Pervious concrete allows water to flow through thereby slowing down the water run-off rate.
Pervious concrete can take in storm water at a rate of 3 to 5 gallons per minute per square foot of surface area. That exceeds the flow rate needed to prevent runoff in most rain events. The rainwater may be stored in a coarse gravel layer underneath the pavement or allowed to percolate into the underlying soil. Because the pavement itself acts as a retention area, it helps to prevent much of the polluted runoff that normally occurs with impervious pavements.
Can it get stopped up? It’s unlikely that a pervious surface will become totally clogged. Reducing erosion and sediment runoff onto the pavement through good design can eliminate most problems. If any voids do become clogged, vacuuming or pressure washing of the pavement can restore most of the permeability.
What are the limitations? While this thirsty pavement is an excellent option for certain situations, it may not always be a viable choice. Because pervious concrete has a rough-textured, honeycombed surface, moderate amounts of surface raveling are normal. This can be a problem on heavily traveled roadways.
Special attention must also be given to the overall design of the pavement system in order for pervious concrete to perform as intended. Proper engineering of the substrate beneath the pavement is essential, since it must be able to temporarily store the water while it percolates into the soil. An initial soils site survey and site-specific stormwater calculations should be performed by a stormwater management engineer.
Installation: Pervious concrete is delivered to the jobsite by conventional ready-mix trucks and placed within
A heavy roller press is used to place pervious concrete.
standard forms. Because pervious concrete is thicker in consistency than regular concrete, a vibrating mechanical screed is used to level it off. Vibration is followed by compaction with a heavy steel roller to attain greater strength.
Because pervious concrete has a low water content, curing is especially critical. After placement, the concrete is misted with water and then covered with plastic sheeting and kept damp for at least 7 days to allow full hydration of the cement.
Often paving crews can complete pervious concrete jobs faster than when installing regular concrete. That’s because pervious concrete doesn’t need to be worked with a bull float or trowel, since these finishing operations can seal off the pavement surface and decrease water penetration.
More:
Ten Strategies for Ensuring a Successful Pervious Concrete Installation
Pervious concrete design ideas
Sources:
www.concretenetwork.com
http://porterworks.com/
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Twitter: greencurmudgeon
Check out this demonstration of how effective pervious paving really is.
Twitter: nahbverifier
Carl that’s hilarious! Thanks for the chuckle!
Carl, how much experience have you had with pervious crete? We have a ton of expansive soils here in Central MS and I’m concerned that feeding H2O into the ground could be trouble. I’m thinking it would be advisable to layer the sub-surface with a membrane in an attempt to help control absorption and expansion? Your thoughts?
Twitter: greencurmudgeon
I actually have limited experience with it. I saw an installation in 1996 – other than the video, that is about it. I will probably be doing some on a new house next year. Good luck with your project.