Article and photos by Gregory Havel
Since the early 1980s, fibers of several materials have been developed to replace or supplement the welded wire mesh that is used as reinforcement in conventional slab-on-grade concrete, in concrete pavement, and in precast concrete tanks and vaults for underground use. The fiber material, dimensions, and mix ratio are determined by the intended use of the concrete. The fibers are added to the concrete in the mixer, usually at a proportion of 0.5-1.0 pound of fiber per cubic yard of concrete (0.3-0.6 kg of fiber per cubic meter of concrete). These fibers are usually made of glass, nylon, polyethylene, polyurethane, polyvinyl acetate, cellulose, steel, carbon, or Kevlar®.
Although fiber reinforcing does add some compressive and tensile strength to the cured concrete, the amount is not significant. Its primary benefits are the control of the plastic shrinkage cracking as the concrete cures; and the increased resistance to impact, fatigue, thermal shock, and abrasion that it provides.
Today, structural applications still require the use of steel-welded wire mesh (photo 1) and steel reinforcing bars (rebar). Fiber reinforcing may be used to supplement the welded wire mesh and rebar in some structural applications. It is sometimes used to replace welded wire mesh in slab-on-grade concrete and pavement. It is also used in the concrete topping over pre-stressed and post-tensioned structural concrete, especially in areas with high traffic.
In its earlier days, it was occasionally used to replace welded wire mesh in structural applications. Although it did not perform as expected, some of these installations are still in place.
Photo 2 shows about one square foot (0.093 square meter) of finished and cured fiber-reinforced concrete. Some of the polypropylene fibers are visible at the surface. They will be concealed by the carpet or vinyl composition tile that will be applied to finish the floor.
This material could be significant for firefighters, since fiber-reinforced concrete may not behave under fire conditions as the ordinary concrete it appears to be. It may also be more resistant to the impact and drilling commonly used in breaching concrete floors.
For additional information, internet search for “fiber-reinforced concrete”, and visit the website of the Fiber Reinforced Concrete Association (FRCA) at www.fiberreinforced.org.
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Gregory Havel is a member of the Town of Burlington (WI) Fire Department; retired deputy chief and training officer; and a 30-year veteran of the fire service. He is a Wisconsin-certified fire instructor II and fire officer II, an adjunct instructor in fire service programs at Gateway Technical College, and safety director for Scherrer Construction Co., Inc. He has a bachelor’s degree from St. Norbert College. He has more than 30 years of experience in facilities management and building construction. |
