Introduction
A tire is made of rubber compounds, steel and fibers. A normal passenger
automobile tire that contributes to the 84%1)
of annual waste tire generation is designed for supporting more than 600
lb. over 20 in2 (approximate contact area of the tire with the
ground). A tires typically last an average of 50000 miles2)
under a variety of road or ground conditions.
Rubber, which is the principal element of the tire, is a thermoset
material whose individual chains have been chemically linked by covalent
bonds during polymerization or by thermal treatment during fabrication.
Once the bonds are formed, these crosslinked networks resist heat softening,
creep and solvent attack, and cannot be thermally re-processed. Such
properties of rubber make it possible to use tires under severe conditions.
The other elements, such as steel and fibers, are also required to have
durability and strength, and all components are chemically or physically
bonded together.
Tire disposal requires special solid waste management because of their
particular properties. The durability and strength of tires make their
disposal and reprocessing extremely difficult. Tires are virtually immune
to biodegradation.
In landfills, tires occupy a large volume since approximately 75% of
the space that a tire occupies is void3).
Tires tend to float or rise in a landfill and come to the surface, piercing
the landfill cover. Therefore whole tire landfilling is undesirable today.
Shredding or splitting the waste tires eliminates the buoyancy problem
and transforms the tire into a material that can be easily landfilled.
However shredding requires additional processing costs, and the processed
material remains immune to biodegradation.
Today, in the U.S., over 48 states have adopted regulations for the
management of scrap tires and over 35 states have banned whole tire landfills4).
Tire stockpiles provide breeding sites for mosquitoes and create fire hazards.
Mosquitoes are a nuisance pest as well as a vector for disease5).
Tire fires are very difficult to extinguish. The toxic gases that
are released pollute the air and fire by-products contaminate the soil6).
The stockpiles have been considered as public health issues.
Ultimately, the best solution to these problems is the elimination of
the stockpiles, which has been the main focus of waste tire management
over the past ten years.
Tire stockpiles have been reduced from 2-3 billion in 1990 to
800 million in 1996 to 500 million in 1998. The maximum recovery
rate was about 70% in 1996, and it was expected that the rate would reach
90% by the end of 1999. However, the facts indicate that, at the
end of 1998, the recovery rate had dropped to 60%.
Thus, the data demonstrate that we still have some serious difficulties
with regard to waste tire management.
Today, in the U.S., approximately 270 million tires are disposed of
each year.
References
Back to Top
| Go to Next