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Chapter 2 2- Fly ash, cement, PVA fibers and fine aggregate. 2.1- Fly Ash 2.1.1- Nature of fly ash and its production. Fly ash is the namedgiven to natural pozzolan,a “siliceousor siliceous-and-aluminous material”. Fly ash is reacting with calcium hydroxide and acquired cementitous properties and thus able to bind different materials/structure where it is applied and form a composite/ united structure (Design and Control of Concrete Mixtures 2010). Fly ash is the ash generated after the combustion of coal in thermal power industries for the generation of electricity. It is actually a particulates matter, a air pollutant obtained as a byproduct of coal usage for which disposal is also a problem. It will create various environmental problems. Disposal of fly ash if not using for our fruitful purpose require a low lying area where it is disposed off. Digging pit is also required in order to dig it underground. It’s a very costing process and hence not economical. So, best alternative choices is rather than it disposed off it can be used as modern civil engineering material and can be used for making bricks and improve one of more properties of cement. The fly ash can also be used in construction industries various purposes viz. in mixing in cement to change of one or more properties of it. Fly ash provides the various advantages over other materials. The fire resistance properties of composite are greatly improved once mix fly ash in that composite. The various advantages with application of fly ash are its cost are less, it’s a environmentalfriendlywhichotherwisecreatesthevariousproblemtotheatmosphere, application of fly ash increases the strength and It enable to conserve other natural resources and material viz. conserve lime stone which is the major requirement in cement production the procedure of production of fly ash is produced in the thermal power industries through the following steps (Bremseth, 2010); Coal is the fossil fuel and the source of energy for generation of electricity through thermal power plant. The coal is used to boil the boiler and thus steam is produced. With the help of grinding mill coal is crushed and makes a fine powder. In the boiler, this fine powder is feed where it is combusted with approx. temperature of 1500 degrees which
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in turn produce heat. There are two mineral are present in coal, one is combustible and other is non-combustible. While the combustible mineral burn and produce heat but non-combustible minerals melts and fuses together in the furnace. These non-combustible minerals are separated from the burning region with the help of exhaust chamber through the exhaust or passes through flue gases. From the flue gases, these mineral is again separated through the cooling action. After cooling, it forms the spherical glassy particles and settled. These glassy particles are known as fly ash and collected by the means of mechanical and electrostatic precipitator. 2.1.2- Physical and chemical properties of fly ash. Since the basic raw material through which fly ash is made is the coal, so the physical and chemical properties are attained by the fly ash is totally depends upon the quality, nature of prerequisite material coal, and how the coal are processed and operating condition of the furnace. By the nature of coal we mean what are the constituents of coal and how pure the coal is?In order to best efficiently use for different purposes, it is urged that the physical and chemical properties of flyash are to be known. Based on physical and chemical properties, fly ash can be used for making the flyash bricks or can be mix in cement to change one or more properties required for different purposes. Based on quality of coal, the chemical composition of fly ash would vary significantly. However, the major constituent of the fly ash is always a Silicon dioxide (SiO2). As per Bremseth, 2010, the chemical contents of flyash is governed by what the composition of different constituents present in coal. Based upon the composition of calcium content, the fly ash is classify as class F and class C. These classifications are given by American Society for Testing and Materials (ASTM) C618-03.In case of class F, the percentage composition of calcium is less while in class C it is high. Concerns of the quality, the quality of class C fly ash is good and can be used for many purposes but class F have limited use. The reason is it contains various unwanted mineral like sulphite and free lime (de Brito & Saikia, 2013). The table below shows the chemical properties of fly ash (Gamage 2011). Chemical CompoundLow calcium fly ash Class F High calcium fly ash Class C Silicon dioxide (SiO2)54.9039.90 Aluminium oxide (Al2O3)25.8016.70
Iron oxide (Fe2O3)6.905.80 Calcium Oxide (CaO)8.7024.30 Magnesium oxide (MgO)1.804.60 Sulfur Trioxide (SO3)0.603.30 Sodiumoxide(Na2O)and Potassium oxide( K2O) 0.601.30 The literature reviews revealed that Fly ash is in irregular to regular shape and size .The diameters may vary range from 0.5μm to 150μm.As per Ramezanianpour, 2014,the size of Fly ash is governed by the type of collector equipment and also by the source. The physical properties of fly ash are presented in table below. Properties-------- Specific gravity2.3 Moisture content19.75% Fineness0.001-0.6 mm Maximum Dry density1.53 g/cm3 Permeability4.87×10-7cm/s Angle of internal friction23°-41° Cohesion3-34 Kpa Compression of index0.15 Coefficient of consolidation0.1-0.5 m2per year 2.1.3- Effect of the fly ash on environment. Fly ash is the ash generated after the combustion of coal in thermal power industries for the generation of electricity. It is actually a particulates matter, an air pollutant obtained as a byproductofcoalusageforwhichdisposalisalsoaproblem.Itwillcreatevarious environmental problems. Disposal of fly ash if not using for our fruitful purpose require a low lying area where it is disposed off. Digging pit is also required in order to dig it underground. It’s a very costing process and hence not economical. As per statistics, according to (Morrison, 2005), the combustion of coal in Australia for generation of electricity through thermal power project generates around 12 million tonnes of fly
ash every years. From which 60 % is dumped in low lying areas. However by doing so may cause various enormous environmental problems including promoting air, water, and land pollutions. Some of the problems are contamination of ground water and ground pollution, fog/ smog, asthma, inhalation problems etc. So, best alternative choices is rather than it disposed off it can be used as modern civil engineering material and can be used for making bricks and improve one of more properties of cement. The Fly ash can be used in manufacturing fly ash brick which is the substitute for tradition brick. The fly ash can also be used in construction industries various purposes viz. in mixing in cement to change of one or more properties of it. By application of fly ash in civil engineering construction, at one side we can dimishes the problem of waste flyash disposal and at the same time we can mitigates the negative effect of global warming due to less emission of carbon-dioxide which otherwise emits excessively due to production of cement in various stages through lime stone. Now to some extent, flyash replace cement and hence safe our scarce resources like lime stone. Fly ash provides the various advantages over other materials. The fire resistance properties of composite are greatly improved once mix fly ash in that composite. The various advantages with application of fly ash are its cost are less, it’s a environmental friendly which otherwise creates the various problem to the atmosphere, application of fly ash increases the strength and It enable to conserve other natural resources and material viz. conserve lime stone which is the major requirement in cement production 2.1.4- Australian Experiences with Fly Ash. Australia started the usage of fly ash in concrete since 1950 after carrying out various extensive research and laboratory experiments in Western Australia on the potential use of fly ash in concrete. The experimentation concluded that there is no any big difference in the strength parameters of concrete made out of either of fly ash or Portland cement and practically have the will have same strength. However the strength gained by 6 month latter by the flyash based made is the same as that of concrete made by portland cement. So from that time the Australia got an innovative substitute material over cement and fine aggregates and hence can be used as a partial replacement of either cement or fine aggregates. Since inception in Australia, there is increase in the usage of flyash for different purposes either for making flyash brick or in cement to change of one or more properties. It can be used as a
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supplementarycementitousmaterialandcanbeusedforpartialreplacementoffine aggregate/sandandcement(AshDevelopmentAssociationofAustralia2009).Some researcher(Gamage,2011) revealed that if 25 to 30 percentages of cement can be replace by fly ash, then there is no any big change in the properties of end product means have had attained same strength. Other researchers revealed that it is also possible to replace up to 60% of cement from flyash then also attained the same strength properties by final good but in this time we need to add some admixtures and followed a proper curing method. The aim of this research lays on to find the optimum fly ash /cement ratio that can be used in concrete mix. Besides fly ash can be used in various civil engineering application viz. premixed concrete, precast concrete, concrete masonry, etc. It is due to its basic properties of pozzalanic action. And also can be used for making flyash bricks. 2.3- Cement 2.3.1- Nature of cement and its production. Cement exhibits both cohesive and adhesive properties. These properties can be used to make the bond between different materials and then forms a composite unit. Cement is used for making theconcrete.Concreteisthehomogeneousmixtureofcement,coarseaggregates,fine aggregates, and water.In concrete or otherwise, cementacts as binding material which binds coarse aggregates (ballast), fine aggregates (sand) after reacting with water and set out in a rigid mass. Cement is also used in finishing work like plastering, neat cement punning, brick work, ashlars masonry work, roofing, flooring, and footing work etc. The usage of cement as a civil engineering material is not limited and scope is very beyond high. In cement, generally ordinary/normal portland cement is one which can be widely used. Due to similarity in color (color being white grey lime stone) and its quality when it hardens as Portland stone, its name is given as Portland cement. The cement production procedure is summarized below. Firstly the limestone is quarried. By using explosive materials, the rocks are blasted from the ground and we get limestone/raw materials in rock form (Glenn Hegar, 2005). These raw materials are then transported to the plant.
Initially the raw materials as mentioned above are crushed, screemed & stockpiled. After these are mixed with definite proportions to obtain raw mix which can be done either through dry (dry mixing) or by water (wet mixing). Preparedraw mix is then fed into the rotary kiln and burn by raising the temperature to 1300-16000C, we then get the output which is known as clinker which is about 0.15-5cm in diameter. This Clinker is then cooled & stored, which is subsequently ground with adding gypsum (3-6%) to adjust setting time, the result is the cement. This cement is then packed and ready for market and marketing The Portland cement is classified as Standard types and special types. The standard cement is used for general building purposes while the special types are used for special purpose of use of cement is special conditions of our requirements. Depending upon the usage in different environmental conditions some oxide/compounds are decreases while other increases in making the cement. 2.3.2- Chemical properties of cement The major oxides present in the cement are CaO, SiO2, Al2O3, and Fe2O3. It contributes to about 90% volume of cement. The percentage composition of different constituents of portland cement are presented in the table(Gamage 2011).
2.3.3- Health and environment effects of cement productions. The real sustainable development can be achieved only by adopting the sustainable technology. Today’s,sustainabilityofcementisthetopicofdebatesamongstthevariousplaying actors/experts. Some think that the use of cement in constructional industries is sustainable as there is no any other alternative substitute over cement. At the same time, other experts think that use of cement creates the health and environmental degradation problem and hence it’s not sustainable. a)Non-sustainability issue: Portland cement is not an eco friendly product. Its product process is one of the causes of greenhouse gas emissions which promote the global warming. Production of cement required the lime stone and thus scarce lime stone are depleted day by day which is the issue of concern today. Inproduction process of cement, the various gases viz. sulphur dioxide, nitrogen oxide and carbon monoxide are emitted to the atmosphere. These gases are reacted with the atmospheric vapour and may result acid rain. Once the acid rain fall upon the land may damage our agricultural land and various health problems viz. breathing, reduce the oxygen
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transport through hemoglobin, lung diseases, asthama, breathing problems etc.are associated with these gases, and acid rain Sustainability Issue: Ash generated in Cement manufacturing utilized in Brick making called as Fly-ash brick and also in blended cement, Generate a large scale employment for the local, regional, global people. Infrastructure development is also enhanced with the growth of such plants.FewimportantbenefitsmayincludeFDI,largescaletechnologytransferand development.Indirect Benefits includes literacy, life style improvement and Better transportation facilities with the development of railways, roads and ports. The industry may help in developing the socio- economic status of the local people and the area by an efficient Corporate Social Responsibility Plan. HenceIf properly used, cement is seems as aviable in construction industries. The chemical composition of cement is tabulated below Table 2.1Chemical properties of fly ash and Portland cement. Chemical CompoundLow calcium fly ash Class F Cement Silicon dioxide (SiO2)54.9022.60 Aluminium oxide (Al2O3)25.804.30 Iron oxide (Fe2O3)6.902.40 Calcium Oxide (CaO)8.7064.40 Magnesium oxide (MgO)1.802.10 Sulfur Trioxide (SO3)0.602.30 Sodiumoxide(Na2O)and Potassium oxide( K2O) 0.600.60 2.6.2- Environment implication of fine Aggregate. If we see in past, the river sand was only considered as a fine aggregates and can be used in making concrete. Due to excessive extraction of sand from the river, it started to degrade the rivers. As a result due to mining operation in the river, it lowers the river/stream bottoms and may leads to the problem of bank erosion. It causes the deepening of rivers due to unrestricted
exploitation of sand from river bed and then saline-water intrusion from nearby sea. Due to continue extraction of sand, it indirectly increases the level of sea water. Besides, sand mining is also threatened to various civil engineering structure viz.bridges, river banks and nearby structures. Directly or indirectly, more extraction of sand from river bodies can damage our environment. Due to various issues, constraints and challenges, there is a need to search alternative over fine aggregates replacement and still the research is going on(Gonçalves, 2007). References: i) Noushini.A.(2012),Effect of Polyvinyl Alcohol Fibre and Fly Ash on Flexural Tensile Properties of Concrete,22nd Australian Conference on the Mechanics of Structures and Materials, ii)Joseph. A., K.,(2017),Mechanical Properties and Shear Strengthening Capacity of High Volume Fly Ash-Cementitious Composite,IOP Publishing,Materials Science and Engineering, 310 iii) K. Kaviya(2015),Utilisation of Fly Ash and Fibre in Concrete, Indian Journal of Science and Technology,Vol 8(32), iv)Erxia Du(2017), Mechanical Property Test of Polyvinyl Alcohol (PVA) Fiber Reinforced Concrete,Journal of chemical engineering transactions, vol.62 v) http://www.buddyrhodes.com/pva-fiber-recs-15/