NATIONAL INSTITUTE OF TECHNOLOGY

JAMSHEDPUR

A Project Report on

“EXPERIMENTAL STUDY ON BEHAVIOR OF STEEL FIBRE REINFORCED COCRETE”

Presented in partial fulfilment of the award of the degree of bachelor of technology (HONS.)

VIII Semester

In

CIVIL ENGINEERING

N.I.T. JAMSHEDPUR

By

Farah Nawaz (138/08) Gyan Prakash Anand (150/08)

Niraj Kumar (215/08) Krishna Murari Pappu (173/08)

Rishi Raj (315/08) Satyendra Kumar Singh (340/08)

Under the esteemed guidance of

Prof. S.R. Pandey

DEPARTMENT OF CIVIL ENGINEERING

APRIL 2012

NATIONAL INSTITUTE OF TECHNOLOGY JAMSHEDPUR

CANDIDATE’S DECLARATION

We hereby certify that the work which is being presented in the Project Work entitled

“Experimental Study on the behavior of Steel Fibre Reinforced Concrete” and submitted

in the Department of Civil Engineering, National Institute of Technology, Jamshedpur is an

authentic record of our own work carried out during 7th and 8th Semesters under the

supervision of Dr. S.R. Pandey, Professor, Department of Civil Engineering, National

Institute of Technology, Jamshedpur.

The matter presented in this Project Work has not been submitted by us for the award of

any other degree of this or any other Institute.

Farah Nawaz (138/08) Gyan Prakash Anand (150/08) Krishna Murari Pappu (173/08) Niraj Kumar (215/08) Rishi Raj (315/08) Satyendra Kumar Singh (340/08)

This is to certify that the above statement made by the candidate is correct to the best of

our knowledge.

(Dr. S.R. Pandey) Supervisor Date: April 18, 2012

The Viva-Voce Examination, has been held on April 18, 2012.

Signature of Examiners

I

CERTIFICATE

NATIONAL INSTITUTE OF TECHNOLOGY

JAMSHEDPUR

REF. NO. …………………. DATE……………………

This is to certify that

Mr. Farah Nawaz (138/08)

Mr. Gyan Prakash Anand (150/08)

Mr. Krishna Murari Pappu (173/08)

Mr. Niraj Kumar (215/08)

Mr. Rishi Raj (315/08)

Mr. Satyendra Kumar Singh (340/08)

Are final year students of Civil Engineering of National Institute of Technology, Jamshedpur have done a bonafide work on a project entitled “EXPERIMENTAL STUDY ON THE BEHAVIOR OF STEEL FIBRE REINFORCED CONCRETE” under my guidance and supervision in partial fulfillment for the award of the degree Bachelor of Technology (HONS.) in Civil Engineering at NIT, Jamshedpur. To the best of my knowledge and belief the same project has not been submitted to any university or institute for award of any degree.

Dr. S.R. Pandey

Professor

Department of Civil Engineering

NIT Jamshedpur.

II

ACKNOWLEDGEMENT

We are extremely thankful and indebted to Dr. S.R. Pandey, Professor, National Institute of Technology, Jamshedpur, for his constant support and encouragement throughout our project which would have been impossible without his help and guidance. He had taken pain inspite of his hectic schedule equipping us with mammoth information in terms of manuals, journals, handbooks and books etc.

The direct and indirect assistance received from the staffs of various laboratories in the Civil Engineering Department, National Institute of Technology, Jamshedpur, is also acknowledged.

Lastly we thank all those who helped us directly or indirectly to complete this project.

Farah Nawaz (138/08)

Gyan Prakash Anand (150/08)

Krishna Murari Pappu (173/08)

Niraj Kumar (215/08)

Rishi Raj (315/08)

Satyendra Kumar Singh (340/08)

PLACE: JAMSHEDPUR

DATE:

III

List of Figures: Page No.

Figure 1.1 Time Line of SFRC test and design methods 3

Figure 1.2 General view of polypropylene fibre 4

Figure 1.3 General view of glass fiber 4

Figure 1.4 Natural Fibres 5

Figure 1.5 Steel Fibres used in the Project 6

Figure 1.6 Fibre Mechanism 12

Figure 1.7 Fibre Pull Out 13

Figure 4.1 Mixing of concrete 29

Figure 4.2 An assembly for proper curing of test cubes at specified temperature to determine its 7-day and 28-day strengths 30

Figure4.3 Compression Testing Machine 31

Figure 4.4 Split Tensile Strength Testing 32

Figure 4.5 Flexural Strength Testing Machine 33

Figure4.6 Testing of Beam specimen 34

Figure 4.7 Steel Fibres used in experiment 37

Figure 4.8 Failure characteristics of cube specimen 39

Figure 4.9 Failure characteristics of cube specimen 40

Figure 4.10 Failure characteristics of cube specimen 41

Figure 5.1 Line Chart for 7-days compressive strength 43

Figure 5.2 Line Chart for 28-days compressive strength 44

Figure 5.3 Line Chart for 7-days tensile strength 45

Figure 5.4 Line Chart for 28-days compressive strength 46

Figure 5.5 Line Chart for 28-days flexural strength 47

IV

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

Tms Target Mean Strength

f ck 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

V

TABLE OF CONTENTS

CHAPTER NO: TITLE PAGE NO

DECLARATION I

CERTIFICATE II

ACKNOWLEDGEMENT III

LIST OF FIGURES IV

LIST OF SYMBOLS V

1. INTRODUCTION 1

1.1 General 1

1.2 History of fibre reinforced concrete 2

1.3 Types of fibre used in fibre reinforced concrete 3

1.4 Steel Fibre Reinforced Concrete 6

1.5 Conventional Reinforced Concrete 10

1.6 Fibre Reinforced Concrete 11

1.7 Manufacturing Methods 11

1.8 Fibre Mechanism 12

1.9 Fibre-Matrix Interaction 12

1.10 Bridging Action 13

1.11 Workability 13

1.12 FEATURES AND BENEFITS OF SFRC 14

1.13 APPLICATIONS OF SFRC 15

1.14 USAGE OF SFRC IN INDIAN PROJECTS 15

2. LITERATURE REVIEW 16

2.1 Historical Background 16

2.2 Indian Scenario 16

2.3 Toughness 17

2.4 Durablity 17

2.5 Seismic Resistance 18

2.6 Shear Resistance 19

2.7 Dynamic Resistance 19

2.8 Bar Confinement 20

2.9 Bond Improvement 20

3. MIX DESIGN 21

3.1 Experimental Test Observation Table 22

3.2 Various Methods of Mix Design Proportioning 24

3.3 CONCRETE MIX DESIGN BY INDIAN STANDARD METHOD 25

4. EXPERIMENTAL PROGRAM 29

4.1 Specimen Preparation 29

4.2 Experimental Set up 30

4.2.1 Compressive Strength Test 30

4.2.2 Split Tensile Test 32

4.2.3 Flexural Strength Test 33

4.3 Materials Used In Experiment 35

4.3.1 Cement 35

4.3.2 Aggregate 35

4.3.2.1 Fine Aggregate 36

4.3.2.2 Coarse Aggregate 36

4.3.3 Water 37

4.3.4 Steel Fibres 37

4.4 Casting Of Specimen 38

4.5 Curing Of Specimen 38

4.6 EXPERIMENTAL BEHAVIOR 39

5.RESULT ANALYSIS AND CONCLUSION 42

5.1 Suggestion for future Work 53

6.REFERENCES 54

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CHAPTER 1

INTRODUCTION

1.1 General

Fibre-reinforced concrete (FRC) is concrete containing fibrous material which increases its structural integrity. It contains short discrete fibres that are uniformly distributed and randomly oriented. Fibres include steel fibres, glass fibres, synthetic fibres and natural fibres. Within these different fibres that character of fibres-reinforced concrete changes with varying concretes, fibre materials, geometries, distribution, orientation and densities. Fibre–reinforced concrete is becoming an increasingly popular construction material due to its improved mechanical properties over unreinforced concrete and its ability to enhance the mechanical performance of conventionally reinforced concrete. Though much research has been performed to identify, investigate, and understand the mechanical traits of fiber–reinforced concrete, relatively little research has concentrated on the transport properties of this material. Material transport properties, especially permeability, affect the durability and integrity of a structure. High permeability, due to porosity or cracking, provides an ingress for water, chlorides, and other corrosive agents. If such agents reach reinforcing bars within the structure, the bars corrode, thus compromising the ability of the structure to withstand loads, which eventually leads to structural failure.

Fibre reinforced concrete (FRC) may be defined as a composite materials made with Portland cement, aggregate, and incorporating discrete discontinuous fibres. Now, why would we wish to add such fibres to concrete? Plain, unreinforced concrete is a brittle material, with a low tensile strength and a low strain capcity. The role of randomly distributes discontinuous fibres is to bridge across the cracks that develop provides some post-cracking “ductility”. If the fibres are sufficiently strong, sufficiently bonded to material, and permit the FRC to carry significant stresses over a relatively large strain capacity in the post-cracking stage.

There are, of course, other (and probably cheaper) ways of increasing the strength of concrete. The real contribution of the fibres is to increase the toughness of the concrete (defined as some function of the area under the load vs. deflection curve), under any type of loading. Thatis, the fibres tend to increase the strain at peak load, and provide a great deal of energy absorption in post-peak portion of the load vs. deflection curve.

When the fibre reinforcement is in the form of short discrete fibres, they act effectively as rigid inclusions in the concrete matrix. Physically, they have thus the same order of magnitude as aggregate inclusions; steel fibre reinforcement cannot therefore

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be regarded as a direct replacement of longitudinal reinforcement in reinforced and prestressed structural members. However, because of the inherent material properties of fibre concrete, the presence of fibres in the body of the concrete or the provision of a tensile skin of fibre concrete can be expected to improve the resistance of conventionally reinforced structural members to cracking, deflection and other serviceability conditions.

The fibre reinforcement may be used in the form of three - dimensionally randomly distributed fibres throughout the structural member when the added advantages of the fibre to shear resistance and crack control can be further utilised . On the other hand, the fibre concrete may also be used as a tensile skin to cover the steel reinforcement when a more efficient two - dimensional orientation of the fibres could be obtained

Building codes require that cracks exposed to weathering be no larger than specified widths in order to assure mechanical structural integrity. However, if cracks of this size significantly increase permeability and allow corrosive agents to reach steel reinforcement, the cracks are clearly too large and the codes should be revised. Knowledge pertaining to permeability can help determine the maximum allowable size of exposed cracks in structures.

In addition, if concrete casings are uses as shielding containers for pollutants and toxic wastes, permeability is of utmost importance in order to assure that no potentially harmful leakage occurs. Because of the important role played by permeability in structural safety, and the increasing use of fibre–reinforced concrete, this paper examines the effects of different fibre volumes (0%,0.5%, and 1%) of steel fibres in fibre–reinforced beam. It was thought that increasing the volume of steel fibres would decrease the permeability of the cracked specimens due to crack stitching by the steel fibres. fibres do not change material porosity.

1.2 History of fibre reinforced concrete

The concept of using fibres as reinforcement is not new. Fibres have been used as reinforcement since ancient times. Historically, horsehair was used in mortar and straw in mud bricks. In the early 1900s, asbestos fibres were used in concrete, and in the 1950s the concept of composite materials came into being and fibre-reinforced concrete was one of the topics of interest. There was a need to find a replacement for the asbestos used in concrete and other building materials once the health risks associated with the substance were discovered. By the 1960s, steel, glass (GFRC), and synthetic fibres such as polypropylene fibres were used in concrete, and research into new fibre-reinforced concretes continues today.

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Steel fibre reinforced concrete (SFRC) was introduced commercially into the European market in the second half of the 1970’s. No standards or recommendations were available at that time which was a major obstacle for the acceptance ofthis new technology. Initially steel fibres were mostly used as a substitute for secondary reinforcement or for crack control in less criticalparts of the construction. Today steel fibres are widely used as the main and unique reinforcing fo rindustrial floor slabs, shotcrete and prefabricated concrete products. They are also considered forstructural purposes in reinforcement of slabs on piles, full replacement of the standard reinforcing cage for tunnel segments, concrete cellars, foundation slabs and shear reinforcement in prestressed elements.

Figure 1.1 Time Line of SFRC test and design methods

1.3 Types of fibre used in fibre reinforced concrete:-

There are four types of fibre reinforced concrete

1) Synthetic Fibre Reinforced Concrete 2) Glass Fibre Reinforced Concrete 3) Natural Fibre Reinforced Concrete 4) Steel Fibre Reinforced Concrete

1) Synthetic Fibre Reinforced Concrete

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It is man-made fibres from petrochemical and textile industries. Low-volume percentage (0.1 to 0.3% by volume) and high-volume percentage (0.4 to 0.8% by volume) Types of Synthetic Fibre Reinforced Concrete eg.Acrylic, Aramid, Carbon, Nylon.

Figure 1.2 General view of polypropylene fibre

2) Glass Fibre Reinforced Concrete Mixed by Portland cement, fine aggregates, water and alkali-resistant glass fibres. High tensile strength (2 – 4 GPa) Elastic modulus (70 – 80 GPa) Brittle stress-strain characteristics (2.5 –4.8% elongation at break) Low creep at room temperature

Figure 1.3 General view of glass fiber 3) Natural Fibre reinforced Concrete

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Obtained at low cost and low levels of energy using local manpower and technology. Unprocessed natural fibres made with unprocessed natural fibres such as coconut coir, sisal, sugarcane bagasse, bamboo, jute, wood and vegetable Processed natural fibres - Wood cellulose is the most frequently used.

Yester

4) Steel fibre

The steel fibre reinforcement not only improves the toughness material, the impact and the fatigue resistance of concrete, but it also increases the material resistance to cracking and, hence to water and chloride ingress with significant improvement in durability of concrete structures. Therefore, the use of SFRC in tunnel structures represents an attractive technical solution with respect to the conventional steel reinforcement, because it reduces both the labour costs (e.g. due to the placement of the conventional steel bars) and the construction costs (e.g. forming and storage of classical reinforcement frames, risks of spalling during transportation and laying). The important properties of steel fibre reinforced concrete (SFRC) is its superior resistance to cracking and crack propagation. As a result of this ability to arrest cracks, fibre composites possess increased extensibility and tensile strength, both at first crack and at ultimate, particular under flexural loading; and the fibres are able to hold the matrix together even after extensive cracking. The net result of all these is to impart to the fibre composite pronounced post – cracking ductility which is unheard of in ordinary concrete. The transformation from a brittle to a ductile type of material would increase substantially the energy absorption characteristics of the fibre composite and its ability to withstand repeatedly applied, shock or impact loading.

Figure 1.4 Natural Fibres

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1.4 Steel Fibre Reinforced Concrete Steel fibre is one of the most commonly used fibres. Generally, round fibres are used. The diameter may vary from 0.25 to 0.75 mm. The steel fibre is likely to get rusted and lose some of its strength. But investigations have shown that the rusting of the fibres takes place only at the surface. Use of steel fibres make significant improvements in flexural, impact and fatigue strength of concrete, it has been extensively used in various types of structures, particularly for overlays of roads, airfield pavements and bridge decks. Thin shells and plates have also been constructed using steel fibres. Types of steel fibres that can be used in SFRC :-

Figure 1.5 Steel Fibres used in the Project

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Comparison of Steel Fibre Reinforced Concrete with Normal Reinforced Concrete

Steel fibre reinforced concrete Normal reinforced concrete

High Durability Lower durability

Protects steel from corrosion Steel potential to corrosion

Lighter materials Heavier materials

More Expensive Economical

With the same of volume ,the Strength is greater

With the Same of volume, the strength is less.

High Workability Less workable

‘Fiber Reinforced Cement’ as a material made from hydraulic cement and

discrete, discontinuous fibres (containing no aggregate). “Fiber reinforced

concrete” (FRC) is made with hydraulic cement, aggregates of various sizes,

in corporating discrete, discontinuous fibers. Both are firmly established as a

new construction material.

Steel fibers and synthetic fibers find applications in civil engineering on a larger

scale by virtue of their inherent advantages; it is of interest to note that the

performance of concrete can be enhanced through the employment of these

micro-reinforcements in a hybrid form. The volume of data available on the

performance studies of hybrid fiber reinforced concrete appears to be

inadequate for a better understanding the investigation, it is proposed to

combine these fibers at different proportions in the beam structural elements

and engineering properties and performance are being investigated.

The necessity for the addition of fibers in structural material is to increase the

strength of the concrete and mortar and also to reduce the crack propagation

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that mainly depends on the following parameters:

• Strength characteristics of fiber

• Bond at fiber matrix interface

• Ductility of fibers

• Volume of fiber reinforcement

• Spacing, dispersion, orientation, shape and aspect ratio of fiber.

High strength fibers, favorable orientation large volume, fiber length and diameter of fiber have been found independently to improve the strength of composites. The steel fiber is known to have possessed high tensile strength and ductility

High strength fibers, favorable orientation large volume, fiber length and diameter of fiber have been found independently to improve the strength of composites. The steel fiber is known to have possessed high tensile strength and ductility.

The most significant factor affecting resistance to crack propagation and strength of the fibrous concrete and mortar are:

• Shape and bond at fiber matrix interface

• Volume fraction of fibers

• Fiber aspect ratio and Orientation of fibers

• Workability and Compaction of Concrete

• Size of Coarse Aggregate

• Mixing.

A) SHAPE AND BOND AT FIBER MATRIX INTERFACE

The modulus of elasticity of matrix must be much lower than that of fiber for efficient stress transfer. Low modulus of fibers such as nylon and polypropylene are therefore unlikely to give strength improvement, but they help in the absorption of large energy and therefore impart greater degree of toughness and resistance to impact.

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High modulus fibers such as steel, glass and carbon impart strength and stiffness to the composite. Interfacial bond between the matrix and the fibers also determine the effectiveness of stress transfer, from the matrix to the fiber.

A good bond is essential for improving tensile strength of the composite. the interfacial bond could be improved by larger area of contact, improving the frictional properties and degree of gripping and treating the steel fibers with sodium hydroxide or acetone.

B) VOLUME FRACTION OF FIBER

The strength of the composite depends largely on the quantity of fibers used in it. The increase in the volume of fibers, increase approximately linearly, the tensile strength and toughness of the composite. Use of higher percentage of fiber is likely to cause segregation and hardness of concrete and mortar.

C) FIBER ASPECT RATIO

Fiber aspect ratio is defined as the ratio of fiber length to the equivalent fiber diameter. In order to utilize fracture strength of fibers fully, adequate bond between the matrix and the fiber has to be developed. This depends on the shape of the fibers viz., straight, crimped, hooked end and its aspect ratio. An aspect ratio 60 to 100 is commonly used.

D) ORIENTATION OF FIBERS

One of the differences between conventional reinforcement and fiber reinforcement is that in conventional reinforcement, bars are oriented in the direction desired while fibers are randomly oriented. It was observed that in fiber reinforced mortar ,the fibers aligned parallel to the applied load offered more tensile strength and toughness than randomly distributed or perpendicular.

E) WORKABILITY AND COMPACTION OF CONCRETE

Incorporation of steel fiber decreases the workability considerably and even prolonged external vibration fails to compact the concrete. This situation adversely affects the consolidation of fresh mix. The fiber volume at which this situation is reached depends on the length and diameter of the fiber and non-uniform distribution of the fibers. Generally, the workability and compaction standard of the mix are improved through increased water/cement ratio or by the use of water reducing admixtures. The overall workability of fresh fibrous mixes was found to be largely independent of the fiber type.

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Crimped fibers produce slightly higher slumps, and hooked fibers were found to be more effective than straight and crimped ones.

F) SIZE OF COARSE AGGREGATE

Several investigators recommended that the maximum size of the coarse aggregate should be restricted to 10mm, to avoid appreciable reduction in strength of the composite. A fiber in effect, as aggregate having a simple geometry, their influence on the properties of fresh concrete is complex. The inter-particle friction between fibers and between fibers and aggregates controls the orientation and distribution of the fibers and consequently the properties of the composite. Friction reducing admixtures and admixtures that improve the cohesiveness of the mix can significantly improve the mix.

G) MIXING

Mixing of fiber reinforced concrete needs careful conditions to avoid balling of fibers, segregation, and difficulty of mixing the materials uniformly. Increase in the aspect ratio, volume percentage and size and quantity of coarse aggregate intensify the difficulties and balling tendencies. It is important that the fibers are dispersed uniformly throughout the mix. This can be done by adding fibers before adding water. When mixing in a laboratory mixer, introducing the fibers through a wire mesh basket will help even distribution of fibers.

1.5 Conventional Reinforced Concrete

Johnston (1994) found that tensile strength of concrete is typically 8% to15% of its compressive strength. This weakness has been dealt with over many decades by using a system of reinforcing bars (rebars) to creature in forced concrete; so that concrete primarily resists compressive stresses and rebars resist tensile and shear stresses. The longitudinal rebarin 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.

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.

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1.6 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

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.

1.7 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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1.8 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 Bayasietal (1989).

1.9 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

Figure 1.6 Fibre Mechanism

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1.10 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%.

Figure 1.7 Fibre Pull Out

1.11 Workability

A shortcoming of using steel fibres in concrete is reduction in workability. Workability of SFRC is affected by fibre aspect ratio andvolume 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 [Vf×(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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1.12 FEATURES AND BENEFITS OF SFRC

• Elimination of manufacturing, handling, storage and positioning of reinforcement cages.

• Reduction in the production cycle time resulting in increased productivity.

• Improved impact resistance during handling, erection.

• Increased load bearing capacity and less spalling damage.

• Enhanced durability.

• Important time savings due to the elimination of the manufacturing, transport, handling and positioning of the conventional reinforcement.

• No damage to sealing due to reinforcement.

• Excellent corrosion resistance, spalling is totally excluded.

• Excellent crack control, the fibres control and distribute the cracks.

• The fibres give resistance to tensile stresses at any point in the shotcrete layer.

• Reinforces against the effect of shattering forces.

• Reinforces against material loss from abrading forces.

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• Reinforces against water migration.

1.13 APPLICATIONS OF SFRC

• Steel fibre reinforced concrete has gained widespread use in applications such as the following.

• Rock slope stabilization and support of excavated foundations, often in conjunction with rock and soil anchor systems.

• Industrial floorings, road pavements, warehouses, Foundation slabs.

• Channel linings, protect bridge abutments.

• Rehabilitation of deteriorated marine structures such as light stations, bulkheads, piers, sea walls and dry docks.

• Rehabilitation of reinforced concrete in structures such as bridges, chemical processing and handling plants.

• Support of underground openings in tunnels and mines.

1.14 USAGE OF SFRC IN INDIAN PROJECTS

Steel Fibre Reinforced Concrete has been used in various Indian projects successfully namely,

1. Chamera hydroelectric project ,Himachal Pradesh 2. Uri dam ,Jammu & Kashmir 3. Sirsisilam project ,Andhra Pradesh 4. Tehri Dam project ,Uttaranchal 5. Ranganadi Hydroelectric project ,Arunachal Pradesh 6. 6.Bombay - Pune National Highway, Maharashtra

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CHAPTER 2

LITERATURE REVIEW

A critical review of the published literature in the field of steel fibre reinforced concrete was studied in the following sub headings.

2.1 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. Thefirst patent for SFRC was filed in California by A.Bernard in 1874. Apatent by H.Alfen in France, 1918 was followed by G.C.Martin in California, 1972 for SFRC pipes. H.Etheridge in 1931 examined the useof 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.

2.2 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

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2.3 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.

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.

2.4 Durablity

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

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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.

2.5 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.

t 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 a130% increase in cumulative energy dissipation in comparison to the conventional joint.

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2.6 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.

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.

2.7 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.

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. Researchers concluded that the average in the uncracked state, applicable to design of machine foundation is 1% critical. Equation are also formulated from the

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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 is improved by the addition of fibre. Resistance to blow was investigated using the Charpy stricking pendulum an improvement in toughness was reported.

2.8 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.

2.9 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%.

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CHAPTER 3

MIX DESIGN Proper design of concrete mixture is intended to obtain such proportioning of ingredients which will produce concrete of high durability performance during the designed life of a structure, usually 50 years.

For a particular strength and long term qualities and performance. Several factors determine these properties.

1. Quality of cement

2. Proportion of cement and other cementations materials in relation to water in the mixture (water/cementation ratio)

3. Strength and cleanliness of aggregate

4. Interaction or adhesion between cement paste and aggregate

5. Adequate mixing of ingredients

6. Proper placing, finishing, and compaction of fresh concrete

7. Curing at a temperature not below 50° F while the placed concrete gains strength

8. Chloride content not exceeds 0.15% in reinforced concrete exposed to chlorides in service and 1% for dry protected concrete.

A study of these requirements shows that most of the control actions have to be taken prior to placing the fresh concrete. Since each control is governed by the proportion and the mechanical ease or difficulty in handling and placing, the development of criteria based on the theory of proportioning for each mixture should be studied.

In addition, a determination has to be made as to the admixtures that need to be prescribed to enhance the long-term high performance and durability of the finished product.

There are several types of strength-modifying admixtures: high range water reducers (super plasticizer), polymers, granulated blast furnace slag, fly ash, or slica fume. However, in mixture proportioning for very high strength concrete, isolating the water/cementation materials ratio W/(C+P) (often called simply w/cm) from the paste/aggregate ratio due to the very low water content can be more effective in arriving at the optimum mixture with fewer trial mixtures and field trial batches. The very low w/cm material ratio required for strength in the range 138 Mpa or higher requires major modification to the present standard approach used in mixture proportioning that seems to work well for strength up to 83 Mpa. The optimum mixture that can be chosen with minimum trials has to produce satisfactory concrete product in both its plastic and hardened states.

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3.1 Experimental Test Observation Table

3.1.1Specific gravity & water absorption of fine aggregates

Material

Notation Value

Mass of empty dry flask,

W gm 645

Mass of flask + water,

W1 gm 1540

Mass of saturated surface dry sample,

W2 gm 252

Mass of flask + sample + water,

W3 gm 1694

Mass of saturated surface dry sample + bottle

W4 gm 896

Mass of oven dry sample,

W5 gm 250

Bulk specific gravity

Sp. gr 2.58

Absorption percentage

Wa (%) 0.8

3.1.2 Specific gravity & water absorption of Coarse aggregates

Material

Notation Value

Mass of empty dry flask,

W gm 644 646

Mass of flask + water,

W1 gm 1058 100

Mass of saturated surface dry sample,

W2 gm 1814 1772

Mass of flask + sample + water,

W3 gm 1540 1538

Mass of saturated surface dry sample + bottle

W4 gm 414 354

Mass of oven dry sample,

W5 gm 409 351

Bulk specific gravity

Sp. gr 2.92 2.95

Absorption percentage

wa 0.5 0.5

Inferred Sp. gr = 2.92

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3.1.3 Bulking of Sand

Material Details

Sand

Mass of empty container, gm

320 gm

Mass of fine aggregate (sand), gm

200 gm

Height of dry sand h, mm

136 mm

Mass of sand gm

Mass of added water (ml)

Height of sand h’, mm

Bulking = ℎ′ −ℎℎ

× 100

S1 S2 S1 S2

200

2 ml

168 164 23.5 20.5

200

4 ml

180 180 32.3 32.3

200

6 ml

184 184 35.2 35.2

200

8 ml

194 196 42.6 44.1

200

10 ml

192 192 41.2 41.2

200

12 ml

188 188 38.2 38.2

200

14 ml

182 172 33.8 26.4

200

16 ml

178 170 30.9 25

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3.1.4 Specific gravity of cement

Material

Notation Value

Mass of empty bottle

W1 gm 10.9

Mass of bottle + cement

W2 gm 28.5

Mass of bottle + kerosine

W3 gm 36.1

Mass of cement + bottle + kerosine

W4 gm 48.7

Sp. gr. of cement, S = 𝑊5(𝑊3−𝑊1)(𝑊5 +𝑊3−𝑊4)(𝑊2−𝑊1)

Sp. gr. 2.90

3.2 Various Methods of Mix Design Proportioning

• Arbitrary proportion • Maximum density method • Fineness modulus method • Surface area method • ACI Committee method • Grading curve method • IRC 44 method • High strength concrete mix design • Design based on flexural strength • Indian standard method

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3.3 CONCRETE MIX DESIGN BY INDIAN STANDARD METHOD (As per IS:10262-1982)

STEP 1: Design stipulation

A) Characteristic compressive strength = 20 N /mm2

B) Max nominal size of aggregate = 20 mm (angular)

C) Degree of workability = 0.8 compacting factor

D) Degree of quality control = good

E) Type of exposure = mild

STEP 2: Test data for materials

Cement used - Portland Slag Cement

Specific gravity of cement = 2.9

Specific gravity of fine aggregate = 2.58

Specific gravity of coarse aggregate = 2.9

Water absorption:

1. Coarse aggregate = 0.5%

2. Fine aggregate = 0.8%

Sand conforming to Zone III (As per IS: 383-1970)

STEP 3: Target mean strength of concrete

Target compressive strength, Tms = fck + t*s

Where, fck= Characteristic compressive strength at 28 days

s = Standard deviation of 4.6 (As per IS: 10262-1982)

t = tolerance factor 1.65(As per IS: 456-2000)

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The target mean strength for the specified characteristic strength,

Tms = 20 + (1.65 × 4.6) = 27.59 N/ mm2

STEP 4: Selection of water-cement ratio

The w/c ratio corresponding to 28 days cement compressive strength (Group ‘E’ i.e. 51.5-56.4 N/mm2) and target mean strength of 27.59 N/mm2 is 0.55 (As per IS: 10262-1982).

For durability consideration maximum w/c ratio = 0.6 (As per IS: 456-2000)

We take lower value i.e. w/c = 0.55

STEP 5: Selection of water and sand content.

Table 4 of IS 10262-1282 (for 20 mm nominal max size of aggregate) and confirming to grading zone-III

Water content per m3 of concrete = 186 kg

Sand content as percentage of total aggregate by absolute volume = 35%

For changes in values in water-cement ratio, sand percentage and compaction factor for following adjustments are required

Change in condition

Adjustment Required

Water Content Sand in total aggregate

For decrease in w/c ratio by (0.60-0.55) i.e. for 0.05 decrease

0 -1%

For increase in compaction factor (0.85-0.8) i.e. 0.05 increase

+1.5% 0

For sand conforming Zone III of IS: 383-1970

0 -1.5%

+1.5% -2.5%

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Therefore required sand content as % of total aggregate by absolute volume = 35-2.5 = 32.5%

Required water content = 186 + (186×1.5)/100 =188.79 l/m3

STEP 6: Determination of cement content

Water cement ratio = 0.55

Water = 198.79 l/m3

Cement = 188.79/0.55

=343.25 kg/m3

This cement content is adequate for mild condition (Under the limits prescribed in IS: 456-2000).

STEP 7: Determine aggregate content

By using equation 3.15 from IS: 10262-1982

V = [w + (C/Sc) + (1/p) + (fa/Sfa)] × (1/1000)

Where,

V = absolute volume of fresh concrete, which is equal to gross volume (m3) minus the volume of entrapped air,

W = mass of water (kg) per m3 of concrete, C = mass of cement (kg) per m3 of concrete,

Sc = specific gravity of cement,

p = ratio of fine aggregate to total aggregate by absolute volume,

fa,Ca = total masses of fine aggregate and coarse aggregate (kg) per m3 of concrete

respectively, and

Sfc ,Sca= specific gravities of saturated surface dry fine aggregate and coarse aggregate respectively.

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From IS: 383 : 1970 specified maximum size of aggregate 20 mm, the amount of entrapped air in the wet concrete is 2%, taking this into account and apply into the above equation.

0.98=[188.79/1000 + 343.25/(2.9*1000) + fa/(.325*2.58*1000)]

Therefore, fa = 572.932 Kg/m3

Similarly,

0.98=[188.79/1000 + 343.25/(2.9*1000) + Ca/(.675*2.9*1000)]

Ca=1317.10 Kg/m3

MIX PROPORTION:

Cement Water Fine Aggregate Coarse Aggregate

343.25 188.79 572.932 1317.10

1 0.55 1.67 3.83

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CAHAPTER 4

EXPERIMENTAL PROGRAM 4.1 Specimen Preparation

• The steel fiber added in the range of 0.25%, 0.50%, 1%, 1.5% and 2.% by volume of concrete specimen.

• The concrete was mixed in hand then the decided quantity of fiber was added evenly and mixed to get the uniform distribution and homogeneous mixer without forming fiber balls.

• The compressive strength, tensile and flexural strength performance were evaluated using 150 mm cube, 150 mm diameter and 300 mm height cylinder and 500X100X100 mm beam.

• The specimens were casted in steel mould. Grease was applied on the inner periphery of the moulds before pouring concrete to ensure easy removal of specimen from moulds after curing has been done. The test specimens were normal cured under water in a curing pond.

Figure 4.1 Mixing of concrete

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Figure 4.2 An assembly for proper curing of test cubes at specified temperature to

determine its 7-day and 28-day strengths

4.2 Experimental Set up

4.2.1 Compressive Strength Test

The compressive strength of concrete is one of the most important and useful properties of concrete. Most structure applications concrete is employed primarily to resist compressive stresses. In those cases where strength in tension or in shear is of primary importance, the compressive strength is frequently used as a measure of these properties. Therefore, the concrete making properties of varies ingredients of mix are usually measured in terms of the compressive strength. Compressive strength is also used as a qualitative measure for other properties of hardened concrete.

The modulus of elasticity in this case does not follow the compressive strength. The other case where the compressive strength does not indicate the useful property of concrete is when the concrete is subjected to freezing and thawing.

Concrete containing about 6 percent of entrained air which is relatively weaker is strength is found to be more durable than dense and strong concrete

The compressive strength of concrete is generally determined by testing cubes or cylinders made in laboratory or field or cores drilled from handed concrete at site or from the nondestructive testing of the specimen or actual structures.

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This test was conducted as per IS 516-1959. The cubes of standard size150x150x150mm 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/cm was applied till the failure of the cube. The maximum load was noted and the compressive strength was calculated.

Cube compressive strength = (σcc) = Pf/Ab in N/mm2

Strength of concrete is its resistance to rupture. It may be measured in a number of ways, such as, strength in compression, in tension, in shear or in flexure.

Figure4.3 Compression Testing Machine

In order to determine the compressive strength, a total number of 24 cubes were casted. After 24 hours of casting, the specimens were de-molded and cured under water in a curing pond.

At the end of curing period, the above specimens were tested in a compressive testing machine as per: IS: 516-1989

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4.2.2 Split Tensile 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 the diameter horizontal. At the top a strip of steel was placed to avoid the crushing of concrete specimen at the points where the bearing surface of the compression testing machine and the cylinder specimen meets.

The Split Tensile Strength (Tsp) = 2P/πdl N/mm2

The test is carried out by placing a cylindrical specimen horizontally between the loading surfaces of a compression testing machine and the load is applied until failure of the cylinder, along the vertical diameter.

When the load is applied along the generatrix, an element on the vertical diameter of the cylinder is subjected to a vertical compressive stress. In order to determine the split tensile strength of various concretes test was conducted as per IS: 5816-1999.

A total number of 24 cylindrical specimens were cast and after 28 days of curing, they were tested in a compression testing machine by loading it on the longitudinal direction

Figure 4.4 Split Tensile Strength Testing

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4.2.3 Flexural Strength Test :

Flexure strength is one of the basic properties of the concrete. Concrete is used to construct a flexure members like beams and girders. Flexure test is used to find the flexure strength of concrete in tension. The testing of concrete in flexure yields more consistent result than those obtained from split tensile test. The standard specimen measures 100X100X500 mm.

The strength in bending is given by the extreme fibre stress on the tension side at the point of failure.

Figure 4.5 Flexural Strength Testing Machine

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If f= modulus of rupture or extreme fibre stress in tension

W= load applied by testing machine b= width of beam at the point of failure d= depth of beam at the point of failure. l= distance from failure point to the nearest support measured along the centre line of the tension face.

a. If fracture occurs within middle third of the span, then f= Wl/bd2

b. When failure occurs outside the middle third of span, then

f= 3Wl/bd2

c. If failure point falls outside the middle third by more than 5% of the span,

the results shall be discarded.

Figure4.6 Testing of Beam specimen

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4.3 Materials Used In Experiment

The materials used and their specifications are as follows:

4.3.1 Cement

Lafarge Portland Slag cement was used and its specific gravity is 2.9.The cement was confirming to IS 269-1976.

Using slag cement to replace a portion of portland cement in a concrete mixture is a useful method to make concrete better and more consistent. Among the measurable improvements are:

• Better concrete workability

• Easier finishability

• Higher compressive and flexural strengths

• Lower permeability

• Improved resistance to aggressive chemicals

• More consistent plastic and hardened properties

• Lighter color

4.3.2 Aggregate

Aggregate are those parts of the concrete that constitute the bulk of the finished product. They comprise 60-80% of the volume of the concrete and have to be so graded that the entire mass of concrete acts as a relatively solid, homogenous, dense combination, with the smaller sizes acting as an inert filler of the voids that exist between the larger particles.

They are two types:

1. Coarse aggregate, such as gravel, crushed stone, or blast furnace slag 2. Fine aggregate, such as natural or manufactured slag

Since the aggregate constitutes the major portion of the mixture, the more aggregate in the mixture, the cheaper is the concrete, provided that the mixture is of reasonable workability for the specific job for which it is used.

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The long term performance if the concrete produced, whether normal strength or high strength is governed to a large extent by the quality of the coarse aggregate, low porosity and low permeability, high resistance to freezing and thawing, high resistance to abrasion strength, and low expansion that can be produce cracking, disintegration, low or no alkali-aggregate reactivity.

Aggregate should always be selected to have minimum drying shrinkage effects. Their choice determines the long term performance of a structure, as drying shrinkage is a long term process that takes several years for the concrete in a structural member to achieve complete drying. The following are the factors to be taken into account in selection of the coarse aggregate.

4.3.2.1 Fine Aggregate

The fine aggregate conforming to zone-II as per IS: 383-1987 was used. Fine aggregate is smaller filler made of sand. A good fine aggregate should always be free of organic impurities, clay, or any deleterious materials or excessive filler of size smaller than N. For radiation-shielding concrete, fine steel shot and crushed iron ore are used as fine aggregate.

A fineness modulus (FM) in the range 2.5-3.2 is recommended for concrete, to facilitate workability. Lower values result in decreased workability and a higher water demand. The mixing water demand is dependent on the void ratio in the sand.

River sand was used and tests were conducted as per IS 2386 (PART I).Specific gravity of fine aggregate is 2.6.Water absorption 0.99%Dry loose bulk density 1502 Kg/m

4.3.2.2 Coarse Aggregate

Crushed granite coarse aggregate conforming to IS: 383-1987 was used. Coarse aggregate passing through 20mm, having the specific gravity and fines modulus vales 2.80-7.20 respectively were used. Properties of the coarse aggregates affect the final strength of the hardened concrete and its resistance to disintegration, weathering, and other destructive effects. The mineral coarse aggregate must be clean or organic impurities and must bond well with the cement gel. The common types are,

1. Natural crushed stone 2. Natural gravel 3. Artificial coarse aggregate

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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 2.68.Water absorption 0.25%Dry loose bulk density 1500 Kg/m

4.3.3 Water

As per IS 456-2000 recommendations, potable water was used for mixing of concrete

4.3.4 Steel Fibres

The steel fibres used in the experiment were obtained from binding steel wires used in tying reinforcement bars. Aspect ratio of the steel fibres was 75. These wires were properly cut to obtain a length of 6 cm. The diameter of steel fibre was 0.8 mm.

Figure 4.7 Steel Fibres used in experiment

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4.4 Casting Of Specimen

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 sprinkled randomly inside the mixture after thorough mixing of the ingredients of concrete so that homogenous mix is formed. For preparing the specimen for compressive, tensile, and flexure strength permanent steel moulds were used. Before mixing the concrete the moulds were kept ready. The sides and the bottom of the all the mould were properly oiled for easy de-moulding.

Specimen Mould Dimension

• Cube 150X150X150 mm

• Cylinder 150X300 mm

• Beam 500X100X100 mm

4.5 Curing Of Specimen

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.

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4.6 EXPERIMENTAL BEHAVIOR OF STEEL FIBRE REINFORCED CONCRETE

4.6.1 Cube Specimen For Compressive Strength Testing

Figure 4.8 Failure characteristics of cube specimen

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4.6.2 Cylindrical Specimen For Tensile Strength Testing

Figure 4.9 Failure characteristics of cylindrical specimen

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4.6.3 Beam Specimen For Flexural Strength Testing

Figure 4.10 Failure characteristics of beam specimen

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CHAPTER 5

RESULT ANALYSIS AND CONCLUSION

In order to study the interaction of steel fibres with concrete under compression, split tension, and flexure a total of 24 cubes, 24 cylinders and 15 beams were casted respectively.

The objective of this investigation was to study the behavior of Steel Fibre Reinforced Concrete (SFRC). Straight rounded steel fibres with aspect ratio of 75 were used.

Specimens were casted without fibres and with fibres of 0.5% , 1%,1.5 % and 2% . Tests were conducted for studying the compressive, tensile, flexural strength .Compressive strength and split tensile tests were conducted on cube and cylinder specimens respectively. A total of 24 cubes of dimension 150X150X150 mm,24 cylinders of dimension 300X150 mm and 15 numbers of beam specimen of dimension 500X100X100 mm were casted.

The steel fibres used in the experiment were obtained from binding steel wires used in tying reinforcement bars. These wires were properly cut to obtain a length of 6 cm. The diameter of steel fibre was 0.8 mm.

Five type of specimens were prepared and designated as S-0, S-1, S-2, S-3 and S-4.

S-0: Control Concrete containing no fibres (PCC).

S-1: Concrete containing 0.5% steel fibres by volume of concrete.

S-2: Concrete containing 1% steel fibres by volume of concrete.

S-3: Concrete containing 1.5% steel fibres by volume of concrete.

S-4: Concrete containing 2% steel fibres by volume of concrete.

The results obtained during the experiment are provided in terms of charts and tables in the proceeding pages. 7& 28 days compressive strength as well as tensile strength of steel fibre reinforced concrete are compared with each other for a clearer representation of how percentage of steel fibres added affects the strength of concrete.

The 28 days flexural strength is also represented in chart as well as table for proper display of strength variation due steel fibre inclusion.

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Figure 5.1 Line Chart for 7-days compressive strength

7 Days Compressive Strength – Design Mix: 1:1.67:3.83 & w/c ratio = 0.55

Sample 1st reading

2nd reading

3rd reading

Average reading

Compressive Strength (N/mm2)

S-0 310 330 320 320 14.22

S-1 360 355 341 352 15.644

S-2 385 365 360 370 16.44

S-3 342 345 333 340 15.11

14.22

15.644

16.44

15.11

13

13.5

14

14.5

15

15.5

16

16.5

17

S-0 (0%) S-1 (0.5%) S-2 (1%) S-3 (1.5%)

Stre

ngth

(N/m

m2 )

Percentage of Steel Fibres

7 Days Compressive Strength

7 Days Strength

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28 Days Compressive Strength – Design Mix: 1:1.67:3.83 & w/c ratio = 0.55

Sample 1st reading

2nd reading

3rd reading

Average reading

Compressive Strength (N/mm2)

S-0 500 490 482 490 21.77

S-1 595 600 590 598 26.55

S-2 610 615 620 615 27.33

S-3 525 538 527 530 23.55

21.77

26.55 27.33

23.55

17

19

21

23

25

27

29

S-0 (0%) S-1 (0.5%) S-2 (1%) S-3 (1.5%)

Stre

ngth

(N/m

m2 )

Percentage of Steel Fibres

28 Days Compressive Strength

28 Days Strength

45 | P a g e

7 Days Tensile Strength – Design Mix: 1:1.67:3.83 & w/c ratio = 0.55

Sample 1st reading

2nd reading

3rd reading

Average reading

Tensile Strength (N/mm2)

S-0 75 80 80 80 1.14

S-1 120 122 120 120 1.7

S-2 145 138 137 140 2.1

S-3 132 130 130 130 1.84

1.14

1.7

2.1

1.84

0

0.5

1

1.5

2

2.5

S-0 (0%) S-1 (0.5%) S-2 (1%) S-3 (1.5%)

Stre

ngth

(N/m

m2 )

Percentage of Steel Fibres

7 Days Tensile Strength

7 Days Strength

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28 Days Tensile Strength – Design Mix: 1:1.67:3.83 & w/c ratio = 0.55

Sample 1st reading

2nd reading

3rd reading

Average reading

Tensile Strength (N/mm2)

S-0 150 140 160 150 2.12

S-1 230 230 232 230 3.253

S-2 255 250 245 250 3.543

S-3 210 208 210 210 2.976

2.12

3.253

3.543

2.976

1

1.5

2

2.5

3

3.5

4

S-0 (0%) S-1 (0.5%) S-2 (1%) S-3 (1.5%)

Stre

ngth

(N/m

m2 )

Percentage of Steel Fibres

28 Days Tensile Strength

28 Days Strength

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28 Days Flexural Strength – Design Mix: 1:1.67:3.83 & w/c ratio = 0.55

Sample 1st reading

2nd reading

3rd reading

Average reading

Flexural Strength (N/mm2)

S-0 12 12 14 12 3.6

S-1 15 15 16 15.5 4.65

S-2 18.5 19 19.5 19 5.7

S-3 21 21 20.8 21 6.3

S-4 17 18 16 17 5.1

3.6

4.65

5.7

6.3

5.1

0

1

2

3

4

5

6

7

S-0 (0%) S-1 (0.5%) S-2 (1%) S-3 (1.5%) S-4 (2%)

Stre

ngth

(N/m

m2 )

Percentage of Steel Fibres

Flexural Strength

28 Days Strength

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7 Days vs. 28 Days Compressive Strength Comparison

Design Mix: 1:1.67:3.83 & w/c ratio: 0.55

Sample 7 Days Compressive Strength (N/mm2)

28 Days Compressive Strength (N/mm2)

S-0 14.22 21.77

S-1 15.644 26.55

S-2 16.44 27.33

S-3 15.11 23.55

14.22 15.644

16.44 15.11

21.77

26.55 27.33

23.55

0

5

10

15

20

25

30

S-0 (0%) S-1 (0.5%) S-2 (1%) S-3 (1.5%)

Stre

ngth

(N/m

m2 )

Percentage of Steel Fibres

Compressive Strength

7 Days Strength

28 Days Strength

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7 Days vs. 28 Days Compressive Strength Comparison

Design Mix: 1:1.67:3.83 & w/c ratio: 0.55

Sample 7 Days Compressive Strength (N/mm2)

28 Days Compressive Strength (N/mm2)

S-0 14.22 21.77

S-1 15.644 26.55

S-2 16.44 27.33

S-3 15.11 23.55

14.22

15.644 16.44

15.11

21.77

26.55 27.33

23.55

10

12

14

16

18

20

22

24

26

28

30

S-0 (0%) S-1 (0.5%) S-2 (1%) S-3 (1.5%)

Stre

ngth

(N/m

m2 )

Percentage of Steel Fibres

Compresive Strength

7 Days Strength

28 Days Strength

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7 Days vs. 28 Days Tensile Strength Comparison

Design Mix: 1:1.67:3.83 & w/c ratio: 0.55

Sample 7 Days Tensile Strength (N/mm2)

28 Days Tensile Strength (N/mm2)

S-0 1.14 2.12

S-1 1.7 3.253

S-2 2.1 3.543

S-3 1.84 2.976

1.14

1.7

2.1

1.84

2.12

3.253

3.543

2.976

0

0.5

1

1.5

2

2.5

3

3.5

4

S-0 (0%) S-1 (0.5%) S-2 (1%) S-3 (1.5%)

Stre

ngth

(N/m

m2 )

Percentage of Steel Fibres

Tensile Strength

7 Days Strength

28 Days Strength

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7 Days vs. 28 Days Tensile Strength Comparison

Design Mix: 1:1.67:3.83 & w/c ratio: 0.55

Sample 7 Days Tensile Strength (N/mm2)

28 Days Tensile Strength (N/mm2)

S-0 1.14 2.12

S-1 1.7 3.253

S-2 2.1 3.543

S-3 1.84 2.976

1.14

1.7

2.1

1.84

2.12

3.253

3.543

2.976

0

0.5

1

1.5

2

2.5

3

3.5

4

S-0 (0%) S-1 (0.5%) S-2 (1%) S-3 (1.5%)

Stre

ngth

(N/m

m2 )

Percentage of Steel Fibres

Tensile Strength

7 Days Strength

28 Days Strength

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CONCLUSION

The strength of the steel fibre reinforced concrete depends largely on the quantity of fibers added to it. The increase in the volume of fibers, increase approximately linearly, the compressive strength, tensile strength and toughness of the composite. Use of higher percentage of fiber is likely to cause segregation and hardness of concrete and mortar and also the workability of concrete is greatly reduced.

The 7 & 28 days compressive strength of the concrete increases linearly with the increase in amount of steel fibres added to it, but to a maximum of 1% steel fibre inclusion. After that the compressive strength decreases. So the optimum percentage of steel fibre inclusion is 1% by volume of the concrete mix.

Same behavior happens with the tensile strength of steel fibre reinforced concrete with a optimum percentage of 1% steel fibre inclusion, maximum strength is gained.

The flexural strength increases with the increase in steel fibre inclusion but to a maximum of 1.5% by volume of concrete mix. After that the flexural strength decreases.

Parameter (28 Days-N/mm2) PCC

Optimum % Of

steel fibre inclusion

Steel Fibre Reinforced

Concrete(SFRC) % increase in

strength

Compressive Strength

21.77 1% 27.33 25.53%

Tensile Strength

2.12 1% 3.543 67.12%

Flexural Strength

3.6 1.5% 6.3 75%

Table Variation of different parameters of steel fibre reinforced concrete

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SUGGESTIONS FOR 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 behavior can be studied.

5. The crack pattern can be studied using fracture mechanics

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REFERENCE:

1. IS 10262:1982 ‘Hand Book of Concrete Mix Design’, Bureau of Indian Standards, New Delhi

2. IS 456:2000, ‘Code of Practice for Plain and Reinforced Concrete’, (4th Revision), Bureau of Indian Standards, New Delhi.

3. IS 383:1970, Specification for coarse and fine aggregates from natural sources for concrete.

4. IS 5816:1999 Splitting Tensile Strength of Concrete Test.

5. M.S. SHETTY (2000), Concrete Technology, S.CHAND and Company Ltd.

6. M.L. GAMBHIR (1998) “Concrete Technology “, Tata McGraw-Hill.

7. ACI Committee 2111, (1994) mechanical properties and time dependent deformation of polypropylene fiber concrete.