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Green concrete

October 11, 2010
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Anyone who has ever taken on the task of developing and building a new carwash facility knows what a headache it can be to satisfy all the requirements in the permitting process. Now you can add another to the long list: states and municipalities are under increasing pressure from the federal level to clean up and control runoff and ground water emissions into local streams and rivers.

While reclaim systems and efficient use of fresh water address sewer and water concerns, we have been at the mercy of more conventional methods in dealing with runoff. How many operators have bemoaned the loss of valuable land for retention ponds and other means of controlling runoff?

There is an answer on the horizon, and it has the added benefit of being “green” — pervious concrete. The use of pervious concrete is listed among the Environmental Protection Agency’s (EPA) Best Manage-ment Practices for the management of storm water runoff.

What is pervious concrete?
Pervious concrete is a concrete product which is porous and allows water to pass through and be absorbed into the soil beneath. While some issues still remain to its widespread use, ongoing research and development should solve those in the very near future.

My brothers and I were introduced to the idea of pervious concrete by an astute engineer who suggested that we take a look. While planning the newest addition to the Greenville Carwash family, we were faced with losing valuable land for the construction of a retention pond, extensive underground catch basins, pipes and the negative attitudes of some city council members. The pervious alternative was the answer to all these problems. It works; it saves land, cuts site prep cost and makes “green” bureaucrats happy, too.

The green concrete process
The first step in the process is to test the soil to determine its ability to absorb water. This will determine how much base stone is needed beneath the concrete itself. For us that was eight inches of number fifty seven stone. This base is where the water is “stored” until it can naturally disperse into the soil.

Next is the concrete itself. This is eight inches and is loosely compacted. The product itself is made using very little fine material. This results in a large proportion of void area within the finished product.

Finishing is far different than with standard concrete and should only be done by specially trained crews using unique equipment. The finished product resembles a giant rice crispy bar, for lack of a better description. The voids within allow water to pass through the concrete to the stone below. The result, thirteen thousand square feet of underground retention with no drains.

The current formulation has one distinct disadvantage. It can not be used in areas of heavy truck (i.e. trash, delivery) traffic, or in the finishing area. However careful layout will allow water from those areas to run to the pervious rather than to drains. So far, it has performed quite well in the stacking and parking areas. Our engineer tells us that the absorption rate will handle a fifty year rain, which meets the requirements for our area.

If planning a new facility, ask your engineers to look at pervious concrete. It works.

Use can result in overall site development cost savings versus conventional methods and you get to utilize the entire site rather than losing a portion to retention. As an added benefit, your local planning commission will love you.


Bruce Culbertson, along with brothers Don and Ed, is a second generation carwasher.
Father, Wes, started in the business in 1967 as a manager, and eventually bought two washes. Together, the family has since built two new facilities.

The newest wash, Greenville Car Wash, opened in March of 2007.
For more information, visit www.perviouspavement.org.