29-07-2011, 04:20 PM
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Fiber Reinforced Concrete
What is a Fiber…?
Small piece of reinforcing material possessing certain characteristic properties.
Can be circular or flat.
Parameter used to describe fiber – “Aspect ratio”.
Aspect ratio is ratio of its length to its diameter.
Typical aspect ratio for fibers ranges from 30 to 150.
What is Fiber Reinforced Concrete (FRC)?
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.
Fibers include steel fibers, glass fibers, synthetic fibers and natural fibers.
Within these different fibers that character of fiber reinforced concrete changes with varying concretes, fiber materials, geometries, distribution, orientation and densities.
Fibers used…
Although every type of fiber has been tried out in cement and concrete, not all of them can be effectively and economically used. Each fiber has some characteristic properties and limitations.
Fibers used are-
Steel fibers
Polypropylene, nylons
Asbestos, Coir
Glass
Carbon
Steel Fiber Reinforced Concrete…
Most commonly used fiber.
Round fiber of diameter 0.25 to 0.75mm.
Enhances flexural, impact and fatigue strength of concrete.
Used for-overlays of roads, airfield pavements, bridge decks.
Thin shells and plates have also been constructed using stell fibers.
Polypropylene/Nylon Fiber Reinforced Concrete…
Suitable to increase impact strength of concrete.
Possess high tensile strength but their low modulus of elasticity and higher elongation do not contribute to the flexural strength.
Asbestos Fiber Reinforced Concrete…
Mineral fiber, most successful of all as it can be mixed with portland cement.
Tensile strength of asbestos varies between 560 to 980 N/mm2.
Asbestos cement paste has considerably higher flexural strength than portland cement paste.
For unimportant concrete work, organic fibers like coir, jute and canesplits are also used.
Glass Fiber Reinforced Concrete…
Recent introduction.
Very high tensile strength 1020 to 4080 N/mm2.
Alkali resistant glass fiber has been developed.
Shows comparable improvement in durability to conventional E-glass fiber.
Carbon Fiber Reinforced Concrete…
Posses very high tensile strength 2110 to 2815 N/mm2 and Young’s modulus.
Cement composite consisting of carbon fibers show very high modulus of elasticity and flexural strength.
Used for cladding, panels and shells.
Factors affecting properties of Fiber Reinforced Concrete…
Transfer of stress between matrix and fiber.
Type of fiber.
Fiber geometry.
Fiber content.
Orientation and distribution of fibers
Mixing and compaction technique of concrete.
Size and shape of aggregates.
Relative Fiber Matrix Stiffness
Modulus of elasticity of matrix must be much lower than that of fiber for efficient stress transfer.
Nylon and propylene fiber impart greater degree of toughness and resistance to impact.
Steel, glass and carbon impart strength and stiffness to the composite.
Interfacial bonds also determine the degree of stress transfer.
Bonds can be improved by larger area of contact, improving frictional properties and degree of gripping and by treating steel fibers with sodium hydroxide or acetone.
Volume Of Fiber
Strength largely depends upon the quantity of fibers used.
Tensile strength and toughness of the composite linearly increase with increase in volume of fibers.
Higher percentage of fibers is likely to cause segregation and harshness of concrete and mortar.
Aspect Ratio Of Fiber
One of the important factor affecting the properties and behavior of composite.
Increase in aspect ration upto 75, increase the ultimate strength of concrete linearly.
Beyond 75 relative strength and toughness is reduced.
Orientation Of Fibers
One of the major difference in conventional reinforcement and fiber reinforcement.
Specimens with 0.5% volume of fiber were tested and it showed that when fibers were aligned parallel to the load applied, more tensile strength toughness was seen as compared to randomly distributed and perpendicular fibers.
Workability and Compaction of Concrete…
Use of steel fibers decrease the workability.
External vibration fails to compact the concrete.
Poor workability is also result of non uniform distribution of fibers.
Fiber volume at which this situation is reached depends on the length and diameter of fiber used.
Workability and compaction standard can be improved with help of water reducing admixture.
Size Of Coarse Aggregates
Maximum size of aggregates should be restricted to 10 mm.
Fibers also act as aggregate.
The interparticle friction and between fibers and between fibers and aggregates controls the orientation and distribution of fibers which affect the properties of composite.
Friction reducing admixtures and admixtures improving the cohesiveness can significantly improve the mix.
Mixing
Mixing is important to avoid balling of aggregates, segregation and to obtain uniform composite.
Increase in aspect ration, volume percentage, size and quantity of aggregates intensify the balling tendencies.
A steel fiber content in excess of 2% by volume and an aspect ratio of more than 100 are difficult to mix.
Addition of fibers before addition of water is important to get uniform dispersion of fibers in concrete mix.
Typical Proportions For FRC…
Advantages Of FRC Over Conventionally Reinforced Concrete…
Increased static and dynamic tensile strength.
Energy absorbing characteristics and better fatigue strength.
Uniform dispersion of fibers throughout the concrete provides isotropic properties.
Applications…
Overlays of air-fields.
Road pavements.
Industrial flooring.
Bridge decks.
Canal lining.
Explosive resistant structure.
Refractory lining.
Fabrications of precast products like pipes, boats, beams, staircase steps, wall panels, roof panels, manhole covers etc.
Manufacture of prefabricated formwork moulds of “U” shape for casting lintels and small beams.
Applications…
Current development in FRC:-
High fibre volume micro-fibre system.
Slurry infiltrated fibre concrete(SIFCON).
Compact reinforced composites.
High fibre volume micro-fibre system:-
Can replace asbestos fibre.
Improves toughness and impact strength.
These properties make it attractive for thin precast products such as roofing sheets ,cladding panels.
Cement composites are useful for repair & rehabilitation works.
Slurry infiltrated fibre concrete:-
SIFCON was invented by Lankard in 1979.
Steel fibre bed is prepared and cement slurry is infiltrated.
Micro-fibre contents up to about 20% by volume can be achieved.
Increase in both flexural load carrying capacity and toughness.
High compressive strength is achieved.
Used for blast resistant structures & burglar proof safe vaults.
Compact reinforced composites(CRC):-
Consist of an extremely strong ,dense cement matrix.
Extremely expensive.
Exhibits flexural strength up to 260Mpa & compressive strength of about 200Mpa.
As strong as structural steel.
Can be moulded and fabricated at site.
Fiber Reinforced Concrete
What is a Fiber…?
Small piece of reinforcing material possessing certain characteristic properties.
Can be circular or flat.
Parameter used to describe fiber – “Aspect ratio”.
Aspect ratio is ratio of its length to its diameter.
Typical aspect ratio for fibers ranges from 30 to 150.
What is Fiber Reinforced Concrete (FRC)?
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.
Fibers include steel fibers, glass fibers, synthetic fibers and natural fibers.
Within these different fibers that character of fiber reinforced concrete changes with varying concretes, fiber materials, geometries, distribution, orientation and densities.
Fibers used…
Although every type of fiber has been tried out in cement and concrete, not all of them can be effectively and economically used. Each fiber has some characteristic properties and limitations.
Fibers used are-
Steel fibers
Polypropylene, nylons
Asbestos, Coir
Glass
Carbon
Steel Fiber Reinforced Concrete…
Most commonly used fiber.
Round fiber of diameter 0.25 to 0.75mm.
Enhances flexural, impact and fatigue strength of concrete.
Used for-overlays of roads, airfield pavements, bridge decks.
Thin shells and plates have also been constructed using stell fibers.
Polypropylene/Nylon Fiber Reinforced Concrete…
Suitable to increase impact strength of concrete.
Possess high tensile strength but their low modulus of elasticity and higher elongation do not contribute to the flexural strength.
Asbestos Fiber Reinforced Concrete…
Mineral fiber, most successful of all as it can be mixed with portland cement.
Tensile strength of asbestos varies between 560 to 980 N/mm2.
Asbestos cement paste has considerably higher flexural strength than portland cement paste.
For unimportant concrete work, organic fibers like coir, jute and canesplits are also used.
Glass Fiber Reinforced Concrete…
Recent introduction.
Very high tensile strength 1020 to 4080 N/mm2.
Alkali resistant glass fiber has been developed.
Shows comparable improvement in durability to conventional E-glass fiber.
Carbon Fiber Reinforced Concrete…
Posses very high tensile strength 2110 to 2815 N/mm2 and Young’s modulus.
Cement composite consisting of carbon fibers show very high modulus of elasticity and flexural strength.
Used for cladding, panels and shells.
Factors affecting properties of Fiber Reinforced Concrete…
Transfer of stress between matrix and fiber.
Type of fiber.
Fiber geometry.
Fiber content.
Orientation and distribution of fibers
Mixing and compaction technique of concrete.
Size and shape of aggregates.
Relative Fiber Matrix Stiffness
Modulus of elasticity of matrix must be much lower than that of fiber for efficient stress transfer.
Nylon and propylene fiber impart greater degree of toughness and resistance to impact.
Steel, glass and carbon impart strength and stiffness to the composite.
Interfacial bonds also determine the degree of stress transfer.
Bonds can be improved by larger area of contact, improving frictional properties and degree of gripping and by treating steel fibers with sodium hydroxide or acetone.
Volume Of Fiber
Strength largely depends upon the quantity of fibers used.
Tensile strength and toughness of the composite linearly increase with increase in volume of fibers.
Higher percentage of fibers is likely to cause segregation and harshness of concrete and mortar.
Aspect Ratio Of Fiber
One of the important factor affecting the properties and behavior of composite.
Increase in aspect ration upto 75, increase the ultimate strength of concrete linearly.
Beyond 75 relative strength and toughness is reduced.
Orientation Of Fibers
One of the major difference in conventional reinforcement and fiber reinforcement.
Specimens with 0.5% volume of fiber were tested and it showed that when fibers were aligned parallel to the load applied, more tensile strength toughness was seen as compared to randomly distributed and perpendicular fibers.
Workability and Compaction of Concrete…
Use of steel fibers decrease the workability.
External vibration fails to compact the concrete.
Poor workability is also result of non uniform distribution of fibers.
Fiber volume at which this situation is reached depends on the length and diameter of fiber used.
Workability and compaction standard can be improved with help of water reducing admixture.
Size Of Coarse Aggregates
Maximum size of aggregates should be restricted to 10 mm.
Fibers also act as aggregate.
The interparticle friction and between fibers and between fibers and aggregates controls the orientation and distribution of fibers which affect the properties of composite.
Friction reducing admixtures and admixtures improving the cohesiveness can significantly improve the mix.
Mixing
Mixing is important to avoid balling of aggregates, segregation and to obtain uniform composite.
Increase in aspect ration, volume percentage, size and quantity of aggregates intensify the balling tendencies.
A steel fiber content in excess of 2% by volume and an aspect ratio of more than 100 are difficult to mix.
Addition of fibers before addition of water is important to get uniform dispersion of fibers in concrete mix.
Typical Proportions For FRC…
Advantages Of FRC Over Conventionally Reinforced Concrete…
Increased static and dynamic tensile strength.
Energy absorbing characteristics and better fatigue strength.
Uniform dispersion of fibers throughout the concrete provides isotropic properties.
Applications…
Overlays of air-fields.
Road pavements.
Industrial flooring.
Bridge decks.
Canal lining.
Explosive resistant structure.
Refractory lining.
Fabrications of precast products like pipes, boats, beams, staircase steps, wall panels, roof panels, manhole covers etc.
Manufacture of prefabricated formwork moulds of “U” shape for casting lintels and small beams.
Applications…
Current development in FRC:-
High fibre volume micro-fibre system.
Slurry infiltrated fibre concrete(SIFCON).
Compact reinforced composites.
High fibre volume micro-fibre system:-
Can replace asbestos fibre.
Improves toughness and impact strength.
These properties make it attractive for thin precast products such as roofing sheets ,cladding panels.
Cement composites are useful for repair & rehabilitation works.
Slurry infiltrated fibre concrete:-
SIFCON was invented by Lankard in 1979.
Steel fibre bed is prepared and cement slurry is infiltrated.
Micro-fibre contents up to about 20% by volume can be achieved.
Increase in both flexural load carrying capacity and toughness.
High compressive strength is achieved.
Used for blast resistant structures & burglar proof safe vaults.
Compact reinforced composites(CRC):-
Consist of an extremely strong ,dense cement matrix.
Extremely expensive.
Exhibits flexural strength up to 260Mpa & compressive strength of about 200Mpa.
As strong as structural steel.
Can be moulded and fabricated at site.
