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What
is pervious concrete paving?
What is the history of pervious concrete?
What is it used for?
What are the advantages of pervious concrete?
How is pervious concrete installed?
Won't it plug up and stop working?
Are there situations where it shouldn't be
used?
What about maintenance?
What is its lifespan?
How much does it cost?
How do I find a qualified contractor?
Where can I see an actual installation?
Where can I find more information?
What
is pervious concrete paving?
Pervious concrete pavement is a mixture of Portland cement,
pea gravel, and water. It is ordinary concrete without the
sand. Because of the absence of sand, the void space is between
15% and 30%, which makes the material look a bit like a rice
cake. This allows water to percolate through the pavement
to the subsoil beneath. Pervious concrete is not a proprietary
product; it is a "recipe" for concrete which can be made to
order by any concrete batch plant. Pervious concrete is installed
without rebar; the thickness is minimum 6 inches for most
applications. Color can be added to the mix if desired.
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What
is the history of pervious concrete?
It was originally used 100 years ago in Europe as structural
insulation in buildings. It has been used as a paving material
in Europe for the past 80 years and in the American Southeast
for the past 20+ years. It is relatively new to the West Coast.
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What
is it used for?
Pervious concrete is used for parking lots, driveways, service
roads, walkways, sidewalks, curbs and gutters, and secondary
roads. It is suitable for light to medium vehicle traffic
at low to moderate speeds. It is not suitable for highways
or other high speed pavement.
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What
are the advantages of pervious concrete?
Because of its absorptive qualities, pervious concrete eliminates
the runoff of rainfall. This results in zero discharge of
polluted runoff into waterways, lessening of urban flooding,
increased groundwater recharge, improved health of adjacent
trees, on-site bioremediation of pollutants, and a reduction
or elimination of the need for storm drain infrastructure.
Because of its light color, it helps to reduce the urban heat
island effect caused by large areas of dark-colored pavement.
It can also significantly reduce the cost of paving. Pervious
concrete meets NPDES regulations.
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How
is pervious concrete installed?
Pervious concrete is prepared at a batch plant and delivered
in a standard ready-mix truck. It must be placed within an
hour of mixing. It must be poured from the truck directly
into the forms; it cannot be pumped due to its low water content
and coarse texture. Once in place, it is leveled with a vibrating
screed and then compacted with a special heavy steel roller.
Although control joints are not necessary in many cases, they
can easily be made with a flanged roller. The slab is covered
with plastic sheeting as soon as it is completed, and it is
allowed to cure under the sheeting for one week. Because of
its texture, there is no finishing required or possible. If
a smoother finish is desired, the material can be ground off
with a standard pavement grinder.
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Won't
it plug up and stop working?
Because the material will absorb up to 450 inches of rainfall
per hour, the vast majority of its absorptiveness could be
lost to sedimentation and the pavement would still easily
absorb even abnormally heavy rainfall of 3-4 inches per hour.
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Are
there situations where it shouldn't be used?
Slopes over 5 percent present special problems for pervious
pavement. Any site that is at risk of siltation from adjacent
areas would be a poor choice for pervious concrete unless
special measures are taken to protect the pavement.
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What
about maintenance?
There is little or no maintenance required. An occasional
cleaning with a vacuum sweeper truck can help restore void
space if desired.
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What
is its lifespan?
The lifespan is the same as conventional concrete. Virtually
all the pervious concrete installed in the Southeast is still
in use.
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How
much does it cost?
The cost per square foot, installed, is usually comparable
to conventional concrete. As installers become more familiar
with the installation process, prices should drop because
there is less to do on most installations. The elimination
or reduction in drainage infrastructure often reduces the
final cost of the project, making pervious concrete the least
costly approach.
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How
do I find a qualified contractor?
In California, contact the California
Cement Promotion Council. (Southern California: David
J. Akers, P.E., (858) 541-0180, Northern California: Andy
Youngs, (916) 332-4841.) You can also contact the Southern
California Ready-Mix Concrete Association.
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Where
can I see an actual installation?
For project locations, contact the California Cement Promotion
Council.
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Where
can I find more information?
In addition to the above contacts, visit the following websites:
Florida Concrete & Products
Association, Georgia
Concrete & Products Association, Pervious
Pavement, County Landscape
& Design.
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