Fiber Reinforced concrete
Concrete reinforced with fibrous material is known as fiber reinforced concrete, fibers are helps to improve structural integrity in concrete. Fiber-reinforced concrete are commonly used in concrete to control cracks and improving the durability concrete and mortar.
Various types of Fiber in concrete
- Metallic fiber
- Steel fiber
- Non metallic fiber
- Glass fiber
- Carbon fiber
- Polypropylene fiber
Effect of fibers in concrete
- Fibers are commonly used in concrete to control cracks due to drying shrinkage.
- Fiber are also reduce the permeability of concrete and thus reduce bleeding of water in fresh concrete.
Properties of fibre reinforced concrete
- Compressive strength
- Tensile strength
- Flexural strength
- Creep and shrinkage
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Compressive strength is much less affected by the addition of steel fibers. Corrosive strength increases from 0 to 15 percent have been observed for 1.5% volume of fiber.
Fibers aligned in the direction of tensile stress can bring very large increases in tensile strength, Increase in strength is very small, with intermediate values being indicated by several investigations, with no increase up to 60% in some instances.
Elements incorporating steel fibers have high flexural rigidity (low deflection) and small crack width when subjected to service loads. The improvement in flexural strength resulting from steel fiber reinforcement is not large enough to deliver steel fibers, which gives the ability to completely replace continuous bars in flexible reinforcing elements. Flexural strength increases from 0 to 20 percent to 1.5 percent by volume of fiber. Optimal conditions in flexural elements can be achieved with conventional steel bars through the use of steel fibers.
Roughness was identified much earlier in the development of fiber reinforced concrete as a special property, which above all else clearly distinguishes concrete without fiber. Under impact conditions, toughness can be demonstrated qualitatively by only trying to break through a thin section with a manually operated hammer.
When using steel fibers in concrete, attention has to be paid to the question of corrosion of the fiber. Because the amount of steel locally very low, when fibers are used, only limited expansion forces develop due to corrosion and usually no spalling occurs. Steel fibers in the immediate surface layer rapidly extend to the depth of surface carbonation, which can give aesthetic defects in the form of rust-colored surfaces.
Creep and shrinkage
Concrete shrinks when it is subjected to a dry environment. The extent of shrinkage on concrete depends on many factors including the properties of the material, temperature and relative humidity of the environment, the age when the concrete is subjected to the drying environment.
Requirements of good fibre
The basic requirement of fiber for improving the strength properties is high tensile strength and elastic modulus, adequate extensibility, a good bond at the interface and good stability. The fiber needs to be able to sense stress over a long period of time. The tensile strength of the fibers may not be significant if the composite falls from an important role in determining the strength capacity of the composite.
This finding is very important since traditionally, people think that reinforced concrete with fibers increase flexibility.
As for pavements, the most prevalent use for FRC is at toll plazas where nonmetallic fibers are used in lieu of metallic reinforcement since they can disrupt electronic toll reader’s signals.
Advantage of Fiber Reinforced concrete
- Better cohesion of the fresh concrete.
- Control and reduce crack.
- Improve load capacity and ductility.
- Increase toughness and abrasion resistance of concrete, this means more energy absorption ability making it suitable for concrete pavement.
- Increase in shear capacity when used in beams and Modest increase in flexural strength.
Disadvantages of Fiber Reinforced concrete
- Higher cost, FRC becomes very expensive compared to R.C.C. in terms of materials only.
- Surface has a lot of difficulty in finishing.
- Difficulty in repairing and maintenance.
- Corrosion of steel fibers.
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