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Assembly Required

Over the second weekend of 2018, lead contractor Barton Malow Co. of Southfield, Mich., mustered 131 tradesmen at the Arlington, Texas, Hilton Garden Inn for a continuous, 6,470-yd. pour, yielding what the project team and owner dubbed the Texas Mega Slab: A 256,000-sq.-ft. expanse of 8-in. thick, steel fiber-reinforced concrete, placed and finished in under 1.5 days, at the GM Arlington Assembly Plant.

Led by Laborer Superintendents Ethan Uhl and Brian Willard, with Project Director Chris Hofe, Senior Project Manager Josiah Goins and Construction Manager Craig Lowell supporting, the Mega Slab proved a successful exercise in planning and mass-concrete placement. During preliminaries at the hotel, project leaders impressed upon tradesmen the a) idea of toughness, as in “Don’t get complacent; stick with the plan”; b) importance of safety on a big project; and, need for quality control. By going over potential hazards and dutifully crossing off each bullet point in the pre-task list, leaders and tradesmen set the stage for something special. Shift teams were defined in color-coordinated patterns, in addition to being staggered to ensure each member was well-rested for what would be a difficult project.

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The Mega Slab supports additional capacity at the GM Arlington Assembly Plant, home to Chevy Tahoe production. Beginning in 2015, the automaker committed $1.4 billion for a three-year expansion of the operation, located between Dallas and Fort Worth.
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One of four conveyors dosing Bekaert steel fibers at 23 lbs./yd. Once fibers were transferred, engineers called for a five-minute mixing cycle—netting stiff, 6-in. slump mixes that challenged placing crews. PHOTOS: Jon Humphrey, courtesy of Barton Malow
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Barton Malow, Lloyd Concrete Services and Unlimited Concrete Solutions assembled a management team and trades crew of four supervisors, four safety representatives, 62 finishers, 42 laborers, eight carpenters, seven operators, two rodbusters and two layout engineers. Their Mega Slab “fleet” included 38 ride-on and 12 walk behind trowel machines, 10 saws, four laser screeds, and four power rakes.
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PHOTOS: Jon Humphrey, courtesy of Barton Malow

The Mega Slab entailed nearly 33 consecutive hours of placing, raking, leveling, troweling and sawing. Barton Malow partnered with Virginia’s Lloyd Concrete Services and Ohio’s Unlimited Concrete Solutions to assemble the large array of specialty labor required.

INTO THE FIRE

Huddled inside the GM facility on Saturday night, the first team gathered to take one last safety moment and a stretch before work started. Crews then filed into the jobsite: A bare subgrade in a hangar lined with steel columns and illuminated by overhead LED lights. Laborers mobilized on the opposite side of the entrance, putting on kneepads and adjusting their hardhats.

On the other side of the building was the familiar din of mixer trucks, dispatched from one of four plants of Redi-Mix Concrete, the Dallas-Ft. Worth business of U.S. Concrete Inc. Halo light hard hats raised their traffic batons and pointed the first trucks to the other side. As they began to discharge loads of stiff mixes bearing 23 lbs. of steel fiber/yard, the sheer size of the project took shape.

Like a symphony, tradesmen began an intricate pattern of controlling the pour and ushering laser screeds for leveling. The Mega Slab started with a relatively small section, but by Sunday morning was two-thirds the way down the hangar. A revolving door of crews ensured everyone got the rest, food and hydration needed before jumping back into the fire. As the team started the second half of the pour, ride-on trowel machines could be seen blading their way across the surface of the hardening slab, looking like go-karts from a distance. As the trowels moved toward the end, saws soon followed.

MASS SUCCESS

By 6 a.m. Monday, the work was finished almost as quickly as it began. Lasting 32.5 hours, the operation resulted in an average placement rate of 315 yd./hour. The slab was burnished, finished and achieved overall FF/FL numbers of 56.22/42.06. Moreover, the site prep crew was able to grade within 3/16th of an inch across the placement’s entire square footage, keeping the concrete order within 2 percent of estimated volume.