Northwestern concrete pour goes off without a hitch (SLIDESHOW, VIDEO)

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Photos courtesy of Northwestern Mutual

A planned 27-hour concrete pour for the Northwestern Mutual Tower and Commons in Milwaukee took slightly longer than expected, but otherwise went off without a hitch.

On March 27 and 28, about 10,000 cubic yards of concrete foundation was formed in a continuous mat foundation pour for the 1.1 million-square-foot Northwestern Mutual project. The new foundation will support a planned 32-story office tower in downtown Milwaukee.

Gilbane/C.G. Schmidt was the general contractor, while Sonag Ready Mix performed concrete work. According to C.G. Schmidt President and CEO Rick Schmidt, the pour was almost completely flawless in execution.

“The team spent months preparing for it, and because the slab had to be poured continuously, we only had one chance to get it right,” Schmidt said. “And the pour went great.”

The Daily Reporter previously detailed the significant coordination that precedes such an activity by interviewing Mike Stern, project manager at J.H. Findorff & Son Inc. Stern was a project engineer on The Moderne project, which required a 3,800-cubic-yard mat pour over 19 hours in 2011. He said that a huge amount of planning was required on such a pour to make sure there is enough cement, sand, gravel and drivers to get the trucks to the job site and continuously fill the foundation with a material that has only a 90-minute lifespan.

At the Northwestern site, the pour took slightly longer than anticipated, finishing after about 29 hours, mainly due to some traffic delays that periodically slowed down the concrete delivery trucks. Preparation for the event required some street and sidewalk closures around the construction site that started at 8 a.m. March 26 and continued through about 5 p.m. March 31.

But otherwise, the project did not experience any complications according to Schmidt. Crews worked in shifts around the clock for the 29 hours without any job-related injuries or incidents.

[youtube http://www.youtube.com/watch?v=z9xEZMOP-qc?list=UUpqT-GdO7vdxxrSbKrfkmDA]

Video by Northwestern Mutual

Planning for the pour included many contingencies. Two extra concrete pumps were on-site for back up, a back-up concrete plant, and additional equipment and personnel were all on stand-by, in case of an unforeseen complication. As it turned out, none of that was needed, as the work proceeded according to plan.

Concrete mix was produced from three different plants and pumped from four different concrete pumps on-site. None of the equipment experienced any major mechanical problems.

Choice Construction installed steel reinforcing bars, Nuvo Construction supplied concrete, and Daar Engineering performed the survey and layout. Their activities accounted for about 25 percent of the cost of the work. About 40 percent of the total hours of work were performed by city of Milwaukee residents who were previously unemployed or underemployed.

Field personnel, working through the dark and the cold, were also on hand. Several local minority subcontractors also participated in the work.

“All of them did a tremendous job,” Schmidt said.

By all accounts, the project, which was the largest continuous concrete pour in the history of the state, was an important project for everyone.

“I couldn’t be more proud of the effort our employees, subcontractors and vendors put into pouring this historic foundation,” Schmidt said. “It was truly a team effort.”

A cooling system was installed inside the slab to maintain the core temperature within the specified range as the concrete cured. Temperature probes, set at various locations and at various depths within the slab, continue be constantly monitored, Schmidt said.

Crews were scheduled to break cylinders and test the concrete at seven, 28, and 56 days after the pour to test the material. Results from the seven-day test, which took place over the weekend, were not yet available, but Schmidt anticipated a good result. Follow @MatthewTaub1