Results

Early technologies

Many of the early technologies were developed specifically with intent to solve the waste tire problem. Sustainable markets did not exist and government involvement was required to assist in market development, to provide capital investment or equipment, or secure markets to reduce new market entry risks. Unfortunately, this tactic was not very successful because it usually required focusing on only one end use of tires while ignoring the others due to limited funds. Competition among the waste tire industries involved often created a position of stalemate so that in the end limited progress was accomplished to reduce the waste tire problem. Risk levels were extremely high when markets were not guaranteed for a dedicated and exclusive end use. This caused likely entries into the waste tire market to hesitate in committing large capital investments in plants and equipment which could process tires as fuel or reduce them to crumb.

However, in cases where certain technologies have been exclusively guaranteed, the waste tire problem either continued to grow beyond facility capacity or the economics of moving waste tires to a specific site had proven to cost more than was sustainable. Public opposition to technologies requiring combustion has also slowed growth in the United States out of fear of contributions to global warming or hazardous emissions. Although these fears seem unfounded, it has definitely caused a down turn expanding TDF markets further.

Pyrolisis technologies offered hope to waste tire program managers in the US during the 1980s and early 1990s. The process involves submitting tires to intense temperatures in a vacuum. The tire decomposes into its base elements, steel, petrochemicals and carbon black. The costs associated with plant construction and lack of sustainable markets for the pyrolitic products have severely limited the growth of this industry. Additionally, failed attempts in establishing this technology have been notorious for abandoning millions of tires at sites throughout the US. This industry, unfortunately, has not had a successful track record.

Mono-filling of tires in landfills or burying tires only at other dedicated sites has been used occasionally to prevent the build up of waste tire stockpiles. This practice could be considered to store tires for future economical or profitable uses but is not currently well controlled. The most significant problem is that the tires or shreds are not protected from soil contamination. Future users will have to first clean tire material unless the developed technology can utilize soiled tires. The mining costs associated with tire recovery could be prohibitive and new waste tires will remain the most economical source of recycled tire rubber.

4.2 Environmentally Economic Solutions

New approaches to solving the waste tire problem should integrate sustainable technologies that provide continuous benefit to the public. Combustion technologies are effective in the disposal of large quantities of waste tires and should be used where feasible and acceptable to the public. However, the combustion of tires does not provide a continuous public benefit and results in a net energy loss when all is considered. Although approximately 15,000 BTUs are recaptured when a tire is combusted, 30,000 BTUs were expended to create each tire. In contrast, the United States Department of Energy has estimated that over 90,000 BTUs can be saved by utilizing asphalt-rubber through reduced materials usage and its long lasting performance (Gaines and Wolsky, 1979). However, the TDF technologies will continue to play an important role in the reduction in waste tire stockpiles. Most importantly, solutions to the waste tire problem must be sought and a stand-off avoided.

5.0 Conclusions

Crumb rubber can not be considered a waste material. It is a valuable commodity with ongoing expansion and growth in diversified markets. Its use in asphalt is not making a highway into a linear landfill. Crumb rubber has proven to be one of the only additives to hot mix asphalt derived from a waste material that has a beneficial impact and actually improves performance. Some conclusions from studying this market may include:

Crumb rubber production is an environmentally economical sound method of waste tire reduction,

Asphalt Rubber has proven long term performance, cost effectiveness, and sustainable market growth, and

Asphalt Rubber paving programs are key components to acceptable and successful waste tire management programs.

All options must be considered to reduce the build up of waste tires. It is far better to remove tires from the waste stream, regardless of disposal method, than to allow the continuation of uncontrollable and disastrous waste tire stockpile fires through out the world. Without question, the emissions from equipment and facilities that process waste tires will always be lower than the emissions from a waste tire fire burning out of control in the open demonstrated by Figure 7.

Figure 7 — Filbin/Oxford tire fire, California, USA. Photo courtesy Sacramento Bee September 1999. Six to Eight million tires in flames.