Using synthetic fibers in precast products acts as an insurance policy against breakage and loss, but fibers have other benefits too. In precast operations, they add early strength, help in handling, and save on labor.
Although fibers can be used in precast concrete for nonstructural reinforcement, they do not provide structural reinforcement. Fibers add impact resistance and durability. Rebar is still needed in products that require significant reinforcement. For fibers to be most effective, they must be evenly distributed throughout the product.
The type of fiber used, its dosage and forms used in precasting make a difference in fuzziness sometimes associated with fibers. This fuzziness is caused when the fibers float to the top of the form. Fuzziness can be eliminated by burning the fibers off or exposing them to the sun.
Considerations in selecting a fiber product include economics, handling, and availability of the material. In making your choice of fibers, find a product that has been field tested, and then perform tests on your own.