A brief description on Light weight Construction Materials, different types of fibre and application fo fibre reinforced concrete.

1. LIGHT WEIGHT CONSTRUCTION MATERIALS
The Northcap University, Gurgaon1
UNIT-1
LECTURE - 5
Brig. S.K. Sharma (Retd.)
Pro Vice Chancellor and Professor
Department of Civil Engineering,
The Northcap University, Gurgaon

2. INDEX
DIFFERENT TYPES OF FIBRES
• STEEL-FIBRE
• POLYPROPYLENE FIBRE
• ASBESTOS FIBRE
• GLASS FIBRE
• CARBON FIBRE
• APPLICATIONS OF FIBRE REINFORCED CONCRETE
(FRC)
• BATCHING, MIXING, PLACING, COMPACTION AND
FINISHING OF FRC
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3. DIFFERENT TYPES OF FIBRES
Although every type of fibre has been tried out in cement
and concrete, not all of them can be effectively and
economically used. Each type of fibre has its characteristic
properties and limitations. Some of the fibres that could be
used are steel fibres, polypropylene, nylons, asbestos,
coir, glass and carbon. They are discussed in succeeding
text.
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4. STEEL-FIBRE: A number of steel-fibre types are
available as reinforcement. Round steel fibres the
commonly used type, and are produced by cutting round
wires into short lengths. The typical diameters lie in the
range of 0.25 to 0.75 mm. Steel fibre having a rectangular
cross section are produced by slitting the sheets about 0.25
mm thick. For improving the mechanical bond between the
fibre and matrix, indented, crimped, machined and hook-
ended fibers are normally produced.
POLYPROPYLENE FIBRE: Polypropylene and nylon
fibres are found to be suitable to increase the impact
strength. They possess very high tensile strength, but their
low modulus of elasticity and higher elongation do not
contribute to the flexural strength.
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5. ASBESTOS FIBRE: Asbestos is a mineral fibre and has
proved to be the most successful of all fibres as it can be
mixed with Portland cement paste. For unimportant fibre
concrete, organic fibres like coir, jute, canes plits are also
used.
GLASS FIBRE: Glass fibre is a recent introduction in
making fiber concrete. It has very high tensile strength of
1020 to 4080 N/mm2. Glass fibre which is originally used in
conjunction with cement was found to be effected by
alkaline condition of cement. Therefore, alkali-resistant
glass fibre by trade name “CEM-FIL” has been developed
and used. The alkali resistant fibre reinforced concrete
shows considerable improvement in durability when
compared to the conventional glass fibre.
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6. CARBON FIBRE: Carbon fibre perhaps posses very high
tensile strength, say from 2110 to 2815 N/mm2. It has been
reported that cement composite made with carbon fibre as
reinforcement will have high modulus of elasticity and
flexural strength. Limited studies have shown good
durability. The use of carbon fibres for structures like
cladding, panels and shells have a promising future.
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7. APPLICATIONS OF FRC
Fibre reinforced concrete is increasingly used on account
of the advantages of increased static and dynamic tensile
strength, energy absorbing characteristics and better
fatigue strength. The uniform dispersion of fibres
throughout the concrete provides isotropic properties not
common to conventionally reinforced concrete.
Uses: Fiber reinforced concrete has been tried on
overlays of air-field, road pavements, industrial
floorings, bridge decks, canal lining, explosive
resistant structures, refractory linings etc. The fibre
reinforced concrete can also be used for the fabrication of
precast products like pipes, beams, stair case steps,
wall panels, roof panels, manhole covers etc.
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8. However, the main applications of SFRC are in highway
and airfield pavements, hydraulic structures, tunnel linings,
industrial floors, bridge decks, repair works etc. specifically,
SFRC can be applied in the following areas:-
HIGHWAY AND AIRFIELD PAVEMENTS: the steel-fibre
concrete can be used in new pavement constructions or in
the repair of existing pavements by the use of bonded or
unbonded overlays to the slab beneath. The major
advantages are: a higher flexural strength results in the
reduction of required pavement thickness; the resistance to
impact and repeated loading is increased.
SFRC gives a smooth riding surface without irregular
depressions. The overlays for the rehabilitation of runways,
taxiways, bridge decks, and the strengthening of existing
runways and taxiways to comply with the rigid requirements
of the newer generation of heavy-duty jet aircrafts, are
extensively used. SFRC can be advantageously used in
the repair of damaged patches in existing runways, and
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9. HYDRAULIC STRUCTURES: The major advantage of
using steel-fiber concrete in hydraulic structures is its
resistance to cavitation or erosion damage by high velocity
water flow. The steel-fiber concrete has been successfully
used in the repair of spilling basin at Tarbela Dam in
Paksitan. The fibre concrete contained about one per cent
(by volume) of 25x0.25x0.55 mm slit steel fibres.
FIBRE SHOTCRETE: Fibre Shotcrete fibre shotcrete has
been used in rock slope stabilization, tunnel lining and
bridge repair. A thin coating of plain shotcrete applied
monolithically on top of the fiber shotcrete, may be used to
prevent surface staining due to rusting.
PRECAST APPLICATIONS: As brought out earlier they
include manhole covers, and concrete pipes. Improved
flexural and impact strengths may allow the use of steel-
fibre concrete components in rough handling situations.
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10. CURRENT DEVELOPMENT IN FRC
The following are the three new developments taking place
in FRC:-
 High fibre volume micro-fibre systems.
 Slurry infiltrated fibre concrete (SIFCON).
 Compact reinforced composites.
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11. BATCHING, MIXING, PLACING,
COMPACTION AND FINISHING OF FRC
Method : The fibres are usually added to the aggregates
before the introduction of cement and water into the mixer. For
laboratory testing, fibres can be added in small amounts to the
rotating drum charged with cement, aggregate and water. For
large batches, the fibres are blown into the previously charged
rotating drum.
A fibre mix generally requires more time and vibration to move
the mix and to compact it into the forms. Surface vibration of
forms and exposed surface is preferable to prevent
segregation.
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12. Some of the precautions taken while mixing placing and
compacting fibre-reinforced concrete are as follows:-
 While mixing small quantities of fibre reinforced concrete
by hand, there is a possibility of steel fibres hitting the
eyes of the worker or pricking the hand. To avoid these
hazards, the hands should be protected by gloves and
the eye with safety glasses.
 A pan mixer of the counter-flow type should be used for
mixing fibre reinforced concrete.
 For uniform distribution of steel fibres, a dispenser should
be used. While dispensing the fibres into concrete, the
rate at which the fibres are fed to the mixer shouldbe
synchronized with rate of mixing.
_______________x________________Video1: Concrete Bridge Repair with Fibre Reinforced Polymers
04:32 min
Video 2: Wire and Steel Fibre Reinforced Concrete Floors
08:41 min
Video 3: EPC, Synthetic Fibre Reinforced Segmental Tunnel
01:07 min
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13. General interest construction videos (May See)
Video1: TMB/ Tunneling 13:42 min
Video2: 30 Story Building Built in 15 days
02:31 min
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14. The Northcap University, Gurgaon14
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