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ABSTRACT
This project is an experimental investigation to study the effects of replacement of cement with certain percentages of fly ash and the effects of addition of steel fiber composites. The mix proportions of our M25grade of concrete was 1:1.40: 2.18 with 0.45 water-cement ratio. Cement was replaced with two different percentages (20%, 25%) of class F fly ash procured from Ennore thermal power plant. Two different percentages of steel fiber were added with 0%,1%,1.5% to the weight of concrete.This study was all about the feasibility of use of steel fibers and their effect due to the variation in percentage of fiber added. Fresh concrete test like slump cone test, compaction factor test were done. Hardened concrete test like compressive strength, split tensile strength, flexural strength for curing days7th and 28th day were done. The total no specimens casted for our project were 108 specimens. Incorporation of steel fiber in concrete gave better result like increase in compressive strength & flexural strength of concrete.
By using steel fiber we can avoid the collapsing of building. We could proof that, which is the nominal concrete blocks are crushed but the steel fiber used blocks cracks only formed which are not crushed.
INTRODUCTION
1.1 GENERAL
The Indian construction industry is today consuming about 400 million tons (MT) of concrete every year and it is expected that this may reach a billion tons in less than a decade. All the materials are required to produce such huge quantities of concrete come from the earth’s crust. On the other hand human activities on earth produce solid waste in considerable quantities. Recent technological development has shown that thus materials are valuable inorganic and organic resource and can produce various useful products. During the 20th century, there has been an increase in the consumption of mineral admixtures by the cement and concrete industries. The increasing demand for concrete is met by partial cement replacement. Sustainable energy and cost savings can result when industrial by products are used as a partial replacement for the energy intense Portland cement. The use of by products is an environmental friendly method of disposal of large quantities of materials that would otherwise pollute land, water and air. The current cement production rate of the world, which is approximately 1.2billion tons per year, is expected to grow exponentially to about 3.5 billion tons per year by 2015.
Concrete is very strong in compression but weak in tension. As Concrete is a relatively brittle material, when subjected to normal stresses and impact loads. The tensile strength of concrete is less due to widening of micro-cracks existing in concrete subjected to tensile stress. Due to presence of fibre, the micro-cracks are arrested. The introduction of fibres is generally taken as a solution to develop concrete in view of enhancing its flexural and tensile strength. Before the use of coal as source of energy, wood was major source of energy as fuel. At present, there is no escape from using coal to generate electricity. It has to be a greater awareness of the enormous environmental damage caused by the combustion of coal. The main problem is that it contains high ash content of solid waste generated as bottom ash.
Low cost materials can be developed by utilizing industrial waste as like fly ash, silica fume, ground granulated blast furnace slag, etc., in cementations materials. Low cost materials are need for the development of low cost building. Fly ash is finely divided residue resulting from the combustion of powdered coal and transported and collected by electrostatic precipitator. Fly ash is the most widely used pozzalonic material all over the world. In India alone, we produce about 75 million tons of fly ash per year, the disposal of which has become a serious environmental problem. The effective utilization of fly ash in concrete making is attracting serious considerations of concrete technologists and government departments. Secondly, cement is the backbone for global infrastructural development. It was estimated that global production of cement is about 1.3 billion tons in 1996. Production of every tone of cement emits carbon dioxide to the tune of about 0.87 ton. Expressing it in another way, it can be said that 7% of the world’s carbon dioxide emission is attributable to Portland cement industry. There is a need to economies the use of cement. One of the practical solutions to economies cement is to replace cement with supplementary cementations materials like fly ash and slag.
In India, the total production of fly ash is nearly as much as that of cement (75 million tons). But our utilization of fly ash is only about 5% of the production. The latter method gives freedom and flexibility to the user regarding the percentage addition of fly ash. There are about 75 thermal power plants in India. The quality of fly ash generated in different plants varies from one another to a large extent and hence they are not in a ready to use condition. To make fly ash of consistent quality, make it suitable for use in concrete, the fly ash is required to be further processed. The fly ash for the project was collected from the ENNORE THERMAL POWER PLANT. It is one of the producing from compulsion of coal in India.
1
CHAPTER 2
LITERATURE REVIEW
The details of the literature survey carried out are presented in the following section.
Khadake S.N, et al.ISSN: 2278-1684volume 4 Nov 2012 presented a paper titledAn Investigation of Steel Fibre Reinforced Concrete with Fly Ash in IOSR Journal of Mechanical and Civil Engineering (IOSR-JMCE).The tensile strength of concrete is less due to widening of micro-cracks existing in concrete subjected to tensile stress. Due to presence of fibre, the micro-cracks are arrested. The introduction of fibre is generally taken as a solution to develop concrete in view of enhancing its flexural and tensile strength. Fly ash can be used particularly in mass concrete applications where main emphasis is to control the thermal expansion due to heat of hydration of cement paste and it also helps in reducing thermal and shrinkage cracking of concrete at early ages.This paper deals with Investigation for M-25 grade of concrete having mix proportion 1:1.50:3.17 with water cement ratio 0.465 to study the compressive strength, and Flexural strength of steel fibre reinforced concrete (SFRC) containing fibres of an interval of 0.5% from 0.0% to 1.5% volume fraction of hook end Steel fibres of 71 aspect ratio were used. The percentage of Fly Ash by weight is to be increased by 10% from 0.0% to 30%. After curing these specimen were tested as per relevant codes of practice Bureau of Indian Standard. A result data obtained has been analyzed and compared with a control specimen. A relationship between Compressive strength vs days, and flexural strength vs days represented graphically. Fibre reinforced concrete (FRC) is mixtures of cement concrete containing short discrete, uniformly dispersed and randomly oriented suitable fibrous material which increases its structural integrity. The amount of fibres added to concrete mix ismeasured as percentage of the total volume of composites. Aspect ratio (l/d) is calculated by dividing fibre length (l) by its diameter (d). The composite matrix that is obtained by combining cement, Fly ash, aggregates and fibres is known as “Fly ash Fibre reinforced concrete”. The fibre in the cement fly ash based matrix acts as crack arresters, which restrict the growth of micro cracks and prevent these from enlarging under load. Marginal increase is observed in the workability as percentage of Fly Ash increases. Density of concrete is more as the percentage ofsteel Fibre increases with Fly Ash content 10%. Compaction factor is increases as the Steel Fibre percentage decreases. Higher percentage of Steel Fibres slump was losing.
Water reducing agent is required for workable mix as percentage of Steel Fibre increases. Stiffness of specimens is increased because of Steel Fibres & Fly Ash.
FalahA.et al. volume 2, Nov 2011 presented a paper titled Physical Properties of Steel Fibre Reinforced Cement Composites Made with Fly Ash in Jordan Journal of Civil Engineering.The structural behavior of steel fibre reinforced fly ash concrete under compression and flexure was studied by conducting tests on standard control specimens. The use of steel fibres in fly ash concrete improves its structural properties, especially the flexural tensile strength. Increasing the percentages of fly ash up to 30% and steel fibres up to 1.5% in concrete enhances the flexural tensile strength as well as the compressive strength. Finally, the use of fibre reinforced fly ash concrete is recommended as an alternative to fibre reinforced plain concrete. The use of pozzolana in concrete is an old age concept. Pozzalonic materials can be used to replace a part of cement in all construction works. The use of artificial pozzolana like “Fly ash” as a partial substitute of cement to the extent of (15%-20%) has been accepted as far back as in the year 1930. Fly ash can be successfully used in concrete due to the numerous advantages over ordinary plain concrete, such as increased compressive strength, improved workability, reduced permeability, reduced shrinkage, less bleeding and more economically, etc. Though the process of hardening in fly ash concrete is slow at the early stage, the final strength can be comparable to or even higher than that of plain concrete. This improvement can be attributed to better workability and reduction in the voids. It is well known that concrete is very good in resisting compressive forces, but it is found to be weak against tensile forces. It has the qualities of flexibility and ability to redistribute stresses, but it possesses a low specific modulus, a limited ductility and a very little resistance to cracking. The addition of fly ash to concrete further improves its compressive strength but contributes less to improve its other properties like tensile strength, ductility, resistance to cracking...etc. Fly ash does not have much cementations properties by itself, but in the presence of water it reacts with free lime either from cement or from any other source forming higher order hydrated products, which not only enhance strength but also improve durability. With cement, it forms calcium silicate hydrate, calcium mono-sulpho aluminates, calcium tri-sulpho aluminates and calcium hydroxide. These products are highly dense resulting in improved strength and reduced permeability.The role of fibres is essential to arrest advancing of crack by applying pinching forces at the crack tips, thus delaying their propagation across the matrix and creating a slow crack propagation stage. The ultimate cracking strain of the composite is thus increased by many times compared to that of unreinforced matrix .The introduction of small, closely spaced, randomly oriented fibres transfers an inherently brittle material with low tensile strength and impact resistance into astrong composite with superior crack resistance, improved ductility and distinctive post cracking behavior prior to failure.Steel fibre reinforced concrete is very effective in resisting flexural tensile stresses as compared to compressive stresses. On the contrary, fly ash reinforced concrete is very effective in resisting compressive stresses as compared to flexural tensile stresses. Specimens containing 1.0 % to 1.5% steel fibres with 15% to 25% replacement of cement by fly ash are more effective in resisting flexural tensile
Stress as well as compressive stresses. Hence, the optimum percentage of steel fibre fly ash reinforced concrete is around 1.0 % to 1.5% of steel fibres and 15% to 25% of fly ash. The ratio of compressive strength to flexural tensile strength can be enhanced by the addition of fly ash and the reduction of steel fibre percentage. The workability of concrete will also get enhanced by the addition of fly ash, which is required especially in higher percentages of steel fibres. The addition of different percentages of steel fibres to fly ash concrete will enhance the flexural tensile stresses up to 87%, but will reduce the compressive stresses to 23 %.Also, the addition of fly ash in different replacement percentages of cement to steel fibre concrete will enhance the compressive stresses up to 27% but will reduce the flexural tensile stresses to 46%. The ductility of concrete will get enhanced by the addition of steel fibres as well as fly ash.
SaravanaRaja Mohan. K, et al. volume 1 Nov 2011 presented a paper titledStrength and behavior of Fly Ash based Steel Fibre Reinforced Concrete Composite inInternational Journal Of Civil And Structural Engineering.The infrastructure needs of our country is increasing day by day and with concrete is a main constituent of construction material in a significant portion of this infra-structural system, it is necessary to enhance its characteristics by means of strength and durability. One of the many ways this could be achieved by developing new concrete composites with the fibres which are locally available that makes even non-engineered construction can work well under severe loads like earthquakes or man-induced attacks. Studies focusing on material properties with different percentage replacement of cement with fly ash are presented and on structural component with use of fly ash concrete and fibre concrete composites It has been found that with high volume of class ‘F’ fly ash, the workability of concrete has increased and the amount of cube compressive strength, split tensile strength, flexural strength has been decreased and no significant effect has been noted on impact strength of plain concrete. This experimental investigation is to study the effects of replacement of cement (by weight) with five percentage of fly ash and the effects of addition of steel fibre composite. A control mixture of proportions 1:1:49:1.79 with w/c of 0.45 was designed. Cement was replaced with five percentages (10%, 15%, 20%, 25% & 30%) of Class C fly ash. Four percentages of steel fibres (0.15%, 0.30%, 0.45% & 0.60%) having 20 mm length were used. This study reports the feasibility of use of steel fibres and their effect due to variation in fibre length, fibre content on structural properties such as cube compressive strength, cylinder compressive strength, split tensile strength, modulus of rupture and modulus of elasticity of this composite. Tests were conducted on beams with optimum fibre parameters, and the results compared with those of identical Reinforced Concrete beam. The maximum compressive strength was 29.20 MPa, obtained for S10F0.3 for a mix with a fibre length of 20mm, 10% fly ash and fibre content of 0.30% by weight and the increase in strength over plain cement concrete was found to be 54.82%. The maximum cylinder compressive strength is 25.45MPa, which is 45.85% more than the ordinary concrete. It is observed that the variation of cylinder compressive strength is very much similar to the cube compressive strength. An ideal choice would be 15% fly ash with 0.15% of fibre gives an increase of 5% to 31 % increase in cube strength at the end of seven days and 12% to 55% at the end of 28 days In general steel fibre composites show better performance upto 20% fly ash and 0.3% fibre content. Optimum could be 0.15% fibre content at 10 or 15% fly ash giving a range of 12 to 54.82 % increase.
PrashantY.Pawade et al. volume 2, March 2012 presented a paper titled Performance of steel fibre on standard strength concrete in compressionin International Journal of Civil and Structural Engineering.In this investigation a series of compression tests were conducted on 150mm, cube and 150mm x 300mm, cylindrical specimens using a modified test method that gave the complete compressive strength, static, dynamic modulus of elasticity, ultrasonic pulse velocity and stress-strain behaviour using silica fume with and without steel fibre of volume fractions 0, 0.5, 1.0, and 1.5 %, of 0.5mm Ø of aspect ratio of 60 on Portland Pozzalonic cement concrete. As a result the incorporation of steel fibres, and cement has produced a strong composite with superior crack resistance, improved ductility and strength behaviour prior to failure. Addition of fibres provided better performance for the cement-based composites, while silica fume in the composites may adjust the fibre dispersion and strength losses caused by fibres, and improve strength and the bond between fibre and matrix with dense calcium-silicate-hydrate gel. The results predicted by mathematically modelled expressions are in excellent agreement with experimental results. On the basis of regression analysis of large number of experimental results, the statistical model has been developed. The proposed model was found to have good accuracy in estimating interrelationship at 28 and 90 days age of curing. On examining the validity of the proposed model, there exists a good correlation between the predicted values and the experimental values as showed in figures. Addition of short, discontinuous fibres plays an important role in the improvement of the mechanical properties of concrete. It increases elastic modulus, decreases brittleness; controls crack initiation, and its subsequent growth and propagation. Deboning and pull out of the fibres require more energy absorption, resulting in a substantial increase in the toughness and fracture resistance of the material to cyclic and dynamic loads. In particular, the unique properties of steel fibre reinforced concrete SFRC suggest the use of such material for many structural applications, with and without traditional internal reinforcement. The use of SFRC is, thus, particularly suitable for structures when they are subjected to loads over the serviceability limit state in bending and shear, and when exposed to impact or dynamic forces, as they occur under seismic or cyclic action. However, there is still incomplete knowledge on the design/analysis of fibre-reinforced concrete FRC structural members. The analysis of structural sections requires, as a basic prerequisite, the definition of a suitable stress-strain relationship for each material to relate its behaviour to the structural response. The compressive strength increases with the increase in silica fume compared with normal concrete. All the properties of concrete, compressive strength (Cube & cylinder) and Modulus of Elasticity increases by addition of steel fibre. On the basis of regression analysis of large number of experimental results, the statistical model showed in figures has been developed. The proposed model was found to have good accuracy in estimating the 28 days Compressive strength of cube with cylinder. Compressive strength of cylinder with static and dynamic modulus of elasticity and ultrasonic pulse velocity, with their inter relationship at 8% Silica Fume & 0%, 0.5%, 1.0%, 1.5% Steel Fibres of both diameters. Strain at peak stress increases with concrete strength. And the increase of strain at peak stress also showed a good agreement with the increase of [Vf]. In general, the significant improvement in various strengths is observed with the inclusion of steel fibres in the plain concrete with high volume fractions. Addition of crimped steel fibres to silica fumes concrete (HPC) chances the basic characteristics of its stress-strain response. The slope of the descending branch increases with increasing the volume of steel fibre. The proposed model is found to have good accuracy in estimating the 28 and 90 days Compressive strength of fibre reinforced concrete, where 100% of the estimated values are within ± 2.6 % of the actual values. A moderate increase in compressive strength, strain at peak stress is also observed, which is proportional to the reinforcing index. The expression proposed is valid for steel fibre reinforcing index ranging from 0 to 3.9.
Konapure C.G et al,volume 3 Feb 2013, presented a paper titled An Experimental Study of Steel Fibre Reinforced Concrete with Fly Ash for M35 GradeinInternational Journal of Engineering Research and Applications. This paper deals with Experimental investigation for M-35 grade of concrete having mix proportion 1:1.23:2.95 with water cement ratio 0.43 to study the compressive strength, and tensile strength of steel fibre reinforced concrete (SFRC) containing fibres of 0.0%,1.0% and 1.5% volume fraction of hook end Steel fibres of 71 aspect ratio were used. The percentage of Fly Ash by weight is to be from 00%, 10% and 20%. A result data obtained has been analysed and compared with a control specimen (0.0% fibre and 0% fly ash). A relationship between workability, compressive strength and flexural strength represented mathematically and graphically. Result data clearly shows percentage increase in 28 days Compressive strength and Flexural strength for M-35 Grade of Concrete is mostly wide construction material in the world due to its ability it can be mould and shape. However concrete has some deficiencies as listed below, Low tensile strength, Low post cracking capacity, Brittleness and low ductility, Limited fatigue life, not capable of accommodating large deformations, Low impact strength. These properties can be improved by the use of steel fibre reinforced concrete. To this mixture, the required quantity of cement, fly ash and fibres in percentage were added. These were mixed to uniform colour. Then water was added carefully so that no water was lost during mixing. The moulds were filled with 0.0%, 0.5%, 1.0% and 1.5% fibres. Fly Ash 00% to 20% by weight of cement was added to this. Vibration was given to the cube moulds using table vibrator. The top surface of the specimen was levelled and finished. After 24 hours the specimens were remoulded and were transferred to curing tank wherein they were allowed to cure for 7 & 28 days Thefibres are dispersed and distributed randomly in the concrete during mixing, and thus improve concrete properties in all directions. The fibre helps to arresting the internal widening cracks and fly ash helps as an admixture for improving the properties of concrete. The introduction of the paper should explain the nature of the problem, previous work, purpose, and the contribution of the paper. The contents of each section may be provided to understand easily about the paper Density of concrete is more as the percentage of steel fibre increases. Slump will lose at the higher percentage of steel fibre & lesser fly ash content. Workability of concrete is improves when fly as percentage increases. The specimen strength is about 80% of target strength at 28th day and 95 to 100% at 45 days, because of steel fibre & Fly Ash. The Super-plasticizer is necessary for higher grade to get required slump & workable mix.
2.1 SUMMARY
From the above journals, it is observed that initially for every addition of fly ash the strength is lesser when compared to conventional concrete and as the curing days increases, the strength also increases. When steel fibre is added to the concrete, itscompressive, split tensile and flexural strength increases.
PROPERTIES OF MATERIALS
4.1 CEMENT
Ordinary Portland cement (OPC) is the most important type of cement. All the discussions that we have done in the previous chapter and most of the discussions that are going to be done in the coming chapters relate to OPC. Prior to 1987, there was only one grade of OPC which was governed by IS 269-1976. After 1987 higher grade cements were introduced in India. The OPC was classified into three grades, namely 33 grade, 43 grade and 53 grade depending upon the strength of the cement at 28 days when tested as per IS 4031-1988. If the 28 days strength is not less than 33N/mm2, it is called 33grade cement, if the strength is not less than 43N/mm2, it is called 43grade cement, and if the strength is not less than 53 N/mm2, it is called 53grade cement. But the actual strength obtained by these cements at the factory is much higher than the BIS specifications.
4.2 FLY ASH
Fly ash is finely divided residue resulting from the combustion of powdered coal and transported by the flue gases and collected by electrostatic precipitator. Fly ash is the most widely used pozzalonic material all over the world. In India, Fly ash was used in Rihand dam construction replacing cement up to about 15 per cent. In the recent time, the importance and use of fly ash in concrete has grown so much that it has almost become a common ingredient in concrete, particularly for making high strength and high performance concrete. Extensive research has been done all over the world on the benefits that could be accrued in the utilization of fly ash as a supplementary cementations material. The use of fly ash as concrete admixture not only extends technical advantages to the properties of concrete but also contributes to the environmental pollution control. Therefore, the use of fly ash must be popularized for more than one reason. There are two ways that the fly ash can be used: one way is to integrand certain percentage of fly ash with cement clinker at the factory to produce Portland pozzolana cement (PPC) and the second way is to use the fly ash as an admixture at the time of making concrete at the site of work.
4.2.1 TYPES OF FLY ASH
CLASS F :Technically the fly ash is considered as or class F fly ash. Such type of fly ash is produced by burning of anthracite or bituminous coal and possesses pozzalonic properties.It usually has less than 5% CaO. Class F fly ash has pozzalonic properties only.
CLASS C :This fly ash will be considered as also called as Calcareous fly ash
Classes C fly ash. This type of fly ash is commonly produced by burning of lignite or sub-bituminous coal and possess both pozzalonic and hydraulic
Properties.
4.2.2 EFFECTS OF FLY ASH ON HARDENED CONCRETE
Fly ash, when used in concrete, contributes to the strength of concrete due to its pozzalonic reactivity. However, since the pozzalonic reaction proceeds slowly, the initial strength of fly ash concrete tends to be lower than that of concrete without fly ash. Due to continued pozzalonic reactivity concrete develops greater strength at later age, which may exceed that of the concrete without fly ash. The pozzalonic reaction also contributes to making the texture of concrete dense, resulting in decrease of water permeability and gas permeability. It should be noted that since pozzalonic reaction can only proceed in the presence of water enough moisture should be available for long time. Therefore, fly ash concrete should be cured for longer period. In this sense, fly ash concrete used in under water structures such as dams will derive full benefits of attaining improved long term strength and water-tightness.
4.3 TYPES OF FIBRES
4.3.1 GLASS
Glass fibre is available in continuous or chopped lengths. Fibre lengths of up to 35-mm are used in spray applications and25-mm lengths are used in premix applications. Glass fibre has high tensile strength (2 – 4 GPa) and elastic modulus (70 – 80 GPa) but has brittle stress-strain characteristics (2,5 – 4,8% elongation at break) and low creep at room temperature. Claims have been made that up to 5% glass fibre by volume has been used successfully in sand-cement mortar without balling. It is suitable for use in direct spray techniques and premix processes and has been used as a replacement for asbestos fibre in flat sheet, pipes and a variety of precast products. GRC products are used extensively in agriculture; for architectural cladding and components; and for small containers.
4.3.2 STEEL
Steel fibres have been used in concrete since the early 1900s.The early fibres were round and smooth and the wire was cut or chopped to the required lengths. The use of straight, smooth fibres has largely disappeared and modern fibres have either rough surfaces, hooked ends or are crimped or undulated through their length. Typically steel fibres have equivalent diameters (based on crosssectional area) of from 0,15 mm to 2 mm and lengths from 7 to 75 mm. Aspect ratios generally range from 20 to 100. (Aspect ratio is defined as the ratio between fibre length and its equivalent diameter, which is the diameter of a circle with an area equal to the cross-sectional area of the fibre). Carbon steels are most commonly used to produce fibres but fibres made from corrosion-resistant alloys are available. Stainless steel fibres have been used for high-temperature applications. Steel fibres have high tensile strength (0.5 – 2 GPa) and modulus of elasticity (200 GPa), a ductile/plastic stress-straincharacteristic and low creep. Steel fibres have been used in conventional concrete mixes, concrete and slurry-infiltrated fibre concrete. Typically, contentof steel fibre ranges from 0,25% to 2,0% by volume. Fibre contents in excess of 2% by volume generally result in poor workability and fibre distribution, but can be used successfully where the paste content of the mix is increased and the size of coarse aggregate is not larger than about 10 mm. Steel-fibre-reinforced concrete containing up to 1,5% fibre by volume has been pumped successfully using pipelines of 125 to 150 mm diameter.
4.3.3 SYNTHETIC FIBRES
Synthetic fibres are man-made fibres resulting from research and development in the petrochemical and textile industries. There are two different physical fibre forms: monofilament fibres and fibres produced from fibrillated tape. Currently there are two different synthetic fibre volumes used in application, namely low-volume percentage (0,1 to 0,3% by volume) and high-volume percentage (0,4 to 0,8% by volume). Most synthetic fibre applications are at the 0,1% by volume level. At this level, the strength of the concrete is considered unaffected and crack control characteristics are sought. Fibre types that have been tried in cement concrete matrices include: acrylic, Aramid, carbon, nylon, polyester, polyethylene and polypropylene.
4.3.4 ACRYLIC
Acrylic fibres have been used to replace asbestos fibre in many fibre-reinforced concrete products. In this process fibres are initially dispersed in dilute water and cement mixture. A composite thickness is built up in layers using a pressure forming process and vacuum dewatering. Acrylic fibres have also been added to conventional concrete at low volumes to reduce the effects of plastic-shrinkage cracking.
4.3.5 ARAMID
Aramid fibres are two and a half times as strong as glass fibres and five times as strong as steel fibres, per unit mass. Due to the relatively high cost of these fibres, Aramid-fibre-reinforced concrete has been primarily used as an asbestos cement replacement in certain high-strength applications
4.3.6 CARBON
Carbon fibre is substantially more expensive than other fibre types. Carbon fibres are manufactured by carbonizing suitable organic materials in fibrous forms at high temperatures and then aligning the resultant graphite crystallites by hot-stretching. The fibres are manufactured as either Type I (high modulus) or Type II (high strength) and are dependent upon material source and extent of hot stretching for their physical properties. Carbon fibres are available in a variety of forms and have a febrile structure similar to that of asbestos. The Type I and II carbon fibres produced by carbonizing suitable organic materials other than Petroleum-based materials are 20 to 40 times stronger and have a modulus of elasticity up to 100 times greater than the pitch-based carbon fibre.
4.3.7 NYLON
Nylon is a generic name that identifies a family of polymers. Nylon fibre’s properties are impacted by the base polymer type, addition of different levels of additive, manufacturing conditions and fibre dimensions. Currently only two types of nylon fibre are marketed for concrete. Nylon is heat stable, hydrophilic, relatively inert and resistant to a wide variety of materials. Nylon is particularly effective in imparting impact resistance and flexural toughness and sustaining and increasing the load carrying capacity of concrete following first crack.
4.3.8 POLYESTER
Polyester fibres are available in monofilament form and belong to the thermoplastic polyester group. They are temperature sensitive and above normal service temperatures their properties may be altered. Polyester fibres are somewhat hydrophobic. Polyester fibres have been used at low contents (0,1% by volume) to control plastic-shrinkage cracking in concrete.
4.3.9 POLYETHYLENE
Polyethylene has been produced for concrete in monofilament form with wart-like surface deformations. Polyethylene in pulp form may be an alternate to asbestos fibres. Concrete reinforced with polyethylene fibres at contents between 2 and 4% by volume exhibits linear flexural load deflection behavior up to first crack, followed by an apparent transfer of load to the fibres permitting an increase in load until the fibres break.
4.3.10 POLYPROPYLENE
Polypropylene fibre was first used to reinforce concrete in the1960s. Polypropylene is a synthetic hydrocarbon polymer, the fibre of which is made using extrusion processes by hot-drawing the material through a die. Polypropylene fibres are produced as continuous mono-filaments, with circular cross section that can be chopped to required lengths, or fibrillated films or tapes of rectangular cross section. Polypropylene fibres are hydrophobic and therefore have the disadvantages of poor bond characteristics with cement matrix, a low melting point, high combustibility and a relatively lowmodulus of elasticity. Polypropylene fibre contents of up to 12% by volume are claimed to have been used successfully with hand-packing fabrication techniques, but volumes of 0,1% of 50-mm fibre in concrete have been reported to have caused a slump loss of 75 mm. Polypropylene fibres have been reported to reduce unrestrained plastic and drying shrinkage of concrete at fibre contents of 0,1 to 0,3% by volume.
4.3.11 NATURAL FIBRES
Natural reinforcing materials can be obtained at low cost and low levels of energy using local manpower and technology. Utilization of natural fibres as a form of concrete reinforcement is of particular interest to less developed regions where conventional construction materials are not readily available or are too expensive. Sisal-fibre reinforced concrete has been used for making roof tiles, corrugated sheets, pipes, silos and tanks.
4.4WATER
Portable tap water available in the laboratory with pH value of 7.0 and conforming to the requirements of IS456-2000 is used for making concrete and curing the specimen as well.
4.5 TESTING FOR CEMENT
4.5.1 FINENESS TEST
The fineness of cement has an important bearing on the rate of hydration and hence on the rate of gain of strength and also on the rate of evolution of heat. Finer cement offers a greater surface area for hydration and hence faster the development of strength. The fineness of grinding has increase Dover the years. But now it has got nearly stabilized. Different cements are ground to different fineness. The disadvantages offline grinding is that it is susceptible to air set and early deterioration. Maximum number of particles in a sample of cement should have a size less than about 100microns. The smallest particle may have a size of about 1.5 microns. By and large an average size of the cement particles may be taken as about 10 micron. The particle size fraction below 3 microns has been found to have the predominant effect on the strength at one day while 3-25 micron fraction has a major influence on the 28days strength. Increase in fineness of cement is also found to increase the drying shrinkage of concrete. In commercial cement it is suggested that there should be about 25-30 per cent of particles of less than 7 micron in size.
4.5.2 SIEVE TEST OF CEMENT
IS 2386(1)-1963 recommended the sieve analysis Weight correctly 100 grams of cement and take it on a standard IS Sieve No 9 (90microns). Break down the air-set lumps in the sample with fingers. Continuously sieve the sample giving circular and vertical motion for a period of 15 minutes. Mechanical sieving devices may also be used. Weigh the residue left on the sieve. This weight shall not exceed10% for ordinary cement.
4.5.3STANDARD CONSISTENCY TEST
For finding out initial setting time, final setting time and soundness of cement, and strength a parameter known as standard consistency has to be used. It is pertinent at this stage to describe the procedure of conducting standard consistency test. The standard consistency of a cement paste is defined as that consistency which will permit a vicat plunger having10 mm diameter and 50 mm length to penetrate to a depth of 33-35 mm from the top of the mould. The apparatus is called Vicat apparatus. This apparatus is used to find out the percentage of water required to produce a cement paste of standard consistency. The standard consistency of the cement paste is some time called normal consistency (CPNC).The following procedures is adopted to find out standard consistency. Take about 500gms of cement and prepare a paste with a weighed quantity of water (say 24 per cent by weight of cement) for the first trial. The paste must be prepared in a standard manner and filled into the Vicatmould within 3-5 minutes. After completely filling the mould, shake the mould to expel air. A standard plunger, 10 mm diameter, 50 mm long is attached and brought down to touch the surface of the paste in the test block and quickly released allowing it to sink into the paste by its own weight. Take the reading by noting the depth of penetration of the plunger. Conduct a 2nd trial (say with 25 per cent of water) and find out the depth of penetration of plunger. Similarly, conduct trials with higher and higher water/cement ratio still such time the plunger penetrates for a depth of 33-35 mm from the top. That particular percentage of water which allows the plunger to penetrate only to a depth of 33-35 mm from the top is known as the percentage of water required to produce a cement paste of standard consistency. This percentage is usually denoted as ‘P’. The test is required to be conducted in a constant temperature (27° + 2°C) and constant humidity (90%).
4.5.4 INITIAL SETTING TIME
Lower the needle © gently and bring it in contact with the surface of the test block and quickly release. Allow it to penetrate into the test block. In the beginning, the needle will completely pierce through the test block. But after some time when the paste starts losing its plasticity, the nearly may penetrate only to a depth of 33-35 mm from the top. The period elapsing between the time when water is added to the cement and the time at which the needle penetrates the test block to a depth equal to 33-35 mm from the top is taken as initial setting time.
4.5.5 FINAL SETTING TIME
Replace the needle © of the Vicat apparatus by a circular attachment (F). The cement shall be considered as finally set when, upon lowering the attachment gently cover the surface of the test block, the center needle makes an impression, while the circular cutting edge of the attachment fails to do so. In other words the paste has attained such hardness that the center needle does not pierce through the paste more than 0.5 mm.
4.5.6 SIEVE ANALYSIS
This is the name given to the operation of dividing a sample aggregate into various fractions each consisting of particles of the same size. The sieve analysis is conducted to determine the particle size distribution in a sample of aggregate, which we call gradation. A convenient system of expressing the gradation of aggregate is one which the consecutive sieve openings are constantly doubled, such as 10 mm, 20 mm, 40 mm etc. Under such a system, employing a logarithmic scale, lines can be spaced at equal intervals to represent the successive sizes .The aggregates used for making concrete are normally of the maximum size 80 mm, 40 mm, 20mm, 10 mm, 4.75 mm, 2.36 mm, 600 micron, 300micron and 150 micron. The aggregate fractions from 80 mm to 4.75 mm are termed as coarse aggregate and those fractions from 4.75 mm to 150micron are termed as fine aggregate. The size 4.75mm is a common fraction appearing both in coarse aggregate and fine aggregate (C.A. and F.A.).Grading pattern of a sample of C.A. or F.A. is assessed by sieving a sample successively through the entire sieves mounted one over the other in order of size, with larger sieve on the top. The material retained on each sieve after shaking, represents the fraction of aggregate coarser than the sieve in question and finer than the sieve above. Sieving can be done either manually or mechanically .In the manual operation the sieve is shaken giving movements in all possible direction to give chance to all particles for passing through the sieve.