Fiber reinforcement is a common addition to concrete because it can help to reduce cracks, increase the impact resistance, and can increase the concrete strength in certain applications. A variety of fiber types and dosages are available in order to accommodate different needs both in commercial and residential use. Some common types are micro-synthetic, macro-synthetic and steel fibers. These are added at the batch plant and can save time, energy and labor cost compared to other common reinforcement options.
When added to concrete, the special packaging dissolves allowing the fibers to mix in with the concrete easily. Synthetic fibers must be mixed thoroughly prior to discharge to ensure equal distribution throughout the mix.
In more technical terms, synthetic fibers provide a secondary reinforcement to both strengthen concrete and increase its durability. It does this by controlling internal cracks caused by gravity and drying conditions. If untreated, these cracks increase the permeability of the concrete allowing salts and other harmful chemicals to take hold. That spells disaster for concrete in the long run.
The first 24 hours after placement of concrete is generally when these cracks occur due to moisture loss, the cement hydration process, and temperature changes. Because most concrete is restrained, volume changes resulting from moisture loss creates stress on the concrete and can causes cracking. Restraint is caused by the difference in shrinkage between the surface and the underlying concrete area.
Synthetic fibers reduce the amount of cracking of concrete in three ways. One, it provides more strength to resist volume changes. Two, it bonds with the fresh concrete and distributes stress more evenly. Three, it reduces evaporation of water by reducing the bleed rate.
Synthetic fibers are easy to use compared to welded wire fabric due to placement issues. (If placed on the bottom of the slab, wire provides no benefit.) Each help control cracking. Wire fabric helps control cracks after they are formed, while fibers help prevent cracks from forming.
Note: Synthetic fibers are not recommended to increase joint spacing or as a substitute for any reinforcement required by building codes and standards. Adding fibers does not justify changing the mix designs in most situations.
Product information provided by the manufactures of synthetic fibers.