FRC

1. FIBRE REINFORCED
CONCRETE
UNIT-IV

2. HISTORY
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The use of fibers goes back at least 3500 years, when straw was used to
reinforce sun-baked bricks in Mesopotamia.
Horsehair was used in mortar and straw in mud bricks.
Abestos fibers were used in concrete in the early 1900.
In the 1950s, the concept of composite materials came into picture.
Steel , Glass and synthetic fibers have been used to improve the
properties of concrete for the past 30 or 40 years.
Research into new fiber-reinforced concretes continues even today.

3. FRC - Historical Perspective
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BC horse Hair
1900 asbestos fibers, Hatscheck process
1920 Griffith, theoretical vs. apparent strength
1950 Composite materials
1960 FRC
1970 New initiative for asbestos cement replacement
1970 SFRC, GFRC, PPFRC, Shotcrete
1990 micromechanics, hybrid systems, wood based fiber systems manufacturing
techniques, secondary reinforcement, HSC ductility issues, shrinkage crack control.
2000+ Structural applications, Code integration, New products.

4. Introduction
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Concrete containing cement, water , aggregate, and discontinuous,
uniformly dispersed or discrete fibers is called fiber reinforced concrete.
It is a composite obtained by adding a single type or a blend of fibers to
the conventional concrete mix.
Fibers can be in form of steel fibers, glass fibers, natural fibers ,
synthetic fibers, etc.

5. Why Fibres are used?
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Main role of fibers is to bridge the cracks that develop in concrete and
increase the ductility of concrete elements.
There is considerable improvement in the post-cracking behavior of
concrete containing fibers due to both plastic shrinkage and drying
shrinkage.
They also reduce the permeability of concrete and thus reduce bleeding of
water.
Some types of fibres produce greater abrasion and shatter resistance in
concrete.
Imparts more resistance to Impact load.

6. Toughening mechanism
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Toughness is ability of a material to absorb energy and plastically deform
without fracturing.
It can also be defined as resistance to fracture of a material when
stressed.

8. How does FRC work?
• https://www.youtube.com/watch?v=XYiRY5o99yQ

9. Necessity
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The use of concrete as a structural material is limited to certain extent
by deficiencies like brittleness, poor tensile strength and poor resistance
to impact strength, fatigue, low ductility and low durability.
It is also very much limited to receive dynamic stresses caused due to
explosions.
The brittleness is compensated in structural member by the introduction
of reinforcement (or) pre-stressing steel in the tensile zone. However it
does not improve the basic property of concrete. It is merely a method of
using two materials for the required performance.
The main problem of low tensile strength and the requirements of high
strength still remain and it is to be improved by different types of
reinforcing materials.

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Further concrete is also deficient in ductility, resistance to fatigue and impact. The importance
of rendering requisite quantities in concrete is increasing with its varied and challenging
applications in pre-cast and pre-fabricated building elements. The development in the requisite
characteristics of concrete will solve the testing problems of structural engineers by the addition
of fibers and admixtures.
The role of fibers are essentially to arrest any advancing cracks by applying punching forces at
the rack tips, thus delaying their propagation across the matrix. The ultimate cracking strain of
the composite is thus increased to many times greater than that of unreinforced matrix.
Admixtures like fly ash, silica fume, granulated blast furnace slag and metakaolin can be used for
such purposes. However addition of fibers and mineral admixtures posses certain problems
regarding mixing, as fibers tends to form balls and workability tends to decrease during mixing

11. Types of Fibres:
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Steel Fibres
Glass Fibres

12. • Natural Fibres (Coir)
Artificial Fibre (Nylon)

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Carbon fibres
Cellulose fibres

14. Aspect Ratio:- Aspect Ratio is the ratio of length
of the Fibre to the diameter of its cross - section.

15. Steel fibers
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Aspect ratios of 30 to 250.
Diameters vary from 0.25 mm to 0.75 mm.
High structural strength.
Reduced crack widths and control the crack widths tightly, thus
improving durability.
Improve impact and abrasion resistance.
Used in precast and structural applications, highway and airport
pavements, refractory and canal linings, industrial flooring, bridge decks,
etc.

16. Glass Fibres
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High tensile strength, 1020 to 4080 N/mm2
Generally, fibers of length 25mm are used.  Improvement in impact
strength.
Increased flexural strength, ductility and resistance to thermal shock.
Used in formwork, swimming pools, ducts and roofs, sewer lining etc.

17. Synthetic fibers
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Man- made fibers from petrochemical and textile industries.
Cheap, abundantly available.
High chemical resistance.  High melting point.  Low modulus of
elasticity.
It’s types are acrylic, aramid, carbon, nylon, polyester, polyethylene,
polypropylene, etc.
Applications in cladding panels and shotcrete.

18. Natural fibers
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Obtained at low cost and low level of energy using local manpower and
technology.
Jute, coir and bamboo are examples.
They may undergo organic decay.
Low modulus of elasticity, high impact strength.

19. ASBESTOS FIBER REINFORCED CONCRETE
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Mineral fiber, most successful of all as it can be mixed with portland
cement.
Tensile strength of asbestos varies between 560 to 980 N/mm2.
Asbestos cement paste has considerably higher flexural strength than
Portland cement paste.
For unimportant concrete work, organic fibers like coir, jute and
canesplits are also used.

20. CARBON FIBER REINFORCED CONCRETE
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Posses very high tensile strength 2110 to 2815 N/mm2 and Young’s
modulus.
Cement composite consisting of carbon fibers show very high modulus of
elasticity and flexuralstrength.

21. Comparision

22. Mechanical Properties of FRC
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Compressive Strength:
The presence of fibers may alter the failure mode of cylinders, but the fiber effect will
be minor on the improvement of compressive strength values (0 to 15 percent).
Modulus of Elasticity:
Modulus of elasticity of FRC increases slightly with an increase in the fibers content.
It was found that for each 1 percent increase in fiber content by volume, there is an
increase of 3 percent in the modulus of elasticity.
Flexure
The flexural strength was reported to be increased by 2.5 times using 4 percent fibers.
Splitting Tensile Strength:
The presence of 3 percent fiber by volume was reported to increase the splitting
tensile strength of mortar about 2.5 times that of the unreinforced one.

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Toughness:
For FRC, toughness is about 10 to 40 times that of plain concrete.
Fatigue Strength:
The addition of fibers increases fatigue strength of about 90 percent.
Impact Resistance:
The impact strength for fibrous concrete is generally 5 to 10 times that of
plain concrete depending on the volume of fiber.

24. Structural behaviour of FRC
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Flexure: The use of fibers in reinforced concrete flexure members
increases ductility, tensile strength, moment capacity, and stiffness. The
fibers improve crack control and preserve post cracking structural
integrity of members.
Torsion: The use of fibers eliminate the sudden failure characteristic of
plain concrete beams. It increases stiffness, torsional strength, ductility,
rotational capacity, and the number of cracks with less crack width.
High Strength Concrete: Fibers increases the ductility of high strength
concrete. Fiber addition will help in controlling cracks and deflections.

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Shear: Addition of fibers increases shear capacity of reinforced concrete
beams up to 100 percent. Addition of randomly distributed fibers
increases shear-friction strength and ultimate strength.
Column: The increase of fiber content slightly increases the ductility of
axially loaded specimen. The use of fibers helps in reducing the explosive
type failure for columns.
Cracking and Deflection: Tests have shown that fiber reinforcement
effectively controls cracking and deflection, in addition to strength
improvement. In conventionally reinforced concrete beams, fiber addition
increases stiffness, and reduces deflection.

26. Factors affecting the Properties of FRC
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Volume of fibers
Aspect ratio of fiber
Orientation of fiber
Relative fiber matrix stiffness

27. Volume of fiber
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Low volume fraction(less than 1%):
Used in slab and pavement that have large exposed surface leading to high
shrinkage cracking.
Moderate volume fraction(between 1 and 2 percent):
Used in Construction method such as Shortcrete & in Structures which
requires improved capacity against delamination, spalling & fatigue.
High volume fraction(greater than 2%):
Used in making high performance fiber reinforced composites.

29. Aspect Ratio of fiber
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It is defined as ratio of length of fiber to it’s diameter (L/d).
Increase in the aspect ratio upto 75, there is increase in relative
strength and toughness.
Beyond 75 of aspect ratio, there is decrease in aspect ratio and
toughness.

30. Orientation of fibers
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Aligned in the direction of load
Aligned in the direction perpendicular to load
Randomly distribution of fibers
It is observed that fibers aligned parallel to applied load offered more tensile
strength and toughness than randomly distributed or perpendicular fibers.

31. Load
Direction

32. Relative fiber matrix
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Modulus of elasticity of matrix must be less than of fibers for efficient
stress transfer.
Low modulus of fibers imparts more energy absorption while high modulus
fibers imparts strength and stiffness.
Low modulus fibers e.g. Nylons and Polypropylene fibers.
High modulus fibers e.g. Steel, Glass, and Carbon fibers.

33. Advantages of FRC
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High modulus of elasticity for effective long-term reinforcement, even in the hardened
concrete.
Does not rust nor corrode and requires no minimum cover.
Ideal aspect ratio (i.e. relationship between Fiber diameter and length) which makes them
excellent for early-age performance.
Easily placed, Cast, Sprayed and less labour intensive than placing rebar.
Greater retained toughness in conventional concrete mixes.
Higher flexural strength, depending on addition rate.
Can be made into thin sheets or irregular shapes.
FRC possesses enough plasticity to go under large deformation once the peak load has been
reached.

34. Disadvantages of FRC
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Greater reduction of workability.
High cost of materials.
Generally fibers do not increase the flexural strength of concrete, and so
cannot replace moment resisting or structural steel reinforcement.

35. Applications of FRC
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Runway, Aircraft Parking, and Pavements
For the same wheel load FRC slabs could be about one half the thickness of plain concrete slab. FRC pavements
offers good resistance even in severe and mild environments. It can be used in runways, taxiways, aprons,
seawalls, dock areas, parking and loading ramps.
Tunnel Lining and Slope Stabilization
Steel fiber reinforced concrete are being used to line underground openings and rock slope stabilization. It
eliminates the need for mesh reinforcement and scaffolding.
Dams and Hydraulic Structure
FRC is being used for the construction and repair of dams and other hydraulic structures to provide
resistance to cavitation and severe erosion caused by the impact of large debris.
Thin Shell, Walls, Pipes, and Manholes:
Fibrous concrete permits the use of thinner flat and curved structural elements. Steel fibrous shortcrete is
used in the construction of hemispherical domes.

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Agriculture
It is used in animal storage structures, walls, silos, paving, etc.
Precast Concrete and Products
It is used in architectural panels, tilt-up construction, walls, fencing, septic tanks, grease trap
structures, vaults and sculptures.
Commercial
It is used for exterior and interior floors, slabs and parking areas, roadways, etc.
Warehouse / Industrial
It is used in light to heavy duty loaded floors.
Residential
It includes application in driveways, sidewalks, pool construction, basements, colored concrete,
foundations, drainage, etc.

37. Difference between FRC and RCC

38. Application of FRC in India & Abroad
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More than 400 tones of Steel Fibers have been used in the construction of
a road overlay for a project at Mathura (UP).
A 3.9 km long district heating tunnel, caring heating pipelines from a
power plant on the island Amager into the center of Copenhagen, is lined
with SFC segments without any conventional steel bar reinforcement.
Steel fibers are used without rebars to carry flexural loads at a parking
garage at Heathrow Airport. It is a structure with 10 cm thick slab.
Precast fiber reinforced concrete manhole covers and frames are being
widely used in India.

39. MIXTURE COMPOSITIONS AND PLACING
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Mixing of FRC can be accomplished by many methods. The mix should have
a uniform dispersion of the fibers in order to prevent segregation or
balling of the fibers during mixing.
Most balling occurs during the fiber addition process. Increase of aspect
ratio, volume percentage of fiber, and size and quantity of coarse
aggregate will intensify the balling tendencies and decrease the
workability.
To coat the large surface area of the fibers with paste, experience
indicated that a water cement ratio between 0.4 and 0.6, and minimum
cement content of 400 kg/m3 are required.

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Compared to conventional concrete, fiber reinforced concrete mixes are generally characterized
by higher cement factor, higher fine aggregate content and smaller size coarse aggregate.
A fiber mix generally requires more vibration to consolidate the mix. External vibration is
preferable to prevent fiber segregation.
Metal trowels, tube floats, and rotating power floats can be used to finish the surface.
Mechanical Properties of FRC Addition of fibers to concrete influences its mechanical properties
which significantly depend on the type and percentage offiber.
High aspect ratio were found to have improved effectiveness. It was shown that for the same
length and diameter, crimped-end fibers can achieve the same properties as straight fibers using
40 percent less fibers[S].
In determining the mechanical properties of FRC, the same equipment and procedure as used for
conventional concrete can also be used.

41. CASTING OF SPECIMENS
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The materials were weighed accurately using a digital the mixture
machine and mixed thoroughly for three minutes.
Steel fibres were mechanically sprinkled inside the mixing machine after
thorough mixing of the ingredients of concrete.
For preparing the specimen for compressive, tensile, and flexure strength
permanent steel moulds were used

42. Steel moulds
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Wooden moulds were fabricated to cast the test specimens for panel
testing. Six wooden moulds were fabricated to facilitate simultaneous
casting of test panels.
Two different thicknesses were adopted for the panels; the panel sizes
adopted were 500×500×50mm and500×500×100mm.
Before mixing the concrete the moulds were kept ready. The sides and the
bottom of the all the mould were properly oiled for easy demoulding.
The panel was kept at an angle of 45° and then the concrete was splashed
over the panel from a distance of one meter. Then the top surface was
given a smooth finish.

44. SFRC using hooked fibre

45. CURING OF SPECIMENS
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The test specimens were stored in place free from vibration and kept at a
temperature of 27˚±2˚C for 24 hours ± ½ hour from the time of addition
of water to the dry ingredients.
After this period, the specimen were marked and removed from the
moulds and immediately submerged in clean fresh water and kept there
until taken out prior to test.
The specimens were allowed to become dry before testing.
The panels were cured by dry curing method, i.e. moist gunny bags were
covered over the panels.

46. CUBE COMPRESSION TEST
• M25 cube made ofsteelfiber reinforced concrete is used in compression
test