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Portland Cement

Portland Cement. Prof. Grobéty B., Inst. de Minéralogie et Pétrographie, Univ. de Fribourg. Technical Mineralogy Department of Geosciences. Technische Mineralogie ETHZ IMP 2008. Introduction. Cementitous materials. Definition: Material, which binds together with solid bodies (aggregates)

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Portland Cement

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  1. Portland Cement Prof. Grobéty B., Inst. de Minéralogie et Pétrographie, Univ. de Fribourg Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  2. Introduction Cementitous materials Definition: Material, which binds together with solid bodies (aggregates) by hardening from a plastic state. Examples: organic polymers inorganic cements Inorganic cements - mixed with water  plastic state - hydration of the components  development of rigidity (setting) - steady increase of strength (hardening) - Examples: Portland cement, gypsum plasters, phosphate cements - when hardening occurs also under water: hydraulic cement - Example: Portland cement Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  3. Introduction Historical background I (www.auburn.edu/academic/architecture/bsc/classes/bsc314/timeline/timeline.htm) 12M BC: Natural production of clinker through the spontaneous combustion of oil shales (Israel) 3000 BC: Egyptians used sulfate and lime based plasters Use of cementitous materials in China (Great Wall) 300 BC: Concrete and mortars based on lime and pozzolanic material (volcanic ashes). Pliny reported a mortar mix of 1 part of lime and 4 part of sand. Examples: 193 BC: Porticu House, Amaelia, 200 AD: Pantheon, Rome (www.romanconcrete.com) http://www.greatbuildings.com/buildings/Pantheon.html Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  4. Introduction Historical background II Middle ages: Decline of cement and concrete technology 1756: John Smeaton, British Engineer, rediscovered hydraulic cement through repeated testing of mortar in both fresh and salt water 1824: Joseph Aspdin, bricklayer and mason in Leeds, England, patented what he called portland cement, since it resembled the stone quarried on the Isle of Portland off the British coast. Portland cement. This was the name given by Joseph Aspdin to the product consisting of limestone and clay, on which he took out a patent in 1824: "Portland", owing to the similarity to the building stone from Portland in England, and "cement" from the Latin caementum, which means chipped stone. Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  5. Introduction Cement: definitions Portland cement: Hydraulic cementitous material based on clinker, a material composed of calcium silicates and aluminates, and a small amount of added gypsum/anhydrite. The clinker is made by burning mixtures of limestone and argilaceous rocks (slates). Mortar: Mixture of Portland cement, fine sand and water (used f.ex. for the construction of brick walls) Neat paste: Mixture of Portland cement and water alone (used for filling cracks and sealing small spaces) Concrete: Mixture of Portland cement, coarse and fine aggregates (rock pebbles, sand), water and chemical additives. The mechanical strength can be reinforced by the insertion of steel bars. Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  6. Introduction C = CaO S = SiO2 A = Al2O3 F = Fe2O3 M = MgO K = K2O N = Na2O S = SO3 T = TiO2 P = P2O5 H = H2O C = CO2 LOI = loss of ignition (≈ H2O+CO2) C-S-H = poorly crystallized calcium silicate hydrates HCP = hydrated cement paste PFA = pulverized fuel ash PC = Portland cement OPC = Ordinary Portland cement Cement: chemical notations Chemical notation Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  7. Introduction Portland Cement I Chemical composition The composition of Portland Cements and puzzolanic additives cover a certain range. Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  8. Introduction Portland cement II Main mineralogical components Name + Chem. Comp Approx. % in OPC Properties Belite C2S 20 Slow strength gain, responsible for long term strength Alite C3S 55 Rapid strength gain, responsible for early strength gain Aluminate C3A 12 Quick setting (contr. by gypsum), liable to sulfate attack Ferrite C4AF 8 Little contribution to setting or strength, responsible for gray color of OPC Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  9. Introduction Portland Cement III Main production steps (http://www.ppc.co.za/Cement/c_cement_manprocess.asp) Quarrying chalk in northern Jutland (Aalborg Cement) Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  10. Introduction Portland Cement IV Main production steps (cont.) Chalk slurry tank (Aalborg cement) Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  11. Introduction Portland Cement V Main production steps (cont.) Preheater, rotary kilns and storage silos Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  12. Introduction Portland Cement VI Main production steps (cont.) Cement silo Shipping by ship Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  13. Introduction Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  14. Introduction World cement productions(minerals.usgs.gov/minerals/pubs/commodity/cement World cement production 2000 (thousand of tons): United States (includes Puerto Rico) 92,300 Brazil 41,500 China 576,000 Egypt 23,000 France 24,000 Germany 38,099 India 95,000 Indonesia 27,000 Italy 36,000 Japan 77,500 Korea, Republic of 50,000 Mexico 30,000 Russia 30,000 Spain 30,000 Taiwan 19,000 Thailand 38,000 Turkey 33,000 Other countries (rounded) 450,000 World total (rounded) 1,700,000 China produces one third of the world cement output! China 576,000 World total (rounded) 1,700,000 Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  15. Introduction Swiss cement industry (www.cemsuisse.ch) Cement plants in Switzerland 1 Eclépens 2 Cornaux 3 Reuchenette 4 Wildegg 5 Siggenthal 6 Thayngen 7 Brunnen 8 Untervaz Total production 1987: 4’478’000 t 1989: 5’461’000 t 2000: 3’715’908 t cement plant klinker mills Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  16. Raw materials Raw materials Main raw materials Calcareous lime stones: - calcite-rich - low in dolomite Shales: - clay rich, usually dominated by illite, smectite and kaolinite. Ideal bulk composition ranges: 55-60wt% SiO2, 15-25wt% Al2O3, 5-10wt% Fe2O3 Corrective constituents Sand, flyash: - adjust SiO2-content in quartz-poor shales Ironores, bauxite: - adjust Fe resp. Al content Additional reactive constituents, which have to be considered, may be introduced through impurities in the fuel. Up of 30% of ash is produced by the firing of brown coal. Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  17. Raw materials Composition of ordinary Portland cements Major components Minor components and traces (deleterious) few %: MgO, SrO2 few tenth of a %: P2O5, CaF2 , alkalis traces: heavy metals SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O SO3 LOI (H2O+CO2) 19.0 - 23.0 3.0 - 7.0 1.5 - 4.5 63.0 - 67.0 0.5 - 2.5 0.1 - 1.2 0.1 - 0.4 2.5 - 3.5 1.0 - 3.0 The composition of different cements, their minimum mechanical properties and their application is regulated by Norm SIA Norm 215.001/002 (http://www.vicem.ch/produits/normes/2_7d.htm) which corresponds to the European Norm ENV 197 (http://www.readymix-beton.de/service/betontechnische_daten/kap_1_1.pdf) Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  18. Raw materials Proportioning of raw materials Targets for an ordinary Portland cement (OPC) -Lime saturation factor (LSF) close to 100% - Free lime content under 1.5wt% - Silica ratio (SR module) between 2.0 and 3.0 - Alumina ratio (AR module) between 1.0 and 2.0 - Hydraulic index (IH) ≈ 2.0 - Low concentration of deleterious components Lime saturation factor The calcium present in the raw materials should be completely bound in the silicate and aluminate phases of the cement clinker. The amount of different oxide components necessary to saturate the amount of lime is given by(in wt%): CaO = 2.8 SiO2 + 1.2Al2O3 + 0.65Fe2O3 Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  19. Raw materials Proportioning of raw materials VII Example (cont.) The proportion p of mix A and 1-p of mix B to get an SR of 3.0 can be obtained through following consideration: The value a can be obtained from S 13.1p + 16.1(1-p) A+F 7.5p + 2.1(1-p) S A +F - SR = = 3.0 - Mix A MixB S 13.1 16.1 A+F 7.5 2.1 = 3.0 =  p = 0.51 Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  20. Klinker production 0.71nm SiO4 Ca R- C3S projected along the c-axis O Polymorphic transformations: T1 T2 T3 M1 M2 M3 R T: triclinic M: monoclinic R: rhombohedral 620°C 920°C 980°C 990°C 1060°C 1070°C Klinker phases I 1. Alite Ca3SiO5 = C3S orthosilicate Max. concentration of impurities: 1.0 wt% Al2O3, 1.2% Fe2O3, 1.5 % MgO impurities stabilize the M1 and or M3 in klinkers, rarely T2 is found Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  21. Klinker production 0.55nm Polymorphic transformations: O1(g) M1(b) M2(aL’) O2(aH’) H1(a) O: orthorhombic M: monoclinic H: hexagonal <500°C 630°C 1160°C 1425° Klinker phases II 2. Belite Ca2SiO4 = C2S a - C2S proj. down c-axis orthosilicate Max. concentration of impurities: 4.0-6.0wt% Al2O3+ Fe2O3 impurities stabilize the b-phase Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  22. Klinker production Klinker phases III 3. Aluminates and ferrites Ca3Al2O6 = C3A (cubic) impurities: up to 4wt% NaO up to 16% Fe2O3+ SiO2 imputirities stabilize an orthorhombic polymorph Ca2AlxFe1-xO10 = C4AF xclinker: around 1.0 impurities: up to 10 wt% MgO +TiO2 + SiO2 Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  23. Klinker production Klinker phases IV Polymorphs and composition of phases present in clinker C3S early crystallized small crystals rich in substitutes: M3 late crystallized large crystals: M2 (single twins), rarely T1 (polysynthetic twins) 3-4% of substituting elements, mainly Mg, Al and Fe C2S usually only in the M1(b) polymorph with parallel twin lamellae M2(aL’) has typical crossed twin lamellae. The transformation M2(b) M(g) sho<uld be avoided, because the accompanying drastic volume increase leads to excessive dusting. 4-6% of substituing elements, mainly Al and Fe C3A polymorphs is coupled with substitution. Clinker aluminate phases are cubic (fine grained) or orthorhombic (lath shapedand twinned) 13% to 20% of substituting elements: Mg, Al, Fe, Si C3AF Main exchange vector Fe-2 SiMg Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  24. Klinker production Klinker phases V Etched microstructures of the different klinker polymorphs Alite crystals with both single and polysynthetic twins Belite crystals with complex twin lamellae (M2(aL’) polymorph) Belite crystals with paralllel twin lamellae (M(b) polymorph) Belite crystals with crack formation along lamellae boundaries (M(b) (M(b) transf.) Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  25. Klinker production Rotary kiln Without preheater/precalciner the kiln aspect ratio is about 30 Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  26. Klinker production Klinker reactions below 1300°C Temp. range products Drying 100°C free water evaporates 100 - 300°C release of adsorbed and crystal water Decomposition of calcite (calcining): 500 - 900°C free lime (CaO) Decomposition of phyllosilicates: 300 - 900°C dehydroxilated, amorphous material Formation of first clinker phases: > 800°C belite, aluminate (different phases), ferrite Formation of first melt phases: > 1000°C Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  27. Klinker production Decomposition of carbonate phases I Decomposition reaction: CaCO3 = CaO + CO2 Equilibrium constant 1.0 P(CO2) 0.75 Rate of decarbonation is influenced by: 0.5 - material temperature (=> K) 0.25 - gas temperature (heat transfer) 890C - external partial pressure of CO2 0.0 750 800 850 900 T(C) - size and purity of the calcite particles Calcite decomposition temperature As function of CO2 partial pressure Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  28. Klinker production reaction progress a a t Decomposition of carbonate phases II Reaction mecanism: formation of a lime layer around calcite Possible rate determining steps 1. heat and mass transport (CO2) through the product layer 2. reaction at the calcite surface Activation energy: 196kJ/mol (Khraisha et al, 1992)  reaction controlled ? Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  29. Klinker production lime quartz amorphous material belite Belite formation 2. Transformation of the belite shells to belite crystal clusters 1. Formation of belite through solid state reaction Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  30. Klinker production Appearance of first melts 1. Alkali and sulfate melts 2. C-S-A melts: lowest eutecticum 1170° Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  31. Klinker production P: typical bulk composition of Portland cement klinkers First melt appearance: 1455°C Phase diagram Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  32. Klinker production Klinker reactions between 1300°C and 1450°C 1. Melting reactions - Melting of ferrite and aluminate phases - Melting of part of the early formed belite 2. Formation of new phases Reaction of melt, free lime, unreacted silica and remaining belite to alite 3. Polymorphic transformation of belite 4. Recrystallization of alite and belite 5. Nodulization (clinkering) Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  33. Klinker production Amount and composition melts II 35 30 25 Liquid phase (wt%) 20 15 SM 1.5 2.0 2.5 3.0 3.5 At 1450°C and above the liquid content depends on the silica modulus Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  34. Klinker production lime amorphous material belite alite Formation and recrystallization of alite 1. Formation of melt around lime crystals 2. Crystallization of alite walls at the contacts between belite cluster and lime 3. Recrystallized and new formed alite replaces lime crystals Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  35. Klinker production 0.1mm 0.05mm Belite clusters replacing previous quartz grains. Alite wall separating CaO and a belite cluster belite alite melt phase (aluminates,ferrites) lime Microtextures I (all pictures FL Smidth review 25) Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  36. Klinker production 0.3mm 0.2mm alite pores lime belite Alite crystallizing at the expense of lime and belite Well crystallized, homogeneous clinker. The raw mix contained few quartz grains and a well controlled carbonate grain size. Microtextures II Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  37. Klinker production Klinker reactions during cooling 1. Crystallization of the restitic melt. Products: aluminates (C3A) and ferrites (C4AF) 2. Polymorphic transformations of alite and belite If cooling is too slow 3. Backreaction of alite to belite + lime 4. Recrystallization aluminates and ferrites Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  38. Klinker production belite rims 0.04mm 0.02mm Backreaction of alite rims to belite plus lime in a belite poor clinker (fast cooling). Etched thin section showing the transformation twins in belite. Microtextures III Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  39. Klinker production 0.05mm 0.05mm Slowly cooled clinker with corroded alite phase and recrystallized belite grains. Fast cooled clinker with euhedral alite and rounded belite crystals. Microtextures IV Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  40. Klinker production Normative mineralogy of clinker I Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  41. Klinker production Normative mineralogy of clinker II Minor elements in the main klinker phases in cements of different cement factories. Most cements contain 5wt% and more minor elements which introduces considerable errors when using Bogues original formula, Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  42. Klinker production Normative mineralogy of clinker III Corrected Bogue equation C3 Scorr = C3 Sbogue + 4.0 MgOclinker + 5.5 K2 Oclinker C2 Scorr = C2 Sbogue - 1.5 MgOclinker - 2.2 K2 Oclinker C3 Acorr = C3 Abogue + 7.8 Na2O + 1.5 AR - 2.1 S3O - 5.0 C4 AFcorr = C4 AFbogue - 6.5 Na2O - 1.7 AR + 5.0 Mn2O3 + 3.0 0.05mm Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  43. Klinker production Normative mineralogy of clinker IV 0.05mm Difference in calculated alite and belite content using the original(top) and the corrected (bottom) Bogue formula Technical Mineralogy Department of Geosciences Technische Mineralogie ETHZ IMP 2008

  44. Klinker production Energy balance in clinker production Temp range 20-450°C wet 100°C ca. 450°C 450-900°C ca. 900°C ca. 900°C 900-1400°C 900-1400°C ca. 1300°C 1400-20°C 900-20°C 450-20°C Process Heating of the material Evaporation of free H2O Removal of H2O from clay heating of the material Dissociation of calcite Crystallisation of dehydrated clay Heating of the decarbonated material Heat of formation of clinker minerals Melting of liquid phases Cooling of clinker Cooling of CO2 Cooling of H2O Total Heat exchange kJ/kg clinker 710 (1800) 170 820 2000 -40 525 -420 100 -1510 -500 -85 4325 -2555 Institut de Minéralogie et Pétrographie Université de Fribourg Technische Mineralogie ETHZ IMP 2008

  45. Klinker production Energy costs of cement production Dry process cement plant 5000t/day Fuel Electricity Cost($/day) kcal/kg cement kwh/ton cement 0 0 2.5 600 1.5 360 0-100 27.0 9813 1.5 360 1.5 360 700 23.0 28853 2.5 600 30.0 7200 1.0 240 4.5 1080 700-800 95.0 49467 Process Quarry Crushers Prehomoginizing and transport Raw mill Raw meal silo Kiln feeder Kiln and cooler Coal mill Cement mill Packing plant Other total Institut de Minéralogie et Pétrographie Université de Fribourg Technische Mineralogie ETHZ IMP 2008

  46. Mineralized cement Improvements in klinker manufacturing 1. Energy savings through: - lowering the melting point of the system. - increasing the burning rate - increasing the burning rate - better insulation, improved heat exchanger etc. - use of alternative raw materials 2. Reduction of CO2 ,SO3 NOx etc output through: - use of alternative raw materials Institut de Minéralogie et Pétrographie Université de Fribourg Technische Mineralogie ETHZ IMP 2008

  47. Mineralized cement Improvements in klinker manufacturing 1. Energy savings through: - lowering the melting point of the system. - increasing the burning rate - increasing the burning rate - better insulation, improved heat exchanger etc. - use of alternative raw materials 2. Reduction of CO2 ,SO3 NOx etc output through: - use of alternative raw materials Institut de Minéralogie et Pétrographie Université de Fribourg Cours bloc 2006

  48. Mineralized cement SiO2 Al2O3 Fe2O3 CaO MgO SO3 F K 2 O Na 2 O C2S C3S C3A C4AF produced in 3500tpd precalciner kiln. (Herfort et al., 1997, Shen et al., 1995) normal PC mineralized 22.4 4.4 3.4 65.8 0.7 0.8 0.1 0.8 0.4 33.3 49.5 4.9 7.7 21.5 4.6 3.6 65.6 0.7 2.0 0.2 0.8 0.4 34.8 46.9 4.0 8.5 2.0 F 1.5 SO3 M(wt%) in silicates 1.0 0.5 0.0 2.5 3.0 0.0 0.5 1.0 1.5 2.0 M (wt%) in clinker Partitioning of SO3 and F between silicates and other phases Bulk composition and mineralogy of mineralized clinkers Institut de Minéralogie et Pétrographie Université de Fribourg Cours bloc 2006

  49. Mineralized cement Mineralizer Mineralizer used in klinker manufacturing: Fluorite CaF2 = CF Gypsum CaSO4.2H2O = CS Effects of mineralizers: - Lowering of the eutectic temperature of the CaO-SiO2-Al2O3-FeO system - Enhancing the crystallization of reactant phases Energy savings: 105 - 630kJ/kg = 3 - 20% Institut de Minéralogie et Pétrographie Université de Fribourg Cours bloc 2006

  50. Mineralized cement Effect of mineralizer concentration on clinker mineralogy 80 80 alite 60 60 belite clinker mineral (wt%) clinker mineral (wt%) 40 40 20 20 0.0 0.0 0.0 2.0 4.0 6.0 0.0 0.25 0.5 0.75 1.0 8.0 F(wt%) SO3 (wt%) Herford et al. 1997 (contained < 0.2wt%F) Shen et al., 1995 (contained 2wt% SO3 ) Institut de Minéralogie et Pétrographie Université de Fribourg Cours bloc 2006

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