Pervious Concrete Pavement with Detention

by Andy Burns on August 31, 2010

One of the things we like to do when possible is try new technologies when it makes sense and our clients agree, especially in the area of  green materials. We recently had the opportunity to install pervious concrete pavement in a new parking area for a client.perviouscement2

The system we installed is comprised of pervious concrete pavement constructed over a clean, coarse aggregate base and an impervious liner for temporary storm-water storage, on a prepared sub-grade. For the duration of its service life, and with minimal maintenance, the finished system will: collect, clean and discharge the storm water; protect the sub-grade, and; carry the traffic for which it was designed.

The concrete is made with controlled amounts of aggregates, water and cementitious materials to create a mass of aggregate particles cover with a thin coating of paste - containing little or no sand making for substantial void content. With sufficient paste to coat and bind the aggregate particles together a system of highly permeable, interconnected voids that drains quickly is created. Typically, between 15% and 25% voids are achieved in the hardened concrete – our installation ranged from 19-25% voids.

ricekrispies

After it cures it looks like a giant flat Rice Krispies Treat.

Additional interesting facts:

  • The unit weight of a typical, normal weight concrete would be in the range of about 142 to 150 pcf.  The void content would be about 2 to 7 percent.  The permeability of a typical concrete would be about  1 x 10-6 inch/hour (or 0.000001 inch/hour).
  • The pervious concrete has a unit weight of about 120 to 129 pcf, a void content of 15 to 25% and a permeability of about 50 to 750 inches/hour.

In addition to storm water control these systems help attain LEED® (Leadership in Energy and Environmental Design) credits for reduction of heat island effect, reduced site disturbance, storm-water credit, and improved energy efficiency.

What’s your experience with pervious concrete?

Rice Krispies photo source:  http://www.quarrygirl.com

{ 6 comments… read them below or add one }

John Downie 09.23.10 at 10:40 am

Andy,

I love the idea of pervious concrete for all of the obvious reasons. I have some questions though:

How does this product get heat-island credits? Is it signifcantly darker? What about cost? How much more expensive is it?

thanks,

JD

Andrew Burns 09.26.10 at 10:07 am

John: as to the cost - keep in mind that in this case the pervious pavement was used as part of a system for collecting storing and then discharging surface storm water. By using this system we were able to eliminate a number of storm water catch basins and structures and a good deal of lineal feet of conductor piping that a more standard design would have utilized. Our analysis showed a wash (excuse the pun) when comparing the pervious pavement with detention to a standard collection system design.

As to the question of LEED heat-island credits I have this excerpt for you from Concrete InFocus, Winter 2008 edition (http://www.nrmca.org/):

LEED Credit SS-C7.1 Landscape and Exterior Design to Reduce Heat Island Effect –
The intent of this credit is to reduce heat islands (thermal gradient differences between developed and undeveloped areas) to minimize impact on microclimate and human and wildlife habitat. This credit requires high albedo materials (reflectance of at least 0.3) and/or open-grid pavement for at least 30% of the site’s non-roof impervious surfaces such as sidewalks, parking lots, drives and access roads. A second method to achieve this credit includes providing shade within five years on at least 30% of non-roof impervious surfaces on the site, including parking lots, walkways, plazas, etc. Pervious concrete acts to reduce the heat island effect of concrete by absorbing less heat from solar radiation than darker pavements. The relatively open pore structure and the light color of pervious concrete store less heat, thereby reducing the heat reflected back into the environment and helping to lower heat island effects in urban areas. The heat island effect can be further minimized by the addition of trees planted in parking lots. The trees offer shade and produce a cooling effect for the paving. Pervious concrete pavement is ideal for protecting trees in a paved environment (many plants have difficulty growing in areas covered by impervious pavements, sidewalks and landscaping because air and water have difficulty getting to the roots). Pervious concrete pavements or sidewalks allow adjacent trees to receive more air and water and still permit full use of the pavement pervious concrete. Pervious concrete has not been explicitly approved for use in SS 7.1 for its high albedo properties; however, the pervious concrete design may be submitted for interpretation. If the concrete producer has reflectance of test results for the pervious concrete mix used on the project, he may choose to submit a letter to the contractor (and architect) indicating the results of the tests, increasing the chance that the SS 7.1 credit will be awarded.

I’ll have some more info on this as we track the performance and durability of the installation over time.

Thanks!

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