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TYPES OF PORTLAND CEMENT, GENERAL FEATURES OF THE MAIN TYPES OF PORTLAND CEMENT, ORDINARY PORTLAND CEMENT (OPC), RAPID HARDENING PORTLAND CEMENT, SPECIAL TYPES OF RAPID HARDENING PORTLAND CEMENT, MANUFACTURE OF PORTLAND CEMENT, Raw Materials, Crushing & Grinding of Raw Materials,Type of cement processes, Wet Process, Dry process, Burning Process, Grinding, storage, packing, dispatch,CEMENT CHEMISTRY,Chemical Compositions,Bogue’s Equations, Fineness of cement

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  1. 1. Topic 6: CEMENT Hassan Z. Harraz 2013- 2014 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement
  2. 2. OUTLINE OF TOPIC 6: CEMENT TYPES OF CEMENTS PORTLAND CEMENT TYPES OF PORTLAND CEMENT GENERAL FEATURES OF THE MAIN TYPES OF PORTLAND CEMENT ORDINARY PORTLAND CEMENT (OPC) RAPID HARDENING PORTLAND CEMENT SPECIAL TYPES OF RAPID HARDENING PORTLAND CEMENT MANUFACTURE OF PORTLAND CEMENT:- 1) Raw Materials 2) Crushing & Grinding of Raw Materials 3)Type of cement processes: a)Wet Process b)Dry process 4) Burning Process 5) Grinding 6) storage, packing, dispatch CEMENT CHEMISTRY  Chemical Compositions  Bogue’s Equations  Fineness of cement 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 2
  3. 3. CEMENT DEFINATION: Cement is the mixture of calcareous, siliceous, argillaceous and other substances. Cement is a hydraulic binder and is defined as a finely ground inorganic material which, when mixed with water, forms a paste which sets and hardens by means of hydration reactions and processes which, after hardening retains it's strength and stability even under water. Popular as building material.  Material with adhesive & cohesive properties. To bind the fine & coarse aggregate together To fill voids in between fine & coarse aggregate particle form a compact mass. 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 3  TYPES OF CEMENTS: Cement may be hydraulic or non-hydraulic: 1)Non-hydraulic cements (e.g. gypsum plaster) must be kept dry in order to retain their strength. 2)Hydraulic cements harden because of hydration, chemical reactions that occur independently of the mixture's water content; they can harden even underwater or when constantly exposed to wet weather. The chemical reaction that results when the anhydrous cement powder is mixed with water produces hydrates that are not water-soluble. Hydraulic cement may be: i) Portland cements ii) Natural cements iii) Expansive cements iv) High-alumina cements
  4. 4. Composition of Cement • Lime Calcium Oxide (CaO) = 60 – 65% (63%) • Silica (SiO2) = 20 – 25% (22%) • Aluminum Oxide = 4 - 8% (6%) • Iron Oxide = 2 – 4 % (3%) • Magnesium Oxide = 1 – 3 % • Gypsum 1 to 4%
  5. 5. CEMENT PORTLAND CEMENT Made by mixing substances containing Calcium Carbonate such as chalk / limestone, with substances containing silica , alumina and iron oxide such as clay/ shale. •Clay/shale: SiO2 Silica (silicon oxide) abbreviated S Fe2O3 Ferrite (iron oxide) abbreviated F Al2O3 Alumina (aluminium oxide) abbreviated A •Limestone/chalk CaCO3 Calcium carbonate abbreviated C •then the mixture heated and became clinker. •Clinker then grounded to powder. •The hardening Portland cement is a chemical process during which heat is evolved. Why is it called "portland" cement? Joseph Aspdin, an English mason who patented the product in 1824, named it portland cement because it produced a concrete that resembled the color of the natural limestone quarried on the Isle of Portland, a peninsula in the English Channel
  6. 6. PORTLAND CEMENT DEFINATION: is a hydraulic cement that hardens in water to form a water-resistant compound. The hydration products act as binder to hold the aggregates together to form concrete. made by finely clinker produced by calcining to incipient fusion a mixture of argillaceous and calcareous materials: Limestone + Shale/Clay + Heat = Clinker +CKD + Exit Gas 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 6
  7. 7. TYPES OF PORTLAND CEMENT According to the ASTM standard, there are five basic types of Portland Cement:. 1) Regular cement, general use, called Ordinary Portland cement (OPC) – Type Ι 2) Moderate sulphate resistance, moderate heat of hydration, C3A < 7% , Modified cement - Type ΙΙ 3) Rapid-hardening Portland cement , With increased amount of C3S, High early strength – Type ΙΙΙ 4) Low heat Portland cement – Type ΙV 5) High Sulfate-resisting Portland cement – Type V It is possible to add some additive to Portland cement to produce the following types:  Portland blastfurnace cement – Type ΙS  Pozzolanic cement - Type ΙP  Air-entrained cement - Type ΙA  White Portland Cement (WPC)  Colored Portland Cement Note:  sulphates can react with C4ASH18 to from an expansive product. By reducing the C3A content, there will be less C4ASH18 formed in the hardened paste.  Physically and chemically, these cement types differ primarily in their content of C3A and in their fineness.  In terms of performance, they differ primarily in the rate of early hydration and in their ability to resist sulfate attack. • The general characteristics of these types are listed in Table 2. • The oxide and mineral compositions of a typical Type I Portland cement were given in Tables.21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 7
  8. 8. GENERAL FEATURES OF THE MAIN TYPES OF PORTLAND CEMENT ASTM Type Classification Characteristics Applications Type I General purpose Fairly high C3S content for good early strength development General construction (most buildings, bridges, pavements, precast units, etc) Type II Moderate sulfate resistance (Modified cement) Low C3A content (<8%) Structures exposed to soil or water containing sulfate ions Type III High early strength (Rapid-hardening) Ground more finely, may have slightly more C3S Rapid construction, cold weather concreting Type IV Low heat of hydration (slow reacting) Low content of C3S (<50%) and C3A Massive structures such as dams. Now rare. Type V High sulfate resistance Very low C3A content (<5%) Structures exposed to high levels of sulfate ions White White color No C4AF, low MgO Decorative (otherwise has properties similar to Type I) 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 8 Chemical composition of the main types of Portland cement
  9. 9. RAPID HARDENING PORTLAND CEMENT  This type develops strength more rapidly than ordinary Portland cement. The initial strength is higher , but they equalize at 2-3 months  Setting time for this type is similar for that of ordinary Portland cement  The rate of strength gain occur due to increase of C3S compound, and due to finer grinding of the cement clinker ( the min. fineness is 3250 cm2/gm (according to IQS 5)  Rate of heat evolution is higher than in ordinary Portland cement due to the increase in C3S and C3A, and due to its higher fineness  Chemical composition and soundness requirements are similar to that of ordinary Portland cement Uses a)The uses of this cement is indicated where a rapid strength development is desired (to develop high early strength, i.e. its 3 days strength equal that of 7 days ordinary Portland cement), for example: i) When formwork is to be removed for re-use ii) Where sufficient strength for further construction is wanted as quickly as practicable, such as concrete blocks manufacturing, sidewalks and the places that can not be closed for a long time, and repair works needed to construct quickly. b) For construction at low temperatures, to prevent the frost damage of the capillary water. c) This type of cement does not use at mass concrete constructions. 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 9
  10. 10. SPECIAL TYPES OF RAPID HARDENING PORTLAND CEMENT A) Ultra High Early Strength Cement  The rapid strength development of this type of cement is achieved by grinding the cement to a very high fineness: 7000 to 9000 cm2/g. Because of this, the gypsum content has to be higher (4 percent expressed as SO3). Because of its high fineness, it has a low bulk density. High fineness leads to rapid hydration, and therefore to a high rate of heat generation at early ages and to a rapid strength development ( 7 days strength of rapid hardening Portland cement can be reached at 24 hours when using this type of cement). There is little gain in strength beyond 28 days.  It is used in structures where early prestressing or putting in service is of importance.  This type of cement contains no integral admixtures. B) Extra Rapid Hardening Portland Cement  This type prepare by grinding CaCl2 with rapid hardening Portland cement. The percentage of CaCl2 should not be more than 2% by weight of the rapid hardening Portland cement.  By using CaCl2:  The rate of setting and hardening increase (the mixture is preferred to be casted within 20 minutes).  The rate of heat evolution increase in comparison with rapid hardening Portland cement, so it is more convenient to be use at cold weather.  The early strength is higher than for rapid hardening Portland cement, but their strength is equal at 90 days.  Because CaCl2 is a material that takes the moisture from the atmosphere, care should be taken to store this cement at dry place and for a storage period not more than one month so as it does not deteriorate. 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 10
  11. 11. MANUFACTURING OF CEMENT 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 11 1) Quarry 2) Raw Material 3) Mixing and crushing of raw materials: a) Dry process b) Wet process 4) Burning 5) Grinding 6) Storage 7) Packing 8) Dispatch
  12. 12. Step in the Manufacture of Portland Cement 1. BLASTING : The raw materials that are used to manufacture cement (mainly limestone and clay) are blasted from the quarry. Quarry face 1. BLASTING 2. TRANSPORT quarry 3. CRUSHING & TRANSPORTATION 2. TRANSPORT : The raw materials are loaded into a dumper. crushing conveyor dumper storage at the plant loader Typical Quarry operation:  Typically shale provides the argillaceous components: Silica (SiO2, Aluminum (Al2O3) & Iron (Fe2O3)  Limestone provides the calcareous component: Calcium Carbonate (CaCO3 )  Raw materials may vary in both composition and morphology.
  13. 13. THE CEMENT MANUFACTURING PROCESS 1. RAW GRINDING : The raw materials are very finely ground in order to produce the raw mix. 1. RAW GRINDING Raw grinding and burning 2. BURNING 2. BURNING : The raw mix is preheated before it goes into the kiln, which is heated by a flame that can be as hot as 2000 °C. The raw mix burns at 1500 °C producing clinker which, when it leaves the kiln, is rapidly cooled with air fans. So, the raw mix is burnt to produce clinker : the basic material needed to make cement. conveyor Raw mix kiln cooling preheating clinker storage at the plant Raw mill
  14. 14. MANUFACTURE OF ORDINARY PORTLAND CEMENT  Ordinary Portland Cement (OPC) is one of several types of cement being manufactured throughout the world.  OPC consists mainly of lime (CaO), silica (SiO2) , alumina (Al2O3) , iron (Fe2O3) and sulphur trioxide (SO3). Magnesium (MgO) and other Oxide elements are present in small quantities as an impurity associated with raw materials.  When cement raw materials containing the proper proportions of the essential oxides are ground to a suitable fineness and then burnt to incipient fusion in a kiln, chemical combination takes place, largely in the solid state resulting in a product named clinker.  This clinker, when ground to a suitable fineness, together with a small quantity of gypsum (SO3) is Portland Cement. SO3 is added at the grinding stage to retard the setting time of the finished cement. Basic Chemical Components of Portland Cement:  Calcium (Ca)  Silicon (Si)  Aluminum (Al)  Iron (Fe) Typical Raw Materials:  Limestone (CaCO3)  Sand (SiO2)  Shale, Clay (SiO2, Al2O3, Fe2O3)  Iron Ore/Mill Scale (Fe2O3) 2/3 calcareous materials (lime bearing) - limestone 1/3 argillaceous materials (silica, alumina, iron)- clay 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 14
  15. 15. 2) Raw Materials for Cement Manufacture  The first step in the manufacture of Portland Cement is to combine a variety of raw ingredients so that the resulting cement will have the desired chemical composition.  These ingredients are ground into small particles to make them more reactive, blended together, and then the resulting raw mix is fed into a cement kiln which heats them to extremely high temperatures.  Since the final composition and properties of Portland Cement are specified within rather strict bounds, it might be supposed that the requirements for the raw mix would be similarly strict. As it turns out, this is not the case. While it is important to have the correct proportions of calcium, silicon, aluminum, and iron, the overall chemical composition and structure of the individual raw ingredients can vary considerably. The reason for this is that at the very high temperatures in the kiln, many chemical components in the raw ingredients are burned off and replaced with oxygen from the air.  Table 1 lists just some of the many possible raw ingredients that can be used to provide each of the main cement elements. Table 1: Examples of raw materials for Portland Cement manufacture Calcium Silicon Aluminum Iron Limestone Clay Clay Clay Marl Marl Shale Iron ore Calcite Sand Fly ash Mill scale Gypsum Shale Aluminum ore refuse Shale Marly limestone Fly ash Phyllite Blast furnace dust Sea Shells Rice hull ash slate slag Cement kiln dust Silica Chalk Sand 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 15
  16. 16. Typical Composition of Raw Materials 21 November Prof. Dr. H.Z. Harraz Presentation Cement 16
  17. 17. 2) Crushing & Grinding of Raw Materials  Due to the variable nature of these components, they are pre-blended prior to their use. It is crushed and stored in a pre-blending hall, utilizing the chevron pile stacking method. In this method, stacking takes place at one end of the pile. At the other end of the pile the material is reclaimed and then stored in a feeding hopper which is ready for use.  The limestone is crushed to less than 25mm in size.  Grinding and blending prior to entering the kiln can be performed with the raw ingredients in the form of a slurry (the wet process) or in dry form (the dry process). The addition of water facilitates grinding. However, the water must then be removed by evaporation as the first step in the burning process, which requires additional energy. The wet process, which was once standard, has now been rendered obsolete by the development of efficient dry grinding equipment, and all modern cement plants use the dry process. When it is ready to enter the kiln, the dry raw mix has 85% of the particles less than 90 µm in size 21 November Prof. Dr. H.Z. Harraz Presentation Cement 17
  18. 18. Mixing and crushing of raw materials: Actually the purpose of both processes is to change the raw materials to fine powder. Dry process Wet process  This process is usually used when raw materials are very strong and hard.  This process is generally used when raw materials are soft because complete mixing is not possible unless water is added.  In this process, the raw materials are changed to powdered form in the absence of water.  In this process, the raw materials are changed to powdered form in the presence of water  Dehydration zone requires a somewhat shorter distance than wet process.  Dehydration zone would require up to half the length of the kiln easiest to control chemistry & better for moist raw materials  74% of cement produced.  26% of cement produced  kilns less fuel requirements  High fuel requirements - fuel needed to evaporate 30+% slurry water- The kiln is a continuous stream process vessel in which feed and fuel are held in dynamic balance  In this process calcareous material such as lime stone (calcium carbonate) and argillaceous material such as clay are ground separately to fine powder in the absence of water and then are mixed together in the desired proportions.  Water is then added to it for getting thick paste and then its cakes are formed, dried and burnt in kilns.  In this process, raw materials are pulverized by using a Ball mill, which is a rotary steel cylinder with hardened steel balls. When the mill rotates, steel balls pulverize the raw materials which form slurry (liquid mixture). The slurry is then passed into storage tanks, where correct proportioning is done. Proper composition of raw materials can be ensured by using wet process than dry process. Corrected slurry is then fed into rotary kiln for burning.
  19. 19. 3) Burning in a Kiln – Formation of Cement Clinker  The next step in the process is to heat the blended mixture of raw ingredients (the raw mix) to convert it into a granular material called cement clinker.  This requires maximum temperatures that are high enough to partially melt the raw mix. Because the raw ingredients are not completely melted, the mix must be agitated to ensure that the clinker forms with a uniform composition.  This is accomplished by using a long cylindrical kiln that slopes downward and rotates slowly.  To heat the kiln, a mixture of fuel and air is injected into the kiln and burned at the bottom end. The hot gases travel up the kiln to the top, through a dust collector, and out a smokestack. A variety of fuels can be used, including pulverized coal or coke, natural gas, lignite, and fuel oil. These fuels create varying types and amounts of ash, which tend to have compositions similar to some of the aluminosilicate ingredients in the raw mix. Since the ash combines with the raw mix inside the kiln, this must be taken into account in order to correctly predict the cement compassion. There is also an increasing trend to use waste products as part of the fuel, for example old tires. In the best-case scenario, this saves money on fuel, reduces CO2 emissions, and provides a safe method of disposal. 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 19
  20. 20. Clinker Burning  For the production of cement clinker, the raw meal which is known as kiln feed at this stage has to be heated to a temperature of about 1550 oC in the long cylindrical rotating kiln.  The kiln feed enters the system at the top of the pre-heater and fall until the lower end of the kiln.  The heat exchange occurs during this process when the hot gases from the kiln end rise up to the top of the pre-heater.  The clinker formation process is divided into four parts: drying, calcining, sintering and cooling. 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 20 And the Hottest
  21. 21. The raw materials used for manufacturing Portland Cement are limestone, clay and Iron ore. a) Limestone (CaCO3) is mainly providing calcium in the form of calcium oxide (CaO) CaCO3 (1000oC) → CaO + CO2 b) Clay is mainly providing silicates (SiO2) together with small amounts of Al2O3 + Fe2O3 Clay (1450oC) → SiO2 + Al2O3 + Fe2O3 + H2O c) Iron ore and Bauxite are providing additional aluminum and iron oxide (Fe2O3) which help the formation of calcium silicates at low temperature. They are incorporated into the raw mix. d) The clinker is pulverized to small sizes (< 75 μm). 3-5% of gypsum (calcium sulphate) is added to control setting and hardening. The majority particle size of cement is from 2 to 50 μm. (Note: “Blaine” refers to a test to measure particle size in terms of surface area/mass) 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 21
  22. 22. Kiln Process Thermochemical Reactions Kiln Process Process Temperature (oC) Reactions Chemical Transformation Drying 20 - <100 Escape of free water (i.e., Free Water evaporates) Pre-heat 100 - 300 Escape of adsorbed water (i.e., Crystallization water driven out) 400 - 750 Chemical water driven out, Decomposition of shale., with formation of metakaolinite Al4Si4O10(OH)8  2(Al2O3.2SiO2) + 4H2O 600 - 900 Decomposition of metakaolinite and other compounds, with formation of reactive oxide mixture Al2O3.2SiO2  Al2O3.+ 2SiO2 Calcining 600 - 1000 Decomposition of limestone, CO2 Driven out, Formation of Free lime , with formation of CS (CaO.SiO2) and CA (CaO.Al2O3) 3CaCO3  3CaO + 3CO2 3CaO + 2SiO2 + Al2O3  2(CaO.SiO2) + CaO.Al2O3 Sintering Clinkering 800 – 1550 (1350 exothermic) Uptake of lime by CS and CA, Formation of Liquid Phase, Formation of: Belite (C2S), Aluminates (C3A) and Ferrites (C4AF) CS + C  C2S 2C + S  C2S CA + 2C  C3A CA + 3C + F  C4AF Cooling 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 22
  23. 23. Dual Line Preheater Planetary Cooler
  24. 24. Burning Process  Kiln is typically about 180 m long and 6 m in diameter, has a downward slope of 3-4%, and rotates at 1-2 revolutions per minute.  The raw mix enters at the upper end of the kiln and slowly works its way downward to the hottest area at the bottom over a period of 60-90 minutes, undergoing several different reactions as the temperature increases. It is important that the mix move slowly enough to allow each reaction to be completed at the appropriate temperature. Because the initial reactions are endothermic (energy absorbing), it is difficult to heat the mix up to a higher temperature until a given reaction is complete.  The general reaction zones are as follows: 1) Dehydration zone (up to ~ 450˚C) 2) Calcination zone (>450˚C – 900˚C) 3) Solid-state reaction zone (>900˚ - 1300˚C) 4) Clinkering zone (>1300˚C – 1550˚C) 5) Cooling zone 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 24
  25. 25. i) Generalized Diagram of a Long Dry Process Kiln Reaction Material Temperature Gas Temperature The kiln exit gas temperature will depend on the process Zone Exhaust GasesRaw Feed Clinker Out
  26. 26. Reaction Zone Temperature (oC) Characteristics Dehydration up to ~ 450 This is simply the evaporation and removal of the free water Even in the “dry process” there is some adsorbed moisture in the raw mix.  Although the temperatures required to do this are not high, this requires significant time and energy. In the wet process, the dehydration zone would require up to half the length of the kiln, while the dry process requires a somewhat shorter distance. Calcination 450˚C – 900 The term calcination refers to the process of decomposing a solid material so that one of its constituents is driven off as a gas. At about 600˚C the bound water is driven out of the clays, and by 900˚C the calcium carbonate is decomposed, releasing carbon dioxide. By the end of the calcination zone, the mix consists of oxides of the four main elements which are ready to undergo further reaction into cement minerals. Because calcination does not involve melting, the mix is still a free-flowing powder at this point. Solid-state reaction >900˚ - 1300 This zone slightly overlaps, and is sometimes included with, the calcination zone. As the temperature continues to increase above ~ 900˚C there is still no melting, but solid- state reactions begin to occur. CaO and reactive silica combine to form small crystals of C2S (dicalcium silicate; Belite), one of the four main cement minerals. In addition, intermediate calcium aluminates (C3A) and calcium ferrite (C4AF) compounds form. These play an important role in the clinkering process as fluxing agents, in that they melt at a relatively low temperature of ~1300˚C, allowing a significant increase in the rate of reaction. Without these fluxing agents, the formation of the calcium silicate cement minerals would be slow and difficult. In fact, the formation of fluxing agents is the primary reason that Portland (calcium silicate) Cements contain aluminum and iron at all. The final aluminum- and iron-containing cement minerals (C3A and C4AF) in a Portland Cement contribute little to the final properties. As the mix passes through solid-state reaction zone it becomes “sticky” due to the tendency Burning Process (Cont.)
  27. 27. Reaction Zone Temperature (oC) Characteristics Clinkering >1300 – 1550 This is the hottest zone where the formation of the most important cement mineral, Alite (C3S), occurs. The zone begins as soon as the intermediate calcium aluminate (C3A) and ferrite (C4AF) phases melt. The presence of the melt phase causes the mix to agglomerate into relatively large nodules about the size of marbles consisting of many small solid particles bound together by a thin layer of liquid. Inside the liquid phase, Alite (C3S) forms by reaction between Belite (C2S) crystals and CaO. (C2S + C  C3S) Crystals of solid Alite (C3S) grow within the liquid, while crystals of Belite (C2S) formed earlier decrease in number but grow in size. The clinkering process is complete when all of silica is in the C3S and C2S crystals and the amount of free lime (CaO) is reduced to a minimal level (<1%). Cooling As the clinker moves past the bottom of the kiln the temperature drops rapidly and the liquid phase solidifies, forming the other two cement minerals C3A (aluminate) and C4AF (ferrite). In addition, alkalis (primarily K) and sulfate dissolved in the liquid combine to form K2SO4 and Na2SO4. The nodules formed in the clinkering zone are now hard, and the resulting product is called cement clinker. The rate of cooling from the maximum temperature down to about 1100˚C is important, with rapid cooling giving a more reactive cement. This occurs because in this temperature range the C3S can decompose back into C2S and CaO, among other reasons. It is thus typical to blow air or spray water onto the clinker to cool it more rapidly as it exits the kiln.  Rapid cooling of the clinker is essential as this hampers the formation of crystals, causing part of the liquid phase to solidify as glass.  The faster the clinker cooling the smaller the crystals will be when emerging from the liquid phase.
  28. 28. Suspension Preheaters and Calciners  The chemical reactions that occur in the dehydration and calcination zones are endothermic, meaning that a continuous input of energy to each of the particles of the raw mix is required to complete the reaction. When the raw mix is piled up inside a standard rotary kiln, the rate of reaction is limited by the rate at which heat can be transferred into a large mass of particles. To make this process more efficient, suspension preheaters are used in modern cement plants to replace the cooler upper end of the rotary kiln. Raw mix is fed in at the top, while hot gas from the kiln heater enters at the bottom. As the hot gas moves upward it creates circulating “cyclones” that separate the mix particles as they settle down from above. This greatly increases the rate of heating, allowing individual particles of raw mix to be dehydrated and partially calcined within a period of less than a minute.  Alternatively, some of the fuel can be burned directly within the preheater to provide even more heating to the suspended particles. The area of the preheater where fuel is burned is called a precalciner. With a precalciner, the particles are nearly completely calcined as they enter the rotary kiln. Preheaters and precalciners save on fuel and increase the rate at which the mix can be moved through the rotary kiln. 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 29
  29. 29. ii) General Diagram of Preheater/Precalciner Reactions
  30. 30. 4) Grinding and the Addition of Gypsum  Now the final process is applied which is grinding of clinker, it is first cooled down to atmospheric temperature.  Grinding of clinker is done in large tube mills.  After proper grinding gypsum (Calcium sulphate CaSO4) in the ratio of 01-04 % is added for controlling the setting time of cement.  Finally, fine ground cement is stored in storage tanks from where it is drawn for packing.  Once the nodules of cement clinker have cooled, they are ground back into a fine powder in a large grinding mill. At the same time, a small amount of calcium sulfate such as gypsum (calcium sulfate) is blended into the cement. The calcium sulfate is added to control the rate of early reaction of the cement  Cement is produced by grinding clinker with gypsum (calcium sulfate) in the finish-grinding mill to a required fineness.  A small quantity of gypsum, about 3 to 5 %, is needed to control the setting time of cement produced.  The amount of gypsum being used is determined by the Sulphuric anhydride (SO3) contents in cement. Cement Grinding
  31. 31. Cement Storage & Distribution • At this point the manufacturing process is complete and the cement is ready to be bagged or transported in bulk away from the plant After the grinding process, cement is pumped into the storage silos. • This silo is preventing the moisture to react with cement. • When needed cement from the silos is packed into bags or loaded into road tankers and rail wagons for dispatch. • However, the cement is normally stored in large silos at the cement plant for a while so that various batches of cement can be blended together to even out small variations in composition that occur over time. 21 November Prof. Dr. H.Z. Harraz Presentation Cement 32
  32. 32. CHEMICAL COMPOSITIONS Oxide Notation CaO C SiO2 S Al2O3 A Fe2O3 F SO3 H2O H MgO M Na2O N  S The properties of cement during hydration vary according to:  Chemical composition  Degree of fineness It is possible to manufacture different types of cement by changing the percentages of their raw materials. 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 33 1) Cement chemistry notation based on oxides CEMENT CHEMISTRY
  33. 33. Chemical Name Chemical Formula Oxide Formula Cement Notation Mineral Name Tricalcium Silicate Ca3SiO5 3CaO.SiO2 C3S(40-60%) Alite Dicalcium Silicate Ca2SiO4 2CaO.SiO2 C2S(16-30%) Belite Tricalcium Aluminate Ca3Al2O6 3CaO.Al2O3 C3A(7-15%) Aluminate Tetracalcium Aluminoferrite Ca2AlFeO5 4CaO.Al2O3.Fe2O3 C4AF(7-12%) Ferrite Calcium hydroxide Ca(OH)2 CaO.H2O CH Portlandite Calcium sulfate dihydrate CaSO4.2H2O CaO.SO3.2H2O CSH2 Gypsum Calcium oxide CaO CaO C Lime Compound Composition of Clinker / Cement 21 November Prof. Dr. H.Z. Harraz Presentation Cement 34
  34. 34. Phase Diagram Tricalcium Silicate Tricalcium Aluminate SiO2 CaO CaOCaO CaO Al2O3 CaOCaO 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 35
  35. 35. Bogue’s Equations – Compound composition  To calculate the amounts of C3S, C2S, C3A, and C4AF in clinker (or the cement) from its chemical analysis (from the mill certificate)  Assumptions in calculations: Chemical equilibrium established at the clinkering temperature  Components maintained unchanged through the rapid cooling period  Compounds are “pure” • A simple estimate of the phase composition of a Portland Cement can be obtained from the oxide composition if one assumes that the four main cement minerals occur in their pure form. • With this assumption, all of the Fe2O3 is assigned to C4AF and the remaining Al2O3 is assigned to C3A. • This leaves a set of two linear equations to be solved for the amounts of C2S and C3S. • This method is named after the cement chemist R.H. Bogue. A standardized version of this simple method is given in ASTM C 150. There are two sets of equations, based on the ratio of A/F in the cement (both inputs and outputs are in weight percent): 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 36
  36. 36. Case 1 : If A/F >=0.64  C3S = 4.071C - 7.6S - 6.718A - 1.43F - 2.852S  C2S = 2.867S - 0.7544C3S  C3A = 2.65A - 1.692F  C4AF = 3.043F Case 2 : If A/F < 0.64  C3S = 4.071C - 7.6S - 4.479A – 2.859F - 2.852S  C2S = 2.867S - 0.7544C3S  C3A = 0  C4AF = 2.10A + 1.702F 21 November Prof. Dr. H.Z. Harraz Presentation Cement 37
  37. 37. Types of Cement Depending upon our requirements i.e. using it at a suitable place, we use different types of cement. Ordinary Portland Cement Rapid Hardening or High early strength Cement Sulphate Resisting Cement Quick setting Cement High Alumina Cement Portland Slag Cement Low Heat Cement Air Entraining Cement White Cement Coloured Cement Portland Pozzolona Cement
  38. 38. Ordinary Portland Cement: It is the variety of artificial cement. It is called Portland cement because on hardening (setting) its colour resembles to rocks near Portland in England. It was first of all introduced in 1824 by Joseph Asp din, a bricklayer of Leeds, England. Chemical Composition of O.P. Cement: O.P.C has the following approximate chemical composition: The major constituents are: 1. Lime (CaO) 60- 63% 2. Silica (SiO2) 17- 25% 3. Alumina (Al2O3) 3- 8% The auxiliary constituents are: 1.Iron oxide (Fe2O3) 0.5- 6% 2.Magnesia (MgO) 1.5- 3% 3.Sulphur Tri Oxide (SO3) 1- 2% 4.Gypsum 1 to 4%
  39. 39. Functions of Cement Manufacturing Constituent (i) Lime (CaO):  Lime forms nearly two-third (2/3) of the cement. Therefore sufficient quantity of the lime must be in the raw materials for the manufacturing of cement. Its proportion has an important effect on the cement. Sufficient quantity of lime forms di-calcium silicate (Ca2SiO2) and tri- calcium silicate in the manufacturing of cement.  Lime in excess, causes the cement to expand and disintegrate. (ii) Silica (SiO2):  The quantity of silica should be enough to form di-calcium silicate (Ca2SiO2) and tri-calcium silicate in the manufacturing of cement. Silica gives strength to the cement. Silica in excess causes the cement to set slowly. (iii) Alumina (Al2O3):  Alumina supports to set quickly to the cement. It also lowers the clinkering temperature. Alumina in excess, reduces the strength of the cement. (iv) Iron Oxide (Fe2O3):  Iron oxide gives colour to the cement. (v) Magnesia (MgO):  It also helps in giving colour to the cement.  Magnesium in excess makes the cement unsound. (vi) Calcium Sulphate (CaSO4) (or) Gypsum (CaSO4 . 2H2O) :  At the final stage of manufacturing, gypsum is added to increase the setting of cement.
  40. 40. Rapid Hardening Cement (or) High Early Strength cement  This type cement gets the strength faster than OPC, However its Initial and Final setting is same as those of OPC. It contains more of Tri-Calcium Silicate and is more finely grounded. It gives out more Heat while setting so it is as such unsuitable for massive concrete. It is Used for the Structures which are Subjected to loads early e.g. Roads, Bridges.  This cement contains more % age of C3S and less % of C2S.  This is in fact high early strength cement. The high strength at early stage is due to finer grinding, burning at higher temperature and increased lime content. The strength obtained by this cement in 4 days is same as obtained by O.P.C in 14 days.  This cement is used in highway slabs which are to be opened for traffic quickly. This is also suitable for use in cold weather areas.  One type of this cement is manufactured by adding calcium chloride (CaCl2) to the O.P.C in small proportions. Calcium chloride (CaCl2) should not be more than 2%. When this type of cement is used, shuttering material can be removed earlier. Quick Setting cement  It sets faster than the Ordinary Portland Cement.  When concrete is to be laid under water, quick setting cement is to used.  This cement is manufactured by adding small % of aluminum sulphate (Al2SO4) which accelerates the setting action.  The setting action of such cement starts with in 5 minutes after addition of water and it becomes stone hard in less than half an hour.  It is required for making concrete that is required to set early as for lying under water or in running water.  Initial setting being very little there is always the danger of concrete having undergone its initial setting. Thus this type of cement is used in more special cases.
  41. 41. High Alumina Cement  It is manufactured by the burning of bauxite ore and lime stone in correct proportions and at high temperature. The resulting product is then ground finely.  It develops Strength Rapidly.  It is of black colour and resists well the attack of chemicals especially of sulphates and sea water.  Its ultimate strength is much higher than OPC.  Its initial setting takes more than 2 hours and the final set takes place immediately thereafter.  Most of the heat it gives in the first 10 hrs as a result it can be conveniently used in freezing temperatures.  At ordinary temperature it is used in thin layers.  This cement contains high aluminate % usually between 35-55%.  It gains strength very rapidly with in 24 hours.  It is also used for construction of dams and other heavy structures.  It has resistance to sulphates and action of frost also. Portland Slag Cement  It is obtained by mixing clinker, gypsum and granulated slag in a proper proportion.  The Properties of this cement is very similar to that of OPC which are as under.  It has lesser heat of hydration and has better resistance of soils, sulphates of alkali metals, alumina and iron.  It has better resistance to acidic water.  This type of cement is mostly used in Marine Works. Low Heat Cement  The Heat Generated by cement while setting may cause the structure to crack in case of concrete. This Heat generation is controlled by keeping the percentage of Tri-calcium silicate and that of Tri-calcium aluminate (C3 A) low.  In this cement the heat of hydration is reduced by tri-calcium aluminate (C3 A) content.  It contains less % of lime than ordinary port land cement.  It is used for mass concrete works such as dams …etc.  Its initial setting and Final setting times are nearly the same as those of OPC. It is not very suitable for Ordinary structures because the use of cement will delayed time of drying. It will also need more curing.
  42. 42. Air Entraining Cement  This type of cement was first of all developed in U.S.A to produce such concrete which would have resistance to weathering actions and particularly to the action of frost.  It is the OPC mixed with some air entraining agents.  Natural resins, fats, oils and fatty acids ….etc are common used as air entraining agents.  These materials have the property of entraining air in the form of fine air bubbles. The bubbles render the concrete to become more plastic, workable and more resistant to freezing. However because of air entrainment the strength of concrete reduces and as such the quantity of air so entrained should not exceed 5%.  It is found that entrainment of air or gas bubbles while applying cement, increases resistance to frost action. Air entraining cement is produced by grinding minute air entraining materials with clinker or the materials are also added separately while making concrete.  Entrainment of air also improves workability and durability. It is recommended that air contents should be 3- 4 % by volume. White Cement  This cement is called snowcrete.  It is the cement of pure white colour and having same properties as those of Ordinary Portland Cement(Greyish colour of cement is due to iron oxide (FeO)).  As iron oxide gives the grey colour to cement, it is therefore necessary for white cement to keep the content of iron oxide as low as possible.  White cement is manufactured from chalk or limestone and China clay free from Iron Oxide are suitable for its manufacturing.  Oil fuel and not the coal is used for the burning of this cement.  It is much more costly than ordinary cement.  This cement is costlier than O.P.C.  It is mainly used for architectural finishing in the buildings. .
  43. 43. Sulphate Resisting Cement:  It is modified form of O.P.C and is specially manufactured to resist the sulphates.  In certain regions/areas where water and soil may have alkaline contents and O.P.C is liable to disintegrate, because of unfavourable chemical reaction between cement and water, S.R.C is used.  This cement contains a low % of C3A not more than 5%.  This cement requires longer period of curing.  This cement is used for hydraulic structures in alkaline water and for canal and water courses lining.  It develops strength slowly, but ultimately it is as strong as O.P.C.
  44. 44. Coloured Cement Various coloured cement are prepared when required in special cases. Suitable pigments are added with OPC to get red or brown cement but for other colours 5 – 10% of desired pigments are grounded with white cement. Pigments used should be chemically inert and also durable so as they must not fade due to the effect of lights sun or weather. Portland Pozzolona Cement Portland Pozzolona cement is produced by grinding together Portland cement and Pozzolona. This cement has properties similar to those of OPC and can therefore be used for all general purpose. Portland Pozzolona cement produces less heat of hydration and offers greater resistance to attack of aggressive water or sulphates bearing than OPC. Portland Pozzolona cement are particularly used in marine works. It takes a little longer to gain strength. Ultimate Strength of this cement is more than OPC
  45. 45. HYDRATION  It's a process of chemical reaction between cement and water.  It results first in setting (the concrete become solid) and then hardening (increase of strength and stiffness).  Heat is liberated during hydration process.  Thus, during the hardening process, the concrete is being continually warmed by internal heat generated
  46. 46. WHAT IS SETTING ?  When cement is mixed with sufficient water, within 1 or 2 hr after the mixing, the sticky paste losses its fluidity ; within a few hours after mixing, noticeable stiffening commences.  Setting can be divided to 2 stage that is: a) Initial Set b) Final Set  Initial set is when the paste begin to stiffen  Final set is when the paste beginning to harden and able to sustain some loads.  Initial Setting Time is the time lapse from the addition of water in the mix to the initial set.  Initial Setting Time and Final Setting Time can be determine by using Vicat Apparatus in laboratory.  They are measure at lab. As the time required for the cement paste to withstand a certain arbitrary pressure.  The time taken for a 1-mm diameter needle in the Vicat apparatus to penetrate a depth of 25mm into the cement past sample is the initial setting time.  The final setting time is reached when in the modified Vicat apparatus only the needle penetrates the surface, while the attachment fails to do so.  The rate of setting is also a measure of the rate of heat of hydration.
  47. 47. Test of Cement •Consistency test •Compressive strength test •Tensile strength test
  50. 50. Consistency Test • It is used to determine the % of water required for preparing cement pastes for other tests Procedure: 1. Take 300g cement, add 30% or 90g of water 2. Mix water and cement on a non-porous surface. Mixing should be done. • Fill the mould of Vicat apparatus. • The interval between the addition of water to the commencement of filling the moulds is known as the time of gauging.  Among the factors affect the setting time are: a) Fineness of cement b) Chemical composition c) Amount of water  Gypsum added to clinker to retard setting and prevent flash set.  Flash set is defined as the rapid development of permanent rigidity of the cement paste along with high heat.  False set is the rapid development of rigidity without the evolution of heat .
  51. 51. Compressive strength • Mortar of cement & sand is prepared, 1:3. • Water is added, water cement ratio 0.4:1 • It is placed in moulds & form cubes of sides 70.6 or 76 mm. • The cement required is 185 or 235g • Compacted in vibrating machine in 2 min. • Moulds placed in damp cabin for 24 hrs • Specimens are removed & placed in water for curing. • It is tested in compressive testing machine after 3 and 7 days. • Every side is calculated and average is taken. • For 3 days: > 115 kg/cm2 or 11.5 N/mm2 • for 7 days: > 175 kg/cm2 or 17.5 N/mm2
  52. 52. Tensile Strength • Procedure: 1. Mortar is prepared cement(1) : Sand (3) 2. Water is added 8% 3. Mortar is placed in briquette moulds
  53. 53. • Typical briquette is formed. • A small heap is formed at its top. • It is beaten down by a standard spatula till water appears on the surface. • Same procedure is repeated for other sides of briquettes. • 12 standard briquettes are prepared • The quantity of cement may be 600g for 12 briquettes • It is kept in damp cabin for 24 hrs. • It is carefully removed from mould and submerged in clean water for curing. • It is tested in testing machine after 3 and 7 days • The cross section of briquettes at least section is 6.45 cm2 • Ultimate tensile stress = failing load 6.45
  54. 54. • After 3 days: > 20 kg/cm2 • After 7 days: > 25 kg/cm2
  55. 55. HARDENING  Hardening is the development of strength over an extended period of time, is completed for months or years.  Hydration is the key for strength development in concrete.  Hydration process are gradual and require continuous presence of water.  Adding water to the cement would cause temperature of the mixture rise rapidly due to reaction between Tricalcium Aluminate and water that is initially quite rapid.  This is because of since it takes some time for the gypsum to dissolve sufficiently to control the reaction of Tricalcium Aluminate.  Gypsum prevents flash setting that happen due to the reaction of Tricalcium Aluminate.  Thereafter, setting and gradual hardening take place by the reaction of Tricalcium Silicate and Dicalcium Silicate with water.  Atmosphere doesn't take part in hydration process  Hydration process can't take place completely without enough water in the mixture.  Hydration rate depends surface area of clinker expose and fineness of grinding.  Rate of hydration decreases continuously with age as the resistance to water penetration of unhydrated cement grains progressively rises.
  56. 56. Characteristics of Cement • Color • Physical properties • Presence of lumps • Strength
  57. 57. Colour should be uniform Typical cement colour (gray colour with light greenish shade) It gives an indication of excess of lime or clay and the degree of burning.
  58. 58. Physical properties Feel smooth when touched or rubbed in between fingers. If felt rough, indicates adulteration with sand. If hand is inserted in cement bag, hand feels cool and not warm. If it immersed in water, it should sink and should not float A paste of cement feel sticky  If it contains clay & silt as adulterant, it give earthy smell.
  59. 59. Presence of Lumps •It should free from hard lumps. •It is due to the absorption of moisture from atmosphere. •If a bag contains lumps it should be rejected.
  60. 60. Strength • It is tested by three methods: 1. Briquettes with a lean or weak mortar are made (75mm x 25mm x 12mm). The proportion of cement & sand is 1:6. Immersed in water for 3 days. • If cement is good it will not be broken easily and difficult to convert powder form. 2. A block is prepared (25 x 25 x 200) and immersed in water for 7 days. • Then it is placed on supports 150 mm apart and loaded 340N. • It should not show signs of failure. 3. Thick paste of cement with water is made on thick glass and kept in water for 24 hours. • It should set and not crack
  61. 61. TO CHECK THE QUALITY OF CEMENT IN THE FILED: 1) Colour greenish grey. 2) One feels cool by thrusting one’s hand in the cement bag. 3) It is smooth when rubbed in between fingers. 4) A handful of cement thrown in a bucket of water should float. QUALITY TESTS OF CEMENT: 1) Fineness Test, 2) Consistency test / setting time test 3) Setting Time Test 4) Compressive strength test
  62. 62. Fineness of cement • Grinding is the last step in processing • Measures of fineness Specific surface Particle size distribution • Blaine’s fineness  Measure of air permeability • Typical surface areas   350m2 / kg (Normal cements)  ~ 500 m2 / kg (High early strength cements) Significance of fineness  Finer cement = Faster reaction  Finer cement = Higher heat of hydration  Large particles do not react with water completely  Higher fineness Higher shrinkage  Reduced bleeding  Reduced durability  More gypsum needed 21 November 2015 Prof. Dr. H.Z. Harraz Presentation Cement 66
  63. 63. (1) Fineness Test: Finer cements react quicker with water and develop early strength, though the ultimate strength is not affected. However finer cements increase the shrinkage and cracking of concrete. The fineness is tested by: By Sieve analysis: Break with hands any lumps present in 100 grams of cement placed in IS sieve No.9 and sieve it by gentle motion of the wrist for 15 minutes continuously. The residue when weighed should not exceed 10 percent by weight of the cement sample.
  64. 64. (2) Consistency Test /Setting Time Test :  This test is performed to determine the quantity of water required to produce a cement paste of standard or normal consistency.  Standard consistency of cement paste may be defined as the consistency which permits the Vicate’s plunger (10 mm, 40 to 50 mm in length) to penetrate to a point 5 mm to 7 mm from the bottom ( or 35 mm to 33 mm from top) of Vicat mould.  When the cement paste is tested within the gauging time ( 3 to 5 minutes) after the cement is thoroughly mixed with water.  Vicat apparatus is used for performing this test.
  65. 65. (3) Setting Time Test: In cement hardening process, two instants are very important, i.e. initial setting and final setting. a) Initial Setting Time: The process elapsing between the time when water is added to the cement and the time at which the needle ( 1 mm square or 1.13 mm dia., 50 mm in length) fails to pierce the test block ( 80 mm dia. and 40 mm high) by ~5 mm, is known as Initial Setting Time of Cement. b) Final Setting Time: The process elapsing between the time when water is added to the cement and the time at which a needle used for testing final setting upon applying gently to the surface of the test block, makes an impression thereon, while the attachment of the needle fails to do so, is known as final Setting Time of Cement.
  66. 66. (4) Compressive Strength test of Cement: This test is very important. In this test, three moulds of (face area 50 cm2) are prepared and cured under standard temperature conditions and each cube tested by placing it between movable jaws of the compressive strength testing machine. The rate of increasing load is zero in the beginning and varies at 350 kg/cm2 per minute. The load at which the cube gets fractured divided by the cross sectional area of the cube, is the compressive strength of the cube. The average of the compressive strengths of three cubes is the required compressive strength of the cement sample.