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

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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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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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.4 The Northcap University, Gurgaon

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.5 The Northcap University, Gurgaon

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.

6 The Northcap University, Gurgaon

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.

7 The Northcap University, Gurgaon

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

highway pavement slab.

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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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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.

10 The Northcap University, Gurgaon

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.

11 The Northcap University, Gurgaon

Some of the precautions taken while mixing placing andcompacting fibre-reinforced concrete are as follows:-

While mixing small quantities of fibre reinforced concreteby hand, there is a possibility of steel fibres hitting theeyes of the worker or pricking the hand. To avoid thesehazards, the hands should be protected by gloves andthe eye with safety glasses.

A pan mixer of the counter-flow type should be used formixing fibre reinforced concrete.

For uniform distribution of steel fibres, a dispenser shouldbe used. While dispensing the fibres into concrete, therate at which the fibres are fed to the mixer shouldbesynchronized 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 min12 The Northcap University, Gurgaon

General interest construction videos (May See)

Video1: TMB/ Tunneling 13:42 min

Video2: 30 Story Building Built in 15 days

02:31 min

13 The Northcap University, Gurgaon

The Northcap University, Gurgaon14

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