CHAPTER-1 INTRODUCTION 1.1 GENERAL The advancement and latest development of major construction is largely associated with improving the efficiency of the building under seismic effect, reducing cost, economic use of new materials etc., concrete is one such material, which is consumed in construction industry next to water consumption in the world. This marvelous material is strong in compression but very weak in tension. Use of dispersed reinforcement in the cement based matrix/concrete attains promising new material and eliminates certain drawbacks and entrances certain property. 1.2 HISTORICAL BACK GROUND Historically, fibers were used to reinforced the brittle material since ancient times, straws were used to reinforce sun-baked bricks, horse hairs were used to reinforce plaster and asbestos fibers were used to reinforce cement. In 1910, porter put the idea that concrete can be strengthened by the inclusion of fibers. Till 1963; there was only slow progress on fiber reinforced concrete (FRC). Romualdi and Batson gave rise to FRC by conducting numerous experimental works to determine the basic engineering properties such as compressive, tensile strength FRC. Typical types of fibers used are steel, acrylic asbestons, glass, xylon, polyster, polyethylene, polypropylene, rayon, rock wool and so on. Steel fibers are available in round, flat, reimped, deformed forms. Steel fibers were used in different structural elements in various zones and investigated its performance. Now-a-days synthetic fibers have become more attractive and used for the reinforcement of cementitious materials.
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‘Fiber Reinforced Cement’ as a material made from hydraulic cement and discrete, discontinuous fibers (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 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.
2
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. 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 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.
3
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. Crimped fibers produce slightly higher slumps, and hooked fibers were found to be more effective than straight and crimped ones.
4
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.
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1.3 SCOPE FOR THE PRESENT STUDY
To study the physical properties of concrete using
polypropylene fiber,
steel fiber
Evaluation of compressive strength and of splitting tensile strength of
concrete with steel fiber
Evaluation of compressive strength and of splitting tensile strength of
concrete with polypropylene fiber.
Evaluation of compressive strength and of splitting tensile strength of
concrete without fiber.
To establish the physical properties of constituents (cement, fine aggregate,
coarse aggregate and fiber)
To design the concrete mix using IS (Indian Standard)
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1.4 EFFECT OF FIBERS IN CONCRETE Fibers are initially used in concrete to control plastic shrinkage and drying Shrinkage cracking. They also lower the permeability of concrete and thus reduce bleeding of water. Some types of fibers produce greater impact, abrasion and shatter resistance in Concrete. The material ductility is increased by the addition of fibers. High-performance fiber-reinforced concrete used in bridges found to provide Residual strength and control cracking. The residual strength is directly proportional to the fiber content. Generally fibers do not increase the compressive strength of concrete. Fibers cannot replace moment resisting or structural steel reinforcement. Some fibers reduce the strength of concrete
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CHAPTER-2 LITERATURE REVIEW A) Waheeb Ahmed al-khaja (1997 volume 7) studied the mechanical properties And time dependent deformation of polypropylene fiber concrete. This investigation conducted to study the effect of PPF used for reinforcing concrete mixes. The compression, tension and flexural strength test were performed changing fiber 0.1 to 3 % of the cement weight content. Adding the 0.5 % of PPF the compressive strength can obtain the maximum value. B) K.Anbuvelan, M.M. Khadar. M.h, M.Lakshmipathy and K.S. Sathyanarayann studies on properties of concretes containing polypropylene, steel and reengineered plastic shred fiber work an attempt has been made to study the influence of polypropylene fibers, steel fibers and re-engineered plastic shreds with0.1 %, 0.5 % and 0.5 % by volume of concrete mix. 1.
With the addition of polypropylene fibers to plain concrete, its strength
is
increased in the range of 4 %-17 %. The improvement in its wear and impact
resistance were 28 %-58 % and 72 %-134 %, respectively and reduction in maximum crack width is to an extent of 21 %-74 %. 2.
The steel fiber added to plain concrete resulted in improvement of the
strength, wear and impact resistance characteristics by 4 %-49 %, 42 %-52 % and 34 %-38 % respectively. The reduction in maximum crack width is found to be 46 %-67 %.
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3.
With the addition of reengineered plastic fibers to plain concrete,
strength, wear and resistance to impact are increased to 20%-17.60%, 31%-48% and 123%-139% respectively. The reduction in its maximum crack width is 59%73%.
C) Maalej and Paramasivam (2002) studied the effectiveness of ductile fiber reinforced cementitious composites (DFRCC) in retarding the corrosion of steel in reinforced concrete beams. A fiber content of 1.5 % PVA & 1.0 % steel fibres was used in a DFRCC and a layer of DFRCC was used around the main longitudinal reinforcement (FRC). The authors concluded that the FGC concept using DFRCC material was very effective in preventing corrosion – induced damage in RC beams and minimizing the loss in the beam load and deflection capacities. They also reported that the functionally graded concrete (FGC) beams have higher resistance against corrosion and cracking compared with conventional reinforced concrete. D) Nataraja, Dhang and Gupta (1999) examined the feasibility of using UPV technique for assessing the quality of steel fiber reinforced concrete. The study parameters included fiber content, aspect ratio of fibres and concrete strength. The pulse velocity readings were taken longitudinally at the centre of cylinders and prisms. The authors concluded that the quality of SFRC could be adequately confirmed using UPV technique. They also reported that the pulse velocity at 7 – days and 28 – days can be estimated knowing the pulse velocity at 1day using amplification factors of 1.11 and 1.13 for both plain and fiber reinforced concrete up to a compressive strength of 50 MPa. E) Mohammed and Kaushik (2000) investigated the influence of mixed aspect ratio of fibres on compressive strength, splitting tensile strength, flexural strength, impact strength and ductility of SFRC. They tried different mixed aspect ratio of fibres with a total volume fraction
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of 1.0%. The authors concluded that the use of 65% long fibres and 35% short fibres gave optimum mechanical properties.
CHAPTER-3 METHODOLOGY Collection of materials Mix proportions (M20 grade of concrete) Casting of specimens
Fiber added with concrete at various %
Control concrete (without fiber)
Steel Fiber
Polypropylene Fiber
Curing of Specimens
Test on Specimens
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Hardened concrete 1. Comprehensive strength test 2. Split tensile strength test
Analysis and discussion of test results
Conclusion
CHAPTER-4 PROPERTIES OF MATERIALS
4.1 PROPERTIES OF CEMENT The properties of ordinary Portland cement as shown in the table 4.1.
Test Particulars
Result Obtained
Requirements as per IS: 12269 1987
Specific gravity Normal consistency (%) Initial setting time (minutes)
3.15 31 37
3.10-3.15 30-35 30 minimum
Final setting time (minutes) Compressive strength (MPa) a) 3 days b) 7 days c) 28 days
570
600 maximum
28 38 44
43 33 23
Table 4.1: Physical properties of ordinary Portland cement
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4.2 PROPERTIES OF FIBERS 4.2.1 STEEL FIBER (METALLIC FIBER) Steel fiber is one of the most commonly used fibers. Generally, round fibers are used. The diameter may vary from 0.25 to 0.75 mm. The steel fiber is likely to get rusted and lose some of its strength. But investigations have shown that the rusting of the fibers takes place only at the surface. Use of steel fibers 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 fibers.
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Figure 4.1: The figure shows the general view of steel fiber
4.2.2 POLYMERIC FIBER Synthetic polymeric fibers have been produced as a result of research and development in the petrochemical and textile industries. Fiber types that have been tired with cement matrices include arcrylic, aramid, nylon, polyester, polypropylene and polyethylene. They all have a very high tensile strength, but most of these fibers (except for aramids) have a relatively low modulus of elasticity. The quality of polymeric fibers that makes them useful in FRC is their very high length to diameter ratios, their diameters are on the order of micrometers. A.POLYPROPYLENE FIBER (PPF)
13
Polypropylene fibers are synthetic types of fibers. Synthetic fibers are gradually replacing steel fibers due to the fact that are cost effective, can be used in low volume fractions and there is no risk of corrosion by there is used in concrete. Polypropylene fibers are currently manufactured in variety of geometries and configuration. These fibers are produced by drawing or stretching the synthetic fiber into film sheets which are then slit longitudinally into tapes. Polypropylene fibers are composed of crystalline and non-crystalline region. Polypropylene fibers have a softening point in the region of 150º c and a melting point at 160 to 170 º c. It is lowest thermal conductivity of all commercial fibers. It has excellent chemical resistance to acid and alkalis, high abrasion resistance.
14
Figure 4.2: The figure shows the general view of polypropylene fiber
B. NYLON FIBER Commercial available nylon fibers are made of nylon 6. They are available in varies lengths in single filament form. Since this fibers are very thin, a number of fibers per pound in the range of 35 million per pound for fiber length of 0.75 inch (19 mm). C. POLYESTER Polyester fibers are made of ethyl acetate monomers. Their physical and chemical properties can be changed substantially by altering manufacturing techniques. The higher modulus of elasticity and better bonding to concrete that is important for FRB application can be achieved by some of this modification.
Figure4.3: The figure shows the general view of polyester fiber Physical properties of polymeric fibers as shown in the given table 4.2 15
Fiber type
Effective Dia × 10-3 (mm)
Specific Gravity
Tensile Strength (MPa)
Elastic Modulus (GPa)
Ultimate Elongation (%)
Nylon
-
1.16
965
5.17
20
Polyester
-
1.34-1.39
896-1100
17.5
-
25-1020
0.96
200-300
5
3
-
0.9-0.91
310-760
3.5-4.9
15
Polyethylene Polypropylene
Table 4.2: Physical properties of polymeric fibers D. POLYETHYLENE Polyethylene fibers are available both in standard length (0.52-2, 12-50 mm)and in pulp form .the longer fiber available in the market have wart-like surface deformation, better bond to concrete. The fibers that are available in pulp form have been promoted has a replacement for asbestos fibers in concrete. These short fibers can also used in cement matrix to improve ductility, impact resistance and fatigue strength
Figure4. 4: The figure shows the general view of polyethylene fiber
16
E. GLASS FIBERS The glass fibers are primarily used for glass fiber reinforced cement (GFRC) sheets. Regular E-Glass fibers were found to deteriorate in concrete.
Figure4. 5; The figure shows the general view of glass fiber
4.2.3 NATURALLY OCCURING FIBERS The oldest forms of fiber reinforced composites were made with naturally occurring fiber such as straw and horse hair. Modern technology has made it possible to extract fibers economically from various plants, such as jute and bamboo to use in cement composites. The unique aspects of this fiber in the low amount of the energy required to extract these fibers. The primary problem with used of this fibers in concrete is their tendency to disintegrate in an alkaline environment. Effects of being made to improve durability of this fiber in concrete by using admixture to make the concrete less alkaline and the subjecting the fibers to special treatment.
17
Natural fibers used in Portland cement composite include akwara bamboo, coconut, flax, jute, sisal, sugarcane bagases, wood, and others mechanical properties of some of these fibers are presented in the succeeding. A. AKWARA FIBERS Akwara is a natural fiber derived from a plant stem grown in large quantities in Nigeria. They are made of a cellular core covered with a smooth sheath. Akwara fibers were found to be durable in alkaline environment of cement matrix, and they are also dimensionally stable under wetting and drying conditions. The disadvantages are their low elastic modulus and brittleness. B. BAMBOO FIBERS Bamboo, which is a member of the grass family, grows in tropical and subtropical region. Plants can grow up to a height of 15 m. their hollow stalks have intermediate joints, the diameters of these stalks range from 0.4 to 4.0 inch (1 to 10 cm).
Special techniques are needed to extract the fibers from bamboo. Bamboo fibers are strong in tension, but have a relatively low modulus of elasticity. Their tendency absorb water adversely affects the bonding between the fibers and the mixture during the curing process. C. COCONUT FIBERS A mature coconut has an outer fibrous husk. Coconut fibers, called coir, can be extracted simply by soaking the husk in water or, alternatively, by using mechanical processes. These short (only a few inches) stiff fibers have been used for making rope for centuries. Coir has a low elastic modulus and is also sensitive to moisture changes. D. FLAX AND VEGETABLE FIBERS 18
Flax is grown for its fiber. Flax fibers are strong under tension and also possess a high modulus of elasticity. Fibers extracted from other plant such as elephant grass, water reed, plantain, and musamba have also been tried as reinforcements for concrete. Most of these fibers are removed from the stems of the plants manually.
Physical properties of naturally occurring fibers as shown in the given table 4.2 Fiber Coconut Type Fiber 52 Length to (mm) 350 Fiber Dia 0.1 (mm) to 0.4 Specific 1.12 Gravity to 1.15 Modulus 19 of to Elasticity 26 (GPA)
Sisal 13 to 16
Sugarcane Bagasse -
Bamboo
Jute
Flax
-
500
0.2 to 0.4 1.2 to 1.3 15 to 19
0.05 to 0.4 1.5
180 to 300 0.1 to 0.2 1.02 to 1.04 26 to 32
33 to 40 19
Elephant Musamba Grass -
-
-
-
-
-
-
Wood fiber 2.5 to 5 0.015 to 0.08 1.5
100
4.9
.9
-
Ultimate Tensile Strength (MPa) Elongatio n of Break (%) Water Absorpti on (%)
120 to 200
280 to 568
170 to 290
350 to 500
250 to 350
1000
178
83
700
10 to 25
3 to 5
-
-
1.5 to 1.9
1.8 to 2.2
3.6
9.7
-
130 to 180
60 to 70
70 to 75
40 to 45
-
-
-
-
50 to 75
Table4. 3: Table shows the physical properties of naturally occurring fiber
4.4 MAJOR ADVANTAGES OF FIBER REINFORCED CONCRETE Various advantages of fiber reinforced concrete are a) Resistance to micro cracking b) Toughness and post failure ductility c) Impact resistance d) Resistance to fatigue e) Improved strength in shear, tension, flexure, and compression f) Reduced permeability
4.5 AREAS OF APPLICATION The areas where these fibers can be used as secondary reinforcement are given as under 20
a) Plain and reinforced concrete b) Plaster (stucco) c) Pre-cast concrete productions d) Trench-less constructions e) Productive lining f) Roofing product
CHAPTER-5 MATERIAL SELECTION
For concrete ingredients are, Cement Aggregate a) Fine aggregate b) Coarse aggregate
Water
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5.1 CEMENT Ordinary Portland cement is hydraulic cement that hardens by interacting with water and forms a water resistance compound when it receives its final set. Compared with non-hydraulic cements such as gypsum and lime, which absorb water after hardening, Portland cement is highly durable and produces high compressive strengths in mortars and concretes. The size of the cement particles has a strong influence on the reaction of cement with water. For a given weight of finely ground cement, the surface area of the particles is greater than that of the coarsely ground cement. Since there are different types of cement for various needs, it is necessary to study the percentage variation in the chemical composition of each type n order to interpret the reasons for variations in behavior. OPC-53 Grade con forming to IS: 12269-1987 was used.
5.2 AGGREGATES 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
22
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. 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.
5.2.1 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 23
3. Artificial coarse aggregate
5.2.2 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.
CHAPTER-6 EXPERIMENTAL STUDY 6.1 GENERAL In order to increase the performance of concrete, many types of mineral and chemical admixtures are added. Addition of fibers may change the performance in the hardened stages. Therefore, it is very essential to evaluate the effect of fibers on mechanical properties of concrete. Thus chapter deals with the properties of materials used in this investigation, methodology,
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preparation of test specimens, experimental test set up and testing procedure that have been performed. 6.2 STRENGTH REQUIREMENTS The age at is a governing criterion for selecting mixture proportions. The standard 28-day strength for normal-strength concrete penalizes high strength concrete since the later continues gaining strength after that age. One has also to consider that a structure is subjected to service load at 60 to 90 days age at the earliest.
Table5.1 shows the Specific gravity test result for fine aggregate by using Pyconometer test. Description
1
2
Pyconometer bottle (W1)
651.5
651.5
Wt of Pyconometer + dry soil (W2)
851.5
855.5
Wt of Pyconometer + dry soil + water
1668
1675
Wt of Pyconometer + water (W4)
1545.5
1549.5
Specific gravity = W2-W1/[(W2-W1)-
2.6
2.6
Average
(W3)
(W3-W4)] 25
2.6
Table5.1: Specific gravity of fine aggregate coarse
Table5,2 shows the Specific gravity test result for coarse aggregate by using Pyconometer test. Description Pyconometer bottle (W1) Wt of Pyconometer + dry soil (W2) Wt of Pyconometer + dry soil + water (W3)
1
2
651.5 881.5 1753.68
651.5 855.5 1765
Wt of Pyconometer + water (W4) Specific gravity = W2-W1/[(W2-W1)-(W3-
1606 2.8
1633 2.8
Average
2.8
W4)] Table 5.2: Specific gravity of coarse aggregate
Table5.3 shows the Sieve analysis test for fine aggregate concrete.
IS Sieve size (mm)
Quantity Retained (g)
10 4.75 2.36 1.18 0.6 0.3 0.15
0 0 120 1425 880 1670 905
Cumulative Wt Retained (g) 0 0 120 1545 2425 4095 5000
% Retained
% Passing
0 0 2.4 28.5 17.6 33.4 18.1
100 100 97.6 69.1 51.5 18.1 0
Table5.3: Sieve analysis of fine aggregate concrete
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Limits for Zone-II (IS383) 100 90-100 95-100 55-90 35-59 8-30 0-10
Table5.4 shows the Sieve analysis test for coarse aggregate concrete.
Sieve Size (mm) 63 40 20 12.5 10 4.75
Quantity Retained (g) 0 0 803 0 12562 374
Cumulative Wt Retained (g) 0 0 803 803 13365 13739
% Retained
% Passing
0 0 5.8 5.8 96.5 99.2
100 100 94.2 94.2 3.5 0.8
Table 5.4: Sieve analysis of coarse aggregate concrete
CHAPTER-7 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
27
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 28
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.
7.1 VARIOUS METHODS OF DESIGN MIX PROPORTIONING Arbitrary proportion Maximum density method Fineness modulus method Surface area method ACI Committee method Grading curve method IRC-44 method
29
High strength concrete mix design Design based on flexural strength Indian standard method
7.2 CONCRETE MIX DESIGN FOR INDIAN STANDARD METHOD STEP 1: Design stipulation A) Characteristic compressive strength = 20 N /mm2 B) Max size of aggregate = 20 mm (angular) C) Degree of workability = 0.9 compacting factor D) Degree of quality control = good E) Type of exposure = severe
STEP 2: Test data for materials Cement used opc = 53 grade Specific gravity of cement = 3.15 Specific gravity of fine aggregate = 2.6 Specific gravity of coarse aggregate = 2.8 Water absorption 1. Coarse aggregate = 0.5% 30
2. Fine aggregate = 1%
STEP 3: Target mean strength of concrete Target compressive strength F ck = f ck + t.s
fck = Characteristic compressive strength at 28 days s = Standard deviation t = tolerance factor (its take 1.65) For using table(1) the target mean strength for the specified characteristic strength 20 + (1.65 × 4.6) = 27.6 N/ mm2 STEP 4: Selection of water-cement ratio The w/c ratio required for target mean strength of 27.6 N/ mm2 is 0.5 from table 5 of IS 456-2000.
STEP 5: Selection of water and sand content. Table 4 of IS 10262-1282 (for 20 mm nominal max size aggregate) And confirming to grading zone-II Water content per m3 concrete = 186 kg sand content as percentage of
total
aggregate by absolute volume = 35% for changes in values in water-cement ratio for following adjustment is required.
31
Changing Condition
Adjustment Required In water content %
For decrease in water cement ratio (0.6-0.5)=0.1 For increase in compacting factor (0.9-0.8)=0.1 For sand conforming zone-II of table 4 IS 383-1970
0
%sand in total aggregate -2.0
+3
0
0
-1.5
3%
-3.5%
Therefore required sand content as % of total aggregate by absolute volume = 353.5 = 31.5% Required water content = 186 + (186×3)/100 =191.6 l/m3
STEP 6: Determination of cement content Water cement ratio = 0.5 Water = 191.6 l Cement = 191.6/0.5 =383 kg/m3 This cement content is adequate for extreme exposure condition. According to IS: 456-2000 32
STEP 7: Determine aggregate content By using equation 3.15 form 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 = total masses of fine aggregate and coarse aggregate (kg) per m3 of concrete respectively, and Sfa = specific gravities of saturated surface dry fine aggregate and coarse aggregate respectively.
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 = [191.6 + (383/31.5) + (1/0.315) + (fa/2.6)] × (1/1000) fa = 545 kg/m3 Therefore 33
Ca = (1-0.315/0.315) × (1/1000) Ca = 1188 kg/m3 fa = amount of fine aggregate Ca = amount coarse aggregate MIX PROPORTION Water 191.6 kg 0.5
Cement 383kg 1
Fine Aggregate 545 kg 1.4
Coarse Aggregate 1188 kg 3.1
CHAPTER-8 TESTING OF SPECIMEN 8.1 SPECIMEN PREPARATION The steel fiber and polypropylene fiber added in the range of 0.25%, 0.50%, 0.75, 2%, and 2.5% 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. 34
The compressive strength and tensile strength performance were evaluated using 150 mm cube, 100 mm diameter and 200 mm height cylinder. The specimens were cast in steel mould. The test specimens were normal cured under water.
8.2 COMPRESSIVE STRENGTH TEST The compressive strength of concrete is one of the most important and useful properties of concrete. I most structure applications concrete is employed primarily to resist compressive stresses. In those case where strength in tension or in shear is of primary importance, 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. The testing of hardened concrete is discussed in the subsequent chapter. 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.
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In order to determine the compressive strength, a total number of 144 cubes were cast. After 24 hours of casting, the specimens were de-molded and cured under water. At the end of curing period, the above specimens were tested in a compressive testing machine as per: IS516-1989. 8.3 SPLIT TENSILE STRENGTH TEST This is also sometimes referred as, “Brazilian Test”. This test was developed in Brazil in 1943.At about the some time this was also independently developed in Japan. 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 96 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.
CHAPTER-9 TEST RESULTS The compressive strength of various percentage steel fibers added are given by the table9.1. Sl. no 1. 2.
Mix CC SF1
Steel fiber (%) 0 0.25
Compressive Strength (Mpa) At 3days At 7 days At 28 days 12.5 15.5 18 13.5 19 20 36
3. 4. 5. 6. 7. 8
SF2 SF3 SF4 SF5 SF6 SF7
0.5 0.75 1 1.5 2 2.5
14.6 14.8 16 18.5 18 17.3
20 21.4 24.2 25.3 23 22
23.5 24.5 26 29 26.3 26
Table 9.1: Compressive strength of M20 grade concrete with and without steel fiber Where CC – Control Concrete SF1– 0.25 % steel fiber added concrete SF2 – 0.5 % steel fiber added concrete SF3 – 0.75 % steel fiber added concrete SF4- 1 % steel fiber added concrete SF5 – 1.5 % steel fiber added concrete SF6 – 2 % steel fiber added concrete SF7 – 2.5 % steel fiber added concrete
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Compressive Strength (MPa)
35 30 25 3 Days 7 Days 28 Days
20 15 10 5 0 0
0.5
1
2
Percentage of Fiber Added
Figure 9.1: Graph showing the compressive strength of M20 grade concrete with and without steel fiber
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The compressive strength of various percentage added Polypropylene fiber added concrete as given by the table9.2. Mix Sl. No 1. 2. 3. 4. 5. 6. 7. 8
Polypropylene
Compressive Strength (Mpa) At 3days At 7 days At 28 days
fiber (%) CC PPF1 PPF2 PPF3 PPF4 PPF5 PPF6 PPF7
0 0.25 0.5 0.75 1 1.5 2 2.5
12.5 13.5 18 17.3 17 16.6 15.3 14
15.5 18.5 21.3 20 19.2 18.6 17.9 17
18 21 25.5 24.3 23 22 21.1 20.8
Table 9.2: Compressive strength of M20 grade concrete with and without polypropylene fiber Where CC – Control concrete PPF1 – 0.25 % polypropylene fiber added concrete PPF2 – 0.5 % polypropylene fiber added concrete PPF3 – 0.75 % polypropylene fiber added concrete PPF4 – 1% polypropylene fiber added concrete PPF5 – 1.5 % polypropylene fiber added concrete PPF6– 2 % polypropylene fiber added concrete PPF7– 2.5 % polypropylene fiber added concrete
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Compressive Strength (MPa)
30 25 20
3 Days 7 Days 28 Days
15 10 5 0 0
0.5
1
2
Percentage of Fiber Added
Figure 9.2: Graph shows the compressive strength of M20 grade concrete with and without polypropylene fiber
The Split tensile strength of various percentage steel fiber added concrete as given by the table9.3.
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Sl. no 1. 2. 3. 4. 5. 6. 7. 8.
Mix CC SF1 SF2 SF3 SF4 SF5 SF6 SF7
Steel fiber (%) 0 0.25 0.5 0.75 1 1.5 2 2.5
Tensile Strength (Mpa) At 3days At 7 days At 28 days 1.5 1.8 3 1.6 2.2 3.1 1.72 2.6 3.3 1.81 2.8 3.5 2 3.31 3.9 2.2 3.8 4.5 2.15 3.6 4.2 2.1 3.52 4.1
Table9.3: Split tensile strength of M20 grade concrete with and without steel fiber Where CC – Control Concrete SF1– 0.25 % steel fiber added concrete SF2 – 0.5 % steel fiber added concrete SF3 – 0.75 % steel fiber added concrete SF4- 1 % steel fiber added concrete SF5 – 1.5 % steel fiber added concrete SF6– 2 % steel fiber added concrete SF7– 2.5 % steel fiber added concrete
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Split Tensile Strength (MPa)
5 4.5 4 3.5 3
3 Days 7 Days 28 Days
2.5 2 1.5 1 0.5 0 0
0.5
1
2
Percentage of Fiber Added
Figure9.3: Graph showing the split tensile strength of M20 grade concrete with and without steel fiber
The Split tensile strength of various percentage Polypropylene fiber added concrete as given by the table9.4.
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Sl. no 1. 2. 3. 4. 5. 6. 7. 8.
Mix CC PPF1 PPF2 PPF3 PPF4 PPF5 PPF6 PPF7
Polypropylene fiber (%) 0 0.25 0.5 0.75 1 1.5 2 2.5
Tensile Strength (Mpa) At 3days At 7 days At 28 days 1.5 2 2.2 2.3 3 2.8 2.72 2.61
1.8 3.8 4 4.1 4.5 4.4 4.32 4.2
3 4.2 4.23 4.5 5.2 5.1 5.02 4.8
Table9.4: Split tensile strength of M20 grade concrete with and without polypropylene fiber Where CC – Control concrete PPF1 – 0.25 % polypropylene fiber added concrete PPF2 – 0.5 % polypropylene fiber added concrete PPF3 – 0.75 % polypropylene fiber added concrete PPF4 – 1% polypropylene fiber added concrete PPF5 – 1.5 % polypropylene fiber added concrete PPF6– 2 % polypropylene fiber added concrete PPF7– 2.5 % polypropylene fiber added concrete
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Split Tensile Strength (MPa)
6 5 4 3 Days 7 Days 28 Days
3 2 1 0 0
0.5
1
2
Percentage of Fiber Added
Figure 9.4: Graphs shows the split tensile strength of M20 grade concrete with and without polypropylene fiber
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Figure 9.5: Photo views on compressive strength testing of specimens
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Figure 9.6: Photo views on split tensile strength testing of specimens
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Figure 9.7: Different photos views on compressive strength test
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Figure 9.8: Different photos views on split tensile strength test
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CHAPTER-10 CONCLUSION The following conclusions have been drawn based on the experimental investigation carried out on concrete mixture. 1. Higher compressive strength is obtained for 1.5 % steel fiber and 0.5% for Polypropylene Fiber added concrete. 2. Higher split tensile strength is obtained for 1.5 % steel fiber and 1% for Polypropylene Fiber added concrete. 3. Concrete attained maximum compressive and split tensile strength when mixing Minimum amount of polypropylene fiber compared to steel fiber.
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CHAPTER-11 REFERENCE 1. IS 10262:1982 ‘Hand Book of Concrete Mix Design’, Bureau of Indian Standards, New Delhi 2. IS 383:2000, ‘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. M.L. GAMBHIR (1998) “Concrete Technology “, Tata McGraw-Hill 7. ACI Committee 2111, (1994) mechanical properties and time dependent deformation of polypropylene fiber concrete. ACI Manual of Concrete Practice. 8.
ACI Committee 544, (1982) properties of concretes containing polypropylene, steel and reengineered plastic shred fiber.
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