Fiber reinforced concrete contains short discrete fibers that are uniformly distributed and randomly oriented. The addition of fibers enhances the concrete's toughness, ductility, and energy absorption. Steel fiber reinforced concrete (SFRC) in particular improves flexural strength, impact resistance, shear strength, and abrasion resistance compared to plain concrete. While SFRC does not significantly increase compressive or tensile strength, it provides residual load-bearing capacity after cracking and improves toughness. Common uses of SFRC include thin sheets, roof tiles, pipes, prefabricated elements, shotcrete, slabs, and structures requiring impact resistance.

1. FIBER REINFORCED
CONCRETE

2. INTRODUCTION
 Concrete is a quite brittle material with very little
tensile strength, so to use concrete in structures it
is necessary to improve its tensile qualities
 The traditional way of doing this is adding steel
bars with high yield strength to take the tensile
forces in the structure element
 Another way to improve the tensile strength of
concrete is to add reinforcement fibers

3. INRODUCTION
 Fiber reinforced concrete (FRC) is a concrete
containing a fibers
 FRC contains short discrete fibers that are
uniformly distributed and randomly oriented
 Addition of fibers will enhance the concrete’s
toughness, ductility, energy absorption under
impact and increase the post crack capacity
along with increase in tensile and flexural
strength of concrete when added in sufficient
quantity

4.  Fibers of various shapes and sizes produced from
steel, plastic, glass, and natural materials are
being used
 However, for most structural and non-structural
purposes, steel fiber is the most commonly used
 The fibers can act in different ways, but mainly in
two mechanisms:
 Can stop micro cracks from developing into larger
cracks either from external loads or from drying
shrinkage
 Secondly, after cracking the fibres that span the
cracks that have formed will give the concrete a
residual load bearing capacity
INRODUCTION

5. FIBER TYPES
 Metallic
 Steel fibers
 Glass Fibers
 Synthetic fibers
 Carbon, Nylon, Polyester, Polyethylene, Polypropylene etc.
 Natural
 Organic
 Coconut, bamboo, Jute, Cellulose (Wood)
 Inorganic
 Asbestose

6. GENERAL REQUIREMENTS FOR FIBERS
 Fibers must have a tensile strength much higher
than that of matrix ( two or three times)
 Bond between the fibers and matrix must have a
strength of at least as same as that of matrix
 Modulus of elasticity of fibers must be at least
three times larger than that of matrix
 Fibres must have a ductility high enough to
prevent fracturing of the fibres due to abrasion or
bending

7.  The Poisson ratio and the coefficient of thermal
expansion of the fibres should be about the same
order as that of the matrix
 If Poisson ratio of the fibres is much larger than that of
the matrix, it may lead to debonding due to lateral
contraction of the fibres
 Fibres must be durable and able to withstand the
alkaline environment in the concrete matrix
GENERAL REQUIREMENTS FOR FIBERS

8. STEEL FIBER REINFORCED
CONCRETE (SFRC)

9. STEEL FIBERS
 Steel fibers are the most commonly used man-
made metallic fibers
 Steel fibers are added to the concrete matrix to
provide increased flexural and tensile strength,
toughness, and impact resistance
 The two physical properties that are used to define
steel fibers are the length to diameter ratio
(aspect ratio) and the geometry of the fiber
(straight, hooked, enlarged-end, etc.)

10. TYPICAL GEOMETRIES OF FIBERS

11. CROSS SECTIONAL GEOMETRIES OF
FIBERS

12.  Steel fibers with hook ends are performing well
due to better anchorage provided
Hooked-ended steel fibers
glued together before
mixing
Separation of fibers occurs
during mixing to ensure
uniform distribution

13. REINFORCEMENT MECHANISMS IN FIBER
REINFORCED (FRC)
 In the hardened state, when fibers are properly
bonded, they interact with the matrix at the level of
micro-cracks and effectively bridge these cracks
thereby providing stress transfer media that
delays their unstable growth
 If the fiber volume fraction is sufficiently high, this
may result in an increase in the tensile strength of
the matrix

14. MIX DESIGN
 To produce a mix of adequate workability, ease of
placing and efficient use of fibers as crack
arresters
 Normal concrete mix proportioning can be
adopted and later workability can be adjusted
when adding steel fibers

15. ACI GUIDE LINES FOR MIX DESIGN
OF SFRC
 Coarse aggregate should be limited to 55% of total
aggregate
 w/c ratio should be kept below 0.55 (0.35 is
recommended)
 Minimum cement content of 320 kg/m3 should be
used
 Reasonable sand content of 750 to 850 kg/m3 is
recommended
 The workability could be improved by increasing
cement paste which is possible by addition of fly
ash or slag to replace cement
 Maximum aggregate size is to be 19 mm

16. MIXING SEQUENCES OF SFRC (ACI
COMMITTEE)
Packed steel fibers
Mechanically
By dumping through a
screen opening into a
hopper which sprinkle it.
Then into conveyor belt
Manually
(or small
jobs)
Five possible sequences
Blend fibers +
aggregates +
cement at
conveyor belt
and convey to
moving mixer
and add
water and
additives
thereafter
Blend fibers +
aggregates
prior to
charge mixer
and then use
normal
mixing
procedure
Blend fibers
and
aggregates in
the mixer,
then add this
at the mixing
speed, lastly
add cement ,
water and
additives
Add fibers to
previously
charged
aggregates
and some
water, then
add cement
and the
remaining
water
Add the fibers
as the last
step of mixing

17. MECHANICAL PROPERTIES
 Toughness
 Toughness is defined as the total energy absorbed prior
to separation of the specimen
 Steel fibers significantly improve the concrete toughness
 Toughness can be calculated as the area under the load-
deflection curve plotted for a beam specimen in flexure
test
 Toughness can be evaluated by testing a simply supported
beam under third point loading
 Toughness indices are calculated by dividing the area
under the load-deflection curve up to a specified deflection
by the area up to the deflection at first crack

18. LOAD-DEFLECTION GRAPH

19.  Flexural strength
 Low flexural strength of plain concrete can be
improved by steel fibers
 Addition of short, randomly-oriented steel fibers
increases the flexural strength of concrete by
about 1.5 to 3 times depending upon the type
and content of steel fibers
 Flexural strength of SFRC is more complicated
than that of plain concrete
After crack toughness imparted by steel
fibers in SFRC

20. LOAD-DEFLECTION GRAPH

21.  Considerable improvement in the post-cracking
behavior of concretes containing fibers
 Although in the fiber-reinforced concrete the
ultimate tensile strength do not increase
appreciably, the tensile strains at rupture do
 Plain concrete fails suddenly once the deflection
corresponding to the ultimate flexural strength is
exceeded on the other
 FRC continue to sustain considerable loads
even at deflections considerably in excess of the
fracture deflection of the plain concrete

22. Steel fibers can sustain stress after cracking at
strains beyond the normal for failure of plain
concrete

23.  First crack flexural strength
 Stress at point at which the load-deflection curve first
becomes non-linear
 Ultimate flexural strength
 Stress at the point of maximum load
 Equivalent flexural strength
 Stress capacity derived at a point of specified load at
specific deflection

24.  Due to the post cracking behavior of SFRC unlike
plain concrete,
 Total flexural strength (design flexural strength) is equal
to the sum of the flexural strength up to the point after
which the elastic zone of the material is exceeded and the
strength that resulted from the plastic phase

25.  Factors influencing flexural strength of SFRC
 Degree of consolidation of mix which is a
function of w/c ratio, consolidation technique and
type and content of fibers
 Uniformity of fiber distribution which is mainly
influenced by the workability and mixing
procedure used
 The surface conditions of steel fibers which
relates to the bond stress generated between the
steel fibers and concrete

26.  Impact strength
 Pavements in many cases are subjected to
impact loads
 Addition of steel fibers improves the impact
strength of concrete
 Tests carried out by ACI committee showed that
SFRC increased the impact resistance by 3 to 4
times as that of plain concrete

27. COMPRESSIVE STRENGTH
Stress-strain relationship of SFRC compression

28.  Compressive strength
 Inclusion of steel fibers increases the
compressive strength relative to the fibre content
 Experimental works conducted in India (on straight
steel fibers with L/D =46/0.91 mm and fibre content
between 0 to 3 % by volume) showed significant
improvement in compressive strength (40% increase
with 3% fiber content)
 Test results showed a linear relation connecting
fiber content and compressive strength

29. )
1
( KP
F
F c
f 

Ff- Compressive strength of SFRC
Fc- Compressive strength of parent concrete
K- Empirical constant (0.123)
P- Percentage of steel fiber (by volume)

30.  Tensile strength
 Two types of tension tests- direct tension and
split tensile test
 Dog-bone shaped specimens are subjected to
direct tension tests
 Split tensile test on cylindrical specimens are
more common
 Results showed that specimens with fibre
content less than 2% do not improve the split
tensile strength
 Increase in fibre content in composite found to
increase the tensile strength

32.  Shear strength
 Steel fibers are found to increase the shear
strength of concrete significantly
 Inclusion of 1 % by volume of hook-ended steel
fibers could increase the shear strength of SFRC
by 144 to 210% relative to the plain concrete
depending upon the aspect ratio of steel fibers
 Mode of failure also changed due to extra shear
capacity (ductile failure was experienced
instead of sudden diagonal failure)
 Shear capacity is important for pavements

33.  Modulus of elasticity
 Inclusion of steel fibers influences the modulus
of elasticity marginally
 Uni-axial tensile stress-strain measurements
on plain and SFRC specimens (100x100x50
mm) showed an increase of 7.5 % with a dosage
of 2.7% by volume of straight steel fibers
 Recent studies also showed that 0.76% by
weight of hook-ended and crimped steel fibre
increases the E-value up to 2.8%

34. PHYSICAL PROPERTIES
 Shrinkage
 Shrinkage is the volume change exhibited by
concrete bodies due to the loss of water
 Two phases of shrinkage exist- plastic
shrinkage and drying shrinkage
 Steel fibers reduce the plastic shrinkage crack
widths relative to that of plain concrete (as high
as 20%)
 Conflicting evidences regarding the effectiveness
of steel fibers in reducing drying shrinkage

35.  Creep
 Long term deformation that a material exhibits
under the application of a sustained load
 Creep studies
 In compression on prismatic specimens (150x150x500 mm)
of SFRC with melt extract and hooked fibers of content
between 0 and 3% shows a significant influence on creep (15-
24% reduction)
 Flexural creep test on SFRC (75kg/m3 enlarged end steel
fibers) showed that flexural creep is considerably less for
SFRC as compared to the plain concrete
 Steel fibers have a negligible effect when low
fiber content is added and a significant
improvement is gained with larger amount of
steel fibers

36.  Durability
 Porosity and permeability are two main factors
 Alkali-acid reaction, leaching characteristics, resistance to
chloride or sulphate attack, reinforcement corrosion and
freezing and thawing characteristics
 Initially, SFRC mixes have high porosity and
permeability due to high w/c used for improving
workability
 Recently, reductions in w/c ratio are possible,
which results in low porosity and permeability
 Tests indicated that permeability of SFRC is same as
that of plain concrete and hence, apart from corrosion of
steel fibers, durability of both are same

37.  Corrosion of steel fibers
 In severe exposure condition, corrosion of
steel fibers is more aggravated than that of steel
bars
 Whereas, unlike steel bars, only limited
expansive force developed due to steel fibers
which leads to less paste disruption and
eventually minimum break down and
weathering rates
 Studies showed that stainless steel fibers can
perform well even under aggressive type of
exposure conditions

38.  Aberration and skid resistance
 Knowledge of aberration and wear resistance
of concrete is important for pavements
 Tests carried to compare the abrasion resistance
of plain concrete specimens (25 Mpa) and SFRC
specimens (75 kg/m3 enlarged end type of steel
fibers) showed an LA value of 50% more than
that of plain concrete
 The skid resistance of SFRC is found to be
same as that of plain concrete at early stages
prior to deterioration of surface and in later
stages, when aberration and wear had
happened, SFRC showed 15% higher skid
resistance compared to plain concrete

39. GENERAL
 Hook-ended fibers were found to be performing
better
 Any of the plain concrete mix proportioning
method for plain concrete can be adopted for SFRC
and thereafter the mix can be adjusted for added
fibers
 The normal transporting, placing and curing
methods for plain concrete can be used for SFRC

40. GENERAL
 Steel fibers have an effect ranging from little to
significant on mechanical properties
 Impact strength and shear strength are significantly
improved
 While compressive strength, E and poisons ratio are
slightly improved
 Flexural strength at first crack and maximum load are
slightly improved and equivalent strength (after crack)
improved significantly due to the imparted toughness

41. GENERAL
 Physical properties are also altered due to the addition
of steel fibers
 Significant effect on plastic shrinkage while little
effect found on drying shrinkage
 Creep is significantly influenced when using high
dosage of steel fibers while little effect is found with
less dosage of steel fibers
 Aberration and skid resistance improved
significantly due to addition of steel fibers
 Durability is not influenced by the steel fibers

42. APPLICATION AREAS
 Thin sheets
 Roof tiles
 Pipes
 Prefabricated shapes
 Panels
 Shotcrete
 Slabs
 Precast elements
 Impact resisting structures