Although those of us in the ready mix business would love nothing better than to sell more concrete, when it comes to pervious concrete we want to make sure that it is the proper material of choice and if so, how much of a job should use it. Question number one should always be, what is the underlying soils percolation rate? If it is at least ½ of rain per hour then pervious concrete is an ideal candidate. If the perc rate is not quite what we would like it to be, chances are we can address that by creating a deeper recharge bed, in other words, build a deeper holding tank under the pavement. If there is any concern about the ability of the soils to take the rain storm that the pavement is designed for, then a good belt and suspenders approach would be to run a perforated pipe halfway in the recharge bed to allow the system to take all of the rain it can and if need be, have an extra outlet rather than have the rain back up into the pervious pavement sections. Studies have shown that even clay soils can now be used under properly designed pervious concrete pavements and with recent mix design improvements pervious concrete is now being used not only for parking lots and sidewalks but for alleyways and residential streets.
When designing a pervious pavement concrete can be very competitive with traditional asphalt designs, especially when we use regular concrete drive lanes and pervious concrete parking stalls. If as a designer you can remove or reduce the number of catch basins, perimeter drains and other underground work, many times a pervious concrete system will be the most economical way to build not only an environmentally friendly but also a safer parking lot.
Bob Banka is President of Concrete Management Solutions and has been involved with the development of pervious concrete for over twenty years. To learn more visit:
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