Recycling Asphalt Roofing Shingles
What are Asphalt Shingles?
The asphalt shingle is an American invention that was first used in 1901. Their popularity soared in the following years, driven by their relatively inexpensive costs and their simple installation methods. By 1939, 11-million tons of asphalt shingles were being used nationwide in the U.S.
Where the Asphalt Comes From
The asphalt in the shingles is the same as the asphalt used in road construction. It is mostly derived from the distillation of crude oil during the refining process (although some asphalt is mined from natural sources). During the refining process, crude oil is boiled at 977 degrees Fahrenheit, and the lighter fractions of the oil (i.e., gasoline, kerosene, diesel, etc.) are vaporized and collected separately via distillation. What is left over is a thick, semi-viscous bitumen termed “asphalt.” About 70% of the asphalt produced in the U.S. is used in road construction, and a large portion of the remaining 30% goes to roofing, including shingle construction.
Asphalt Shingle Construction
The basic construction of an asphalt shingle consists of a flexible base material, onto which asphalt is impregnated. The upper surface of the shingle is covered with granules of ceramic, schist, stone, vitrified brick, quartz, or slate, while the back side is covered with mica, sand or talc to stop the shingles from sticking together when they are stacked/palletized before use. The top surface granules help block ultra-violet light, which causes deterioration of the shingles and provides some physical protection of the asphalt. The upper surface coating also gives the shingles their color. Some shingles have copper or other materials added to the surface to help slow down the growth of algae on the shingles.
Asphalt Shingles and Building Codes
Asphalt shingles have been improved over the years. Prior to 1960, the base material the asphalt is applied on to was either felt or other material of organic origin. After 1960, fiberglass and materials of non-organic origins were used in shingle construction. Adhesive strips were added to give the shingles better ability to withstand windstorms; important to coastal cities on the Atlantic seaboard and the Gulf of Mexico, where hurricanes and large seasonal storms in the 1990s and 2000s caused building codes to become more restrictive. The American Society of Civil Engineers has published ASTM D7158 as the standard most United States residential building codes are based on. Asphalt shingles are fastened to the roof deck using either staples or roofing nails, and the attachment technique must abide by the building code currently in place.
Lifespan of an Asphalt Shingle Roof
The long-chain hydrocarbons in the asphalt are what provide the protective nature of the asphalt shingle. Over time the sun’s rays cause the asphalt to deteriorate, and rainfall gradually washes out the asphalt and protective cover. Eventually the loss of the heavy oils causes the shingle to shrink, and it starts to lose its waterproofing qualities. Ultimately, the time arrives when the roof needs to be replaced. An asphalt roof should last between 20 and 40 years, though most shingle manufacturers will only guarantee their product for 15-25 years.
Several Million Tons of Asphalt Shingle-Waste are Generated Each Year
Currently, the amount of waste asphalt roofing shingles generated in the U.S. is around 11 million tons every year. Re-roofing jobs make up about 10 million tons of this total, with another 1 million tons coming from scrap material derived from the shingle manufacturing process. These quantities generally fluctuate with the fortunes of the building industry. A major natural disaster might also cause roof-damage across entire metropolitan areas—such as what happened from Louisiana to Florida along the Gulf Coast during the 2004 and 2005 hurricane seasons.
Recycling – the Best Way to Handle Shingle-Waste
As landfill availability decreases and waste tipping-fees increase, solid waste operators are becoming more interested in finding alternative ways of managing shingle-waste. Asphalt shingles have great potential for recycling, rather than just throwing them away.
Shingles in the waste stream might contain old shingles made with the old felt/organic mat or the newer fiberglass mat. The waste stream may also contain nails and bits of wood from the roof deck, if it was also replaced or repaired.
The recycling of asphalt shingles begins with grinding the waste. The size of the ground shingle pieces depends on the type of grinding equipment used and what the ground shingle-waste will be used for. After grinding, the shingle-waste must be purged of contaminants. A powerful magnet is used to remove the excess bits of nails or staples, and this metal is recycled separately from the shingle-waste. A method for removing wood-bits is to flood the shingle-waste in a water bath and float the wood-bits away. The bath also serves to clean the waste grindings.
Seven Ways Asphalt Shingle-Waste is Re-used
1. Asphalt Paving Material for Roads
Ground shingle-waste is added to hot-mix asphalt road-paving mix, where it can replace up to 20% of the virgin asphalt that would be needed as a binder. The states which allow this each have their own rules pertaining to how shingle-waste can be used for road-paving mixes. The shingle-waste supposedly improves the quality of the road-mix; increasing pavement’s resistance to wear, resistance to moisture, and decreasing the tendency for deformation and rutting, fatigue-cracking, and thermal wear.
2. Aggregate Base and Sub-Base for Roads
Another use for ground asphalt shingle-waste is to use it in the aggregate base and sub-base used in road-paving. The aggregate base supports the asphalt road pavement, and shingle-waste added to this aggregate can improve its compactability.
3. Cold Patch for Potholes
Asphalt shingle-waste makes a useful material for patching potholes in roadways. It can also be used to fill utility cuts as well as repair sidewalks, bridges, driveways, ramps, and parking lots.
4. Ground Cover
Ground shingle-waste can be used as a ground cover for dust control on bare ground. It is also an economical alternative to using gravel, stone, or wood chips in low traffic areas, and low-traffic farm lanes/rural roads, etc.
5. Expansion Joints
Fine ground shingles combined with virgin asphalt can be made into expansion joints for concrete pavements.
6. New Roofing Materials
Some business entities have experimented with using asphalt shingle-waste as feedstock for the manufacture of new shingles. This has been somewhat hampered by quality-control issues with the recycled shingles feedstock and the assimilation of recycled shingles into the manufacturing process.
7. Fuel Oil
The asphalt may also be recovered from the shingle-waste and then be refined into fuel oil for domestic or industrial use.
Potential Asbestos Exposure
Between 1963 and 1977, three of the largest shingle manufacturers in the U.S. added small amounts of asbestos (0.02%-0.00016%) in the fiber mat of their shingles. USEPA feels that after 2016, most roofs containing the asbestos-impregnated shingles will have already been replaced, so asbestos in shingle-waste should not be an issue after that time.
Summary of Asphalt Shingles
Asphalt shingles were developed in America and have been in use since the early 20th Century. Their popularity stems from their low-cost and ease of use. An estimated 11-million tons of asphalt shingle-waste is generated in the U.S. each year. Fortunately, much of this can be recycled into other products and uses. This material works well when integrated into road-paving, and for repairing potholes in roads. It also makes really good ground-cover, and can be used in expansion joints by the concrete-laying industry. The asphalt from the shingle-waste can further be recovered and converted into fuel oil. Experimentation has also taken place to integrate shingle-waste into new shingle construction.