Let’s be clear – paving a surface does not reduce storm water run-off, but if you must create a street, parking lot, driveway, or any other form of this detriment, an apples-to-apples comparison between pervious concrete and asphalt paving will show many exciting benefits from this innovative form of paving. First of all, those little air pockets mean less material overall, and with the cost of oil as unstable as the resource itself, petroleum-based asphalt is no longer the cheapest form of paving. For the first time in history, the cost of concrete and asphalt have reached comparable dollar values. Add in the cost of additional storm water management devices – grids of piping directed towards drains and retention ponds, and suddenly permeable concrete starts making a lot more sense. Then there is the environmental cost of leaching toxic chemicals, such as polycyclic aromatic hydrocarbons (PAHs) used as a sealcoat on asphalt, into what should be nature’s flow of water back to the ground table.
The key is to compare drainage ‘systems’ and not just the surface material itself. While concrete production is a major producer of green house gases, it is inert once it’s solid, and it does not require periodic resurfacing like asphalt. Pervious concrete is made of larger aggregate cementitiously bonded with a 12-20% void ratio and a flow ratio of about 3-8 gallons of water drainage per minute.
As with all design, site-appropriate material selection is key. The Concrete Network has Ten Steps to Ensuring a Successful Pervious Concrete Installation. Sites with high clay content may not be the best candidates for permeable paving because they are prone to clogging. However, one tactic being used on many projects in the Pacific Northwest, is to combine paving types, so that large drainage strips of permeable paving can replace the traditional underground piping and covered drains. Concrete Thinker has case studies of projects with permeable paving which help show how and where this intuitive paving type is best used, and the National Ready Mix Concrete Association has installation demos available. To find out more about permeable paving and where to find local ready mix providers and installers, visit www.ConcreteNetwork.com