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Sound Barrier Wall Containing Recycled Rubber and Plastic

        Sound Barrier Wall Containing Recycled Rubber and Plastic

In a new process, scrap tire waste can be used in combination with a structural element
to create an aesthetic, functional, and long-lasting barrier wall.  The wall can use
~250,000 lb of scrap tire rubber per mile of barrier.

Each year the United States discards ~285 million tires.  About 100 million of those
tires are productively reused or recycled.  The remaining 185 million tires are added to
stock piles, landfills, or illegal dumps across the country. Those wasted tires could be
recycled for use in sound barrier walls.  With the expansion of freeways in urban
America, the public is demanding sound barrier walls to abate highway noise.  To date,
over 700 miles of sound barrier walls have been built in the United States and the
number of miles constructed each year is increasing.

Concept Description
In a new process, scrap tire waste can be used in combination with a structural element
to create an aesthetic, functional, and long-lasting barrier wall.  The recycled scrap tire
core consists of a mixture of several crumb rubber sizes and a phenolic binder.  A
ten-foot-high, one-mile-long wall would consume ~250,000 lb of scrap tire rubber.
The structural element, shaped into a tongue-and-groove building plank, is a
fiberglass-reinforced plastic composite that has consistent and predictable mechanical
properties with an expected life cycle of 50 years.  The glass-reinforced plastic contains
flame retardant, is self-extinguishing, and is protected by ultraviolet inhibitors to prevent
solar degradation.  The tongue- and-groove structural element is manufactured by a
continuous process that ensures high quality and structural soundness to meet the
load-bearing requirements of the sound wall.

The figure depicts the structural shape and dimensions of the channel.  The wall is
lightweight and modular and can be erected with small erection equipment.  Similarly,
the wall can be removed, repaired, or moved to a new location without large
construction equipment.  The wall can be manufactured in virtually any color or with
variable shading.

Economics and Market Potential
Virtually every state now builds noise barrier walls as part of their freeway construction. 
The number of miles being constructed is increasing every year.  As traffic increases
and the public becomes more aware and sensitive to environmental issues, this trend is
expected to continue.

Scrap tire rubber is available in every state and is a major problem in the waste stream,
providing the incentive for states to take advantage of a new product and at the same
time solve a local environmental issue.  The scrap tire filler for the core can be
manufactured locally anywhere in the country as a simple cold process that is
environmentally sound. The Carsonite sound barrier wall can be constructed, including
posts and foundations, for an estimated $15 to $17/ft2.  In 1989, the national average
cost for construction of noise barrier walls was $15/ft2; this cost included all kinds of
walls, such as earth mounds, which are relatively inexpensive.  Considering adjustment
for inflation, the Carsonite sound barrier wall can compete with other walls of similar
construction and projected life.

Carsonite has used this process in developing and manufacturing over 100 million
linear feet of similar, structural-reinforced composite elements.  These elements are
used by many agencies, including highway departments, public works departments,
utility companies, major pipeline companies, the U.S. Forest Service, and the Bureau of
Land Management. 

Key Experimental Results
A first-generation prototype of the noise barrier wall was constructed at the plant,
demonstrating the wall's feasibility and effectiveness as a noise barrier.  Several tests
were performed that reflect barrier's acceptability under environmental requirements: 
noise attenuation; flame spread; toxic characteristic leach procedure; reactivity;
corrosivity; and ignitability.

These tests indicate that the wall's components meet all regulatory requirements
relative to toxic material specifications, safety, and barrier effectiveness.  Additional
tests are being performed on optimum combinations of scrap rubber gradations for the

Future Development Needs
A second-generation prototype of the wall will be built in the near future.  To refine and
facilitate construction, the several activities need further research, development, and
funding.  For example, a source of mixing equipment for core material must be found,
and engineering analysis of different facial treatments must be conducted.  Also,
assembly-line techniques for mass production of wall sections must be developed, and
contractors must be identified for preparing core material and assembling wall sections. 
Various combinations of scrap crumb rubber and scrap polyvinyl chloride must be
identified that will function as a suitable core.  Finally, other post and foundations
designs must be investigated.

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