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Pervious Concrete |
Pervious pavements are less
able to absorb and store heat than conventional pavements. The lower density
of the material (15 - 25% void spaces) reduced heat storage capacity. The lighter
colors of some porous pavement systems reduce the heat absorbing capacity of
the pavement. The open void structure in the porous pavement allows cooler earth
temperatures from below to cool the pavement. These factors allow porous pavement
systems to approach natural ground cover in heat absorbing and storage capacity.
Unlike traditional concrete or asphalt, pervious pavements typically provide
a void content of 15-25%, offering improved filtration and an enormous amount
of surface area to catch oils and chemical pollutants. Some experts believe
that the bacteria living in these spaces break down pollutants preventing much
of the polluted runoff that normally occurs with traditional pavements. Parking
lots, in particular, hold a tremendous potential for this material because of
the amount of oil and other hydro-carbon liquids that seep from parked cars.
Pervious pavements can be made of concrete, asphalt, open-celled stones, and
gravel, that are mixed in a manner that creates an open cell structure allowing
water and air to pass through. Certain types of porous pavement can pass 3-5
gallons of water per minute, which is far greater than most conceivable rain
events and highly effective in controlling stormwater drainage.
Because pervious pavements allow rainwater to seep into the ground through the
pavement:
The strength and durability of pervious pavement appears to be equal to traditional materials. There are several examples of parking lots built more than twenty years ago with pervious pavement that are still structurally sound and in use. Pervious pavement is also less susceptible to freeze-thaw cracking, due to large void spaces.
Concerns about clogging of pervious pavements can be "designed out", by reducing erosion and sediment runoff through strategic design and water retaining ground cover. Studies indicate that pressure washing a "clogged" pervious concrete pavement can restore 80-90% of the permeability.
A new mind set is needed when designing stormwater management systems. Rather than designing a system to pass huge storm events (that may occur only twice a century) rapidly from an area, water management planners should consider the benefits of capturing and recharging water from the smaller, more frequent rain intervals. Atlanta, for example, receives significantly more than half its annual rainfall from precipitation events of less than an inch. The ecosystem lives and dies on daily events. A stormwater system incorporating pervious pavement will be much more effective in reducing total runoff and increasing the amount of filtered groundwater. The material's ability to retain stormwater while improving water quality and enhancing tree and vegetation growth, makes this material a very exciting example of green and sustainable building practice.
The American Concrete Institute
(ACI) has recently published document ACI 522R-06 on pervious concrete.
For more information, contact:
John
Love, P.E.
Director of Technical Services
GC&PA
100 Crescent Centre Parkway
Suite 110
Tucker, Georgia 30084
770-621-9324
Or visit the following website: