Page 73 - Highway Engineering Handbook Building and Rehabilitating the Infrastructure

56 CHAPTER ONE

of detritus. Construction wastes generated and the associated annual tonnage produced are
presented below. Tonnage estimates were collected from numerous sources and summa-
rized in NCHRP Synthesis 199.
Reclaimed Asphalt. Asphalt pavement from the demolition of parking lots, roads, and
highways can be reclaimed. Most states are making at least some use of reclaimed asphalt
pavement (RAP) in highways, with use within asphalt pavement as the most prevalent use.
Estimated tonnage of available RAP is 50 million tons annually. Because the use of RAP
interferes with the ability to control hot-mix temperatures during formulation, asphalt mix-
tures can contain only between 20 and 50 percent RAP. Achieving 50 percent RAP content
is practical only in a laboratory setting, where thorough blending of the RAP and new
aggregate can be controlled. When plant efficiency is a concern, 50 percent RAP in hot mix
is not practical. The differential between the temperature of the discharged gases and the
discharged asphalt mix reaches 70 F (21 C). High exhaust gas temperatures can lead to
premature corrosion of plan equipment. Thus the percentage of RAP that can be incorporated
efficiently is based on the plant efficiency that can be maintained. (U.S. Army Corps of
Engineers, Hot-Mix Asphalt Paving Handbook, AC 150/5370-14, July 1991, Appendix 1,
pp. 1–21, and 2–45.)

Reclaimed Concrete Pavement (RCP). The recycling of concrete pavement began in this
country many years ago, first as unbound aggregate, then in asphalt-wearing surfaces, and
later as concrete aggregate. Improved methods of breaking up concrete and separating out
the rebar have made the use of RCP more cost-competitive. Many states now recycle con-
crete pavements either as new concrete or as aggregate in subbase material or base course.
This does not include demolition debris of concrete structures.

Roofing Shingles. Scrap and leftover materials from composite shingle manufacturing
operations results in a large quantity of waste annually. The waste includes fragments,
asphalt binder, and granules. These wastes can be recycled as asphalt paving material.
Shingle waste from roofing contractors and demolition operations is less viable because of
possible contamination.
Sandblasting Residue. Many uses of sandblasting grit are possible if the removed paint
was not lead based. If the paint was lead based or contained other metals, the debris would
have to be analyzed to determine if it was nonhazardous before suitable use.
Demolition Debris. Demolition debris is a major component of waste. Much of this
debris can not be received in municipal landfills. To be viable for recycling, the debris has
to be separated into homogeneous materials. Rubble material has many recycling uses in
highways. Wood debris can be chipped and used for lightweight fill and mulch, but only
if it is untreated. Disposing of asbestos-containing material (ACM, prevalent in buildings
constructed before 1979) is difficult because chrysotile asbestos fibers are known to
increase cancer risk if inhaled. If demolition of buildings with ACM from state trans-
portation right-of-way is required in a project, it is possible in some states to arrange for
on-site disposal in a state-monitored landfill.

1.6.4 Industrial Waste

9
Approximately 150 million tons (136 10 kg) of industrial waste of the type that can be
potentially reused to some degree in highway projects is produced annually in the United
States. Little of this waste can be landfilled. Many kinds of industrial wastes are not