Page 646 - Materials Chemistry, Second Edition

CAT3525_C21.qxd 1/27/2005 12:56 PM Page 617
Construction and Demolition Debris 617
Approximately 11 million tons of waste asphalt roofing shingles are generated in the United
States per year (Franklin Associates, 1998). Reroofing accounts for 10 million tons, with 1 million
tons from manufacturing scrap. Old roofs are often covered over with a set of new shingles, so some
tear-offs contain two layers.
To recycle shingles for use in new products, the shingles must be ground to a specified size and
the contaminants removed. Primary grinding may produce fragments measuring 2 or 3 in. across.
Secondary grinding may be needed to produce smaller pieces; for example, aggregate base may
require ¾ in. or smaller, and asphalt pavement may require 1/2 or 1/4 in. or smaller. Depending on
the desired use, the shingles may have to be sieved after grinding (CIWMB, 2002). For virtually all
uses, contaminants must be removed. Possible contaminants may include metals, which can be
removed by a rotating magnet, and wood.
Common uses for recycled asphalt shingles include asphalt for paving and new roofing materi-
als. Asphalt shingle scrap can be used in a variety of products, including:

● Asphalt pavement
● Aggregate base and subbase
● Cold patch for potholes, sidewalks, utility cuts, driveways, ramps, bridges, and parking lots
● Pothole patch
● Road and ground cover
● New roofing
● Fuel oil
Meeting the specifications for paving and roofing materials limits the above applications.
Preconsumer manufacturing scrap is used in hot mix asphalt; however, postconsumer scrap (8 to 10
million tons per year), which is less uniform in composition, is not as widely used in hot mix asphalt
(Button, 1997; Franklin Associates, 1998).

21.4.6 ASBESTOS SHINGLES
Asbestos is a naturally occurring mineral of both the serpentine and amphibole groups. Its histori-
cal popularity has been due to its ability to withstand excess heat and its resistance to conducting
electricity and chemical decomposition. Furthermore, asbestos can be woven into useful fabrics,
pastes, and muds for use in construction.
The occurrence of asbestos-containing shingles in roof replacement jobs is rather low. The total
asbestos content of asphalt shingles manufactured in 1963 was 0.02%; in 1977, the percentage
decreased to 0.00016% (CIWMB, 2002). Asbestos is no longer used in the manufacture of asphalt
roofing shingles; however, due to the practice of covering an old roof with new shingles, asbestos
may still be found in the shingle waste stream.
The agencies regulating asbestos include the U.S. EPA, the U.S. Occupational Safety and
Health Administration (OSHA), and city and county health departments. The U.S. EPA regulates
friable asbestos over 1%. OSHA regulates friable and nonfriable asbestos over 0.1%. Processors
need to contact these agencies to determine any relevant permitting and monitoring requirements
(Figure 21.6).

21.5 REDUCTION OF C & D DEBRIS

As with all other waste management strategies, waste minimization must be given high priority
in order to limit any adverse environmental impacts, hold down disposal costs, and minimize
future liability. Regarding C&D wastes, reduction strategies should begin with the earliest
choices made in the building process, including architectural design and material selection (U.S.
EPA, 2002). Design concepts should include waste prevention, product durability, and recycla-
bility of materials.