To date, energy use is recognized as an important component of successful scrap tire management programs within the United States because of its ability to allow scrap tires to be used productively. The net result has been substantial conservation of non-renewable fossil fuels. Good scrap tire management programs recognize the importance of diverse applications, the Handbook states. Thus, when the demonstrated performance of tires as an energy resource is objectively evaluated, many jurisdictions have concluded that the environment is better served by recognizing the value of this resource rather than wasting it while waiting for ideal solutions.
The Handbook goes on to say that the use of scrap tires in civil engineering applications, in some cases , can be a viable alternative to tire-derived fuel. This is because tire derived aggregate TDA , an engineered product made by cutting scrap tires into to millimeter mm pieces, has inherent properties that provide many solutions to geotechnical challenges.
Since it is lightweight, TDA produces low lateral pressures on walls It is a good thermal insulator, in fact, eight times better than soil.
TDA has high permeability, good shear strength, and absorbs vibrations. Each cubic meter of TDA fill contains the equivalent of passenger car tires, the Handbook said. True to its theme, the Handbook looks at ground rubber applications within the context of traditional recycling hierarchy and examines their role in advancing scrap tire markets throughout the U. The documentation should be retained to aid in resolution any subsequent problems or issues.
Much can be learned from the successes and failures of the wide array of strategies used to address this serious problem. This chapter is an effort to capture and share the collective knowledge of U. This can be done through thoughtful application of regulatory policy and available resources along with careful planning and execution of cleanup projects.
Based on the experiences of state and federal authorities in the U. This chapter has provided an outline of the essential elements that states have considered in planning and implementing abatement programs and individual cleanup projects. After decades of catastrophic tire fires and other health-related impacts of illegal scrap tire piles, it is clear that these practices can be effective in protecting human health and the environment from these hazards.
The processing of tires into ground rubber can be done by machinery to shred or grind them and sorting the resulting pieces which will determine its use. Additional processing may be necessary to remove all metal beading dependent on its intended market.
Ground rubber can be used for a wide variety of products, ranging from animal mattresses and traffic cones to athletic surfaces and as additive to asphalt, each of which will be discussed in this chapter. Within the traditional recycling hierarchy, the highest-value applications the special uses to which scrap tires are put for scrap tires use ground rubber itself for its specific performance characteristics. To maximize the value of scrap tire resources, tremendous financial, technical, and creative resources have been devoted to developing tire processing technology to make ground rubber and applications to use it.
Results have been mixed, however. The Rubber Manufacturers Association estimates that, after more than 20 years of concerted effort, only about 17 percent of the waste tires generated in the United States in were processed into ground rubber for use in many creative applications Ref.
Since these applications have historically developed slowly and do not consume enough tires, they cannot be the primary focus of a new scrap tire management program. However, they remain a sound recycling option and an important component of market diversity. Export Other Asphal Exhibit Ground Rubber Market Distribution Source: Rubber Manufacturers Association The energy and civil engineering markets are larger and can be developed more rapidly, so they deserve initial program focus to accelerate full use of waste tire resources.
As a result, this guide focuses on these applications. However, major ground rubber markets can be identified and developed concurrently. In addition, with the experience gained in the United States, it may be possible to accelerate market growth in Mexico. Initial development of civil engineering and tire- derived fuel TDF applications will not prevent ground rubber processors from obtaining scrap tires as needed in the future.
As ground rubber markets develop, waste tires will naturally be diverted to products with higher value. Ground rubber products generate higher product revenue, allowing processors to attract waste tires by charging lower tipping fees. Waste tires generally move to the lowest-cost disposal or recycling option, so higher- markets like ground rubber naturally displace lower-value civil engineering and TDF markets. However, it can provide examples of applications that have a proven ability to be manufactured and a willingness by consumers to purchase, two critical components of market development.
Molded and extruded products - Many products, including mats, bumpers, and other creative products. Rubber modified asphalt and sealants - Addition of ground rubber to asphalt binder to improve highway performance characteristics, including how long the road will last.
Other Primarily Coarse Rubber - Ground rubber is used primarily as colored mulch in landscaping applications. The percentage of ground rubber used in each of the major market segments in is shown in Exhibit , based on estimates made by the U. Rubber Manufacturers Association Ref. I The following sections are intended to identify and briefly describe major market segments, focusing I on those with the highest growth rate in the United States and the greatest potential for initial development in other countries, for example, I Mexico.
This market segment encompasses a wide variety of applications and additional variations within them. The following discussion briefly summarizes the two largest applications within this market segment: synthetic sports turf, and playground safety surfacing.
Synthetic Sports Turf Natural grass is a traditional sports field mainstay, but increasing usage of limited grass fields leads to turf failure, athletic injuries, and unattractive appearance of the field. In addition, standing water during wet weather can prevent use of grass fields and damage the field. Good grass surfaces require routine watering, fertilizing, and turf replacement, resulting in significant maintenance costs.
Damaged grass surfaces may contribute to injuries when the ground is hard, muddy, or loses traction. Awareness of costs associated with maintenance and injuries has led to development of alternatives.
Initial synthetic sports surfaces were developed for indoor arenas where the absence of sunlight prevented use of natural turf. One of the early examples was the Astrodome in Houston, Texas, which caused the trademarked name Astroturf to become a generic description for an early generation of artificial playing surfaces. More sophisticated systems that use ground rubber were developed in the s to overcome some of the issues associated with the initial artificial surfaces.
These advanced turf systems were initially applied in high-profile U. Description The current generation of artificial sports turf uses 7.
The carpet is spread over a sophisticated drainage system capable of removing rain water rapidly and is in-filled with silica sand, ground rubber, or layers of each. A schematic representation of the FieldTurfTarkett design is shown in Exhibit The polyethylene grass-like blades add containment to the ground rubber, and the rubber provides cushioning while the combined synthetic turf system bears the physical forces of athletic activity.
Each manufacturer has variations intended to offer technical or economic advantages. An example of a U. Current Market Status Synthetic sports turf has grown rapidly to an estimated 1, field installations in in North America and hundreds more in Europe, according to the Synthetic Turf Council www.
These installations range from large stadiums to smaller municipal playing fields. The turf has been installed for international football, American football, field hockey, baseball, other sports, and practice facilities. The company FieldTurfTarkett is one of the earliest manufacturers of synthetic sports fields and is believed to have installed more than half of these fields. Many of these companies sponsor web sites identifying regional offices, representatives, and authorized installers.
A partial list of installations in Mexico is provided in Table This list is not complete, but it indicates that there are more than 30 installations in major stadiums and venues in Mexico.
The Necaxa Soccer Club facility, installed in in Aguascalientes, Mexico, is shown below as an example. Some of these installations have been in place for more than 10 years, providing a base of local experience. Furthermore, some of the systems have been tested and approved by the Federation Internationale de Football Association FIFA, the International Federation of Association Football in Zurich, Switzerland governing body for their grass- like performance. Ground Rubber Requirements Each of the major synthetic turf systems uses ground rubber as the primary infill material surrounding the green polyethylene blades.
The type and size of the ground rubber vary depending on the turf manufacturer. Some use primarily cryogenic ground rubber produced by freezing shredded rubber before it is fractured in a high-speed hammermill, a machine that pulverizes the rubber into fine particles. The resulting product has smooth sides and tends to flow easily when applied to a sports field. Others use "ambient" rubber, produced in a series of shear and compression equipment at ambient temperatures. This product tends to have a more irregular surface shape with a more cohesive consistency.
A"crambient" product made by a primary cryogenic process followed by secondary ambient processing to yield hybrid performance characteristics is also used. Piece size requirements for ground rubber also vary by turf manufacturer. The most common distributions of piece sizes for sports fields are 30 mesh and mesh.
The specifications also generally require removal of virtually all the reinforcing fabric and wire that is initially present in scrap tires. Experience has shown that proper quality control of the ground rubber is critical for proper performance of synthetic turf. Approximately 3 pounds of ground rubber are generally used per square foot of synthetic turf, depending on the manufacturer, design, and desired surface characteristics.
As a result, the estimated 1, new fields in North America with an average size of about 7, square meters 80, square feet would be expected to use about million kilograms million pounds of ground rubber in This amount represents continuing growth from the Rubber Manufacturers Association's estimate of fields installed in It is also one of the largest individual ground rubber markets.
Industry participants feel that the market has further potential for growth and has not reached maximum demand. Application Benefits and Issues Virtually any product has advantages and disadvantages, and questions are commonly raised about new products. According to a National Collegiate Athletic Association NCAA study that compared injury rates during the academic year, the injury rate during practice was 4. Other studies indicate that frequency of injury is similar for both surfaces, but that the severity of injuries is worse on natural grass turf.
There are more head, neural, and ligament injuries on natural grass, while there are more epidural, muscle trauma, and temperature- related injuries on synthetic turf Refs. In some cases, budget, knowledge, and the availability of labor may limit proper maintenance of grass fields. Conversely, synthetic turf drains rapidly, allowing use quickly after heavy downpours. In addition, synthetic grass turf can reportedly tolerate up to 3, hours of use per year, about four times more use than natural grass turf, allowing the fields to be used more heavily for different sports.
These factors have fueled its rapid growth. Some questions have also been raised about the synthetic turf system. The following is a brief discussion of major issues and the status or conclusions based on available data. Other surfaces also tend to exceed ambient temperatures, even cement roadways and light-colored sand on beaches.
The New York State Department of Environmental Conservation conducted a study in indicating that surface temperatures of synthetic turf are warmer than natural grass or sand, but that differences in wet bulb globe temperatures that more accurately reflect actual heat stress were similar, with minimal impact on athletes Ref.
Customer reactions have ranged from no concern to limiting use during peak temperature times or using a water spray to cool the surface before use Ref. Metals Leaching -Tire rubber contains zinc, sulfur, and small quantities of other materials that are naturally in the environment at concentrations greater than can be leached by water flowing through rubber above the water table.
These metals are within the vulcanized rubber rubber which has been chemically altered to increase elasticity and decrease temperature sensitivity polymer matrix, but can be leached from the rubber surface by water.
Multiple studies indicate that these metals do not represent an acute or chronic health or environmental hazard under conditions likely to be encountered on athletic fields based on established scientific evaluation criteria Refs.
Organic Chemical Emissions- Studies indicate that a range of organic compounds may be emitted onto or from the surface of ground rubber pieces. Detailed studies conducted in Europe concluded that these materials do not represent a significant hazard to players or spectators in outdoor sports arenas with synthetic sports turf Refs 11 to Maintaining a minimum air turnover rate within the normal building design range was suggested to limit exposure in indoor sports arenas.
These studies were prompted by concerns raised in Europe in Athletic federations examined the data and decided that the surfaces with ground rubber were suitable for use by their athletes.
The issue has been raised again in the northeastern United States. Additional reviews of available data have been prepared, generally reaching the same conclusions about safety and environmental concerns.
A list of representative studies is provided in the reference section at the end of the ground rubber section Refs. None of these studies indicates that the thousands of surfaces in the United States or Europe have caused health problems in athletes or spectators.
Some cite the need for additional data, especially practical data from actual field installations. The U. State of New York issued its report in May with its structured field tests, confirming the acceptability of this material and surface Ref. California is currently planning structured field tests to further broaden the available database Ref. Playground Safety Surfaces Sand, wood chips, and small gravel are commonly used as cushioning materials around playground equipment, but each has limitations.
Wood chips deteriorate with time, causing loss of cushioning and requiring frequent addition of more wood chips.
Sand and gravel are limited in their ability to absorb impact. The development of scrap tire processing technologies created products suitable for use in three alternative types of playground cushioning surfaces that have been accepted in the United States.
Description The three playground cushioning alternatives involving ground rubber in different forms are: 1 loose fill, 2 pour-in-place, and 3 molded tiles. Loose fill, pictured in Exhibit , was the first playground safety material derived from Exhibit Some loose fill is made from fabric- reinforced truck tires or off-road tires to be sure that no wire is present. It is spread under and around playground equipment. A cm 6-inch -thick layer generally provides protection for falls from critical heights of about 3 m 10 to 12 feet , about double the height for an equivalent thickness of traditional materials.
The ground rubber loose fill is normally placed over a substrate that freely drains liquids with a wooden border to keep loose fill from spreading away from the playground area.
Tires are black, but loose fill can also be colored before it is installed to improve the aesthetic appearance of the playground. Pour-in-place installations at playgrounds, shown in Exhibit , use a polyurethane binder to bond ground rubber or buffings from tire retread operations into a protective surface mat 5 to 10 cm 2 to 4 inches thick.
The ground rubber and polyurethane binder are commonly mixed on site in a portable cement mixer and then trowelled into place. A surface layer of colored ethylene- propylene-diene monomer EPDM rubber is generally bonded to the ground rubber base to provide distinctive colored surface patterns or pictures.
Pour-in-place is normally installed over a hard surface such as asphalt to provide a stable foundation. The installation should be designed and tested to provide fall protection from heights associated with the various equipment at the playground. Ground rubber can also be molded into thick interlocking tiles specifically designed to provide protection from falls.
Interlocking Tile Installation Photo courtesy of Calgary, Canada, Parks and Recreation commonly glued to a hard sub-base such as asphalt. Each tile is designed and manufactured to provide a durable surface that meets specific cushioning specifications. Current Market Status All three of these ground rubber products for cushioning playgrounds have been broadly used, but no published market data define the specific quantities of ground rubber used annually for these installations.
It is substantial, but not growing rapidly. Many states have encouraged use of these products through cost-sharing grants, but volumes have been limited outside of these special programs.
California, Florida, Kentucky, and Illinois are among the states that have aggressively promoted this application.
Loose fill is the least expensive to install. It has been widely used in Florida and Kentucky. The primary cost is the ground rubber itself, plus preparation of the base under the loose fill and the border around the perimeter of the area that will contain the ground rubber.
Initial cost is generally more expensive than wood chips, but ground rubber does not degrade, so the annual replacement cost is lower. All loose playground cushioning products must be periodically re-leveled to maintain the desired thickness under and around equipment. The total installed cost of pour-in-place and tiles are typically four to 10 times more than loose fill because of base preparation, the expense of binders, and labor for installation.
Pour-in-place and tiles have been used extensively in California and Florida under state government grant programs that foster market development, but have seen limited use outside of these programs. Ground Rubber Requirements A range of ground rubber piece sizes is used in each of these playground surfaces. Heavy bead wire around the rim of a tire is removed by debeading equipment before tires are processed or by magnets after processing.
The material must be free of particles smaller than 20 mesh to minimize dust generation and small particles that cling to skin and clothes like dirt. Residual fluff from reinforcing fabric in tires is sometimes left in the ground rubber; it may improve resiliency, but it may also decrease the flash point of the mixture and allow it to be ignited by vandals more readily. In both cases, the fabric is removed to improve the efficiency and effectiveness of the binder, and the wire must be removed to minimize scrapes and cuts.
A layer of colored synthetic rubber, known as EPDM ethylene propylene diene Monomer rubber or M-class rubber is commonly added to the ground rubber surface to add color and enhance surface aesthetics. Light colors can decrease light absorption and lower the surface temperature in warm weather. Application Benefits and Issues Durability - Rubber is flexible, resilient, and durable, properties that make it a good outdoor cushioning material.
Some loose-fill playgrounds have been in place for more than 10 years with minimal need to add more ground rubber to replace material lost.
The longevity of pour-in-place and tile surfaces is controlled by the effectiveness of the installation, binder, foundation, and usage, but manufacturers typically project a duration of more than 5 years. Accessibility - Accessibility of equipment by children in wheelchairs or on crutches can be an important consideration. Loose fill's excellent cushioning characteristics also make it less stable under point loads such as wheel chairs, but some products have reportedly passed tests that demonstrate accessibility.
Pour-in-place and tiles have excellent accessibility, so some playgrounds use them for access pathways and around some of each equipment type to assure access.
Loose fill is used in other areas to control cost. Fires have occurred in loose-fill installations, but there were no injuries or environmental damage other than the initial smoke. The California Department of Resources Recycling and Recovery CalRecycle documented a detailed examination of one playground fire site and found no residual environmental damage Ref. Application Public Health Benefits and Issues Latex Sensitivity - A small percentage of people are sensitive to the latex present in some types of rubber.
CalRecycle tested for latex sensitivity in styrene- butadiene rubber SBR derived from scrap tires as part of its comprehensive review of ground rubber playground surfacing. The testing showed no sensitivity using established testing procedures on SBR and EPDM ground rubber, and no documented cases were found in a literature search Ref. CalRecycle's detailed report addresses many of these concerns. It 1 identified no issues that would preclude using the superior cushioning characteristics of ground rubber on playground safety surfaces and 2 fully recognized the benefits of reducing injuries through use of ground rubber.
Impact Cushioning -The primary objective of playground safety surfacing is reducing the impact of falls from equipment, and all three of these alternatives can serve this function as well as, or better than, natural materials when properly installed and maintained Ref. Consumer Product Safety Commission has prepared a guide that provides detailed data and discussion of safety parameters for playgrounds, including surfaces.
It is available on the web site at www. This market is very versatile and can create a wide variety of products ranging from pet toys, car bumpers, gaskets, and garden hoses to complex components for medical and electrical equipment. These products represented 36 percent of ground rubber usage in the United States in This market is continuing to grow. It is a diverse market in terms of products and manufacturing technology and may have significant potential applicability in Mexico.
The objective of this summary is to identify major product categories and technologies, and then provide references for additional depth. Description Molded products have been made from buffing dust rubber particles removed from a tire carcass during retreading for many years, but the range of products and the size of the markets have expanded significantly in the past 5 to 10 years. Three primary technologies are used to produce Sample of molded rubber traffic cone Photo courtesy of Candy Lee products that use ground rubber by itself or in blends with other materials.
The following is a brief discussion of these technologies. Molded Products Many initial products were relatively small molded parts such as wheels for trash cans. There are many variations in molding technology, all using a similar basic process.
A primary raw material or mixture is pretreated to allow it to flow into a mold where the material is cured, cooled, and released from the mold to yield a solid designed shape that meets defined specifications. Pretreatment can involve heat, mixing, and additives to create a semi-viscous homogeneous raw material. Once it has been introduced into the mold, temperature, pressure, and reaction time allow the material to solidify. There are also broad variations in degree of automation, balancing capital and labor costs for a specific operating environment.
This basic technology has been fully demonstrated with many polymers and rubber materials, including mixtures with ground rubber.
Each component of the process requires experimentation to optimize efficiency and product quality. This technology can be labor intensive in its basic form, making Mexico's labor economics potentially attractive to the manufacturing of these products as well as to increasing employment. One example and potentially viable market that uses this process is the production of traffic cones also known as road cones, safety cones, or pylons.
The cone base is produced through compression molding of ground rubber obtained from scrap tires. The cone portion is made from recovered plastic material. The recycled materials content can range from 50 to percent, depending on the production process, making these products environmental friendly. More information on the use of ground rubber in traffic cones can be found on line at www. Bound Systems Bound or bonded rubber products generally refer to use of polyurethanes, sulfur, latex, or other ingredients to bond particulate materials into a desired product.
This is sometimes done using pressure and temperature to increase density or optimize efficiency. This technology was initially used on large, low-volume products such as railroad crossing fillers and speed bumps. With improved binders and product creativity, a broad range of higher-volume products have been produced and marketed successfully. The initially simple welcome mats using bound ground rubber evolved into attractively designed mats with mass market appeal, becoming a major consumer of ground rubber.
Other mats gained acceptance in agricultural, recreational, and building applications. For instance, mats placed in livestock areas have been shown to increase milk production in dairy cattle and enhance weight gain in beef cattle. This provides an economic driving force for this large, established market segment in North America.
The playground safety tile discussed in the preceding section is an example of a bound product. It can also be manufactured as sized sheets. Many binders have been used, but polyurethanes and sulfur are the most common. Sulfur is considered more durable and suitable for ultraviolet UV exposure in outdoor applications.
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EPA's comprehensive waste management program. RCRA directed EPA to prepare guidelines for purchasing retread tires in federal agencies and agencies using federal funds to purchase supplies. These guidelines were issued in November As of November 17, , all agencies of the federal government which purchase tires were required to implement a preference program favoring the purchase of retread tires or tire retreading services to the maximum extent practicable.
These programs reflect the special needs of each state. The Act also fpife Disposal Pilot Program. It authorized the Minne MPCA to conduct a study of the scrap ti recommend optimum ways to address ani was amended in to expand the progn was estimated that Minnesota had appro By , MPCA tire dump cleanup acti removal of 7.
Ohio Senate BiB governing facilities, and I the system by inspectio research for establfsl Wisconsin prehensive regulatory system ige, monocell, monofill, recovery will develop rules for governing! Department of Natural Resources nuisance tire dumps. The objective is to year. There are approximately nuislrt c0 ely In each cleanup case, DNR will ask the responsible the cleanup.
If they do not comply, DNR can proqeedwifegal recourse and seek cost recovery for the cleanup. Please contact the appropriate state contact, shown in Appendix A, for current, specific information about an individual state's Scrap Tire Management Program.
There are currently several barriers impeding waste tire recovery, recycling, and reuse. However, there are also mechanisms available which can assist in overcoming these barriers. Before a company can begin utilizing scrap tires, whether collecting and processing whole tires into a product or burning tires as a fuel, all applicable federal and state permit requirements must be met. These include airand water quality permits as well as applicable scrap tire storage and transportation requirements.
The costs of obtaining these permits, which can include conducting tests and installing pollution control devices, must be considered. Industry can address this situation by sharing information, such as test burning procedures, reducing the unknowns and risks to such ventures. The current state rules and regulations pertaining to scrap tire management are briefly described in the previous section. However, these are subject to change. The most current information on applicable federal and state requirements can be obtained by contacting the appropriate state or federal agency.
A complete list of state and federal environmental agencies involved in scrap tire management is contained in Appendix A. Sizable industries have developed to process scrap tires into usable feedstocks for products or use processed tire material in the manufacture of new products. New technologies for processing scrap tires are still evolving and research into new applications for scrap tires is currently underway in several states.
Independent research projects conducted by universities and private enterprises are also underway. Further information on such projects is available through the sources and references listed in the Appendices. To encourage scrap tire use, several upper midwest states have established market development programs which make resources available for new areas in recycling.
Such resources include low interest loans, grants, rebates, and technical assistance to localities, individuals or companies interested in recycling tires.
These misconceptions must be addressed in order for tire recycling to be successful. Several organizations exist which have useful information available for those interested in tire recycling, retreading or reuse.
A listing of several national and trade organizations that have information available about these uses is contained in Appendix c. Waste tires should be used again in their whole form or be reprocessed for inclusion in numerous final products or end uses. ENERGY o Most alternative end uses for scrap tires require that the tires be split, shredded or finely ground before they can be incorporated into a final product.
Scrap tire processing equipment has changed to meet the needs of a maturing industry. When shredded tires were identified as a potential fuel source or a component in molded products or asphalt, technology again changed to meet new demand specifications. Improved shredder design produced a greater supply of shredded scrap tires, sparking the development of more lucrative end use markets for scrap tires than landfills offered. The equipment used to process tires is commercially available.
Appendix C presents a partial list of tradejournals related to solid waste management. These journals are valuable resources for finding manufacturers and distributors of tire processing equipment. Retreading - Worn, used tires can be rejuvenated by applying a new tread onto an old tire that still has a good casing.
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