By Brian Johnson
Dolan Media Newswires
Minneapolis — A section of Interstate 35 in Duluth is a testing ground for an unusual concrete grinding process designed to make tires hum rather than squeal on older concrete surfaces.
So far, the noise reduction process, which applies to decades-old concrete surfaces that produce high-pitched tire noise when cars zoom by, appears to be working as advertised.
But there’s a catch: It’s more expensive than traditional concrete diamond grinding, so its use is limited.
Concrete insiders call it a Next Generation Concrete Surface, or NGCS, project. It was used on a 3.7-mile portion of I-35 near Duluth as part of a larger I-35 improvement project.
The Minnesota Department of Transportation opted to go with NGCS after some positive test results at its facility near Monticello.
Pat Huston, resident construction engineer for MnDOT’s District 1, said early indications are the process reduced tire noise by about 80 percent in Duluth.
“But the other thing is, it’s quite expensive,” he said. “Concrete grinding in general is quite expensive. We did the equivalent of 3.7 miles long-by-four lanes wide (in Duluth). And that cost nearly half a million (dollars), so that is not something we can do everywhere.”
Matt Zeller, executive director of the Concrete Paving Association of Minnesota, said the NGCS diamond grinding is, at most, 25 percent more expensive than traditional diamond grinding.
The Duluth project is the first extensive use of NGCS on an urban interstate concrete pavement, according to the International Grooving and Grinding Association, which is promoting the paving technique.
The New York-based IGGA worked with the American Concrete Pavement Association, Portland Cement Association and Purdue University to develop the paving process, according to the IGGA.
“Tire pavement noise has become a serious issue facing transportation departments worldwide, and we have reacted to this need by developing a quiet, environmentally friendly and economical concrete pavement surface that will provide service for many years to come,” according to a statement attributed to John Roberts, executive director of the IGGA.
Tire noise isn’t an issue with modern concrete surfaces. But many older surfaces, such as the one in Duluth, were built with “tines” designed to prevent hydroplaning. A side effect of the tines is tire squeal.
Diamond grinding takes away the “tining” effect, according to Zeller.
Traditional diamond grinding involves a series of blades that dig into the concrete surface, with slight spaces between each blade. It leaves behind surface that resembles a corduroy material, Zeller said.
But the newer technique eliminates the fins in the corduroy, producing a smoother, quieter surface, Zeller said.
A lot of concrete pavements across the Twin Cities are good candidates for the technique, according to Zeller.
“We have some pretty loud concrete,” he said, adding that the roads were built that way decades ago because that’s what transportation departments specified at the time.
NGCS diamond grinding has been tried on a number of smaller jobs throughout the country, including a stretch of Interstate 94 near Monticello, Zeller said.
The Duluth area was a logical site for the test pavement project because freeway noise has been a concern there.
John Bray, special assistant to the district engineer for MnDOT’s District 1, said a lot of hotels are in the project area and the noise from the freeway was very loud.
A before-and-after test shows the project reduced noise by about eight decibels, he said.
Zeller said weather is not a factor as long as the concrete is durable from the beginning. And without the fins, the smoother road should be easier on tires, too.