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RECYCLED ASPHALT SHINGLES IN ROAD APPLICATIONS
An Overview of the State of Practice
September, 1999
A literature review was undertaken to identify previous research on the use of waste asphalt shingles in
road applications. This review revealed a that a number of states, universities, and public and private
organizations have performed relevant research or have experience in the subject. The findings of these
studies, particularly as they relate to the individual phases of this project, are summarized below. The
principal investigators will continue to research new initiatives throughout the duration of the project.
Asphalt Shingles:
The composition and properties of asphalt shingles are characterized in studies by the states of
Minnesota [1] and North Carolina [2], the University of Maryland [3], the National Asphalt
Pavement Association [4], asphalt plant manufacturer Astec Industries Inc. [5], and others.
There is good correlation in the information presented by the different entities, with only some
minor deviation in the details. Based on the studies it can be concluded:
? In the United States, approximately 7 - 9 million tons of old asphalt shingles roofing
(“tear-offs”) is removed from existing building each year, and about 0.5 to 1.0 million
tons of factory rejects and tab cut-outs (“factory scrap”) are generated each year.
? The exact composition of a particular shingle depends on the manufacturer and the
roofing application, but the shingle manufacturing process is similar in each instance.
The process begins with a layer of organic (cellulose or wood fiber) or fiberglass
backing felt. The felt is impregnated with liquid asphalt, then coated on both sides with
additional asphalt. The asphalt used as the saturant is of a different type than the asphalt
used as the coating, but both are harder than asphalt generally used in pavement. Both
types of asphalt are “air-blown”, or bubbled, during production, a process that
incorporates oxygen into the asphalt and further increases the viscosity. Powdered
limestone (70% passing the No. 200 sieve) is also added to both types of asphalt as a
stabilizer.
Once coated with the appropriate thickness of asphalt, one side of the shingle is then
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surfaced with granules for protection against physical damage, and damage from
ultraviolet rays of the sun. The granules which are exposed in the roofing application are
comprised crushed rock coated with ceramic metal oxides, and the headlap granules
are coal slag. Both types of aggregate are relatively uniform is size, most ranging from
0.3 - 2.36 mm, and both are hard and angular.
Finally, a light coating of fine sand (< 0.425 mm) is applied to the back surface to
prevent the individual shingles from adhering to each other during packaging and
transport.
Typical Shingle Composition
Component Organic Shingles Fiberglass Shingles
Asphalt 30-35% 15-20%
Felt 5-15% 5-15%
Mineral Filler 10-20% 15-20%
Mineral Granules 30-50% 30-50%
? Tear-off shingles usually contain a greater percentage of asphalt than new shingles, due
to the loss of a portion of the surface granules from weathering. The asphalt in tear-off
shingles is hardened from oxidation and the volatilization of the lighter organic
compounds. Tear-offs are often contaminated with nails, paper, wood, and other
debris.
? The American Society for Testing and Materials (ASTM) has set out specifications for
roofing shingles. However, the specifications, ASTM D 225-86 (Asphalt Shingles
[Organic Felt] Surfaced with Mineral Granules) and ASTM D3462-87 (Asphalt
Shingles Made from Glass Felt and Surfaced with Mineral Granules), allow for a fairly
wide range of products. Each shingle manufacturer has more detailed specifications for
their own roofing products.
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? Information regarding the inclusion of asbestos in roofing shingles is inconsistent.
Certainly, asbestos is not used in the production of new asphalt shingles, and it is
unclear as to what degree asbestos was ever used in shingle manufacturing. The
California Integrated Waste Management Board reports that the total asbestos content
of asphalt shingles manufactured in 1963 was 0.02 percent; in 1977, it had dropped to
0.00016 percent. [6] The Georgia Department of Transportation relates that asbestos
was used in roofing shingles as late as the 1980s [7], while the Iowa Department of
Transportation reports the asbestos usage in roofing shingles was discontinued in 1973.
[8] The same Iowa DOT study reported that of 368 shingle samples analyzed, only 3
(0.8%) contained asbestos.
Personal communication with roofers, the Vermont Department of Health, and a
Vermont-certified asbestos laboratory indicate that asbestos in roofing is generally
confined to commercial “built-up” roofing, older roof coatings, and roofing cement.
Asbestos-containing roofing shingles are rare.
Processing Roofing Waste:
? Shingles must be shredded or ground to be used successfully for virtually any road
application. For hot mix asphalt (HMA) and cold patch, generally the smaller the
shreds, the better they will be incorporated into the mix. In these applications, the
shingle pieces must be smaller than ½", and preferably smaller than 1/4". Specifications
written for the Texas Department of Transportation requires that 100% of the shingle
shreds pass the 19 mm (3/4") sieve, and 95% pass the 12.5 mm (½") sieve. [9] The
Georgia DOT requires that 100% of the shingle scrap pass the 12.5 mm sieve. [7 ]
Guidance from the FHWA also recommends shreds sized less than ½". [10]
? Crushers, hammer mills, and rotary shredders have been used with various success to
process waste shingles. Often the shingles are passed through the processing
equipment twice for size reduction.
? Tear-off roofing is easier to shred than factory scrap. Factory scrap tends to become
plastic from the heat and mechanical action of the shredding process. Tear-off roofing
is hardened with age and is less likely to agglomerate during processing.
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? Water is sometimes added during shredding to both keep the shingles cool and to limit
dust, but obviously the added moisture is undesirable in producing HMA.
Alternatively, the shreds may be blended with up to 20% sand or screenings that would
otherwise be added later in the production of the HMA or cold mix asphalt patching
material. [9] The roofing shingle shreds may also be mixed with recycled asphalt
pavement (RAP) to prevent clumping of the stockpile.
? Tear-off roofing is much more variable in composition than factory scrap, and is more
contaminated with debris which complicates processing. Nail removal is accomplished
by magnets after shredding. Paper and lightweight contaminants may be removed by
blowers or vacuums.
Roofing Shingles as Aggregate:
? Although the usage of processed roofing shingles as aggregate in road construction or
maintenance seems to becoming more common, very little scientific research on its
performance was found. Most of the projects are field tests or commercial endevours,
with only anecdotal observations as findings.
? Probably the best example is a 1995 Iowa Department of Transportation study on the
use of ground shingles as a surface treatment on an unpaved road. [8] Approximately
300 tons of tear-off shingles were ground to pieces less than 1-inch, and approximately
600 tons of tear-off shingles were ground to less than 2-inch pieces. The two sizes of
shingles were mixed together prior to use. 500 tons of the processed shingles were
applied onto newly lain crushed limestone. The shingles were graded back and forth to
achieve a uniform shingle/limestone mixture of about 2.5-inch in thickness. After two
years of observations, the study concluded that shingles are very effective for dust
control on rural roads, result in better lateral control of vehicles, reduced the loss of
granular material into the ditches, and resulted in a quieter and smoother roadway.
Processing the shingles costed $30 per ton, $10 less than the tipping fee at the local
landfill, effecting an economic benefit to the project.
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? Bituminous Roadways, a Minnesota shingle processor, and the Minnesota Department
of Transportation are cooperating on research on using processed scrap shingles as
dust suppression on gravel roads. [11] Preliminary feedback has been positive; the
shingle scrap resulted in less dust, better driving conditions, and does not need frequent
re-application as do conventional dust suppressants. The firm is also exploring the use
of processed shingles top-coated with an emulsifier in low volume applications such as
driveways and parking areas.
? C.C. Mangum, Inc., of Raleigh, North Carolina, is marketing coarse ground factory
scrap shingles as a low-cost driveway and parking area surface treatment. [12] Cost of
the material is $9.00 F.O.B. at the Mangum plant.
? Commercial Paving, Inc., Scarborough, Maine, uses tear-off scrap roofing in several
different paving applications. [13] Processed shingle material is incorporated in
“R&R”, a blend of aggregate, crushed and screened demolition waste, virgin
aggregates, and an asphaltic emulsifier. “R&R” is manufactured to a variety of
specifications, and is used as base and subbase material.
Roofing Shingles in Cold-Applied Asphalt:
? It appears that little applied research has been done with incorporating asphalt shingles
into cold-applied paving mixes. The New Jersey Department of Transportation
(NJDOT) did pave a small section of a low traffic volume ramp with a “RePave” a
shingle based product which is marketed as a pot hole patching material. [14] While the
State was pleased with Repave’s performance, the product is not available anymore in
bulk qunatities.
Button et al., [9] reports that several entities have formulated cold-applied, shingle
containing mixtures for light traffic paving applications, but no specific data was
available.
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? Recycled asphalt shingles have been used relatively extensively as an ingredient in coldapplied
maintenance mixtures; that is