No of Tires Percentage of 242 Method of RecoveryIn millions Million Scrap Tires

Energy/Burning 25.9 10.7

Reclaim 2.9 1.2

Splitting 2.5 1.0

Crumb Rubber for Pavements 2.0 0.8

Other Crumb 8.6 3.6

Whole Tires 0.3 0.1

Total Recovered 42.2 17.4

Used Export 12 5.0

Landfill, Stockpile and 188 77.6 Dumping

Total Scrap Tires* 242 100.0

* Retreads (33.5 million) and reused tires (10 million) are not counted as scrap tires. Source: Franklin Associates, Ltd. and Dr. Robert Hershey. Estimates based on published data and technical discussions.

Used Export 5.0%

Energy/Burning 10.7%

Other Recovery 6.7%

Other Recovery 6.7%

Figure 3: Destination of Waste Tires, 1990 Sources: Table 5

are to drill holes in the tires so that the water drains or to remove the tire bead and turn the carcass inside out. This has been practiced on a small scale by individuals (3).

Fire Hazards

For as long as it has been known that waste tires harbor mosquitoes, it has been known they pose a fire hazard. Tire fires are particularly bad because of the difficulty in extinguishing them. This is because of the 75 percent void space present in a whole waste tire, which makes it difficult to either quench the fire with water or cut off the oxygen supply. Water on tire fires often increases the production of pyrolytic oil and provides a mode of transportation to carry the oils off-site and speed up contamination of soils and water.

The potential fire hazard presented by waste tire stockpiles has been realized a number of times in the past decade. Several stockpiles have burned until their tire supplies were exhausted which, depending on weather conditions, may be a few days to more than a year. Air pollutants from tire fires include dense black smoke which impairs visibility and soils painted surfaces. Toxic gas emissions include polyaromatic hydrocarbons (PAHs), CO, S02, NOz, and HC1. Following tire pile fires, oils, soot, and other materials are left on site. These tire fire by-products, besides being unsightly, may cause contamination to surface and subsurface water as well as the soils on which the tires were located. For these reasons, multimillion dollar cleanups are sometimes required to avoid further environmental problems (2).

If stockpiles for waste tires are carefully monitored, the fire hazard can be reduced. Shredded tires pose less of a threat for fires. Tire shreds behave differently than whole tires when burning and because they have less air space, they can be extinguished more easily by allowing water to smother the fire (4). Other precautions that may reduce the fire hazards of tire stockpiles are mandatory fire lanes and fire plans so that a fire can be attended to as quickly as possible (3).

Ultimately, the best solution to the problems of waste tires as fire hazards and mosquito breeding grounds is to eliminate stockpiles. At the least, the number of tires in a stockpile should be minimized, thus reducing the number of breeding sites for mosquitos and fuel for fires.

SOURCE REDUCTION OF WASTE TIRES

There are two options for reducing the number of tires landfilled, stockpiled, and dumped. One is to increase recovery, which is discussed later in this report, and the other is to reduce the number of tires generated in the first place (source reduction). Source reduction measures that have limited potential for reducing the number of tires to be disposed include:

Design of extended life tires Reuse of used tires Retreading.

Design Modifications

Great strides have been made in the last 40 years in tire manufacturing that have more than doubled the useful life of tires. Further increases in life would require higher pressure, thicker treads, or less flexible materials. Each of these methods would result in more gas consumption, higher cost, and/or rougher rides. Currently steel-belted radial passenger tires last about 40,000 miles. If these tires are properly inflated, rotated, and otherwise cared for, 60,000 to 80,000 mile lifetimes may be achieved. It is not expected that any major design changes will occur in the near future that will significantly increase tire life (5).

Reuse

Frequently, when one or two tires of a set are worn, the entire set is replaced with new tires. Useful tread may remain on one, two, or three of the tires removed. Many tire stores and tire haulers sort out the usable tires for resale. Virtually every major city in the USA has stores that sell used tires. These tires are often sold for second cars or farm equipment.

Although the reuse of partially-worn tires cannot be expected to solve the scrap tire problem in the USA, it has been estimated that a minimum of one additional year of tire life can be achieved out of 25 percent of the tires removed from vehicles (6). Assuming this to be the case, then the reduction of the scrap tire problem by the reuse of used tires can be estimated. Suppose a set of four tires is removed after 40,000 miles. If 25 percent (one tire), on average still has a useful tread of 10,000 miles left, this is equivalent to the set of four tires lasting 42,500 miles instead of 40,000, an increase in life of 6 percent. It is not known how many good used tires are currently being reused, but based on contacts with several tire stores, it is evident that a significant portion (estimated 50 percent) of the good used tires are currently being reused. If the other 50 percent were also used, a 3 percent reduction in tire disposal could be realized.

Retreading

The third source reduction measure which can extend the useful tire life, and therefore reduce the number of tires scrapped, is retreading. Retreading is the application of a new tread to a worn tire that still has a good casing. Retreading began in the 1910s and has always played a role in the replacement tire market. There are currently over 1,900 retreaders in the United States and Canada; however, that number is shrinking because of the decreased markets for passenger retreads. Truck tires are often retreaded three times before being discarded and the truck tire retreading business is increasing. On the other hand, passenger tire retreading is declining. This decline is primarily due to the low price of new tires and the common perception that retreads are unsafe. The price of inexpensive new passenger tires ($50 to $60) is often at or near the price of quality retreads.

The National Tire Dealers and Retreaders Association claims that properly-inspected retreaded tires have lifetimes and failure rates comparable to new tires. Mileage guarantees and/or warranties for retreads are often similar to or identical to new tire warranties.

In 1987, about 23 million passenger and light truck tires and 14 million truck tires were retreaded. By 1990, the passenger and light truck retreads dropped to 18.6 million while truck retreads increased to 14.9 million (7). It is estimated that most good truck tire casings are being retreaded due to the high cost of new truck tires, but that at least twice as many passenger car and light truck tires would be suitable for retreading. While retreading will not by itself solve the nation's tire problem, growth in retreading would reduce the number of new replacement tires needed each year and, therefore, reduce the number requiring disposal. For example, if the markets could be developed so that all the passenger and light truck tires suitable for retreading were actually retreaded, then about 20 million fewer new replacement tires would be needed annually. This would reduce the number of waste tires generated per year by almost 10 percent.

DISPOSAL OF WASTE TIRES

The removal of waste tires from the generator's property is generally performed by a tire jockey or solid waste hauler. Some hauling is done by tire users, tire dealers, or retreaders, but the majority of the over 193 million tires that go to dumps or stockpiles go by way of a hauler who is paid to remove waste tires from the dealer's property. The hauler may be held accountable for the number of tires and how they were disposed of, depending on the state. Haulers may be paid $0.35 to $5.00 per tire to dispose of the tires. If they then dispose of the tires legally, they must pay a fee at a landfill or processing facility. If they stockpile the tires or illegally dump them, the tires create serious health hazards.

Whole Tire Disposal

There are no known whole tire disposal methods without adverse effects. Disposing of the tires above ground creates the hazards of mosquitoes and fires. The alternate disposal method is landfilling or burial, which is also not without problems. In landfills, tires require a large volume because about 75 percent of the space a tire occupies is void. This void space provides potential sites for gas collection or the harboring of rodents. Some landfill operators report that tires tend to float or rise in a landfill and come to the surface, piercing the landfill cover.

The primary advantage to whole tire disposal is that processing costs are avoided. However, landfills' bad experience with whole scrap tires has led to extremely high tipping fees or total bans on whole tires. Landfill fees for small quantities range from $2.00 per passenger tire to $5.00 per truck tire. For mass quantities, tipping fees range from $35.00 per ton to over $100 per ton for whole tires, depending on the region of the country. These fees are generally at least twice the fee for mixed municipal solid waste.

Shredded Tire Disposal

Shredding or splitting of tires is becoming increasingly common as part of the disposal process. Shredded tires stored above ground pose less of a hazard than do whole tires. Shredding eliminates the buoyancy problem and makes tires into a material that can be easily landfilled. Shredding can reduce a tire's volume up to 75 percent. This volume reduction can also reduce transportation costs 30 to 60 percent simply because fewer trips are required and maximum hauling weights may be achieved more easily.

Haul costs depend on many factors, including truck size, distance hauled, local labor rates, etc. For semi-truck loads of 1,000 whole auto tires hauled over 100 miles, typical costs are in the 15 to 20 cents per ton-mile range. This is equivalent to 15 to 20 cents per 100 tires per mile. Shredding can reduce this cost by 30 to 60 percent.

The main disadvantage of shredding before landfilling is that an extra processing step is required, which adds costs. Shredder companies charge from $19 to $75 per ton to shred scrap tires (8). T.Y.R.E.S., Inc. of the Los Angeles area is currently shredding for $18.50 a ton. But they say these costs will soon increase significantly because of labor and liability insurance that is required by the city. They said that about 20 tons per hour need to be processed to make the shredding profitable. They have a mobile operation and must transport the machine from landfill to landfill (9). Saturn Shredders, maker of mobile shredding equipment, has broken down typical costs of a 500 to 800 tires per hour shredding operation. These are the cost per tire to the shredder company and do not include any profit or fees. The cost breakdown is outlined in Table 6. For the two processing rates, the cost per tire for coarse shredding (4- to 8-inch) ranges from 18 to 25 cents per tire, or 18 to 25 dollars per ton, assuming passenger tires at 20 pounds per tire.

Shredding costs are fairly constant nationally except for labor and fuel, which may change the total cost up or down 10 percent. When shredding costs are added to solid waste disposal fees, it reflects the cost of landfilling shredded waste tires. For comparison, several examples of tipping fees for whole waste tires in mass quantities were obtained representing the northeast, midwest, south, and west region. These values were not regional averages, but are thought to be values that are representative of the areas.

Table 7 compares the cost of landfilling whole tires and shredded tires in the United States. Shown are estimates of the money saved or lost by shredding prior to landfilling. In the northeast region of the United States, where landfill costs are highest, $38.00 per ton can sometimes be saved by shredding tires before landfilling them. In other areas of the country, disposal costs may increase by as much as $3.00 per ton by shredding before landfilling. These cost estimates are generalizations, and each community would need to determine if shredding before landfilling is economical. It becomes apparent through these comparisons that as landfill space is used up, shredding will become more beneficial, not only in terms of reducing hazards, but also in terms of saving money.

State Legislation Affecting Tire Disposal

Scrap tire legislation is increasing rapidly at the state level. In 1990, twelve states passed or finalized scrap tire laws, regulations, or amendments (12). Thirty-six states now have scrap tire laws or regulations in effect, and all but 9 states regulate or have bills proposed or in draft form to regulate tires. A summary of the states' laws in effect in January 1991 is provided in Table 8. The legislations' contents are summarized in Table 9.

Several states have considered or are considering legislation that would ban all whole tires from landfills. Minnesota has already banned all tires from landfills. In some other states, landfills have such high tipping fees that whole tires are

Table 6

ESTIMATED TIRE SHREDDING COSTS

Table 6

ESTIMATED TIRE SHREDDING COSTS

Mobile Shredders (In dollars and cents per tire)

CAPITAL COSTS

800 Tires/hr(1)

500 Tires/hr(l )

Shredder Shredder Stand Diesel Generator Infeed Conveyor Discharge Conveyor

155,000 48,000 30,000 15.200 i 6,800

155,000 48,000 30,000 15.200 16.800

Total Capital Cost (2)

265,000

265,000

ANNUAL COSTS

Debt Financing (3)

43,128

43,128

Operating & Maintenance Labor (3 at $10/hr) Maintenance & Supplies Cutter replacement and sharpening Electricity @ 8 cents/kw-hr Overhead, Administrative,insurance

62,400 8,100 54,800 25,000 30.000

62,400 5,063 33.800 16,000 30.000

Total 0 & M

180,300

147,263

Total Annual Cost

223.428

190,390

Tires Processed Per Year (25% downtime)

1,248,000

780,000

Shredding Cost (cents/tire)

17.9

24.4

(1) Capacity for passenger tires.

(2) Tractor for moving from location to location not Included.

(3) Financing Assumptions:

(1) Capacity for passenger tires.

(2) Tractor for moving from location to location not Included.

(3) Financing Assumptions:

10 percent Interest 1 0 year amortization

Source: Franklin Associates, Ltd; based on estimates supplied by Saturn Shredders.

Table 7

COSTS OF LANDFILLING AUTOMOTIVE WASTE TIRES IN THE UNITED STATES (In dollars per ton or cents per tire) 1/

Costs by Region

Northeast Midwest South West

Shredded

Landfill Fee 2/ 45 18 16 13

Processing Cost 25 25 25 25

Total 70 43 41 38

Whole

Landfill Fee 3/ 108 75 50 35

Total 108 75 50 35

Savings Realized 38 32 9 -3 by Shredding 4/

1/ Since automotive scrap tires weigh 20 pounds each on average, dollars per ton is equivalent to cents per tire. 2/ Reference 10. 3/ Reference 11.

4/ Total costs of landfilling whole tires - total costs of landfilling shredded tires.

effectively banned. Florida and Oregon have required that the tires be reduced in volume by methods such as slicing or shredding.

Another landfill restriction method, in addition to banning tires or requiring shredding, is to require that tires be disposed of in tire monofills, either whole or shredded. This allows precautions to be taken that will keep the tires buried. It also keeps open the potential for mining the material for some useful purpose at a later date. Specific rules for tire disposal in monofills will be drafted by Ohio in 1991, following the completion of a feasibility study that is examining the engineering properties and leaching potential of shredded tires.

UTILIZATION ALTERNATIVES

In this section, tire utilization methods are described. These include the recycling of tires into whole tire and processed tire products. The recycling discussion is followed by a discussion of "tire utilization methods that capture their energy value. These are incineration and pyrolysis.

Applications of Whole Waste Tires

Whole waste tires can be used for artificial reefs, breakwaters, erosion control, playground equipment, and highway crash barriers.

a) Artificial Reefs and Breakwaters. In the late 1970s, the Goodyear Tire and Rubber Company researched a number of uses for whole tires. Among these uses were artificial reefs and breakwaters. Goodyear billed these applications as being major outlets for scrap tires. They claimed that by 1978 they had built some 2,000 reefs. In Ft. Lauderdale, Florida alone they were said to have used 3 million tires and were adding one million tires per year to that reef alone. Besides stimulating the fishing industry it was believed that tires would later be mined for their raw materials. Since that time, enthusiasm for this use has waned and scrap tire reefs are now only built in minimal numbers.

Breakwaters are barriers off shore that protect a harbor or shore from the full impact of the waves. Breakwaters using scrap tires have been tested by the U.S. Army Corps of Engineers and were found to be effective on small-scale waves. It was recognized at the outset that this application would never use a great number of scrap tires, but tires perform well in applications where floats are needed. Scrap tires for breakwaters and floats are filled with material, usually foam, which displaces 200 pounds of water and can be used to float a number of devices such as marinas and docks and serve as small breakwaters.

Topper Industries of Vancouver, Washington, has patented the concept of a material-filled floating tire. The concept employs scrap tires as a durable container for holding the flotation material together (13). Topper Industries is the only known producer of scrap tire flotation devices and that company estimates that they

SCRAP TIRE LEGISLATION STATUS January, 1991

Draft

Proposed

Regs

Law

Dratt

Proposed

Reqs

Law

Alabama

X

Montana

Alaska

Nebraska

X

Arizona

X

Nevada

Arkansas

X

New Hampshire

X

California

X

New Jersey

Colorado

X

New Mexico

X

Connecticut

X

New York

X

X

Delaware

North Carolina

X

Florida

X

North Dakota

Georgia

Ohio

X

Hawaii

Oklahoma

X

Idaho

Oregon

X

Illinois

X

Pennsylvania

X

Indiana

X

Rhode Island

X

Iowa

X

South Carolina

X

Kansas

X

South Dakota

X

Kentucky

X

Tennessee

X

Louisiana

X

Texas

X

Maine

X

Utah

X

Maryland

X

Vermont

X

Massachusetts

X

X

Virginia

X

Michigan

X

Washington

X

Minnesota

X

Wisconsin

X

Mississippi

X

West Virginia

X

Missouri

X

Wyoming

X

Draft - draft being written/bill in discussion Prop - proposed/introduced in 1990 legislature

Regs - regulated under specific provision of solid waste or other laws (e.g., automotive wastes) Law - scrap tire law passed

Source: Scrap Tire News, Vol. 5. No. 1, January 1991

Table 9

CONTENTS OF SCRAP TIRE LEGISLATION

Funding

Storage

Processor

Hauler

Landfill

Market

Source

Reqs

Reqs

Reqs

Restrictions*

Incentives

Arizona

2% sales tax on retail sale

X

X

California

$0 25/tire disposal lee

X

X

X

Colorado

X

X

Connecticut

X

Florida

)1.00/tire retail sales

X

X

X

X

R&D grants

Illinois

$0 50/vehide title fee

X

X

X

grants/loans

Indiana

permit fees/tire storage sites

X

X

grants

Iowa

X

Kansas

$0.50/tire retail sales

X

X

X

X

grants

Kentucky

$ t.OO/lire retail sales

X

X

Louisiana

X

X

Maine

$1.00/tire disposal tee

X

X

draft

grants/loans

Maryland

state budget appropriations

X

X

X

Michigan

$0.50 vehicle title fee

X

X

X

grants

Minnesota

$4.00/vehicle title transfer

X

X

X

X

grants

Missouri

$0.SO/lire retail sales

X

X

X

funds/testing

Nebraska

}t.OO/lire retail aales

grants

New Hampshire

graduated vehicle regist. fee

X

North Carolina

1% sales tax on new tires

X

X

X

X

funds/collection

Ohio

X

Oklahoma

St.OO/new *'~e (surcharge)

X

X

X

grants

Oregon

tl.OOMew tire (dspl lax)

X

X

X

X

$0.01 /lb

Pennsylvania

X

R&D grants

Rhode Island

$0.50/new tire sales tax

X

X

South Dakota

X

X

X

Tennessee

X

Taxas

X

X

Utah

graduated tax per tire size

$20/ton

Vermont

X

funds/testing

Virginia

)0.SO/new tire (dspl tax)

X

Washington

X

X

X

grants

Wisconsin

$2.00/!ire vehicle title fee

X

X

X

X

$20/ton

The majority of state» have imposed regulations that require tires to be processed (cut, sliced, shredded) prior to landfiiling. Some ol the states allow lor storage (above ground) of shreds at landfills. OH, NC, CO are among the stales considering or allowing monofills for tire shreds. Whole tires are discouraged from landfills (in almost all cases) either by law (e.g., MN) or more frequently by high disposal fees.

ft g

Source: Scrap Tire News, Vol. 5, No. 1, January 1991.

use 30,000 to 50,000 tires per year. These tires are included in breakwaters, marina and dock floats, buoys, and other flotation applications. Topper Industries, Inc. obtains its tires from junk dealers within a 100-mile radius of Vancouver, Washington. They then sell the floats to a market covering primarily the western half of the United States.

Costs for constructing flotation devices are determined on a dollar per pound basis. Topper Industries claims a one-half to three-fourth cost savings by using scrap tire floats over wood, wood-fill, or other alternatives. The tire floats cost approximately $0.06 to $0.08 per pound, whereas the economically closest alternative, foam-filled plastic, costs $0.10 to $0.14 per pound of flotation (14).

Breakwaters and flotation devices presently consume approximately 30,000 to 50,000 tires per year. If tire floats were to acquire the major portion of the flotation market, it may be possible to increase the current tire consumption by a factor of three to four, which would still be less than 1 percent of the annual generation of scrap tires in the United States.

Artificial reefs are constructed by splitting tires like bagels leaving about six inches attached and then stacking them in triangular fashion. Holes are drilled through this stack and about 45 pounds per tire of concrete are poured in the holes to anchor the reef. The 1,800 pound 3-foot high reefs are then hauled by barge 4 to 12 miles off the coast and dumped in 60 to 100 foot deep water. They then provide habitat for marine organisms and fish (14).

The largest operations of building artificial reefs from scrap tires are occurring in Cape May and Ocean Counties, New Jersey. These two counties consume about 120,000 tires per year in making reefs. Cape May County has a goal of using 100,000 tires per year for reefs, by combining tires with concrete and placing them in the ocean (15). This is the only disposal option for scrap tires within Ocean County. It is likely that reefs are being built in other states, particularly Florida, but quantities of tires used are small and on an irregular basis (15).

In Ocean and Cape May Counties, tires are brought in by individuals or haulers wishing to dispose of the tires. The counties may have an influx of tires when area fire departments require that storage sites be abated. Ocean County charges one dollar per tire to accept the tires, while Cape May County charges $25.25 per ton (equivalent to 25 cents per tire).

While artificial reefs do not hold the potential to solve the scrap tire problem, they do have the potential to consume more than they consume now. Currently there are an estimated 120,000 to 150,000 tires used annually in constructing reefs. The goal of Cape May and Ocean Counties is to construct reefs with about 200,000 tires annually. Currently they are doing about 60 percent of this. One estimate of national potential is between one and 1.5 million tires used yearly (16). This is much higher than current levels because only two counties are actively constructing reefs. But, it is low compared to scrap tires generated annually because artificial reefs are restricted to fairly calm sandy coastline, where reef development is needed. Much of the northwest coast has rough water and Oregon has even banned artificial reefs from their sea waters (17). Cape May and Ocean Counties do not foresee an end to their activities as long as the state fish and wildlife agency continues to provide sites to place the reefs.

Costs for constructing reefs are about $3.50 per tire. This cost is somewhat offset by charging $1 per tire in Ocean County to accept tires or $25.25 per ton to accept tires in Cape May County. This compares to the average of $45.25 per ton to landfill the tires in the northeastern United States. Since haulers in Cape May County save money by taking tires to the reef builders, tire supply is not a problem. In Ocean County, costs are minimized by using prison labor for building reefs; and a county owned barge takes the reefs to the dump site (15).

b) Playground Equipment. The only large producer of tire playground equipment is Tire Playground, Inc. in New Jersey. President William Weisz says that his company currently uses up to 4,500 truck tires per year, but has used up to 7,500 per year in the past. In addition to this are the small-scale local and backyard recreational uses of tires. The tire consumption cannot be easily determined, but it is thought to be small compared to the scrap tire supply. The demand for Tire Playground's products is declining as the east coast economy improves and schools and parks select wooden playground equipment. The material cost for the tire playgrounds is one-fourth of the cost of alternative equipment (18).

Even if the market for tire playgrounds were developed completely, it would require less than a million tires per year, which is less than one-half percent of the annual generation.

c) Erosion Control. The California Office of Transportation Research has designed and tested several erosion control applications of scrap tires. Scrap tires were banded together and partially or completely buried on unstable slopes in tests conducted between 1982 and 1986. They found that tires used with other stabilization materials to reinforce an unstable highway shoulder or protect a channel slope remained stable and can provide economical and immediate solutions. Construction costs were reduced from 50 to 75 percent of the lowest cost alternatives such as rock, gabion (wire-mesh/stone matting), or concrete protection. Information on the applications has been distributed since 1988, but it is difficult to determine the number of times these designs have been used. John Williams of the California Transportation Laboratory believes it would be fair to say that fewer than 10,000 tires are used annually for erosion control. He says it is difficult to estimate the potential annual consumption by this method as tire designs are not always appropriate and tires for this use may not be acceptable in highly visible areas (19).

d) Highway Crash Barriers. The use of scrap tires as crash barriers was studied in the late 1970s by the Texas Transportation Institute. They determined that stacked tires bound by a steel cable and enclosed with fiber glass would reduce or absorb impact of automobiles traveling up to 71 miles per hour.

Since that time, no widespread use of tires in this application has occurred. State transportation departments generally prefer sand-filled crash barriers because they have excellent absorption characteristics and are easier to erect and dismantle.

Applications of Processed Waste Tires

Tire processing includes punching, splitting, or cutting tires into products; processing tires into crumb rubber for use in rubber or plastic products, railroad crossings, rubber reclaim, or asphalt paving; and chopping tires into small pieces or chips for use as gravel or wood chip substitutes.

Various rubber products can be manufactured using rubber from scrap tires to replace some or all of the virgin rubber or other material in the product. Tires may be either split, punched, or stamped to yield shapes suitable for fabrication, or the tires may be processed to crumb size to make new products, usually by mixing with other materials.

In this section the primary focus is on reuse of the rubber from tires. However, the fabric and steel may also be recycled.

a) Splitting/Punching of Tires. Splitting involves the removal of the steel bead and then using a stamp or punch to achieve the desired shape. Splitters purchase tires on the market either graded or ungraded. They are responsible for disposal of the part of the tires that are left as well as the unrecyclable tires, so they generally buy only appropriate tires. For example, steel-belted radials create problems for the splitters and are usually not wanted.

Products from the splitting of tires include floor mats, belts, gaskets, shoe soles, dock bumpers, seals, muffler hangers, shims, washers, insulators, and fishing and farming equipment. The market for this type of product is very limited; however, one Massachusetts company reports they use 2,000 tires per day to manufacture fishing equipment, such as net parts, rubber discs, rollers, chain covers, strips for traps, etc. Because this industry is so diversified and there are no published data, it is difficult to make good estimates of the nationwide usage of split rubber products. Estimates made in 1987 indicate the U.S. market for these products is about 2.5 to 3.0 million tires per year (20). In the absence of additional data, it is assumed that the markets in 1990 remained at the same level.

b) Manufacture of Crumb Rubber from Scrap Tires. Crumb rubber is made by either mechanical or cryogenic size reduction of tires. Because of the high cost of cryogenic size reduction (at liquid nitrogen temperatures), mechanical size reduction by chopping and grinding is used most often. Typically tires are shredded to reduce them to 3/4-inch chips. Then a magnetic separator and fiber separator remove all steel and polyester fragments. The rubber chips are then reduced to pebbles by a cracker grinder or granulator. A series of screening and regrinding operations achieves the desired crumb size, which may be 600 to 800 microns. This rubber may be used in rubber or plastic products, or processed further into reclaim rubber or asphalt products. A significant portion of the crumb rubber market demand is met by buffings and peels from retread shops.

Crumb rubber can be mixed with other materials to make new products, including plastic floor mats and adhesives. It can also be mixed with asphalt as an additive to make cement products.

1) Crumb Rubber in Rubber and Plastic Products. Crumb rubber may be incorporated into rubber sheet and molded products such as floOr mats, vehicle mud guards, and carpet padding or into plastic products, including plastic floor mats and adhesives. Additional uses that have contributed to the expansion of this market over the last three years are rubber play surfaces, tracks and athletic surfaces, and garbage cans. In 1987 about 2.3 million tires (1 percent) were utilized in this manner. 1990 estimates have risen to 8.6 million tires per year, or 3 percent of the scrap tires generated that year.

2) Crumb Rubber in Railroad Crossings. OMNI Products, Inc., a subsidiary of Reidel Environmental Technologies, Inc., has a patented process for using crumb rubber to make solid rubber railroad crossings (21). The molded panels fit between the tracks and fasten to the ties. OMNI is operating in three locations: Portland, Oregon; Lancaster, Pennsylvania; and Annis, Texas. Currently only buffings from tire retreading operations are being used, but the company is testing the use of crumb rubber that still contains the fiber.

Rubberized crossings compete with crossings made of asphalt and timbers. The installed cost of the OMNI product is about 35 percent higher than timber and about 100 percent higher than asphalt. The manufacturer claims that the life cycle cost of rubberized crossings can be lower than competing materials because they expect their product to last about 10 to 20 years compared to 3 to 4 years for asphalt, depending on the traffic.

In 1990 OMNI used at least 14 million pounds of crumb rubber for railroad crossings. Another company, Park Rubber Company of Illinois, used less than 1 million pounds of crumb rubber for the same purpose. If 20 million pounds were used for rubber railroad crossings, this would be equivalent in weight to about a million scrap automotive tires. However, if only buffings are used, only about 10 percent of each tire is used, and the tire disposal problem is not solved.

There is a potential for growth of the rubber railroad crossing market. There are 185,800 public railroad crossings and at least as many private ones in the U.S. Less than 2 percent have rubber crossings. A typical railroad crossing consumes about 350 pounds of rubber per track foot.

3) Rubber Reclaim. For the traditional rubber "reclaim," crumb rubber is mixed with water, oil, and chemicals and heated under pressure, thus rupturing the carbon-sulfur bonds that cross-link the molecular matrix. The resulting partially devulcanized rubber may be formed into slabs or bales and shipped to manufacturers who process and vulcanize it for use as an alternative to virgin rubber to use in tires or to make mats and other rubber products.

Reclaim rubber tends to lose its elastic properties during processing and, therefore, is no longer extensively used in tires because of the flex needed. That is, it does not become like new rubber. Howeyer, some new tires routinely contain one to 2 percent crumb rubber (5).

Because of the increased use of synthetic materials in making new tires after World War II, the reclaim industry has dramatically decreased in size. During World War n, about 60 percent of the rubber in tires was reclaimed rubber. Each of the major tire manufacturers has discontinued operating reclaim plants in the last 8 to 10 years, until now only about one to 2 percent of the raw material for tires is reclaim. There are currently only two companies that produce reclaim rubber, i.e., partially-devulcanized rubber, from whole tires for use in tires and other rubber products. These companies are Midwest Rubber Reclaiming Co. in East St. Louis, Illinois and Rouse Rubber, Inc., in Vicksburg, Mississippi (22).

In 1987, the equivalent of 3.4 million tires were consumed for reclaim rubber. By 1989 this figure had declined to 2.9 million tires (23). The reclaim industry's production capacity is estimated to be between 100 and 144 million pounds per year, (5 to 7 million tires per year), indicating a capacity of utilization of about 40 to 60 percent, due to limited market demand. The Department of Commerce is no longer updating its reclaim rubber production figures yearly. It is estimated that production remained 2.9 million tires or less in 1990.

A new reclaim producer, Rubber Research Elastomers (RRE) of Minneapolis declared bankruptcy in August, 1989 (24). RRE, under Chapter 11, is currently exploring options for restructuring its operations. Since RRE's "Tirecycle" products have generated considerable interest, the process is worth discussing.

In the Tirecycle process, first developed in 1982, finely ground scrap rubber is treated with a liquid polymer to form a reclaimed rubber product. RRE literature claims superior bonding properties and suggests use in tread rubber and other products including washers, mats, car parts, and tiedowns. The Tirecycle product is claimed to be useful with thermoplastics such as polypropylene, polyethylene, and polystyrene, as well as polyvinyl chloride, polyesters, and urethanes.

The RRE facility in Babbitt, Minnesota, financed by St. Louis County and the state, was envisioned to have a capacity to process three million tires per year, all of Minnesota's scrap tires. Actual production never reached over 10 percent of that value.

A study by the University of Minnesota completed May 19,1989 (25), concluded that there are adequate rubber markets for Tirecycle products, but that the Tirecycle product performance and delivery often failed to live up to customers' expectations. The study also concluded that the operation needs a large infusion of cash (over two million dollars) before reaching 60 percent of capacity and reaching breakeven conditions under an optimistic scenario. As a result of the University of Minnesota study, St. Louis County and the state decided not to continue funding the RRE Tirecycle project.

4) Crumb Rubber Additives for Pavements. Crumb rubber can also be combined with asphalt for use as a paving material. There are two main types of processes for doing this. Advantages claimed for both include increased durability, flexibility, and longevity, when compared with conventional asphalt pavements. One application, referred to as Rubber Modified Asphalt Concrete (RUMAC), or the dry process, involves the displacement of some of the aggregate in the asphalt mixture with the ground whole tires. For this application the tire crumbs or chips may still contain some of the reinforcing materials such as polyester, fiber glass, and steel. PlusRide™ is the commercial name by which one kind of RUMAC is marketed. The TAK system, a non-patented generic system being tested by the State of New York and others, is another form. PlusRide™ and the TAK system each have a different size distribution of the rubber aggregate in the asphalt mixture.

The second application of crumb rubber in asphalt (also a patented process) involves the blending/reactivating of a certain percentage of the asphalt cement with a ground rubber that is free of other tire constituents such as polyester, fiber glass, or steel. This application is referred to as asphalt-rubber (A-R), the Arizona process, or the wet process. While A-R typically uses only one-third of the rubber per mile of pavement that RUMAC uses (assuming equal thicknesses of material), it has been tested at more locations of the United States over a longer period of time. In the following pages, the technologies and uses of RUMAC and A-R are described. This is followed by a brief summary of research on pavements containing rubber.

(a) Rubber Modified Asphalt Concrete. The PlusRide™ technology typically uses 3 percent by weight (60 pounds per ton of total mix) of granulated coarse and fine rubber particles to replace some of the aggregate in the asphalt mixture (26). Wire and fabric must be removed from the tire crumb and the maximum moisture content is 2 percent. The granulated rubber is graded to specifications, and in the PlusRide™ system, the aggregate is gap graded to make room for the rubber to be uniformly dispersed throughout the paving mixture. The granulated rubber is graded to specifications as follows:

Percent

Sieve Size Passing by Weight

1/4 inch 100

TAK, the non-patented RUMAC system being tested by the New York State Department of Transportation, uses a uniformly graded rubber crumb, and therefore does not require gap grading of the aggregate. The New York DOT is testing this system in highway strips using 1, 2, and 3 percent rubber in total asphalt mix. The results will be compared with results from PlusRide™ test strips. It is too early for any test results, since the strips were laid in the fall of 1989 (27).

The asphalt binder used in both types of RUMAC is the same as that used in conventional asphalt. Therefore, conventional equipment is used for mixing the final product. A belt conveyor is used to feed the rubber into the mixer.

The formula for PlusRide™ was invented in Sweden in the late 1960s and was patented in the United States by the PaveTech Corporation located in Seattle, Washington under the trade name PlusRide™. Marketing is done by several companies across the country.

PlusRide™ modified asphalt is currently being tested in highways, streets, bridges, and airports. PlusRide™ and TAK use all the rubber in waste tires, including the sidewall interliner and tread portions, recycling all but the steel and fabric. Chief advantages over conventional asphalt are claimed to be increased flexibility and durability, which make it attractive for rehabilitating road surfaces with severe cracking.

(b) Asphalt-Rubber. Asphalt-rubber was developed in the late 1960s and has been used primarily in the City of Phoenix, Arizona (28). The asphalt-rubber process involves the blending of presized granulated rubber into standard asphalt heated to over 400 degrees Fahrenheit. Blending occurs for about 45 minutes. A-R is produced by one of two procedures. In the Arizona Refinery procedure, an oil extender is added to the asphalt before heating and adding rubber, and in the McDonald procedure, kerosene is added to the hot blended mixture. Either procedure is performed just before application at the job site, as A-R cannot be stored for more than 3 days without adjustment of the mix.

The composition of A-R is highly dependent on the needs of the project. Rubber content is generally 15 to 25 percent of the binder by weight and the crumb size used ranges from fine to coarse in six different sizes. The crumb used is produced by a crumb rubber company which separates the ferrous and fabric materials from the tire and then shreds to a specific rubber particle size. Various polymers may also be added to the formula. The crack seal industry has many different mixes from which to choose.

The application process is also dependent on the type of project. Asphalt-rubber used as a seal coat is sprayed on the surface with equipment designed for asphalt-rubber's high viscosity and need for constant stirring to suspend the rubber. Hot mix projects require little special equipment as the asphalt-rubber is premixed with the aggregate and applied in the same manner as a standard overlay (29).

For the more than 20-year history of asphalt-rubber, most applications have been used for testing or experimental projects. The exception has been the wide use and success of A-R in Arizona and other southwestern states, including California and Texas. Some states that have not used A-R extensively in the past are awaiting material and application specifications to be established (30). This situation may soon be remedied as the Asphalt Rubber Producers Group (ARPG) is currently working with the American Society for Testing and Materials (ASTM) and the American Association of State Highway and Transportation Officials (AASHTO) to establish specifications for the A-R industry (29).

Applicators with royalty agreements for A-R are located in Phoenix, Los Angeles, East Texas, Washington, and Rhode Island. These companies are able to meet the current levels of use competitively. These companies are shown in Table 10.

When A-R is applied, the applicator usually obtains crumb rubber from the shredder company that is geographically closest to the project site. Since there are a limited number of crumb rubber shredders, scrap tires may not originate from the community buying the A-R application. If, for example, a city or state buying an A-R application is located outside the 200 to 300 mile radius of the crumb producer who is providing the crumb rubber, it is likely that their own scrap tire supply is not being consumed.

The A-R process consumed 1.9 million tires in its U.S. production in 1989 (31), which is almost a 60 percent increase over 1987. In 1986, 35,000 tons of A-R were placed by five U.S. applicators. In 1989, 47,000 tons were used, and the ARPG predicts about 65,000 tons will be used in 1990 (31).

The longer pavement life claimed for asphalt rubber is attributed to higher viscosity and impermeability of asphalt-rubber. These properties have decreased thermal cracking, potholing, deformation, and reflective cracking in most states in which tests were performed. Studies by the Alaska Department of Transportation showed decreased stopping distances as a result of asphalt-rubber being more flexible and preventing ice formation (32).

Table 10

ASPHALT-RUBBER APPLICATOR COMPANIES

International Surfacing Phoenix, Arizona

Cox Paving Company Blanco, Texas

Eagle Crest Construction Company Arlington, Washington

Manhole Adjusting Contractors Monterey Park, California

Asphalt Rubber Systems Riverside, Rhode Island

Source: Asphalt Rubber Producers Group

The Asphalt Rubber Producers Group (ARPG), which promotes asphalt-rubber, suggests that the doubled life of A-R pavements provides two options for departments of transportation. In one case, an inexpensive application of A-R applied to severely deteriorated pavements can extend that pavement's life. For new pavements, they suggest a long-term cost benefit by performing more than twice as long as a standard pavement even though its original cost was less than twice as much.

(c) Research and Demonstration of RUMAC and Asphalt-Rubber. Procurement guidelines for the use of rubber in asphalt were proposed by the U.S. EPA in 1986, but have been tabled since that time because many state highway departments felt that not enough research had been completed at that time to justify promotion of this technology nationally through procurement guidelines. Questions still remain about the life expectancy, suitability in different climates, and recydability.

Research on RUMAC in the United States, beginning in 1981, has been conducted by a number of institutions and states, including the University of Oregon, the University of Idaho, the California, Alaska, New York, and New Jersey Departments of Transportation, and the Colorado Department of Highways. Tests are still under way, although most test results to date indicate improved durability and skid resistance and less cracking.

Because the initial cost of PlusRide™ is higher than conventional asphalt and because of the long times required for satisfactory testing, it is not being used routinely at this time. Since 1979, however, this material has been used in over 60 test applications in the United States.

Asphalt-rubber has been tested in at least 25 states over the last 2 decades. It has been used primarily as a maintenance tool to save existing distressed surfaces, and most recently as a preventive maintenance tool. It is not being used routinely in new construction.

One of the concerns regarding both RUMAC and A-R highways is their recyclability. Old asphalt is typically heated and mixed with fresh material to create new asphalt. There is concern that when the rubber modified asphalt is reheated, it may catch fire or produce noxious smoke. The industry claims that this will not occur, and that recycling of rubberized asphalt has been successfully done in Sweden. However, many state highway departments are not yet convinced.

In 1985 the New York State Department of Transportation indicated a possibility of health and environmental problems in using rubber in asphalt. They felt the presence of carbon black, carcinogens, and unhealthy fumes may cause problems in utilizing rubber in asphalt (33). Since 1985, New York has had no evidence that rubber significantly increases the health problems of asphalt (27). The California Department of Transportation, which has experience with both RUMAC and A-R, indicated they are not aware of any additional health problems due to the addition of rubber (34).

d) Markets and Life Cycle Cost of RUMAC and Asphalt-Rubber. Asphalt-rubber is diversifying into new markets with the construction of geomembranes for lining of evaporation tanks, hazardous waste storage sites, and ponds. A-R provides impermeable linings which restrict the movement of the substances to be contained (33). Though the A-R applicators promote these applications, they realize they are only a small supplement to the pavements market. The greatest potential for utilizing large quantities of asphalt-rubber remains in road, runway, and parking lot construction applications.

Pavement applications for asphalt-rubber include:

Crack and joint sealants Seal coats Interlayers

Hot mix binder in overlays.

Crack and joint sealants are applied only on cracks and joints. Seal coats include hot asphalt-rubber sprayed on the surface followed by precoated aggregate. Interlayers are the application of seal coats followed by either a standard overlay or an asphaltic-rubber overlay. Asphalt-rubber, when blended with an aggregate hot mix at about 9 to 10 percent by weight, serves as a binder in the thin overlay applied to the road surface. The hot mix binder holds the greatest potential for using large quantities of scrap rubber because of the thickness and quantity of the overlay. Fifteen to 25 percent of the binder is crumb rubber. Current investment and research projects are concentrated in this use of asphalt-rubber (29).

A general rule in comparing costs of standard asphalt and A-R or RUMAC is that the rubberized material will be between 40 and 100 percent higher than the cost of standard asphalt. The lack of an exact cost ratio between the alternatives is caused by the variability in the cost determining factors that are involved. In a California study in 1988, standard dense graded asphalt concrete controls cost approximately $3.04 per square yard, while equal thicknesses of asphalt-rubber and RUMAC applications averaged about $6.13 per square yard (36). Table 11 compares cost estimates from five areas, including New York, California, Washington, Phoenix, and Wisconsin.

Only Wisconsin has had negative results with regard to service life of asphalt-rubber. Wisconsin tried rubber mixed with recycled asphalt and got 10 times more cracking than with recycled asphalt alone. They now have 3 new A-R projects planned for 1990, using new asphalt. ARPG defends pavement life increases of two and one-half to three times greater than conventional. Standard pavements consistently last 10 to 12 years, whereas asphalt-rubber pavements last 20 or more years. The ARPG claims that if an asphalt-rubber pavement were designed to last the same length of time as a standard pavement by making the layer thinner, the costs will be the same.

The increased pavement life can be attributed to higher viscosity and impermeability of rubberized asphalt. These properties have decreased thermal cracking, potholing, deformation, and reflective cracking in most states in which tests were performed. Studies by the Alaska Department of Transportation showed decreased stopping distances as a result of rubberized asphalt being more flexible and preventing ice formation (37).

c) Lightweight Road Construction Material. Since 1986, the State of Minnesota has been using chipped tires as a lightweight fill material where roads cross marginal subgrade (38). In some areas of the country, this technology has potential for recycling a large number of tires. This technology was developed when the Department of Natural Resources, Division of Forestry, was interested in developing low cost means for crossing peat and other soft soils. Wood chips are often used for this purpose. Because wood chips and rubber chips are lightweight compared to gravel, settling of roadways is greatly reduced.

Rubber chips for this technology are coarse shredded to four to six inches in diameter. Steel may be left in the shredded tires. The cost of these tire chips is very competitive with wood chips.

Minnesota has used close to a million tires to date for road fill. In one 100-foot section north of the Twin Cities, where the road crosses a peat bog, 3,000 cubic yards of tire chips were used. This is equal to about 81,000 tires.

In late 1989, Minnesota tested tires for leachate and found that leaching of heavy metals, polynuclear aromatic hydrocarbons, and total petroleum hydrocarbons from tire chips could not be completely ruled out (38). Now the preferred method is to use wood chips below the water table and tire chips above the wood chips. This is expected to extend the life of the fill over using just wood chips, since wood chips degrade in the unsaturated zone.

Table 11

COMPARISON OF RUMAC AND ASPHALT-RUBBER COSTS WITH STANDARD ASPHALT COSTS

Study

New York Department of Transportation (1)

California Department of Transportation (2)

Washington State (3)

Phoenix (4)

Wisconsin Department of Transportation (5)

Ratio of Rubberized Asphalt to Standard Costs

RUMAC 1.50

Both

RUMAC

Predictions of Life Extension

No data yet

3 times No data yet 2 times

No improvement to slightly worse

(1) Phone conversation with Tom Van Bramer, NY State DOT, 1990.

(2) Phone conversation with Robert Doty, CA DOT, 1990.

(3) Phone conversation with Dale Clark, WA DOE, 1990.

(4) Phone conversation with Bob Draper, City of Phoenix, 1990.

(5) Phone conversation with Clint Solberg, WI DOT, 1990.

Source: Franklin Associates, Ltd.

The Minnesota Pollution Control Agency estimates that about 20 to 30 percent of Minnesota's tires that are recycled will be used as lightweight roadway fill. At this time other states are not using this technology. Wisconsin, however, is planning to evaluate it soon.

d) Playground Gravel Substitutes. At least two companies make a playground gravel substitute from chipped used tires. Waste Reduction Systems in Upper Sandusky, Ohio, is marketing colorized tire chips (one-fourth to one-half inch) for use under and around playground equipment and for running tracks. The tire chips provide a better cushion than the standard materials such as asphalt, stone, and wood chips. For this use it is important that all steel is removed from the chips. By shredding to one-fourth to one-half inch, magnets can be used to remove all steel.

Dye is used to color the chips. It is report

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