Upload
deviprasadha
View
6.551
Download
6
Embed Size (px)
DESCRIPTION
Experimental Study on the Behaviour of Steel Fibre Reinforced Concrete
Citation preview
1
EXPERIMENTAL STUDY ON THE BEHAVIOUR OF
STEEL FIBRE REINFORCED CONCRETE
A PROJECT REPORT
Submitted by
DEVI PRASADH.A NANDA KUMAR.S
in partial fulfillment for the award of the degree
of
BACHELOR OF ENGINEERING
in
CIVIL ENGINEERING
HINDUSTAN COLLEGE OF ENGINEERING
CHENNAI 603 103
ANNA UNIVERSITY
CHENNAI 600 025
APRIL 2005
2
To our beloved parents
3
ACKNOWLEDGEMENT
4
ACKNOWLEDGEMENT
First the authors thank the Almighty whose blessings made this project
a success.
This experimental work couldn’t have been made possible without the
support of Larsen & Toubro ltd. The authors thank the L&T for their
technical and other facilities provided at various stages of this research
programme.
The authors express their sincere gratitude and heartfelt thanks to
Dr.B.Sivarama Sarma, Head, R&D, Larsen & Toubro ltd, Chennai for his
valuable guidance and supervision throughout the project work.
The authors express their heartfelt thanks to Mr.Sankaralingam, Deputy
General Manager, (Bridges) L&T, Chennai whose guidance made this project
possible.
The authors express their heartfelt thanks to Mr.S.N.Rajan, Mr.S.Manohar,
Mr.V.Senthil Kumar, Mr.R.Selvam, Mr.M.Senthil Kumar an, of R&D
department in L&T for their support during the experimental work. They also
express their sincere thanks to Laboratory staff of L&T for providing all
possible logistic support to carry out the experimental programme.
The authors express thanks to Ms.P.S.Joanna, Lecturer, Hindustan
College of Engineering for her supervision for this project work.
The authors are grateful to Dr.M.Neelamegam, Assistant director, SERC,
Chennai for his esteemed suggestions and guidance for this work.
The authors express their special thanks to Ms.T.Ch.Madhavi, Senior lecturer
of Hindustan College of Engineering for her insight illuminating guidance.
The authors express their sincere thanks to Dr.L.N.Ramamurthy , Honorary
Professor, Hindustan College of engineering for his valuable suggestions for
this work.
5
The authors also thank Ms.JessyRooby, Ms.PratheepaPaul,
Dr.AngelinePrabavathy, Mr.Kalyan Kumar and other faculty members of
Civil Engineering department, HCE who contributed to the development of this
work in many ways.
The authors express their heartfelt thanks to their parents, brothers, sisters,
and friends for their good wishes and constant encouragement throughout the
period of this research work.
The authors sincerely thank all others who have helped directly or indirectly at
various stages of this work.
The authors
6
ABSTRACT
KEYWORDS: Steel Fibre Reinforced Concrete, Static load, Panels, Beams,
Toughness, Energy Absorption.
The objective of this investigation was to study the behaviour of
Steel Fibre Reinforced Concrete (SFRC). Hooked end fibres and
corrugated fibres with aspect ratio of 55 were used. Specimens were cast
without fibres and with fibres of 0.5% and 1%. Tests were conducted for
studying the compressive, tensile, flexural strength and energy
absorption.
Compressive and split tensile tests were conducted on cubes and
cylinders respectively. 15 Beams of dimension 700x150x150mm were
cast and tested under two point loading to find flexural strength,
toughness and stiffness. An empirical equation for finding the toughness
index was developed based on fibre percentage.
30 panels were cast with dimension 500x500x50mm and 500x
500x100mm. Static point load test was conducted on each panel to
calculate the energy absorption, ductility index and secant stiffness was
found.
7
ANNA UNIVERSITY CHENNAI 600025
BONAFIDE CERTIFICATE
Certified that this project report “EXPERIMENTAL STUDY ON THE
BEHAVIOUR OF STEEL FIBRE REINFORCED CONCRETE”
is the bonafide work of “DEVIPRASADH.A & NANDA KUMAR.S”
who carried out the project work under our supervision.
Dr.V.BALAKRISHNAN Dr.B.SIVARAMA SARMA HEAD OF THE DEPARTMENT HEAD, RESEARCH & DEVELOPMENT DEPARTMENT OF CIVIL ENGINEERING EDRC HINDUSTAN COLLEGE OF ENGINEERING LARSEN & TOUBRO LIMITED CHENNAI-603103 CHENNAI-603089 Ms.P.S.JOANNA SUPERVISOR LECTURER DEPARTMENT OF CIVIL ENGINEERING HINDUSTAN COLLEGE OF ENGINEERING CHENNAI-603103
8
TABLE OF CONTENTS
CHAPTER NO: TITLE PAGE NO:
ABSTRACT iv
LIST OF TABLE vii
LIST OF FIGURES viii
LIST OF SYMBOLS x
LIST OF ABBREVIATONS xi
1. INTRODUCTION 1
1.1 GENERAL 1
1.2 CONVENTIONAL REINFORCED CONCRETE 2
1.3 FIBRE REINFORCED CONCRETE 3
1.4 MANUFACTURING METHODS 4
1.5 FIBRE MECHANISM 5
1.6 FIBRE - MATRIX INTERACTION 5
1.7 BRIDGING ACTION 6
1.8 WORKABILITY 7
1.9 FEATURES AND BENEFITS OF SFRC 8
1.10 APPLICATIONS OF SFRC 9
1.11 USAGE OF SFRC IN INDIAN PROJECTS 9
1.12 ORGANISATION OF THESIS 10
2. OBJECTIVE OF THE EXPERIMENT 11
3. LITERATURE REVIEW 12
3.1 HISTORICAL BACKGROUND 12
3.2 INDIAN SCENARIO 13
3.3 TOUGHNESS 13
3.4 DURABILITY 15
3.5 SEISMIC RESISTANCE 16
9
3.6 SHEAR RESISTANCE 17
3.7 DYNAMIC RESISTANCE 18
3.8 BAR CONFINEMENT 20
3.9 BOND IMPROVEMENT 20
4. EXPERIMENTAL INVESTIGATION 21
4.1 EXPERIMENTAL PROGRAM 21
4.2 EXPERIMENTAL SETUP 23
4.2.1 CUBE COMPRESION TEST 23
4.2.2 SPLIT TENSILE TEST 23
4.2.3 FLEXURAL TEST 24
4.2.4 TOUGHNESS 26
4.2.5 STIFFNESS 26
4.2.6 EMPRICAL EQUATION 26
4.2.7 STATIC LOAD TEST 25
4.2.8 DUCTILITY INDEX 27
4.2.9 SECANT STIFFNESS 26
4.3 MATERIALS USED IN EXPERIMENT 30
4.3.1 CEMENT 30
4.3.2 FINE AGGREGATE 30
4.3.3 COARSE AGGREGATE 30
4.3.4 WATER 30
4.3.5 STEEL FIBRES 31
4.3.5.1 HOOKED END STEEL FIBRES 31
4.3.5.2 CORRUGATED STEEL FIBRES 31
4.3.6 CASTING OF SPECIMENS 32
4.4 CURING OF SPECIMENS 34
5. RESULTS AND DISCUSSIONS 35
5.1 RESULTS 35
5.2 DISCUSSIONS AND COMPARISONS 57
5.2.1 COMPRESSIVE STRENGTH 57
5.2.2 SPLIT TENSILE STRENGTH 57
10
5.2.3 FLEXURE STRENGTH 58
5.2.4 TOUGHNESS INDICES 58
5.2.5 ENERGY ABSORPTION 59
5.2.6 DUCTILITY INDEX 60
5.2.7 SECANT STIFFNESS 61
6. CONCLUSION AND SUGGESTIONS 61
6.1 CONCLUSION 61
6.2 SUGGESTIONSFOR FUTURE WORK 62
7. REFERENCES 64
11
LIST OF TABLES
Title Page No
Table 5.1 Compressive strength 35
Table 5.2 Split tensile strength 36
Table 5.3 Flexure strength 38
Table 5.4 Toughness indices 40
Table 5.5 Stiffness for beams 42
Table 5.6 Energy absorbed by control panels 43
Table 5.7 Energy absorbed by SFRC panels 44
Table 5.8 Ductility index for panels 46
Table 5.9 Secant stiffness for panel specimens 47
12
LIST OF FIGURES
Title Page No
Figure 1.1 Fibre mechanism 6
Figure 1.2 Fibre Pull-out 7
Figure 4.1 Schematic representation of the experimental work 22
Figure 4.2 Cube testing machine 23
Figure 4.3 Compression testing machine for cylinder 24
Figure 4.4 Beam test setup 25
Figure 4.5 Features of panel test setup 28
Figure 4.6 Steel fibres used in the experiment 31
Figure 4.7 Wooden moulds for panels 32
Figure 4.8 Casting of panel 33
Figure 4.9 SFRC using corrugated fibre 34
Figure 4.10 SFRC using hooked fibre 34
Figure 5.1 Bar chart for compressive strength 37
Figure 5.2 Bar chart for split tensile strength 37
Figure 5.3 Bar chart for flexure strength 39
Figure 5.4 Empirical Equations for CSFRC 41
Figure 5.5 Empirical Equations for HSFRC 41
Figure 5.6 Energy absorption for 50mm panels 45
Figure 5.7 Energy absorption for 100mm panels 45
Figure 5.8 Load Vs Deflection for beams (0.5%) 48
Figure 5.9 Load Vs Deflection for beams (1.0%) 48
Figure 5.10 Load Vs Deflection for beams (Both 1.0% & 0.5%) 49
13
Figure 5.11 Load Vs Deflection for 50mm panel (0.5%) 50
Figure 5.12 Load Vs Deflection for 50mm panel (1.0%) 50
Figure 5.13 Load Vs Deflection for 50mm panel (Both 1.0% & 0.5%) 51
Figure 5.14 Load Vs Deflection for 100mm panel (0.5%) 52
Figure 5.15 Load Vs Deflection for 100mm panel (1.0%) 52
Figure 5.16 Load Vs Deflection for 100mm panel (Both 1.0% & 0.5%) 53
Figure 5.17 Crack propagation of SFRC 54
Figure 5.18 Panel failure in static load 55
Figure 5.19 First crack in panel 55
Figure 5.20 Fibre pull-out in panel 55
Figure 5.21 Failure pattern in 50mm panels 56
14
LIST OF SYMBOLS
σcc Cube compressive strength
Pf Failure load
Ab Bearing area of the cube
Tsp Spilt tensile strength
d Measured diameter of specimen
b Breadth of beam
l Measured length of specimen
fb The modulus of rupture
fck Characteristic compressive strength of concrete
Sc Specific gravity of cement
Sfa Specific gravity of saturated surface dry fine aggregate
Sca Specific gravity of saturated surface dry coarse
aggregate
µd Displacement ductility
δu Ultimate deflection
δy Yield deflection
15
LIST OF ABBREVIATONS
DESIGNATION FOR BEAM
S:no Type of fibre % of fibre Specimen ID
1 --- 0 B-a
2 --- 0 B-b
3 --- 0 B-c
4 Hooked 0.5 BHF-0.5a
5 Hooked 0.5 BHF-0.5b
6 hooked 0.5 BHF-0.5c
7 Hooked 1.0 BHF-1.0a
8 Hooked 1.0 BHF-1.0b
9 Hooked 1.0 BHF-1.0c
10 Corrugated 0.5 BCF-0.5a
11 Corrugated 0.5 BCF-0.5b
12 Corrugated 0.5 BCF-0.5c
13 Corrugated 1.0 BCF-1.0a
14 Corrugated 1.0 BCF-1.0b
15 corrugated 1.0 BCF-1.0c
16
DESIGNATION FOR PANEL
Sl.no
Thickness
Type of fibre
% of fibre
Specimen ID
1 50mm --- 0 P1-a
2 50mm --- 0 P1-b
3 50mm --- 0 P1-c
4 100mm --- 0 P2-a
5 100mm --- 0 P2-b
6 100mm --- 0 P2-c
7 50mm Hooked 0.5 P1HF0.5-a
8 50mm Hooked 0.5 P1HF0.5-b
9 50mm Hooked 0.5 P1HF0.5-c
10 100mm Hooked 0.5 P2HF0.5-a
11 100mm Hooked 0.5 P2HF0.5-b
12 100mm Hooked 0.5 P2HF0.5-c
13 50mm Hooked 1.0 P1HF1.0-a
14 50mm Hooked 1.0 P1HF1.0-b
15 50mm Hooked 1.0 P1HF1.0-c
16 100mm Hooked 1.0 P2HF1.0-a
17 100mm Hooked 1.0 P2HF1.0-b
18 100mm Hooked 1.0 P2HF1.0-c
19 50mm Corrugated 0.5 P1CF0.5-a
20 50mm Corrugated 0.5 P1CF0.5-b
21 50mm Corrugated 0.5 P1CF0.5-c
22 100mm Corrugated 0.5 P2CF0.5-a
23 100mm Corrugated 0.5 P2CF0.5-b
24 100mm Corrugated 0.5 P2CF0.5-c
25 50mm Corrugated 1.0 P1CF1.0-a
26 50mm Corrugated 1.0 P1CF1.0-b
27 50mm Corrugated 1.0 P1CF1.0-c
28 100mm Corrugated 1.0 P2CF1.0-a
29 100mm Corrugated 1.0 P2CF1.0-b
30 100mm Corrugated 1.0 P2CF1.0-c
17
CHAPTER 1
INTRODUCTION
18
CHAPTER 1
INTRODUCTION
1.1 GENERAL
Concrete is one of the most versatile building materials. It can be
cast to fit any structural shape from a cylindrical water storage tank to a
rectangular beam or column in a high-rise building. The advantages of
using concrete include high compressive strength, good fire resistance,
high water resistance, low maintenance, and long service life. The
disadvantages of using concrete include poor tensile strength, low strain
of fracture and formwork requirement. The major disadvantage is that
concrete develops micro cracks during curing. It is the rapid propagation
of these micro cracks under applied stress that is responsible for the low
tensile strength of the material. Hence fibres are added to concrete to over
come these disadvantages. The addition of fibres in the matrix has many
important effects. Most notable among the improved mechanical
characteristics of Fibre Reinforced Concrete (FRC) are its superior
fracture strength, toughness, impact resistance, flextural strength
resistance to fatigue, improving fatigue performance is one of the primary
reasons for the extensive use of Steel Fibre Reinforced Concrete (SFRC)
in pavements, bridge decks, offshore structures and machine foundation,
where the composite is subjected to cyclically varying load during its
lifetime.
Today the space shuttle uses fibres in heat shield ties to control the
effects of thermal expansion and the human body’s strongest and most
flexible structures, muscles are made up of fibres. The fact is fibres of
almost any description improve the ability of substances to withstand
strain.
19
The main reasons for adding steel fibres to concrete matrix is to improve
the post-cracking response of the concrete, i.e., to improve its energy
absorption capacity and apparent ductility, and to provide crack resistance
and crack control. Also, it helps to maintain structural integrity and
cohesiveness in the material. The initial researches combined with the
large volume of follow up research have led to the development of a wide
variety of material formulations that fit the definition of Fibre Reinforced
Concrete. Steel fibre’s tensile strength, modulus of elasticity, stiffness
modulus and mechanical deformations provide an excellent means of
internal mechanical interlock. This provides a user friendly product with
increased ductility that can be used in applications of high impact and
fatigue loading without the fear of brittle concrete failure.
Thus, SFRC exhibits better performance not only under static and quasi-
statically applied loads but also under fatigue, impact, and impulsive
loading.
1.2 CONVENTIONAL REINFORCED CONCRETE
Johnston (1994) found that tensile strength of concrete is typically 8% to
15% of its compressive strength. This weakness has been dealt with over
many decades by using a system of reinforcing bars (rebars) to create
reinforced concrete; so that concrete primarily resists compressive
stresses and rebars resist tensile and shear stresses. The longitudinal rebar
in a beam resists flexural (tensile stress) whereas the stirrups, wrapped
around the longitudinal bar, resist shear stresses. In a column, vertical
bars resist compression and buckling stresses while ties resist shear and
provide confinement to vertical bars. Use of reinforced concrete makes
for a good composite material with extensive applications.
20
Steel bars, however, reinforce concrete against tension only locally.
Cracks in reinforced concrete members extend freely until encountering a
rebar. Thus need for multidirectional and closely spaced steel
reinforcement arises. That can’t be practically possible. Steel fibre
reinforcement gives the solution for this problem
1.3 FIBRE REINFORCED CONCRETE
Fibre reinforced concrete is a concrete mix that contains short discrete
fibres that are uniformly distributed and randomly oriented. As a result of
these different formulations, four categories of fibre reinforcing have
been created. These include steel fibres, glass fibres, synthetic fibres and
natural fibres. Within these different fibres that character of Fibre
Reinforced Concrete changes with varying concrete's, fibre materials,
geometries, distribution, orientation and densities.
The amount of fibres added to a concrete mix is measured as a percentage
of the total volume of the composite (concrete and fibres) termed Volume
Fraction (Vf). Vf typically ranges from 0.1 to 3%. Aspect ratio (l/d) is
calculated by dividing fibre length (l) by its diameter (d). Fibres with a
non-circular cross section use an equivalent diameter for the calculation
of aspect ratio. If the modulus of elasticity of the fibre is higher than the
matrix (concrete or mortar binder), they help to carry the load by
increasing the tensile strength of the material. Increase in the aspect ratio
of the fibre usually segments the flexural strength and toughness of the
matrix. However, fibres which are too long tend to "ball" in the mix and
create workability problems.
21
Unlike resin and metal the fibre composites in which the fibres are
aligned and amount to 60 - 80 % of the composite volume, fibre
reinforced Cement or Concrete composites contain a less percentage of
fibres which are generally arranged in planar or random orientations.
Unidirectional fibres uniformly distributed throughout the volume
are the most efficient in uniaxial tension. While flexural strength may
depend on the unidirectional alignment of the fibres dispersed for away
from the neutral plane, flexural shear strength may call for a random
orientation. A proper shape and higher aspect ratio are also needed to
develop an adequate bond between the concrete and the fibre so that the
fracture of the fibres may be fully utilized.
1.4 MANUFACTURING METHODS
Round steel fibres are produced by cutting or chopping wire, typically
having diameter of 0.25 to 0.76 mm. Flat steel fibres having cross
sections ranging from 0.15 to 0.41mm in thickness by 0.25 to 0.90mm in
width are produced by shearing sheets or by flattening wire. Crimped or
deformed steel fibres have been produced both full length and crimped or
bent at ends only. Steel fibres are also produced by the melt- extraction
process. This method uses wheel that touches a molten metal surface, lifts
off liquid metal and rapidly freezes it into fibres which are thrown off
centrifugal force. The fibres have an irregular surface and a crescent
shaped cross section.
22
1.5 FIBRE MECHANISM
Fibres work with concrete utilizing two mechanisms: the spacing
mechanism and the crack bridging mechanism. The spacing mechanism
requires a large number of fibres well distributed within the concrete
matrix to arrest any existing micro-crack that could potentially expand
and create a sound crack. For typical volume fractions of fibres, utilizing
small diameter fibres or micro fibres can ensure the required number of
fibres for micro crack arrest.
The second mechanism termed crack bridging requires larger straight
fibres with adequate bond to concrete. Steel fibres are considered a prime
example of this fibre type that is commonly referred to as large
diameter fibres or macro fibres. Benefits of using larger steel fibres
include impact resistance, flexural and tensile strengths, ductility, and
fracture toughness and this was proved by Bayasi et al (1989).
1.6 FIBRE - MATRIX INTERACTION
The tensile cracking strain of cement matrix (less than 1/50) is very
much lower than the yield or ultimate strain of steel fibres. As a result,
when a fibre reinforced composite is loaded, the matrix will crack long
before the fibres can be fractured.
Once the matrix is cracked the composite continues to carry increasing
tensile stress; the peak stress and the peak strain of the composite are
greater than those of the matrix alone and during the inelastic range
between first cracking and the peak, multiple cracking of matrix occurs as
indicated in the Figure 1.1.
23
Figure 1.1 Fibre mechanism
1.7 BRIDGING ACTION
Pullout resistance of steel fibres (dowel action) is important for
efficiency. Pullout strength of steel fibres significantly improves the post-
cracking tensile strength of concrete. As an SFRC beam or other
structural element is loaded, steel fibres bridge the cracks, as shown in
Figure 1.2. Such bridging action provides the SFRC specimen with
greater ultimate tensile strength and, more importantly, larger toughness
and better energy absorption.
An important benefit of this fibre behaviour is material damage tolerance.
Bayasi and Kaiser (2001) performed a study where damage tolerance
factor is defined as the ratio of flexural resistance at 2-mm maximum
crack width to ultimate flexural capacity. At 2% steel fibre volume,
damage tolerance factor according to Bayasi and Kaiser was determined
as 93%.
24
Figure 1.2 Fibre Pull-out
1.8 WORKABILITY
A shortcoming of using steel fibres in concrete is reduction in
workability. Workability of SFRC is affected by fibre aspect ratio and
volume fraction as well the workability of plain concrete.
As fibre content increases, workability decreases. Most researchers limit
V f to 2.0% and l/d to 100 to avoid unworkable mixes.
In addition, some researchers have limited the fibre reinforcement index
[V f×(l/d)] to 1.5 for the same reason. To overcome the workability
problems associated with SFRC, modification of concrete mix design is
recommended. Such modifications can include the use of additives.
25
1.9 FEATURES AND BENEFITS OF SFRC
i. Elimination of manufacturing, handling, storage and positioning of
reinforcement cages.
ii. Reduction in the production cycle time resulting in increased
productivity.
iii. Improved impact resistance during handling, erection.
iv. Increased load bearing capacity and less spalling damage.
v. Enhanced durability.
vi. Important time savings due to the elimination of the
manufacturing, transport, handling and positioning of the
conventional reinforcement
vii. No damage to sealing due to reinforcement.
viii. Excellent corrosion resistance, spalling is totally excluded.
ix. Excellent crack control, the fibres control and distribute the cracks.
x. The fibres give resistance to tensile stresses at any point in the
shotcrete layer.
xi. Reinforces against the effect of shattering forces.
xii. Reinforces against material loss from abrading forces.
xiii. Reinforces against water migration.
26
1.10 APPLICATIONS OF SFRC
Steel fibre reinforced concrete has gained widespread use in applications
such as the following:
i. Rock slope stabilisation and support of excavated foundations,
often in conjunction with rock and soil anchor systems.
ii. Industrial floorings, road pavements, warehouses, Foundation
slabs.
iii. Channel linings, protect bridge abutments.
iv. Rehabilitation of deteriorated marine structures such as light
stations, bulkheads, piers, sea walls and dry docks.
v. Rehabilitation of reinforced concrete in structures such as bridges,
chemical processing and handling plants.
vi. Support of underground openings in tunnels and mines
1.11 USAGE OF SFRC IN INDIAN PROJECTS
Steel Fibre Reinforced Concrete has been used in various Indian projects
successfully namely,
i. Chamera hydro electric project , Himachal Pradesh
ii. Uri dam ,Jammu & Kashmir
iii. Sirsisilam project , Andhra Pradesh
iv. Tehri Dam project ,Uttaranchal
v. Ranganadi Hydroelectric project, Arunachal Pradesh
vi. Bombay - Pune National Highway, Maharashtra
27
1.12 ORGANISATION OF THESIS
The thesis is organized into five chapters. The first chapter gives an
introduction to the present study. The second chapter presents the
objective of this investigation. Literature survey is explained in the
chapter three. The experimental works done on the steel fibre reinforced
concrete are explained in chapter four. Chapter five gives the comparison
of test results and discussions. Chapter six gives the conclusion drawn
from this investigation and suggestions for future work.
28
CHAPTER 2
OBJECT IVE OF THE EXPERIMENT
29
CHAPTER 2
OBJECTIVE OF THE EXPERIMENT
The objective of the present study was to investigate experimentally the
properties of Steel Fibre Reinforced Concrete (SFRC) with the following
test results:
1) Compressive strength
2) Split Tensile strength
3) Flexure strength
4) To establish the load-deflection curves
5) Toughness indices of the beam specimens
6) To calculate the stiffness of beam specimens
7) To develop an empirical equation for calculating toughness index
8) To evaluate the energy absorption capacity of the panel specimens
9) To calculate the ductility index of panel specimens
10) To find secant stiffness for panels
And these test results are compared with conventional concrete of M40 grade.
30
CHAPTER 3
LITERATURE REVIEW
31
CHAPTER 3
LITERATURE REVIEW
A critical review of the published literature in the field of steel fibre
reinforced concrete was studied in the following sub headings.
3.1 HISTORICAL BACKGROUND
Historically fibre have been use to reinforce brittle materials since ancient
times; straws were used to reinforce sunbaked bricks, horse hair was used
to reinforce plaster and recently asbestos fibres are being used to
reinforce Portland cement. The low tensile strength and brittle character
of concrete have bypassed by the use of reinforcing rods in the tensile
zone of the concrete since the middle third of the nineteenth century. The
first patent for SFRC was filed in California by A.Bernard in 1874. A
patent by H.Alfen in France, 1918 was followed by G.C.Martin in
California, 1972 for SFRC pipes. H.Etheridge in 1931 examined the use
of steel rings to address the anchorage of steel fibres.
The World War II and later years saw G.Constatineso taking patents out
in England, 1943 and U.S.A., 1954. This was followed by numerous
patents, but the widespread use was hindered by high cost, poor testing
facilities and parallel rapid development of concrete reinforced with steel
bar and wire system. It was not until by James Romualdi in 1962 at the
Carnegie Institute of Technology that a clearer understanding of the
properties of SFRC emerged. Steel fibre reinforce shotcrete has been a
later extension of this understanding, with the first application being to
stabilise the rock slope of a tunnel portal, Idaho in 1972.
32
3.2 INDIAN SCENARIO
The Indian scenario offers the widest opportunities, but equally the
greatest challenge to the scientists, engineers and concrete technologists
in the use of fibre-cement composites in the construction industry.
Research and development work on FRC composites started in India in
early 1970s. A number of studies have been reported on the flexural
behaviour of Steel Fibre Reinforced Concrete (SFRC) beams and Slurry
Infiltrated Fibre reinforced Concrete (SIFCON) elements with particular
reference to improvements in cracking resistance, stiffness and ductility.
If there is a specific Indian standard code for steel fibre reinforced
concrete it will give positive impact on Indian infrastructure
development. Construction and maintenance provide an unlimited scope
for wide range of applications where the unique properties of FRC
materials can be used to the advantage of society, and to contribute to
better quality of living.
The main properties of Steel Fibre Reinforced concrete are discussed
below:
3.3 TOUGHNESS
The main reason for incorporating steel fibres in concrete and shotcrete is
to impart ductility to an otherwise brittle material. Steel fibre
reinforcement improves the energy absorption, impact resistance and
crack resistance of concrete. Steel fibre reinforcement enables the
concrete to continuously carry load after cracking ,called post crack
behaviour variety of tests have been developed to measure and quantify
the improvements achievable in steel fibre reinforced concrete.
33
Countries like U.S.A, Japan and European countries like France,
Germany, Belgium, Austria, Spain and Netherlands etc have specific
standards in this respect.
In order to measure the influence of the fibres on the toughness,
(American Society for Testing and Materials) ASTM C-1018(U.S.A) and
(Japan concrete Institute) JCI SF4 (Japan) prescribe very similar bending
tests in which the load has been recorded according to an applied
deflection of the specimen.
Gopalakrishnan et al (2003) of Structural Engineering Research Centre
(SERC), Chennai have studied the properties of steel fibre reinforced
shotcrete namely the toughness, flexural strength, impact resistance, shear
strength ductility factor and fatigue endurance limits. It is seen from the
study that the thickness of the Steel Fibre Reinforced Shotcrete (SFRS)
panels can be considerably reduced when compared with weld mesh
concrete. The improvements in the energy absorption capacity of SFRS
panels with increasing proportions of steel fibres are clearly shown by the
results of static load testing of panels. This investigation has clearly
shown that straight steel fibres of aspect ratio 65 can be successfully used
in field application.
Taylor et al (1996) reported on strength and toughness measurement on
the range of normal and high strength concrete mixes with and without
fibre reinforcement. The toughness measurements were carried out
through two fracture type test specimens rather than four point loading
arrangement. The rheology of these concrete is such that they can be
reinforced by sufficient volumes of polypropylene and steel fibres to
significantly increase their toughness, while their strengths in
compression and tension remain relatively constant.
34
3.4 DURABILITY
The corrosion resistance of Steel Fibre Reinforced Shotcrete (SFRS) is
governed by the same factors that influence the corrosion resistance of
conventionally reinforced concrete. As long as the matrix retains inherent
alkalinity and remains uncracked, deterioration of SFRC is not likely to
occur.
It has been found that good quality SFRC when exposed to atmospheric
pollution, chemicals or a marine environment, will only carbonate to a
depth of a couple of millimeters over a period of many years. Steel fibre
immediate layer of corrode to the depth of surface carbonation, causing
some rust colored surface staining. In a trafficked or abrasive exposure
environment such corroded surface fibres rapidly wear away and
disappear. The interior fibres beneath the immediate carbonated surface
layer, however, remain totally protected, provide the SFRC remains
uncracked.
Krishnamoorthy et al (2000) of SERC, Chennai have carried out
investigations to find out the influence of corrosion of steel fibres on the
strength of SFRC. There concrete specimens were subjected to
accelerated corrosion and it was found that there was no corrosion of steel
fibres in SFRC even after 250 cycles of corrosion. Additions of steel
fibres in concrete matrix have resulted in decreased crack width. It was
also noted that the addition of steel fibres in concrete results in delayed
cracking of concrete.
35
3.5 SEISMIC RESISTANCE
By using SFRC in a beam-column joint, some of the difficulties
associated with joint construction can be overcome and a greater seismic
strength can be provided. Michael Gebman (2001) of San Diego State
University, U.S.A made two half-scale joints, constructed to reflect U.S
building code, two SFRC joints were constructed with a hoop spacing
increased by 50%, and two SFRC joints were constructed with a hoop
increased by 100%. Hooked-end steel fibres with a length of 1.2-in (31-
mm), a diameter of 0.020-in (0.50-mm) and an aspect ratio of 60 were
used at a volume fraction of 2%.
After simulating a quasi-static earthquake loading, the SFRC joints were
found to have dissipated more energy than the conventional joints. A 90%
increase in energy absorption was found for SFRC joints with hoop
spacing increased by 100%. A 173% increase in energy absorption was
found for SFRC joints with hoop spacing increased by 50%.
Earthquake loading is best represented by a burst of energy applied to
structures. In conventional joints, such energy is dissipated by concrete
cracking, steel deformation, steel bending etc. In steel fibrous joints, the
goal is to dissipate such energy via progressive fibre pullout from
concrete. Henager (1974) was the first to publish a paper on testing of
steel fibre reinforced concrete beam-column joints. Two full-scale joints
were constructed. One joint was built according to ACI 318-71. The other
joint was reduced steel congestion common in seismic resistant joints by
replacing hoops with steel fibre concrete. Brass plated steel fibres with a
length of 1.5-in (38-mm) and an aspect ratio of 75 were added to the
concrete mix at a volume fraction of 1.67%. An earthquake loading was
simulated using a quasi-static loading rate utilizing an applied double
acting hydraulic actuator.
36
It was found that the steel fibre reinforced concrete joint had a higher
ultimate moment capacity, had better ductility, was stiffer, and was more
damage tolerant. Henager concluded that hoops, in the joint, could be
replaced with steel fibres. Henager also concluded that SFRC could
provide for a more cost effective joint.
Lakshmipathy and Santhakumar (1986) presented results of SFRC frame
testing conducted at Anna University. Two frames, representing a 7 level
single bay frame, were constructed at 1/4 scale; one frame was made out
of reinforced concrete and the other out of SFRC. Fibres with a length of
1.57-in (40-mm) and an aspect ratio of 100 were used at a volume
fraction of 1%. An earthquake loading was simulated by applying load
via hydraulic jacks at the 7th, 5th and 3rd levels of the frame.
It was found that the SFRC frame had a ductility increase of 57% and a
130% increase in cumulative energy dissipation in comparison to the
conventional joint.
3.6 SHEAR RESISTANCE
Large earthquakes result in high shear forces within the beam-column
joint. To withstand such forces, hoop spacing is decreased within the joint
region. This can sometimes result in congestion problems that can result
in construction difficulty. SFRC can be used with increased hoop spacing
to provide higher shear resistance.
Craig et al (1984) examined the shear behaviour of 21 short columns
under double curvature bending. The steel fibres used had a length of
1.18-in (30-mm), an aspect ratio of 60 and were used at volume fractions
of 0.75% and 1.5%. It was found that the failure mode changed from
explosive to ductile as steel fibre content increased.
37
Jindal and Hassan (1984) found that the shear resistance of SFRC joints
was greater than that of conventional joints. Steel fibres with a length of
1-in (25-mm), and an aspect ratio of 100 were used at a volume fraction
of 2%. It was observed that SFRC increased the shear and moment
capacities by 19% and 9.9% respectively. It was also observed that the
failure mode for SFRC specimens was ductile.
Kaushik et al (1987) found that a strength ratio of 1.67 can be achieved
with the addition of 1.5% volume fraction of steel fibres with aspect ratio
of 100 and the average maximum strain in fibre reinforced concrete
beams were of the order of 0.007 as compared to 0.0035 for plain
reinforced concrete beams.
3.7 DYNAMIC RESISTANCE
Dynamic strength of concrete reinforced with various types of fibres
subjected to explosive charges, dropped weights and dynamic tensile and
compressive load has been measured. The dynamic strength of various
types of loading was 5 to 10 times greater for fibre reinforced than for
plain concrete. The greater energy requirement to strip or pull-out the
fibres provides the impact strength and the resistance to spalling and
fragmentation. Steel fibre concrete was found to provide high resistance
to the dynamic forces of cavitations under high head, high velocity water
flow conditions .Still greater cavitations resistance was reported for steel
fibre concrete impregnated with the polymer. An impact test has been
devised for fibrous concrete which uses 10-lb hammer dropping on to
steel ball resting on test specimen. For fibrous concrete, the number of
blows to failure is typically several hundred compared to 30 to 50 for
plain concrete.
38
Srinivasalu et al (1987) examined that the dynamic behaviour of
reinforced concrete beams with equal tension and compression reinforced
and varying percentages of steel fibres was studied at SERC. The test
beams were subjected to particular static loads those simulated different
levels of cracking before they were subjected successively to steady state
forced vibration tests. Dynamic flexural rigidity and damping were from
the data collected from the test.
Tests show that that the dynamic stiffness of SFRC beams in the
uncracked state was only marginally high (15% for a fibre volume
content of 1%) than for reinforced concrete beams.
However large increase in stiffness in the post cracking stage was
observed: but this was nearly the same for all the fibre volumes studies
(0.5% to 1%).
The damping values exhibited by SFRC beams showed significant
scatter. Researches concluded that the average in the uncracked state,
applicable to design of machine foundation is 1% critical. Equation are
also formulated from the test results to estimate the dynamic stiffness in
the beams in post cracking stage for use in the designs involving SFRC
elements in blast and earthquake resistant structures.
Tests concluded on SFRC specimens by Jacob et al at Institute of
Material and Structure Research, Yugoslavia also showed that the
inclusion of fibres improve the dynamic properties of concrete. It is also
found that resistance to blow fatigue are improved by the addition of
fibre. Resistance to blow was investigated using the Charpy stricking
pendulum an improvement in toughness was reported.
39
3.8 BAR CONFINEMENT
Confinement of the rebar in a structure is very important for the
performance of the joint in an earthquake. The bond between concrete
and rebar is affected by the amount of steel congestion in a joint. If there
are a lot of hoops overlapping with small spacing in a joint, then the bond
between concrete and rebar can be poor. Poor bond results when there is
not enough space between the bars to allow the concrete to pass through.
A joint with increased hoop spacing will have better bar confinement, as
there will be ample room for the concrete to flow around the bars and to
properly bond.
However, in a seismic beam-column joint it can be nearly impossible to
allow for an increased hoop spacing providing better confinement
because the high shearing forces present in a joint require numerous
hoops. To remedy this situation, steel fibre concrete can be used in place
of some hoops.
3.9 BOND IMPROVEMENT
Soroushian and Bayasi (1991) tested bars embedded in concrete blocks to
examine the bond improvement gained by using SFRC. Steel fibres with
a length of 2-in (50.8-mm), and an aspect ratio of 57 were added at a 2%
volume fraction. It was found that local bond resistance increased by 55%
and frictional resistance increased by 140%.
40
CHAPTER 4
EXPERIMENTAL INVESTIGATIONS
41
CHAPTER 4
EXPERIMENTAL INVESTIGATION
4.1 EXPERIMENTAL PROGRAM
In order to study the interaction of steel fibres with concrete under
compression, split tension, flexure and static load, 45 cubes, 45 cylinders,
15 beams, 30 panels was casted respectively. The experimental program
was divided into five groups.
Each group consists of 9 cubes, 9 cylinders, and 3 beams, 3 panels of
50mm thickness and 3 panels of 100 mm thickness.
� The first group is the control (Plain) concrete with 0% fibre (PCC)
� The second group consisted of hooked end steel fibre of Vf 0.5%
(HSFRC 0.5)
� The third group consisted of hooked end steel fibre of Vf 1.0%
(HSFRC 1.0)
� The fourth group consisted of corrugated steel fibre of Vf 0.5%
(CSFRC 0.5)
� The fifth group consisted of corrugated steel fibre of Vf 1.0%
(CSFRC 1.0)
A schematic representation of the current experimental has been shown in
the figure 4.1.
42
EXPERIMENT ON
SFRC
0% V f SFRC
0.5% V f SFRC
1.0% V f SFRC
9 CUBES,
9 CYLINDERS, 3 BEAMS
PANELS
9 CUBES,
9 CYLINDERS, 3 BEAMS
PANELS
9 CUBES,
9 CYLINDERS, 3 BEAMS
PANELS
3
50MM PANELS
3
100MM PANELS
3
50MM PANELS
3
100MM PANELS
3
50MM PANELS
3
100MM PANELS
HOOKED,
DRAMMIX FIBRES (HSFRC)
CORRUGATED,
STEWOLS FIBRES (CSFRC)
Figure 4.1 Schematic representation of the experimental work
43
4.2 EXPERIMENTAL SETUP
4.2.1 CUBE COMPRESION TEST
This test was conducted as per IS 516-1959. The cubes of standard size
150x150x150mm were used to find the compressive strength of concrete.
Specimens were placed on the bearing surface of UTM, of capacity 300
tones without eccentricity and a uniform rate of loading of 140 Kg/cm2
per minute was applied till the failure of the cube. The maximum load
was noted and the compressive strength was calculated. The results are
tabulated in Table 5.1
Cube compressive strength (σcc) in MPa = Pf/Ab
Figure 4.2 Cube testing machine
4.2.2 SPLIT TENSION TEST
This test was conducted as per IS 5816-1970. The cylinders of standard
size 150mm diameter and 300 mm height was placed on the UTM with
capacity 200tones, with the diameter horizontal. At the top and bottom
two strips of wood where placed to avoid the crushing of concrete
specimen at the points where the bearing surface of the compression
44
testing machine and the cylinder specimen meets. The maximum load
was noted down. The results are tabulated in Table 5.2
The spilt tensile strength (Tsp) = 2P/пdl (MPa)
Figure 4.3 Compression testing machine for cylinder
4.2.3 FLEXURAL TEST
SFRC beams of size 150x150x700mm were tested using a servo
controlled UTM (MTS) as per the procedure given in ASTM C-78. The
specimen was turned on its side with respect to its position as moulded
and centred on the bearing block. The beam was simply supported over a
span of 600mm, and a two point loading system was adopted having an
end bearing of 50mm from each support.
45
The load applying block was made into contact with the surface of the
specimen at the third point between the supports. The UTM was operated
at a rate of 0.1mm/min, load and displacement was recorded constantly.
The first crack load and the corresponding deflection were noted. The
loading was continued upto six times the first crack deflection. The
maximum load was measured. It took about 40 minutes to complete the
test on each specimen. The results are tabulated in Table 5.3
The modulus of rupture was calculated using the formula,
The modulus of rupture (fb) =Pl/bd²
Figure 4.4 Beam test setup
46
4.2.4 TOUGHNESS
Toughness was calculated as the energy equivalent to the area under the
load deflection curve as per the procedure given in the American society
for testing and material’s ASTM C-1018.
Toughness index was calculated as the number obtained by dividing the
area upto a specified deflection by the area upto the first crack deflection.
The first crack is the point on the load deflection curve at which the curve
first becomes non linear (approximately the on set of cracking on the
matrix). Toughness indices I5 and I10 were calculated as area upto 3.0
times and 5.5 times the first crack deflection by the area upto a first crack
deflection respectively. Toughness indices are tabulated in Table 5.4.
4.2.5 STIFFNESS
Stiffness is an important property which determines the rigidity of the
material. Stiffness is the ability of the material to resist deformation under
the applied load.
Stiffness of the beam specimen was found as the slope of the load-
deflection curve upto the elastic region of the curve.
4.2.6 EMPIRICAL EQUATION
The empirical equations for finding the toughness indices were found
using the I5 and I10 values from the experimental results using Microsoft
Excel office program. If the toughness was known the percentage of
fibres required can be calculated easily.
Empirical Equations for CSFRC and HSFRC are given in the Figure 5.4
and Figure 5.5 respectively.
47
4.2.7 STATIC LOAD TEST
Static load test was performed on panels of dimension 500 mm×500
mm×50 mm and 500 mm×500 mm×100mm. The specimen was placed on
a simply supported condition on all four sides and a concentrated load
was applied over an area of 61sq.cm.
The actuator as operated at a rate of 1.5 mm/min and the corresponding
load & deflection was measured as per the European Specification for
Sprayed Concrete (EFNARC). The bottom deflection was also monitored
using a Linearly Variable Differential Transducer (LVDT). The testing
was continued till a deflection of 25mm or failure which ever occurred
earlier. The energy absorption upto the deflection of 25mm was
calculated as area under load deflection curve for that deflection, with an
increment of 2mm.
48
Figure 4.5 Features of panel test setup
LVDT
BOTTOM SUPPORT PLATE
49
4.2.8 DUCTILITY INDEX
Ductility index was calculated as the ratio of the deflection upto the
ultimate load to the deflection upto the first crack load. The ultimate
deformation has been considered as the deformation corresponding to
15% load drop i.e. 85% of the ultimate load drop. The ductility so
calculated is called the displacement ductility.
Ductility µd = δu / δy
The results are tabulated in the Table 5.8
4.2.9 SECANT STIFFNESS
Modulus of elasticity most commonly used in practice is secant modulus.
There is no standard method of determining the secant modulus. Hence in
this investigation secant modulus was calculated for selected points on
the load deflection curve for concrete panels and was called secant
stiffness. Straight line was drawn from the origin to the selected points;
the slope of that line gives the secant stiffness.
Secant stiffness was calculated for first crack load, ultimate load and
0.5%ultimate load drop. The results are tabulated in the Table 5.9
50
4.3 MATERIALS USED IN EXPERIMENT
The materials used and their specifications are as follows:
4.3.1 CEMENT
Ordinary Portland cement was used and its specific gravity is 3.15*.
The brand used was “UltraTech” with P53 grade.
The cement was confirming to IS 269-1976*.
4.3.2 FINE AGGREGATE
River sand was used and tests were conducted as per IS 2386 (PART I).
Specific gravity of fine aggregate is 2.65.
Water absorption 0.99%
Dry loose bulk density 1502 Kg/m3
4.3.3 COARSE AGGREGATE
Crushed granite stone aggregates of maximum size of 20 mm was used
tests were conducted as per IS 2386 (part III) of 1963.
Specific gravity of coarse aggregate is 2.73.
Water absorption 0.25%
Dry loose bulk density 1500 Kg/m3
4.3.4 WATER
As per IS 456-2000 recommendations, potable water was used for mixing
of concrete.
Note: * as per the manufacturers report.
51
4.3.5 STEEL FIBRES
4.3.5.1 HOOKED END STEEL FIBRES
Hooked end steel fibres commercially called as Dramix steel fibres
manufactured by Bekaert Corporation were used which had a length of
30 mm and a diameter of 0.55 mm resulting in an aspect ratio of about
55 and conforms to American standard ASTM A820 and Belgium
standard 1857*.
The tensile strength of fibre is in the range of 1100 N/mm2*
4.3.5.2 CORRUGATED STEEL FIBRES
Corrugated steel fibres from Stewols & Co were used which had a length
of 25 mm and a diameter of 0.45 mm resulting in an aspect ratio of about
55 and conforms to American standard ASTM A820*.
The tensile strength of fibre is in the range of 1200 N/mm2*
Figure 4.6 Steel fibres used in the experiment
52
4.4 CASTING OF SPECIMENS
The materials were weighed accurately using a digital weighing
instrument. For plain concrete, fine aggregates, coarse aggregate, cement,
water were added to the mixture machine and mixed thoroughly for three
minutes. Steel fibres were mechanically sprinkled inside the mixture
machine after thorough mixing of the ingredients of concrete.
For preparing the specimen for compressive, tensile, and flexure strength
permanent steel moulds were used.
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 and
500×500×100mm.
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 metre. Then the top surface was
given a smooth finish.
Figure 4.7 Wooden moulds for panels
50mm Panel 100mm Panel
53
Figure 4.8 Casting of panel
54
Figure 4.9 SFRC using corrugated fibre
Figure 4.10 SFRC using hooked fibre
4.6 CURING OF SPECIMENS
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.
55
CHAPTER 5
DISCUSSIONS OF TEST RESULTS
56
CHAPTER 5
RESULTS AND DISCUSSIONS
5.1 RESULTS
Table 5.1 COMPRESSIVE STRENGTH
Average Compressive strength in N/mm2
Specimen Type
3days 7 days 28 days
PCC
25.27
39.59
59.89
HSFRC 0.5
24.50
37.29
58.24
CSFRC
0.5
27.38
39.76
58.43
HSFRC 1.0%
26.32
38.04
59.01
CSFRC
1.0
40.35
32.17
60.00
57
Table 5.2 TENSILE STRENGTH
Average Tensile Strength in N/mm2
Specimen Type
3 days 7 days 28 days
P.C.C
2.55
3.54
4.81
HSFRC 0.5
2.90
4.76
5.19
CSFRC
0.5
3.40
5.02
4.83
HSFRC
1.0
4.01
5.66
6.37
CSFRC
1.0
3.82
5.29
6.27
58
Figure 5.1 BAR CHART FOR COMPRESSIVE STRENGTH
0
10
20
30
40
50
60
70
3days 7days 28days
CO
MP
RE
SS
IVE
ST
RE
NG
TH
N/m
m2
PCC
HSFRC0.5%
CSFRC0.5%
HSFRC1.0%
CSFRC1.0%
Figure 5.2 BAR CHART FOR SPLIT TENSILE STRENGTH
0
1
2
3
4
5
6
7
3days 7days 28days
SP
LIT
TE
NS
ILE
ST
RE
NG
TH
N/m
m2
PCC
HSFRC0.5%
CSFRC0.5%
HSFRC1.0%
CSFRC1.0%
59
TABLE 5.3 FLEXURAL STRENGTH
Specimen
Type
First
crack
load in
kN
28 days flexural
In N/mm2
Average flexural
strength in
N/mm2
B-a 34.00 6.04
B-b 28.50 5.06
B-c 30.00 5.33
5.48
BHF-0.5-a 28.50 4.59
BHF-0.5-b 27.00 4.80
BHF-0.5-c 25.50 4.53
4.64
BHF-1.0-a 33.75 6.00
BHF-1.0-b 32.00 5.68
BHF-1.0-c 32.00 5.69
5.79
BCF-0.5-a 26.00 4.62
BCF-0.5-b 27.00 4.80
BCF-0.5-c 27.00 4.80
4.74
BCF-1.0-a 26.50 4.71
BCF-1.0-b 27.00 4.80
BCF-1.0-c 29.00 5.16
4.91
60
Figure 5.3 BAR CHART FOR FLEXURAL STRENGTH
0
1
2
3
4
5
6
28 DAYS
FLE
XU
RA
L S
TR
EN
GT
H N
/mm
2
PCC
HSFRC0.5%
CSFRC0.5%
HSFRC1.0%
CSFRC1.0%
61
Table 5.4 TOUGHNESS INDICES
Toughness index
Specimen ID
I5
I10
B-a 1.00 1.00
B-b 1.00 1.00
B-c 1.00 1.00
BHF-0.5-a 3.26 5.00
BHF-0.5-b 3.44 4.67
BHF-0.5-c 3.18 4.86
BHF-1.0-a 3.79 5.63
BHF-1.0-b 4.16 5.88
BHF-1.0-c 3.81 6.23
BCF-0.5-a 2.51 3.16
BCF-0.5-b 2.70 4.18
BCF-0.5-c 3.12 4.08
BCF-1.0-a 3.1 5.02
BCF-1.0-b 3.71 5.92
BCF-1.0-c 2.65 6.00
62
FOR I5 y = 0.7533x + 2.4FOR I10 y = 3.68x + 1.9667
0
2
4
6
8
10
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25Percentage of Fibre
Tou
ghn
ess
Indi
ces I5
I10
Expon.(I5)
Expon.(I10)
Figure 5.4 Empirical Equations for CSFRC
FOR I5 y = 1.2533x + 2.6667FOR I10 y = 2.14x + 3.7733
0
2
4
6
8
10
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25Percentage of fibre
Tou
ghne
ss In
dice
s
I5
I10
Expon. (I5)Expon. (I10)
Figure 5.5 Empirical Equations for HSFRC
63
Table 5.5 STIFFNESS FOR BEAMS
Specimen
ID
Load
in
kN
Deflection
in
mm
Stiffness
in
kN/mm
Average Stiffness
in
kN/mm
B-a 34.00 1.30 26.15
B-b 28.50 1.13 25.30
B-c 30.00 1.10 27.28
26.24
BHF-0.5-a 28.50 1.00 28.50
BHF-0.5-b 27.00 1.30 20.77
BHF-0.5-c 25.50 0.90 28.33
25.86
BHF-1.0-a 33.80 1.00 33.80
BHF-1.0-b 31.50 1.00 31.50
BHF-1.0-c 32.00 1.00 32.00
32.27
BCF-0.5-a 26.00 1.00 26.00
BCF-0.5-b 27.00 1.10 24.55
BCF-0.5-c 27.20 1.20 22.67
24.47
BCF-1.0-a 26.50 1.30 20.38
BCF-1.0-b 27.50 1.10 25.00
BCF-1.0-c 29.00 1.05 27.60
24.33
64
Table 5.6 ENERGY ABSORBED BY CONTROL PANELS
Specimen ID
Maximum
Deflection in
mm
Experimental
Peak load in
kN
Energy
Absorbed in
Nm
P1-a
2.00
10.92
12.60
P1-b
2.40
8.54
10.30
P1-c
1.60
7.30
5.76
P2-a
3.40
31.36
53.55
P2-b
2.80
40.04
56.00
P2-c
3.10
37.51
58.13
65
Table 5.7 ENERGY ABSORBED BY SFRC PANELS
Specimen ID
First crack load
in kN
Experimental
Peak load in
kN
Energy absorbed
for 20mm
deflection in Nm
P1HF0.5-a 10.56 25.91 288.50
P1HF0.5-b 8.65 15.92 243.87
P1HF0.5-c 10.38 17.91 259.50
P2HF0.5-a 37.63 77.62 936.00
P2HF0.5-b 44.83 87.55 1105.80
P2HF0.5-c 51.69 84.26 988.00
P1HF1.0-a 9.87 19.35 327.50
P1HF1.0-b 12.61 23.94 262.63
P1HF1.0-c 9.30 23.16 338.25
P2HF1.0-a 50.0 94.00 890.00
P2HF1.0-b 33.43 100.00 952.70
P1CF0.5-a 8.75 13.23 164.50
P1CF0.5-b 8.82 18.74 180.00
P1CF0.5-c 11.4 17.97 211.44
P2CF0.5-a 46.58 90.0 544.00
P2CF0.5-b 49.45 62.59 564.50
P2CF0.5-c 46.20 89.89 644.25
P1CF1.0-a 11.15 31.14 361.50
P1CF1.0-b 16.37 21.78 303.25
P1CF1.0-c 9.57 23.51 274.25
P2CF1.0-a 41.06 88.00 791.00
P2CF1.0-b 45.18 95.00 769.88
66
0
50
100
150
200
250
300
350
0 5 10 15 20 25
Deflection in mm
En
erg
y ab
sorp
tio
n i
n N
m PCC
HSFRC0.5CSFRC0.5HSFRC1.0CSFRC1.0
Figure 5.6 Energy absorption for 50mm panels
0
200
400
600
800
1000
1200
0 5 10 15 20 25Deflection in mm
En
erg
y ab
sorb
tio
n in
Nm
PCC
HSFRC0.5CSFRC0.5HSFRC1.0CSFRC1.0
Figure 5.7 Energy absorption for 100mm panels
67
Table 5.8 DUCTILITY INDEX FOR PANELS
Specimen ID
First Crack Deflection in
mm
Deflection upto 0.15%
ultimate load drop in mm
Ductility
Index
Average Ductility
Index
P1-a 1.56 1.56 1.00
P1-b 2.31 2.31 1.00
P1-c 1.51 1.51 1.00
1.00
P2-a 2.88 2.88 1.00
P2-b 3.06 3.06 1.00
P2-c 3.33 3.33 1.00
1.00
P1HF0.5-a 2.28 10.75 4.72
P1HF0.5-b 2.22 12.10 5.45
P1HF0.5-c 2.8 13.00 4.64
4.94
P2HF0.5-a 3.67 11.50 3.73
P2HF0.5-b 3.32 8.60 2.56
P2HF0.5-c 4.43 11.00 2.46
2.72
P1HF1.0-a 2.12 10.15 4.77
P1HF1.0-b 2.28 11.10 7.87
P1HF1.0-c 2.34 10.00 4.27
4.64
P2HF1.0-a 3.42 7.10 2.08
P2HF1.0-b 3.97 10.00 2.52
P2HF1.0-c 3.41 9.50 2.77
2.46
P1CF0.5-a 2.18 9.00 3.26 P1CF0.5-b 2.47 6.60 4.47
P1CF0.5-c 2.87 10.1 4.04
3.92
P2CF0.5-a 2.13 6.75 3.17
P2CF0.5-b 2.65 5.10 1.93
P2CF0.5-c 2.94 6.80 2.31
2.47
P1CF1.0-a 1.84 9.10 4.95
P1CF1.0-b 2.06 9.00 4.37
P1CF1.0-c 1.94 10.75 5.54
4.95
P2CF1.0-a 2.60 8.10 3.12
P2CF1.0-b 2.73 8.20 3.00
P2CF1.0-c 3.84 8.15 2.87
3.00
68
Table 5.9 SECANT STIFFNESS FOR PANEL SPECIMENS
Average Stiffness in kN/mm
Specimen ID
First crack load
Ultimate load
0.5% ultimate load drop
Control panel 50mm 5.08 5.08 5.08
Control panel 100mm 11.93 11.93 11.93
0.5% Hooked fibre 50mm
4.17 2.34 0.65
0.5% Hooked fibre 100mm
11.85 12.17 2.81
1.0% Hooked fibre 50mm
4.39 2.92 0.58
1.0% Hooked fibre 100mm
12.52 15.38 3.72
0.5% Corrugated fibre 50mm
4.62 3.39 0.68
0.5% Corrugated fibre 100mm
16.01 16.11 4.29
1.0% Corrugated fibre 50mm
6.14 3.37 0.78
1.0% Corrugated fibre 100mm
17.01 15.61 3.39
69
3,000
2,500
2,000
1,500
1,000
500
0
8 7 6 5 4 3 2 10Deflection in mm
Lo
ad in
kg
fPCC
HSFRC
CSFRC
Figure 5.8 Load Vs Deflection for beams (0.5%)
3,500
3,000
2,500
2,000
1,500
1,000
500
0
8 7 6 5 4 3 2 10Deflection in mm
Lo
ad
in k
gf
PCC
HSFRC
CSFRC
Figure 5.9 Load Vs Deflection for beams (1.0%)
70
3,500
3,000
2,500
2,000
1,500
1,000
500
0
8 7 6 5 4 3 2 10
Deflection in mm
Load
in k
gf
PCC
HSFRC 0.5
CSFRC 0.5
HSFRC 1.0
CSFRC 1.0
Figure 5.10 Load Vs Deflection for beams (Both 1.0% & 0.5%)
71
Figure 5.11 Load Vs Deflection for 50mm panel (0.5%)
0
500
1000
1500
2000
2500
3000
3500
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22Deflection in mm
Lo
ad
in k
gf
PCC
HSFRC
CSFRC
Figure 5.12 Load Vs Deflection for 50mm panel (1.0%)
72
0
500
1000
1500
2000
2500
3000
3500
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Deflection in mm
Load
in k
gf
PCC
HSFRC 0.5
CSFRC 0.5
HSFRC 1.0
CSFRC 1.0
Figure 5.13 Load Vs Deflection for 50mm panel (Both 1.0% & 0.5%)
73
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23Deflection in mm
Loa
d in
kg
fPCC
HSFRC
CSFRC
Figure 5.14 Load Vs Deflection for 100mm panel (0.5%)
0
2000
4000
6000
8000
10000
12000
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22Deflection in mm
Lo
ad
in k
gf
PCC
HSFRC
CSFRC
Figure 5.15 Load Vs Deflection for 100mm panel (1.0%)
74
0
2000
4000
6000
8000
10000
12000
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
Deflection in mm
Load
in k
gf
PCC
HSFRC 1.0
CSFRC 1.0
HSFRC 0.5
CSFRC 0.5
Figure 5.16 Load Vs Deflection for 100mm panel (Both 1.0% & 0.5%)
75
Figure 5.17 Crack propagation of SFRC in beam
76
Figure 5.18 Panel failure in static load
Figure 5.19 First crack in panel
Figure 5.20 Fibre pull-out in panel
77
Figure 5.21 Failure pattern in 50mm panels
PCC
CSFRC 0.5 CSFRC 1.0
HSFRC 0.5 HSFRC 1.0
78
5.2 DISCUSSIONS
5.2.1 Compressive Strength
The Compressive strength of concrete mixed with steel fibres was found
to vary marginally, the variation was about -1% to 1% at 28 days.
The 3 days strength of CSFRC with volume fraction 0.5% and 1% was
8% and 27% greater than that of control concrete. 50% of the 28 days
strength of CSFRC was obtained in 3 days. The compressive strength of
ordinary concrete and fibre reinforced concrete are tabulated in Table 5.1
and bar chart is plotted in Figure 5.1.
5.2.2 Split Tensile Strength
The tensile strength was found to be increased as the percentage of fibre
was increased. For the hooked fibre with volume fraction of 0.5% and
1.0% the increase in tensile strength was 8 % and 32.4%respectively. The
increase was about 30% for corrugated fibres with volume fraction of
1.0% and there was no increase in case of CSFRC of volume fraction
0.5%. The 28 days strength of 0.5% volume fraction of HSFRC was 7%
greater than that of CSFRC of same volume fraction. In all the SFRC
cylinders, the specimen was not broken into two as that of control
concrete. The comparison of tensile strength of ordinary concrete and
fibre reinforced concrete and the results are tabulated in Table 5.2 and bar
chart is plotted in Figure 5.2.
79
5.2.3 Flexure Strength
The flexure strength was found to decrease marginally. The failure was
brittle in case of plain concrete and failure was ductile in case of steel
fibre reinforced concrete. When the ultimate load was reached the
concrete matrix failed, the first crack appeared on the beam. In all the
SFRC beams the failure was only by pullout of fibres at the maximum
deflection and not by tearing of fibres. In all the specimens (with and
without steel fibre) the failure was between the mid-third points. The
results are tabulated in table 5.3 and bar chart is plotted in Figure 5.3.
5.2.4 Toughness Indices
The addition of steel fibre resulted in a consistent increase in ductility of
the beams. The toughness index for all the control beams was found to
be 1. For all the SFRC beams the I5 and I10 values are greater than 2.75
and 4 respectively.
The toughness indices I5 and I10 for 1.0% volume fraction of HSFRC
is 13% and 27% more than that of 0.5% volume fraction of HSFRC.
The toughness indices I5 and I10 for 1.0% volume fraction of CSFRC
is 13% and 30% more than that of 0.5% volume fraction of CSFRC.
The toughness indices I5 and I10 for 0.5% volume fraction of HSFRC
is 18% more than that of 0.5% volume fraction of CSFRC.
For 1% volume fraction there is only a marginal difference between the
two types of fibres. The toughness indices were calculated for all the
specimens and are tabulated in Table 5.4.
80
5.2.5 Stiffness
The stiffness for control beam was found as 28.46Nm. The stiffness for
0.5% volume fraction of HSFRC was reduced by 9% and for 1% volume
fraction of HSFRC; it was increased by 13.4%.
For CSFRC the stiffness was same for both 0.5% and 1% volume
fraction; it was reduced by 14%
The stiffness for 1.0% volume fraction HSFRC was 24% morethan that of
0.5% volume fraction of HSFRC. The stiffness values are tabulated in
Table 5.5
5.2.5 Energy absorption
The maximum load and energy absorbed are tabulated in table 5.6 and
5.7.The peak load obtained with steel fibre reinforced concrete was found
to increase more than 2 times when compared to control (plain) concrete
of same thickness.
50mm panels:
For HSFRC with 0.5% and 1% volume fraction the energy absorbed was
27.5 and 32.4 times that of control concrete.
For CSFRC with 0.5% and 1% volume fraction the energy absorbed was
19.4 and 32.8 times that of control concrete.
The energy absorbed by 0.5% volume fraction of HSFRC was 42% more
than that of 0.5% volume fraction of CSFRC.
The energy absorbed by 1% volume fraction of HSFRC and CSFRC was
almost equal.
The energy absorbed for 1% volume fraction of HSFRC was 17% more
than that of 0.5% volume fraction of HSFRC.
The energy absorbed for 1% volume fraction of CSFRC was 69% more
than that of 0.5% volume fraction of CSFRC.
81
100mm panels:
For HSFRC with 0.5% and 1% volume fraction the energy absorbed
was 18.6 and 15.6 times that of control concrete.
For CSFRC with 0.5% and 1% volume fraction the energy absorbed
was 10.5 and 13.7 times that of control concrete.
The energy absorbed by 0.5% volume fraction of HSFRC was 73%
more than that of 0.5% volume fraction of CSFRC.
The energy absorbed by 1.0% volume fraction of HSFRC was 7.7%
more than that of 1.05% volume fraction of CSFRC
The energy absorbed for 0.5% volume fraction of HSFRC was 20%
more than that of 1.0% volume fraction of HSFRC.
The energy absorbed for 1% volume fraction of CSFRC was 33% more
than that of 0.5% volume fraction of CSFRC.
5.2.6 Ductility Index
The failure of the control panels was brittle and all the panels failed at
deflection of about 3 mm. In 100mm thick panels with corrugated
fibres all the panels failed at a deflection of about 15mm.The ductility
index was calculated for all panels and the results are tabulated in
Table 5.8. The ductility index for control concrete was found to be
1.00. The ductility index for all SFRC panels was found to vary
between 4-5 for all 50mm thick panels and 2-3 for 100mm panels.
82
5.2.7 Secant stiffness
Secant stiffness for all panels was found at first crack load, ultimate load
and 0.5% ultimate load. Secant stiffness results are tabulated in
Table 5.9.
50mm panels:
Secant stiffness for 1% volume fraction of CSFRC was increased by 27%
when compared to control panel. For all other SFRC panels the stiffness
was decreased about 13%
100mm panels:
For 0.5% volume fraction of HSFRC, the secant stiffness was reduced by
1% and for1% volume fraction of HSFRC it was increased by 1%. For
0.5% and 1% volume fraction of CSFRC the secant stiffness was
increased by 35% and 42% respectively.
83
CHAPTER 6
CONCLUSIONS AND SUGGESTIONS FOR FUTURE WORK
84
CHAPTER 6
CONCLUSIONS AND SUGGESTIONS
6.1 CONCLUSIONS
The following results are inferred based on the experimental results
discussed on the previous chapters.
1. Addition of steel fibres to concrete increases the compressive
strength of concrete marginally.
2. The addition of steel fibres increases the tensile strength.
The tensile strength was found to be maximum with volume
fraction of 1%.
3. By the addition of steel fibres the flexure strength was found to
decrease marginally.
4. The addition of fibres to concrete significantly increases its
toughness and makes the concrete more ductile as observed by the
modes of failure of specimens.
5. The stiffness of beams was studied and was found to be maximum
for hooked end fibre with 1% volume fraction.
6. The empirical equations developed in this experiment can be used
for calculating the toughness indices or percentage of fibre
whichever is required.
85
7. The ductility of steel fibre reinforced concrete was found to
increase with increase in volume fraction of fibres and the
maximum increase was observed for hooked fibres with 1%
volume fraction.
8. The improvement in the energy absorption capacity of steel fibre
reinforced concrete panels with increasing percentage of steel fibre
was clearly shown by the results of the static load test on panels.
9. The 100mm thick panel absorbed the maximum energy of 1010Nm
with Hooked end steel fibre with volume fraction 0.5% for a
deflection of 20mm.
10. Secant stiffness was found to be maximum for corrugated fibre
with volume fraction 1%.
6.2 SUGGESTIONSFOR FUTURE WORK
1. The aspect ratio and types of fibres can be varied and studied.
2. Admixture can be added and the properties can be studied.
3. Reinforced concrete specimens can be tested along with fibres of
various proportions.
4. Stress-strain curve can be plotted and their behaviour can be
studied.
5. The crack pattern can be studied using fracture mechanics.
86
CHAPTER 7
REFERENCES
87
CHAPTER 7
REFERENCES
1. ASTM C-1018 (1997) “Standard Specification for flexural toughness and first
crack strength of fibre reinforced concrete & shotcrete” American society for
testing and materials
2. ASTM C1116 (1997) “Standard Specification for fibre reinforced concrete &
shotcrete” American society for testing and materials
3. ASTM C78-97 (1997) “Standard Specification for flexural strength of
concrete” (Using simple beam with third point loading) American society for
testing and materials
4. ASTM A820-97 (1997) “Standard Specification for steel fibres for reinforced
concrete” American society for testing and materials
5. ACI 506.1R.84 (1984) “State of the art report on fibre reinforced shotcrete”
ACI committee report, American Concrete Institute
6. ACI Committee 544 (1984) "Guide For Specifying, Mixing, Placing, and
Finishing Steel Fibre Reinforced Concrete", American Concrete Institute.
7. “Measurement of Fibre Reinforced Concrete,” ACI Committee 544, American
Concrete Institute Materials Journal, Vol. 85, No. 6, pp. 583-593, American
Concrete Institute 1988.
8. I.S: 10262-1982 “Indian code for recommended guidelines for concrete mix
design”.
88
9. I.S 456-2000 “Indian code of practice for plain and reinforced concrete
(Fourth Revision)”.
10. I.S 516-1959 “Indian code for method of tests for concrete”.
11. Bayasi, Z. Bhatacharya, R. and Posey, M. (1989) "Fibre Reinforced Concrete:
Basics and Advancements," Proceedings, Symposium on Advancements in
Concrete Materials, Bradley University, pp. 1-1 to 1-27.
12. Bayasi, Z. and Kaiser, H. (April 2001) "Steel Fibres as Crack Arrestors in
Concrete." The Indian Concrete Journal.
13. Craig, R., S. Mahadev, C.C. Patel, M. Viteri, and C. Kertesz. "Behaviour of
Joints Using Reinforced Fibrous Concrete." Fibre Reinforced Concrete
International Symposium, SP-81, American Concrete Institute, Detroit, 1984,
pp. 125-167.
14. Craig, R. McConnell, J. Germann, N. Dib, and Kashani, F. (1984) "Behaviour
of Reinforced Fibrous Concrete Columns." Fibre Reinforced Concrete
International Symposium, SP-81, American Concrete Institute, Detroit,
pp. 69-105.
15. Gopalakrishnan, S. Krishnamoorthy, T.S. Bharatkumar,B.H. and
Balasubramanian, K.(December 2003) “Performance Evaluation of Steel Fibre
Reinforced Shotcrete” National seminar on advances in concrete technology
and concrete structures for the future, Annamalai University
16. Henager, C.H. (1977) "Steel Fibrous, Ductile Concrete Joint for Seismic
Resistant Structures." Reinforced Concrete Structures in Seismic Zones, SP
53-14, American Concrete Institute, Detroit, pp. 371-386.
17. Jindal, R. and Hassan, K. (1982) "Behaviour of Steel Fibre Reinforced
Concrete Beam-Column Connections." Fibre Reinforced International
Symposium, SP-81, American Concrete Institute, Detroit, pp. 107-123.
89
18. Johnston, C. (1994) "Fibre Reinforced Concrete." Significance of Tests and
Properties of Concrete and Concrete-Making Material, ASTM STP 169C,
pp. 547-561.
19. Kaushik S.K., Gupta.V.K., and Tarafdar.N.K., (1987) “Behaviour of fibre
reinforced concrete in shear” proceedings of the international symposium on
Fibre Reinforced Concrete International Symposium, volume I, chapter II,
pp 1.133-1.149
20. Krishnamoorthy, T.S. Bharatkumar, B.H. Balasubramanian, K. and
Gopalakrishnan, S. (February 2000) “Investigation on durability
characteristics of SFRC” Indian Concrete Journal page 94-98
21. Lakshmipathy, M. and Santhakumar, A. (July 1986) "Experimental
Verification of the Behaviour of Reinforced Fibrous Concrete Frames
Subjected to Seismic Type of Loading." Third International Symposium on
Developments in Fibre Reinforced Cement and Concrete, Rilem.
22. Marc vandevalle, N.V. and Ganesh, P. (March 2003) Fibres in Concrete
Indian Concrete Journal, pp 939-940
23. Marc vandevalle, N.V. (1998) “Tunnelling the world” Dramix reference
manual
24. Parameswaran, V.S. (October 1996) “Research and applications of FRC in
Indian scenario” Indian concrete journal, , pp.553-557
25. Sivarama Sarma, B. (1997) , “Investigations on laced reinforced concrete
beams with normal and fibre reinforced concrete under monolithic and cyclic
loading” Ph.D Thesis, IIT, Madras.
90
26. Shetty, M.S. (2005), “Concrete Technology theory and practice”, (First
edition-1982) S.Chand and Company, New Delhi.
27. Soroushian, P. and Bayasi, Z. (December 1991) "Strength and Ductility of
Steel Fibre Reinforced Concrete under Bearing Pressure." Magazine of
Concrete Research, pp.243-248.
28. P.Srinivasalu, N.Lakshmanan, K.Muthumani, B.Sivarama Sarma (1987)
“Dynamic behaviour of fibre reinforced concrete” proceedings of the
international symposium on Fibre Reinforced Concrete International
Symposium, volume I, chapter II, pp 2.85
29. Swamy, R.N. (October 1996) “Fibre reinforced concrete: Prospect and
challenges, Indian Concrete Journal, pp 517-517
30. Taylor, M.R. Laydon, F.D. and Barr, B.I.G. (October 1996) “Toughness
characteristics of fibre reinforced concrete”, Indian Concrete Journal
pp.525-531