There
are over 4.5 billion tons of waste generated in the United
States on an annual basis. Many of these materials have been
or are presently under consideration as aggregate substitutes
in highway construction. In theory, recycling of these waste
materials into the highway environment conserves valuable
natural materials and makes use of materials frequently considered
as wastes. Many such materials are routinely used in Europe
and Japan in highway construction where a more institutionalized
framework is present based on the general scarcity of natural
aggregates. Wastes presently being used or under consideration
in the United States include reclaimed asphalt pavement (RAP),
Portland cement concrete (PCC) recycled concrete pavement
(RCP), coal fly ash (CFA), waste tire products (crumb rubber,
chipped tires), blast furnace slags, steel slags, coal bottom
ash, MSW incineration bottom ash, construction debris, foundry
sands, mining wastes, and contaminated soils. Certain materials
such as RAP, RCP, and CFA are widely used in highway construction.
The use of many other waste materials has been done on an
ad hoc basis and frequently limited to regional or state demonstrations
driven more by local pressures to avoid disposal of the wastes.
There is a need to bring together Federal and State interests
and initiatives to address this situation.
Recycling
and reuse of wastes is not new to the highway industry. There
is an implicit waste utilization hierarchy that is presently
used in highway construction. Wastes associated with pavement
manufacturing (e.g., RAP, RCP) are generally the highest priority
for recycling back into the manufacture of new pavements.
This is usually observed nation-wide with 80% recycling rates
for RAP. However, care must also be taken when incorporating
waste materials of unknown or limited long-term performance
experience into pavements. Questions regarding long-term performance,
future environmental behavior, economics, recyclability, and
worker health remain.
In
the late 1960's through the mid-1970's, FHWA sponsored a major
research program to examine the use of incinerator residues,
CFA and coal bottom ash, sulfate wastes, sewage sludge, waste
rubber, RAP, and RCP in the construction of highway facilities.
At the time, these studies focused more on physical performance
issues (mix design, construction) with little emphasis on
environmental performance. It is now recognized that environmental
performance is an equally important component for the waste
utilization concept.
More
recently, and in part in response to Section 1038 of ISTEA
in 1991, there has been an increased interest on the subject
of recycling in the highway environment on the part of the
Federal Highway Administration (FHWA), the Transportation
Research Board (TRB), the American Association of State Highway
and Transportation Officials (AASHTO), and the U.S. EPA. While
there has been much focus on various institutional issues,
engineering property issues, and economic issues, there has
been no central research or outreach focus to these efforts.
The Center can play an important central role to help coordinate
these efforts.
It
is important to also stress that the Center serves as a resource
for FHWA and State transportation departments, by developing
and maintaining the information they need. Decisions on permitted
uses will continue be made through existing mechanisms at
the State level. The only change is that those decisions can
now be based on data collected and evaluated by the Center
as an independent third party, thus permitting decisions based
on objective outside analysis.
