MINNEAPOLIS -- Road crews used jackhammers to remove concrete from the Interstate 35W bridge the day the span collapsed, but state officials declined to say Wednesday whether they believe the work contributed to the disaster.

For the first time Wednesday, the Minnesota Department of Transportation detailed the bridge deck repairs that were under way when the structure suddenly plummeted into the Mississippi River.

“We’re not going to speculate about the cause,” said Bob McFarlin, assistant to the state transportation commissioner. “We’ll leave that to the NTSB (National Transportation Safety Board).”

The road work has been a focus of discussion among the public and engineering experts since the Aug. 1 collapse. State officials have repeatedly said the maintenance work was routine.

“The deck has nothing to do with the structure,” McFarlin said. “It’s just the deck.”

The $9 million repair began in July. Progressive Contractors, an experienced road construction company based in St. Michael, Minn., was resurfacing the bridge’s concrete deck and completing repairs to lighting and guard rails.

The project was about 70 percent complete, said Liz Benjamin, a state construction engineer overseeing the work. The job mainly entailed grinding off the top 2 inches of the road’s surface and repaving with new concrete.

Crews also replaced a series of expansion joints, which are narrow breaks between slabs that allow concrete to expand and contract with the weather.

In addition, workers searched for areas where the concrete was eroded below the surface. When they found such spots, they used jackhammers to remove all 9 inches of the concrete deck.

By July 31, the contractor had completed work on two lanes in each direction and begun working on two of the four remaining lanes. On Aug. 1, the day of the collapse, crews spent much of their time using 45-pound jackhammers to remove concrete from various weak spots, Benjamin said.

Plans for that evening had called for workers to begin resurfacing two lanes. They had heavy equipment and tons of material used to make the concrete staged on the bridge.

About 20 workers were on the span when it collapsed. Greg Jolstad, a Progressive Contractors employee, remains missing.

Some experts have speculated the repair work somehow triggered the collapse.

“At first, I thought that would be the focus,” said Michael Oliva, an engineering professor at the University of Wisconsin-Madison.

Oliva said he speculated that crews may have affected the tension and compression needed to hold the bridge together when they removed decking material. But Oliva said he later reviewed the bridge’s design – which features a system of trusses and support beams – and concluded the deck played no role in holding up the bridge.

Still, Oliva said the project may have indirectly affected the span by shifting traffic loads. At the time of the collapse, four of the eight lanes were open – two in each direction. The two lanes on the downstream side of the bridge were closed, meaning the remaining three-quarters of the deck was bearing all the traffic.

Road crew members told a rescue worker they'd felt the span "wobbling" in the days prior to the collapse, according to the Minneapolis Star Tribune. State officials have declined to address that issue and referred questions on that matter to the NTSB.