WHAT IS FIBRE REINFORCED CONCRETE?

FIBRE REINFORCED CONCRETE

In conventional concrete, micro-cracks are develop even before loading because of drying shrinkage and other causes of volume change. When the structure is loaded, the micro cracks open up and propagate. The development of such micro cracks is the main reason of inelastic deformation in concrete.
The weakness can be removed by inclusion of small, closely spaced and uniformly dispersed fibres in concrete. The addition of fibres in concrete substantially improve its static and dynamic properties. These fibres offer increased resistance to crack growth, through a crack arresting mechanism and improve tensile strength and ductility of concrete.
Fibre reinforced concrete (FRC) can be defined as a composite material consisting of concrete and discountinuous, discrete, uniform dispersed fine fibres. The continuous meshes, woven fabrics and long wires or rods are not considered to be discrete fibres.

FACTORS AFFECTING PROPERTIES OF FIBRE REINFORCED CONCRETE :


  1. Volume of fibres : The strength of fibre reinforced concrete depends upon the volume of fibres used in it. It has been found that increase in the volume of fibres, increases approximately linearly tensile strength and toughness of the concrete. 
  2. Aspect ratio of fibres : The aspect ratio of 75, increase in the aspect ratio increases the strength and toughness of concrete. Beyond 75, relative strength and toughness are reduced.
  3. Orientation of fibres : In the conventional, reinforcement bars are oriented in desired direction while in fibre reinforcement, Fibres are randomly oriented. Hence they gives more tensile strength and toughness.
  4. Size of coarse aggregate : Investigation showed that the maximum size of coarse aggregate should not exceed 20 mm to avoid appreciable reduction in strength of the composite.
  5. Workability and compaction of concrete : Addition of steel fibres decrease the workability of concrete. Poor workability adversely affect the compaction of concrete. Another consequences of poor workability is non uniform distribution of the fibres in the mix.
  6. Mixing : Fibres should be mixed in concrete thoroughly, to avoid balling of fibres and segregation. Mixing of fibres becomes difficult, when aspect ratio and volume of fibre is more. 
Typical proportion for fibre reinforced concrete are as under :

cement content                                : 325 to 500 kg/cu.m
w/c ratio                                           : 0.4 to 0.6
Maximum size of C.A                       : 10 mm
Sand content, % of total aggregate : 50 to 100 %
Air content                                        : 5 to 9 %
Fibre content                                    : 0.5 to 2 % by volume of                                                              mix


Advantages of FRC :

  1. Reduction in shrinkage and cracking.
  2. Improvement in bond strength.
  3. Enhancement of fatigue strength and endurance limit.
  4. Better toughness.
  5. Lower permeability of concrete.

Application of FRC :
  1. The most extensive use of FRC has been for pavements, floors and overlays to take advantage of high strength, reduction in cracking and expansion.
  2. It is used for overhead water tanks and underground sumps because they need to be watertight. Fibre contribute to control plastic and shrinkage cracks, resulting in the watertightness.
  3. The FRC can also be used for the fabrication of precast products like pipes, boats, beams, wall panels, staircase steps, roof panels, manhole covers etc.
  4. FRC has been used as a wearing surface to existing bridges and culverts in areas especially troubled by degredation caused through abrasion by studded tyres.
  5. FRC is cohesive and easy to work provided fibres which are thoroughly mixed in the cement matrix. It is an ideal material for repair and rehabilitation work.

Comments

Popular Posts

TYPES OF CRACKS IN R.C.C COLUMNS

CHECKLIST FOR TERRACE WATERPROOFING (BRICK BAT COBA)

CLASSIFICATION OF STAIR AND THEIR USES