Page 72 - Highway Engineering Handbook Building and Rehabilitating the Infrastructure

ENVIRONMENTAL ISSUES 55

• Price competition
• Availability
Also, under RCRA, specifications cannot be written to discriminate against materials
with recycled constituents. In addition, EPA was authorized to prepare guidelines for recy-
cling, and resource recovery guidelines addressing procurement practices and information
on research findings about the uses and availability of recycled materials. Guidelines cov-
ering coal fly ash in portland cement, recycled paper, retreaded tires, building insulation,
and rerefined oil have been developed. While not specifically required by EPA, the guide-
lines encouraged most state highway programs to prepare specifications allowing the sub-
stitution of fly ash in concrete.
Intermodal Surface Transportation Efficiency Act (ISTEA). ISTEA authorized DOT
to coordinate with EPA and state programs in developing information on the economic
savings, technical performance qualities, and environmental and public health threats
and benefits of using recoverable resources in highway construction. TEA-21 provided
technical corrections to ISTEA. ISTEA specifically calls out requirements for the per-
centage of asphalt pavement containing recycled rubber from scrap tires.
In addition, state legislation has been developing to promote both research into the per-
formance and viability of recycled materials and the procurement of such materials. Many
have established mandatory recycling laws and most have used wastes or waste by-
products in their highway programs.

1.6.2 Waste Material Generated
Waste material can be categorized as construction wastes, industrial wastes, mining or
mineral wastes, agricultural wastes, or domestic wastes (of which scrap tires are a signifi-
cant subset). Many advanced recycling programs have been established to make use of
these wastes, such as requiring identifying codes for the base resin in plastic products to
enable more refined recycling of plastics. Some of these wastes are not suitable for or do
not make a significant recycling contribution to highway use. For example, only a small
amount of the total crop waste (estimated to be about 9 percent of all the total nonhazardous
solid waste generated each year in the United States) has a beneficial highway use.
Potential uses are as an asphalt extender or portland cement additive.
In another example, it has been shown that wastes can be rendered essentially benign
when used in asphaltic concrete installations. In a demonstration to the Minnesota
Department of Transportation, the toxicity of bottom ash from a municipal sewage sludge
incinerator was shown to be less than or equal to the toxicity of the asphaltic concrete
matrix to which it was attached (Request for Approval of WIA in MnDOT Asphaltic
Concrete Non-Wear Course Projects, Final report, S. David, Jan 16, 2002).
The following articles contain brief descriptions of the types of wastes that research has
indicated have the potential for use in highway projects (NCHRP Synthesis 199).

1.6.3 Construction Waste
Much construction demolition debris consists of wastes with little recycling value for high-
ways, such as wood and plaster. However, demolition debris also includes concrete, glass,
metal, brick, and asphalt, most of which can be reused in highways as aggregate. In order
to be a viable resource and meet the standard specifications as aggregate when crushed, the
construction and/or demolition rubble must be separated from the other debris and cleaned