SFOR
CLING
E
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This summary report (SW-32c.1) was prepared
by IRENE KIEFER
ft is based on work done under contract No. CPE-R-70-0047
to the Federal solid waste management program
U.S. ENVIRONMENTAL PROTECTION AGENCY
1974
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402
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INCENTIVES FOR
TIRE RECYCLING
AND REUSE
Over 180 million rubber tires are discarded in the
United States every year. Although they make up only a
small fraction of our national solid waste burden, tires
are among the most intractable components.
Burned in concentrations in a typical municipal incin-
erator, rubber tires give off large quantities of unburned
hydrocarbons. The smoke, highly visible and noxious,
must be controlled to meet new and tighter air pollution
regulations. This can be done by adding more air to the
incinerator furnace to improve combustion and by using
scrubbers and electrostatic precipitators to clean the ex-
haust. Thus, a modern incinerator can solve the air pol-
lution problem. But still another problem remains: the
large quantities of heat released by concentrated burning
rubber damage incinerator grates and refractories.
Tires are just as troublesome in sanitary landfills.
Whole tires compacted in bulk into a sanitary landfill
spring back to their former shape and tend to work up
while the fill is settling. Ultimately they emerge at the sur-
face, where their appearance is objectionable and they
-------
offer refuge for rats and other disease carriers. Further-
more, tires are resistant to natural decomposition, mak-
ing them a permanent and ever-increasing solid waste
problem.
A more attractive alternative to disposing of tires by
conventional incineration or landfilling is the possibility
of recovering energy from the combustion of tires. The
heat value per pound of tires, which is equal to or greater
than that of coal, may eventually make feasible the use of
tires as a fuel, either in a supplementary role or as a sole
source of energy. While the economics of tire supply and
pollution control need to be addressed before energy re-
covery from tires could become commonplace, this alter-
native end-use for tires holds much promise for the future
and is, in fact, the subject of some study at the present
time.
As part of its resource recovery efforts, the U.S.
Environmental Protection Agency's Office of Solid Waste
Management Programs contracted with International Re-
search and Technology Corporation, of Washington, D.C.,
to develop a number of national strategies to pn
recycling and reuse of tires, thereby preventing them
becoming solid waste problems.
The study started on the premise that the n
could be separated by existing processes from othe
terials in tires and converted into a uniform subs
that could then be incorporated into new tires. Some
ber is now reclaimed by such processes, but it has
reported that the product lacks the uniformity, te
strength, and heat- and abrasion-resistance of new rul
Small amounts are now used in tires to make new ru
easier to work. Reclaimed rubber, however, is not
suited to operation at high speeds.
At present, therefore, there appears to be little [
pect of increasing the use of reclaimed rubber in
manufacturing enough to make it an effective mean
disposing of scrap tires. The output of the reclair
industry dropped in the 1960's and is expected to <
tinue to drop during the 1970's.
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Tire Market Model
Tire
nufacturer
'.'.".• . "•
— w
• • . " •••-'•
Auto
Manufacturer
fc ^
Tire Retail
'•"•':: T. :/;;'
Auto Retail
^v^^Uvfv-^
'""•: •'..••'•••'•'•.•'•••'-',•'
•'• : .•'.'-, - .''.';;:;'->-i
^ '.-.. -i-/ .:;>;.^ :»••;.
- V "" . ';>^ -, ' '•• ^ *.
'--." •. • <" ' '•
\ • ,' - -"'' ! ' .
"' ' '•" - ,
Retread
^-X^/'*^
Consumer
1 •"'• '" ,-J' •
. '; -"- -.: . "•
",..:,-;£• jo.
Disposal
p w ^
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THE TIRE WASTE STREAM
The IR&T study considered a range of alternatives
along the complicated route a tire takes between its
manufacture and ultimate disposal.
Tire Manufacturers
There are 182 manufacturers of rubber tires, tubes,
and tire products in the United States, with a total em-
ployment of about 93,000 and annual sales of $3.7 bil-
lion. In 1969, these companies shipped 229.9 million
new pneumatic tires of all kinds. About 200 million were
for passenger cars, trucks, and buses, with smaller per-
centages being for bicycles, industrial vehicles, tractors,
aircraft, and motorcycles. An additional 14 million new
tires were imported either separately or as original equip-
ment on imported cars. More than 46.5 million retreaded
tires were sold in the same year. Thus a total of 290.4
million pneumatic tires were shipped or sold in the United
States in 1969.
Passenger Cars Take More Than Three-Fourths <
Output of Pneumatic Tires
Passenger Car
Truck and Bus
\SteyeJe
5,0%
I Industrial
Tractor and Otttws 3.056
3.0%
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In making these tires, the manufacturer uses syn-
ic, natural, and reclaimed rubber, as well as steel
d and fiber glass, steel, rayon, nylon, and polyester
i. In choosing among these materials, the manufac-
.•r is guided by their abrasion resistance, heat resis-
:e, tensile strength, uniformity, the ease with which
/ can be worked, and their costs. Guided primarily by
rket demand, he decides whether to make the materials
> regular two- or four-bias-ply tires, bias-belted tires,
ial tires, snow tires, or solid tires. His decision will
re a major effect on the life of a new tire and its suit-
lity for retreading, both of which, in turn, have a major
ect on the total number of scrap tires entering the
ste stream in any given period.
A number of design factors influence a tire's dis-
sal. Size—set primarily by the automobile man-
acturer—is a factor in that large-diameter tires are
eoretically capable of wearing longer than smaller tires
cause they reduce heat buildup (which is the major
,'terminant of tread wear) and also require fewer revolu-
tions per mile. The proliferation of tire sizes has a bearing
on retreading. Some retreaders discard odd-sized tires
because they do not accumulate in sufficient numbers to
justify the additional molds required to retread them.
Another consequence of the proliferation of tire sizes
is that tires of two, three, or four different sizes are some-
times mounted on the same car, leading to excessive tire
wear. The automobile manufacturer, of course, shares the
responsibility for the numerous tire sizes. Great stan-
dardization of tire sizes and specifications should be pos-
sible in the existing new-car market for, although scores
of different-sized tires are produced for passenger cars,
10 sizes account for 85 percent of all sales.
Structural characteristics make some tires more suit-
able for retreading than others. The new fiber-glass-belted
tire, for example, was originally somewhat harder to re-
tread than a rayon or nylon cord bias-ply tire. This was
due in part to the fact that the carcass is more rigid and
sometimes has slight irregularities in its contours. These
irregularities cause difficulties in the buffing process that
-------
precedes application of new tread. Quality control is im-
proving, however, and carcass rigidity may turn out to be
an asset in retreading, rather than a liability, as sizes
and shapes are more accurately controlled. Glass-belted
tires have grown from 6 percent of the market in 1968 to
70 percent in 1971. This trend is expected to continue,
so retreadability of glass-belted tires will have an impor-
tant impact on the number of carcasses entering the
waste stream.
The radial tire, which is also growing in popularity,
is subject to less flexing than other types and consequently
is expected to give better mileage than bias ply, at least
for some cars. While their cost-per-mile ratios are not
necessarily better than those of much cheaper tires, ra-
dials have the virtue of reducing sharply the frequency
with which carcasses must be disposed of. Suitably re-
treaded, a steel-belted radial tire might last 100,000 miles.
Are New Tires Matte by Domestic I
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Glass-Belted Tires Have Taken Over Major Share
of Tire Sales
too
80
60
40
20
% Belted-bias
% Radial
OMi
1968
1969
1970
1971
Automobile Manufacturers
Tire manufacturers sell between a quarter and a
third of their output to automobile manufacturers. As the
largest single buyer of new tires, the automobile industry
plays a leading role in tire design.
Two aspects of automobile engineering—perfor-
mance and suspension characteristics—affect tire waste
markedly. Faster acceleration and cruising speeds in-
crease heat buildup and reduce the amount of reclaimed
rubber that can be used in new tires. Automobile suspen-
sions influence the air pressure called for in tires. High
air pressure reduces tire flexing and so reduces tread
wear directly. Also, flexing leads to excessive heat build-
up. At the same time, high pressure reduces the damping
effect of the tires on shock vibrations transmitted from
road surface to suspension system. U.S. automobile de-
signers, relying on the tires to absorb as much vibration
as possible, tend to recommend the lower tire pressures
that promote flexing while improving traction.
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Tire Retailers
The remaining two-thirds to three-fourths of the tires
made in the United States go to tire dealers. The principal
outlets are gasoline service stations and independent tire
dealers, each accounting for about one-third of all retail
sales. The remaining third is accounted for by manufac-
turers' outlets, department stores, auto supply stores,
new car dealers, and garages. Almost 95 percent of all
purchasers of replacement tires leave their old tires with
the retailer who sells them their new tires.
The retail salesman influences tire waste through his
advice to the consumer on what kind of tires to buy and
on how to maintain them. There are several areas in which
maintenance can make a difference in tire wear or ultimate
retreadability. These include air pressure recommenda-
tions (improperly inflated tires wear out more rapidly),
advice about wheel balancing and alignment (poor balance
or alignment increases wear), reminders about periodic
rotating (unrotated tires wear unevenly), and warnings
about the danger of allowing a tire to wear down too rr
(bald tires cannot be retreaded).
Nearly a million people handle retail sales of a
mobile tires. The bulk of sales are handled by about 2\
000 people, so at least this number would have to
reached by any educational program designed to reach
majority of consumers through personal contact.
Consumers
Through his buying habits and maintenance pr
tices, the consumer has a direct effect on the durability
the new tires he buys, the mileage he gets from tires
a given specification, the suitability of his used tires
retreading, and the success with which retreads compi
for sales against new tires.
When the consumer selects the type and grade
tire he will purchase, he decides among relatively in»
pensive retreads, expensive or inexpensive two- or foi
bias-ply tires, or more expensive radials or bias-belt
-------
is. He may choose snow tires with or without steel
ds, or he may choose a tire with a particular styling
iracteristic, like a white sidewall, a red stripe, or wide
il design. He will be guided by considerations of cost,
ety, durability, brand, and style. His decision will be
luenced by advertising, habit, and, at least with respect
studded snow tires, State regulation.
His decisions have a direct bearing on the number
scrap tires generated. Only about a third of all retail
les are premium-line tires, so a change in the buying
bits of a majority of tire buyers is needed to signifi-
ntly reduce the total number of tires being scrapped
ch year. Not only do better tires wear longer, but they
oduce better quality carcasses for retreading.
The maintenance a consumer gives a tire has a
arked effect on the mileage he will receive from it. One
irvey indicated that on cars for which manufacturers
icommended pressures of 24 pounds per square inch,
3.4 percent of the cars had one or more tires inflated to
3 pounds or less, with some as low as 12.
Retreaders
At the present time, the retreading industry carries
out the only major recycling function within the tire waste
stream, although, of course, each tire must ultimately
be discarded. The industry's 7,000 plants recapped an
estimated 46.5 million truck and passenger car tires in
1969. The number of passenger retreads has been con-
stant in recent years, but the number of truck tires re-
capped has been growing steadily. Retreading could be
increased still more by:
• Increasing the life of each retread
• Increasing the percentage of tires re-
treaded
• Increasing the number of times a carcass
is retreaded
Retreaders buy the entire unsorted accumulation of
tire carcasses left with major retailers. In the process,
retreaders evaluate 60 percent of all discarded tires, find-
-------
ing an average of 35 percent of them to be retreadable.
The proportion accepted seems to depend primarily on the
quality standards of the retreader. When a major tire man-
ufacturer retreads under contract to a big mail order
house, only 20 to 30 percent may be accepted.
The result of this culling process is that tires are seg-
regated from other wastes, and to a degree—sometimes
to a very great degree—centrally collected by the existing
market structure before they are disposed of. This is an
unusual situation in the waste field and a big advantage,
since the need to separate wastes is a major stumbling
block in many recycling efforts.
The retreader generally pays about 75 cents for each
usable tire. When local retailers can't supply enough car-
casses, he will pay a carcass wholesaler or tire broker
from $1.25 to $3.00 for a carcass, depending on the size,
model, and condition. In some areas, the demand for re-
treads exceeds the present supply of retreadable car-
casses.
In practice, retreading is plagued by a number of
Total Retreads Growing on Strength of Increases
10
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tacles, most of them resulting from the different de-
es of minor variations each manufacturer permits in
ndard tire sizes. These variations will affect both the
ount of smooth rubber left on the carcass by the
fing process and the effectiveness of the molding pro-
iS itself. In addition, there are variations in the inter-
e between fabric and original tread in new tires; some
these variations cause the thin layer of original rubber
t on the fabric after buffing to separate from the car-
is when the retread is being used. Finally, different
mufacturers use slightly different compounds of elas-
ners and fillers to make their synthetic rubber. An ad-
sive used to attach new tread may work well with one
bber but not as well with another.
There are at least two areas in which use of retreads
uld be increased immediately, without awaiting further
iprovements in bonding technology. First, the percentage
tires discarded in retreadable condition could be in-
eased. Many tires are damaged so as to be unretread-
>le while they are being removed from the rim. More
care on the part of the retailer removing the tire could
prevent such damage.
The consumer, too, can help. Because bald tires are
not retreadable, he must not allow his tires to become
completely worn. If consumers had incentives to trade in
their tires with 1/16 inch of tread remaining, the per-
centage of tires discarded in retreadable form would rise
by more than 35 percent. Steps have already been taken
in this direction. Since August 1968, the U.S. Department
of Transportation has required that all passenger car tires
incorporate a tread wear indicator that becomes visible
when only 1/16 inch of tread remains. Periodic safety
inspections in 19 States now require more than 1/16
inch of tread.
A major deterrent to greater consumer acceptance
of retreading is the availability of new tires at competitive
prices. Cheaper tires do not normally have the structural
strength necessary for retreading. Cheaper tires may not
perform as well as a properly retreaded tire, but being
new, they have a market advantage.
11
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The presence of many unretreadable carcasses—
either because of damage during removal, excessive wear,
or lack of structural strength—increases the cost of the
culling and sorting required to obtain reusable carcasses.
Another problem faced by the retreader is that many re-
treadable carcasses are too far away to be collected eco-
nomically. Or they may not be accumulated in large
enough quantities; this is most frequently the case at
service stations, where not enough tires are left to war-
rant frequent pickups ana where storage space is at a
premium.
The IR&T study team calculated that the retreading
industry, both carcass dealers and retreaders, examines
about 100 million passenger car tires annually; 161.8
million were available in 1968, assuming one was left
with a retailer for every tire sold. If collection had been
economically feasible, then 35 percent of those 57.5 mil-
lion unexamined tires, or an additional 20 million, could
have been retreaded, sold profitably, and diverted from
the solid waste stream.
The second area in which the use of retreads c<
be increased immediately is tire maintenance. Exces
heat is a special problem in retreads, since it can
treads to become free of their bondings and fly off i
casses at high speeds. If consumers complied more v
recommended tire pressures, less heat would build
leading to significant improvements in new tire durabil
in the proportion of used tires that could be retread
and in retread life.
Beyond a certain point, the quantity and quality
retreading cannot be increased without further advances
technology. There is persuasive evidence, according to 1
IR&T study team, that passenger car retreads can
made safer and more durable for high-speed driving. Wh
retreads make up 22 percent of replacement sales in t
passenger car tire market, they make up 37.5 percent
the truck and bus tire market.
The average truck or bus tire is retreaded 1.8 time
and many are retreaded four or five times. Large bus lini
generally do not buy their tires but rent them from ti
12
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nufacturers whose employees maintain tire pressures
J make all decisions regarding when to change and
read tires.
Tires of commercial jet aircraft are commonly re-
laded four or five times, notwithstanding the high per-
rmance and safety demands placed on them. Commer-
il propeller aircraft tires are sometimes retreaded as
any as 15 times.
Developing new technology can be approached in
10 ways. One is to accelerate research and development
i find an adhesive suitable for many different rubbers.
lis might require considerable time and effort, with no
srtainty the objective can be achieved. The second ap-
roach is to standardize the composition of the rubber in
assenger car tires. This does not appear feasible in the
nmediate future.
Barring the use of carcasses which can be retreaded
hree or four times, retreading cannot eliminate the bulk
if the scrap tire problem. A carcass intended for retread-
ng up to 100,000 miles, or the full life of a car, would
reduce tire waste by as much as 80 percent, but would
necessitate major changes in the tire industry. In general,
the entire future of retreading is threatened by the fact
that tire technology is not guided by retreading considera-
tions, an example being the new, difficult-to-retread glass-
belted tire.
Disposal
Eventually almost all tires, some after one or more
retreadings, enter the solid waste stream. About 10 billion
pounds of rubber wastes are discarded each year; about
6 billion pounds are scrap tires and tubes. Every year
the average American discards 51 pounds of rubber
wastes, or, roughly, one tire plus 20 pounds of miscel-
laneous rubber wastes. This figure does not include the
2 pounds per capita of dust and gas resulting from tread
wear.
The rubber reclaiming industry used about 7 million
scrap tires in 1968, or about 4 percent of all tires dis-
carded that year; rubber splitters used less than 1
13
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percent. Retreaders, who dispose of most scrap tires,
generally pay handling and transportation charges if a
reclaiming plant is within 200 to 300 miles. Some re-
claimers pay $6 to $10 a ton for tires delivered according
to schedules; others pay nothing. The need to dispose of
scrap tires is so urgent, however, that retreaders in remote
areas who cannot get rid of their tires pay all handling
charges, as well as freight charges of $12 per ton, to
deliver tires to any reclaimer who will accept the tires,
free of cost at his plant.
The overwhelming majority of unrecappable tires are
disposed of on the land. Retreaders either pay contractors
to haul tires away, or haul them themselves. Costs range
from 5 to 20 cents per passenger car tire and 75 to 80
cents per truck tire. A retreader with access to a municipal
dump willing to accept his scrap tires often pays $7 to
$10 a ton, in addition to his handling and hauling costs.
Some sanitary landfills set aside special areas, charging
as much as $2 per cubic yard. Private landowners and
municipal incinerators sometimes accept scrap tires.
END USES FOR WASTE
RUBBER TIRES
Automobile tires can be put to a number of u
once their original tread has worn off. Extended tire
and expanded retreading are the most obvious and e
nomically attractive form of tire recycling. But since t
are inherently incapable of being an end use, the IR
study team surveyed existing and possible end uses,
well as methods for disposal. It then identified those
believes to be the most promising and developed co
parative cost data.
14
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COSTS AND BENEFITS MUST BE CONSIDERED IN EVALUATING END USES OF SCRAP TIRES
Costs and uses without direct
economic benefits
Collection
Handling, loading, unloading
Manual
Palletized
Transportation
Train 100 miles
300 miles
1,000 miles
Truck 100 miles
300 miles
Grinding, chopping*
Incineration*
Mixed with municipal waste
In special tire incinerator
Roadbuildmg*
Landfill*
Sanitary landfill not including grinding
Dumping
Artificial reefs*
Reuse intact other than reef building*
(depending on structural design)
Cost
per tire
SO 37
04
02
06
12
20
04
21
10-25
05-06
20-40
40
01 04
0025- 005
1 45
10-50
Costs and uses with direct
economic benefits
Power production (equals SO 49 per million Btu or 5/6
of the cost of energy from natural gas, 2/3
of the cost of the energy from oil)
Destructive distillation (estimated eventual cost
exclusive of credit for sale of resulting products
Profit will depend on market for end products )
Hydrogenization (estimated eventual cost before
credit for sale of resulting products Profit could
approximate SO 23 per tire if carbon black were
to sell for SO 04 per pound )
Carbon black recovery (present cost,
which is expected to decline)
Retreading, including cost of retreadable carcass
(resulting product sells for S12 to $14)
Cost
per tire
13
03- 10
.14
1 44-1 92
645
^Figures exclude collection, handling, and transportation costs
15
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Power Production
The Btu content of used tires is comparable, pound
for pound, to that of coal. The principal difficulty in using
scrap tires to generate power is that even the largest
cities do not discard enough to sustain a power plant
big enough to be commercially feasible. For example, the
tires accumulating in New York City could supply the
power needs of only 15,000 people. A tire-burning plant
would probably have to operate as a supplementary unit
to augment a larger plant's output at peak load.
Because of the special combustion properties of rub-
ber, scrap tire furnaces are likely to be 'ess efficient than
coal furnaces. A conservative estimate is that a tire
furnace of moderate size would generate steam in a water
tube boiler at an overall efficiency of 30 percent, less than
half that of a comparable coal furnace. But even at this
efficiency, tires may be competitive with conventional
fuels. A British firm, the Watts Tyre and Rubber Com-
pany, operates a plant which consumes 700 tires per
hour and generates 3,500 pounds of steam per hour
savings of about $110 per day over the cost of coal
cheapest conventional fuel available. The company
its own supply of scrap tires and incurs no collection
handling costs.
While there is general agreement in the rubbe
dustry about the potential value of scrap rubber as
there is some disagreement about actual costs. Acco
to one estimate, the total cost of generating power
tires would average 49 cents per million Btu, excli
of collection costs, as compared to 35 cents for coa
cents for natural gas, and 75 cents for oil. These c
include, in addition to the fuel itself, the costs of ca
equipment (three times as high for tires as for coal), :
age, handling, preparation, and air pollution control.
cause heated rubber may melt and form compa
masses which are slow and difficult to burn, the fun
grate must be carefully designed. Because burning
ber generates smoke which is so obnoxious and a<
the stack controls must be particularly effective. Tf
16
-------
;s may be more than 50 percent higher for tires than
coal.
The environmental impact of using rubber tires for
I is no different from that of using coal of good quality,
vided the required afterburners and equipment are
id to control particulate air pollution. The sulfur con-
t of tires is between 1 and 2 percent. While this is
/er than most coal, it is above the 1 percent or less re-
ired by progressively more demanding municipal air
llution ordinances.
Because the plants would have to be small, power
sed on burning rubber would inevitably cost a great
al more than power from conventional fossil fuel, even
tires were delivered to the plant. If, however, power
oduction is regarded as a means of disposing of tires
low cost and obtaining benefits in return, it might be
tractive when large concentrations are available. More-
rer, a hospital or manufacturing plant that wanted to be
dependent of large power failures might benefit from
aving its own power supply.
Destructive Distillation,
Carbonization, and Hydrogenization
Although present reclaiming processes do not yield
rubber of a quality comparable to new rubber, it is pos-
sible, by more complex processes, to recover some of the
chemical constituents of tires and recycle them into new
synthetic rubber. At least three such processes are under
development. None can yet operate at a profit, but sig-
nificant amounts of private capital are currently being
invested in the expectation that the processes will be
profitable once they have reached the commercial scale.
Two of the processes, destructive distillation and
carbonization, are forms of pyrolysis, a controlled heating
process that decomposes materials in the absence of
oxygen. Hydrogenization, on the other hand, is a process
of chemical synthesis. It entails addition of hydrogen, the
element which is removed from oil to make synthetic
rubber, in order to return the rubber to its original form.
Tires are composed of 83 percent carbon, 7 percent
17
-------
hydrogen, and 6 percent ash, plus small quantities of
nitrogen, oxygen, and sulfur. Pyrolysis of tires yields oils,
gases, and a carbon-containing residue. The main dif-
ference between destructive distillation and carbonization
is temperature. At carbonization's higher temperatures,
the main product is carbon black, which makes up from
one-fourth to one-third of the synthetic rubber from which
tires are made. The present costs of carbonization are
from three to four times the cost of making carbon black
commercially from petroleum.
In destructive distillation as many as 50 gases and
liquids are formed, plus a residue consisting mostly of
carbon and representing from 35 to 60 percent of the
original weight. Production costs and market demand
would determine which products would be manufactured
by destructive distillation. The residue would be a high
quality fuel, except that it contains 1.5 percent sulfur.
Using the residue as a source of carbon black for new
tires or of activated charcoal has been investigated, with
little success to date.
To be commercially feasible, pyrolysis or h
genization would require large regional plants. T
serving metropolitan areas would need to pay only
costs of local collection. Those serving less densely
ulated areas would have to pay higher collection ci
as well as shipping costs. Under these circumstances,
sparsely populated areas would probably continue to
pose of tires by open dumping unless legally compe
to do otherwise. The most likely candidates to ope
pyrolysis or hydrogenization plants are the rubber c
panies. Not only would they use the end product, but
scrap tires could use the same distribution system
which new tires travel from manufacturer to consume
It is too soon to know whether pyrolysis or hy<
genization will be commercially profitable, or if not prc
able, at what cost they could be used to dispose of sc
tires. With the reserves of commercially recoverable
troleum dwindling, the processes offer the tire Indus
an opportunity to liberate itself from complete reliai
on a raw material that will become more expensive.
18
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ladbuilding
In contrast to some other end uses which either de-
or reduce the solid waste problems, roadbuilding could
/e the waste problem immediately and almost com-
;ely. The possibility of incorporating rubber into roads
, been considered and tested sporadically over the past
years.
As an aggregate in the roadbed, chopped rubber ap-
irs to be equal to, but not superior to, crushed rock.
bber has also been used in the surface itself as an
)halt additive. Compounds made largely of reclaimed
is have been used in at least 52 road surfacing projects
nine States. The majority of projects with good controls
re begun in the early or mid-1960's, so results are
II inconclusive. In some projects, no differences have
en observed. But a number of others have shown minor
t consistent differences, rubberized pavements show-
g less tendency to shove, crack, and ravel. In none of
e projects using low concentrations of rubber has rubber
shown a negative effect on a road. The present cost of
adding rubber to asphalt, usually in concentrations of 3
to 8 percent, ranges from $1.50 to $2.50 per ton of mix.
One recent research project has reported very sub-
stantial improvement in durability of road repairs, and
potentially in new road construction, when a mixture of
1/3 ground scrap tires, 1/3 sand, and 1/3 asphalt and
water emulsion is used as a film between the old road
surface and the new surfacing material. Tests indicate
that a 1/4-inch film should increase by 440 percent a
road surface's ability to withstand expansion and con-
traction without cracking.
Artificial Reefs
Reefbuilding, like roadbuilding, could solve the
waste problem immediately and almost completely. Since
1965, the U.S. Department of Interior's Bureau of Sport
Fisheries and Wildlife has been experimenting with build-
ing artificial reefs in coastal waters where fish nutrients
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are plentiful but protective structures on the ocean bed
are scarce. The Bureau evaluated three scrap materials
on the basis of life expectancy, surface area, encrustation
characteristics, and variability of reef design. In these
experiments, scrap tires outperformed both scrap auto-
mobile bodies and ship hulks.
At the present time, there are 43 small tire reefs in
place off East Coast waters. The Bureau estimates that
1 billion tires would be required to build reefs on sites
warranted by present recreational demands on the East
Coast alone. Extending the reefs to other waters, as well
as to commercial fishing, opens a potential capacity for
many decades, probably longer than the problem itself
will continue to exist in its present form. Insofar as dollar
costs alone are concerned, building artificial reefs may
be the most expensive way of all to dispose of scrap tires,
but it is an immediate solution and one that enhances the
recreational value of coastal waters. Furthermore, it illus-
trates the principle that society can make profitable use
of its undesirable by-products. The use of tire reefs in
marine gamefish management has been studied in z
project of the Department of Commerce, Environn
Protection Agency, and the National Tire Dealers an
treaders Association, and findings were recently rep
in a publication of the Office of Solid Waste Manage
Programs, "Scrap Tires as Artificial Reefs" (SW-119
The full effects of artificial reefs on the environ
are not yet fully understood, however. Observations b
Bureau of Sport Fisheries and Wildlife suggest that
may be no measurable effects. Tires submerged in c
water for 10 years show no signs of deterioration.
does sea water appear to be contaminated "by prolo
exposure to tires. What happens after longer exposun
well as what possible effects large masses of syntl
rubber might have on the ocean environment, are
unknown. Adding to the difficulty of measuring the eff
of tires on the ocean environment is the difficulty of \
casting what other demands—scientific, aqua-culti
recreational, commercial or otherwise—might be mad
the future.
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use Intact
The oldest and simplest method of disposing of
J tires—other than simply throwing them away—is
se them intact for nontransportation purposes. Linked
rther with flexible connectors, tires can be used on
king facilities and highways to absorb the energy of
act. Or, laced together tread to tread in mats, they
be used to control erosion along river banks or across
d dunes.
Scrap tires can also be used for retaining walls and
'round cover for soil erosion control. Retaining walls of
;ked tires are easier to handle than stone and deterio-
j less rapidly than wood. Structurally, a wall can be
de exceptionally stable when the tires are strung on
tical piles driven into the ground and filled with con-
te or dirt.
Such nontransportation uses could absorb large quan-
es of tires for a limited time only. These uses share
jther drawback. Prominently and permanently em-
placed in large numbers along roadways or shorelines,
they may be visually objectionable to many people.
Incineration
While incineration, as opposed to power production,
is simply a means of disposal rather than an end use, it
was considered by the IR&T study team because of its
importance in the scrap tire cycle. A modern incinerator
can solve the excess heat and air pollution problems
posed by scrap tires, particularly if they are chopped and
if small amounts (no more than 5 percent) are mixed
with other wastes.
The heat value contained in tires, while presently
detrimental to equipment if the tires are incinerated
whole, has interesting possibilities for energy recovery
applications.
Another alternative is to build special incinerators.
In 1964, Continental Tire Factory built an incinerator in
Hanover, Germany, to burn tires and process wastes,
including scrap rubber, carbon black, paper, oil, and
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grease. While burning tires separately is more expensive
than burning them with other municipal wastes, the cost
is not out of the question, according to the IR&T study
team. An incinerator with a capacity of 1 ton of scrap
tires per hour could burn tires for between 20 and 40
cents each. A plant of this size would service a city the
size of Washington or Cleveland, and 225 plants would
service the entire country.
Transportation costs would be lower for incineration
than for some of the end uses because of the large num-
bers of incinerators, either for mixed wastes or tires only.
With three-fourths of the population residing in urban
areas, incinerators could be located within a few miles
of the places where most tires are discarded. This would
leave some rural areas unable to transport tires econom-
ically to incinerators.
The residues from incineration, as well as the air-
borne effluents, are more capable of environmental insult
than the tires themselves, so their control is an important
aspect of any plan calling for burning scrap tires.
Stockpiling
The IR&T study team also considered stockp
the tires against the time when commercially extrac
amounts of petroleum are in short supply and recy
technology is developed. To facilitate storage and
ping, the tires could be chopped.
Ten regional disposal sites, each 300 acres, v\
accommodate all discards for two decades. Or the
could be stored in strip mines or existing excavations.
This approach has the advantage of disturbing
environment less than any other approach IR&T ir
tigated. Once set in motion, it would tend to encou
private research and development by increasing and
centrating supplies of waste tires. Its principal drawl
is political. It has the initial appearance of postponii
decision because it is difficult and of paying good me
for trash. It would succeed only if the public were i
vinced that the technology needed to make the stock
profitable is being developed.
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TRATEGIES
In developing reuse strategies from these end uses,
e IR&T study team started by recommending a tire dis-
isal tax to subsidize recycling and reuse. The tax would
iually be imposed at the time the consumer buys the
•e. A tax imposed at an earlier point would be passed
ong to the consumer anyway—along with an increased
rerhead charge.
A number of ways of paying the subsidies were con-
dered. Indirect subsidy in the form of tax exemptions
as ruled out on the grounds that, once granted, the
mounts are unknown and cannot be controlled; further-
lore, indirect subsidy conceals certain types of Federal
upport, while other direct subsidies receive dispropor-
onate publicity. For these reasons, and because pollution
batement is politically popular, the IR&T study team
recommended that financial support be granted in terms
of direct subsidy. The subsidy could be translated into
less direct terms in the future, should it serve the public
interest to do so.
The study team generally suggested that the pro-
ceeds of the tax could be paid into a Federal tire disposal
trust fund. The team felt that the trust fund device isolates
the costs and revenues and suggests that each strategy
should be self-supporting. It noted that there are, how-
ever, valid arguments against special trust funds: they
tend to be self-perpetuating, they can generate make-
work when revenues exceed expenditures, and they are
invulnerable to changes in national priorities.
Incentives to improve collection of old tires were
incorporated into several of the strategies. In some, the
retreader is paid to collect tires from small retailers. In
others a person or organization (usually a municipal, gov-
ernment) is paid a bounty for disposing of scrap tires
through an approved reuse or recycling method. These
incentives would not only affect tires in the hands of
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retailers and retreaders but should also reach tires that
have already been abandoned or that, for one reason or
another, were not surrendered to retailers when new tires
were purchased.
The payments would have to be large enough to
enable the municipality or retailer to pass some of it along
to those providing the tires. Generally, tires will come
from low overhead scavenging enterprises such as vol-
unteer groups and junk dealers, as well as from individual
consumers willing to make a modest effort to obtain some
cash benefit in exchange for used tires. Occasionally, the
municipality or retreader may enter directly into the scav-
enging business, especially if there are large accumula-
tions of scrap tires nearby.
Eleven strategies were devised by the IR&T study
team. Each strategy was analyzed as to charges, financing
arrangements, and the need for government regulation,
educational programs, and research and development. The
strategies were then evaluated according to eight criteria
that cover various technical and economic-political issues.
Evaluating Strategies for Reusing Scrap Rubber Tir
The IR&T team developed 11 strategies for reusi
scrap rubber tires, then evaluated them according
these eight criteria:
Technical criteria
How soon will the strategy
be technically feasible?
How much land/air/water
residual does the specific
use leave?
How long will this strategy
be possible?
How much of the year's
output of scrap tires could
the use absorb?
Economic-political criteria
How much cost per unit
will be recovered?
How much nonmonetary
benefit will be recovered?
How much will the strategy
change the existing tire
market?
How compatible is the
strategy with other solid
waste management
practices?
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Three of the strategies involve retreading. One seeks
increase the life of both new and retreaded tires and
leave as many tires as possible in retreadable condition.
is strategy calls for the National Highway Safety Bureau
conduct a program to educate the public on the safety
plications of the 1/16-inch tread depth and on the
istence and function of tread depth indicators, coupled
th a program to encourage all States to require tread
pth in automobile safety inspections. In addition, the
ireau would stress the importance of proper tire inflation
i both safety and wear. This strategy has the advantage
being able to be put into effect quickly and at low cost.
; with the other retreading strategies, it does not provide
i end use but merely reduces the rate at which scrap
•es are discarded.
A second retreading strategy would be more compre-
jnsive and would aim at making the retreading industry
ore competitive. It calls for removing the existing excise
x on retreads and graduating the tax on new tires. The
sorer the durability and retreading characteristics, the
higher the tax; new tires with the best characteristics
would not be taxed at all. The retreader would be paid
to take all the retailer's scrap tires and to dispose of the
unretreadable tires properly. The public education program
would be expanded to explain to the consumer how he
can reduce the solid waste problems posed by automobile
tires.
A third retreading strategy involves expanding re-
treading by having passenger car tires rented in the same
way that many bus tires are now. Local service stations
would serve as manufacturers' agents, checking tire pres-
sure and condition when the consumer buys gasoline. The
service station would replace tires as necessary and return
the old ones to the manufacturer for retreading. To en-
courage rental of tires, rather than purchase, a large
excise tax would be imposed on the sale of tires.
There are two major difficulties with this strategy.
First, it creates a restraint on trade. A consumer who has
contracted for the use of tread is not as free to switch
to a different make of tires as he is in the existing market.
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Second, there is a high degree of Federal coercion. Even
though this strategy involves no binding regulations, the
large excise tax on the sale of a tire would force every
tire company to switch to a rental system to remain com-
petitive with the first company to switch.
The three chemical processes (destructive distilla-
tion, carbon black recovery, and hydrogenization) offer
the clearest opportunity to recycle a very large proportion
—more than half of each used tire—back into new tire
use. The existing processes are too expensive for their
products to compete on even terms. This strategy pro-
poses a heavy initial federally supported research and
development program, followed by a bounty arrangement
to make early operation profitable and encourage invest-
ment in construction of suitable plants once the tech-
nology has been developed.
Combining pyrolysis or hydrogenization with power
production might make a profitable strategy. The products
of pyrolysis could be sold, while the residue could be
burned to produce power. These operations could be
housed in a single plant or in coordinated neighbo
plants. The most likely location would be near a i
producing plant. The distribution system of the tire p
could be used to collect the tires, and, in turn, the
plant would buy the products of the pyrolysis or hy(
genization plant. In principle, there are no obstacles
these combinations, but several years might be requi
even for development of plants which perform eit
function on a commercial scale, even at a loss.
The chemical processes and reef building wo
require regional collection systems, so they were group
into a single strategy. Reef building is immediately fe
ible and could absorb all scrap tires now being discardi
but it would be possible only for a few decades. By tl
time, however, the chemical processes should have be
perfected. The environmental impact of this strategy
a major uncertainty.
The strategy of stockpiling scrap tires for futu
processing is technically feasible now. Its principal di
advantage is that it appears to be a policy of inactio
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Stockpiling is facilitated by using chopped fragments,
in incineration. Roadbuilding requires chopped tire
jments, so these three end uses were grouped into a
l\e strategy. An advantage of this strategy is that it
easily be adapted either to variations in local condi-
is (such as seasonal deterioration of local roads), in
hnology (such as development of more heat-resistant
inerators), or in municipal waste disposal practices
1 facilities. The shredding equipment is readily avail-
e, and the tires wouldn't have to be transported long
tances. The scrap tires would just be chopped up and
iposed of in the most appropriate manner.
One of the strategies involves no specific end use
cause none of the existing technologies is satisfactory
d because the problems of tire disposal and reuse vary
different parts of the country. For example, the coastal
ates might be willing to go to the expense of building
tificial reefs as an inducement to tourists. Or densely
ipulated metropolitan areas that have experienced re-
sated power shortages might want to consider an inde-
pendent power system for facilities that must operate at
all times.
In this strategy, the Federal solid waste management
program would initially approve a series of end uses such
as suitably controlled incineration, stockpiling of chopped
tires, road surfacing, or reef building. It would also deter-
mine what were recycling and nonrecycling programs.
Under this strategy, Federal funds would be allocated
to the States in proportion to their tire sales. For the first
three years, the States would use their funds to build
disposal or recycling facilities. After this initial construc-
tion phase, each State would be paid the portion of its
allocated share corresponding to the number of scrap
tires it handles in an approved manner.
This strategy also provides for a continuous public
education program to explain the importance of proper
tire inflation and encourages replacement of tires when
tread depth indicators are exposed. In addition, the States
that do not yet include tread wear inspection in their
automobile safety standards would be encouraged to do
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so. And, finally, the strategy provides for a Federal pro-
gram to stimulate development of new recycling tech-
nology.
Another strategy quite similar in concept to the pre-
ceding one was also formulated. The principal difference
is that it relies on direct Federal payments to persons
disposing of tires in approved uses, rather than using the
States as a mechanism for making such payments.
This series of strategies provides the means by
which the Nation can begin to decrease the solid waste
problems posed by scrap tires, as well as to increase
recycling of the valuable resources these tires represent.
Mff643
This summary is based on "Incentives for Tire Recycling
and Reuse," a research report written by Charles H. Hump-
stone, Edward Ayres, Sam G. Keahey, and Theodore Schell of
International Research and Technology Corporation.
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