According to the Industrial Resources Council, over 300 million scrap tires are generated annually of which almost 40 million end-up in landfills each year. This is in addition to about 180 million tires in stockpiles. The three major markets for scrap tires are: fuel, civil engineering applications, and ground rubber. Of the three, tire derived fuel(TDF) is by far the largest market with users including cement kilns, pulp and paper mills, electric utilities, and industrial facilities. TDF is popular because the energy provided by tires is comparable to that of oil and greater than that of coal, plus tires are low in sulphur and NOx gas emissions.
However, the use of shredded scrap tires, also referred to as tire-derived aggregate(TDA), and rubberized asphalt concrete(RAC), is showing great potential for road construction applications as well as a way to divert a significant number of tires. TDA has ideal properties for civil engineering use, is generally a low cost option, and can use large-scale numbers of scrap tires. RAC, which is made by blending ground tire rubber with asphalt to produce a binder and then mixed with conventional aggregate materials, has many of the same advantages. It is cost effective, durable, safe, quiet, and environmentally friendly.
Among the uses that have been found for TDA are slope stabilization, retaining wall backfill, lightweight embankment fill, vibration mitigation, various landfill applications, and more.
The California Department of Transportation(Caltrans) first used TDA to successfully repair sections of Highway 101 in Mendocino County in 2009. TDA was used because of its lightweight properties and low cost. It saved Caltrans $320,000, and in the process, used about 270,000 scrap tires. Meanwhile, the California Department of Resources Recycling and Recovery (CalRecycle) has partnered with local governments to successfully use TDA on landslide highway repair projects in Mendocino and other counties.
The state of Arizona has had excellent success with RAC. The number of RAC projects has increased from 1 in 1988 to 54 in 2000 and have used over 14 million scrap tires in the process. Using RAC means that much less material is used than would be typically required of conventional asphalt material making it exceptionally cost effective. Ongoing road maintenance is also reduced because RAC lasts longer – often 50% longer. On top of all that, RAC reduces noise. Research has shown that noise can be reduced as much as 85 percent in some instances. RAC also provides better traction and visibility in wet weather making the roads safer to drive on. Finally, RAC is environmentally friendly. A one-mile section of four-lane highway using RAC will result in 8,000 scrap tires not going to landfills!
For heavy/highway contractors, if saving money and helping the environment warm your cockles, you might want to explore these options in the near future.