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Permeable Concrete Reduces Water Runoff

March 30, 2012 Environment, Featured, Planning & Design 12 Comments

Permeable, or pervious, concrete is becoming more and more common around the region but what is it?

Pervious concrete is a special type of concrete with a high porosity used for concrete flatwork applications that allows water from precipitation and other sources to pass directly through, thereby reducing the runoff from a site and allowing groundwater recharge. The high porosity is attained by a highly interconnected void content. Typically pervious concrete has little or no fine aggregate and has just enough cementitious paste to coat the coarse aggregate particles while preserving the interconnectivity of the voids. Pervious concrete is traditionally used in parking areas, areas with light traffic, residential streets, pedestrian walkways, and greenhouses. It is an important application for sustainable construction and is one of many low impact development techniques used by builders to protect water quality. (Wikipedia)

Sounds good but what does it look like?

ABOVE: Permeable concrete on the left during construction on South Grand, May 2011
ABOVE: Pervious concrete under the parked cars on the left at Dardenne Prairie City Hall

The rough texture takes some getting used to although in a context like South Grand it’s a nice contrast with the smooth concrete of the sidewalk area.What’s your thought on this type of concrete?

– Steve Patterson


Currently there are "12 comments" on this Article:

  1. Moe says:

    I don’t think it takes any getting  use to at all.  I rather like it.  AND it helps keep rain water underground….perhaps in the long term, this will help refill the aquafiers that are being depleted as well as limit run off.  My 3 concerns are 1) You missed mentioning the test alleys in the Tower Grove Heights neighborhood using this same material.  2) the long term viability of this mix in our winters with the constant freeze/thaw cycles. 3) cleaning.  I know it sounds vain because I like it when concrete is washed down and cleaned off, but in this case, I believe cleaning is an important maintainance step so the porous material doesn’t get clogged over time.    But in any case, I hope the use of this material grows drastically.  Go Green!

  2. JZ71 says:

    I get the concept, but I have serious doubts about its long-term practicality.  I can see siltation being a big issue – Drano wouldn’t be in business unclogging much bigger holes if it weren’t an issue – and much depends on the soil type below the concrete, as well – clayey soils and expansive soils both have water-absorbing issues, creeks and rivers existed for centuries before we started paving everything.  Have there been real-world, empirical tests done here?  Where, say, 500 sq. ft. of porous concrete and 500 sq. ft. of regular concrete have been laid side by side, sloped to points where runoff can be measured and measurements taken over multiple years?  How different are they?  2%?  20%?  80%?  And how does the reinforcing steel work?  Typically, the goal is to keep the steel dry, to keep it from rusting, not to subject it to repeated wet-dry cycles.

  3. Msrdls says:

    I have no first-hand knowledge of pervious concrete because it is not used in structural work, but I’ve overheard colleagues discuss its use. Pervious concrete is not a proprietary product. It is the result of a certain design mix. Pervious concrete is similar to “regular” concrete but essentially without the sand. The absence of sand creates voids. 3-8 gallons of water per minute per SF of surface area can pass through the voids, depending on the specified concrete mix design and substrate conditions .

    In areas where natural subgrade/substrate materials contain lower percentages of expansive clays, water passes freely through the subgrade. Otherwise, the subgrade is often amended  to allow water to more freely pass. The costs of amending subgrade might discourage product use when on a tight budget. It is obvious why Southern California, Arizona, Nevada and similar soils provide optimum subgrade conditions.

    Pervious concrete Installation costs vs those of conventional troweled concrete are typically a wash, unless union labor assignments are made on the basis of SF of concrete area to be  finished. In those cases, pervious concrete costs exceed those of conventional concrete. Pervious material costs are typically greater because pervious SOG thickness are specified at 6″ vs 4″ for non-reinforced concrete sidewalks.But labor costs of pervious concrete are typically lower because  fewer finishers are  needed to place pervious concrete because the finish product is rough and is easier/faster to achieve. It resembles rice cakes, and it is placed using a vibratory screed and then rolled. This is a simpler process than is typically involved in pouring and finishing conventional sidewalks, particularly if those walks are edged and troweled vs screeded and broomed.

    Pervious concrete is totally non-structural, and there would be no reason to specify steel reinforcing in a sidewalk condition or in a light vehicular apron, etc. . Sometimes bamboo “reinforcing” is used in pervious pedestrian sidewalks/driveways and aprons, only for the purpose of attempting to maintain vertical alignment in the event of heaving due to trapped, frozen moisture.

    Pervious concrete has been used for 10+ years or maybe more in California. Frequently it is used not in a solid field of concrete as it is shown in the above photographs, but rather it is often poured with blocked-out voids to allow plantlife to grow though. Use of plants softens the appearance and the plantlife tends to conceal normal/expected concrete deterioration, degradation and degranulation.

  4. Moe says:

    What a good summation.  I do remember them pouring it thick up on South Grand and it is placed next to spaces for native plants to grow (to minimize watering and care) as well as basins to trap excess water and slow release. The sidewalks are of normal cement, I would attempt to guess as because they get more wear and tear then the medium strip (between sidewalk and street).  HOWEVER…knowing the nature of the PERVIOUS concrete….it seems to me that Dardenne Prairie made a MAJOR MISTAKE…why would one put pervious concrete where cars would park, and therefore pollute the ground and ground water with auto fluids. 

    • Msrdls says:

      I’ve never visited the So.Grand area, but based on the photographs, I suppose I question why pervious concrete was specified in the first place between the curb and the sidewalk. Lanscaped planters will absorb surface water, and they’re obviously much less costly…and some would say more attractive .An alternative, cobblestone or other pavers placed  with 1-1/2″ to 2″ zoysia-filled gaps will provide a durable/pedestrian friendly  low-maintenance surface that absorbs surface water and without plantlife to interfere with car doors. The grass strips are easily mowed with a power mower. This is used all over the SW as a sometimes alternative to the more costly pervious concrete paving.

    • samizdat says:

       It’s quite possible–probable, in fact–that the earth below will act as a filter, provided the foundation of the concrete was composed of a fairly thick layer of sand and crushed rock.

  5. Msrdls says:

    I suppose there are those who feel that it is preferable to pollute the ground than to send the pollutants directly/immediately to the lakes and rivers. (I feel everyone should drive a Toyota, because Toyota vehicles just don’t leak!)

  6. Moe says:

    @Msrdls….landscaped planters don’t absorb water fast enough, and cobblestone or grass is uneven footing for both pedestrians and tables etc.   While a long strip of grass works well in front of someone’s house, it does not wear well in front of a shop with pedestrians  not to mention road polutants.

  7. Msrdls says:

    I wasn’t suggesting using cobblestone below tables, but rather in the “parking” area between curb and sidewalk. I agree that cobblestones in the “parking” area may be a poor choice because of the unevenness (I remember visiting the STL Riverfront years ago, and I noticed the use of cobblestones there posed problems to pedestrians), but in Santa Monica, Venice, even Malibu, I’ve seen ashlar-cut landscaping blocks used successfully in conjunction with strips of grass, and the combination appears not to render an uneven walking surface, certainly one appropriate enough to walk on while getting in and out of a parked vehicle. Use of road salt, though, does pose another issue, one not found in So. California, so maybe the stone/grass combination would work better in areas not subject to substantial exposure to road salts.  On second thought, maybe I’ll shut up and learn to like (or live with)  the pervious concrete.

  8. Very good parking places the cars are parked very systematic and looking that its a good valet parking place of the city.

  9. Valet in la says:

    Nice facilities has been provided by this valet parking company while parking.They are proving the parking attended also for parking the car.


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