Pervious concrete. No doubt you've heard of it and its "green" possibilities. But how much do you know about pervious concrete and its presence in today's concrete industry?
Pervious concrete is similar to conventional concrete but manufactured without most or all of the sand in order to create voids allowing water to flow through the concrete and drain through the subgrade for filtration, ground water recharge and reduction in overall stormwater runoff, says Dan Huffman, vice president of national resources for the National Ready Mixed Concrete Association (NRMCA). Pervious concrete has been in limited use in Europe for over 100 years but took hold in the United States about 30 years ago, Huffman adds.
Pervious concrete started in Florida on small projects but since then has spread across the states and applications have grown in size. Pervious concrete has gone from "experimental" projects to larger installations, say Scott Erickson of Evolution Paving Resources, a company in Salem, Ore., that is dedicated to improving the quality of pervious concrete.
"Five or 10 years ago we were talking driveways and sidewalks. Now, while those are still happening all over the place, we're also talking large commercial and multi-acre facilities with pervious concrete," Huffman adds.
The need for pervious has also grown, and today the proper use of pervious concrete is among the recommended Best Management Practices (BMPs) of the US Environmental Protection Agency (EPA) for compliance with federal stormwater law requirements and is otherwise accepted for use by many local stormwater management agencies across the country. Pervious allows for increased site optimization because in most cases its use should totally limit the need for detention and retention ponds, swales and other more traditional stormwater management devices that are otherwise required for compliance with federal stormwater regulations on commercial sites of one acre or more, Huffman says.
Even with pervious installations growing in size and number, pervious concrete hasn't reached its potential. "We still don't see it as 'mainstream.' It's definitely growing and spreading but we still have a long way to go," says Dale Fisher, CEO of PCI Systems, LLC in Woodstock, Ga., and one of only four contractors nationwide to attain the NRMCA designation as a pervious "craftsman." Fisher started installing pervious concrete in the mid-1980s and formed an exclusively pervious company in the late 1990s. He has been involved in pervious long enough to see it grow, but he also notes that in some areas it hasn't advanced at all.
One major problem hurting pervious concrete is an abundance of incorrect pervious mix design specs online, says Erickson, who works in pervious research and development for Evolution Paving Resources. He points out that incorrectly designed mixes, improperly installed or improperly cured pervious concrete are the most likely reasons for defects and failure.
But the concrete industry is working to prevent these failures and provide correct specs. ACI 522 Pervious Specification was created as a standard for pervious concrete, and these specs are always being updated as the industry learns more, Erickson says. Another plus: most good specifications now require training and certification of pervious installers so more people are taking the time to become trained and certified in pervious concrete and its installation.
The mix design
As pervious concrete has evolved in the concrete industry so has its mix design. There has been a tendency to create pervious mix designs using round pea gravel that is 3/8 inch or larger, says Huffman. However, he is seeing a trend toward aggregates smaller than 3/8 inch and the use of crushed angular material in many markets.