Page 77 - Highway Engineering Handbook Building and Rehabilitating the Infrastructure

60 CHAPTER ONE

would be required at individual landfills to determine the potential for use. However,
there have been occasions when a highway right-of-way traverses a landfill. In such
cases, analysis to find appropriate on-site placement of the refuse instead of costly
relocation and disposal has been found to be cost-effective. The refuse was spread in
thin layers and compacted into embankment material or used for raised medians.

Paper and Paperboard. Approximately 40 percent of the domestic waste generated in the
United States is paper or cardboard. Approximately 25 percent of the wastepaper products
are recycled each year and used primarily in making more paper, cardboard, and related
materials. A highway use of wastepaper, particularly slick paper such as magazine paper,
is in the production of mulch material.
Yard Waste and Compost. There are over 1400 yard waste composting stations in the
country. Yard waste is banned completely from landfills in many states. Compost material
must meet pathogen control, pH, metal concentration, nitrogen ratio, water-bearing capacity,
maturity, particle size, and nutrient content control standards set by the EPA. Compost mate-
rials are used for mulching, soil amendment, fertilizers, and erosion control. Concerns related
to leaching potential, odors, worker health and safety, long-term exposure, and public accep-
tance have limited use in highways to the experimental stage, except in landscape use.
Plastics. The amount of plastic waste generated each year is growing. Recycling plastics
is complicated in that plastics are developed from at least six different resin bases, which
must be sorted for the most-effective recycling. About 30 percent of the plastics made from
polyethylene terephthalate (PET), the resin base of soda bottles, is recycled. One use of
PET is as a geotextile. Low-density polyethylene (LDPE) resin from film and trash bags
can be recycled into pellets for use as an asphalt modifier in paving mixes. High-density
polyethylene (HOPE) from milk jugs has been used in manufacturing plastic posts. Reuse
of commingled plastics is more difficult but has been applied in fencing and posts. Such
plastics have also been used as traffic delineators.

Glass. The amount of glass containers produced each year is declining, but about
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12.5 million tons (11.3 10 kg) of glass is disposed of as domestic waste each year. To
be reused in glass manufacturing, glass must be sorted according to color. Uses in high-
ways include as fine aggregate in unbound base courses, as pipe bedding, as aggregate in
asphalt mixes, and as glass beads in traffic paint.
Ceramics. Ceramic waste consists of factory rejects and discarded housewares and
plumbing fixtures. Only in infrequent instances are large quantities of waste ceramics avail-
able for reuse in large applications, such as highway projects. In California, crushed porce-
lain has been used as an unbound base course aggregate. Crushed porcelain has been found
to meet or exceed quality requirements for concrete aggregate.

Incinerator Ash. Incinerator ash results from the burning of municipal waste. About
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26 million tons (24 10 kg) of incinerator ash is produced each year, of which 90 percent
is bottom ash and the remainder is fly ash. Fly ash often exceeds regulatory limits for con-
centrations of lead and cadmium. Fly ash is most often mixed with bottom ash, and this
mixture generally does not contain sufficient concentrations of metals to render it haz-
ardous. Incinerator ash has been used successfully as a partial replacement of coarse aggre-
gate in asphalt mixtures, as roadway fill, and in base course construction when stabilized
with Portland cement. Concerns on the part of the EPA about the leaching of heavy metals
have initiated several studies.