“That’s called bioaugmentation,” said Pat Kiel, executive director of the Indiana Ready Mix Concrete Association. “Concrete science meets bioscience.”
Nearly 90 percent of pollutants are typically carried by the first 1-1/2 inches of a daily rainfall into rivers and streams, according to the U.S. Environmental Protection Agency.
The EPA requires that the first threefourths of an inch of rain each day be maintained on site until treated. Typically, most of that water, which includes “first flush” contaminants, is collected in retention ponds, then managed via underground stormwater infiltration systems.
The larger pervious concrete surface captures and degrades much of the hydrocarbon residue and the soil breaks down most of the rest. A 5-inch-thick pervious concrete pavement can absorb an inch of rainfall before any runoff occurs.
“It’s a very, very thirsty concrete,” Kiel said.
The water that drains out through a subbase of crushed stone is up to 85-percent cleaner-by EPA standards-than when it went in.
The environmentally friendly concrete
There’s a new concrete in town.
And it’s designed to help clean up runoff water that makes its way into area creeks and rivers.
It’s also capable of providing developers with more revenue-generating surface area because it can eliminate the need for retention ponds.
It’s called pervious concrete and, while it’s been around in other parts of the country and Europe for years, it just started showing up in Indiana in the last couple of years.
As its name implies, most of the water that hits pervious concrete runs through it instead of off of it, reducing the sheer volume of water that runs off parking lots, sidewalks and other flat surfaces. And that reduces erosion at the edges and the amount of sediment that gets deposited in local waterways.
The concrete is inhabited by microbes, which are activated by Indiana soybean oil. As the water passes through to the soil, the tiny “bugs” eat hydrocarbons from automobile oil and other contaminates collected from the surface.
has gotten the nod from the state’s Agriculture Department.
In addition to its benefits to the environment, the concrete’s use of oil from the state’s soybean production makes its use a valuable resource from Indiana’s agriculture standpoint, said Kim Wininger, district support specialist with the Division of Soil Conservation.
“It looks good from everything I’ve seen,” Wininger said “The capacity for use is huge.”
The best uses for pervious concrete are parking lots, walking paths, ditches and driveways. It’s also being used in horse stalls, greenhouses and tennis courts.
Besides eliminating the need for retention and detention ponds, the pervious concrete eliminates the need for curbs and storm sewer structures, reducing costs for developers.
Locally based Paragon Development Inc. is getting ready to pour 372 cubic yards of it for a new retail development in Brownsburg.
“The project wouldn’t have happened if we would have had to allocate space for a pond,” said Charlie Hill, vice president of sales and marketing at Paragon.
The additional space available made the project economically viable, Hill said.
“From a developer’s standpoint, it’s how much leasable square footage can I get out of that area?” Hill said. “How many apartment units, houses, etc., can I put on that area?”
The concrete, which looks rougher because more stone is exposed than in regular pavement, can also be poured closer to trees and landscaping because-since water runs through it-roots aren’t choked off.
Besides adding to the cost of development, ponds can be a liability for property owners due to potential drownings, Hill and others say.
While pervious concrete started showing
up in the South about 25 years ago, it was slower to make its way here for a couple of reasons, Hill said.
The fairer weather in the South does not expose concrete to as much freezing and thawing as occurs here, so some developers worried that might pose problems, Hill said.
“Some would say it’s a risk,” he said. “We don’t think so.”
In fact, both Wininger and Kiel say data they’ve seen shows the concrete holds up in colder temperatures.
In fact, the concrete may improve icy conditions in parking lots and on other surfaces because water can be absorbed into the pavement before it has a chance to freeze.
And because air goes through it, the ground stays warmer, which could cause snow to melt quicker, potentially saving money on snow removal, Kiel said.
And because trees can be planted within 12 inches of the concrete, parking lots in the future may include more of them, which will help keep the surface cool in the summer months.
But the wear and tear from freezing and thawing wasn’t the only reason pervious concrete was slow to reach Indiana.
“It has a very specific mix design,” Kiel said. “We wanted to wait until we were comfortable with production and placement methods.”
The Indiana Ready Mix Concrete Association is training producers and contractors, and is working to initiate a mandatory certification for companies that use it.
“We’ve learned from other states’ mistakes,” said Rich Gardner, promotions manager with the association. “It’s not rocket science, but it’s different.”
Creating a mixture that is too wet makes the paste slide off the sub-base. If it’s too dry, it can’t bond with the underlayer, creating a gravel parking lot.
And while the price is slightly higher than regular concrete, its benefits should more than offset the cost, Hill said.
“It sounds too good to be true,” Kiel said. “But it’s for real.”
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