Garmin International is a worldwide leader in the design, manufacturing, and marketing of navigation and communication products utilizing GPS technology. From a handful of employees in 1989, the organization has grown to more than 7000 associates worldwide. Growth of this magnitude has resulted in numerous expansions to its office campus in Olathe, Kan. Most recently, the existing warehouse was enlarged via a 230,268-square-foot addition to accommodate growing inventory reserves to supply the company's global market.

The expansion included 184,191 square feet of slab on grade specified Fmin60. Where defined traffic slabs typically are placed in 12- to 16-foot-wide strips, the Garmin expansion required 42-foot-wide strips. Each pour had three defined traffic aisles that had to meet the Fmin60 specification.

"Less than 1% of the floors constructed in the United States are classified as defined traffic," says Ryan McLaughlin, project manager for JE Dunn Construction. "The specified Fmin60 slabs and their 42-foot width were unlike any our concrete crews had done in 10 years. Since 2001, Dunn and Garmin have had a strong working relationship and it was our goal to renew and extend that relationship well into the future. We were determined to meet the challenge issued to the complete satisfaction of our client."

In addition to stringent superflat specifications, there was a very tight schedule that all parties had to follow. All concrete flatwork was to be completed through the winter months. The building had to be fully enclosed and climate controlled. Also, because the building was an addition to the existing warehouse, care had to be taken to limit vibrations and noise, as well as ensure that the existing structure remained climate controlled.

The slab-on-grade portion of the project was specified at Fmin60 ±1/8 inch in 6 feet. Due to the type of forklifts used and height of racks in the warehouse, the slab on grade had to be extraordinarily flat and level. Anything outside the specified tolerance had to be ground down to meet the allowable tolerance so as not to throw forklifts out of balance when carrying loads. Dunn completed several in-place mock-ups in the dock area of the warehouse to be certain that all prep work, materials, placement, and finishing techniques were consistent and expectations were defined clearly.

The 10-inch-thick slab on grade was placed under roof in a climate controlled environment at 50º to 56º F and 30% to 40% humidity. Because all the structural steel was already in-place, Dunn opted to use a telebelt to place the concrete. The dimensions of each bay (42 x 273 feet) and the location of rebar (1 1/2 inches from the surface) made placement very challenging. Thirteen pours, averaging 360 cubic yards per pour, were completed at a pour rate of 70 to 75 yards per hour.

JE Dunn opted to use a 45-foot vibratory truss screed with a 1/8-inch camber. All edge forms were beveled and capped with a piece of angle iron with shims at 1 foot on center. Carpenters checked grade every foot with an eye level. Diamond dowels were used at all construction joints and load plate baskets at all control joints (which only run parallel to the racks to eliminate spalling from forklifts traffic). Dunn carpenters and ironworkers built devises to attach to the columns allowing the 45-foot-wide truss screed to pivot on grade and pass by columns that were 42 feet from center to center.

Of equal importance to the prep was the consistency of the concrete. Fordyce provided concrete that was consistently within 1/4 inch of the specified slump. This consistency helped the concrete set at the same pace all the way through the pour.

Once concrete was placed, Dunn finishers first hit the slab with check rods. Second, they bump-cut both north to south and east to west. Third, they used the riding trowels with pans. The last step was riding trowels with finish blades. Dunn performed minimal grinding: only 2.15% of the specified Fmin60 areas required grinding. Industry standards show that 3% to 5% grinding is considered "good" and 8% to 10% is average.

The result was a warehouse floor that pleased the client. "We had specified only a part of the slab on grade meet Fmin60. The Dunn crews came in with mock-ups for the big pours and used the same principals on the entire floor We wound up with superflat throughout the warehouse," says Chris Wolfe, facilities manager for Garmin. "The concrete slab that we've got now goes well beyond our defined traffic areas giving us a warehouse environment that is both efficient and effective." CC

Kevin Shipley is general superintendent of JE Dunn Construction.