January/February 2002
The future prospects for scrap tires remain bright, thanks to old and new markets—from tire-derived fuel to road projects to septic drainage fields to sports surfacing, and more.
By Kent Kiser
Kent Kiser is editor and associate publisher of Scrap.
When it comes to scrap tires, the Mid-Atlantic region is a well-developed market with good infrastructure, efficient collection, and sufficient processing capacity. In short, “the area is in pretty good shape,” said Michael Blumenthal of the Scrap Tire Management Council (Washington, D.C.) at the first Mid-Atlantic regional scrap tire conference, held in Annapolis, Md., in November. His hope is “for the markets to increase.”
That hope applies not only to the Mid-Atlantic region, but to the larger scrap tire market as well. Fortunately, progress has been made in the past 10 years. Of the estimated 273 million scrap tires generated annually in the United States, 196 million—or 72 percent—have a market. About 125 million of those tires are consumed as tire-derived fuel (TDF), while 30 million go into civil engineering uses and 20 million are consumed in ground rubber markets.
Speakers at the Mid-Atlantic conference offered insights into those and other markets, showing that—while there’s always room for improvement—the U.S. scrap tire industry is rolling along quite nicely.
TDF’s Advantages
Currently, there are about 75 consumers of TDF in the United States, with the majority of them found in the cement, utility, and pulp and paper industries, explained Terry Gray of T.A.G. Resource Recovery (Houston).
These industries use TDF in their boilers and kilns because of its benefits compared with fuels such as coal, including low moisture content, low ash content, a better volatile fixed carbon ratio, a good carbon/hydrogen ratio, and lower nitrogen content. Also, TDF has a higher heat content per pound than coal, serving as an “octane booster” when burned, Gray said, stating that “TDF can be an environmental, economical, and technically attractive alternative energy resource when it’s used in the right place.”
The “right place” is indeed critical since all TDF consumers can’t use the same type of material, noted Charles Astafan of Columbus McKinnon Corp. (Sarasota, Fla.). The type of TDF a consumer uses depends on its type of boiler, feed system, ash-handling system, and other factors. For instance, scrap tire-to-energy plants and cement kilns can consume whole tires and TDF containing bead and tread wire because the iron content isn’t a problem (in fact, it’s beneficial to the cement-making process.
In contrast, utilities and pulp and paper mills prefer bead-free or wire-free TDF because they don’t want the iron content (it can increase some emissions) and because the wire can clog the grates or ash pipelines in their systems. The point is that tire processors must know the particulars of their consumers’ systems to ensure that they’re delivering the appropriate TDF, Astafan said.
Making Quality TDF. What must processors know to prepare the different types of TDF—wire-in, bead-free, and wire-free?
Wire-in TDF is produced using a shear/shredder, which processes tires with knives on two counter-rotating shafts. A critical factor with a shear/shredder is the knife-to-knife tolerances because the tolerances “are what’s going to give you very clean cuts and minimize protruding wire,” Astafan explained.
Bead-free TDF is 99-percent free of bead wire but still contains the tread wire. The bead wire can be removed prior to shredding by a debeading machine, or it can be removed after shredding by a magnet system. Close knife tolerances and clean cuts are important in this grade since it’s critical to limit the amount of protruding belt wire. The magnet system can pose additional processing concerns since some magnets can pull not only the bead wire but “20 to 40 percent of your product flow out of the system,” Astafan said.
Wire-free TDF has more than 99 percent of bead wire and 90 percent of tread wire removed. This grade is prepared using a primary granulator, also called a knife hog, rasper, grizzly, and liberator. This equipment has one rotor with serrated or straight blades that cut material against a stationary knife. A primary granulator works opposite from shredders—instead of cutting the rubber cleanly, a granulator rips the rubber to open it up and remove the tread wire, Astafan noted. As a result, a granulator needs wider tolerances compared with shredders.
Civil Engineering Market Poised for ‘Major Growth’
Though civil engineering uses are already the second-largest market for scrap tires, this niche still has “major growth potential,” said Dana Humphrey, a professor in the University of Maine’s Department of Civil and Environmental Engineering (Orono, Maine).
Currently, scrap tire shreds measuring 3 to 12 inches are used in civil engineering applications such as lightweight fill for highway embankments; backfill for retaining walls and residential housing foundations; insulation under roads; drainage layers for landfills; and septic tank drainage fields, Humphrey said.
Scrap tire shreds are used in these sorts of projects because they have many physical properties that civil engineers need, including:
• light weight—50 pounds per cubic foot compared with 125 pounds for soil;
• low earth pressure—tire shreds don’t exert much pressure from behind on retaining walls, allowing the walls to be thinner and saving on material costs;
• good thermal insulation—shreds are good at retaining heat, which is important when used in projects in cold climates;
• excellent drainage—the gaps between tire shreds allow fluids to drain without causing erosion; and
• compressibility—tire shreds can be compacted to create a secure foundation.
If these properties are needed in a civil engineering project, then tire shreds can be the cheapest raw material to use, Humphrey said. At an embankment project in Maine, for instance, tire chips had an in-place cost of $25 per cubic yard and cost 37 cents for a pound of weight credit, he noted. Compare those costs with those of other lightweight-fill materials such as extruded polystyrene ($80 per cubic yard and 66 cents for a pound of weight credit) and expanded shale ($80 per cubic yard and $1.60 for a pound of weight credit).
Another reason to use tire shreds in civil engineering projects is that such projects can consume large amounts of scrap rubber. To illustrate this point, Humphrey pointed to several projects in Maine, noting that a 170-foot-long abutment consumed 400,000 tires; a 600-foot-long interchange required 1.2 million tires; and a landfill drainage layer used more than 500,000 tires.
In the future, tire shreds could find use in other civil engineering uses such as vibration-damping layers for rail lines (which could consume 900,000 scrap tires per kilometer of track) and as backfill around bridge foundations to improve earthquake resistance (which could use 25,000 tires per bridge), Humphrey said.
Groundwater quality is an important consideration when using tire shreds in projects above the water table, he cautioned. Fortunately, tests indicate that tire shreds are inert. They have no effect on primary drinking water standards, yield elevated but acceptable levels of manganese (from the steel belts) in secondary drinking water standards, and have no effect on volatile and semivolatile organics, Humphrey said.
Before using tire shreds in civil engineering projects, it’s critical to know that tire-shred layers can’t be more than 10 feet thick—otherwise, excessive heat could build up. Multiple layers of tire shreds must be separated by several feet of dirt or other material, and shreds should not be used if they’ve been contaminated with gasoline, oil, or grease.
(For more details on the required properties of tire shreds for civil engineering applications, processors should consult the ASTM guideline D6270-98, Humphrey noted.)
Tire shreds aren’t the only way to use scrap rubber in civil engineering applications. Since 1999, Chautauqua County, N.Y., has used bales of scrap tires as a subbase in three road projects, consuming 20,000 tires in one, 200,000 tires in another, and 36,000 tires in the third, noted Ken Smith of the county’s Department of Public Works, Division of Transportation & Engineering (Falconer, N.Y.).
To execute these road projects, the county purchased a mobile tire-baling machine that it could transport to various stockpiles. Low-risk prison laborers worked on-site to feed tires into the baler, which size-reduces tires by a factor of 5 to 1 into bales of 100 tires. The county decided to bale tires rather than shred them for cost reasons, Smith said, noting that it cost 40 cents a tire for baling compared with $2 for shredding. Among their advantages, baled tires:
• don’t hold water since they are compressed so tightly,
• provide excellent insulation under the road—an important factor in frigid upstate New York;
• weigh less than rock subbase materials—910 pounds per cubic yard versus 3,000 pounds for rock; and
• cost $3,000 less per 1,000 feet of road than rock, Smith said.
A Septic Solution. Another county—Horry County, S.C.—has found success in another civil engineering niche—using tire chips as a replacement for rock in septic drainage fields.
About 1,200 septic fields are installed annually in Horry County, and currently about 99 percent of its systems use tire chips in their drainage fields, with each system capable of using 800 scrap tires, said Clifton Roberts of the of the South Carolina Department of Health and Environmental Control (Conway, S.C.). Thus far, he noted, the county has consumed more than 1 million tires in its septic projects.
In septic systems, tire chips offer several advantages over #5 stone:
• Chips offer more void spaces, or storage volume, compared with rock—62 percent versus 44 percent;
• Chips are lighter than rock—25 pounds per 5-gallon container compared with 70 pounds;
• Chips are less than half the cost of stone;
• Chips are easier to use; and
• Chips reduce the use of stone—a natural resource—and put scrap tires to a beneficial reuse.
There can be some drawbacks to using chips, Roberts said. For instance, chips with too much wire can create problems, the quality of processed chips can vary greatly, and there may not be an adequate supply of chips in certain areas. Plus, using chips in septic fields is still a new idea that must overcome resistance among contractors and the public, Roberts said.
Horry County plans to publish a report on its use of chips in septic fields this spring. Already, the county’s tests have shown that septic fields with chips have less water in them, a sign that the chips are helping to disperse water in the septic field. Also, chip trenches contain beneficial organisms that don’t appear in stone trenches, and the chips themselves don’t seem to leach any worrisome elements into the ground, Roberts said.
The Good Way to Landfill Tires. While many scrap tires used to be discarded in landfills, now tire shreds are being used in applications covering “the full cycle of a landfill’s life,” including the leachate/ drainage collection layer, operations layer, daily cover, gas collection trench, and underdrain layer, said Krzysztof Jesionek of GeoSyntec Consultants (Walnut Creek, Calif.).
Landfill projects usually use tire shreds measuring 2 to 12 inches, he noted. While tire wire doesn’t have to be removed for some applications, in situations where the wire could cause damage—such as puncturing a landfill’s geotextile membrane—there are limits on allowable wire, Jesionek said.
Tire shreds offer a less expensive alternative to gravel in landfill drainage applications, serve as a source of daily cover in areas with inadequate soil supplies, and free up landfill airspace that might otherwise have been occupied by whole tires, among other benefits, Jesionek said.
On the downside, tire shreds must be processed and wire must sometimes be removed, which adds cost, plus they still face hurdles as an unconventional material.
Crumb Rubber Struggles Through Adolescence
Though crumb rubber applications are “the highest and best use for scrap rubber,” these markets are still experiencing growing pains, said Terry Gray of T.A.G. Resource Recovery.
In North America, there are about 83 crumb rubber producers, 47 of which reportedly make crumb from scrap tires while the others make it from tire buffings, he noted.
In the early 1990s, the crumb rubber market grew quickly, in part due to the federal Intermodal Surface Transportation Efficiency Act (ISTEA), which promised to boost demand for crumb in asphalt rubber. Unfortunately, ISTEA was killed, hampering crumb rubber demand and leading to significant excess capacity in the crumb rubber market. The result has been more than $100 million of business failures.
To succeed in the crumb rubber market, Gray said, processors must:
• be able to operate without subsidies;
• understand the end markets for crumb rubber, the lead times involved in product development, and the specifications of the products using the rubber;
• know how to price their crumb rubber appropriately and competitively;
• ensure that the supply of scrap tires is adequate in their area to meet demand;
• understand the function and true operating costs of the sophisticated equipment needed to make crumb rubber;
• ensure professionalism in their operations, including making a crumb product that meets the necessary quality standards for the end product; and
• become more aggressive marketers of crumb rubber to build markets.
“This industry is in its early adolescence,” Gray stated. “It’s making a lot of mistakes. It’s making some of those mistakes twice or more. But it really is growing up. Someday this industry is going to be a valuable, mature, contributing member of our industrial society.”
Putting the Rubber in the Road. One of the biggest potential markets for crumb rubber is asphalt rubber, which offers many benefits compared with traditional asphalt, said Cliff Ashcroft of FNF Construction (Fullerton, Calif.) and second vice president of the Rubber Pavements Association (Tempe, Ariz.).
These benefits include:
• greater resistance to cracking;
• reduced thickness, with asphalt rubber able to be used in half the thickness of traditional asphalt. This allows contractors to use less material when surfacing a road as well as overlay a road that would have otherwise had to be completely reconstructed if using asphalt at the usual thickness;
• lower cost. In life-cycle cost analyses, there’s a $2.52-per-square-yard savings using asphalt rubber chip seals versus asphalt chip seals, a $3.36-per-square-yard savings using a thin blanket of asphalt rubber versus asphalt, and a $7.34-per-square-yard savings using a structural overlay of asphalt rubber compared with asphalt.
• noise reduction, with asphalt rubber damping tire noise by 3 decibels—about 50 percent less than asphalt; and
• better water runoff because asphalt rubber is a “gap-graded” mix rather than a “dense-graded” mix like asphalt.
Sporting Chances for Crumb. Beyond the asphalt market, crumb rubber is gaining ground in sports-surfacing markets such as playgrounds, running tracks, and artificial turf fields, said Dave Quarterson of Florida Tire Recycling Inc. (Port St. Lucie, Fla.).
Overall, sports-surfacing markets consume 1.1 million passenger-tire equivalents a year, Quarterson stated. On average, a playground can consume 50,000 pounds of rubber (about 2,500 tires); a running track can use 100,000 pounds (around 5,000 tires); and one football-field turf system can use 250,000 pounds of rubber (approximately 12,500 tires), he reported.
In the playground market, “the quality of the surface in the playground is the single most important safety issue,” Quarterson said—and therein lies crumb rubber’s advantage over competing materials such as wood mulch and fine sand. A major factor is the material’s “critical height”—its ability to absorb the impact of a child’s fall. According to Quarterson, 6 inches of mulch will absorb a fall from 4 feet; sand, 6 feet; and crumb rubber, 12 feet.
Rubber is also a better playground surface because it doesn’t compact like mulch and sand, doesn’t deteriorate and need to be replenished like the other materials, doesn’t attract insects, and is cost-competitive—$1.10 per square foot compared with $1 for sand and 78 cents for mulch, Quarterson said.
Crumb rubber continues to gain favor in the running-track and artificial turf markets, meanwhile, thanks to its durability and ability to absorb impact. In turf applications, the rubber is incorporated in a 1/4-inch foundation layer under the turf and can also be packed on top of the turf as extra padding, Quarterson said.
Using Rubber in Engineered Products. Recycled ground rubber can be used successfully—and profitably—in engineered products, providing a source of competitive advantage and yielding savings by displacing more expensive raw materials, said Mike Schnekenburger of NRI Industries Inc. (Toronto, Ontario).
“If you’re in the recycling business, there’s a way to make money and that’s to specialize, or to rely on certain niches of high-quality products,” he stated.
Recycled rubber can be used in vulcanization, thermoplastics, and polyurethane-bound rubber to make value-added engineered products such as automotive components. When making such products, keep the following issues in mind, Schnekenburger said:
• Quality and quantity of supply. The same grade of recycled rubber can vary from one supplier to the next, so you must make sure the material meets your technical needs. Plus, make sure there are adequate supplies of rubber to prevent delays in your manufacturing process and late deliveries to your customers;
• Cost of the recycled rubber compared with competing commodities such as virgin rubber;
• Physical requirements of the finished product. Using recycled ground rubber can degrade a product’s characteristics, so make sure your product still meets the customer’s specifications;
• Type of rubber. Make sure there’s compatibility among your different rubber streams; and
• Form of recycled rubber. The size of the recycled rubber and the approach used to process it can affect the quality of your finished product.
A Roundup of Mid-Atlantic States
True to its title, the Mid-Atlantic scrap tire conference offered the following overview of the scrap tire efforts in seven Mid-Atlantic states and the District of Columbia, with information provided by Michael Blumenthal of the Scrap Tire Management Council and John Rist of the Maryland Department of the Environment (Baltimore):
• Delaware has no official scrap tire program, though it reportedly plans to develop scrap tire regulations by September 2002. The state has one large producer of crumb rubber.
• Though the District of Columbia has a $1 fee on new tires sold within the district, the fee hasn’t been collected. Most of the scrap tires generated in the district are hauled to adjacent states for recovery.
• Maryland funds its scrap tire program with a 40-cent fee on new tire sales, which raises about $2.2 million a year. The major components of Maryland’s program include stockpile cleanups; compliance and enforcement actions; scrap tire projects (including playgrounds, landfills, equestrian arenas, a youth employment program, a scrap tire amnesty program to prevent tire dumping, and public information/education); and licensing for companies in the scrap tire chain. The state has issued 3,070 licenses, encompassing 2,382 collection facilities, 681 haulers, three TDF consumers, two recyclers, and two waste-to-energy facilities. In fiscal year 2001, Maryland generated 5.5 million scrap tires and processed 6.7 million.
• New Jersey has no tire fee, with most of its scrap tire efforts handled on the county level and focused on stockpile cleanup. The state has several small-to-medium-sized scrap tire processors, though its one large TDF consumer has shut down.
• New York passed a bill in 2000 creating a 17-member panel to consider a scrap tire fee and plan a scrap tire program. The state generates around 20 million scrap tires a year and claims to have 25 million stockpiled tires (though it could have twice that total). There are five permitted scrap tire collection/processing locations in New York, no ground rubber production, no TDF markets, and some work on road civil engineering projects.
• Though Pennsylvania has a $1 tire fee, the funds are used to subsidize mass transit rather than support scrap tire projects. Instead, the state takes money out of its general funds to pay for stockpile cleanups. Pennsylvania, which awards grants and loans to innovative scrap tire enterprises, generates 12 million scrap tires a year and has markets for most of them. There are three TDF consumers and three crumb rubber producers in the state.
• Virginia has an “effective” scrap tire program thanks to its 50-cent tire fee and its subsidies of $22.50 a ton for processed tires ($50 a ton if the tires come from a stockpile). Significant quantities of processed tires are used as alternative daily landfill cover, though a percentage is consumed by the three TDF users in the state.
• West Virginia imposed a tire fee two years ago for stockpile abatement. There has been little work done on market development in the state, with most recovered tires going into landfills.•
The future prospects for scrap tires remain bright, thanks to old and new markets—from tire-derived fuel to road projects to septic drainage fields to sports surfacing, and more.