Permeable Concrete

Permeable concrete, also called pervious concrete, is an exciting development in the field of site design that addresses regulatory requirements for stormwater quality and quantity. Permeable concrete allows water to pass rapidly through pavement and to be infiltrated into the underlying soils. Allowing the “first flush” of stormwater runoff to seep into the ground prevents phosphorus, a major stormwater pollutant, from leaving the site. Infiltration of the water into the soils also reduces the peak runoff rate which helps prevent downstream erosion and flooding.

This pavement technology creates more efficient land use by eliminating the need for retention ponds, swales, and other stormwater management devices. In doing so, pervious concrete has the ability to lower overall project costs on a first-cost basis and also allows a better economic return for development.

The Richmond office of Draper Aden Associates recently completed construction of a section of permeable concrete in the parking lot in cooperation with East River Construction. The permeable concrete will serve as a learning and demonstration tool to gain firsthand knowledge concerning this technology that is relatively new to Virginia.

	This photo demonstrates the difference in impervious pavement and pervious pavement materials. Notice how during a heavy downpour, rain water collects and runs off conventional pavement while the section of pervious pavement in the foreground allows water to seep through to the soil underneath.
*Parking lot at Draper Aden Associates’ Richmond Office.*

How does it work?

In permeable concrete, carefully controlled amounts of water and cementitious materials are used to create a paste that forms a thick coating around aggregate particles. A pervious concrete mixture contains little or no sand, creating a substantial void content. Using sufficient paste to coat and bind the aggregate particles together creates a system of highly permeable, interconnected voids that drains quickly.

All in all, however, the use of porous asphalt, permeable concrete, paving stones and bricks for roadways and parking lots is proving to be successful in minimizing the impacts of stormwater on our water quality. It demonstrates a feasibility and cost effectiveness of an original project or a retrofit that aids in meeting LEED requirements and encourages stewardship of our environment.