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International Journal of Research and Innovation (IJRI)

International Journal of Research and Innovation (IJRI) 1401-1402

Flexural Behavior of Fibrous Reinforced Cement Concrete Blended With Fly Ash and Metakaoline

C.Dheeraj1, K. Mythili2, B.L.P. Swami3 1.Research Scholar, Department of Civil Engineering,At Aurora S Scientific And Technological And Research Academy, Hyderbad - , India. 2.M.Tech(Structural Engineering),Associate Proffesor At Aurora S Scientific And Technological And Research Academy,Bandlaguda, Hyderbad - ,India. 3.Professor and Co-ordinator,Research and Consultancy, VCE,Hyderabad,India

Abstract Research for high strength and better performance characteristics of concrete are leading the researchers for developing better structural concrete and new structural application techniques.New types of concrete have come in application in construction by using supplementary cementitious materials like fly ash, silica fume metakaoline, nanosilica and other materials using various reinforcing materials like different type of fibers for achieving better performance for the composite compared to the normal concrete.In the present experimental investigation, a mix design for high strength concrete of M80 is tried using triple blending technique with ternary blend of metakaoline and fly ash as partial replacement by weight of cement at various blended percentages ranging between 10%-40% with steel fibers having aspect ratio of 50. The various percentages of steel fibers to be tried are 0%, 0.5% and 1% by volume of concrete. The workability is measured for its consistency using compaction factor method.The project aims at finding the optimum replacement of cement by fly ash and metakaoline from which maximum benefit in various strengths and workability of the mix can be obtained. The results of fiber reinforced specimens with various percentages of ternary blend are compared with control specimens to study the behaviour of FRC properties with various percentages of the blends as partial replacement by weight of cement. Sufficient number of cubes and beams will be cast. The case specimens will be tested for the change in compressive and flexural strengths at 7 & 28 days for M80 concrete.It is expected that the results of present investigation would help to arrive at the optimum percentages of the admixtures and fibre reinforcement to achieve optimum strength properties of the composite. *Corresponding Author: C.Dheeraj, Research Scholar, Department of Civil Engineering,At Aurora S Scientific And Technological And Research Academy, Bandlaguda, Hyderbad - 500005, India. Published: December 17, 2014 Review Type: peer reviewed Volume: I, Issue : III

Citation: C.Dheeraj,,Research Scholar (2014) Flexural Behavior of Fibrous Reinforced Cement Concrete Blended With Fly Ash and Metakaoline

INTRODUCTION Concrete Composite

Concrete is the key material used in various types of construction, from the flooring of a hut to a multi storied high rise structure from pathway to an airport runway, from an underground tunnel and deep sea platform to high-rise chimneys and TV towers. In the last millennium concrete has demanding requirements both in terms of technical performance and economy while greatly varying from architectural masterpieces to the simplest of utilities. It is the most widely used construction materials. It is difficult to point out another material of construction which is as versatile as concrete. Concrete is one of the versatile heterogeneous materials, civil engineering has ever known. With the advent of concrete civil engineering has touched highest peak of technology. Concrete is a material with which any shape can be cast and with equal

strength or rather more strength than the conventional building stones. It is the material of choice where strength, performance, durability, impermeability, fire resistance and abrasion resistance are required. Cement concrete is one of the seemingly simple but actually complex materials. The properties of concrete mainly depend on the constituents used in concrete making. The main important materials used in making concrete are cement, sand, crushed stone and water. Even through the manufacturer guarantees the quality of cement it is difficult to produce a fault proof concrete. It is because of the fact that the building material is concrete and not only cement. The properties of sand, crushed stone and water, if not used as specified, cause considerable trouble in concrete. In addition to these, workmanship, quality control and methods of placing also play the leading role on the properties of concrete. Concrete is that pourable mix of cement, water, sand, and gravel that hardens into a super-strong building material. It has good compressive & flexural strengths and durable properties among others. Generally people use the words cement & concrete as if they were the same, but theyâ&#x20AC;&#x2122;re not. Concrete has cement in it, but also includes other materials, were cement is what binds concrete together. In the last millennium concrete has demanding requirementâ&#x20AC;&#x2122;s both in terms of technical performance and economy while greatly varying from architectural masterpieces to the simplest of utilities. Itâ&#x20AC;&#x2122;s is mouldable, adaptable and relatively fire resistant. The fact that it is an engineered material which satisfy almost any reasonable set of performance specifications, more than any other material currently 94

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available has made it immensely popular construction material. In fact every year more than 1m3 of concrete is produced per person (more than 10 billion tonnes) worldwide. Strength (load bearing capacity) and durability (its resistance to deteriorating agencies) of concrete structures are the most important parameters to be considered while discussing concrete. The deteriorating agencies may be chemical â&#x20AC;&#x201C; sulphates, chlorides, CO2, acids etc. or mechanical causes like abrasion, impact, temperature, etc. The steps to ensure durable and strong concrete encompass structural design and detailing, mix proportion and workmanship, adequate quality control at the site and choice of appropriate ingredients of concrete. Type of cement is one such factor. In this paper, the significance and effect of the type of cement on strength and durability of its corresponding concrete is focussed on. Depending upon the service environment in which it is to operate, a concrete structure may have to encounter different load and exposure regimes. In order to satisfy the performance requirements, cements of different strength and durability characteristics will be required. The main properties of concrete mainly depend on the constituents used in concrete making. The main important material used in making concrete are cement, sand, crushed stone and water. Even though the manufacturer guarantees the quality of cement it is difficult to produce a fault proof concrete. It is because of the fact that the building material is concrete and not only cement. The properties of sand, crushed stone and water, if not used as specified, cause considerable trouble in concrete. In addition to these, workmanship, quality control and methods of placing also plays the leading role on the properties of concrete. Compressive strength of concrete comes primarily from the hydration of alite and belite in Portland cement to form C-S-H. Alite hydrates rapidly to form C-S-H and is responsible for early strength gain; belite has a slower hydration rate and is responsible for the long term strength improvements. Alite: 2Ca3Sio5+6H2Oâ&#x2020;&#x2019;3CaO.2Sio2.3H20+ 3Ca(OH)2 Belite: 2C2S + 4H2O = C3S2H3 + CH

When alite and belite hydrate they produce a byproduct, calcium hydroxide (CH), which crystallizes around the aggregate to create a weak zone called the interfacial transition zone (ITZ). The ITZ is where concrete paste has a higher porosity and lower strength than the surrounding paste and allows the greatest penetration of harmful contaminants.

High Strength Concrete High strength concrete is used extensively throughout the world like in the oil, gas, nuclear and power industries are among the major uses. The application of such concrete is increasing day by day due to their superior structural performance, environmental friendliness and energy conserving implications. Apart from the usual risk of fire, these concrete are exposed to high temperatures and pressures for considerable periods of times in the above mentioned industries. High strength concrete (HSC) is a relatively new construction material. Technology for producing high strength concrete has sufficiently advanced that concrete with compressive strength greater than 40MPa are commercially available and strength much higher than that can be produced in laboratories. High strength concrete offers significantly better structural engineering properties, such as higher compressive and tensile strengths, higher stiffness, better durability, when compared to the conventional normal strength concrete (NSC). High-strength concrete is specified where reduced weight is important or where architectural considerations call for small support elements. By carrying loads more efficiently than normal-strength concrete, high-strength concrete also reduces total amount of material placed and lower the overall cost of the structure. High-strength concrete columns can hold more weight and therefore be made slimmer than regular strength concrete columns, which allows for more useable space, especially in lower floors of buildings. High strength concrete are also used in other engineering structures like bridges. From the general principles behind the design of high-strength concrete mixtures, it is apparent that high strengths are made possible by reducing porosity, inhomogeneity, and micro cracks in the hydrated cement paste and the transition zone. The utilization of fine pozzolanic material in highstrength concrete leads to a reduction of size of the crystalline compounds, particularly, calcium hydroxide. Consequently, there is a reduction of the thickness of the interfacial transition zone in highstrength concrete. The densification of the interfacial transition zone allows for efficient load transfer between the cement mortar and the coarse aggregate, contributing to the strength of the concrete. For very high-strength concrete where the matrix is extremely dense, a week aggregate may become the weak link in concrete strength. Concrete of high strength entered the field of construction of high raised buildings and long span bridges. In India, there are cases of using high strength concrete for prestressed concrete bridges. The higher strength concrete could be achieved by using one of the following methods or a combination some or many of the following:

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• Higher cement content • Reducing water cement ratio • Better workability and hence better compaction The utilization of fine pozzolanic materials in highstrength concrete leads to a reduction of the size of the crystalline compounds, particularly, calcium hydroxide. Consequently, there is a reduction of the thickness of the interfacial transition zone allows for efficient load transfer between the cement mortar and coarse aggregate, contributing to the strength of the concrete. For very high-strength concrete where the matrix is extremely dense, a weak aggregate may become the weak link in concrete strength. The requirement of high strength concrete requires mixtures, which could be in the range of 400kg plus per m3. The hunger for the higher strength leads to other material to achive the desired results thus emerged the contribution of cementitious material for strength of concrete. Addition of pozzolanic admixture like the pozzulanic fly ash (PFA) or condensed silica fume (CSF) which helps in the formation of secondary C-S-H gel there by improvement of strength. The addition of pozzolanic admixture like fly ash used as admixture will reduce the strength gain for the first 3 to 7 days of concrete will show gain beyond 7 days and give a higher strength on long term. With the addition of highly reactive pozzolanic admixtures like the silica fume will start contributing in about 3 days. Applications of mineral admixtures such as metakaolin, silica fume and ground granulated blast furnace slag in concrete are effective easy to future increase the strength and make durable for high strength concrete. The addition of admixtures to the concrete mixture increases the strength by pozzolanic action and filling in the small voids and that are created between cement particles. Metakaolin is the pozzolanic material which is mainly derived from a clay mineral “kaolinite”. Since it is calcined at higher temperatures it is named as “Metakaolin”. A further advantage of pozzolan mortars is their lower environmental impact. When compared to cement mortars, due to lower energy consumption during production and CO2 absorption by carbonation. The addition of metakaolin to mortars and concrete also has a positive effect in terms of durability. Calcium hydroxide accounts for up to 25% of the hydrated Portland cement, and calcium hydroxide does not contribute to the concrete’s strength or durability. Metakaolin combines with the calcium hydroxide to produce additional cementing compounds, the material responsible for holding concrete together. Less calcium hydroxide and more cementing compounds means stronger concrete.Metakaolin, because it is very fine and highly reactive, gives fresh concrete a creamy, nonsticky texture that makes finishing easier.

Blended Cements Blended cements are defined as hydraulic cements "consisting essentially of an intimate and uniform blend" of a number of different constituent materials. They are produced by "inter grinding Portland cement clinker with the other materials or by blending Portland cement with the other materials or a combination of inter grinding and blending." It is a fact that their use save energy and conserve natural resources but their technical benefits are the strongest. They affect the progress of hydration, reduce the water demand and improve workability. The concrete containing GGBFS, on vibration becomes ‘mobile’ and compacts well. Silica fumes greatly reduces, or even eliminates bleeding, the particles of Pozzolanic Fly Ash (PFA) are spherical and thus improves the workability. Their inclusion has the physical effect of modifying the flocculation of cement, with a resulting reduction in the water demand. The pore size in concrete is smaller. The fine particles ‘fit in’ between cement particles, thereby reducing permeability. Use of Fibers in Concrete Fiber Rein forced Concrete is a concrete composed of normal setting hydraulic cements, fine or fine and coarse aggregates and discontinuous discrete fiber with different proportions, different length and different gauges as parameters. Fibers help make the concrete stronger and more resistant to temperature extremes. The Steel fiberreinforced concrete is basically a cheaper and easier to use form of rebar reinforced concrete. Rebar reinforced concrete uses steel bars that are laid within the liquid cement, which requires a great deal of preparation work but make for a much stronger concrete. Steel fiber-reinforced concrete uses thin steel wires mixed in with the cement. This imparts the concrete with greater structural strength, reduces cracking and helps protect against extreme cold. Steel fiber is often used in conjunction with rebar or one of the other fiber types. Steel fibers: • Improved structural strength • Reduced steel reinforcement requirements • Improved ductility • Reduced crack widths and control of crack widths thus improving durability • Improved impact & abrasion resistance • Improved freeze-thaw resistance When the loads imposed on concrete approach that for failure, cracks will propagate, sometimes rapidly, fibers in concrete provide a means of arresting the crack growth. Reinforcing steel bars in concrete have, the same beneficial effect because they act as long continuous fibers. Short discontinuous fibers have the advantage however of being uniform. If the modulus of elasticity of the concrete or mortar binder, the fibers help to carry the load, thereby increasing the tensile strength of the material. Increases 96

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in the length, diameter ratio of the fibers usually augment the flexural strength and toughness of the concrete. Blends of both steel and polymeric fibers are often used in construction projects in order to combine the benefits of both products; structural improvements provided by steel fibers and the resistance to explosive spalling and plastic shrinkage improvements provided by polymeric fibers. In certain specific circumstances, steel fiber can entirely replace traditional steel reinforcement bar in reinforced concrete. This is most common in industrial flooring but also in some other precasting applications. Typically, these are corroborated with laboratory testing to confirm performance requirements are met. Care should be taken to ensure that local design code requirements are also met which may impose minimum quantities of steel reinforcement within the concrete. There are increasing numbers of tunnelling projects using precast lining segments reinforced only with steel fibers. The values of this ratio are usually restricted to between 100 and 200 sincefibres which are too long tend to “ball” in the mix and create workability problems. As a rule, fibres are generally randomly distributed in the concrete; however, processing the concrete so that the fibres become aligned in the direction of applied stress will result in even greater tensile or flexural strengths. Advantages of Triple Blending The proper us of metakaol in can result in increased concrete strength (particularlyearlystrength),improv edchlorideandsulphateresistance, reduced efflorescence an improveddurability.Usedat5-15% replacement ofcement by weight,metakaol in will contribute to: increased strength, reduced permeability,greater durability and effective control of efflorescence and degradations caused by alkali-silica reaction in concrete.In addition ,the brighter colour imparted to the concrete by metakaolin could improve the night driving visibility if metakaolin concrete were used in highway and bridge construction and would improve the appearance of exposed concrete. Main influence of fly ash is on water demand and workability. For a constant workability, reduction in water demand due to flyash is usually between 5 to 15 percent by comparison with a Portland cement only.A concrete mix containing fly ash is cohesive and has a reduced blending capacity. Together with flyash and metakaolin as a replacement to cement, impart advantages of both flyash and metakaolin. The advantages include durability, better workability, and reduced heat of hydration. One of the main advantages is that the strength reduction due to flyash is compensated by addition of metakaolin, hence making the mix economical as

well as of high strength. Aim of the Present Project and Details Of The Present Study The aim of our project is to study the compressive strength of high strength mix of M70 grade, with a partial replacement of cement with metakaolin and flyash. Our project includes the concept of triple blending of cement with metakaolin and flyash, this triple blend cements exploit the beneficial characteristics of both pozzolanic materials in producing a better concrete.

Literature Review In order to fulfill the aims and objectives of the present study following literature have been reviewed. Notable Previous Research A number of reports have demonstrated that concretes containing combinations of flyash and metakaolin with Portland cement are superior in certain respects to concretes containing Portland cement. The type and source of the cement,characteristics and amounts of flyash and metakaolin affected the results. Current Use of Metakaolin in Concrete Technology Metakaolin can be used to replace or add to OPC or can be combined with other pozzolans. The proper use of metakaolin can result in increased concrete strength (particularly early strength), improved chloride andsulphateresistance, reduced efflorescence an improved durability. Metakaolin,derived from purified kaolin clay, is a white, amorphous, alumino-silicate which reacts aggressively with calcium hydroxide to form compounds with cementitious value. Used at 5-15% replacement of cement by weight, metakaolin will contribute to: increased strength, reduced permeability, greater durability and effective control of efflorescence and degradations caused by alkali-silica reaction in concrete. In addition , the brighter colour imparted to the concrete by metakaolin could improve the night driving visibility if metakaolin concrete were used in highway and bridge construction and would improve the appearance of exposed concrete. Uses Of Metakaolin • High performance, high strength and light weight concrete. • Precast concrete for architectural, civil, industrial and structural. • Fibrecement and ferrocement products, glass fiber reinforced concrete. • Mortars,stuccos, repair material, pool plasters. • Manufactured repetitive concrete products. • Increased compressive and flexural strengths. 97

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• Reduced permeability and efflorescence. • Increased resistance to chemical attack and prevention of alkali silica reaction • Reduced shrinkage. • Improved finishability, colour and appearance. Pozzolanic Substitution Substituting metakaolin for silica fume in existing formulations will: • Maintain or increase compressive strength at early age (1-28 days) • Maintain long term compressive strength development (>28days) • Disperse more easily in the mixer with less dust • Not darken the color of the paste or mortar and • Reduce superplasticizer demand for the target slump. Metakaolin is compatible with chemical admixtures, as well as with other pozzolansand supplementary cementing materials, i.e. flyash, ground granulated blast furnace slag. Alkali Silica Reaction Problem Quality concrete is a carefully selected composition of materials which, when properly manufactured, proportioned, mixed, placed, consolidated, finished and cured will have sufficient strength and durability in accordance with the desired application. Alkali silica reaction can be explained as the situation where cement alkalis reactwith certain forms of silica in the aggregate component of a concrete, forming an alkali-silica gel at the aggregates surface. This formation, often referred to as ”reaction rim” has a very strong affinity for water, and thus has a tendency to swell. These expanding compounds can cause internal pressures sufficiently strong to cause cracking of the paste matrix, which can then result in a compromisedconcrete with an open door to an increasing rate of deterioration. The Metakaolin Solution When a pure form of metakaolin is employed as a pozzolanic mineral admixture at 10-15% weight of cement, the calcium hydroxide level can be reduced sufficiently to render any gels that are formed as non –expansive. The protection is further enhanced in view of themetakaolin addition’s effect on overall reduced concrete permeability and in a slight reduction in the alkalinity of the pore solution. Efflorescence The phenomenon commonly known as efflorescence, occurs when calcium hydroxide a soluble reaction by-product of the hydration process of ordinary Portland cement is carried to the surface of cementbased products by migrating water. Exposed to the atmosphere, calcium hydroxide reacts with carbon

dioxide to form calciumcarbonate deposits which remain apparent as unsightly, whitish stains. Two forms of efflorescence have been identified- primary and secondary. They are distinguished by the point in time at which they occur in relation to the curing process. Primary efflorescence occurs during the curing process. Excess water in the matrix bleeds to the surface where it eventually evaporates, leaving behind deposits of calcium hydroxide crystals(Ca(OH)2) which,when exposed to the carbon dioxide(CO2) in the air, form calcium carbonate (CaCO3) in the surface pores. Secondary efflorescence occurs in the cured concretes and composites, which are in contact with moisture or are subjected to cycles of re-wetting and drying. Moisture penetrates in to and leaches from the matrix dissolving soluble calcium hydroxide Ca(OH)2 that remains as a normal byproduct of Portland cement hydration. Upon subsequent drying the water with the lime in solution can migrate to the surface where upon evaporation, leaves deposits of calcium hydroxide Ca(OH)2 and subsequently, calcium carbonate CaCO3. Metakaolin Solution For Efflorescence • Eliminate free lime from the system through rapid pozzolanic reaction. • Increase the density and reduce the porosity and permeability of the paste system. • Reduce the cement content with pozzolan substitution 5-15% (the dilution effect). Pozzolanic Reactivity Metakaolin is a lime hungry pozzolan that reacts with free calcium hydroxide to form stable, insoluble, strength-adding, cementitious compounds. When metakaolin reacts with calcium hydroxide (CH) a cement hydration by product, a pozzolanic reaction takes place where by new cementitious compounds (C2ASH8) and (CSH), are formed. These newly formed compounds will contribute cementitious strength and enhanced durability properties to the system in place of the otherwise weak and soluble calcium hydroxide. Metakaolin has been engineered and optimized to contain a minimum of impurities and to react efficiently with cement’s hydration by-product calcium hydroxide. Primary efflorescence can be reduced by using metakaolin at 5-15% replacement of cement by weight. The use of highly reactive metakaolin works to the root of the efflorescence problem by eliminating the calcium hydroxide from the system. Once fully cured an optimized highly reactive metakaolin formulated product cannot exhibit secondary efflorescence as virtually all of the available free lime has been chemically combined by pozzolan.

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Reduced Permeability Concrete’s porosity, pore interconnectivity and overall permeability to fluids have direct influence on the concrete’s ultimate durability and useful service life. Where quality concrete’s mortars and other cement-based products are produced with careful control of materials and water to cement ratios, performance can be significantly influenced by the addition of highly reactive pozzolans. The addition of metakaolin to these materials at a515% replacement b weight of cement will contribute to a more compact arrangement of cementitious products where increased paste densities, mechanical interlock and paste-aggregate bond are the result. In addition, the pozzolanic reaction, as described above, has a direct and significant influence on the materials service permeability. As soluble hydration byproducts in a non-pozzolan enriched concrete are leached out by migrating moisture, they leave behind opened and more interconnected pore systems which will set the stage for an increased risk and rate of efflorescence discoloration, fading and staining. By chemically combining with calcium hydroxide, the pore system is rendered much more stable.

due resulting, from combustion of pulverized coal or lignite. It is collected by mechanical or electro static separators called hoppers from flue gases of power plants where powdered coal is used as fuel. This material, once considered as a by-product finding difficulty to dispose off, has now become a material of considerable value when used in conjunction with concrete. Classification of flyash ASTM-C 618-93 categories natural pozzolannas in to the following categories. Class N fly ash: Raw or calcined natural pozzolannas such as some diatomaceous earths, opalinechert and shale, stuffs volcanic ashes and pumice comes in this category. Calcinedkaoline clay and laterite shale also fall in this category of pozzolanas. Class F fly ash: Fly ash normally produced from burning anthrdoete or bituminous coal falls in this category. This class of fly ash exhibits pozzolanic property but rarely if any, self –hardening property. Class C fly ash: Fly ash produced from lignite or sub-bituminous coal is the only material included in this category. This class of fly ash has both pozzolanic and varying degree of self cementations properties.

Cement Replacement the Dilution Effect

Reaction mechanism of fly ash

Metakaolin has the potential to produce high strengths in cement based products at 5-155 replacement by weight of cement. As such, it is common to see increases in concrete or mortar compressive strengths (>20%) such that a further cement reduction beyond pound for pound cement replacement can be taken if strength gains of this degree are not required or beneficial. It is possible for metakaolin to replace cement by weight at 1:2 to 1:3,this would, of course, require trial mixes with specific materials to confirm the exact formula.

Reaction mechanism for fly ash can be basically explained as pozzolanic reaction mechanism. Flash is considered to be a pozzolona. Pozzolannas are materials which, though not cementitious in themselves, contain certain constituents, which at ordinary temperatures in the presence of water, will combine with lime to form stable insoluble compounds with cementitious properties behaves as a more or less inert material and serves as a precipitation nucleus for lime {Ca(OH)2} and calcium –silicate hydrate-gel originating from the cement hydration. The subsequent pozzolanic reaction appears to be a slow process. Fly ash from bituminous coal consists of a major part of glass phase with crystallization inclusions, the glass being an alumina-silica-glass. The pozzolanic reaction starts when the glass of the flyash particles dissolves. The formation of C-S-H gel takes place when the glass of the fly ash particles has gone in to solution. The decomposition of the glass network appears to be strongly dependent on the alkalinity of pore water. The glass structure of the flyash is only decomposed substantially beyond pH of about 13.2 or 13.3.

Metakaolin Features • Rapid reaction. The potential to react with more than its own weight equivalent in calcium hydroxide. • A minimum of impurities • Stable to enhanced early strength performance (<24hours) • This unique package of features and benefits makes metakaolin stand out within the world of admixtures as the performance leader and preferred pozzolan for use in quality and high performance architectural and structural applications-especially where engineering properties, aesthetics and durability are important. Fly Ash Fly ash, an artificial pozzolana is the unburned resi-

Various factors influencing the fly ash reaction are Cement type: Rapid hardening cements develop high alkalinity faster than ordinary cements. Consequently, fly ash reaction starts earlier. Similarly 99

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different cements effect accordingly. Temperature: Development of hydroxyl concentration appears to be much slower at 20oC . At 40oC the pH reaches a high value within one day of hydration so that the reaction of fly ash can start from first day. Temperature also affects the reactivity of fly ash itself. That means at a higher temperature the reaction will be initiated at lower alkalinity. Water cement ratio: There is strong relation between fly ash activity and water/cement ratio. Higher the W/C ratio, lower the alkalinity and slower the reaction.

control is assured. The proportions of fly ash and cement are pre determined and mix proportion is limited. The second method allows for more use of fly ash as a component of concrete. Fly ash plays many roles such as, in freshly mixed concrete, it acts as a fine aggregate and also reduces water cement ratio in hardened state, because of its pozzolanic nature, it becomes a part of the cementitious matrix and influences the strength and durability. The assumptions made in selecting an approach to mix proportioning fly ash concretes are

Types of fly ash: Pozzolanic activity or reaction of fly ash depends upon parameters such as fineness, amorphous matter, chemical and mineralogical composition and un-burnt carbon contents.

• It reduces the strength of concrete at early stages • For same workability, concrete containing fly ash requires less water than concrete containing ordinary Portland cement.

Effects of fly ash on concrete

The basic approaches that are generally used for mix proportioning are

Main influence of fly ash is on water demand and workability. For a constant workability, reduction in water demand due to flyash is usually between 5 to 15 percent by comparison with a Portland cement only.

• Partial replacement of cement • Addition of fly ash as fine aggregates and • Partial replacement of cement, fine aggregate and water

A concrete mix containing fly ash is cohesive and has a reduced blending capacity. Reduction in water demand of concrete caused by presence of fly ash is usually described to their spherical shape, which is called “ball-bearing effect” Neville AM (2005).

At earlier stages fly ash exhibits very little cementing effects and acts as a fine aggregate, but at later ages cementing activity becomes apparent and its contribution in the development of strength is observed.

However, other mechanisms are also involved and may well be dominant. In particular, in consequence of electric charge, the finer flyash particles become adsorbed on the surface of cement particles. If enough fine fly ash particles are present to cover the surface of the cement particles, which thus become deflocculated, the water demand for a given workability is reduced.

Applications of Fly ash:

Proportioning of fly ash concrete Using of fly ash in concrete has to meet one or more of the following objectives. • Reduction in cement content • Reduced heat of hydration • Improved workability and • Gaining levels of strength in concrete beyond 90 days of testing. Fly ash is introduced in to concrete by one of the following methods. • Cement containing fly ash may be used in place of OPC • Fly ash is introduced as an additional component at the time of mixing. The first method is simple and problems of mixing additional materials are not there, there by uniform

Fly ash is highly recommended for mass concrete applications, i.e. large mat foundations, dams etc. Fly ash can be used for the following 1. Filling of mines. 2. Replacement of low lying waste land and refuse dumps 3. Replacement of cement mortar 4. Air pollution control 5. Production of ready mix fly ash concrete 6. Laying of roads and construction of embankments 7. Stabilizing soil for road construction using limefly ash mixture 8. Construction of rigid pavements using cement – fly ash concrete 9. Production of lime –flyash cellular concrete. 10. Production of precast fly ash concrete building units 11. Production of sintered fly ash light light weight aggregate and concrete and 12. Making of lean-cement fly ash concrete. Properties of fresh concrete with fly ash Time of setting: the initial setting time of 7.5 h are compared to those of control concrete made with the water content and water/cementitious materials, whereas the final setting time of set were re100

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tarded by 3h compared with that of control. Bleeding: Bleeding tests performed on high strength fly ash concrete have shown that this concrete does not bleed. Density of fresh concrete: this is comparable to the density of Portland cement concrete without fly ash. Dosage requirement of super plasticizer because of the very low water/cementitious materials, the use of super plasticizers is mandatory. Properties of hardened concrete with fly ash Temperature rise: Because of the very low cement content the temperature rise in the first few days after placement is normal. Strength properties: Fly ash concrete exhibits adequatestrength development characteristics both at early and late ages. Youngâ&#x20AC;&#x2122;s modulus of elasticity: The modulus of elasticity of fly ash concrete is somewhat higher than the modulus of elasticity of probably due to the glassy, unhydrated fly ash particles acting as a fine filler material in the concrete. Creep characteristics: The creep stains of high strength fly ash concrete at 1 year is comparable to or lower than that of Portland cement concrete of comparable strength. Fibers Plain concrete possesses a very low tensile strength, limited ductility and little resistance to cracking. Internal micro cracks are inherently present in the concrete and its poor tensile strength is due to the propagation of such micro cracks, eventually leading to brittle fracture of the concrete. In plain concrete and similar brittle materials, structural cracks (micro cracks) develops even before loading, particularly due to drying shrinkage or other causes of volume change. The width of these initial cracks seldom exceeds a few microns, but there two dimensions may be of higher magnitude. When loaded, the micro cracks propagate and open up and owing to the effect of strength concentration, addition cracks from the places of minor defects would usually happen. The structural cracks proceed or by tiny jumps because they are retarded by various obstacles, changes of direction in by passing the more resistant grains in matrix. The development of such micro cracks is the main cause of elastic determination of concrete. It has been recognized that the addition of small, closely spaced and uniformly dispersed fibres to concrete would act as crack arrester and would substantially improve its static and dynamic properties and does not notably increase the mechanical

properties before failure but governs the post failure behavior. Thus, plain concrete which is quasi-brittle material is turned on the pseudo ductile material by using fibre reinforced. This type of concrete is known asâ&#x20AC;? fibre reinforced concreteâ&#x20AC;? Short fibres full of steel, glass, carbon or hemp is mixed with concrete, which builds the matrix. After matrix initialization, the stresses are absorbed by bridging fibres and the bending moments are redistributed. The concrete element does not fail spontaneously when the matrix is cracked; the deformation energy is absorbed and the material becomes pseudo-ductile. Factors affecting properties of fibre reinforced concrete Fibre reinforced concrete is the composite material containing fibres in the cement matrix in an orderly manner or randomly distributed manner. Its properties would obviously, depend upon the efficient transfer of stress between matrix and the fibres, which largely dependent on the type of fibre, fibre geometry, fibre content, orientation and distribution of the fibres, mixing and compaction techniques of concrete, and size and shape of the aggregate. These factors are briefly discussed below.The properties of various fibres are given in table Properties of different types of fibres Type of fibre

T e n s i l e Youngs Ultimate S p e c i f i c strength ( Modulus elongation Gravity MPa) (GPa) (%)

Acrylic

210-420

2.1

25-45

1.1

Asbestos

560-980

84-140

0.6

3.2

Carbon

1800-2400

230-380

0.5

1.9

Glass

1050-3850

1.5-3.5

2.5

Nylon

770-840

4.2

16-20

1.1

Polyestor

735-875

8.4

11-13

1.4

Polyethylene

700

0 . 1 4 0.42

0.9

Polypropylene

560-770

3.5

0.9

Rayon

420-630

10-25

1.5

Rock wool

490-770

70-119

0.6

2.7

Steel

280-2800

203

0.5-3.5

7.8

Relative fibre matrix stiffness The modulus of elasticity of matrix must be much lower than that of fibre for efficient stress transfer. Low modulus of fibres such as nylons and polypropylene are unlikely to give strength improvement, but they help in the absorption of large energy and therefore impart greater degree of toughness and resistance to impart. High modulus fibres such as 101

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steel, glass and carbon impart strength and stiffness to the composite. Interfacial bond between the matrix and the fibres also determine the effectiveness of stress transfer from the matrix to the fibre. 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 by treating the steel fibres with sodium hydroxide or acetone.

Cement Locally available Ordinary Portland Cement of 53 grade of ULTRATECH Cement brand confirming to ISI standards has been procured and following tests have been carried out as shown in table Physical properties of OPC 53 grade ultratech brand cement S.NO

Property

Test Value

Requirements as per IS:122691987

Fineness of cement

4.52

10%(should not be more than)

Specific gravity

2.99

3.15

Normal consistency

33%

Setting time Initial setting time Final setting time

40 min 6 hours

should not be less than 30 min should not be greater than 600 min

Compressive strength at 3 days 7 days 28 days

34N/mm2 44.8N/mm2 59N/mm2

27N/ mm2(min) 37N/ mm2(min) 53N/ mm2(min)

Volume of fibres The strength of the composite largely depends on the quantity of fibres used in it. Increase in the volume of fibres, increases linearly the tensile strength and toughness of the composite. Use of higher percentage of fibre is likely to cause segregation and hardness of concrete and mortar. Aspect ratio of the fibre Another important factor which influences the properties and behavior of the composite is the aspect ratio of the fibre. Orientation of fibres One of the differences between conventional reinforcement and reinforcement is that in conventional reinforcement, bars are oriented in the direction desired while fibres are randomly oriented. To see the effect of randomness, mortar specimens reinforced with 0.5% volume of fibres were tested. In one set specimens fibres were aligned in the direction of the load, in another in the direction perpendicular to that of the load, and in the third randomly distributed. It was observed that the fibres aligned parallel to the applied load offered more tensile strength and toughness than randomly distributed or perpendicular fibres.

Experimental Investigation Investigation The scope of present investigation is to study strength properties on plain concrete, concrete with replacement of varying percentages of metakaolin and flyash along with steel fibres in different total percentages of 0%, 0.5% and 1% for M70 concrete mix. Materials Used In the Experimentation Experimental study is carried out to investigate the strength variations in concrete.

Fly ash Fly ash is the finely divided mineral residue resulting from the combustion of coal in electric generating plants. Fly ash consists of inorganic, incombustible matter present in the coal that has been fused during combustion into a glassy, amorphous structure. Fly ash particles are generally spherical in shape and range in size from 2 Îźm to 10 Îźm. They consist mostly of silicon dioxide (SiO2), aluminium oxide (Al2O3) and iron oxide (Fe2O3). Fly ash like soil contains trace concentrations of the following heavy metals: nickel, vanadium, cadmium, barium, chromium, copper, molybdenum, zinc and lead. The chemical compositions of the sample have been examined and the flyash are of ASTM C618 Class F. Physical properties of Fly ash Color

Whitish grey

Bulk density

0.994 g/cm3

Specific gravity

2.288

Moisture %

3.14

Average particle size

6.12Âľ

Metakaolin The Metakaolin is obtained from the 20 Microns limited Company at Vadodara in Gujarat by the brand name Metacem 850C. The specific gravity of Metaka-

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olin is 2.5. The Metakaolin is in conformity with the general requirement of pozzolana (1,8,12,16). The Physical and chemical results are tabulated.

Coarse Aggregate

Specific Gravity:

2.54

D10 particle size

<2.0um

Physical form:

Powder

D50 particle size

<4.5um

Machine crushed granite confirming to IS 383-1970 consisting 20mm maximum size of aggregate has been obtained from the local quarry.It has been tested for physical and mechanical properties such as Specific Gravity, Sieve Analysis, Bulk density, Crushing and Impact values and the results have been shown below.

Colour:

Off-White

D90 particle size

<25um

physical properties of coarse aggregate

Brightness:

80-82 Hunter L

Bulk Density(lbs/ ft3):

20-25

Bulk Density(g/ cm3):

0.4

Physical properties of Metakaolin given by the distributer

BET: surface area

15 m2/gram

Chemical composition of Metakaolin given by the distributer

S.No

Property

Coarse aggregate

Specific gravity

2.70

Bulk density Loose Compacted

13.29kN/m3 15.00kN/m3

Water absorption

0.7%

Flakiness index

14.22%

SiO2

51-53%

CaO

<0.20%

Elongation index

21.33%

AlO3

42-44%

MgO

<0.10%

Crushing value

21.43%

Fe2O3

<2.20%

Na2O

<0.05%

Impact value

15.5%

TiO2

<3.0%

K 2O

<0.40%

SO4

<0.5%

L.O.L

<0.5%

Fine Aggregate The locally available Natural river sand confirming to grading zone-II has been used as Fine aggregate. Following tests have been carried out per the procedure given in IS383 (1970). • Specific Gravity • Bulk Density • Grading • Fineness Modulus of Fine aggregate Physical properties of fine aggregate S.No

Property

Value

Specific Gravity

2.68

Fineness Modulus

2.78

Bulk Density Loose Compacted

14.67kN/m3 16.04kN/m3

Grading

Zone-II

S.No

I.S Sieve Designation

Weight Retained

% of Weight Retained

Cumulative % of Weight Retained

%of Passing

4.77mm

1.50

98.50

2.36mm

1.60

3.10

96.90

1.18mm

5.90

9.00

91.00

600µ

7.8

16.8

83.2

300µ

375

37.50

54.30

45.70

150µ

392

39.2

93.50

6.50

75µ

6.0

99.50

0.50

Total=277.70

S.No

I.S Sieve designation

Weight Retained (gm)

% of Weight Retained

Cumulative % of Weight Retained

% of Passing

20mm

935

18.70

18.7

81.30

10mm

3930

78.6

97.30

2.7

4.75mm

120

2.40

99.70

0.30

2.36mm

99.70

0.30

1.18mm

99.700

0.30

600µ

99.70

0.30

300µ

99.70

0.30

150µ

99.70

0.30

Fineness modulus=7.14

Sieve analysis of Fine aggregate

Fineness modulus =2.78

Sieve analysis of coarse aggregate

Total=714.20

Steel Fibres In the present experimental project, steel fibres are used. Fibres have 0.9mm diameter and aspect ratio of 40 to 50. The fibres are having random orientation. Fibres are mixed at 3 different volume percentages of 0, 0.5 and 1.0 %. The properties of various types of fibres including steel fibres are given in table Water Potable water has been used in this experimental program for mixing and curing. Super plasticizer The super plasticizer used in this experiment is CONPLAST 430. It is manufactured by M/S FOSROC INDIA Ltd, Bangalore.

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International Journal of Research and Innovation (IJRI)

Super Plasticizers are new class of generic materials which when added to the concrete causes increase in the workability. They consist mainly of naphthalene or melamine sulphonates, usually condensed in the presence of formaldehyde. Super Plasticised concrete is a conventional concrete containing a chemical admixture of super plasticizing agent. As with super plasticizer admixtures one can take advantage of the enhanced workability state to make reductions in water cement ratio of super plasticized concrete, while maintaining workability of concrete. The use of super plasticizers in ready mixed concrete and construction reduces the possibility of deterioration of concrete for its appearance, density and strength. On the other hand, it makes the placing of concrete more economical by increasing productivity at the construction site. Up to 4% by weight of cement is used to maintain the workability. MIX Design by Doe Method The selection of mix materials and their required proportion is done through a process called mix design. There are number of methods for determining concrete mix design. The method that we have adopted is called the D.O.E Method which is in compliance to the British Standards. The objective of concrete mix is to find the proportion in which concrete ingredients-cement, water, fine aggregate and coarse aggregate should be in order to provide the specified strength, workability and durability and possibly meet other requirements has listed in standards such as IS:456-2000. Mix design can be defined as the process of selecting suitable ingredients of concrete and determining their relative proportions with the objective of producing concrete of certain minimum strength and durability as economically as possible. The design of concrete mix is not a simple task on account of widely varying properties of the constituent materials, the condition that prevail at the work and the condition that are demanded for a particular work for which mix is designed. Design of concrete mix requires complete knowledge of various properties of the constituent materials, the complications, in case of changes on these conditions at the site. The design of concrete mix needs not only the knowledge of material properties of concrete in plastic condition, it also needs wider knowledge and experience of concerning. Even then the proportion of the material of the concrete found out at the laboratory requires modifications and readjustments to suit the field conditions. Details of DOE Method The DOE method overcomes some limitations of the IS method. In DOE method, the fine aggregate content is a function of 600micron passing fraction

of sand and not the zone of sand. The 600micron passing fraction emerges as the most critical parameter governing the cohesion and workability of concrete mix. Thus sand content in DOE method is more sensitive to changes in fineness of sand when compared to the IS method. The sand content is also adjusted as per workability of mix. It is well accepted that higher the workability greater is the fine aggregate required to maintain cohesion in the mix. The water content per m3 is recommended based on workability requirement given in terms of slump and Vee-Bee time. It recommends different water contents for crushed aggregates and for natural aggregates. The quantities of fine and coarse aggregates are calculated based on plastic density plotted from graphs. However the DOE method allows simple correction in aggregate quantities for actual plastic density obtained at laboratory. Procedure of Mix Design Step 1:Assume standard deviation =5 N/mm2 Assume slump of concrete =75 mm Step 2: Find the target mean strength from the specified characteristic strength. Target mean strength = specified characteristic strength + standard deviation * risk factor. Step 3: Calculate the water/cement ratio using table and figure shown below. Table gives approximate compressive strength of concrete made with a free w/c ratio of 0.50. Using this table find 28 days strength for the approximate type of cement and types of C.A mark a point on the Y-axis in fig equal to the compressive strength read from the table which is at a w/c ratio of 0.50. Through this intersection point, draw a parallel doted curve nearest to the intersection point. Using the new curve we read of w/c ratio as against target mean strength. Step 4: Decide water content water require workability express in terms of slump or Vee-Bee time taking into consideration the size of aggregate and its type. Step 5: Find the cement content knowing the w/ c ratio and the water content. Step 6: Find out the total aggregate content and find out wet density of fully compacted aggregates. The value of specific gravity of 2.7 for crushed aggregate can be taken. The aggregate content is obtained by subtracting the weight of cement and water content from weight of fresh concrete. Step 7: Proportion of fine aggregate is determine in the total aggregate. Maximum size of coarse aggregate, the level of workability, w/c ratio and the percentage of fine passing 600micron sieve. Once the proportion of fine aggregate is obtained multiplying by the weight of total aggregate gives the weight if fine aggregate. Then the weight of the C.A can be found out. 104

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Calculation for M70 Mix Design:

The ratio comes out to be 1:0.97:1.7

Materials

Trial Mixes

Cement : OPC 53 grade Coarse aggregates : crushed stone of size 20mm down graded Fine aggregates : natural river sand locally available

After several trial mixes we got the Mix proportions as 1: 1.12: 1.68 Cementv= 625 kg Fine aggregate =701.44kg Coarse aggregate = 1052.1 kg Water =150 kg W/C = 0.28 Super plasticizer =0.9

Step by Step Calculations Step 1: Assume standard deviation=5 N/mm2 Assume slump of concrete=75 mm Step 2: Target mean strength = (specific characteristic strength) + (standard deviation * riskfactor) =70 + (5*1.65)=78.25 Mpa Step 3: W/C for 78.25 MPa = 0.32 Step 4: Water content for slump of 75mm and 20mm uncrushed aggregates =195kg/m3 Step 5: With W/C ratio of 0.28 and water content of 195 kg/m3 The cement content = 195/0.32= 625 kg

Triple Blending With Mineral Admixtures In the present investigation triple blending cement concrete mixes have been tried for various strength properties. Mineral admixtures like flyash and metakaolin have been employed along with cement and triple blended cement concrete mixes are prepared. The percentages of Flyash are 0%, 15%, 25% and 40 %. The percentages of metakaolin are 0%, 5%, 10% and 15%. Both the mineral admixtures are added simultaneously to OPC to carry out triple blending. In addition steel fibres are added in percentages of 0%, 0.5% and 1.0% to the triple blended concrete. The various combinations of fibrous triple blended concrete nixes tried in the present investigation are given in table In total there are 48 combinations. Various Combinations of Fibrous Triple Blended Cement Concrete

Step 6:

S.No

Mix no.

Cement

F.A

Metacem

Fibre

For water content of 195 kg/m3,20mm uncrushed aggregate of specific gravity of 2.64, the density of fresh concrete i.e., wet density =2450

100

0.0

100

0.0

0.5

100

0.0

1.0

0.0

5.0

0.0

5.0

0.5

0.0

5.0

1.0

0.0

0.5

0.0

1.0

C10

0.0

C11

0.0

0.5

C12

0.0

1.0

C13

0.0

C14

0.0

0.5

C15

0.0

1.0

C16

5.0

0.0

C17

5.0

0.5

C18

5.0

1.0

C19

0.0

C20

0.5

C21

1.0

C22

0.0

C23

0.5

Weight of total aggregates =2450-(195+609.38) =1645.63 kg/m3 Step 7: For 20mm size aggregate, w/c ratio of 0.32, slump of 75mm and for 50% of fines passing through 600 micron sieve, the percentage of fine aggregate =36% Step 8: Weight of fine =592.43 kg/m3

aggregate

Step 9: Weight of coarse =1053.20 kg/m3

aggregate

1645.63*(36/100)

=1645.63-592.43

Estimated quantities for 1m3 of concrete

Cement Fine aggregate Coarse aggregate Water

=609.38 kg =592.43 kg =1053.20 kg =195 kg

105

International Journal of Research and Innovation (IJRI) 24

C24

1.0

C25

0.0

C26

0.5

C27

0.0

1.0

C28

5.0

0.0

C29

5.0

0.5

C30

5.0

1.0

C31

0.0

C32

0.5

C33

1.0

C34

0.0

C35

0.5

C36

1.0

C37

0.0

C38

0.0

0.5

C39

0.0

1.0

C40

5.0

0.0

C41

5.0

0.5

C42

5.0

1.0

C43

0.0

C44

0.5

C45

1.0

C46

0.0

C47

0.5

C48

1.0

Mixing Of Concrete Initially the ingredients of concrete viz., coarse aggregate, fine aggregate cement and Metakaolin were mixed to which the fine aggregate and coarse aggregate were added and thoroughly mixed. Water was measured of uniform colour and consistency was achieved which is then ready or casting. Prior to casting specimens, Workability is measured in accordance and is determined by slump test and compaction factor test. Super plasticizer SP430 supplied by M/S.Fosroc (India) Ltd. was added upto 1% to maintain the mix in workable condition as shown in photographs. Workability The following tests have been done to measure the workability of concrete according to Indian Standard. Slump test Slump test is a most commonly used method for measuring the consistency of concrete which can be employed either in laboratory or at site of work. It is used conveniently as a control test and gives an indication of the uniformity of concrete from batch to batch. The slump test is performed as per standard procedure with standardized apparatus. Bottom diameter of frustum of cone =20cm Top diameter of frustum of cone =10cm Height of the cone =30cm

The initial surface of the mould is thoroughly cleaned. The mouldis placed on a smooth horizontal right and non-absorbent surface. The mould is then filled four layers approximately one fourth of the height of the mould. Each layer is tamped 25 times by tamping rod taking care to distribute the strokes evenly over the cross section. After the top layer has been robbed the concrete is struck of level with a trowel and tamping rod. The mould is removed from the concrete immediately by raising it slowly and carefully in vertical direction. This allows the concrete to subside. This subsidence is referred as slump of concrete. The difference in level between the height of the mould and that of the highest point of the subsided concrete is measured. This difference in height in mm is taken as slump of concrete. Compaction factor test The compaction factor test is more precise and sensitive than the slump test and is particularly useful for concrete mix of low workability. It measures the workability of concrete interms of internal energy required to compact the concrete fully. The apparatus consists of two hoppers, each in shape of frustum of a cone and one cylinder. The hopper is filled with concrete this being placed gently so that this stage no work is done on the concrete to produce compaction. This is similar than the upper one and therefore filled to overflowing and this always contains approximately the same amount of concrete in standard state this reduces the influence of the personnel and the concrete falls into the cylinder. Excess concrete is cut by two floats of slide across the top of the mould and the net weight of the concrete in the known volume of the cylinder is determined. CF=

(Partially compacted concrete) (Fully compacted concrete)

To maintain medium workability (C.F= 0.85 to 0.9) by adding super plasticisers whenever necessary. Casting of Specimens The cubes were cast in steel moulds of inner dimensions of 100*100*100mm. All materials i.e., cement, Metakaolin, flyash, fine aggregate, coarse aggregate, super plasticizer. The cement, sand, flyash and metakaolin were mixed thoroughly by manually. Approximately 25% of water required added and mixed thoroughly with a view to obtain uniform mix. After that the balance of 75% of water was added and mixed thoroughly with a view to obtain uniform mix. When fibres are used they should be soaked for a minute in water. This water is then added to the cement batch. For all test specimens, moulds were kept on table vibrator and concrete was poured into the moulds in three layers by tamping with a tamping rod and the vibration was effected by table vibrator after filling of the moulds. The vibration was effected 106

International Journal of Research and Innovation (IJRI)

for one minute and it was maintained constant for all the specimens. The moulds were removed after 24 hours and the specimens were kept immersed in a clear water tank. After curing the specimens in water for a period of 28 days the specimens were removed out and allowed to dry under shade. SpecimensCasted • Combinations : 48 • No of samples per combinations : 4 (2cubes & 2 prisms) • Total no of samples : 48*4=192 Test Setup and Testing The cube specimens cured as explained above are tested as per standard procedure I.S.516, after removal from curing tank and allowed to dry under shade. The cube specimens are tested for • Compressive strength test • Flexural strength test Compressive strength test Age at test Tests shall be made at recognized ages of the test specimens, the most usual being 7 and 28 days. The ages shall be calculated from the time of addition of water to the dry ingredients. Procedure Specimens stored in water shall be tested immediately on removal from the water and while they are still in the wet condition. Surface water and grit shall be wiped off the specimens and any projecting fins removed. Placing the specimens in the testing machine The bearing surfaces of the testing machine shall be wiped clean and any loose sand or other material removed from the surfaces of the specimen which are to be in the contact with the compression platens. In the case of cubes, the specimen shall be placed in the machine in such a manner that the load shall be applied to opposite sides of the cubes as cast, i.e., not to the top and bottom. The axis of the specimen shall be carefully aligned with the centre of thrust of the spherically seated platen. No packing shall be used between the faces of the test specimen and steel platen of the testing machine. The load shall be applied without shock and increased continuously at a rate of approximately 140kg/cm2/min until the resistance of the specimen to the increasing load breaks down and no greater load can be sustained. The maximum load applied to the specimen shall then be recorded and the appearance of the concrete and any unusual features in the type of failure

shall be noted. Calculation The measured compressive strength of the specimen shall be calculated by dividing the maximum load applied to the specimen during the test by the cross sectional area and shall be expressed to the nearest kg/cm2. Cube compressive strength was tested and results were tabulated. Flexural strength test Apparatus The testing machine may be of any reliable type of sufficient capacity for the tests and capable of applying the load at the rate specified in 3.10.2.2. The bed of the testing machine shall be provided with 2 steel rollers 38mm in diameter, on which the specimen is to be supported, and these rollers shall be so mounted that the distance from centre to centre is 60cm for 15cm specimen or 40cm for 10cm specimens. The load shall be applied through 2 similar rollers mounted at the third points of the supporting span, i.e., spaced at 20 or 13.3cm centre to centre. The load shall be divided equally between the 2 loading rollers and all rollers shall be mounted in such a manner that the load is applied axially and without subjecting the specimen to any torsional stresses or restraints. Procedure Test specimens stored in water at a temperature of 24-300C shall be tested immediately on removal from water while they are still in a wet condition. No preparation of the surface is required. Placing the specimen in the testing machine The bearing surfaces of the supporting and the loading rollers shall be wiped clean and any loose sand or other material removed from the surfaces of the specimen where they are to make contact with the rollers. The specimen shall then be placed in the machine in such a manner that the load shall be applied to the upper most surface as cast in the mould, along 2 lines spaced 20 or 13.3 cm apart. The axis of the specimen shall be carefully aligned with the axis of the loading device. No packing shall be used between the bearing surfaces of the specimen and the rollers. The load shall be applied without shock and increasing continuously at a rate such that the extreme fibre stress increases at approximately 7kg/cm2/min i.e., at a rate of loading of 400kg/min for the 15cm specimen and at a rate of 180kg/min for the 10cm specimen. The load shall be increased until the specimen fails, and the maximum load applied to the specimen during the test shall be recorded. The appearance of 107

International Journal of Research and Innovation (IJRI)

the fractured faces of the concrete and any unusual features in the type of failure shall be noted.

Curing of the specimens

Calculation The flexural strength of the specimen shall be expressed as the modulus of rupture Modulus of rupture =

Load*Span Breadth*Depth*Depth

Pan mixer

Testing for Compression

Casting of the specimens Testing for Flexure

Vibration Table for Compaction Failure pattern of the beam

108

International Journal of Research and Innovation (IJRI)

Results and Discussions Presentation of Results The present project deals with the flexural properties of Fibrous Triple Blended High Strength Cement Concrete. Triple blending was carried out by replacing OPC with flyash and metakaolin in various percentages. Percentage of steel fibers has varied from 0.0% to 1.0%. The reference concrete mix is of M70 grade. There are in total 48 combinations of mixes (table 3.1) tried in the present investigation. The average 28 day compressive strength results are given in table 4.1. The compressive strength results are also plotted and shown in figures 4.1 to 4.6.The values of ultimate load and the corresponding deflection recorded for various specimens are given in table 4.2. The flexural strength results are also plotted and shown in figures 4.7 to 4.12. Typical load (vs) deflection values are given in tables 4.3 to 4.15. The load (vs) deflection relationships for the same are plotted and shown in figures 4.13 to 4.24. High Strength Concrete Mixes To derive higher compressive and flexural strengths high strength concrete mixes are required. They are designed by any one of the available methods like DOE method, ACI method etc and by trial. In the modern constructions of various large and prestigious structures like long span bridges ,prestressed concrete bridges,very tall multi storeyed buildings high strength and high performance concrete mixes are being employed. In the case of high strength concrete mixes the quantity of cement required per cubic metre of concrete is very high. In the present M70 design mix the quantity of cement per cubic metre of concrete is 625 kg and it will be more for still higher strengths. By using mineral admixtures like flyash, metakaolin, condensed silica fume (CSF), GGBS etc as replacement to cement by certain proportion, the quantity of cement can be reduced and more economical concrete mixes can be used. In addition to this mineral admixtures impart many other beneficial properties to concrete. Hence adding certain dosage of mineral admixture as replacement to OPC is essential for High Performance Concrete (HPC). To increase the tensile and flexural strengths of high strength concrete certain percentage of steel fiber is added. Addition of steel fiber also helps in the reduction of cracks, impart strength and ductility. By adding two admixtures instead of one, additional advantage can be derived. This is the basis for production of Fibrous Triple Blended Cement Concrete (FTBCC) in the present project work. Workability of Triple Blended Mixes In the present reference M70 design mix, the water cement ratio is 0.28 which is lower as such the concrete mix becomes sufficiently hard with low

workability. In addition mineral admixtures and steel fibres are also being added to develop optimum FTBCC. As a result the workability gets further reduced. To maintain the workability almost at medium level super plasticizer (CONPLAST 430) has been employed at a percentage varying from 0.8% to 1.0%. This enables concrete to be mixed thoroughly and cast the specimens without voids and dense. Hence, it is necessary to use super plasticizer to maintain the workability level in the case of high strength concrete mixes where the W/C ratio is low. Compressive Strength Results By referring to table 4.1 and figures 4.1 to 4.6, it can be seen that in general with the increase in fibre percentage the compressive strength gets increased for all combinations. Considering various combinations, it can also be seen that as the flyash percentage is increased the strength gets reduced for a given percentage of metakaolin and percentage of fibre. Similarly with increase in metakaolin percentage the strength gets gradually increased. It is noted that 15% of metakaolin gives the highest compressive strength for various combinations. Adding fibres contributes towards increase in compressive strength to some extent. For example the compressive strength of basic reference mix is 76.8 N/mm2. The compressive strength of concrete mix with 0% flyash,15% metakaolin and 0% fibre is 83.5N/mm2. There is an increase of 9% in the compressive strength. The same mix with 1% fibre has a compressive strength of 86.20 N/mm2 showing a total increase of 12% compared to the reference mix. It can be seen that flyash is contributing towards strength increase marginally upto 15% only. With 15% flyash,15% metakaolin and 1% fibre the highest compressive strength recorded is 86.50 N/mm2. This is the optimum mix showing a maximum increase of nearly 13% in compressive strength compared to the reference mix. So beyond 15% of flyash in the mix there is gradual decrease in the compressive strength. Hence an optimum combination of flyash and metakaolin is to be struck to obtain the optimum compressive strength. Beyond 15% metakaolin strength again gets decreased. A combination of 15% flyash and 15% metakaolin in triple blended concrete mix generates highest strength. Addition of steel fibres contribute towards increase in compressive strength to certain extent. Flexural Strength Results By referring to table 4.2 and figures 4.7 to 4.12, it can be seen that in general with the increase in fibre percentage the flexural strength gets increased for all combinations. Considering various combinations, it can also be seen that as the flyash percentage is increased the strength gets reduced for 109

International Journal of Research and Innovation (IJRI)

a given percentage of metakaolin and percentage of fibre. Similarly with increase in metakaolin percentage the strength gets gradually increased for a given combination. It is noted that 15% of metakaolin gives the highest flexural strength for various combinations. Adding fibres contributes towards increase in flexural strength . For example the flexural strength of basic reference mix is 4.2 N/mm2. The compressive strength of concrete mix with 0% flyash, 15% metakaolin and 0% fibre is 4.8 N/mm2. There is an increase of 14% in the flexural strength compared to the reference mix. The same mix with 1% fibre has a flexural strength of 5.8 N/mm2 showing a total increase of 38% compared to the reference mix. It can be seen that flyash is contributing towards strength increase marginally upto 15% only. With 15% flyash,15% metakaolin and 1% fibre the highest flexural strength recorded is 6.4 N/mm2. This is the optimum mix showing a maximum increase of nearly 52% in flexural strength compared to the reference mix. So beyond 15% of flyash in the mix there is gradual decrease in the flexural strength. Hence flexural strength of triple blended mix increases with increase in fibrepercentage.In the case oftriple blended cement concrete mixes 15% flyash with 15% metakaolin and 70% OPC can be taken as the optimum combination to give optimum flexural strength. With the addition of steel fibres the flexural strength further increases. With an optimum combination of 15% flyash,15% metakaolin and 1% fibre,there is an increase of nearly 52% in the flexural strength. Role of Fibers Even in the case of triple blended cement concrete mixes,steelfibres contribute towards strength increase. Presence of fibres increases the compressive strength of the matrix to certain extent. In the present experimental investigation it was found that 1% fibre has increased the compressive strength upto 13% compared to the reference mix without mineral admixtures. In the case of optimum mix having 15% flyash and 15% metakaolin there is a further increase in compressive strength by nearly 4% with the addition of 1% fibres. A similar tendency of compressive strength results can be observed even in the case of flexural strength results also. Without flyash and metakaolin and 1% fibre the flexural strength is increased by 14% nearly. With 15% flyash,15% metakaolin and 0% fibre the increase in flexural strength is 14% nearly. In the case of the optimum combination of 15% flyash,15% metakaolin and 1% fibre,there is a maximum increase of 52% nearly compared to the reference mix.

Hence,steel fibres contribute towards increase in the compressive strength to some extent .But the flexural strength is increased substantially with the presence of fibres in the matrix. In the case of triple blended cement concrete mixes addition of fibres would help to produce an optimum fibrous concrete having higher values of both compressive strength and flexural strength. Cracking Characteristics All the beams were tested for flexure in the present investigation. The reference beam without mineral admixtures and fibre has undergone brittle failure. It has failed suddenly at the ultimate flexural load just with one crack occurring. Even in the case of triple blended cement concrete specimens,the flexural failures is brittle when there are no fibres. There is a difference in the flexural behaviour of the specimens having steel fibres. In the case of fibrous specimens it is observed that cracking has started somewhere between 50 to 70% of the ultimate load, it is followed by more cracks as the load is increased. The failure behaviour is gradual and ductile. Finally it is observed that at the ultimate load even when the specimen has become into two pieces they are held in position by the fibres without dropping down. Hence it is clear that the fibres have contributed towards gradual cracking behaviour and ductility. Flexural Deformations and Ductility Steel fibres have contributed for gradual increase in deformations in the flexural specimens. In the case of reference mix without any admixture and fibre, the ultimate load is 10.5 KN and the corresponding ultimate deflection is 0.3mm. These values have become 12 KN and 0.42 mm with 1% fibre. In the case of triple blended mix with 15% flyash and 15% metakaolin, the ultimate load recorded is 13 KN and the corresponding deflection is 0.50 mm. For the same mix the ultimate load has increased to 15 KN and the ultimate deflection has become 0.54 mm. In general it is observed that the presence of fibres is contributing towards the increase in the flexural load as well as the flexural deformation. Hence fibrous specimens show better deformation characteristics, they have recorded higher ultimate flexural load and higher flexural deformation. Ductility Characteristics In general it is observed that the fibrous specimens are showing more ductile flexural behaviour. It is seen that in the case of fibrous specimens, flexural deformation is more at a particular load compared to that of specimens without fibre. Hence by incorporating steel fibers by certain percentage in triple blended cement concrete mixes there is not only an increase in the flexural load but 110

International Journal of Research and Innovation (IJRI)

also in the flexural deformations resulting in more ductility.

C26

0.5

76.47

C27

1.0

79.65

Optimum Combinations

C28

78.00

C29

0.5

81.15

Based on the experimental study conducted on various combinations of fibrous triple blended cement concrete mixes of high strength, it is concluded that 15% flyash with 15% metakaolin combination gives the highest compressive strength. From the fiber percentages tried, 1% fibre is giving the highest compressive as well as flexural load. Hence 15% flyash plus 15% metakaolin with 1% fiber is found to be optimum from study undertaken.

C30

1.0

82.50

C31

80.00

C32

0.5

82.50

C33

1.0

83.75

C34

83.00

C35

0.5

83.50

C36

1.0

84.75

C37

68.00

C38

0.5

68.50

C39

1.0

71.75

C40

69.50

C41

0.5

70.50

C42

1.0

72.25

C43

72.15

C44

0.5

73.25

C45

1.0

74.50

C46

74.75

C47

0.5

75.25

C48

1.0

76.00

Metacem

Fiber

Overall Recommendations High strength high performance concrete mixes are prepared with the addition of mineral admixtures like flyash, metakaolin, CSF are added in certain percentage as replacement to OPC to achieve higher strengths,economy and many other beneficial properties. As fibres impart higher flexural strength, it is an added property to high performance concrete. Hence it is recommended that not only a certain percentage of steel fibre makes high performance concrete with more desirable properties. In the present project work durability properties are not included.

Flexural Strength Results S.No.

Compressive Strength Results

Mixno.

OPC

Flyash

Ult. Load KN

Flex ural stre ngth

Defl etion

S.No (%)

Mix no

OPC (%)

Flyash (%)

Metacem (%)

Fiber(%)

Avg compressive strength (N/ mm2)

100

78.84

100

10.5

4.2

0.3

80.30

100

0.5

11.5

4.6

0.32

100

1.0

12.0

4.8

0.34

100

0.5

N/ mm2

100

1.0

82.15

79.20

0.0

11.0

4.4

0.31

0.5

81.50

0.5

13.5

5.4

0.32

1.0

82.75

1.0

15.5

6.2

0.35

82.50

0.0

11.5

4.6

0.33

0.5

83.45

0.5

12.0

4.8

0.34

1.0

84.50

1.0

15.6

5.8

0.36

C10

83.50

C10

0.0

12.0

4.8

0.34

C11

0.5

84.50

C11

0.5

12.5

5.0

0.36

C12

1.0

86.20

C12

1.0

15.8

5.8

0.37

C13

78.00

C13

0.0

11.0

4.4

0.31

C14

0.5

80.00

C14

0.5

12.5

5.0

0.32

C15

1.0

82.00

C15

1.0

13.5

5.4

0.33

C16

78.50

C16

0.0

11.5

4.6

0.40

C17

0.5

81.50

C17

0.5

13.0

5.2

0.44

C18

1.0

84.24

C18

1.0

14.5

5.8

0.46

C19

82.00

C19

0.0

11.7

4.7

0.35

C20

0.5

83.00

C20

0.5

12.5

5.0

0.38

C21

1.0

85.00

C21

1.0

15.0

6.0

0.47

C22

83.00

C22

0.0

12.2

4.8

0.45

C23

0.5

85.00

C23

0.5

13.0

5.2

0.50

C24

1.0

86.50

C25

73.93

C24

1.0

16.0

6.4

0.54

C25

0.0

10.0

4.0

0.30

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International Journal of Research and Innovation (IJRI) 26

C26

0.5

10.7

4.2

0.31

C27

1.0

11.5

4.6

0.33

C28

0.0

10.5

4.2

0.31

C29

0..5

11.2

4.5

0.33

C30

1.0

11.5

4.7

0.35

C31

0.0

12.0

4.6

0.32

C32

0.5

12.5

5.0

0.33

C33

1.0

13.0

5.2

0.35

C34

0.0

12.6

5.0

0.33

C35

0.5

13.7

5.5

0.34

C36

1.0

14.5

5.6

0.35

C37

0.0

8.7

3.5

0.29

C38

0.5

9.5

3.8

0.30

C39

1.0

10.0

4.0

0.31

C40

0.0

9.2

3.7

0.30

C41

0.5

9.7

3.9

0.32

C42

1.0

10.5

4.2

0.33

C43

0.0

9.7

3.9

0.31

C44

0.5

10.5

4.2

0.32

C45

1.0

11.0

4.4

0.34

C46

0.0

10.5

4.2

0.32

C47

0.5

11.0

4.4

0.33

C48

1.0

11.5

4.6

0.34

Fig Average compressive strength (vs) metakaolin percentage for 0.5 % fibre and flyash 15% and 40 %

Fig Average compressive strength (vs) metakaolin percentage for 1 % fiber and flyash 0% and 25%

FIG Average compressive strength (vs) metakaolin percentage for 0 % fibEr and flyash 0% and 25%

Fig Average compressive strength (vs) metakaolin percentage for 0.5 % fibre and flyash 15% and 40 %

Fig Average compressive strength (vs) metakaolin percentage for 0 % fiber and flyash15% and 40 % Fig Load (vs) Deflection for FTBCC beam Noâ&#x20AC;&#x2122;s 2 & 8

112

International Journal of Research and Innovation (IJRI)

Load (vs) Deflection for FTBCC beam No’s 3 & 9

Load (vs) Deflection for FTBCC beam No’s 0 & 7

Load (vs) Deflection for FTBCC beam No’s 25 & 31

Ultimate flexural load (vs)flyash percentage for 0% fiber and metakaolin 0% and 5%

Load (vs) Deflection for FTBCC beam No’s 26 & 32

Ultimate flexural load (vs) flyash percentage for 0.5 % fiber And metakaolin 0% and 5%

Load (vs) Deflection for FTBCC beam No’s 27 & 33

Ultimate flexural load (vs) flyash percentage for 1 % fiber and metakaolin 0% and 5%

113

International Journal of Research and Innovation (IJRI) in fibre percentage. 7.In the case of triple blended cement concrete mixes 15% flyash with 15% metakaolin and 70% OPC can be taken as the optimum combination to give optimum flexural strength. With the addition of steel fibres the flexural strength further increases. 8.With an optimum combination of 15% flyash,15% metakaolin and 1% fibre there is an increase of nearly 52% in the flexural strength. 9.Steel fibres contribute towards increase in the compressive strength to some extent .But the flexural strength is increased substantially with the presence of fibres in the matrix.

Ultimate flexural load (vs) flyash percentage for 0% fiber andmetakaolin 10 % and 15 %

10.In the case of triple blended cement concrete mixes addition of fibres would help to produce an optimum fibrous concrete having higher values of both compressive strength and flexural strength. 11.It is clear that the fibres have contributed towards gradual cracking behaviour and ductility. 12.Fibrous specimens show better deformation characteristics, they have recorded higher ultimate flexural load and higher flexural deformation. 13.By incorporating steel fibres by certain percentage in triple blended cement concrete mixes there is not only an increase in the flexural load but also in the flexural deformations resulting in more ductility. 14.15% flyash plus 15% metakaolin with 1% fibre is found to be optimum from study undertaken.

Ultimate flexural load (vs) flyash percentage for 0.5 % fiber andmetakaolin 10 % and 15 %

15.It is recommended that not only a certain percentage of steel fibre makes high performance concrete with more desirable properties.

References 1) Abeles PW, Bardhan-Roy BK. Prestressed concrete designer’s handbook. In: cement and concrete association .Wexham Springs: A Viewpoint publication;1981.F.W. Lydon, concrete mix design, 2nd ed., Applied science, London, 1982. 2) JASS 5(Revised 1979); Japanese Architectural Standard for Reinforced Concrete, Architectural Institute of Japan, Tokyo, 1982(March). 3) Nevile, A.M., Properties of Conrete, 4th Edition, Longman, England, 1995.I.S:10262- 2009, “recommended guide lines for concrete mix design”.BIS. Ultimate flexural load (vs) flyash percentage for 1 % fiber andmetakaolin 10 % and 15 %

4) I.S: 516 – 1959: “Indian standard Methods of Tests for strength of Concrete” – Bureau of Indian Standards.

Conclusions

5) I.S: 4037 – 1988 : “Indian standard methods of physical test for Hydraulic cement” – Bureau of Indian Standards.

1.Based on the present project work on Fibrous Triple Blended High Strength Cement Concrete mixes-study of compressive and flexural strength characteristics, the following conclusions are drawn. 2. It is necessary to use super plasticizer to maintain the workability level in the case of high strength concrete mixes where the W/C ratio is low. 3.An optimum combination of flyash and metakaolin is to be struck to obtain the optimum compressive strength. Beyond 15% metakaolin strength again gets decreased. 4.A combination of 15% flyash and 15% metakaolin in triple blended concrete mix generates highest strength. 5.Addition of steel fibres contribute towards increase in compressive strength to certain extent. 6.Flexural strength of triple blended mix increases with increase

6) IS: 1344 – 1968 : “Indian standard specifications for pozzalonas” - Bureau of Indian Standards. 7) I.S: 2386 – 1963 : “Indian Standards methods for aggregates of concrete” – Bureau of Indian standards, New Delhi 8) I.S: 380 – 1970 : “Indian standard specifications for coarse and fine aggregates (natural)” - Bureau of Indian Standards (revised). 9) I.S : 456 – 2000 : Plain and reinforced concrete Indian standard specifications 10) M.S Shetty : “Concrete Technology” – 2006. 11) N. Krishnaraju : “Design of concrete mix” – CBS publisher – 1985. 12) Bredy,P.etal’Microstructure and porosity of metakaolin blended cements’ProcMater,ResSocSymp 1989;137;431-6.

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International Journal of Research and Innovation (IJRI) 13) I.S 12269-1987,”Specification for 53 grade ordinary Portland cement”,BIS. 14) Swammy and Hannat,’Fibre Reinforced Concrete. 15) P.K.Mehtha&J.J.M.Paulo,”concrete micro structure properties and materials”-Mc Graw Hill publishers 1997. Authour K. Mythili M.Tech(Structural Engineering), Associate Proffesor At Aurora S Scientific And Technological And Research Academy, Bandlaguda, Hyderbad - 500005, India.

C.Dheeraj Research Scholar, Department of Civil Engineering,At Aurora S Scientific And Technological And Research Academy, Bandlaguda, Hyderbad - 500005, India.

B.L.P. Swami Professor and Co-ordinator, Research and Consultancy, VCE, Hyderabad,India

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