Dolan Media Newswires
The eyes of the world, it seems, are on a $1.4 million paving project in Shoreview, Minn.
Construction groups, civil engineers and public works officials are touring the job site. Just the other day, a group from Sacramento, Calif., flew in to take a look at the project. There’s even an eye-catching video on YouTube.
“We have been talking to people from New York to California about this thing,” said Mark Maloney, Shoreview’s public works director. “It is very unusual to be involved with an infrastructure project that has that much national attention.”
The fuss is about pervious concrete, a green technology that allows water to pass through instead of running off the surface, thus reducing the need for expensive storm water retention ponds and other infrastructure.
Pervious concrete also provides a natural filter for polluted runoff — such as petroleum products — that would otherwise flow unimpeded into lakes, streams and rivers.
Pervious concrete has been used in Minnesota for at least five to 10 years, mostly on walkways, parking lots and the like. But Shoreview is using the technology on a three-quarter-mile residential roadway — the first time, in Minnesota at least, that this type of concrete has been applied to a project of this size.
The project began in July and is wrapping up. It features a seven-inch bed of pervious concrete on top of 18 inches of aggregate.
The concrete is made up of a matrix that’s designed to let water pass through, according to Mendota Heights, Minn.-based Cemstone Products Co., which is supplying 1,800 cubic yards of concrete for the project.
“The water goes through the pervious concrete, gets in this layer of crushed aggregate, and naturally filters into the soil,” said John Lee, a sales manager with Cemstone. “For lack of a better analogy, it looks like a Rice Krispies bar.”
The concept differs from traditional cold-climate concrete use.
In northern climates, the industry has typically designed concrete to keep water out, thereby preventing freeze-thaw damage. So it’s not surprising that there’s some skepticism about the future of pervious concrete in Minnesota.
The jury is still out on the Shoreview project; a lot more will be known about its durability after its first winter.
But Lee said the early indications are promising. In a recent demonstration that’s documented on YouTube, crews dumped 1,000 gallons of water on a finished portion of the street.
The water “disappeared in about a minute,” according to Lee.
“When we go to the site, appearancewise, the concrete looks remarkably well,” Lee added. “The contractor (Ramsey, Minn.-based North Country Concrete Inc.) has done an absolutely fabulous job. The appearance looks very uniform. As far as driving on it, and walking on it, it feels like a regular pavement.”
The pavement isn’t cheap; its upfront cost is about 50 percent more than traditional concrete, Lee said. But he added that it’s cost-effective considering that “you are getting a storm water management system” instead of just a driving surface.
“When you net out what you don’t have to build — mainly ponds and piping and catch basins and manholes — when you consider the cost of those things, it is almost a break-even,” Maloney said. “We would not be doing the project if that weren’t the case.”
As more contractors become familiar with the product, and learn how to apply it with the proper tools and techniques, the price is likely to fall.
Maloney said the city’s construction bids specified that experience with pervious concrete, including the proper certification, is a must.
North Country is a paving subcontractor for general contractor Veit Cos. on the project.
“It’s the largest project we as a company have completed as far as pervious goes,” North Country project manager Cliff Swenson said. “It’s a pretty big undertaking for us.”
From a construction standpoint, pervious concrete differs from standard concrete paving, Swenson said.
Tools and techniques are different. For example, crews must take care not to over-compact, a mistake that could prevent water infiltration.
The curing is “really, really important,” Swenson said.
“The process — it is pretty critical. You don’t have a lot of time. You need to get it down, rolled and cured as quickly as you can.”