128628506 fibre reinforced concrete
DESCRIPTION
important notes on FRC...will be useful for main projects and mini projects.........TRANSCRIPT
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. 2
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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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3. ASPECT RATIO OF THE FIBRE
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Aspect Ratio of a fibre = Length/Diameter
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 9
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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. 17
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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 19
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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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