Ready-Mix Producer/Pumper Partners with Design/Build General For Value Engineered Project 2007

A long and successful history with General Contractors Opus Corporation, Minneapolis, MN helped Twin Cities based producer/pumper Apple Valley Ready-Mix (AVR/AME) secure the concrete supply and pumping for a new campus in the northern suburb of Mounds View. The owner, Medtronics, Inc. – a rapidly expanding medical device company based in Minnesota – is building three office towers and a parking structure covering more than 2.5 million square feet.

“We were able to partner with Opus to bring economies to the project that would help to reduce the concrete costs and speed construction, “ according to Dan Lien, an AVR/AME Sales representative. With more than 50,000 yards to be pumped, speed and cost savings were important to the owner and Opus. The fast track schedule assisted by AVR/AME’s fleet of concrete pumps resulted in remarkable progress in less than nine months.

“The fact that Opus is a design/build firm helps to streamline communications and because we are supplying both concrete and pumps makes scheduling even easier,” says Dan Rentz, AVR/AME’s Concrete Pump Manager. Rentz covers the metro area concrete pumping market with a fleet of Schwing pumps ranging from 32-meters to 58-meters.

According to Opus Project Superintendent, Greg Swanson, “We like flexibility and reliability in both boom size and type of equipment when we choose a pumping contractor, Apple Valley brings both of those qualities to our projects.”

One of the first things AVR/AME decided to do was to erect a portable plant on-site. “We have plants around the Twin Cities, but for the majority of the mix it was more economical for us to have the supply close at hand. Early on in the project there was room to produce on-site. We had to remove the plant after about seven months but it was value added in the long run,” according to Rentz. A mild start to winter benefited the project but pours in January and February were made in sub zero temperatures.

The majority of the decks on the seven and eight story office buildings were pumped with AVR/AMEs S 45 SX boom pumps. These machines are equipped with 148- foot, 4-section Overhead Roll and Fold™ Booms. This is a unique long boom that allow the first section to be angled away from the pour and the other three sections to be inserted deep into the structure. “The 180-degree articulation of that first section really saved us time and expense by reducing the amount of system we attached to the tip section,” Rentz noted.

The machines are also equipped with Schwing’s Super X Outriggers that telescope out from the chassis and provide a compact footprint. The outriggers don’t extend in front of the cab allowing the operators to place the machines very close to the buildings and take full advantage of the boom reach.

A contributor to AVR/AME’s value engineering on the project was a proprietary mix design developed in conjunction with General Resource Technology(GRT), a chemical ad mixture company based in Eagan, MN. Working with the AVR/AME staff, a mix was developed for placement on the metal decks that achieved the designed strength in seven days. The slump of the concrete was 9-10.5 inches (spread of 16”; which is very close to the 20” spread of self consolidating concrete.) According to GRT sales and engineering representative Darrell Stahlecker, a new chemical ad mixture “PolyChem SPC” was used to increase cement efficiency and hydration while providing cohesive high-flow concrete. developed that achieved early strengths in seven days. “We were able to economize on cement costs and in conjunction with the use of 1-7/8” limestone aggregate shrinkage was reduced and controlled. “It‘s a very coarse mix but the pumps were able to handle it with no problems,” he added.

Swanson added, “The ability to adjust the mix for finishability by adjusting ad mixtures showed the Apple Valley team’s understanding of our needs. Whenever I can coach the decision to use a ready-mix producer that pumps, I vote for it.”

The concrete mix supplied to the parking decks consisted of 100-percent ¾” crushed limestone and in conjunction with the PolyChem SPC was designed to produce cohesive, flowable concrete (6-8“ slump.) This helped to consolidate the concrete around the post tension cables and steel. Placement was enhanced and the “The fill rate around the cables and steel was especially good, “ according to Stahlecker, “ The speed of placement and the finished appearance are excellent: all of which are critical to Opus Corp.” The mix design’s increased performance and ease of placement allowed stressing to begin the next morning (18-20 hours after concrete had been placed.)

The sheer size of the three level parking structure - which is the third largest in the state - made the full reach of the 45-meter boom pumps even more valuable. The last pours were made in sub zero weather that can challenge even Minnesota pumpers. Rentz says proper care of the hydraulic system is important to reliable winter operation so he makes sure filters are clean and the oil is changed regularly. Pumps that are going out for below zero pours are stored inside. Heat exchangers that carry engine coolant are installed in the water tanks to prevent freeze up. Mix hauled even short distances in the cold is batched with heated sand and water.

In extreme cold, Rentz will not take the chance of resetting a pump – and freezing up in the process - but instead will add a pump if the entire pour cannot be reached from one set-up. He also forgoes insulating the pipeline preferring to have easy access to a pipe section if there is a problem. “The key is you’ve got to keep it flowing in the cold. Opus understands this and will increase the number of men on the deck so there are no delays.” Slab on grade pours that require pumping into an enclosed area on frigid days are pumped directly from the discharge outlet on the pump into system to eliminate the potential of freezing up the boom. System that runs between the pump discharge outlet and the enclosed pour is insulated with blankets.

Cold weather issues aren’t new to AVR/AME, nor are they new to the employees of Medtronic. All the office buildings are designed for the cold weather of Minnesota. Every floor of every building is joined to the adjacent building’s floors with enclosed walkways.