Pervious Concrete

Water quality throughout our nation is degrading from the pressures of more people consuming more goods and services, and paving over mother nature's natural filtration system of wetlands, and We are just not keeping up with the pressures on our water resources. As more and more water runs off paved surfaces, flooding problems are exacerbated, and ground water is not recharged.

Storm water run-off carries pollutants into our rivers, lakes, and the coastal waterways. Motor oil, hydraulic fluid, grease, and rubber from car tires; asphalt in roads and roofs; among other common household pollutants from lawns are too often carried by rain water directly into bodies of water.

Most new developments are required to install water retention ponds to capture storm water, so it can percolate into the soil where pollutants are filtered out and ground water can be recharged, however, this is a partial solution to the ever growing acreage of impervious paved surfaces.

Zelonedom was designed to dramatically reduce or eliminate storm water run off through a series of rain gardens and the use of pervious materials for patios walk ways and the driveway. One major solution to storm water run-off is pervious concrete. Pervious concrete has the properties of concrete, but allows water to percolate into the soil through porous voids in the concrete.

Glacier has been a leader in the Northwest in the development of pervious concrete, but it is still very new. Jim Bozich, Pervious Concrete Solutions Inc, Gig Harbor, WA, had only done one other pervious concrete job, and ours was the 3rd that we know of in Thurston County. However, in Florida, pervious concrete has been around since the 1970s as a way minimize flooding, erosion, and storm water run-off.

While the cost might be a bit higher for pervious concrete, there are offsetting savings for large commercial projects because drains and water retention ponds do not need to be consturcted. There is no finishing or smoothing required.

Eight inches of pea gravel were used as a base. Then our driveway and entry walks were formed as would any concrete work, except that the concrete depth was 6 inches rather than a normal 4 inches.A 3/8th inch strip was added to the top of the form. The pervious concrete was poured, screed or leveled. Then the stips were removed and the concrete was packed by a roller creating a smooth surface. The roller goes over a plastic film sheet which hold water in the concrete and allows it to cure slowly.

Pervious concrete uses pea gravel and not sand to create channels for water to penetrate into the concrete. It should absorb 3-5 gallons of water per square foot per minute. Pacing a garden hose on our driveway creates a small splash area and the water runs through the concrete into the pea gravel underlay as if it were loose pea gravel.

This has been written following a 1/4 inch rain. The drive and walk ways totally absorbed this small rain and the area under our cars remained dry. Time will tell how the concrete performs through the wet and cold winter, especially if there is freezing.

One interesting item on the drive is that regular maintenance involves vacuuming the drive so that dust in the voids does not block the water channels. This is suppose to be done once per year. We'll see!

We welcome your comments on this site.
You can email Christine Garst at cbgarst@aol.com
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Sunday December 17, 2006 05:34 PM -0800