Experimental Study on the Behaviour of Steel Fibre Reinforced Concrete

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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

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To our beloved parents

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ACKNOWLEDGEMENT

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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.

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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

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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.

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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

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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

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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

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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

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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

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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

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Figure 5.11 Load Vs Deflection for 50mm panel (0.5%) 50


Figure 5.13 Load Vs Deflection for 50mm panel (Both 1.0% & 0.5%) 51



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

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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

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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

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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










19 50mm Corrugated 0.5 P1CF0.5-a

20 50mm Corrugated 0.5 P1CF0.5-b

21 50mm Corrugated 0.5 P1CF0.5-c










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CHAPTER 1

INTRODUCTION

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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.

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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.

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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.

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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.

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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.

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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%.

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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.

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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.

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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

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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.

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CHAPTER 2

OBJECT IVE OF THE EXPERIMENT

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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.

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CHAPTER 3

LITERATURE REVIEW

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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.

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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.

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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.

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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.

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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,


PANELS

9 CUBES,


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


11.85 12.17 2.81


4.39 2.92 0.58


12.52 15.38 3.72

0.5% Corrugated fibre 50mm

4.62 3.39 0.68


16.01 16.11 4.29


6.14 3.37 0.78


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


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


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


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.

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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.

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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


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


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.

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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

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88

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Experimental Study on the Behaviour of Steel Fibre Reinforced Concrete

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