FIBRE REINFORCED CONCRETE

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FIBRE REINFORCED CONCRETE

• BUILDING TECHNOLOGY AND MANAGEMENT

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NEED

• PCC has low tensile strength, limited ductility
  and little resistance to cracking
• PCC develops micro-cracks, even before loading
• Addition of small, closely spaced and uniformly
  distributed fibres act as crack arresters.
• FIBRE REINFORCED CONCRETE is a composite
  material consisting of mixtures of cement, mortar
  or concrete and discontinuous, discrete,
  uniformly dispersed suitable fibres.

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Factors Affecting The Properties Of Frc

• Relative Fibre Matrix Stiffness
• Volume of Fibres
• Aspect Ratio of the Fibre
• Orientation of Fibres
• Workability and Compaction of Concrete
• Size of Coarse Aggregate
• Mixing

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1. Relative Fibre Matrix Stiffness

• Modulus of elasticity of matrix must be much
  lower than that of fibre. E.g. steel, glass,
  carbon
• Fibres with low modulus of elasticity- nylon,
  polypropylene
• Interfacial bond between the matrix and the
  fibres determine the effectiveness of stress
  transfer

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2. Volume Of Fibres
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3. Aspect Ratio of the Fibre
Aspect Ratio of a fibre Length/Diameter
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4. Orientation of Fibres

• The effect of randomness, was tested using
  mortar specimens reinforced with 0.5 volume of
  fibres, by orienting them
• parallel to the direction of the load
• perpendicular to the direction of the load
• in random

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• 5. Workability and Compaction of Concrete
• Fibres reduce workability
• 6. Size of Aggregate
• Size of CA is restricted to 10mm

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7. Mixing

• Cement content 325 to 550 kg/m3
• W/C Ratio 0.4 to 0.6
• of sand to total aggregate 50 to 100
• Maximum Aggregate Size 10 mm
• Air-content 6 to 9
• Fibre content 0.5 to 2.5 by vol of mix
• Steel -1 - 78kg/m3
• Glass -1 - 25 kg/m3
• Nylon -1 - 11 kg/m3

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Types Of Frcs
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Steel Fibre Reinforced Concrete (SFRC)

• Aspect ratios of 30 to 250
• Diameters vary from 0.25 mm to 0.75 mm
• Hooks are provided at the ends to improve bond
  with the matrix

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Introduction of steel fibres modifies

1. Tensile strength
2. Compressive strength
3. Flexural strength
4. Shear strength
5. Modulus of Elasticity
6. Shrinkage
7. Impact resistance
8. Strain capacity/Toughness
9. Durability
10. Fatigue

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Applications OF SFRC

• Highway and airport pavements
• Refractory linings
• Canal linings
• Industrial floorings and bridge-decks
• Precast applications - wall and roof panels,
  pipes, boats, staircase steps manhole covers
• Structural applications

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Polypropylene Fibre Reinforced Concrete (PFRC)

• Cheap, abundantly available
• High chemical resistance
• High melting point
• Low modulus of elasticity
• Applications in cladding panels and shotcrete

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Glass Fibre Reinforced Concrete (Gfrc)

• High tensile strength, 1020 to 4080 N/mm2
• Lengths of 25mm are used
• Improvement in impact strengths, to the tune of
  1500
• Increased flexural strength, ductility and
  resistance to thermal shock
• Used in formwork, swimming pools, ducts and
  roofs, sewer lining etc.

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Other Fibres
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Asbestos Fibres

• High thermal, mechanical and chemical resistance
• Short in length (10 mm)
• Flexural strength is 2 to 4 times that of
  unreinforced matrix
• Contains 8-16 of asbestos fibres by volume
• Associated with health hazards, banned in many
  countries

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Carbon Fibres

• Material of the future, expensive
• High tensile strengths of 2110 to 2815 N/mm2
• Strength and stiffness superior to that of steel

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Organic/Vegetable Fibres

• Jute, coir and bamboo are examples
• They may undergo organic decay
• Low modulus of elasticity, high impact strength