## 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