A micro-seal applied less than four months ago is rapidly deteriorating on the surface of a 3.25-mile section of state Highway 75 just south of Ketchum.
The problem may be even worse, according to the Idaho Transportation Department, whose officials are worried that a newly applied layer of asphalt directly beneath the micro-seal may also be coming apart.
Deterioration of the micro-seal can easily be seen on the section of highway between Timber Way, about a quarter-mile north of East Fork Road, and the bridge over the Big Wood River near St. Luke's Wood River. The remaining portions of the 10-mile stretch of highway between Hailey and Ketchum also received a new surface last fall but ITD has not reported problems there.
ITD launched an investigation this week to determine the cause of the problem. However, ITD was reticent on Wednesday to place any blame on Knife River Corp., the Bismarck, N.D., company that had the contract for the highway work.
"The contractor fulfilled the contract—there was not a warranty on the work," said Nathan Jerke, spokesman for ITD District 4 in Shoshone. "ITD has already determined the work was done to specification. The work was accepted at the time and it will be difficult to come back on Knife River."
Knife River issued the following statement Thursday through spokeswoman Pam Link.
"I did talk to our management team with the Southern Idaho Division and yesterday was the first that they had heard of an issue with the micro-seal, and we are currently looking into the situation internally," Link said. "Yesterday, we had an initial discussion with personnel at the Idaho Transportation Department to see what they have learned, and we'll continue to look into the issue."
ITD awarded Knife River a $5.4 million contract in 2011 to put a new surface on the highway last summer. The work was originally expected to be started in August and finished in September. However, delays because of equipment problems pushed most of the work into October and even early November.
The 3.25-mile section of highway experiencing surface deterioration was treated differently during construction than the remaining portions of highway between Hailey and Ketchum because the 3.25-mile portion is scheduled to be reconstructed in 2013 as part of a Highway 75 expansion project.
On other portions of the road, the old crumbling surface and bed were milled away and a thick new layer of asphalt was applied.
On the 3.25-mile section of road, no milling was done, and instead only a new 1-inch thick layer, referred to as a "scrub coat," of asphalt was applied, followed by the micro-seal. Application of the micro-seal was completed in late September.
Jerke said micro-seals typically are expected to last from five to seven years.
"It shouldn't be coming up this early," Jerke said. "From what I understand, our engineers are going to go up and look at it and try to figure out why it's failing. They need to do a full investigation.
"It could be more than just the micro-seal itself. The scrub coat underneath may also be failing. Just by the description we've received, that could be the scenario. Obviously, we're as disappointed that it's coming apart as quickly as it is as are members of the public."
Micro-seals are typically about a quarter-inch thick. The main purpose of a micro-seal, a combination of small gravel and emulsion applied as a slurry, is to protect the lower main layer of asphalt from moisture, which can cause the asphalt to expand and contract and eventually crumble as the moisture freezes and thaws.
Jerke said ITD is hopeful that motorists will not have to drive on a crumbling road as they did last year before the new surface was applied.
"There's not a lot that can be done to repair it right now," he said. "If holes do develop, our maintenance people will be out there to patch them the best they can."
Terry Smith: firstname.lastname@example.org