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Scrap
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Using Scrapped Truck Tires
For Drainage Culverts Low Tech, Low Cost Recycling
by Bill Siuru
Throughout
the U.S., indeed, the entire world, disposing of scrap tires is
a problem. Researchers at Iowa State University have found a novel
use for at least some of these tires, especially the harder to
recycle truck tires - use them as drainage culverts.
The concept
is quite simple. Groups of three whole truck tires held together
with steel strapping are placed side by side in a trench to form
the culvert. The bottoms of the tires are filled with sand which
serves as ballast to hold the tires in place. Filling also prevents
water from puddling and stagnating inside the casings. Then the
"culvert" is backfilled.
There are several
advantages to this low-tech use of discarded tires besides ridding
the countryside of an eyesore and an environmental hazard. Using
whole tires eliminates the need for shredding or grinding which
leads to high production costs that often had made recycling of
tires for applications as crumb rubber filler for asphalt, processed
chips for fuel or raw material for new products economically uncompetitive.
Truck tires, in particular, are difficult to grind and process
because of the heavy bead wire used.
By using whole
tires internal belts will not be directly exposed to the leaching
action of water. Finally, tire culverts offer lower material production
costs. The material cost for the truck tire culverts is about
$30 per meter length ($9 per foot). This can be compared with
plastic and concrete culverts of approximately the same diameter.
Concrete pipe is about $72 per meter ($22 per foot) and plastic
is about $53 per meter ($16 per foot).
Experience
gained during this demonstration showed that tires are more stable
in the trench and can be installed faster if they are banded together
in groups of three. However, sections of four or more banded tires
are difficult to handle and are not recommended.
The researchers
conducted several tests to determine how the truck tire culverts
respond to heavy loads. Buried conduit tests were conducted on
a truck tire culvert consisting of 18 tires -- six groups of three
tires banded together - placed in a shallow trench with fill about
0.6 meters (2 feet) above the top of the tire. Also Dodger Enterprises
built a 330 meter (1082 feet) long prototype culvert system on
previously undisturbed land near Fort Dodge.
Bruce Kjartanson
and Bob Lohnes, professors in the Iowa State University's Civil
and Construction Engineering Department conducted tests on the
culverts to quantify performance and develop design guidelines.
Testing showed that the culvert's ability to handle heavy loads
depends on the condition and thickness of tire tread, tire wear
and damage and the diameter of the tires. Bald tires without threads,
excessively worn tires and tires with holes or other damage in
the sidewalls were found to have the lowest bearing capacity and
should not be used for a truck tire culvert. Smaller tires with
deeper treads were found to be generally stiffer.
The researchers
also concluded that the load-carrying capacity of the culverts
depends on strength and stiffness of the backfill and, for shallow
trenches, on the location of the loading along the culvert's length.
As expected, the culvert with uncompacted backfill experienced
more tire deflection than the culvert with compacted backfill
support. Where loads were heaviest, the truck tire culverts experienced
more deflection, and a couple of bald tires buckled.
Truck tire
culverts should be used only for partial flow conditions due to
the high roughness co-efficient as well as to avoid any buoyancy
effects associated with air trapped in the top of tires. The maximum
water depth inside the pipe should be limited to 75 percent of
the pipe diameter. This means that with an opening of about 0.5
meter (20 inches) diameter, these culverts don't allow for huge
amounts of flow.
Fifty meters
(164 feet) of truck tires banded together use up about 190 tires.
Therefore, while tire culverts will only put a small dent in the
scrap tire inventory, it represents an easy solution that does
not require sophisticated or expensive equipment. Thus it could
be particularly attractive in parts of the world without resources
to purchase tire recycling equipment, need simple ways to cure
drainage problems and have lots of old tires.
For more information
: B.H. Kjartanson, Iowa State University Department of Civil and
Construction Engineering, Ames, IA 50011-3232; Tel: (515) 294-2140;
Fax: (515) 294-8216; [email protected]
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