Page 76 - Highway Engineering Handbook Building and Rehabilitating the Infrastructure

ENVIRONMENTAL ISSUES 59

They have been used as fill materials, in base courses, and in asphalt mixtures for years in
areas where they are abundant and conventional sources are limited. Because of the metal
content in the mill tailings, the stockpiles must be carefully analyzed to characterize
leachate properties before use would be is deemed appropriate.
Waste Rock. Surface mining operations and subsurface mining operations produce an
estimated 1 billion ton of waste rock annually in the United States. Some have been used
as construction aggregate and in embankments; however, transportation costs from remote
mines to construction areas often render the use of the rock economically infeasible. Where
transportation is reasonable, waste rock can be used as stone fill for embankments or as
riprap, or crushed for aggregate. These uses have been shown to be successful.
Environmental considerations of leachate, low-level radiation, and sulfuric acid content
should be investigated before use is deemed appropriate.

1.6.6 Agricultural Waste
Recycled agricultural waste has potential for use in many applications not related to high-
ways. Uses of agricultural wastes (with a few notable exceptions) in highways are usu-
ally restricted to landscaping applications. It is estimated that more than 2 billion tons
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(1.8 10 kg) of agricultural waste is produced each year in the United States. This rep-
resents about 46 percent of the total waste produced in the United States each year.
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Animal Manure. Animal manure is produced at a rate of 1.6 billion tons (1.5 10 kg)
annually in the United States. Other than its use as fertilizer or as composting material for
landscaping rights-of-way, it has little recycling value for highways.
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Crop (Green) Waste. Of the 400 million tons (363 10 kg) of crop waste produced
annually from harvesting operations and grain processing, the potential to use rice husk ash
to increase compressive strength in concrete is the most promising highway use. Research
has also been conducted into converting cellulose waste to an oil appropriate as an asphalt
extender.

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Logging and Wood Waste. It is estimated that about 70 million tons (64 10 kg) of
lumber waste from logging and milling operations is produced each year. Only about one-
third of the wood from logged trees is used as lumber. Much of the remainder is used in
other industry applications. Uses in highways include mulching and lightweight fill mate-
rial for embankments or to repair slides. Application as lightweight fill material has been
well documented and proven to be successful. Life expectancy of such embankments is
estimated at 50 years.

1.6.7 Domestic Waste
It is estimated that approximately 4 lb of domestic refuse is generated every day for every
person in the United States, of which about 3 lb (1.4 kg) per day goes to domestic land-fills
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and 11 percent is recycled. It is estimated that about 185 million tons (168 10 kg) of
domestic waste is generated per year in the United States. Several of these wastes have a
potential for reuse in highways.
Refuse. Landfill refuse is not sought for reuse in highway construction because there
is little homogeneity among landfill refuse, and so a great deal of analysis and separation