workplace exposure. EPA regulates handling and disposal.
Getting started using shingles
A question frequently asked by asphalt paving contractors is, “How do I get started using shingles?” and “How do I know if it’s economical for me to use them?”
Tom Peterson of Colorado Asphalt Pavement Association says “the three key considerations for a paving contractor in deciding to use asphalt shingles, are the availability of the supply; the up-front costs of processing the shingles; and the openness to use of the shingles by counties, cities, states and pavement consultants.” He adds that “checking out the quality control of the shingles processing is also a key consideration.”
If there is a shingle supplier nearby, and if the handling and processing costs are less than the supplier’s transportation and tipping fees, and if the local agencies are open to the use of shingles in pavement, the HMA contractor may find it profitable to enter the RAS market.
Perhaps the one most important consideration is that the local agencies have specifications that allow shingle use. In some instances, the contractor might have to do a demonstration project to show that RAS performs well.
Cooperation equals success
“We’re successful because we sit down with the local agencies and discuss the benefits of using shingles,” says Steve Jackson of West Contracting in St. Louis. He says the big thing that scares most agencies is the fear of the unknown, because they have never used shingles in their pavement.
“Budgets are also important,” says Jackson. “We discuss the material and the cost benefits with the engineers. We have a dollar and cents discussion.”
Jackson claims that the biggest reason for the success of Missouri road contractors on the state level is the cooperation between them and the Missouri DOT (MODOT). “We have quarterly meetings together where we pound out the issues,” Jackson says. “We’ve developed good communication between all parties. Missouri is one of the top users of recycled shingles in the U.S. The state is looking at using 48,000 tons of shingles on state road work in 2011.”
Across the nation, state and local agencies have noted that pavements containing asphalt shingles have shown satisfactory performance. Agency spokesmen say they see some increased resistance to wear and decreased rutting and deformation, but they generally agree that shingle pavements have not been down long enough to reach any categorical conclusions.
Research by Ross Associates in North Carolina showed that adding 5 or 10 percent shingles “significantly hardened asphalt binder, but showed decreased susceptibility to rutting because of the asphalt stiffness and shingle granules.”
Mix sampling by Georgia DOT showed that HMA mixes containing RAS performed similarly to conventional HMA mixes. Georgia DOT testing showed that pavement containing shingles compared favorably with conventional mix pavements. The DOT modified their specs to allow factory scrap and tear-off shingles at the rate of 5 percent by weight of the total HMA mix.
Missouri is one of the nation’s leaders in the use of RAS. They did their first RAS job in 2005 and it has performed well. Nearly all of the 13 major road contractors in Missouri are currently doing some RAS work.
MODOT recently put a “green credit” clause in its spec, which set a green credit incentive and bonus. By using shingles or RAP, or both, the contractor gets a credit—and a bonus. The use of RAS is spreading, and so are its “green” aspects.