Fiber reinforced concrete (FRC) is concrete containing fibrous material which increases its structural integrity. It contains short discrete fibers that are uniformly distributed and randomly oriented.
Reduced water absorption is a function of the fibres ability to reduce plastic shrinkage cracking, reducing the ability of water to permeate into the bleed in a concrete. Reducing another possible entry by water into the concrete in its hardened state.
Introduction of fibres improves the toughness of the concrete, with improvements in impact and abrasion resistance. Coupled with the above, helps make the concrete less susceptible to freeze thaw damage.
Dosage and Performance
Fibrillated fibres are introduced into the concrete mix at a rate of 0.9kg/mþ. No adjustment to the mix design is required. Fibre reinforced concrete requires no special precautions and can be power floated, pumped and trowelled like other concretes.
Note: Fibres are not a substitute for structural steel reinforcement.
Admixtures
Admixtures are added to concrete during mixing to alter its properties, such as workability, curing temperature range, set time or color.
They fall into the following catorgies each with its own benifits and uses :
- Retarding admixtures
- Accelerating admixtures
- Super plasticizers
- Water reducing admixtures
- Air-entraining admixtures
Retarding admixtures
Retarding admixtures slow down the hydration of cement, lengthening set time. You ise retarders mainly in hot wather, or where a large pour is been done and and the workability and setting time needs to be maintained.
Retarders are commonly used in floor screeds, giving increase workability over long periods
Accelerating admixtures
Accelerators shorten the set time of concrete, allowing a cold-weather pour, early removal of forms, early surface finishing, and in some cases, early load application. Proper care must be taken while choosing the type and proportion of accelerators, as under most conditions, commonly used accelerators cause an increase in the drying shrinkage of concrete.
Super plasticizers
Super plasticizers, also known as plasticizers, include water-reducing admixtures. They can maintain a specific consistency and workability at a greatly reduced amount of water. They can also produce a high strength concrete.
Water reducing admixtures
Water reducing admixtures require less water to make a concrete of equal slump, or increase the slump of concrete at the same water content. They can have the side effect of changing initial set time. Water reducers are mostly used for hot weather concrete placing and to aid pumping.
Air-entraining admixtures
Air-entraining agents entrain small air bubbles in the concrete. The major benefit of this is enhanced durability in freeze-thaw cycles, especially relevant in cold climates. While some strength loss typically accompanies increased air in concrete, it generally can be overcome by reducing the water-cement ratio via improved workability (due to the air-entraining agent itself) or through the use of other appropriate admixtures.
