Road and Bridges magazine reported (PDF) on the space saving drainage capabilities of pervious concrete. The video above highlights the concrete’s capabilities, as 400 gallons of water disappears virtually instantly upon hitting the ground.
As the largest pervious concrete paving project in the U.S., the Williamsburg, VA site included approximately 7.5 acres of the pavement. Hat tip to Greg in Williamsburg for sending us this footage!
Pervious concrete pavement is a unique cement-based product; its porous structure permits free passage of water through the pavement and into the soil without compromising the pavement’s durability or integrity.
It is usually a mixture of 3/8 to 1/2 in. average diameter aggregate (although sometimes larger aggregate, especially granite may be used), hydraulic cement, other cementitious materials, admixtures and water. When properly placed, pervious slabs will contain voids that would be normally filled by sand. Like a honeycomb these voids are held together with cement paste. Typically, the void content is 15 to 30 percent, equating to a flow rate of 3 to 5 gallons per minute per square foot, or 270 to 450 inches per hour. These irregular voids also add strength to the slab that, when cured, resembles popcorn slabs.
Although it’s not a new product, pervious concrete is enjoying a new popularity in large part for environmental reasons, viz., that rainwater passes into the ground below rather than running off into storm and sanitary sewer systems, or into streams. It has been recognized by the EPA as a storm water pollution prevention best management practice device. Another benefit in comparison to asphalt is that pervious concrete decreases the urban island heating effect, which helps keep the ambient air temperature cool.
When used as an infiltration alternative to the more traditional options (i.e., grassy swales and drain invert filtration systems), pervious concrete pavement can also reduce or eliminate the need for expensive sewer tie-ins and provide the inherent durability, safety and low life-cycle cost expected of concrete pavement.
The Re-Nest blog has more pictures and information about one specific brand, Filtercrete