Fibre Reinforced Concrete

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.

Factors Affecting The Properties Of Fibre Reinforced Concrete

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

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

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

Workability and Compaction of Concrete

Fibres reduce workability

Size of Aggregate

Size of CA is restricted to 10mm

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

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