Pervious concrete is a paving material that keeps stormwater on site and helps return it to the aquifer or directs it to a holding area to be used for irrigation or other purposes. The ingredients for pervious concrete are found at every ready mix plant and include Portland cement, course aggregate, water. Fibers are often used to enhance the void structires and admixtures help tailor performance characteristics. Many ready mix producers have their own mix design that has been used time and again with success, but it is imperative that you discuss with your ready mix producer your project and needs.
Pervious concrete is similar to traditional concrete in durability and has sufficient strength to serve in typical parking lot applications. Pervious parking lots built more than 20 years ago are still in service and pervious concrete has also been used successfully for low volume streets, driveways, sidewalks, golf cart paths, retaining walls, and French drains.
How does pervious concrete work? Rainwater falling or flowing onto the surface of the pavement passes through the pervious concrete readily. The infiltration rate is much greater than the rainfall intensity of even the most severe design storm. There is minimal impediment to vertical flow from the pervious concrete through the gravel base to the soil. Exfiltration is primarliy determined by the base soil. For soils with slow 'perking cycles' like clay, systems can be successfully designed to accommodate slower exfiltration rates.
A typical pervious concrete section will have 6 inches of pervious on 6-8 inches of clean gravel base. After the pervious concrete is placed, it needs to be covered with plastic and cured for 7 days. It is important during those 7 days that the owner takes proper precautions to allow the pervious to be undisturbed during that time. After curing, the pervious area can be opened for use.