FIBRE REINFORCED

CONCRETE

BUILDING TECHNOLOGY AND MANAGEMENT

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

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

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

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

3

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

4

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

2. VOLUME OF FIBRES

5

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

3. ASPECT RATIO OF THE FIBRE

6

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

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

7

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

5. Workability and Compaction of

Concrete

Fibres reduce workability

6. Size of Aggregate

Size of CA is restricted to 10mm

8

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

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

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

TYPES OF FRC’S

10

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

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

11

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

12

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

13

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

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

14

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

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

15

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

POLYPROPYLENE FIBRE REINFORCED CONCRETE (PFRC)

Cheap, abundantly available

High chemical resistance

High melting point

Low modulus of elasticity

Applications in cladding panels and shotcrete

16

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

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

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

OTHER FIBRES

18

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

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

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

CARBON FIBRES

Material of the future, expensive

High tensile strengths of 2110 to 2815 N/mm2

Strength and stiffness superior to that of steel

20

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E

ORGANIC/VEGETABLE FIBRES

Jute, coir and bamboo are examples

They may undergo organic decay

Low modulus of elasticity, high impact

strength

21

FIB

RE

RE

INF

OR

CE

D C

ON

CR

ET

E