Relief From The 100-Hour Work Week

Dayton Plant Manager John Thompson is responsible for an operation likely to become a template for future ready mixed facilities in major markets where aggregate sources have been depleted

Steven Prokopy

Dayton Plant Manager John Thompson is responsible for an operation likely to become a template for future ready mixed facilities in major markets where aggregate sources have been depleted. A 30-year veteran of ready mixed and block production in the Twin Cities, with five years at Cemstone, he will oversee the build out of Dayton as a key source of ready mixed along a high-growth corridor; major aggregate and cement depot; and, Cemstone Contractor Supply location.

The Dayton assignment follows a brief, but intense, tour of duty as project manager for the $234 million Interstate 35W/Mississippi River replacement bridge, the highest-profile project in Cemstone’s 80-plus-year history. Along with his fellow coordinators on the bridge Û Bill Bunker, co-project manager, and John Dickey, vice president of operations Û Thompson met the challenge of the rebuild with a tight schedule, difficult site geography, and harsh winter climate. Cemstone’s Engineering Services Group, led by Kevin MacDonald, designed unique mixes that surpassed MnDOT performance specs. Designed for a service life of 100 Minnesota winters, the white concrete bridge required the Cemstone team to develop four primary concrete mixes to provide durability and multiple levels of structural redundancy.

In the superstructure, resistance to scaling, abrasion and chloride ion penetration was critical. The superstructure mix is a blend of cement, fly ash and silica fume, with cement in a 60 percent range of the total cementitious faction. A second mix was used for the below-grade foundation elements, consisting of drilled shafts, primary mass concrete components seven to eight feet in diameter. Using self-consolidating concrete, the third mix addressed the substructure, consisting of massive elements, footings and pier stems of varying dimensions, with cement accounting for less than 50 percent of the binder. Formulated for low heat-of-hydration, the final mix called for two-thirds slag cement and 15 percent portland cement, allowing for an adiabatic heat rise of about 50_F.

To assure strict QC/QA, representatives from MnDOT, primary engineer and contractor Flatiron-Manson, Cemstone, and an independent testing company all checked every load before it was placed. MnDOT and Flatiron-Manson did additional verification testing, conferring with lead designer Figg Engineering. This was definitely over and above a typical MnDOT job in terms of testing, explains Thompson. At any given time, we had eight to 10 inspectors at each pour just monitoring the concrete. We also had inspectors at the [segment] plant every day.

Thompson estimates that Cemstone’s north Minneapolis plant supplied about 70,000 yd. to the project, between the precasting yard (which handled about 120 pieces) and site pours. Cemstone and Nordic Contracting provided pumping services. Work typically paced 10-14 hour days, seven days a week. A peak output day saw 2,220 yd. placed for a footing. It was a great experience, he says. The project was something I hadn’t done before, especially at that pace. I probably wouldn’t want to do it again, because I don’t relish the idea of 100-hour work weeks.

The segment casting yard was set up on the freeway at the south end of the bridge and serviced by the north Minneapolis plant. Flatiron-Manson was responsible for transporting the segments the half-mile distance to the river bottom where they were lifted into place. The plant can do 2,000-2,400 yds. in a day, so we weren’t stretched to capacity by this job, says Thompson. And we’re used to supplying concrete in the winter using a hot water boiler. We can even run sand and gravel through our dryer to heat it up when it’s especially cold. We typically want the concrete at about 65_-70_ at the site, depending on where it’s getting placed.