BUILDING TECHNOLOGY AND MANAGEMENT NEED PCC has low tensile strength limited ductility and little resistance to cracking PCC develops microcracks even before loading Addition of small closely spaced and uniformly distributed fibres act as crack arresters ID: 582985
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FIBRE REINFORCED CONCRETE
BUILDING TECHNOLOGY AND MANAGEMENTSlide2
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 FibreOrientation of FibresWorkability and Compaction of ConcreteSize of Coarse AggregateMixing
FIBRE REINFORCED CONCRETE
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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, carbonFibres with low modulus of elasticity- nylon, polypropyleneInterfacial 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
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FIBRE REINFORCED CONCRETE
Aspect Ratio of a fibre
= Length/DiameterSlide7
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/m
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W/C Ratio : 0.4 to 0.6% of sand to total aggregate : 50 to 100%Maximum Aggregate Size : 10 mmAir-content : 6 to 9%
Fibre content : 0.5 to 2.5% by vol of mix
: Steel -1% - 78kg/m
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: Glass -1% - 25 kg/m
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: Nylon -1% - 11 kg/m
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Types Of Frc’s
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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 matrix11FIBRE REINFORCED CONCRETESlide12
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Introduction of steel fibres modifies:
Tensile strength
Compressive strength
Flexural strengthShear strengthModulus of ElasticityShrinkage
Impact resistanceStrain capacity/Toughness
Durability
Fatigue
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Applications OF SFRC
Highway and airport pavements
Refractory linings
Canal liningsIndustrial floorings and bridge-decksPrecast applications - wall and roof panels, pipes, boats, staircase steps & manhole coversStructural applications
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Polypropylene Fibre Reinforced Concrete (PFRC)
Cheap, abundantly available
High chemical resistance
High melting pointLow modulus of elasticityApplications in cladding panels and shotcrete
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Glass Fibre Reinforced Concrete (Gfrc
)
High tensile strength, 1020 to 4080 N/mm
2Lengths of 25mm are usedImprovement 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 matrixContains 8-16% of asbestos fibres by volumeAssociated 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/mm
2Strength and stiffness superior to that of steel20
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Organic/Vegetable Fibres
Jute, coir and bamboo are examples
They may undergo organic decay
Low modulus of elasticity, high impact strength21FIBRE REINFORCED CONCRETE