Fiber-Reinforced Concrete Withstands Heavy Loads
by Kate Hamilton
The fiber-reinforced concrete at the Caterpillar warehouse in Michigan was designed to withstand the weight of heavy-duty construction equipment
The Grand Rapids, Mich.-based Caterpillar warehouse demands a lot of its 110,000-square-foot concrete slab. Composed of showrooms, exterior pavements, composite metal decks, and engine service bays, it gets a beating from the several-ton heavy-duty construction equipment constantly moving in and out of the warehouse. So when an addition to the service department was planned in 2005, contractor Pioneer Construction, Grand Rapids, Mich., returned to the original slab’s design.
Ralph Den Hartig, JDH Engineering, Grandville, Mich.—the original engineer of the initial warehouse construction in 1995—turned to steel fiber-reinforced concrete as the answer to withstanding the tremendous loads the heavy-duty equipment imposes on the floor keeping concrete surface weaknesses and defects to a minimum.
To reinforce the new slab, Pioneer Construction used a blend of Fibermesh 300—a fibrillated synthetic fiber, and Novocon XR—a steel fiber manufactured by Propex Concrete Systems. The synthetic fibers help control early-age cracking caused by intrinsic stresses created when the concrete settles and shrinks over the first 24 hours after placement. The steel fibers serve as long-term agents helping to control drying shrinkage cracking that can happen weeks, months, or even years later. These fibers are unlike conventional steel reinforcement, which only function after the concrete cracks.
Ready-mix company GR Gravel added the fibers to the concrete mix at the plant, eliminating any placing, handling, or installation on the job-site. The fibers also smoothed out the pumping process, reducing line pressures. In addition, no equipment needed to be hoisted or lifted, and the slab was finished with standard techniques, thus eliminating the extra cost and labor required with conventional steel reinforcement. In addition to the cost and labor savings, the fiber reinforcement eliminated the need for workers to handle and position welded fabric, resulting in a safer working environment.
As a result of the combined fibers, the slab can withstand greater stress, both prior to and after cracking. If cracks or chips occur due to heavy impacts, the steel fibers provide superior crack width control by interlocking with aggregate at the cracks and contraction joints. This increases load carrying capacity and provides more stable load transfer at the joints.
The fiber blend was critical especially in the composite metal deck construction, which often cracks because of deck flexing and movement restraint. The stress and movements can cause the concrete to shrink away from the metal deck. However, in this case the evenly distributed fibers provided improved mechanical bonding and reduced concrete cracking in critical areas such as over structural support beams.
The 100,000-square-foot addition to the Caterpillar warehouse included 19 new heavy equipment bays, totaling 210,000 square feet of fiber-reinforced concrete.