Published on June 24th, 2013 | by UC&D Magazine0
A Case for Pervious Concrete
By Brad Fullmer
A person who takes a casual glance at Chris Bedford’s driveway will see that it’s far from ordinary, with an array of Southwestern-style colors highlighted with forest green swirls.
Beyond the color, the driveway is also unique in that it is made of pervious concrete – concrete that has the appearance of a giant Rice Krispie treat, but is considered an up-and-coming ‘green’ concrete technology for its ability to reduce stormwater runoff by allowing water to pass directly through its surface.
A self-admitted advocate of pervious concrete, Bedford’s purpose for having his old driveway torn out and replaced with pervious concrete was two-fold. He wanted to 1) mitigate the amount of stormwater discharged from his property into the local storm drain system and 2) show the general public that pervious concrete should be a technology that is more widely considered by building owners in both commercial and residential applications.
“Pervious concrete is not being effectively utilized to its capacity in the Utah construction market,” said Bedford, who is a technical sales representative with fly ash magnate Headwaters Resources Inc. of South Jordan, and has been working in the concrete industry for more than 30 years. “Owners and developers don’t fully understand the potential benefits pervious concrete offers. With any new technology there is an education process and I want the industry to realize pervious should be more widely used.”
“If developers would really look at pervious concrete and the inherent benefits they’d realize it makes sense and would use it on certain projects. The only reason it’s not utilized more is because it hasn’t been used much in this state, and people tend to stick with what they know works rather than try something new.” – Chris Bedford
Bedford’s driveway was placed during the first week of June 2011 by ACME Construction of West Jordan. The concrete mix was designed by Lonnie Gray, research and development manager for Staker Parson Companies of North Salt Lake, and included 20 percent fly ash and 4 percent white silica fume.
The driveway was placed on two separate days, then covered with 6 mm plastic poly sheets and cured for 11 days. After a month, Bedford sprayed on pigmented soybean oil then carefully placed a top coating of acrylic sealer on the surface with a half-inch nap roller so as to not compromise the concrete’s void system.
“That gave it a high-gloss sheen and added a layer of protection to the concrete,” said Bedford. After two full years, he says the pavement has exceeded expectations. “I couldn’t be happier with it,” he said. “I will have to re-apply the soybean oil in some areas every couple of years, but it’s held up better than I expected.”
Pervious concrete has been used on a handful of commercial projects in Utah in recent years, including parking lots at the Utah Museum of Natural History near the University of Utah, the Associated General Contractors of Utah’s headquarters, Wasatch Touring in Salt Lake City, Taylorsville City Hall, and the Sutton Geology Building at the U. The Swaner Eco Center in Park City, the first building in Utah to earn LEED Platinum certification, also incorporated pervious concrete for parking areas and sidewalks.
“Our pervious parking lot has been a stellar performer,” said Rich Thorn, President/CEO of AGC of Utah. “There has been very little maintenance on it – we vacuum it once a year – and it has not had any cracks or fractures. From an environmental standpoint it’s also been good.”
But the use and acceptance of pervious concrete is still in its infancy. Part of the reason is that cities and municipal owners simply haven’t required it in development projects. In addition, land is still relatively cheap compared to other major metropolitan areas and the mentality ‘if it ain’t broke don’t fix it’ still exists in regards to stormwater prevention.
“No cities have (pervious concrete) as a standard, so it’s not an option for us right now,” said Brad Mackay, a civil engineer and senior project manager for Ivory Homes. “We’d have to explore the cost to see if it makes sense.” According to Mackay, an average storm drain detention system costs approximately $150,000 to $175,000 per development, which includes the $100,000 cost for the land itself (one-third to one-half acre).
“There are not enough examples in the industry to warrant the use of pervious concrete yet,” Mackay adds. “You have to see if it’s cost prohibitive, and also the longevity of it, how it holds up over time versus asphalt or (regular) concrete. For commercial developments I can see it being more of an application because you need to utilize every square foot for parking or drive isles.”
Even though municipalities haven’t fully embraced the concept of pervious concrete, it is regarded as something that can easily improve general water quality in communities.
“Any sort of pollutant or garbage on a street or gutter that ends up downstream lowers water quality,” said Bob Thompson, watershed scientist with Salt Lake County. “Pervious (concrete) helps act as a stopgap by allowing water to drain through it while catching some pollutants.” Thompson said pervious concrete isn’t applicable for every development, but certainly makes sense for some.
“It depends on location,” he said. “In the Salt Lake valley you have very sandy, porous soils. Any hardscape allows water to run down to the lower part of the valley. If it were allowed to permeate the ground where there are porous soils, it would help recharge the aquifer. It’s not a great application for every project but in some situations it does make sense.”
Scott Rocke, a civil engineer with Psomas in Salt Lake City, believes pervious concrete aids in diminishing stormwater runoff volumes.
“Pervious concrete drastically reduces the amount of runoff from a parking lot or site and helps reintroduce water naturally into the aquifer as opposed to running off and into a concentrated storm drain facility,” said Rocke. “We’ve used it in some drainage swells in low-flow situations to help keep water from ponding at the bottom. It’s successful if designed properly.”
Installation of pervious concrete is a little more challenging than regular concrete for the contractor, but proper training and protocol alleviates any real concerns.
“Conventional concrete can be temperamental and that’s magnified with pervious,” said Paul Franzen, project manager for ACME Construction of West Jordan, who placed Bedford’s driveway. “It takes more experience with how it works. You can overwork it; it’s a fast-moving product.”
Franzen said it’s important for contractors wanting to get into it to get certified through the American Concrete Institute (ACI), which is not difficult.
“We had to place 10,000 SF to get certified; during that process we learned about how long to work it and making sure to get Visqueen (polyethylene plastic) on in time. Certification is key. It works well in applications where water buildup is an issue. There are a lot of benefits.”
Jerry Hall, director of operations for Geneva Rock Products in Salt Lake City, believes it’s just a matter of time before pervious concrete is utilized on more projects.
“You’ll see more of it as people want to be greener and as land space becomes more of an issue,” said Hall. “It’s a way to conserve space. The LDS Church has shown a huge interest in it and big corporations are interested in it. Owners are still hesitant. I think we’ll see in the future (residential) developments that don’t have curb and gutter – they’ll have pervious roadways and sidewalks. Think about how much money a developer could save not having to build storm drains and curb and gutter (systems).”
“It’s a matter of educating people at this point,” Bedford added. “If developers would really look at pervious concrete and the inherent benefits they’d realize it makes sense and would use it on certain projects. It makes sense financially and environmentally. The only reason it’s not utilized more is because it hasn’t been used much in this state, and people tend to stick with what they know works rather than try something new.”