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Of the over 250 projects currently listed in the database, 60 percent are located in the Southeast United States, with the majority being in North Carolina. Another 20 percent are located in California. The remainder is spread across the country and includes northern regions such as Pennsylvania, Ohio, Vermont and Minnesota.

The projects vary in size and function and include sidewalks, cart and walking paths, driveways and even local streets. The lion's share, however, are parking lots. This is not surprising since it is where pervious concrete can best provide its most desirable benefits of reducing quantity and improving quality of stormwater runoff. The sizes of these lots range from as small as several parking spaces to projects of one or more acres. The largest site in the database is a 7-acre parking lot in Westminster, Md. Additionally, a 7½-acre project is soon to be completed in Williamsburg, Va.

The fact that most of these pervious sites are located in more temperate climates can be attributed to the apprehension that spawns our second inquiry.

The freeze-thaw question?
Many design professionals have the initial perception that, because of its porosity, pervious concrete would have little or no freeze-thaw durability. And yet, it is actually the porosity that accounts for pervious concrete's ability to withstand severe cold climates.

Due to the average 20 to 25 percent void structure of pervious concrete, stormwater passes directly through the pavement and into the aggregate subbase and the subgrade below. The pavement itself is rarely in a fully saturated state. In the event that there is moisture present at freezing temperatures, the void structure of the pervious concrete provides ample room for expansion, minimizing the undue pressures that would normally be exerted on the concrete.