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 1
To our beloved parents
2
ACKNOWLEDGEMENT
3
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 Kumaran, 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.
4
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
5
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 HINDUSTAN COLLEGE OF ENGINEERING CHENNAI-603103
EDRC LARSEN & TOUBRO LIMITED 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
8
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
9
6.
7.
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
CONCLUSION AND SUGGESTIONS
61
6.1 CONCLUSION
61
6.2 SUGGESTIONSFOR FUTURE WORK
62
REFERENCES
64
10
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
11
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
12
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
13
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
14
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
15
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
16
CHAPTER 1
INTRODUCTION
17
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. 18
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 quasistatically 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. 19
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 (V f). 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.
20
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.
21
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.
22
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 postcracking 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%.
23
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 Vf 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.
24
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.
25
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
26
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.
27
CHAPTER 2
OBJECT IVE OF THE EXPERIMENT
28
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.
29
CHAPTER 3
LITERATURE REVIEW
30
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.
31
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.
32
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
compression and tension remain relatively constant. 33
strengths in
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.
34
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 (31mm), 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. 35
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.
36
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.
37
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.
38
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%.
39
CHAPTER 4
EXPERIMENTAL INVESTIGATIONS
40
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.
41
EXPERIMENT ON SFRC
HOOKED, DRAMMIX FIBRES (HSFRC)
0% Vf SFRC
9 CUBES, 9 CYLINDERS, 3 BEAMS
3 50MM PANELS
CORRUGATED, STEWOLS FIBRES (CSFRC)
1.0% Vf SFRC
0.5% Vf SFRC
PANELS
9 CUBES, 9 CYLINDERS, 3 BEAMS
3 100MM PANELS
PANELS
3 50MM PANELS
9 CUBES, 9 CYLINDERS, 3 BEAMS
3 100MM PANELS
3 50MM PANELS
Figure 4.1 Schematic representation of the experimental work 42
PANELS
3 100MM PANELS
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 43
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.
44
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
45
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 loaddeflection 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.
46
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.
47
LVDT
BOTTOM SUPPORT PLATE
Figure 4.5 Features of panel test setup
48
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
49
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.
50
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
51
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.
100mm Panel
50mm Panel
Figure 4.7 Wooden moulds for panels
52
Figure 4.8 Casting of panel
53
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.
54
CHAPTER 5
DISCUSSIONS OF TEST RESULTS
55
CHAPTER 5
RESULTS AND DISCUSSIONS
5.1 RESULTS Table 5.1 COMPRESSIVE STRENGTH
Specimen Type
Average Compressive strength in N/mm2 3days 7 days 28 days
25.27
39.59
59.89
24.50
37.29
58.24
27.38
39.76
58.43
HSFRC 1.0%
26.32
38.04
59.01
CSFRC
40.35
32.17
60.00
PCC
HSFRC 0.5
CSFRC 0.5
1.0
56
Table 5.2 TENSILE STRENGTH
Specimen Type
P.C.C
HSFRC 0.5
Average Tensile Strength in N/mm2 3 days 7 days 28 days 2.55
3.54
4.81
2.90
4.76
5.19
3.40
5.02
4.83
4.01
5.66
6.37
3.82
5.29
6.27
CSFRC 0.5
HSFRC 1.0
CSFRC 1.0
57
Figure 5.1 BAR CHART FOR COMPRESSIVE STRENGTH
COMPRESSIVE STRENGTH N/mm2
70 60 PCC 50 40
HSFRC 0.5%
30
CSFRC 0.5%
20
HSFRC 1.0%
10
CSFRC 1.0%
0 3days
7days
28days
Figure 5.2 BAR CHART FOR SPLIT TENSILE STRENGTH
SPLIT TENSILE STRENGTH N/mm2
7 PCC
6 5
HSFRC 0.5%
4
CSFRC 0.5%
3
HSFRC 1.0%
2 1
CSFRC 1.0%
0 3days
7days 58
28days
TABLE 5.3 FLEXURAL STRENGTH First Specimen
crack
28 days flexural
Average flexural
Type
load in
In N/mm2
strength in N/mm2
kN B-a
34.00
6.04
B-b
28.50
5.06
B-c
30.00
5.33
BHF-0.5-a
28.50
4.59
BHF-0.5-b
27.00
4.80
BHF-0.5-c
25.50
4.53
BHF-1.0-a
33.75
6.00
BHF-1.0-b
32.00
5.68
BHF-1.0-c
32.00
5.69
BCF-0.5-a
26.00
4.62
BCF-0.5-b
27.00
4.80
BCF-0.5-c
27.00
4.80
BCF-1.0-a
26.50
4.71
BCF-1.0-b
27.00
4.80
BCF-1.0-c
29.00
5.16
59
5.48
4.64
5.79
4.74
4.91
Figure 5.3 BAR CHART FOR FLEXURAL STRENGTH 6
5
FLEXURAL STRENGTH N/mm2
PCC
HSFRC 0.5%
4
CSFRC 0.5% 3
HSFRC 1.0% CSFRC 1.0%
2
1
0 28 DAYS
60
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
61
FOR I10 y = 3.68x + 1.9667
FOR I5 y = 0.7533x + 2.4
Toughness Indices
10 I5
8
I10
6 Expon. (I5) Expon. (I10)
4 2 0 0
0.25
0.5
0.75
1
1.25
1.5
Percentage of Fibre
1.75
2
2.25
Figure 5.4 Empirical Equations for CSFRC
FOR I10 y = 2.14x + 3.7733
FOR I5 y = 1.2533x + 2.6667
Toughness Indices
10 I5
8
I10
6
Expon . (I5) Expon . (I10)
4 2 0 0
0.25 0.5
0.75 1 1.25 1.5 Percentage of fibre
1.75
2
2.25
Figure 5.5 Empirical Equations for HSFRC
62
Table 5.5 STIFFNESS FOR BEAMS Specimen
Load
Deflection
Stiffness
Average Stiffness
ID
in
in
in
in
kN
mm
kN/mm
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
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
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
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
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
63
26.24
25.86
32.27
24.47
24.33
Table 5.6 ENERGY ABSORBED BY CONTROL PANELS
Maximum
Experimental
Energy
Deflection in
Peak load in
Absorbed in
mm
kN
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
Specimen ID
64
Table 5.7 ENERGY ABSORBED BY SFRC PANELS
First crack load
Experimental
Energy absorbed
in kN
Peak load in
for 20mm
kN
deflection in Nm
10.56
25.91
288.50
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 P1CF0.5-b
8.75
13.23
164.50
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 P1CF1.0-b
11.15
31.14
361.50
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
Specimen ID P1HF0.5-a P1HF0.5-b
65
Energy absorption in Nm
350 PCC
300
HSFRC 0.5 CSFRC 0.5 HSFRC 1.0 CSFRC 1.0
250 200 150 100 50 0 0
5
10
15
20
25
Deflection in mm
Figure 5.6 Energy absorption for 50mm panels
Energy absorbtion in Nm
1200 1000 PCC
800
HSFRC 0.5 CSFRC 0.5 HSFRC 1.0 CSFRC 1.0
600 400 200 0 0
5
10 15 Deflection in mm
Figure 5.7 Energy absorption for 100mm panels
66
20
25
Table 5.8 DUCTILITY INDEX FOR PANELS Specimen ID
First Crack Deflection in mm
Deflection upto 0.15% ultimate load drop in mm
P1-a P1-b P1-c P2-a P2-b P2-c P1HF0.5-a P1HF0.5-b P1HF0.5-c P2HF0.5-a P2HF0.5-b P2HF0.5-c P1HF1.0-a P1HF1.0-b P1HF1.0-c P2HF1.0-a P2HF1.0-b P2HF1.0-c P1CF0.5-a P1CF0.5-b P1CF0.5-c P2CF0.5-a P2CF0.5-b P2CF0.5-c
1.56 2.31 1.51 2.88 3.06 3.33 2.28 2.22 2.8 3.67 3.32 4.43 2.12 2.28 2.34 3.42 3.97 3.41 2.18 2.47 2.87 2.13 2.65 2.94 1.84 2.06 1.94 2.60 2.73 3.84
1.56 2.31 1.51 2.88 3.06 3.33 10.75 12.10 13.00 11.50 8.60 11.00 10.15 11.10 10.00 7.10 10.00 9.50 9.00 6.60 10.1 6.75 5.10 6.80 9.10 9.00 10.75 8.10 8.20 8.15
P1CF1.0-a P1CF1.0-b P1CF1.0-c P2CF1.0-a P2CF1.0-b P2CF1.0-c
67
Ductility Index
1.00 1.00 1.00 1.00 1.00 1.00 4.72 5.45 4.64 3.73 2.56 2.46 4.77 7.87 4.27 2.08 2.52 2.77 3.26 4.47 4.04 3.17 1.93 2.31 4.95 4.37 5.54 3.12 3.00 2.87
Average Ductility Index
1.00
1.00
4.94
2.72
4.64
2.46
3.92
2.47
4.95
3.00
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 0.5% Hooked fibre 100mm 1.0% Hooked fibre 50mm 1.0% Hooked fibre 100mm 0.5% Corrugated fibre 50mm 0.5% Corrugated fibre 100mm 1.0% Corrugated fibre 50mm 1.0% Corrugated fibre 100mm
4.17
2.34
0.65
11.85
12.17
2.81
4.39
2.92
0.58
12.52
15.38
3.72
4.62
3.39
0.68
16.01
16.11
4.29
6.14
3.37
0.78
17.01
15.61
3.39
68
3,000 PCC
L o a d in kg f
2,500
HSFRC
2,000
CSFRC
1,500 1,000 500 0 0
1
2
3 4 Deflection in mm
5
6
7
8
Figure 5.8 Load Vs Deflection for beams (0.5%) 3,500 PCC
3,000
HSFRC
Load in kgf
2,500
CSFRC
2,000 1,500 1,000 500 0 0
1
2
3 4 5 Deflection in mm
Figure 5.9 Load Vs Deflection for beams (1.0%)
69
6
7
8
3,500
PCC 3,000
HSFRC 0.5 CSFRC 0.5
2,500
HSFRC 1.0 Load in kgf
2,000
CSFRC 1.0 1,500
1,000
500
0 0
1
2
3
4
5
De fle ction i n mm
Figure 5.10 Load Vs Deflection for beams (Both 1.0% & 0.5%)
70
6
7
8
Figure 5.11 Load Vs Deflection for 50mm panel (0.5%)
3500 3000 PCC 2500 L o a d in kg f
HSFRC
2000
CSFRC
1500 1000 500 0 0
1 2 3
4 5 6
7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Deflection in mm
Figure 5.12 Load Vs Deflection for 50mm panel (1.0%)
71
3500 PCC
3000
HSFRC 0.5 CSFRC 0.5
2500 Load in kgf
HSFRC 1.0
2000
CSFRC 1.0
1500 1000 500 0 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
Figure 5.13 Load Vs Deflection for 50mm panel (Both 1.0% & 0.5%)
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9,000 8,000 PCC 7,000
HSFRC
L oa d in kg f
6,000
CSFRC
5,000 4,000 3,000 2,000 1,000 0 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
Figure 5.14 Load Vs Deflection for 100mm panel (0.5%)
12000 PCC
L oad in kg f
10000
HSFRC CSFRC
8000 6000 4000 2000 0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Deflection in mm Figure 5.15 Load Vs Deflection for 100mm panel (1.0%)
73
12000 PCC
Load in kgf
10000
HSFRC 1.0 CSFRC 1.0
8000
HSFRC 0.5 CSFRC 0.5
6000 4000 2000 0
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 Figure 5.16 Load Vs Deflection for 100mm panel (Both 1.0% & 0.5%)
74
Figure 5.17 Crack propagation of SFRC in beam
75
Figure 5.18 Panel failure in static load
Figure 5.19 First crack in panel
Figure 5.20 Fibre pull-out in panel 76
PCC
CSFRC 0.5
CSFRC 1.0
HSFRC 0.5
HSFRC 1.0
Figure 5.21 Failure pattern in 50mm panels
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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 than that of 0.5% volume fraction of CSFRC. 80
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.
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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.
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CHAPTER 6
CONCLUSIONS AND SUGGESTIONS FOR FUTURE WORK
83
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. 84
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.
85
CHAPTER 7
REFERENCES
86
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.
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8. I.S: 10262-1982 “Indian code for recommended guidelines for concrete mix design”.
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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”.
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Krishnamoorthy,
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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
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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. 88
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
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T.S. S.
Bharatkumar, (February
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Balasubramanian,
“Investigation
on
K.
and
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.
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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
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