CEMENTThe name "cement" goes back to the Romans who used the term"opus caementitium" to describe masonry which resembled c...
Examples of concrete constructions
Viaduct de Millau,     France                     reinforced concrete                     steel
The Øresund bridgeLarge Infrastructure Great Belt,           Denmark
History of Portland Cement  In 1824, Joseph Aspdin, a British stone mason, obtained a patent for a                        ...
CEMENT Definition – part cited from European standard EN 197-1:„Cement is a hydraulic binder, i.e. a finely ground inorgan...
CEMENT               (Portland cement and blended cements)• is finely ground inorganic material• is hydraulic binder. It s...
COMMON CEMENTSCovered by European standard (STN) EN 197-1 EN 197-1 covers five main types of cement: • CEM I         Portl...
PORTLAND CEMENT
PORTLAND CEMENT- is finely ground hydraulic binderIt is produced by pulverizing clinker with calcium sulfate andeventually...
MANUFACTURE OF PORTLAND CEMENT             RAW MATERIALS      BURNING OF PORTLAND CLINKERCHEMICAL AND MINERALOGICAL COMPOS...
MANUFACTURE OF PORTLAND CEMENT          SCHEME OF DRY PROCESS      Mining (quarrying) of raw materials Limestone          ...
F.PEŤKO, T.VINICKÝ , J. PETLUŠ           quarry                      Limestone     Manufacture of cement                  ...
Grinding of clinker with gypsum and/or other materials to cement                                       finely ground mater...
RAW MATERIALS FOR PRODUCTION OF CLINKER          MAIN RAW MATERIALS                                 ADDITIONAL            ...
COMPOSITION OF MIX OF RAW MATERIALSTo evaluate suitable composition of raw materials mixture (clinker)- the values of foll...
Limestone quarry – fy. Cement Hranice, a.s.http://geologie.vsb.cz/loziska/suroviny/anorganicka_pojiva.html
Transport of limestone from a quarry
• limestone• clay, shale              HOMOGENIZATION OF RAW MATERIALS
Correction of composition        of raw mix
MANUFACTURE OF PORTLAND CEMENT             RAW MATERIALS  BURNING OF PORTLAND CLINKERCHEMICAL AND MINERALOGICAL COMPOSITIO...
F.PEŤKO, T.VINICKÝ , J. PETLUŠ             Burning of raw mixture in cement kilns                     into Portland clinke...
BURNING OF PORTLAND CLINKER     CLINKER is made by burning of raw mixture in                   cement kilnsFUELS: pulveris...
Fuel used in                cement              production             CoalUsed tyres   Other solid fuels              Cze...
MANUFACTURE OF PORTLAND CEMENT       RAW MATERIALS COMPOSITION       FIRING OF PORTLAND CLINKERCHEMICAL AND MINERALOGICAL ...
PROCESSES DURING BURNING OF CLINKER• Decomposition of some raw materials  (limestone, kaoline clay) in the preheater or th...
High-temperature reactions at clinker burning                                            3CaO.SiO2 (CaCO3)              Si...
PROCESSES AND REACTIONS DURING BURNING OF CLINKER                           Informative scheme• 100-200°C   - evaporation ...
COMPARRISON: HYDRAULIC LIME - PORTLAND CEMENT                                          burning 1250 °C  Impure limestone, ...
Burner                                            Clinker                                            leaving              ...
Edison – patent 1905
COOLING OF CLINKERClinker is discharged red-hot from the lower end of the kiln andtransferred to coolers to lower the clin...
MANUFACTURE OF PORTLAND CEMENT            RAW MATERIALS      FIRING OF PORTLAND CLINKERCHEMICAL AND MINERALOGICAL  COMPOSI...
MAIN MINERALS IN PORTLAND CLINKER     tricalcium silicate                           3CaO.SiO2    (C3S)   ALITE     dicalci...
Conventional cement chemist notationIs used to simplify the formulas are used mainly in chemistry ofcement. It is used for...
MAIN MINERALS IN PORTLAND CLINKER        Main products of high-temperature reactions in the kiln tricalcium silicate      ...
CHEMICAL COMPOSITION OF PORTLAND CLINKER (%)CaO MgO SiO2 Al2O3 Fe2O3                       Na2O + K2O          SO362-67 0....
MANUFACTURE OF PORTLAND CEMENT                   RAW MATERIALS          FIRING OF PORTLAND CLINKERCHEMICAL AND MINERALOGIC...
GRINDING OF CEMENT                    Steel balls in the mill                     A 10 MW cement mill, producing cement at...
GRINDING OF CEMENT AND DISPATCHClinker and 2,5-5 % of gypsum (or also other components) are finelyground together in rotar...
Dispatch of cement
Výrobcovia cementu na Slovensku1 - HOLCIM, a.s. Rohožník2 - CEMMAC, a.s. Horné Srnie3 - Cementáreň Turňa, a.s. Turňa nad B...
SETTING AND HARDENING OF  PORTLAND CEMENT  (Cement mortars and concrete)Reaction of cement with water Hydration of clinker...
SETTING AND HARDENING     OF PORTLAND CEMENTCement paste or slurry- is obtained by mixing of cement and water- consistency...
definitionsHydration of cement           - the reaction of cement with water Setting      is stiffening of cement paste wi...
Strength development during hardening of cement paste                                                Hydration of cement  ...
Cement hydration                             setting   →   hardening  Rate of heat evolutionCement hardeningContribution o...
Reaction of cement with water (hydration of cement)                             ≅ 23 %      Cement           + water   →  ...
Hydration of C3S a C3S        formation of hydrated reaction products                                     Idealized ratio ...
Hydration of C3A                  (similarly also C4AF)   Main reaction products are:   - calcium aluminate hydrates (C4AH...
Characteristic of clinker minerals – during hydration  Tricalcium silicate, C3S:         • hydrates rapidly   • strongly c...
STRUCTURE AND COMPOSITION OF            HARDENED CEMENT PASTEHardened cement paste (HCP) is composed of:• interlocked hydr...
Soroka, 1979
Simplified scheme of hydrated cement paste microstructure1. Unhydrated cement2. C-S-H gel containing gel   pores (interlay...
Hydrated cement paste microstructure                                      C-S-H                                           ...
Simplified scheme of hydrated cement paste microstructure                                                       Capillary ...
Schematic representation of volumetric proportions in cement paste before and during hydration Microstructureof cement paste
Influence of the water/cement ratio on the distribution of pore size in                       hydrated cement paste
CHEMICAL COMPOSITION OF PORE SOLUTION               Portland            K2O 50-70 %               cement                  ...
Composition of pore solution is of prime importance forchemical properties of cement composites. Although solubilityof Ca(...
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Stud l6-1-cement-manufacture

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Stud l6-1-cement-manufacture

  1. 1. CEMENTThe name "cement" goes back to the Romans who used the term"opus caementitium" to describe masonry which resembled concreteand was made from crushed rock with burnt lime as binder. Thevolcanic ash and pulverized brick additives which were added to theburnt lime to obtain a hydraulic binder were later referred to ascementum, cimentum, cäment and cement. Cements used inconstruction are characterized as hydraulic or non-hydraulic.
  2. 2. Examples of concrete constructions
  3. 3. Viaduct de Millau, France reinforced concrete steel
  4. 4. The Øresund bridgeLarge Infrastructure Great Belt, Denmark
  5. 5. History of Portland Cement In 1824, Joseph Aspdin, a British stone mason, obtained a patent for a cement.He heated a mixture of finely ground limestone and clay in stove andground the mixture into a powder.He created a hydraulic cement - that hardens with the addition of water.Aspdin named the product portland cement because it resembled a stone on theIsle of Portland, British Coast.With this invention, Aspdin laid the foundation for todays portland cement industry.
  6. 6. CEMENT Definition – part cited from European standard EN 197-1:„Cement is a hydraulic binder, i.e. a finely ground inorganic materialwhich, when mixed with water, forms a paste which sets andhardens by means of hydration reactions and processes and which,after hardening, retains its strength and stability even under water.“„Cement conforming to EN 197-1, termed CEM cement, shall, whenappropriately batched and mixed with aggregate and water, becapable of producing concrete or mortar which retains its workabilityfor sufficient time and shall after defined periods attain specifiedstrength levels and also possess long-term volume stability.“
  7. 7. CEMENT (Portland cement and blended cements)• is finely ground inorganic material• is hydraulic binder. It sets and hardens by reacting chemically with water and is able to harden under water. Setting and hardening is due to hydration reactions of compounds of cement (mainly calcium silicates, also calcium aluminates and -alumino ferites) with water. This is called hydraulic hardening.• hardened cement paste (cement + water) is stable in water.• cement paste acts as adhesive when is mixed with sand and aggregate (gravel,crushed rocks). Hardened cement paste - binds the particles of sand - CEMENT MORTAR - binds fine and coarse agregate - CONCRETEPrepared cement concrete or mortar after mixing shall beworkable for sufficient time.
  8. 8. COMMON CEMENTSCovered by European standard (STN) EN 197-1 EN 197-1 covers five main types of cement: • CEM I Portland cement • CEM II Portland-composite cement Blended • CEM III Blastfurnace cement cements • CEM IV Puzzolanic cement • CEM V Composite cement
  9. 9. PORTLAND CEMENT
  10. 10. PORTLAND CEMENT- is finely ground hydraulic binderIt is produced by pulverizing clinker with calcium sulfate andeventually other compounds.Main constituent:Portland cement clinker - is composed primarily of - calcium silicates - calcium aluminates and - calcium alumino-feritesSet controlling admixture: controls setting of cementCalcium sulfate - usually gypsum (CaSO4.2H2O), or (3-5 %) - hemihydrate (CaSO4.1/2H2O), or - anhydrite (CaSO4), or acts as set retarder - mixture of them
  11. 11. MANUFACTURE OF PORTLAND CEMENT RAW MATERIALS BURNING OF PORTLAND CLINKERCHEMICAL AND MINERALOGICAL COMPOSITION OF CLINKER GRINDING OF CEMENT
  12. 12. MANUFACTURE OF PORTLAND CEMENT SCHEME OF DRY PROCESS Mining (quarrying) of raw materials Limestone Argilaceous materials Iron ore Clay, shale, marl corrections grinding, blending, correctioning of composition of raw materials burning (sintering) a raw mixture up to 1450oC into clinker - in cement kilns (mainly rotary kilns) cooling of clinker - in a cooler grinding of clinker with gypsum into cement quality control of cement, packing and expedition
  13. 13. F.PEŤKO, T.VINICKÝ , J. PETLUŠ quarry Limestone Manufacture of cement According: Holcim Rohožník crusher conveyer Clay-pit: mining of clay Burning of clinker Preheater (or precalciner) tower 1450 oChomogenization cooler and storage Rotary kiln grinding mill
  14. 14. Grinding of clinker with gypsum and/or other materials to cement finely ground material Clinker from the kiln cement silos Clinker silo (clinker storage) rotary ball mill grinding of cement expedition
  15. 15. RAW MATERIALS FOR PRODUCTION OF CLINKER MAIN RAW MATERIALS ADDITIONAL (corrections) marl SiO2 -quartz sand limestone clay, shale.... Fe2O3 – iron ore Al2O3.2SiO2.2H2O CaCO3 (MgCO3) Al2O3 - bauxite e.g. kaolinite CaO (MgO) SiO2, Al2O3, Fe2O3 Hydraulic oxides RAW MIXTURE MIXTURE must have suitable chemical composition Evaluated by HM = CaOhydraulic modulus SiO 2 + Al 2 O 3 + Fe 2 O 3 HM = 1,9 - 2,4Generally, raw materials consist of combinations of limestone, shale, clay,sand, or iron ore. Most are mined from a quarry near the plant
  16. 16. COMPOSITION OF MIX OF RAW MATERIALSTo evaluate suitable composition of raw materials mixture (clinker)- the values of following modules (parameters) are used (chemical formulae represent weight percentages): hydraulic modulus: CaO HM = HM = 1,9 - 2,4 SiO 2 + Al 2 O 3 + Fe 2 O 3 silicate modulus SiO 2 SM = SM = 1,7-3,5 Al2O 3 + Fe 2O 3 aluminate modulus Al2O 3 AM = AM = 1,5 - 3,0 Fe 2O 3 Oxide composition in raw materials for clinker is usually about CaO MgO SiO2 Al2O3 Fe2O3 Na2O + K2O SO3 62-67 0,5-4 18-24 3-8 1,5-4,5 0,4 - 1,2 1,3
  17. 17. Limestone quarry – fy. Cement Hranice, a.s.http://geologie.vsb.cz/loziska/suroviny/anorganicka_pojiva.html
  18. 18. Transport of limestone from a quarry
  19. 19. • limestone• clay, shale HOMOGENIZATION OF RAW MATERIALS
  20. 20. Correction of composition of raw mix
  21. 21. MANUFACTURE OF PORTLAND CEMENT RAW MATERIALS BURNING OF PORTLAND CLINKERCHEMICAL AND MINERALOGICAL COMPOSITION OF CLINKER GRINDING OF CEMENT
  22. 22. F.PEŤKO, T.VINICKÝ , J. PETLUŠ Burning of raw mixture in cement kilns into Portland clinker Cyclones use waste heat (air) Rawmix is fed from the kiln into preheater Preheater (or precalciner) tower 1450 oC homogenization and storage Clinkering zone grinding cooler mill Rotary kiln Output ofFig. According: Holcim Rohožník clinker
  23. 23. BURNING OF PORTLAND CLINKER CLINKER is made by burning of raw mixture in cement kilnsFUELS: pulverised coal, petroleum coke, waste oil, natural gas, spent tyres, Burning temperature Shaft kilns Rotary kilns Max. 1450 °C Steel tube - refractory lined Slope: 1 - 4° Length: 40 - 200 m Diameter: 3 - 7 m Rotation: about 1 revolution / min Rawmix is fed at the upper end and slowly moves downhill toward burner (counterflow movement)Process: dry (wet is not used today)
  24. 24. Fuel used in cement production CoalUsed tyres Other solid fuels Czech republic
  25. 25. MANUFACTURE OF PORTLAND CEMENT RAW MATERIALS COMPOSITION FIRING OF PORTLAND CLINKERCHEMICAL AND MINERALOGICAL COMPOSITION OF CLINKER Portland clinker
  26. 26. PROCESSES DURING BURNING OF CLINKER• Decomposition of some raw materials (limestone, kaoline clay) in the preheater or the kiln ≤ 800 °C CaCO3 → CaO + CO2 Al2O3.2SiO2.2H2O → Al2O3.2SiO2 + 2H2O• High-temperature reactions taking place in the kiln ≤ 1450 °C about 25 percent of the raw material mixture melts (partial fussion) CaO SiO2 Al2O3 Fe2O3 Burning changes raw mix into cement clinker. Produkts of reactions that compose Portland clinker are Minerals (compounds): Calcium silicates, calcium aluminates, and – alumino ferites
  27. 27. High-temperature reactions at clinker burning 3CaO.SiO2 (CaCO3) SiO2 + Al2O3 + Fe2O3 2CaO.SiO2 CaO 3CaO.Al2O3 4CaO. Al2O3.Fe2O3 CaCO3 → CaO + CO2 900 °C 3CaO + Al2O3 → 3CaO. Al2O34CaO + Al2O3 + Fe2O3 → 4CaO. Al2O3. Fe2O3 2CaO + SiO2 → 2CaO.SiO2 ≤ 1200 °C 2CaO.SiO2 + CaO → 3CaO.SiO2 1200 - 1450 °C
  28. 28. PROCESSES AND REACTIONS DURING BURNING OF CLINKER Informative scheme• 100-200°C - evaporation of physical water• 200-600 °C – releasing of water from clay minerals (dehydroxylation)• 600-800 °C – decomposition of MgCO3, formation of CA, C2F (C2S)• 800-900 °C – decomposition of CaCO3 (free CaO)• 900-1100 °C - formation and decomposition of C2AS, - begining of formation of C3A and C4AF, - maximum content of free CaO (unbound)•1100-1200 °C - most of C3A and C4AF is formed, - maximum content of C2S CaO + 2SiO2→ 2CaO.SiO2• 1260 °C - occurs first partial fussion (melted material)• 1200-1450 °C - C3S forms 2CaO.SiO2 + CaO → 3CaO.SiO2 and content of free CaO therefore decreases
  29. 29. COMPARRISON: HYDRAULIC LIME - PORTLAND CEMENT burning 1250 °C Impure limestone, limestone-marl Hydraulic lime (natural Calcite Clay minerals hydraulic lime) CaCO3 + SiO2 + Al2O3 + Fe2O3 - CaO (free, quicklime) - calcium silicates (C2S) HYDRAULIC OXIDES - calcium aluminatesCaO CO2 - calcium alumino-ferites Marl, limestone-marl burning 1450 °C Limestone + clay, shale Portland clinker Calcite clay minerals almost any free CaO CaCO3 + SiO2 + Al2O3 + Fe2O3 - calcium silicates (C2S, C3S) HYDRAULIC OXIDES - calcium aluminates (C3A)CaO CO2 - calcium alumino-ferites
  30. 30. Burner Clinker leaving s) r ial ke the kiln ter clin ma of w nt (ra me ve MoRotary kiln BURNING OF CLINKER
  31. 31. Edison – patent 1905
  32. 32. COOLING OF CLINKERClinker is discharged red-hot from the lower end of the kiln andtransferred to coolers to lower the clinker temperaturePortland cement clinker
  33. 33. MANUFACTURE OF PORTLAND CEMENT RAW MATERIALS FIRING OF PORTLAND CLINKERCHEMICAL AND MINERALOGICAL COMPOSITION OF CLINKER
  34. 34. MAIN MINERALS IN PORTLAND CLINKER tricalcium silicate 3CaO.SiO2 (C3S) ALITE dicalcium silicate 2CaO.SiO2 (C2S) BELITE tricalcium aluminate 3CaO.Al2O3 (C3A) tetracalcium aluminoferite 4CaO.Al2O3.Fe2O3 (C4AF) CELITE Optical microscope image of clinker minerals (polished sections) Brown crystals - alite blue crystals - belite bright interstitial material - ferrite small dark inclusions of aluminatehttp://www.understanding-cement.com/clinker.html
  35. 35. Conventional cement chemist notationIs used to simplify the formulas are used mainly in chemistry ofcement. It is used for „short hand“ way of writing the chemicalformula of some oxides and water. List of the abbreviations used: Actual Abbr. Actual Abbr. Actual Abbr. Formula Formula Formula CaO C MgO M H 2O H SiO2 S K2O K CO2 Al2O3 A Na2O A SO3 Fe2O3 F TiO2 T - - Examples: • 2CaO.SiO2 ≡ C2S; • Ca(OH)2 ≡ CH • 3CaO.Al2O3.13H2O ≡ C3AH13
  36. 36. MAIN MINERALS IN PORTLAND CLINKER Main products of high-temperature reactions in the kiln tricalcium silicate 3CaO.SiO2 (C3S) ALITE dicalcium silicate 2CaO.SiO2 (C2S) BELITE tricalcium aluminate 3CaO.Al2O3 (C3A) tetracalcium aluminoferite 4CaO.Al2O3.Fe2O3 (C4AF) CELITE 2CaO(Al2O3,Fe2O3) C2(A,F)
  37. 37. CHEMICAL COMPOSITION OF PORTLAND CLINKER (%)CaO MgO SiO2 Al2O3 Fe2O3 Na2O + K2O SO362-67 0.5-4 19-24 4-8 1.5-4.5 0.4 – 1.1 0,3 - 1 MINERALOGICAL COMPOSITION OF PORTLAND CLINKER (%) 3 CaO.SiO2 C3S 45 - 60 % Dominant 2 CaO.SiO2 C2S 15 - 30 % phases 3 CaO.Al2O3 C3A 3 - 15 % 4CaO.Al2O3.Fe2O3 C4AF 10 - 20 % free lime < 1.5 (2) % High content of unreacted oxides (CaO, MgO) can cause expansion of cement (unsoundness) and affect setting time. - result of insufficient burning and high content of lime in clinker
  38. 38. MANUFACTURE OF PORTLAND CEMENT RAW MATERIALS FIRING OF PORTLAND CLINKERCHEMICAL AND MINERALOGICAL COMPOSITION OF CLINKER GRINDING OF CEMENTRotary ball mill Clinker + Gypsum 2.5-5 % Portland cement
  39. 39. GRINDING OF CEMENT Steel balls in the mill A 10 MW cement mill, producing cement atFired clinker 270 tonnes per hour. Wikipedia
  40. 40. GRINDING OF CEMENT AND DISPATCHClinker and 2,5-5 % of gypsum (or also other components) are finelyground together in rotary ball mills to form final cement product.- particles size of ground cement vary mostly from 1 - 200 μm (200 μm)- blended cements contain, besides clinker and gypsum, also latent hydraulic or pozzolanic constituents- cement is stored in an bulk silo until needed by the customerFineness of ground cement is evaluated by its specific surface. > 220 m2/kg according air permeability Blaine methodFineness of cement affects almost all important properties of cementExpedition /dispatch of cement- in bulk - by trucks, rail, or barge- in bugs - baged cement www.gassmann-gmbh.com/frames.php?sprache=en
  41. 41. Dispatch of cement
  42. 42. Výrobcovia cementu na Slovensku1 - HOLCIM, a.s. Rohožník2 - CEMMAC, a.s. Horné Srnie3 - Cementáreň Turňa, a.s. Turňa nad Bodvou4 - Považská cementáreň, a.s. Ladce5 - Stredoslovenská cementáreň Banská Bystrica, a.s.6 - ZEOCEM, s.r.o. Bystré
  43. 43. SETTING AND HARDENING OF PORTLAND CEMENT (Cement mortars and concrete)Reaction of cement with water Hydration of clinker minerals Release of heat Setting and hardening Structure development
  44. 44. SETTING AND HARDENING OF PORTLAND CEMENTCement paste or slurry- is obtained by mixing of cement and water- consistency (fluidity) remains nearly constant for some time- mixture can be cast (placed) into different shapesSetting and hardening of cement paste Is due to chemical reactions of cement with water setting starts (initial set) 2 and 3 hours after mixing setting develops until final set is obtained hardening (strength gain) starts after final set strength gain continues a long time with decreasing speed
  45. 45. definitionsHydration of cement - the reaction of cement with water Setting is stiffening of cement paste without significant development of compressive strength. It typically occurs within a few hours.Hardening is significant development of compressive strength It is normally a slower process Lea: p.113Exotermic chemical reaction accompanied by heat release reaction Hydration of cement is exotermic reactionConsistency
  46. 46. Strength development during hardening of cement paste Hydration of cement Strength development grains with different sizeCompressive strength [MPa] Time [days]Hydration of clinker minerals in cement paste is slow: e.g. 3 μm after 7 days → strength increses gradually
  47. 47. Cement hydration setting → hardening Rate of heat evolutionCement hardeningContribution of Portland cement minerals to strength of cement (after Bogue and Lerch)
  48. 48. Reaction of cement with water (hydration of cement) ≅ 23 % Cement + water → main hydration products clinker C 3S Ca(OH)2 (portlandite) C 2S 3CaO.2SiO2.3H2O (CSH-gel) + H2O C3 A C4AF 3CaO.Al2O3.3CaSO4.32H2O 3CaO.Al2O3.CaSO4.12H2O gypsum 4CaO.Al2O3.13H2O CaSO4.2H2O (3CaO.Al2O3. 6H2O) regulates the rate of setting Calcium aluminate hydrates
  49. 49. Hydration of C3S a C3S formation of hydrated reaction products Idealized ratio of CaO : SiO2 : H2O2(3CaO.SiO2) + 6H2O → 3CaO.2SiO2.3H2O + 3Ca(OH)22(2CaO.SiO2) + 4H2O → 3CaO.2SiO2.3H2O + Ca(OH)2 Calcium silica hydrates Calcium hydroxide CSH gel or (C-S-H phase) imperfect crystals, gel structure relative large crystals coloidal dimensions (1 - 500 nm) low strength large surface area solubility 1.5 g/L easily carbonatize main contribution to strength very low solubility (hydrolysis) Ca(OH)2 + CO2 → CaCO3 + H2O
  50. 50. Hydration of C3A (similarly also C4AF) Main reaction products are: - calcium aluminate hydrates (C4AH13 or C4AH19, C3AH6) - complex calcium aluminate sulfate hydrates (ettringite, monosulfate)1. Ettringite (trisulfate) forms by hydration of C3A in the presence of CaSO4 (e.g.gypsum). Reaction takes place at beginning of hydration of cement. 3CaO.Al2O3 + 3 CaSO4 + 32 H2O → 3CaO.Al2O3.3CaSO4.32H2O2. After gypsum is consumed, C3A reacts with ettringite to form monosulfate: 2(3CaO.Al2O3) + 3CaO.Al2O3.3CaSO4.32H2O + 4 H2O → → 3(3CaO.Al2O3.CaSO4.12 H2O)3. Later C3A reacts with water to form mostly tetra calcium aluminate hydrate 3CaO.Al2O3 + Ca(OH)2 + 18 H2O → 4CaO.Al2O3.19H2O Ca(OH)2 is formed at hydration of calcium silicates
  51. 51. Characteristic of clinker minerals – during hydration Tricalcium silicate, C3S: • hydrates rapidly • strongly contributes to early and final strength of cement pastes • has high heat of hydration: (670 kJ/kg) Dicalcium silicate, C2S: • hydrates slowly • strongly contributes to strength at later ages (> 1 week). • increases chemical resistance of cement • has low heat oh hydration: (350 kJ/kg) Tricalcium Aluminate, C3A: • hydrates very rapidly; • contributes slightly to early strength development. • reduces chemical resistance of cement to sulfates (soils, waters) (low percentage of C3A is required for sulfate resisting cement). • large heat of hydration: (1060 kJ/kg), rapid during the first few days Tetracalcium Aluminoferrite, C4AF: It contributes little to strength. (iron and aluminum in raw mixture reduce the clinkering temperature during clinker manufacture) and gives cement its gray color (Fe). Low heat of hydration:
  52. 52. STRUCTURE AND COMPOSITION OF HARDENED CEMENT PASTEHardened cement paste (HCP) is composed of:• interlocked hydration products of cement (portlandite, C-S-H gel, hydrated calcium aluminates and - alumino ferites)• unhydrated residual cement grains• pores of various dimensions (characterized by pore size distribution) • gel pores in CSH gel < 3 nm • capillary pores -space between hydrating grains 10 nm – 1 000 nm • air pores or air voids > 50 μm up to about 2 mm.Pore solution in hardened cement paste (HCP)• Pores in HCP are partially filled with pore solution.• Pore solution is saturated solution of Ca(OH)2 it contains also NaOH and KOH• pH is about 13 -13,5 (from PC; lower from blended cements)
  53. 53. Soroka, 1979
  54. 54. Simplified scheme of hydrated cement paste microstructure1. Unhydrated cement2. C-S-H gel containing gel pores (interlayer water)Gel (or interlayer) pores havesize of 0.5-2.5 nm and occupyabout 28 vol. % of C-S-H gel3. Capillary pores (capillary water)Capillary pores can have sizesfrom 10 to 1000 nm (1 μm) andeven up to 5 μm. Volume andsize depends on water/cement 4. Hexagonal crystals of calciumratio and degree of hydration hydroxide (portlandite)
  55. 55. Hydrated cement paste microstructure C-S-H © 2010 Rouhollah Alizadeh, all rights reservedFeldman-Sereda model for the The flaky C-S-H crystalsmicrostructure of C-S-H grown after 2 weeks ofBlack lines: C-S-H sheet, Circles: hydration of C3S (W/C=0.8).Adsorbed water, Crosses: Interlayer The stoichiometric C/S ratio of C-S-Hwater and morphology of its crystals in conventional cement systems depend on the curing condition. http://www.cementlab.com/cement-art.htm
  56. 56. Simplified scheme of hydrated cement paste microstructure Capillary pore in hydrated The transition zone (Ref 7) cement paste (8) 7. Mehta, P.K. "Concrete Structures Properties and Materials", Prentice Hall, 1986 8. Feldman, F., and P.J. Sereda, Eng. J.. Vol 543, No. 8/9, 1970
  57. 57. Schematic representation of volumetric proportions in cement paste before and during hydration Microstructureof cement paste
  58. 58. Influence of the water/cement ratio on the distribution of pore size in hydrated cement paste
  59. 59. CHEMICAL COMPOSITION OF PORE SOLUTION Portland K2O 50-70 % cement Pore solution Na2O 40-60 %Solubility of Ca(OH)2 in the presence alkalies Ions [mol/dm3] 0,03 [Ca ][OH ] − 2 Na+ + K+ 0,2 - 1Ca2+ (mol/l) 2+ Ks = γ3 ± 0,02 OH- 0,2 - 1 Ca2+ ≅ 0,001 0,01 SO42- 0,02 0 pH 13,4 - 14 0 0,4 0,8 1,2 NaOH (mol/l)
  60. 60. Composition of pore solution is of prime importance forchemical properties of cement composites. Although solubilityof Ca(OH)2 in water is about 0.02 mol.dm-3 at 20 °C and the pHvalue of saturated solution is about pH 12.5; these parametersare substantially affected by alkali metals. Alkali metals arereleased from cement during its hydration. Because they do nottake part in the composition of the major cement hydrationproducts they accumulate in the pore solution forming Na+, K+and OH− ions, respectively. Increase in OH− ion concentrationreduces significantly solubility of Ca(OH)2.Pore solution in cement based composites therefore containsrelatively high concentration of Na+, K+ and OH- ions (up to 1mol.dm-3), but concentration of Ca2+ and also SO42- isconsiderably lower, for Ca2+ is often only about 1 mmol.dm-3.The pH-value of the pore fluids in cement composites(containing alkali metals) may well be greater than pH 12.5 inthe case of Portland cement the pH can prevail pH 13.5.
  61. 61. Thank you

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