When it Rains...
Why Use Pervious Concrete?
Parking lots are considered to be primary point sources of pollution. When rain falls on a conventional, impervious parking lot it usually runs off carrying pollutants with it. Polluted stormwater runoff eventually finds its way into our streams, rivers and lakes.
Parking lots paved with pervious concrete, however, assist the process by capturing rainwater and allowing it to percolate into the underlying soil. Because water is allowed to absorb into the ground, nearby vegetation is watered, groundwater is recharged and stormwater run-off is reduced.
Pervious Concrete Composition
Pervious concrete is a mixture of hydraulic cement, coarse aggregates (stone), water and admixtures. Pervious concrete contains little or no sand, and is sometimes referred to as a "no-fines" concrete. The cement and water forms a paste that binds the coarse aggregates together. Only enough paste is added to the mix to glue the aggregate together where they touch each other, but not enough to fill all the space between the aggregates.
A typical pervious concrete mixture will contain about 17-25% void space within the concrete. Many of the void spaces within the pervious concrete will be interconnected, forming channels that allow water and air to pass freely through the pavement structure.