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Archives > April 2013 > Permeable Clay Pavers Solve Stormwater Issues, While Preserving Historic Character of College Campuses

Permeable Clay Pavers Solve Stormwater Issues, While Preserving Historic Character of College Campuses

No matter what your status is at a private college, from a frazzled freshman to a tenured department chair, a sudden downpour has the same effect: Everybody gets wet. But for those in charge of facilities planning, that rainfall is taking on additional significance.

By: Ted Corvey

In a college setting, especially a college that has been built up over a number of decades, that water is going to fall more and more on hard surfaces: parking lots, tennis courts, walkways, roads and the like.

Off campus, local municipalities are increasingly tightening stormwater mitigation requirements. Many are finding ways through incentives-or penalties-to convince college campuses, business parks and other facilities that have large expanses of pavement to treat their own stormwater on site.

For both new projects and renovations, many colleges are turning to a solution that's already in place on countless college campuses today: clay brick pavers for sidewalks, parking lots and streets. Long associated with shady quads and red-brick buildings trimmed with stone accents, clay pavers-sometimes with the names of donors inscribed on them from a longpast capital campaign-are a mainstay of the American college campus.

The new solution-permeable clay pavers-look virtually identical to those that may have been there for generations, but they're a bit different.

They are manufactured to be set in place slightly farther apart. Instead of gravel and sand underneath, there are precisely layered strips of differently sized rocks, or aggregates, underneath. Instead of sand in between them, there are tiny bits of gravel.

A new method to handle drainage
It works like this: the rain falls onto the pavers; the water drains between them and is then collected and held briefly in the aggregate bed. From there, it slowly flows into the ground, where it is naturally filtered.

Think of it another way. Take a glass aquarium. Put large rocks on the bottom, then layers of progressively smaller rocks on top of that. Top it off with a layer of pea-sized gravel. Smooth it all out so that it is level. Put the pavers atop that in a pattern that looks like a section of sidewalk. Put more of the small gravel in between the pavers. Now, spray the top of the pavers with a garden hose. The water will flow across the paver surface, then drain into the gaps between them and flow downward.

The spaces between the rocks, underneath the pavers, are where the water is held. The rocks themselves are there to hold up the pavers. If this were a natural example, there would be no bottom on the aquarium-there would only be dirt-and the water would gradually flow into the ground.

One additional bonus: Because the water flows readily in between the pavers, it doesn't puddle up and become ice as temperatures drop.

Using the clay pavers in this way shows several examples of green construction. Modern clay pavers are made out of shale and water, two of the most abundant building materials on the planet. Because they last virtually forever, they are the definition of sustainability. Since the color goes all the way through and is colorfast, they will look the same 100 years from now as they do today. If you need to do an underground repair, you can take the pavers out and set them to one side, do the repair and then put the pavers back into place.

And should you want to move the sidewalk entirely-say to put in another building, even-you can. Pick the pavers up, stack them to one side and rebuild the sidewalk in another place with the same pavers.

It's also useful to keep in mind that clay pavers are more durable than they used to be. Many years ago, pavers used to be manufactured the same way that bricks used for exterior walls in brick buildings are made. Some recycled pavers on the market today were actually used to build walls of buildings that have been demolished.

The problem is that while they were durable enough for buildings, they were never meant to withstand the weight of vehicles and often crumbled.

Actual pavers are designed specifically for vehicular use and are thus much more durable. Additionally, today's pavers are made to precise tolerances and fired in the kiln at hotter temperatures for much longer than they used to be. They're also tested for strength-and some can withstand up to 16,000 pounds per square inch of pressure.

Clay permeable pavers on private-college campuses today
Wake Forest University is an example of one campus that opted for clay permeable pavers. Ryan Swanson, university architect, says the project's design concentrated on three things: aesthetics, practical design and available space.

So far, Wake Forest has installed an eight-foot wide sidewalk alongside a campus street. Next summer, the sidewalk will be lengthened and a new 24- foot walkway 120 yards long-built to handle fire trucks and other emergency vehicles-will link the central campus housing area with student parking lots.

From the aesthetics standpoint, clay brick pavers fit in well here. Wake Forest University's campus is literally on top of one of the richest deposits of shale (the dense red clay that is used in brick manufacturing) in the world. When the campus was moved to Winston-Salem from near Raleigh in 1956, the college went with so many red brick buildings that the nearby Pine Hall Brick Company now makes a special color called "Deacon Blend" (after the college's mascot, the Demon Deacons) just for the college, to complement the original handmade bricks used to build the original buildings more than fifty years ago.

Swanson says the practical design part of the equation relates to an effort on the university's part to meet Winston-Salem's stormwater mitigation efforts. Like many commercial installations, universities require a fair amount of hard surfaces, including parking lots, sidewalks, driveways, roads and rooftops, in a limited space. Were the land left undeveloped, rainfall would be absorbed naturally.

Once the area is built up, rainfall has nowhere else to go. The excess water can cause a surge downstream that can cause erosion, flooding and property damage. As a result, cities and counties are requiring owners to install storm water management mechanisms, such as permeable pavers and other means, to keep more rainwater on site and return downstream flows closer to a volume that would occur naturally.

The available space part of the equation comes from how stormwater is mitigated. At Wake Forest, two large concrete cisterns, capable of handling 110,000 gallons, were installed underneath a parking lot. The cisterns were used in connection with three bioswales-hollowed out areas in the earth-to slow water flow into a lake and a creek. At a new residence hall, two bioswales were created that collect rainwater into a crushed rock bed that's five feet deep.

The bioswales are excellent, but they take up a lot of land area, which is at a premium on college campuses. The permeable pavers represent an opportunity to allow rainwater to filter through a field of bricks and be absorbed by 18 inches of aggregate beneath them. The aggregate keeps the pavers stable, while at the same time collecting the rainwater and slowly releasing it.

"In a tight space where a large amount of sidewalk is programmed, permeable pavers are much more cost efficient than underground cisterns, allowing water to naturally seep into the ground feeding nearby trees and grass," says Swanson. "And as most would agree, they look great at the same time."

Do permeable pavers work in the frozen North or the sunny South? Yes.
Another advantage that modern permeable clay pavers have is that they work well whether in cold or hot climates. Take the difference between, say, Vermont in winter and Florida in summer.

At Champlain College in Burlington, Vermont, the college set out to pave a main promenade that directs pedestrians to Perry Hall, which houses admissions and the enrollment center. The goals were to have a hard surface that would withstand the weight of both pedestrians and vehicles, while allowing stormwater and snow melt to seep into the ground, which is significant, given that the town averages 81 inches of snowfall each winter.

John Caolo, associate vice president of campus planning and auxiliary services, explained that permeable pavement was required under the renovation plans for Perry Hall, which was converted from a 19th century residential structure into its new use. The college decided early on to pursue LEED platinum status, which has as one of its requirements that site improvements be sustainable.

Part of the requirement was that the pavement look as though it belonged there. "The building is a muted brick with a very 21st century metal panel addition, so it has one foot firmly in the past and one foot firmly in the future," says Caolo. "That's the metaphor we were shooting for."

The particular color of clay permeable paver rose to the top over several other materials under consideration because of its aesthetics, its permanence and its ease of maintenance. It also had the advantage because of its demonstrated tolerance for exposure to repeated freezing and thawing and its durability to withstand frequent use of road salts and other de-icers, which arose from its use in other cold climates. Magnesium chloride is recommended for de-icing.

That wasn't a problem for another installation, this one at Flagler College in St. Augustine, Florida, which has spring break weather virtually every day. Kenan Hall, a classroom and facilities building that's used by 2,000 students on a daily basis, was the home of an ankle-deep puddle out front each time it rained. A conventional solution would have been to pour a patio and install a drain. But that wasn't possible, because St.Augustine, Florida, no longer accepts new tie-ins to its storm drain system and requires all new construction to keep its storm drainage on-site.

Sharon Fowler, principal of the landscape architecture firm Hauber, Fowler & Associates, said the two main goals were to complement and reflect the historic architecture of the site and to find a solution to the drainage issues on the site.

From the historic perspective, St. Augustine is the oldest continuously occupied European-established city in the continental United States. The historic district guidelines require that buildings within the Historic Preservation District use materials that reflect the architecture and the materials used at the time.

Kenan Hall was built in the 1880s, originally as a building to house employees of the Ponce De Leon Hotel, which was a draw for the wealthy who would travel, along with their servants, from the cold Northeast to spend the winter months in the Florida sunshine. It was the first large building in the United States to be made entirely of poured coquina-shell concrete, trimmed in terra-cotta red.

Permeable clay pavers in two colors, light gray and a terra-cotta blend, were used to build a 5,300-square-foot plaza. The new plaza has movable tables, chairs and umbrellas that are clustered around columns that are wired for electricity. Classes sometimes meet there to enjoy an outdoor session and a break away from the classroom. After class, it's used for student-sponsored events, meals and parties, or fairs where potential employers and representatives of graduate schools meet with students.

When it rains, the water hits the pavers and disappears. Larry Weeks, director of business services and campus planner, said the solution was not the only one, but was the best one. In the past, the campus had used underground exfiltration systems, which look similar to plastic Lego boxes, to fulfill the city's stormwater ordinances But underground boxes don't deliver the benefits of a popular gathering spot where students and faculty can gather to watch a movie under the stars, for example.

"This was more innovative, at about the same price, and it was much more aesthetically pleasing," says Weeks. Fowler said the successful outcome is a testimony to the college's foresight. "They are one of the best clients I have ever worked with," says Fowler. "They want to do the right thing and they want to do it in the right way. They sincerely support quality development and they focus on doing the right thing for their students."

 

 

About The Author
Ted Corvey

is vice president of sales and marketing at Pine Hall Brick Company (www.PineHallBrick.com), America's largest manufacturer of clay brick pavers, including StormPave and RainPave permeable pavers; the two installed in a permeable pavement system can help qualify for LEED points in a number of categories.

 

 

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