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 Most states in the US initiated legislation to control the flow of waste tires in the 1990s in response to heightened environmental concerns. (Scrap Tire Management Council) For example, in 1989 only five states regulated the flow of waste tires. By 1991, thirty-five states had adopted tire legislation. By 1998, forty-eight states had implemented scrap tire legislation or regulations. Thirty-five states banned the practice of tire disposal in landfills. Fees related to tire sales or vehicle registrations were established to provide funding for pile clean up efforts and to stimulate waste tire market development to divert the flow of scrap tires from tire piles. Funding is typically made available to tire processors through grants or direct reimbursement to product output. This paper focuses on programs within Arizona, California and Florida. Arizona Arizona generates approximately 4 million scrap tires annually. (Arizona Department of Environmental Quality) Of these, three million are diverted to a crumbing facility near Phoenix. Approximately 2.6 million are used in paving applications and the remainder are used in molded products, gardening products, or playground safety material. See Table 6. The remaining million are collected in regions beyond the economically feasible trucking radius of the plant and are either exported to a neighboring state, or shredded and used as daily landfill cover. Although two companies are licensed to operate TDF facilities, the equipment has never been installed. Counties are required to maintain tire collection facilities which take tires from retailers at no charge. The counties then contract with processors paying a negotiated per tire fee to have them processed. The average fee paid to processors is $93 ton. All parties other than tire retailers with manifests or county residents with five or fewer tires must pay a tipping fee when disposing of tires at collection centers. Funds are made available through the Department of Environmental Quality in the form of grants to conduct research and development of emerging technologies which utilize scrap tires.
California produces nearly 30 million waste tires each year. (Vitetta Group, 1999) A $0.25 waste tire fee was initiated in 1990 to provide funding for the reduction of stockpiles containing over 45 million tires in total. The tire program is administered by the California Integrated Waste Management Board (CIWMB). The fee is collected at the point of sale with 10% retained by the tire dealer for overhead. The remaining $0.225 is deposited in the state Tire Fund. Approximately $5 million is generated annually. Based on the amount collected, it appears that approximately 8 million tires escape the fee. The Tire Fund provides for permitting, enforcement and clean up activities, as well as market development programs and administrative costs. Approximately 50% of the annual waste tire flow is diverted to alternative end uses. Table 7 depicts end uses for waste tires in California according to the CIWMB.
Due to large volume of waste tires, limited program funding, difficulties in controlling the flow (enforcement), and economic barriers to alternative end uses, many tires are land-filled or illegally stockpiled. Clean up costs of stockpiles range from $0.54 to $2.26, with a median cost of $1.27 per tire. Recent studies indicate that the tire program is under-funded and legislation is currently being proposed to increase the tire fee and to include tires that are not currently participating in the fee such as wholesale fleet sales and truck tires. Grants are made available through the CIWMB to private enterprise and other public agencies to purchase waste tire processing equipment and for projects which divert tires from the waste stream. The CIWMB conducts an aggressive market development program. Historically, nearly 50% of the Tire Fund has been used for activities such as biennial tire recycling conferences and regional technology centers to name a few. For a more detailed listing of market development programs contact the Board at 1-916-255-2000 or visit the web site: http://www.ciwmb.ca.gov. The Florida tire program was established in 1988. (Florida Department of Environmental Protection) At the time an estimated 18 million tires were stockpiled around the state. Today, less than 3 million tires remain. Clean up costs range from $0.85 to $2.00 per tire. Florida generates approximately 20 million waste tires annually. The waste tire program is funded through the Solid Waste Management Trust Fund which is funded by a $1.00 fee on the sale of each new tire. Funds are also raised by a 0.2% sales tax collection allowance and an annual sales tax registration fee. Over $17.3 million in revenue was generated in 1998. End uses of waste tires are depicted in Table 8.
Land filling whole tires is prohibited by law. However, shredded tires may be used as daily cover. It is assumed by the Florida Department of Environmental Protection that the "missing" 1.6 million tires in the table above were used for this purpose.
Enterprising individuals are continuously developing new technologies to overcome the waste tire problem. Certainly, established government programs encourage growth in these industries. Some notable entries include tire chips as in septic leachate fields, soil amendment, playground safety material and noise absorption systems. Various civil engineering uses of scrap tires in highway applications have been explored extensively in the last decade. Using shreds in light fill in embankments can use large quantities of scrap tires. One use that has been only partially explored is the use of scrap tires in sound walls. Rubber has demonstrated very desirable sound absorbing characteristics. Early technologies involved labor intensive construction of barriers using whole or parts of tires attached to or embedded within the wall structure. Later technologies developed hollow planks or boards filled with crumb. Recent work at Arizona State University’s College of Civil and Environmental Engineering has explored using ground tire rubber in sound absorbing surface coatings for existing sound walls along urban highways. (Zhu, 1999) Ongoing experimentation with the sound absorptive coating has led to the use of no. 8 sieve crumb rubber mixed with liquid acrylic and alkyd polymers in a 1:1 ratio. The material has been applied with conventional spray technologies from the paint and stucco industries. Sound absorption tests are being conducted by Riverbank Acoustical Laboratories in Illinois to determine the amount of decibel reduction that can be obtained from the use of this material. Test sections will be constructed if significant noise reduction levels are obtained in lab tests. Convergent Spray Technology ™ developed for the aerospace industry holds promise for crumb rubber based sound absorbing spray equipment. This equipment mixes the materials, both liquid polymers and dry rubber particles, at the point of dispersion (nozzle tip). This type of technology offers several advantages. The mixing occurs at the nozzle tip, so very little of the mixture is wasted and eliminates mixture storage requirements. Additionally, the equipment has a high volume application rate and provides a uniform and homogenous material. Preliminary testing results for an acrylic based crumb rubber spray are encouraging. The noise reduction coefficient measured by Riverside Acoustical Laboratories was 0.35. This coefficient is a measure of the acoustical absorption performance calculated by averaging sound absorption coefficients at 250, 500, 1000 and 2000 Hz. Sound absorption coefficients range from 0.01 for marble slate to almost 1.0 for long absorbing wedges used in anechoic rooms. Another measurement provided by the testing lab was sabins. A sabin is a measure of the sound absorption of a surface; it is the equivalent of one square foot of a perfectly absorptive surface. Table 9 provides some preliminary measurements of the crumb rubber based spray. It should be noted that the specimen area was roughly 64 square feet to give meaning to the sabin measurements. Additionally, the material was more absorptive in relation to higher frequencies which are more typical of highway traffic noise. Future tests should provide greater sound absorptive figures. The first sample was relatively dense due to higher percentages of polymers in the mix. The next sample to be tested will be from the nozzle mixed equipment which allows for lower percentages of liquid polymers in the mix. Tests should be available on the web-site: www.rubberpavements.org by December 1999.
Rubber
Pavements Association
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