Rubberized Asphalt Concrete
Source Reduction and Improvement of Content
Not only is tire incineration dangerous, it is also unnecessary. There are a number of much better solutions to the tire waste crisis.
Reuse and Recycling
Tires and tire material can often be reused. One method of reuse is tire re-treading.1 Since about 60% of the tire material is in the casing, re-treading can make a significant impact. A quality car tire can be re-treaded about three times, and larger vehicles can be re-treaded as many as 12 times. Unfortunately only 10% of cars and light trucks are re-treaded. If this were to change, the result would be a major reduction in tire waste.
Tires can also be utilized for an almost unlimited range of creative uses including auto parts, sound barriers, and railroad ties, just to name a few. They should not be considered safe for use in playgrounds, however. See safehealthyplayingfields.org and the Tireless and Non-Toxic Playgrounds and Fields Facebook page for information on why tires should not be used in playgrounds. Further resources on the hazards of ground-up rubber tires in playgrounds, athletic fields, or garden mulch can be found at Environment & Human Health, Inc. (Yale toxicologists), No Toxic Turf, Turf Grass Forum, and SynTurf.org.
A good place to look for ideas on tire reuse is the "Recycling" page of Montanans Against Toxic Burning (the source of the above statistics).2 The Rubber Manufacturers Association's report on Scrap Tire Markets is another great source of information on markets other than TDF burning.3
As with all waste management solutions, source reduction and reuse are the highest goals. However, it's also necessary to recycle as much as possible, without "downcycling" the material to a lower use that can no longer be made back into the same product. Actual recycling of scrap tires is very rare, but recycling technology is advancing and becoming more of an option. For details, read the report on "Increasing the Recycled Content in New Tires" published in May 2004 for the state of California.4
The Canadian province of Nova Scotia has banned landfilling and incineration of tires in 1996. Nova Scotia has a strong tire recycling program. In Kemptown, a company named Atlantic Recycled Rubber Inc. uses a patented cryogenic process to freeze scrap tires, remove fibers and metal wire, and produce crumb rubber sorted into different mesh sizes to be recycled into various rubber products.
Rubberized Asphalt Concrete
Rubberized Asphalt Concrete (RAC) is a "downcycling" use of scrap tires that could drastically reduce this waste stream. RAC is created by a process in which tires are shredded and ground into dust, then mixed with traditional asphalt. The result is a high quality concrete that can be used to pave roads. RAC is already in use in California, Arizona, Florida, and around the world. According to Joyce Eden of West Valley Citizens Air Watch, "Most if not all of the used tires could be used in RAC. RAC is better, longer lasting, uses only 2" versus 4" of material to make the road cover, is quieter and...the tires on the cars and trucks last longer because the surface is more giving." 5 The California Integrated Waste Management Board noted in 1992 that "Rubberized asphalt has the potential to use all the scrap tires in the State in the future." 6
However there are currently some serious political obstacles to widespread RAC use. The cement industry is generally opposed to RAC because it is more difficult to apply than traditional concrete and it is less profitable because it lasts longer. There are also some legitimate health concerns: There is evidence that RAC may pose an occupational hazard to workers applying it. Additionally, a study performed in 1995 by allergy specialists indicated that dust from RAC could potentially cause serious allergic reactions in motorists who are allergic to latex.7
Still, the benefits of RAC are enticing. Below is an excerpt from the transcript of a Dateline NBC story on RAC.8
MORRISON: (Voiceover) George Way is an engineer with the Arizona Department of Transportation. He showed us this test road. On one side, a stretch of conventional asphalt four inches thick. On the other, just two inches of rubberized asphalt. The difference was striking. Take a look at the rubberized asphalt. Even after seven years of wear and tear it's still nearly as good as new.
(Way and Morrison talking; road)
Mr. GEORGE WAY: Virtually no crack in it at all, in this section, and that's been down seven years.
MORRISON: By golly, it's amazing.
Mr. WAY: It is. It's darn amazing. It's pretty impressive.
MORRISON: (Voiceover) As for the other stretch of road with four inches of regular asphalt, the constant stream of traffic has taken a heavy toll.
Mr. WAY: (Voiceover) That section actually started to crack up the first year, and it's gotten progressively worse every year.
As this excerpt demonstrates, RAC is an impressive and valuable use of tire waste, despite its current problems. For this reason, environmental scientists like Dr. Seymour I. Schwartz advocate the use of RAC. While recognizing that "There are also occupational health concerns arising from RAC use...[which] should be examined more fully to establish if the rubber additive is capable of causing serious health problems", Schwartz insists that "Mandating RAC use is a policy option for realizing its potential for recycling millions of tires per year...." Schwartz recommends that government agencies "offer grants for RAC research that study methods for enhancing the granulated rubber’s effectiveness as an asphalt modifier, and the health effects on workers paving roads. Offer other grants to train paving contractors and workers in appropriate application methods, and to provide an incentive to local governments to use RAC." 9
Possibly the single most promising solution to waste tires is devulcanization, a process by which cured rubber can be broken down and recycled. Recent innovations in this field have opened up a whole new realm of possibility for genuine tire recycling.
Vulcanization is the process by which rubber is combined with other ingredients, heated, and hardened in order to render it into a state where it can be made into products like boots, hoses, raincoats, and tires. It used to be thought that the vulcanization process was irreversible. According to Ron Kovalak, a "master chemical technician" for Goodyear, "Earlier methods devulcanized by using everything from microwaves, cryogenic processes, pyrolysis, ultrasonic waves, alkali metals to organic solvents, which typically yielded 1 to 2 percent recovery." 10
That has changed. Goodyear has recently invented a new devulcanization process that can recover 80% of the rubber from waste tires, which can then be revulcanized and made into new products (including tires).
Dr. Aavram I. Isayev of the University of Akron explains UA's own patented devulcanization process:
"When tires and waste rubbers are devulcanized, they can be reprocessed, shaped and revulcanized in much the same as virgin rubber. Our novel...technology is based on the use of high power ultrasonics...The scope of materials with this state-of-the-art technology includes all kinds of rubbers such as GRT (Ground Rubber Tire), SBR, NR, Silicone rubber, EPDM, etc. and crosslinked thermoplastics like crosslinked PE, EVA, etc. their blend systems, and thermosets such as polyurethane, SMC, etc...This new technology will revolutionize the way rubber and crosslinked plastics are recycled." 11
Dr. Seymour I. Schwartz comments further on the impact that devulcanization will have:
Economically, the market potential of devulcanized rubber should be strong because it is capable of replacing virgin rubber and polypropylene in high-value products at a recycled content of up to 40 percent. Thus, markets will come to it – to the high quality recycled rubber – rather than needing market development efforts to create or promote end uses that often must be subsidized. Natural rubber imports and polypropylene production are each multi-billion dollar components of the U. S. economy, suggesting that the market potential for substitute devulcanized tire rubber products is huge. Perhaps the most immediate uses for devulcanized rubber are in asphalt formulations and in passenger tires.12
Devulcanization is clearly preferable to tire incineration and may very likely be the key to solving the waste tire crisis if the technology becomes practical for widespread use. Duroplas, a corporation in northeastern Maryland, is already paving the way with new chemical devulcanization technology that can use scrap SBR (the rubber used in tires).13
Until devulcanization and genuine recycling processes are fully developed, a practical short-term alternative to tire incineration is the use of monofills. Monofills are disposal sites for shredded tires. They differ from normal landfills because they only contain waste tires and can be retrieved at a later date to be ground into Rubberized Asphalt Concrete or can be devulcanized and recycled into new tires.
According to the California Integrated Waste Management Board, “Shredding reduces the volume and eliminates other problems associated with landfilling and storage” and “...shredding and monofilling tires is a method to safely store this valuable resource...”. Dr. Schwartz adds that "Retrievable storage provides an essential component of a transitional strategy capable of bridging the gap between the present and a long-term future that features true recycling in an environmentally sound manner."9
Monofills are only a temporary solution, but when combined with other technologies like devulcanization, they present a real and permanent alternative to tire incineration.
Aside from the aforementioned alternatives, another important goal is source reduction, that is curbing the quantity of tires produced and the toxic substances within them.
According to the West Valley Citizens' "In 1999, Ford Windstars are using Michelin tires which use 5% recycled rubber. Michelin's tests show that they could use 10% used tire rubber material in new tires and get the same results -- performance and lasting time same as 100% new rubber material. If all tire manufacturers did this, this alone would reduce the amount of used tires by millions of tires per year."14
Dr. Schwartz suggests a strategy to make this happen. Although his proposal is geared toward the state of California, the same concept should apply anywhere. To quote him at length:
Michelin and Yokahama already sell tires with a treadwear rating of 620, which translates to approximately 124,000 miles of expected use, and Goodyear sells a tire with a rating of 540 (approximately 108,000 miles) so there is no question about the necessary technology being available. The only question is how to get the largest number of long-lived tires on vehicles as quickly as possible. Educating consumers to buy long-lived replacement tires at a premium price is the wrong answer. These tires must be installed on new cars as original equipment, so it will only be necessary to convince or require auto makers to install them. The extra cost relative to today’s original equipment tires is small, probably less than $100 per car – a relatively insignificant amount on the average $20,000 price of a new car. Furthermore, the buyer does not see the cost of tires itemized, so the extra cost will not be a factor in the consumer’s decision or cause a problem for the auto maker. Driving their new cars more than 100,000 miles on a single set of tires will be the best marketing device to convince vehicle owners to buy long-lived replacement tires.
I believe that state law should mandate that all new cars sold in California be equipped with tires that have a minimum treadwear rating of 500 (equivalent to 100,000 miles of expected wear). Surely, if the [California Integrated Waste Management] Board can make the case on public health grounds that it is necessary to burn 22 million tires per year as fuel, it can make the case that new passenger vehicles be equipped with long-lived tires in order to reduce the negative health impacts of both uncontrolled fires and controlled burning using TDF.12
- Tire Retread Information Bureau.
- "Tire Recycling," Montanans Against Toxic Burning.
- "U.S. Scrap Tire Markets 2005," Rubber Manufacturers Association, Nov 2006.
https://www.rma.org/getfile.cfm?ID=894&type=publication (796 KB PDF file) [Local copy]
- "Increasing the Recycled Content in New Tires," California Integrated Waste Management Board, May 2004.
- Joyce Eden. Letter. www.portaec.net/local/tireburning/california_integrated_waste.thml.html
- California Integrated Waste Management Board. Annual Report. 1992.
- P. Brock Williams et. al., "Latex allergen in respirable particulate air pollution." JOURNAL OF ALLERGY AND CLINICAL IMMUNOLOGY Vol. 95, No. 1, Part 1 (January 1995), pgs. 88-96.
Also see www.rachel.org/bulletin/bulletin.cfm?Issue_ID=686
- National Broadcasting Co. Inc. DATELINE NBC. (8:00 PM ET) October 23, 1998. http://www.portaec.net/local/tireburning/used_tires.html
- Dr. Seymour I. Schwartz. Letter to California Integrated Waste Management Board. January 21, 1998.
www.portaec.net/local/tireburning/dr_schwartz.html [Local copy]
- AOL News. "Goodyear Patents Process to Recover Rubber from Tires." Wednesday, September 8, 1999. www.energyjustice.org/files/tires/files/goodyeardevulc.html
- "Dr. Isayev's rubber and plastic recycling home"
- Dr. Seymour I Schwartz, Letter to California Integrated Waste Management Board. August 31, 1999. http://www.energyjustice.net/files/tires/files/schwarts2ciwmb.pdf
- West Valley Citizens' Air Watch, "Tire Derived Fuel Issues Summary." March 1999. www.portaec.net/local/tireburning/tire_derived_fuel_issues_summary.html