Fibre reinforced concrete is a type of concrete containing fibres that increase its structural integrity. It is made of Portland cement reinforced with randomly distributed fibres. The fibres are used to overcome concrete's weakness in tension and brittleness. Common fibre types include steel, glass, carbon and polypropylene. Factors like fibre volume, aspect ratio, orientation and relative stiffness affect FRC properties. FRC exhibits improved tensile cracking behaviour and increased toughness, energy absorption and fracture resistance compared to conventional concrete.

1. “FIBRE REINFORCED CONCRETE”
by
MAYAKUNTLA PRASANNAKUMAR
VENKATESHA A

2. What is Fibre?
• Fibre is a small piece of reinforcing material
which increases structural integrity.
Why Fibre ?
Concrete:
• Weak in tension
• Brittle

3. What is fibre reinforced concrete
• FRC is a Portland cement reinforced with
more or less randomly distributed fibres .

4. Types of fibres
1. Steel fibre:

5. 2. Glass fibre:

6. • Asbestos fibre:

7. • Polypropylene fibre:

8. • Carbon fibre:

9. • Aramid fibre:

10. Source: Santa Kumar

11. Factors effecting the properties of FRC
1. Volume of fibres:
• low volume fraction (less then 1%):
Used in slabs and pavement that have large
exposed surface leading to shrinkage cracking
• Moderate volume fraction(between 1 and 2%):
Used in construction method such as shotcrete
• High volume fraction(greater then 2%):
Used in making high performance FRC

12. 2. Aspect ratio of fibre:
= fibre length/fibre diameter
Source: M.S Shetty

13. 3. Orientation of fibres:
• Aligned in the direction of load
• Aligned in the direction perpendicular to load
• Randomly distribution of fibers

14. 4. Relative fibre matrix:
• Fibre should be significantly stiffer than matrix
• Low modulus of fibres imparts more energy
absorption while high modulus of fibres imparts
strength and stiffness.
• Low modulus fibres e.g. nylon, polypropylene
• High modulus of elasticity e.g. steel, glass and
carbon fibres.

15. 5. Workability and compaction of concrete:
• Usage of steel fibres , higher aspect ratio and
non-uniform distribution of fibres will reduce
workability
• Prolonged external vibration fails to compact the
concrete
• These properties can be improved by increasing
water/cement ratio or by using water reducing
admixtures

16. 6.Size of coarse aggregate:
• Restricted to 10mm
• Friction between fibres and between fibres and
aggregates controls orientation and distribution.
7. Mixing:
• Mixing of FRC needs careful precautions to
avoid balling effect and segregation
• Increase in aspect ratio, volume percentage and
size of coarse aggregate will increase the
difficulties.

17. Developments in FRC
1.High fibre volume micro fibre system:
• length – 3mm
• Diameter – 25 microns
• Specific surface > 200 cm2/gram
• Mixing of FRC needs careful conditions to avoid balling
effect
• Sand particles of size not exceeding 1mm
• Low sand to cement ratio.
• Requires large dosage of super plasticizers
• Omni mixer is used for mixing

18. Omni mixer used in
high volume FRC

19. 2. Slurry infiltrated fibre concrete(SIFCON):
• Invented by lankard in 1979
• Pre-placing the dry fibres and cement slurry
is infiltrated.
• Volume of fibres can be increased to 20%
• increase in flexural capacity and toughness.
• used in blast resistant structures
• better suited for three dimensional application
such as zones of reinforcing bars anchorages

20. 3. Slurry infiltrated mat concrete (SIMCON):
• Infiltrating continuous steel fibre mats with a
specially designed cement based slurry.
• Mats are made up of stainless steel.
• Fibre volume is less than that required for
SIFCON, but same flexural strength and energy
absorption.
• Aspect ratio exceeding 500 can be used.
• Since mat is predefined configuration, handling
is minimized and balling effect is reduced

21. • Cracks are small and discontinuous and
possibility of water seepage is low .
• Concrete slurry uses very little water to pack
the mat very tight some of the cement remains
unhydrated.

22. Applications of SFRC
• Highway and airfield pavements

23. • Hydraulic structures

24. • Fibre shotcrete

25. • Precast applications

26. • Structural applications

27. Behaviour of SFRC in Tension
• Effect of incorporating fibres – delay and control tensile cracking
• Fibres (ductile) + matrix (brittle) composite (ductile)
• Sharing of tensile load (most predominant feature of FRC)
 until the matrix cracks ( fibre & matrix)
 once matrix cracks (fibres)
 this mechanism gives rise to favourable dynamic properties
1. Energy absorption
2. Fracture toughness

28. • Mangat reference (1976)
“ The effect of fibres in a cementitious material is principally to
cause relief of tensile stress at the crack tip and prevent unstable
crack propagation”

29.  Kelly (1970)
• Investigated the mechanism of pull-out.
• Load-elongation curve of fibres in tension depends on volume
fraction of fibres.
• Response in tension (based on FRC or SIFCON)
stage1: before cracking the composite elastic- (elastic stage)
stage2: after cracking –fibres tend to pull out – sudden change in
load elongation curve.
- if maximum post cracking stress › cracking stress – (multiple
cracking stage)
stage 3: beyond the peak point - failure and/or pull out of fibres
across single critical crack.
• Note : the post cracking strength increases with increase in bond
strength, aspect ratio and volume fraction of fibres.

30. • In the curve OA – debonding of fibre
• In case of short fibres – debonding occurs at max load
• Debondind energy per unit area =
(area of OAB under the stress-strain curve)/(surface area of fibre)
• The additional energy dissipation of fibre concrete results from
debonding energy as well.
Source: santakumar

31. Source: M.S Shetty

32. Behaviour of FRC in Compression
• Increase in compressive strength of FRC is marginal and ranges
from 0% to 20%.
• However, post cracking compressive stress-strain response
changes substantially.
• Change is due to Increase in strain at peak load & ductility
beyond ultimate load – higher toughness
• Higher toughness – prevents sudden & catastrophic failures
(especially in case of EQ & blast type of loads)

33. •Toughness = total area (A1+A2) / area A1
Source: M.S Shetty

34. Behaviour of FRC in Flexure
• There are 3 stages of response in flexure
stage1: process zone
- more or less linear response up to elastic limit.
- transfer stress from matrix to the fibres by interfacial shear
- imposed stress is shared between matrix and fibre until
first crack.
stage2: pseudo-plastic zone
- it is the non-linear portion between the elastic point and
max load capacity point.
- stress in matrix is progressively transferred to the fibres.
- fibres pull-out from the matrix (non-linear load-deflection)
- results in multiple cracking

35. stage3: stress free zone
- descending portion following peak strength until strain
limit.
- load-deflection curve represents ability of the fibre
composite to absorb large amounts of energy before failure.
- fibres are completely pulled-out
• Flexural strength of fibre composite is
fc = ultimate strength of fibre composite
fm = max strength of plain matrix (concrete)
C and D are constants determined experimentally
for plain concrete C=1 and D=0
for FRC ultimate strength C=0.95,D=4.95
for FRC first cracking strength C= 0.85, D= 4.95

36. Source: M.S Shetty

37. Crack Arresting
• Crack resistance is lower than the ultimate stress
• Once cracking is subjected to coupling impact of increased loads,
material ageing, structure fatigue – increase microcracks
• Microcracks – upward shifting of N-A, tension area of concrete is
lost – decrease of structural rigidity – deterioration of structural
durability.
• Propogation of micropcracks – emergency situation
• Fracture mechanics – stress singularities at crack tips
• Stress intensity factor › critical stress intensity factor of FRC –
Propagation of cracks - functional obsoleteness & structural
failure

39. Bridging action of steel fibres

40. CASE STUDY
• Research program is funded by National Basic Research
Program of china
• Published in 15 may 2013 in JESTR

41. Case study to arrest cracks
Crack arresting and strengthening

42. • Supposing unilateral crack under pure bending
• Stress concentration factor of edge crack is more than central
penetrated crack under same loading – unstable propagation
• HFRP is bonded to the surface – resists stress concentration of
crack at crack tip– edge crack in to internal eccentric crack
• From the super position principle
where, are stress intensity factors at crack tip A, the
rebar and the HFRP sheet.
• HFRP – one layer of unidirectional CFRP sheet (300 g/m^2) &
one layer of unidirectional GFRP sheet (600 g/m^2)
adhered to the bottom by epoxy

43. Tensile strength is increased by 171% &
fracture elongation is increased by 70%

45. 2 no. of specimens, 8mm dia bars, 3% of nylon (tensile- 6 Mpa)

46. FEM analysis results
STRESS INTENSITY FACTOR VS CRACK HEIGHT WITHOUT HFRP

47. STRESS INTENSITY FACTOR VS CRACK HEIGHT WITH HFRP
•HFRP increases ductility separately by 36% and 106%

48. Mix Design Procedure
• Corresponding to required 28-day field flexural strength of
SFRC – design strength of laboratory mix is determined.
• For known geometry, stipulated volume fraction- w/c ratio is
selected between 0.45 and 0.60
• Depending on max size of agg. & fibre concentration – cement
paste content is determined by mass
• Ratio of FA to CA varies from 1:1 to 1:3, ratio of 1:1.5 is a good
start for volume % of fibre up to 1.5 and length of fibre up to
40mm.

49. • From w/c ratio & paste content – cement & water content
• Fibre content is obtained by taking density of fibres as 7850
kg/m^3
• Total quantity of agg. Is determined as
wt. of agg. = wt. of FRC – ( wt. of water, cement & fibre)
• Quantities of FA &CA are determined by ratio of FA:CA= 1:1.5
• Trial mix is checked for workability by appropriate test.

50. Applications in India and abroad
• More than 400 tones of Shakti man Steel Fibers have been used recently in
the construction of a road overlay for a project at Mathura (UP).

51. • A 3.9 km long district heating tunnel, carrying 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.

52. • Steel fibers are used without rebars to carry flexural loads is a
parking garage at Heathrow Airport. It is a structure with 10 cm
thick slab.

53. Conclusions
• The total energy absorbed in fiber i.e., area under the load-deflection
curve is at least 10 to 40 times higher for fiber-reinforced
concrete than that of plain concrete.
• Addition of fiber to conventionally reinforced beams increased the
fatigue life and decreased the crack width under fatigue loading.
• At elevated temperature SFRC have more strength both in
compression and tension.
• Cost savings of 10% - 30% over conventional concrete flooring
systems.