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Reinforcing concrete to keep it from cracking is nothing new -- even the earliest civilizations used natural fibers to inhibit cracking in masonry structures. Today, synthetic-fiber reinforcement is available to reinforce non-structural concrete applications with superior results. Currently, the most widely-accepted form of reinforcement is welded-wire fabric (WWF), a mesh of steel wires that is placed in concrete. However, synthetic-fiber reinforcement avoids the increased labor costs and difficulty in placement that are associated with WWF.
Synthetic-fiber reinforcement prevents cracks in concrete, unlike WWF, which controls crack width -- cracks actually need to occur before the WWF goes to work. Small-diameter synthetic fibers (nylon, glass, steel or polypropylene) are now being added to concrete to reduce shrinkage cracking by more than 80% according to independent lab tests. Reducing cracks improves concrete impermeability, increases its toughness and long-term weatherability, and can reduce callbacks in concrete slab floors, decks, driveways, and walks. According to fiber manufacturers, the placement, curing, or finish characteristics of the concrete are not affected by the addition of fibrous reinforcement.
Larger-diameter synthetic fibers (steel or polyolefin), added at higher content by volume (0.5% to 1.5% respectively), also enhance hardened flexural strength, but at increased cost.
Fibrous reinforcement is primarily used to reduce cracking in non-structural concrete applications. However, steel fibers rust and can cause surface discoloration.
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Adding fibers to the concrete during mixing can add to the cost of concrete, but avoids the labor cost and time to place reinforcing steel or WWF.
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Fibrous concrete reinforcement reduces concrete cracking and permeability, and increases strength, impact resistance, and durability of concrete non-structural slabs.
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Fibrous reinforcement is generally sold directly to ready-mix concrete suppliers. The suppliers add the fiber product to the concrete during the mixing process. Some of the higher performance and more costly products can be sold directly to users for a specific project.
Cost of fibrous concrete reinforcement is competitive with steel reinforcing bars and welded wire fabric, and because it is mixed in the concrete, does not have the added labor cost of placing reinforcing steel.
Not Applicable
All manufacturers attest to compliance with ASTM C 1116-95, which provides the specification for Fibrous Reinforcement. The Residential Concrete Code for One and Two Family Dwellings, ACI Committee 332 (Draft) allows use of WWF and Fibrous Reinforcement in nonstructural concrete applications. The CABO One and Two Family Dwelling Code (1995) no longer specifies a minimum amount of WWF or equivalent reinforcement to be used in concrete floors on grade. The International Code Council (ICC) Evaluation Service (ICC-ES) has reviewed and accepted fibrous concrete reinforcement products, and has issued Evaluation Service Legacy Reports. Information on these Legacy Reports can be obtained by contacting ICC at their web site (www.icc-es.org).
Not Applicable
Fibers are added directly to the concrete during mixing to distribute the filaments evenly throughout the concrete. Putting fibers in the concrete adds to the concrete cost, but avoids the labor associated with placement of reinforcing steel or WWF.
Not Applicable
Fibrous reinforcement reduces concrete slab cracking, permeability, and flaking or spalling. Increases in impact resistance, strength, and durability claims vary by manufacturer. Uniform distribution of fibers through the concrete mixture assures proper placement of the reinforcement, often an issue with WWF. Fibrous reinforcement is reported to add as little as $7 to $10 per cubic yard of ready mixed concrete, which is about the same cost as material and labor to place WWF. Some fibrous concrete products with significantly higher fiber content can add $50 to $60 per cubic yard.
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