|Increasingly, California homeowners make it a priority to consider sustainability features when choosing which products and materials to use in their home construction and renovation projects. If your project includes exterior paving, pervious concrete is well worth exploring. The environmental benefits of pervious concrete include protecting the watershed, recharging groundwater, reducing heat island effect, and protecting trees on your property.
Pervious concrete differs from regular concrete in that it uses little to no sand in the concrete mix. This results in an open structure (15-25% void) that allows 3-8 gallons of water per minute to pass through each square foots. Because it is porous, pervious concrete is one of the leading green methods of managing storm water.
Normally, after rainfall or irrigation, water is concentrated into channels and other drainages. As it passes over impervious surfaces, it picks up sediment and other particles, nutrients, pathogens and chemical pollutants that cause pollution. Anything that enters a storm sewer system or that flows from your residence directly to a nearby stream or lake is left untreated.
After water passes through pervious concrete, it is detained in an underlying stone basin and eventually placed back in the ground water table, where nature intended for it to go. While passing through the pervious concrete and stone detention basin, first flush pollutants like break dust, oil and hydrocarbons are broken down through a process called microbial conversion, placing filtered water back into the earth.
Although it may seem insignificant when considering one individual house or lot, polluted storm water runoff from all of our residential areas collectively poses a great threat to our waters. For these reasons, many homeowners are using pervious concrete, and are experiencing additional benefits such as eliminating puddling, preventing erosion, and saving the expense of tying into local storm sewer systems. Some common applications include driveways, walkways, and patios.
Bill Beeson of Beeson Masonry and Concrete has been working with pervious concrete for years and also helps instruct construction crews on how to properly install the material. He brings up yet another environmental benefit of the product: reduction of heat island effect. “Pervious concrete is cool when you walk across it,” he points out. Why is this important? Because as surfaces that were once permeable and moist become impermeable and dry (for example, asphalt or non-porous paving), these regions become warmer. According to the Environmental Protection Agency, this effect has negative impacts on the environment, including increased energy consumption and elevated emissions of air pollutants and greenhouse gases as the demand for air conditioning increases; the formation of ground-level ozone; compromised human health and comfort; and impaired water quality, as excess heat is transferred to storm water which can be stressful to aquatic ecosystems.
Beeson explains that pervious concrete allows moisture from below to evaporate, which acts to cool the concrete. It also has less thermal mass so it doesn’t absorb as much heat from the sun. Because pervious concrete does not absorb and store much heat, it helps to mitigate the heat island effect. Additionally, pervious concrete improves the health of trees by allowing transfer of air and water to the roots, which helps them flourish.
Owen Dell, a leading landscape architect with hundreds of projects in his portfolio, and the author of “Sustainable Landscaping for Dummies” and “Green Your Home for Dummies”, chose to replace the driveway in his Santa Barbara home with pervious concrete.
|“Mine was the first pervious residential driveway in California, that I’m aware of,” says Dell. “I chose pervious because it is a watershed friendly landscape feature. I’m on very sandy soil, and we poured the pervious concrete on the native soil - right on top of the weeds. The infiltration is tremendously fast.” In the six years since his pervious concrete driveway was installed, Dell says he has only had to vacuum or hose it three times to restore its permeability. “I’ve had no trouble with it at all. I’m totally happy with it. It hasn’t cracked or lost any surface or changed in any way.”
Dell’s driveway was installed by certified pervious concrete contractor Brent Smith, who says that homeowners have come to him asking about pervious concrete. To those interested in paving with pervious concrete, Smith stresses the importance of using a certified contractor. “The material behaves quite differently than regular concrete,” he explains, “and the contractor installing it needs to know how to work with it properly.” The National Ready Mixed Concrete Association certifies pervious concrete contractors. The goal of their program is to ensure that knowledgeable contractors are selected to place the product and thereby minimize the chance for failure. In California, the program is administered by the Southern California Concrete Producers (SCCP). You can access a list of certified pervious concrete contractors near you by visiting their website, www.sccpconcrete.com.
Bill Beeson echoes Smith’s assertion about the importance of hiring certified contractors. Beeson was recently hired to fix a pervious driveway in Malibu that was installed by contractors without certification. The driveway did not turn out properly, and the homeowners were unhappy and ready to dismiss pervious concrete altogether, until Beeson’s expert crew showed them a different project they had done. The homeowners decided to give pervious concrete another chance, and Beeson repaved the driveway with fantastic results. “It turned out great, and the homeowner is very satisfied with it,” he says.
T.B. Penick & Sons, one of the most reputable contracting companies in Southern California, has installed hundreds of thousands of square feet of pervious concrete in southern California. Executive VP Frank Klamaske points out the maintenance advantages of pervious concrete. “Maintaining pervious concrete is easy and cost-effective,” he explains. “The material’s life expectancy is equal to that of regular concrete. When properly constructed, most pervious concrete surfaces can last 20 to 40 years.”
The majority of pervious concrete pavements will function well with little or no maintenance, but there may be instances in which sand, dirt, leaves and other debris infiltrate the void structure and inhibit the surface’s permeability. In these cases, routine cleaning can help restore permeability. Pressure washing and vacuum sweeping are two effective methods of dislodging the clogging particles. Utilizing these cleaning practices can greatly improve the infiltration rate of a clogged pervious concrete pavement.
After placement, pervious concrete has a rustic, textured, organic surface, similar to that of a rice cake. The look of pervious concrete can provide a contrasting hardscape texture for aesthetic uses, and can also be colored with pigment. “Pervious concrete is a remarkable material,” says Klamaske, “And if you look at life-cycle costs, it’s economical as well.”
Considering all the benefits of pervious concrete, it’s no wonder that homeowners are rapidly starting to take more interest in this material as a practical alternative in their residential paving projects. For more information, contact Larry Maes, Education Director at the SCCP at lmaes [at] sccpconcrete [dot] com.
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