The report also states that pervious concrete pavement should not be considered for areas experiencing freeze-thaw cycles with a ground water level less than 3 feet below the ground surface. The final choice to use porous pavement in place of a traditional pavement will most likely be driven by the need to address site-specific stormwater management challenges with an efficient and cost-effective method.DEVELOPING A DESIGN STANDARD
Because of specific site characteristics, development of a pervious pavement standard does not follow a “one size fits all” approach. For guidance in writing a spec, public works departments can contact material associations such as the National Asphalt Pavement Association (NAPA), the Portland Cement Association (PCA), NRMCA, or the Interlocking Concrete Pavement Institute (ICP1). Environmental consulting firms experienced on a national level in pervious pavement design, such as Cahill & Associates, located in West Chester, Penn., can also provide valuable assistance.
In addition to development of a standard, each municipality must consider and choose which pavement materials will be allowed. Currently pavements have successfully been constructed of concrete, asphalt, or paving blocks, and there are existing pavements in place to demonstrate the performance of each type.
Concrete pervious pavement has been used for the past 25 years in the coastal regions of the United States. In this application, the concrete surface is commonly constructed with a mix design containing no sand, a No. 89 washed stone and 20% to 25% voids—creating a texture similar to that of a Rice Krispies treat. An open-graded stone base placed on a nonwoven geotextile fabric supports the concrete. Use of pervious concrete to construct parking lots and sidewalks has been successfully implemented by the city of Atlanta.
Asphalt porous pavements, first developed in the 1970s at the Franklin Institute in Philadelphia, are constructed with approximately 2 to 3 inches of an open graded friction course (OGFC) over a stone layer placed on a nonwoven geotextile fabric. The Ford Motor Co. installed an asphalt porous pavement in 1999 on the parking lot of their newly renovated Rouge River Facility in Dearborn, Mich.
Permeable pavers, interlocking paving units mechanically installed over an aggregate base, have been used over the past decade to address stormwater management issues in many areas.
“The use of permeable pavers is increasing in communities all across the United States,” said Donna DeNinno, director of marketing for UNI-GROUP U.S.A., an association of UNI Paver manufacturers in Palm Beach Gardens, Fla. “Areas such as the Chesapeake Bay, Minnesota Lakes region, the Pacific northwest, New England, Florida, and California are at the forefront as they have increasingly restrictive guidelines regarding construction and pollution impact on surrounding surface waters. We have projects that have been in as long as nine years that are still functioning well.” UNI-GROUP U.S.A.'s UNI Eco-Stone concrete pavers were installed in 1995 by the city of Wilton Manors, Fla., on more than 30,000 square feet of a parking lot serving a recreational facility.BUILDING A PERVIOUS PAVEMENT
Proper placement of pervious pavement is essential to successful performance. Gordon Kenna, a consultant on environmental issues for Georgia Concrete & Products Association, Tucker, Ga., said. “An experienced installation contractor is highly recommended.”
Industry publications, including the “Porous Asphalt Pavement” design guide developed by NAPA, offer the following recommendations to ensure a successful project: keeping equipment off the sub-grade to avoid compaction, scheduling completion of the pavement as one of the last operations along with keeping construction equipment off the completed pavement to eliminate deposition of fines that would clog the surface, and finally using clean, washed stone for the base.
Although the same equipment is used to construct porous asphalt pavement as is used for a more traditional asphalt roadway, the equipment and methods used to place a concrete pervious pavement are somewhat different from those used to construct a traditional concrete surface.