The Importance of Tire Recycling

Old Tires Are Being Increasingly Utilized

What Is Tire Recycling

Tire recycling is the process of converting end-of-life or unwanted old tires into material that can be utilized in new products. End-of-life tires typically become candidates for recycling when they become no longer functional due to wear or damage, and can no longer be re-treaded or re-grooved. 

 Background

There are over one billion end-of-life tires generated annually, worldwide, and it is estimated that four billion unwanted end-of-life tires exist in landfills and stockpiles.

Scrap tires are generated at about the rate of one per person in the US, or about 300 million per year, and as a result, the importance of tire recycling cannot be understated. Going back 100 years or so into the history of tires, tire recycling was a priority, with the price of an ounce of rubber rivaling the price of an ounce of silver. Such economic incentives faded, however, with the introduction of synthetic rubber made from cheap imported oil, as well as by the adoption of steel belted radial tires which were much more challenging to recycle. As a result, worn out tires increasingly found their way to landfills or were often dumped illegally, creating unanticipated hazards. Fortunately, tires are now increasing diverted from landfills. While there was a market for only 17 percent of old tires in 1990, this had risen to 80.4 percent by 2003, according to the U.S. Environmental Protection Agency.

The Urgency of Diversion

Tires sent to landfills or dumped illegally are a significant concern. Old tires provide shelter for rodents, and can trap water, providing a breeding ground for mosquitoes. In landfills, tires consume up to 75 percent air space, In addition, tires may become buoyant and rise to the surface if they trap methane gases.

This action can rupture landfill liners that are designed to prevent contaminants from polluting surface and ground water. Approximately 700 to 800 million old tires were estimated to be illegally stockpiled in 1994, with that total reduced to approximately 275 million by 2004. Recycling has been assisted through such programs as the Tire Stewardship BC Association and the work of leading recyclers such as Liberty Tire Recycling.

Of the 233 million tires utilized in 2003, proportion by use included:

  • retreaded – 7.1 percent
  • used as fuel - 44.7 percent
  • recycled or used in civil engineering projects - 19.4 percent
  • converted into ground rubber and recycled into products - 7.8 percent
  • converted into ground rubber and used in rubber-modified asphalt -4.3 percent
  • exported - 3.1 percent (often for use as retreads)
  • recycled into cut/stamped/punched products - 2.0 percent
  • used in agricultural and miscellaneous uses - 1.7 percent

 

Markets for Scrap Tires

The three largest markets for scrap tires include tire-derived fuel (TDF), civil engineering applications, and ground rubber applications/rubberized asphalt.

Tire Derived Fuel
About 130 million end-of-life tires, amounting to 45 percent of the industry total, were utilized as TDF in 2003.

EPA acknowledges tire-derived fuels as a viable alternative to the use of fossil fuels, as long as proper regulatory controls are in place. Scrap tires are prized for their high heating value, and are used effectively in Portland cement kilns as well as other industrial applications.

Depending on the type of combustion system, tires can be burned whole or in shredded form. Oftentimes tires must be reduced in size to fit combustion units, in addition to other preliminary processing. EPA notes the following benefits to burning tires for fuel:

  • Tires produce the same amount of energy as oil and 25% more energy than coal;
  • The ash residues from TDF may contain a lower heavy metals content than some coals;
  • Results in lower NOx emissions when compared to many US coals, particularly the high-sulfur coals.

    EPA stresses that facilities utilizing TDF should have a tire storage and handling plan, necessary permits for applicable state and federal environmental programs; and be in compliance with all the requirements of that permit.

    Civil Engineering Applications
    Civil engineering applications are diverse. They can replace other materials such as polystyrene insulation blocks, drainage aggregate, or other types of fill. The EPA notes that significant material for civil engineering applications come from stockpiled tires, which are usually dirtier than other sources of scrap tires and can be used as embankment fill and in landfill projects.

    Ground Rubber Applications
    Ground rubber is used to manufacture a number of products, ranging from asphalt rubber, through to track material, synthetic sports field underlay, animal bedding, and more.

    The largest use of ground rubber is for asphalt rubber, utilizing approximately 220 million pounds or 12 million tires annually. The largest users of asphalt rubber are the states of California and Arizona, followed by Florida, with usage anticipated to grow in other states as well.

    Examples of other uses for ground rubber include:

    • Groundcover under playgrounds
    • Playground tiles
    • Anti-fatigue mats
    • Animal bedding
    • Running tracks
    • Equestrian footing
    • Underlay and infill for athletic fields

    Emerging Trends

    Innovative technologies for tire recycling continue to emerge, as well as ideas for closing the loop on material recovery. For example, Timberland has launched a tire which at end-of-life, plans to recycle into footwear.