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City Saves 40 to 50% Using FDR With Cement
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| According to the July Producer Price
Index, asphalt prices rose 3.1%, the thirteenth consecutive
monthly increase for asphalt.. Asphalt prices now are 37% higher
than one year ago, and have grown 23.1% in the last six months.
Concrete prices have risen 10.8% and 3.7% over the same time
frames.
Source: U.S. Department of Labor, Bureau
of Labor Statistics.
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Budgeting for pavement construction projects is becoming more and
more challenging. Rising oil prices and changes in the price of
asphalt in particular have put a strain on maintenance costs. Additionally
complicating matters is that refiners are producing more gasoline
and diesel from a barrel of oil, contributing to a reduction in
the supply of asphalt. Increasing asphalt costs coupled with the
fixed budget of most local roadway maintenance departments has resulted
in fewer miles of deteriorating pavement that can be repaired.
There is a bright spot for road construction, however. A process
called full-depth reclamation or FDR with cement reduces the amount
of asphalt required to rebuild roads and streets. By using cement
to recycle the old pavement into a stabilized base, only a thin
riding surface of asphalt is required.
Asphalt prices are directly linked to oil. The price of coal and
natural gas, the principal fuel sources for cement production, has
not risen as rapidly as oil and, according to figures from the U.S.
Bureau of Labor Statistics, cement prices have increased only modestly
compared to the increases in asphalt.
Full-depth reclamation has been used successfully for many years.
Its popularity was initially recognized during the petroleum crisis
of the mid-1970s, when FDR proved to be an excellent alternative
to expensive thick asphalt overlays. Today with a similar rise in
the price of asphalt and the growing interest in recycling and sustainable
development, FDR is an ideal solution for providing long-term performance
at an economical price.
The traditional "band-aid" approach of spot patching
failed areas followed by an asphalt overlay does not provide the
performance nor the economic benefits of FDR. In addition, FDR is
environmentally friendly. It reuses the all the existing in-place
materials with little to no waste. Congestion, fuel consumption,
and pollution caused by truck traffic used for removing existing
material and hauling in new base material is eliminated. Disposal
of the removed material and the need for new base material is also
eliminated
FDR is a very simple process. A pulvermixer, a type of large rotor-tiller,
is used to mix the existing roadway surface and base material with
cement and water. Once mixed the material is compacted and cured.
The result is a much improved, more durable roadbed. A chip seal
or thin friction course topping can be applied for the riding surface.
There are many ways of breaking up and mixing the existing road.
Most commonly used equipment consists of large, self-propelled reclaiming
machines. This type of equipment is ideally suited for FDR work,
but it's not the only way to recycle a street.
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| Inspecting mixing tines on the Aspahlt Zipper. |
In Texas, the City of Brownwood Street Superintendent, Terry Garrett,
employs a method that is simple, versatile and cost effective. He
mounts an attachment called an Asphalt Zipper on the blade of a
front-end loader to mix the existing road and base material.
The operation begins by first spreading cement on top of the existing
road. Then the front-end loader drives slowly forward, allowing
the Zipper to pulverize and mix the existing asphalt surface, base
material and cement into a homogeneous blend. Once the road has
been mixed (approximately one hour for a block-long street), a road
grader blades the material to the outside and water is added, then
the grader turns it back in and more water is added. This brings
the material up to optimum moisture content prior to compaction.
Next, a rubber tire roller is used to compact the mixed material.
The entire process can be completed in one day, allowing residents
access to their homes in the evening. A surface treatment can then
be applied to the recycled road, which for the City of Brownwood
typically consists of a simple chip seal.
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| Mixing cement into roadway. |
Blading the mixed material. |
According to Garrett, the cost for this type of roadway rehabilitation
runs 40 to 50% less than an asphalt overlay. With the FDR process,
Garrett estimates he can do twice as many miles of maintenance within
the same budget. "Not only is the City of Brownwood able to
complete more streets for the same money, but we are fixing the
full depth of the street and not just repairing the surface. It's
true the initial cost savings are important, but the long-term savings
are incomparable!"
With very little flexibility in fixed budgets, city and county
officials need an economical method of maintaining their streets
and roads. Full-depth reclamation with cement is certainly one way
of doing it.
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