In Woodbury, 60 miles of asphalt streets are falling apart
Woodbury is suffering from a case of pavement pox, and other Minnesota communities might have it, too.
Telltale holes and crumbling have popped up along 60 miles of Woodbury's asphalt streets, a problem that is expected to cost the city about $20 million in the next 10 years.
"This has thrown us for a loop," said Klay Eckles, Woodbury's public works director.
There are no statewide estimates of miles of streets affected, but a recent survey by the Minnesota Department of Transportation showed that 35 cities and counties are reporting the same problem. Of those, five cities and one county said more than half their streets were crumbling.
Road experts disagree on whether the cause is defective asphalt or the way it was installed. But they agree on the results: Streets are crumbling 15 years sooner than they should.
"We are kind of a bellwether city," Eckles said. That's because Woodbury was growing quickly in the 1990s and installed many miles of asphalt streets.
Woodbury employees noticed the problem in 2009. That's when small, shallow holes began to develop in some streets, followed by crumbling of the top layer.
The problem seems to be bubbles. Water apparently seeps into the air spaces. When it freezes, the ice expands and cracks the pavement.
A task force that monitors Woodbury's streets reported a "precipitous drop" in pavement quality during the past two years. Last spring, after a high number of destructive freeze-thaw cycles, the problem grew worse.
At a meeting Oct. 16, the city council got the bad news.
Over the next five years, Woodbury has already budgeted $20.5 million to repave about 16 miles of streets. But thanks to the new problem, an additional 30 miles will need repair.
That will cost the city $10 million more. And the same will happen five years after that -- 30 additional miles to be fixed, for another $10 million.
It isn't known exactly who will pay. Eckles said homeowners normally pay about a third of the cost of street improvements. But that ratio is being questioned, he said.
"What is the right portion? We do not have a couple million dollars a year to deal with this issue," he said.
Eckles said that how the asphalt was applied is not a factor. "We do the inspections; we do the testing," he said.
He blames the asphalt mix itself.
The material is a blend of asphalt, which is a form of oil, and a mineral aggregate such as crushed rock or concrete. The MnDOT regularly issues a report with a recommended recipe for the mix.
Most cities follow those recommendations the way a cook follows recipes. In some years, the state will change the recipe, depending on what new research may have shown.
Eckles said that's what happened in the 1990s: The recipe called for less oil and allowed more recycled materials. "The reason they made the change was that oil was very expensive," he said.
But that's not the problem, MnDOT says.
"The short answer is that we have used this mix and had good success with it," spokesman Kevin Gutknecht said.
He said asphalt durability depends on the recipe, the preparation of the roadbed and the way the asphalt mix is applied.
"If you paint over rust, it eventually comes through. It's the same with a road," Gutknecht said.
The rules for the application, including details such as the proper weight of rolling machines, are essential.
"When MnDOT does this work, it has inspectors on site who ensure that the mix is right and that the application is done correctly," Gutknecht said.
In MnDOT's survey, 35 of 66 respondents reported that they had noticed the problem. The survey was taken in 2010, and results were included in a report last April.
Ramsey County, Maplewood, Stillwater, Mound, Richfield and Vadnais Heights reportedly had the damage on half their roads.
In their comments, several officials said -- as Woodbury's Eckles did -- that they suspected faulty asphalt mix.
But whatever the problem is, it isn't hitting all asphalt streets equally.
A spot check of three other cities that grew rapidly in the 1990s -- Blaine, Lakeville and Maple Grove -- showed few signs of similar deterioration.
In Maple Grove, public works director Ken Ashfeld said the city built plenty of asphalt streets in that decade. But he has seen only small amounts of the "stripping" -- the crumbling of the top layer.
"Is it something I lose sleep over? Probably not," he said.
In Lakeville, public works director Chris Petree has seen a small amount of the same problem. He suspects it is related to sealcoating -- the practice of maintaining roads by spraying a layer of asphalt, then covering it with small rocks.
In Stillwater, where MnDOT said half the streets were affected, public works director Shawn Sanders said he believes the damage is less widespread than that.
But because of the problem, the city has stopped sealcoating.
"We are going to quit until something better comes along," Sanders said. That could be a better asphalt recipe or a better application technique for sealcoating.
He sees the problem affecting not an entire roadway, but parts of it.
"It might be one lane-width, or along a gutter line," he said. "It means a lot of patches."
Bob Shaw can be reached at 651-228-5433. Follow him at twitter.com/BshawPP.