City tests permeable concrete to reduce street flooding
5th July 2011 · 0 Comments
By Susan Buchanan
The Louisiana Weekly
The city’s drainage system is so strained that after 10 minutes of rainfall, cars wade through ponds on the street and pedestrians wear rubber boots just to reach the corner drugstore. To minimize that familiar slosh, local officials, along with green-builders Make It Right Foundation and others, are experimenting with pervious pavement—a porous material with an underlying layer that captures water and oily contaminants.
Cedric Grant, New Orleans Deputy Mayor of Facilities, Infrastructure and Community Development, said last week that the city is testing the benefits of using pervious concrete in the Lower Ninth Ward.
“About 300 feet of heavily deteriorated asphalt on North Prieur Street between Jourdan and Deslonde was repaved with pervious concrete this spring,” he said. That was the first local, street application of the material. “The city partnered with Hard Rock Construction, Lafarge North America and the Make It Right Foundation to test this project.”
University of New Orleans engineering students did the design work needed to pave the project’s single, city block.
“At this time, the city is testing the installation of the newly paved road for strength and durability,” Grant said. Officials want to see if pervious concrete can help manage flooding by draining water from streets.
Grant said that “all Make It Right homes utilize pervious concrete sidewalks and driveways, totaling more than 35,000 square feet in the Lower Ninth Ward.” Started in 2007 by actor Brad Pitt, the Make It Right Foundation has built 75 homes for families who returned after Katrina, and plans to double that number.
Frank Fromherz II, a New Orleans-based, civil engineer, has worked with Make It Right over the last three years. He said pervious concrete is a mixture of coarse aggregates of uniform size, along with water, cement and a polymer or reinforcing agent. “A cement paste coats the aggregate, leaving about 18 percent to 20 percent void spaces,” he said. “If you dump a cup of water over a chunk of pervious concrete, the water quickly runs right through it.”
He continued, saying “in the pavement process, pervious concrete is poured over an aggregate base, also made of a coarse material. On North Prieur Street, eight inches of pervious pavement and eight inches of base were used for most of the block.” And for comparative purposes, twelve inches of base were used in one small area to gauge those results.
Fromherz explained that initial runoff from rain is stored in the concrete and the base, until the material is full. “Then rainwater overflows into the public drainage system,” he said. “The stored rain enters the soil, distributing moisture over a wide area and recharging groundwater. Some of the stored rain evaporates.”
He said “with pervious concrete, an urban drainage system can handle a larger rainfall. Initial runoff at the beginning of a storm never makes it to the city’s drainage system, so for the overtaxed infrastructure in New Orleans, the benefits of using more pervious concrete would be huge.”
Pervious concrete has been around for 20 years or more, but its use in New Orleans is fairly recent, he noted.
As an adjunct professor at UNO, Fromherz was assigned a hands-on, academic course this spring, instructing nearly two dozen, civil engineering seniors in design work associated with paving the 4800 block of North Prieur St. “The block has one building on it, a Make It Right house, and other than that, it’s wide open,” he said.
“My students were downright busy this spring,” Fromherz said “They did a topographical survey, performed road-design calculations, calculated impacts on the city’s drainage system, and prepared drawings and modified them to reflect construction conditions.”
In early April, Hard Rock Construction, a Metairie based-contractor, poured pervious concrete on the north side of the North Prieur block, and in mid-April the firm completed the south side. “Make It Right supplied a lot of the materials, Lafarge supplied the pervious concrete mix and the city provided the contractor,” Fromherz said.
He said “we found that using pervious concrete on this project only added 10 percent to costs compared to what it would have cost with conventional concrete. But the block didn’t have the gutters, curbs, underground utilities and sidewalks that you have on a typical city street, affecting costs.”
On larger-scale projects, the city should be able to save on its drainage budget by using permeable concrete on roads and sidewalks. “Pervious concrete on this one block of North Prieur will reduce the amount of rainwater pumped into nearby Bayou Bienvenue,” Fromherz said.
Pierre Moses, a project manager at Make It Right Foundation, said pervious concrete is a supplemental strategy to manage storm water and a way to ease pressure on the existing drainage system. He said “we have seen tremendous results from our pervious sidewalks and driveways over the past three years.” The foundation uses certified, pervious installation companies.
Moses sees little to prevent the city from using pervious concrete in sidewalks and streets, except that it’s a relatively new material that may take some getting used to. “After a year or two of data and evidence, the city should be in a position to utilize it on a larger scale,” he said.
One advantage on a street or in a parking lot is that oily discharges from vehicles drop into the pervious material, where it’s trapped as food for natural bacteria and fungi, Moses said. The oil biodegrades into simpler components that are released into the atmosphere, reducing the flow of contaminants into waterways. Using pervious concrete is one of the U.S. Environmental Protection Agency’s recommended approaches or Best Management Practices for handling storm water.
After forty years in the concrete business, New Orleans-based Bernard Brothers got involved in pervious concrete a year ago. President John Bernard said “water seeps through a pervious parking lot, almost as if it were grass, and the owners don’t need to invest in a storm drain on the lot.”
He said “we did a pervious parking lot at LSU in Baton Rouge and one at the Mary Bird Perkins Cancer Center in Houma, and are about to do one at Dillard University. My son, Lawrence Bernard is in Connecticut now, getting his certificate to become a supervisor for projects pouring pervious concrete.”
Two years ago, Brent Magee, president of Mandala Concrete, LLC in New Orleans, was the first contractor in the state to become licensed to pour pervious material by the Concrete and Aggregates Association of Louisiana, or CAAL, and the National Ready Mixed Concrete Association, or NRMCA.
In April, Magee’s company finished a 9,000-square-foot pervious parking lot—the biggest of its kind in Louisiana—at the New Orleans BioInnovation Center on Canal St. for Gibbs Construction, LLC and Harcon, Inc. “With nine inches of pervious concrete over 18 inches of limestone, the lot is able to hold 13 inches of water within its pavement,” Magee said.
Magee cited several benefits of permeable concrete, saying that in addition to eliminating expenses for drains and underlying drainage, pervious parking lots remove the need for water-retention ponds that are often required at lots of big box stores and suburban shopping malls.
“And contractors using pervious concrete earn LEED points for green building that can be used for federal tax credits,” Magee said. Leadership in Energy and Environmental Design, or LEED, is a rating system developed by the U.S. Green Building Council to evaluate product performance.
Magee is building more than parking lots. “We also did pervious concrete sidewalks, driveways and curbs for five Housing Authority of New Orleans scattered-home sites in Uptown and Mid City New Orleans,” among other projects, he said.
The local pervious industry is keeping an eye on developments elsewhere, like the rainy Pacific Northwest states, where the number of permeable parking lots is growing, Magee said.
And if you have a chance to visit China, check out the Beijing National Stadium, built for the 2008 Summer Olympics, he said. Next to that facility, Chinese contractors poured miles of colored, pervious concrete in parking lots, sidewalks and streets—all of which have held up well in weather extremes.
This article originally published in the July 4, 2011 print edition of The Louisiana Weekly newspaper.