BYRON TOWNSHIP, Mich. -- When a stretch of M-6 needed repairs only seven years after opening, the Michigan Department of Transportation began asking questions. The section of the expressway between US-131 and I-196 was opened in 2004.
"We saw in that pavement at 10 years old, for instance, what we wouldn’t see in a pavement for 30 years," said John Staton, concrete operations and materials engineer for MDOT.
Though highway contracts include warrantees, blame did not fall on the contractor. "The contractor met the specifications at the time," said Jerry Byrne, deputy managing director of the Kent County Road Commission. The KCRC has been patching M-6 west of Wilson Avenue for three years now, pavement that was designed to last 20 years.
"We reached out to the national research experts to ask them, Have you seen problems like this in your state?" said Staton. "They said yes."
And the same response came from transportation departments in Minnesota, Illinois, Indiana, and Ohio, all states with winters full of snow and ice.
"Water is one of our greatest assets, overall as a state," said MDOT pavement operations engineer Curtis Bleech, "but it can also be one of our biggest potential concerns in the pavement arena."
But water is not just a problem during the winter months, because there's something about concrete most of us wouldn't guess at. "Concrete is basically like a sponge," said Staton. "When that sponge freezes, it falls apart."
Then why use concrete at all?
It's the law.
"In Michigan, we have state legislation that requires us to perform a life cycle cost analysis," explained Bleech. "It compares the cost of concrete pavement versus hot mix asphalt." When highways are built or rebuilt, the choice between concrete or asphalt will come down not only to price but availability, and it works to the taxpayer's advantage for asphalt and concrete companies to compete.
But once the concrete is in place, what can be done about the water and salt that gets into it? Studies are being done, but it takes years to observe and measure wear-and-tear on active highways. A recent study by the Center for Transportation Research and Education at Iowa State University shows promising results from sealing the concrete, but more study is needed.
Meanwhile, MDOT is watching those studies, said Staton, and uses any new information that comes out of them, even as the studies are still being done.
And a decades-long study comparing asphalt with concrete will be instituted on sections of US-131 in Kent County. In 2017, new asphalt will be laid north of 14 Mile to see if it can last 30 years. In 2018, new concrete pavement will be laid on US-131 between 10 Mile and 14 Mile to see if that pavement can last just as long.
Since the concrete portion of M-6 was built (it's mainly asphalt east of US-131), MDOT has changed specifications for concrete used in highway pavement to increase its durability against water, ice, and winter de-icing compounds.