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Influence of Hooked-End Steel Fibers on Some Engineering Properties of SIFCON Yashar SHAFAEI Submitted to the Institute of Graduate Studies and Research In partial fulfillment of the requirements for the
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Influence of Hooked-End Steel Fibers on Some Engineering Properties of SIFCON Yashar SHAFAEI Submitted to the Institute of Graduate Studies and Research In partial fulfillment of the requirements for the Degree of Master of Science in Civil Engineering Eastern Mediterranean University April 2012 Gazimağusa, North Cyprus Approval of the Institute of Graduate Studies and Research Prof. Dr. Elvan Yılmaz Director I certify that this thesis satisfies the requirements as a thesis for the degree of Master of Science in Civil Engineering. Assist. Prof. Dr. Mürüde ÇELİKAĞ Chair, Department of Civil Engineering We certify that we have read this thesis and that in our opinion it is fully adequate in scope and quality as a thesis for the degree of Master of Science in Civil Engineering. Assoc. Prof. Dr. Özgür EREN Supervisor Examining Committee 1. Assoc. Prof. Dr. Özgür EREN 2. Assist. Prof. Dr. Serhan ŞENSOY 3. Assist. Prof. Dr. Alireza REZAEI ABSTRACT Slurry infiltrated fiber concrete (SIFCON) has been applied since 1979 in USA. Since it is not possible to use more than 2% of fiber in SFRC (steel fiber reinforced concrete) because of workability and mixing issues, SIFCON is applied to contain fiber amount as high as 12%. Having higher mechanical properties in both strength and durability is an advantage of SIFCON in comparison with SFRC. In light of this advantage, this study has been carried out on fibers having length/aspect ratio of 80/60, 80/50, and 30/65 for approximate fiber amounts of 1%, 2%, 3% and 4% by the volume of concrete. Fiber orientation can also seriously affect properties of SIFCON where one can control the orientation easily. These properties are modulus of elasticity, flexural strength, stress strain behavior, absorbed energy, impact energy, and water permeability (depth of water penetration). Some of these parameters are studied in comparison with conventional concrete. At the end of this study results are analyzed to end up with optimum orientation and fiber type and volume fraction of fibers to reach admirable energy absorption capacity and durability. Keywords: SIFCON, flexural strength, impact energy, water permeability. iii ÖZ Yüksek oranda çelik tel içeren çimento bulamacı (SIFCON) 1979 yılından beridir uygulamalarda kullanılmaktadır. Bunu ortaya çıkmasının esas sebebi ise normal çelik telli betonlarda kullanılabilecek lif oranının işlenebilirlik ve karıştırmadaki zorluklardan dolayı en çok %2 olmasındandır. SIFCON ile çelik tel oranı %12 seviyelerine kadar rahatlıkla çıkarılabilmektedir. Mukavemet ve dayanıklılıktaki daha iyi sonuçlardan dolayı yüksek oranda çelik tel içeren çimento bulamacı (SIFCON) normal çelik telli betondan daha avantajlı duruma geçmektedir. Bundan dolayı, bu çalışmada boy/narinlik oranları 80/60, 80/50ve 30/65 olan çelik teller değişik karışım oranlarda kullanılarak (%1, %2, %3 ve %4) SIFCON üretilmiş ve hedeflenen özelliklerindeki değişimler bulunmuştur. Öte yandan çelik telin beton içerisindeki duruşu ve yönü SIFCON un özelliklerini önemli ölçüde ekilediği bilinmektedir. Bu özellikler ise elastil modülü, çekme dayanımı, çekme şekil değiştirme davranışı, kırılma enerjisi ve su geçirgenliğidir. Yapılan çalışmada yukarıdaki özellikler kontrol betonu ile karşılaştırılmış ve optimum tel boyu/narinlik oranı ve karışım oranları bulunmuştur. Anahtar Kelimeler: SIFCON, çekme dayanımı, kırımla enerjisi, su geçirimliliği. iv DEDICATION To my dear Father and Mother v ACKNOWLEDGMENT I would like to express my most sincere gratitude to my supervisor Assoc. Prof. Dr. Özgür EREN. The guidance, support, and kindness which he showed throughout the thesis study have been incredibly valuable for me. I am also obliged to Mr. Ogün KILIÇ for his help and suggestions during experimental tests and Laboratory investigations. I would like to express my greatest appreciation to my father, mother, sister who are the most valuable people for me on the earth. The love, support, strength, understanding, patience and guidance they have provided me throughout my life made me the person who I am. Besides, a number of friends had always been around to support me morally. I would like to thank them as well. vi TABLE OF CONTENTS ABSTRACT... iii ÖZ... iv DEDICATION... v ACKNOWLEDGMENT... vi LIST OF TABLES... x LIST OF FIGURES... xi LIST OF ABBREVIATIONS... xiii LIST OF SYMBOLS... xiv 1 INTRODUCTION General Statement of the problem Works done Objectives of this study Guide to thesis LITERATURE REVIEW AND BACKGROUND Introduction Preparation Materials and mix properties Steel fibers Fiber properties Matrix of SIFCON Mix proportions Engineering and mechanical properties of SIFCON vii 2.6.1 Unit weight Behavior in compression Behavior under flexural loading Applications of SIFCON EXPERIMENTAL STUDY Introduction Materials Cement Steel fibers Aggregates Mixing water Preparation and casting of test specimens SIFCON specimens Control concrete Experimental tests Mix proportions Flexural test Impact energy test Depth of penetration of water under pressure RESULTS AND DISCUSSION Introduction Load-deformation behavior of beams Effect of fiber content on absorbed energy Effect of length of fiber on absorbed energy Effect of tensile strength of fibers on energy absorption viii 4.2.4 Effect of fiber diameter on energy absorption Depth of penetration of water Impact energy test CONCLUSIONS REFERENCES APPENDIX Appendix A: A part of the data of a load-deflection Test for Control concrete ix LIST OF TABLES Table 1 - Some SIFCON slurry mix designs from the literature (by weight of cement)... 9 Table 2 - Reported slurry mix designs and strength values Table 3 - Reported fiber properties Table 4 - Flexural strength of SIFCON Table 5 - Chemical analysis of the cement used in the study Table 6 - Specifications of steel fibers used in the experimental work (Provided by the manufactures) Table 7 - Characteristics of fibers in this study Table 8 - Fiber amounts used in the study Table 9 - Proportions of concrete used in study Table 10 - Mixture proportions Table 11 - Summary of absorbed energy obtained from flexural strength tests Table 12-Increases in absorbed energy for SIFCON Table 13 - Results from depth of water penetration Table 14 - Impact energy test results x LIST OF FIGURES Figure 1 - Placement of fibers for SIFCON... 5 Figure 2 - Various steel fiber geometric... 7 Figure 3 - Effect of fiber amount of unit weight Figure 4 - Compressive strength vs. water/binder ratios Figure 5 - Flexural load behavior of SIFCON Figure 6 - Uniaxial compression load of SIFCON and conventional steel fiber Figure 7 - Typical effects of fiber type on stress-strain curve of SIFCON in compression Figure 8 - Tensile stress-strain response of hooked fiber Figure 9 - Load-deflection curves in flexure for hooked-end Figure 10 - Flexural strength versus fiber contents Figure 11 - Comparison of load-deflection curves for SIFCON with FRC Figure 12 - Effect of fiber content on SIFCON Figure 13 - Comparison of load-deflection behavior of Specimens with and without Silica fume Figure 14 - Schematic diagram of a hardened silo Figure 15 - Fibre types used in this study Figure 16 - Filling molds with mortar Figure 17 - Schematic diagram of a suitable apparatus for flexure test of third-point loading method Figure 18 - Flexural third point test apparatus Figure 19 - Sample of beam for control concrete and SIFCON xi Figure 20 - Drop-weight impact testing machine for SIFCON and conventional concrete Figure 21- Specimens before and after test energy Impact test Figure 22 - Arrangement for water penetration test Figure 23 - Apparatus for water permeability test Figure 24 - Specimens used for water permeability Figure 25- Depth of water penetration Figure 26 - Load-deformation for SIFCON Figure 27 - Load-deformation curve for RC8060BN 1, 2, 3, and 4% Figure 28 - Absorbed energy vs. fiber percentage and type (J) Figure 29 - Absorbed Energy for different hooked-end steel fiber types and volumes Figure 30 - Absorbed energy vs. length of fibers Figure 31 - Effect of fiber tensile strength on absorbed energy of SIFCON Figure 32 - Effect of fiber diameter on absorbed energy Figure 33 - Depth of water penetration influenced by fiber amount and fiber type.. 50 Figure 34 - Impact energy test xii LIST OF ABBREVIATIONS ACI ASTM BS EN FRC LVDT SFRC SIFCON W/C American Concrete Institute American Society for Testing Materials British European Standard Fiber Reinforced Concrete Linear Variable Differential Transformer Steel Fiber Reinforced Concrete Slurry Infiltrated Fiber Concrete Water to Cement ratio xiii LIST OF SYMBOLS B C d I l/d L f N R SP V f ΔL σ Bright fiber Glued fiber Diameter of fiber Impact factor Aspect ratio, length of fiber /diameter Length of fiber Low carbon fiber Hooked end fiber Superplasticizer Volume fraction Length difference Compressive strength xiv Chapter 1 1 INTRODUCTION 1.1 General Slurry Infiltrated Fiber Concrete (SIFCON) is a type of high performance concrete in which discrete fibers are preplaced into molds either to a full capacity or desired volume fraction (V f ) rather than adding fibers to concrete mixer. It is possible to dispense fibers rather by hand or with fiber-dispensing units. Then liquid cement paste or slurry or mortar is poured on fibers to fill up the mold. During dispensing and filling molds, vibration can be held to avoid pores happen in concrete (Lankard,1985). In conventional Steel Fiber Reinfoced Concrete (SFRC) it is not easy to use fiber amounts above 1% by volume of concrete, while SIFCON method makes it possible to use fiber as high as 12%. Slurry Infiltrated Fiber Concrete (SIFCON) is a type of fiber reinforced concrete in which formwork molds are filled to capacity with randomly-oriented steel fibers, usually in the loose condition, and the resulting fiber network is infiltrated by cement based slurry. Infiltration is usually accomplished by gravity flow aided by light vibration or by pressure grouting (ACI544.2R, 1987). Typical uses of fibers in SFRC are when it is used in structural applications, steel fiber reinforced concrete should only be used in a supplementary role to inhibit cracking, to improve resistance to impact or dynamic loading, and to resist material disintegration. In structural members where flexural tensile or axial tensile stresses will occur, such as in beams, columns, suspended slabs (i.e., not slabs 1 on grade), the reinforcing steel must be capable of resisting the tensile stresses (ACI544.2R, 1987). SIFCON is advantegous in mechanical properties compared to SFRC. Differences between SFRC and SIFCON can be summerized as; higher volume fraction (V f ) of SIFCON, and absence of coarse aggregate in SIFCON. Furthermore SIFCON has got more cement and water content compred to SFRC. Although SIFCON may seem to be expensive but it would be cost effective if we consider all structural elements and extra dead load made by larger elements. It is realized when SIFCON is viewed as a total interlated system. Application of SIFCON is quite easy and cost effective, expert labour is not needed and in fact, it has been shown that placing of the fibers and slurry can be automated in several applications. (Lankard, 1984 b) 1.2 Statement of the problem There is not a study available on Influence of fibers especially hooked end steel fibers on properties of SIFCON such as absorbed energy, depth of water penetration and impact energy. 1.3 Works done Applications of SIFCON has been widly used since 1980 s such as explosiveresistant containers, security blast-resistance vaults, repair of structural components, bridge decks, airfield pavements and abrasive-resistance surfaces (Shah & Balaguru, 1992).Also, Various durability aspects of SIFCON has been investigated by Gilani (2007). 2 1.4 Objectives of this study Objectives of this study are to demonstrate behavior of single class of concrete in flexural test by analyzing absorbed energy results obtained from third point loading and make comparative interpretations effect of parameters influencing this study such as fiber geometry (length, diameter, aspect ratio) and fiber amount. The behavior under flexural loading plays an important role in field applications. Energy impact test will be carried out on SIFCON to demonstrate effect of fibers on impact resistance. Also durability aspect of SIFCON will be analyzed based on results of water permeability test, to observe SIFCON s resistance in aggressive environment. 1.5 Guide to thesis The following narrative covers the topics listed below: In Chapter 1, an introduction for the thesis has been given, and previous studies consulted in the thesis described. The object and the scope of the thesis are stated. In Chapter 2, the reader is given relevant information about a literature survey on SIFCON and its background. In Chapter 3, material properties, mechanical properties of control concrete and apparatus and details on various tests conducted on SIFCON and control concrete are presented. In Chapter 4, results gained from experimental studies are introduced, and compared. In Chapter 5, conclusions and recommendation of this study will be provided. 3 Chapter 2 2 LITERATURE REVIEW AND BACKGROUND 2.1 Introduction In 1979, SIFCON was produced by Lankard Materials Laboratory, Columbos, Ohio, USA via large amount of steel fibers in steel fiber reinforced composites. Slurry Infiltrated Fiber Concrete (SIFCON) is a type of fiber reinforced concrete in which formwork molds are filled to capacity with randomly-oriented steel fibers, usually in the loose condition, and the resulting fiber network is infiltrated by cement based slurry. Infiltration is usually accomplished by gravity flow aided by light vibration, or by pressure grouting (ACI544, 1987). Steel Fiber Reinforced Concrete (SFRC) is concrete made of hydraulic cements containing fine or fine and coarse aggregate and discontinuous discrete steel fibers (ACI544, 1987). The main difference between SIFCON and conventional SFRC are the following two items; first SIFCON contains larger volume fraction of fibers from 8 to 12 percentages but value up to 25 percentage have been reported. Another difference is higher strength and ductility due to fine particles in the matrix (Lee, 2003). The fiber volume (V f ) depends upon the fiber type, i.e. length and diameter, and the vibration effort utilized to fill the form. Smaller or shorter fibers will pack denser 4 than longer fibers, and higher fiber volumes can be achieved with increased vibration time. 2.2 Preparation SIFCON can be considered as a preplaced fiber reinforced concrete comparable with prepared aggregate concrete. The first step to cast SIFCON is placing randomly distributed steel fibers in a mold or form. It can be placed by hand or commercial fiber dispensing units. Two parameters which specifically identify steel fibers are aspect ratio (l/d) and length. By the use of commercial steel fibers, SIFCONs from 5 to 18 percentage of fiber has been achieved (Lankard,1985). First, steel fibers are placed in molds, as shown in Figure 1 and then slurry cement based mixture is poured on top of them with help of external vibration so that the infiltration of mortar gets complete to the steel fibers. Also fibers can be pressureinfiltrated from bottom of the molds (Lankard, 1985). The condition of grain sizing of aggregate must be such that the minimum particles exceed the smallest opening in the packed fiber bed. If this condition does not happen the fiber will be clogged with aggregate particles and further infiltration will be impossible (Lankard, 1985). The curing procedure for SIFCON would be same as other concretes. Figure 1 - Placement of fibers for SIFCON 5 2.3 Materials and mix properties SIFCON is produced by mainly steel fibers and cement based slurry. The matrix can be from: 1. Only cement (slurry or cement), 2. Cement and sand (mortar), 3. Cement and other additives (mainly fly ash or silica fume). For enhancing a good workability and complete infiltration of cement paste to steel fibers, superplasticizers can be used. This will be achieved without increasing the Water to cement (w/c) ratio. The effect of superplasticizers is significant on infiltration and cohesiveness of matrix Steel fibers Many different types of fibers have been investigated for SIFCON (Lankard, 1985). To maximize the bond and mechanical anchorage of steel fibers and cement paste, fibers can be changed along their length by mechanical deformations or by roughing the surface. Hooked and crimped fibers are mostly used in case of SIFCON. Surface deformed and straight fibers are less common (Homrich, 1987 ; Balaguru, ; Mondragon, 1987 ; Reinhardt, 1989). The steel fibers are defined short with aspect radio (l/d) of 20 to 100 with variety of cross sections. Four classes of steel fibers defined by ASTM (ASTMA820) are the following; Type I Cold-drawn wire. Type II Cut sheet. Type III Melt-extracted. Type IV Other fibres (Figure 2). (ACI544, 1987) 6 Figure 2 - Various steel fiber geometric For SIFCON in most of the times cross section of fibers are circular, other types are rectangular, square or flat. Most common steel fibers are from 26 mm to 60 mm and diameter varies from 0.4 mm to 1 mm, and the common range of aspect ratio is 40 to 80 (Naaman, 2003) Fiber properties Important parameters for fibers are stiffness, fiber strength and ability of fibers to bond with concrete. Bonding of fibers with concrete is dependent to aspect ratio. Aspect ratio is the ratio of length to diameter of the fiber. Diameter may be equivalent diameter. Equivalent diameter is the diameter of a circle with an area equal to the crosssectional area of the fiber. For SFRC, equivalent fiber diameter, d, is calculated by equation 1: (Lankard, 1985) Where: f = for d in mm [1] 7 f = for d in inches D = fiber diameter SG = fiber specific gravity Normal range of aspect ratio is from 20 to 100 and length dimensions vary from 6.5 to 76 mm. Steel fibers enhance high strength and modulus of elasticity. They can be protected by alkaline environment of cementitious materials from corrosion. The bond of fibers to concrete can be achieved by mechanical anchorage and surface roughness. Long term loading does not have negative effects on mechanical properties of SIFCON. In high factory refractory applications fibers can be helpful. The behavior of fiber in high temperature will be different due to amount of fibers (Lankard, 1985). Minimum tensile strength and bending requirements and tolerance for length, diameter and aspect ratio are offered by ASTM (ASTMA820), minimum amount for tensile yield strength is 345 MPa. (Lankard, 1985) 2.4 Matrix of SIFCON Practically, SIFCON does not contain coarse aggregate and the reason why SIFCON does not contain coarse aggregate is that coarse aggregates will not possibly pass through tiny spaces of fibers. The matrix contains cement, cement-sand, cement flyash,, cement silica fume, cement sand fly, cement sand fly ash, cement sand silica fume (Homrich, 1987 ; Balaguru, ; Naaman, 2003 ; Kosa &Naaman, 1991 ; Hamza 1992 ; Wood, 2000 ; Doğan, 1998). Fly ash and silica fume will improve shrinkage disadvantages of the matrix (Shah & Balaguru, 1992.). Also silica fume increases the strength and on the other hand, fly ash causes decrease in strength 8 (Mondragon, 1987). The results obtained showed that by increasing sand content, compressive strength could increase (Sonebi, 2005). 2.5 Mix proportions Variables in SIFCON are fiber content and matrix composition. By placement technique, fiber geometry and fiber volume fraction is controlled. Suitable w/c ratio for SIFCON is 0.4 or less. If there is a need for more flowability, superplasticizers can be used to guarantee the infiltration of cement paste through fibers and avoiding honeycombs in con
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