Motorists can forget about exiting from Piedmont Avenue onto Interstate 35 south for a while.
A single crew used a hydraulic breaker — like a large metal finger — Tuesday morning to begin tearing down parts of what people know locally as the “can of worms” section of I-35 in Duluth.
“He pokes through the bridge, it crumbles down on top of the gravel, and we’ll salvage it from the bottom for recycling,” said major projects construction manager Pete Marthaler of the Minnesota Department of Transportation office in Duluth, describing how the crumbling concrete will be used in future road-paving materials.
New ramps and roadways able to handle oversized loads and carry traffic more safely through Lincoln Park are planned as part of the ongoing $343 million Twin Ports Interchange reconstruction project.
Throughout the confluence of I-35, I-535 to Wisconsin and U.S. Highway 53 to and from the mall, there is ongoing work being done — new bridge piers and decks being built, scores of backhoes moving earth all around, workers in fluorescent vests carrying through areas previously used by high-speed traffic.
“The contractors are putting in 4,000 to 4,500 (person) hours per week, that’s the equivalent of about 100 people,” Marthaler said of the joint construction venture between Ames Construction, of Burnsville, Minnesota, and Kraemer Construction, of Duluth.
The U.S. Highway 53 “flyover” ramp to I-35 south was the first bridge to close and endure the hammer Tuesday, but it will be far from the only one.
Marthaler described at least 13 bridges, designated by letters A through M, to be coming down as part of the four-year project, ending in 2024, with major construction completed by fall 2023.
But the coming days will focus attention on four elevated sections of roadway.
“Starting today and for the next three weeks, we’ll have demolition ongoing for those four bridges,” Marthaler said, pointing to bridges which led south onto I-35 from Wisconsin and from Highway 53 to I-35 north.
Both exits were destined for the chopping block.
As demolition took place on the ramp, traffic sailed through to Wisconsin higher above it. Highway 53 to Wisconsin via I-535 and the Blatnik Bridge will remain open for now.
But by the end of the next two or three days, there will exist a void where the Highway 53 bridge used to be which only a 1970s daredevil would entertain.
Asked if MnDOT had considered dynamite to bring down its bridges, Marthaler answered: “It would be quite spectacular, but, no, we do it safer than that.”
Under crystal blue skies, he stood over another aspect of the interchange project, a fresh trench that will soon contain a diverted Coffee Creek, a portion of which will remain in the open air through the neighborhood for the first time in decades after construction.
As the hammering commenced, the bridge crumbled to reveal its metal insides. Marthaler described it as precarious work, requiring an excavator that's only big enough to do the job. Once the operator starts breaking down the overpass, things destabilize quickly, so it's better to be nimble and as lightweight as possible backing up off the bridge.
“There’s so much rebar in there it starts looking sinuous, almost like tendons in your body,” Marthaler said. “It’s what affords the concrete its tension. Concrete is very good at compression, but very bad at tension.”
Concrete, rebar and steel are being used to build the new bridges, too. The new steel girders will contain higher levels of chromium, making the steel more corrosion-resistant.
“Ideally, it will extend the life of our bridges to 75 or 100 years,” Marthaler said.
Until then, the demolishing of bridges built before 1976 will continue for the foreseeable future. Once bare of concrete, cranes will come in to lift out the steel beams, which will be carried away on flatbed trucks to salvage yards.
As he watched a worker use a hose to spray the area with water to contain dust, Marthaler expressed his admiration for the engineers and contractors who came before him. The individual bridges that make up the interchange become instantly unstable once the first materials start to crumble and fall away.
“They didn’t use any more materials than they had to,” Marthaler said. “They were very efficient.”