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Technology
Brief
SHREDDED SCRAP TIRES AS LIGHTWEIGHT FILL IN ROAD EMBANKMENTS |
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Technology
Brief
SHREDDED SCRAP TIRES AS LIGHTWEIGHT FILL IN ROAD EMBANKMENTS |
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Each year in the United
States land slips occur under road embankments because a weak plane in the
in-situ soil is overloaded and fails.
One preferred repair technique is to return the road to its original
elevation using a lightweight fill instead of normal soil.
When properly done, this technique prevents the road structure from
overloading the weak slip plane again. In
the past, sawdust or chipped lumber has been used as the fill material. However, these materials tend to rot in repeated wet/dry cycles
and are becoming more expensive with the rising cost of wood fiber. This technology brief provides information
on a viable alternative to conventional lightweight fill ¾ using shredded scrap tires.
Tires As Lightweight
Embankments
Road embankments have the potential
to use an enormous quantity of tires. For example, an eight-mile, 20-foot embankment for a two-lane road
would use approximately 50,000 tires. Scrap
tires have been tested as lightweight fill for road embankments in Washington
and a number of other states. The
Federal Highway Administration sponsored an experimental project in Oregon
(1). Some of the valuable attributes
of shredded scrap tires documented in this and other studies are described
below.
Compaction. Shredded scrap tires are easy
to compact and are very lightweight with a density of 24 to 33 pounds per
cubic foot (pcf) in haul trucks. They
have a compacted density of around 45 pcf (a little less than half the weight
of ordinary compacted soil) before being surcharged with soil, the pavement
structure, and traffic. The maximum
density of the shredded tire fill after completion of the pavement structure
and several months of traffic is approximately 52 pcf. Vibratory compaction equipment does not work
well with shredded tires because the material tends to "bounce"
rather than compact. One successful
compacting technique is to place approximately three feet of loose tire shreds
and then compact with three "full coverage" passes of a D-8 or equivalent
bulldozer.
Permeability. Voids between tire shreds give
shredded scrap tire fill the permeability of clean gravel, but with significantly
less weight. This is of particular
importance because the light weight and permeability of shredded tire fill
minimizes the load increase on the weak slip plane during rainy periods.
To prevent the migration of fines into the fill and possible settlement
in the surrounding soils, shredded tire fills are commonly encapsulated in
geotextile fabric.
Installation. Shredded tires should be dumped
from haul trucks and spread by steel-tracked equipment to
prevent flat tires, as steel
wires protruding from tire shreds can penetrate the inflated tires of loaded
trucks.
Leachate. To address concerns about the
potential leaching of heavy metals and polynuclear aromatic hydrocarbons (PAHs)
from shredded scrap tires, the Rubber Manufacturers Association conducted
the EPA's Toxicity Characterization Leaching Procedure (TCLP) on tires and
other rubber products. According to
the results, the leachates from rubber products do not exceed federal standards.
However, recent tests indicate that if tires are submerged
in confined, relatively small amounts of water for several days to weeks,
the water becomes acutely lethal to some varieties of fish (2, 3 ,4).
While not similar to rain water flowing through a shredded tire fill,
this situation could be replicated by slow flowing ground water seeping through
a large tire fill. Until ongoing tests determine which compound(s)
are causing the lethality, the best practice when using shredded tire fills
is to keep the bottom of the fill above the historic high of the ground water
table.
Other Uses For
Shredded Tires
Like rubber, tire shreds have a high coefficient of
friction. With the angle of repose
for compacted tire chips as high as 85O (5), steep slopes can easily be maintained with shredded
tires. Combining both a high coefficient
of friction and high permeability, shredded tire scraps will also work well
as backfill behind retaining walls (6). Shredded scrap tire fill has also been used as an effective insulating
layer below roads to minimize frost penetration. Field tests have shown that a 6-inch thick
tire chip layer can reduce frost penetration by up to 40% (7).
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For More Information |
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For a copy of the report, Shredded Scrap Tires As Lightweight Fill In Road Embankments (#T-95-4), call the CWC subscription line at (206) 587-5520. For more information call CWC at (206) 443-7746, email info@cwc.org, or visit the CWC Internet Website at www.cwc.org. This technology brief was prepared by CWC, Managing Partner of the Recycling Technology Assistance Partnership (ReTAP). ReTAP is an affiliate of the national Manufacturing Extension Partnership (MEP), a program of the U.S. Commerce Department's National Institute of Standards and Technology. ReTAP is also funded by the U.S. Environmental Protection Agency and the American Plastics Council. CWC is a division of the Pacific NorthWest Economic Region, 2200 Alaskan
Way, Suite 460, Seattle, Washington, 98121. |
References
1. Experimental Project Use of Shredded Tires for Lightweight Fill. FHWA Experimental Project No. 1 (DTFH-71-90-501-OR-11). Federal Highway Administration, 1991.
2. Abernethy. The Acute Lethality to Rainbow Trout of Water Contaminated by an Automobile Tire. Ontario, Canada, 1994.
3. Nelson et. al. Identification of Tire Leachate Toxicants and a Risk Assessment of Water Quality Effects Using Tire Reefs in Canals. U.S. Department of the Interior, Bureau of Reclamation, 1993.
4. Kellough. The Effects of Scrap Automobile Tires in Water. Ontario Ministry of the Environment, 1991.
5. Edil and P. Bosscher. Development of Engineering Criteria for Shredded Waste Tires in Highway Applications. University of Wisconsin-Madison, 1992. p. 15.
6. D. Humphrey and T.C. Sanford. “Tire Chips as Lightweight Subgrade Fill and Retaining Wall Backfill.” Proceedings of the Symposium on Recovery and Effective Reuse of Discarded Materials as By-Products for Construction of Highway Facilities. Denver, CO, 1993.
7. Humphrey and R. Eaton. Tire Chips as Subgrade Insulation - Field Trial. University of Maine - Orono, 1994.
Additional Resources
A Report on the RMA TCLP Assessment Project, Rubber Manufacturers Association, Washington, DC, 1989.
This technology brief was prepared
by the Clean Washington Center. The Clean Washington Center is the Managing
Partner of the Recycling Technology
Assistance Partnership (ReTAP). ReTAP’s
mission is to advance industry’s use of recycled materials through technology
extension services. ReTAP is an affiliate
of the national Manufacturing Extension Partnership (MEP), a program of the
U.S. Commerce Department's National Institute of Standards and Technology.
ReTAP is also funded by the U.S. Environmental Protection Agency and
the American Plastics Council.
Fact Sheet Issue Date: August 1995