portland cement

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

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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) - PowerPoint PPT Presentation

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Page 1: Portland Cement

Prof. Grobéty B., Inst. de Minéralogie et Pétrographie, Univ. de Fribourg

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 2: Portland Cement

Introduction

Cementitous materialsDefinition: Material, which binds together with solid bodies (aggregates)by hardening from a plastic state. Examples: organic polymers

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

Inorganic cements

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 3: Portland Cement

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 plastersUse of cementitous materials in China (Great Wall)

300 BC: Concrete and mortars based on lime and pozzolanic material

http://www.greatbuildings.com/buildings/Pantheon.html

(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)

Introduction

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 4: Portland Cement

Middle ages: Decline of cement and concrete technology1756: John Smeaton, British Engineer, rediscovered hydraulic cement through repeated testing of mortar in both fresh and salt water1824: 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.

Historical background II

Introduction

Technical MineralogyDepartment of Geosciences

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.

Technische MineralogieETHZ IMP 2008

Page 5: Portland Cement

Cement: definitionsPortland 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 fillingcracks 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.

Introduction

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 6: Portland Cement

Cement: chemical notations

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 hydratesHCP = hydrated cement pastePFA = pulverized fuel ash PC = Portland cementOPC = Ordinary Portland cement

Chemical notation

Introduction

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 7: Portland Cement

Portland Cement IChemical compositionThe composition of Portland Cements and puzzolanicadditives cover a certain range.

Introduction

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 8: Portland Cement

Portland cement II

Name + Chem. Comp Approx. % in OPC Properties Belite C2S 20 Slow strength gain, responsible

for long term strengthAlite C3S 55 Rapid strength gain, responsible

for early strength gain Aluminate C3A 12 Quick setting (contr. by gypsum),

liable to sulfate attackFerrite C4AF 8 Little contribution to setting or

strength, responsible for gray color of OPC

Main mineralogical components

Introduction

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 9: Portland Cement

Portland Cement IIIMain production steps (http://www.ppc.co.za/Cement/c_cement_manprocess.asp)

Quarrying chalk in northern Jutland(Aalborg Cement)

Introduction

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 10: Portland Cement

Portland Cement IV

Chalk slurry tank (Aalborg cement)

Main production steps (cont.)

Introduction

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 11: Portland Cement

Portland Cement VMain production steps (cont.)

Preheater, rotary kilns and storage silos

Introduction

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 12: Portland Cement

Portland Cement VIMain production steps (cont.)

Cement siloShipping by ship

Introduction

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 13: Portland Cement

Introduction

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 14: Portland Cement

World cement productions (minerals.usgs.gov/minerals/pubs/commodity/cement

World cement production 2000 (thousand of tons):United States (includes Puerto Rico) 92,300Brazil 41,500China 576,000Egypt 23,000France 24,000 Germany 38,099India 95,000Indonesia 27,000Italy 36,000Japan 77,500 Korea, Republic of 50,000Mexico 30,000Russia 30,000Spain 30,000Taiwan 19,000 Thailand 38,000Turkey 33,000Other countries (rounded) 450,000World total (rounded) 1,700,000

Introduction

China 576,000 China produces one third ofthe world cement output!

World total (rounded) 1,700,000

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 15: Portland Cement

Swiss cement industry (www.cemsuisse.ch)

Cement plants in Switzerland

cement plant

klinker mills

1 Eclépens2 Cornaux3 Reuchenette4 Wildegg5 Siggenthal6 Thayngen7 Brunnen8 Untervaz

Total production 1987: 4’478’000 t1989: 5’461’000 t2000: 3’715’908 t

Introduction

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 16: Portland Cement

Raw materials

Calcareous lime stones: - calcite-rich - low in dolomite

Corrective constituents

Shales: - clay rich, usually dominated by illite, smectite and kaolinite. Ideal bulk composition ranges: 55-60wt% SiO2, 15-25wt% Al2O3, 5-10wt% Fe2O3

Main raw materials

Sand, flyash: - adjust SiO2-content in quartz-poor shalesIronores, 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.

Raw materials

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 17: Portland Cement

Composition of ordinary Portland cements

SiO2Al2O3 Fe2O3CaOMgOK2ONa2OSO3LOI (H2O+CO2)

Minor components and traces(deleterious)

few %: MgO, SrO2few tenth of a %: P2O5, CaF2 , alkalistraces: heavy metals

Major components

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)

19.0 - 23.03.0 - 7.01.5 - 4.5

63.0 - 67.00.5 - 2.50.1 - 1.20.1 - 0.42.5 - 3.51.0 - 3.0

Raw materials

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 18: Portland Cement

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

Proportioning of raw materials

Lime saturation factorThe calcium present in the raw materials should be completely bound in thesilicate 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

Raw materials

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 19: Portland Cement

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)

- SR = = 3.0

- Mix A MixB S 13.1 16.1A+F 7.5 2.1

S A +F

= 3.0 = p = 0.51

Raw materials

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 20: Portland Cement

Klinker phases I1. Alite Ca3SiO5 = C3S

Polymorphic transformations: T1 T2 T3 M1 M2 M3 RT: triclinic M: monoclinic R: rhombohedral

620°C 920°C 980°C 990°C 1060°C 1070°C

Max. concentration of impurities: 1.0 wt% Al2O3, 1.2% Fe2O3, 1.5 % MgOimpurities stabilize the M1 and or M3 in klinkers, rarely T2 is found

orthosilicate 0.71nm

R- C3S projected along the c-axis

SiO4

Ca

O

Klinker production

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 21: Portland Cement

Klinker phases II

2. Belite Ca2SiO4 = C2S

Polymorphic transformations: O1() M1() M2(L’) O2(H’) H1()O: orthorhombic M: monoclinic H: hexagonal

<500°C 630°C 1160°C 1425°

Max. concentration of impurities: 4.0-6.0wt% Al2O3+ Fe2O3impurities stabilize the -phase

orthosilicate0.55nm

- C2Sproj. downc-axis

Klinker production

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 22: Portland Cement

Klinker phases III

3. Aluminates and ferritesCa3Al2O6 = C3A (cubic) impurities: up to 4wt% NaO

up to 16% Fe2O3+ SiO2imputirities stabilize an orthorhombicpolymorph

Ca2AlxFe1-xO10 = C4AF xclinker: around 1.0impurities: up to 10 wt% MgO +TiO2+ SiO2

Klinker production

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 23: Portland Cement

Klinker phases IVPolymorphs and composition of phases present in clinker

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

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 FeC2S usually only in the M1() polymorph with parallel twin lamellae M2(L’) has typical crossed twin lamellae. The transformation M2() M() sho<uld be avoided, because the accompanying drastic volume increase leads to excessive dusting.

4-6% of substituing elements, mainly Al and Fe

C3AF Main exchange vector Fe-2 SiMg

Klinker production

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 24: Portland Cement

Klinker phases VEtched microstructures of the different klinker polymorphs

Alite crystals with bothsingle and polysynthetic twins

Klinker production

Belite crystals withcomplex twin lamellae(M2(L’) polymorph)

Belite crystals withparalllel twin lamellae(M() polymorph)

Belite crystals withcrack formation alonglamellae boundaries(M() (M() transf.)

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 25: Portland Cement

Rotary kiln Without preheater/precalcinerthe kiln aspect ratio is about 30

Klinker production

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 26: Portland Cement

Klinker reactions below 1300°C

Decomposition of calcite (calcining): 500 - 900°C free lime (CaO)

Decomposition of phyllosilicates: 300 - 900°C dehydroxilated, amorphous material

Temp. range products

Formation of first clinker phases: > 800°C belite, aluminate (different phases), ferrite

Formation of first melt phases: > 1000°C

Drying 100°C free water evaporates 100 - 300°C release of adsorbed

and crystal water

Klinker production

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 27: Portland Cement

Decomposition of carbonate phases I

Decomposition reaction: CaCO3 = CaO + CO2

Equilibrium constant

Rate of decarbonation is influenced by:

- gas temperature (heat transfer)- material temperature (=> K)

- external partial pressure of CO2

- size and purity of the calcite particles

Klinker production

Calcite decomposition temperatureAs function of CO2 partial pressure

0.0

0.25

0.5

0.75

1.0

750 800 850 900

890C

T(C)

P(CO2)

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 28: Portland Cement

Decomposition of carbonate phases II

Reaction mecanism:

Possible rate determining steps

2. reaction at the calcite surface

1. heat and mass transport (CO2) through the product layer

formation of a lime layer around calcite

Activation energy: 196kJ/mol (Khraisha et al, 1992) reaction controlled ?

a

t

reaction progress a

Klinker production

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 29: Portland Cement

Belite formation

1. Formation of belite through solid state reaction

quartzamorphous materialbelite

2. Transformation of the belite shells to belite crystal clusters

lime

Klinker production

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 30: Portland Cement

Appearance of first melts

2. C-S-A melts: lowest eutecticum 1170°

1. Alkali and sulfate melts

Klinker production

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 31: Portland Cement

P: typical bulk composition of Portland cement klinkers First melt appearance: 1455°C

Phase diagram

Klinker production

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 32: Portland Cement

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 phasesReaction 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)

Klinker production

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 33: Portland Cement

Amount and composition melts II

At 1450°C and above the liquid content depends on the silica modulus

Klinker production

15

20

25

30

35

1.5 2.0 2.5 3.0 SM

Liqu

id p

hase

(w

t%)

3.5

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 34: Portland Cement

Formation and recrystallization of alite

amorphous material

limebelite

alite

1. Formation of melt around lime crystals

2. Crystallization of alite walls at the contacts between belite cluster and lime3. Recrystallized and new formed alite replaces lime crystals

Klinker production

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 35: Portland Cement

Microtextures I (all pictures FL Smidth review 25)

0.05mm

Alite wall separating CaO and abelite cluster

alite melt phase (aluminates,ferrites) belite lime

Belite clusters replacing previous quartz grains.

0.1mm

Klinker production

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 36: Portland Cement

Alite crystallizing at the expense oflime and belite

0.3mm

Microtextures II

lime belite

alite

Well crystallized, homogeneous clinker. The raw mix contained fewquartz grains and a well controlledcarbonate grain size.

pores

0.2mm

Klinker production

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 37: Portland Cement

Klinker reactions during cooling

1. Crystallization of the restitic melt. Products: aluminates (C3A) and ferrites (C4AF)

2. Polymorphic transformations of alite and belite

3. Backreaction of alite to belite + lime

4. Recrystallization aluminates and ferrites

If cooling is too slow

Klinker production

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 38: Portland Cement

Microtextures III

Backreaction of alite rims to beliteplus lime in a belite poor clinker (fast cooling).

0.04mm

beliterims

Etched thin section showing thetransformation twins in belite.

0.02mm

Klinker production

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 39: Portland Cement

Slowly cooled clinker with corrodedalite phase and recrystallized belitegrains.

0.05mm

Microtextures IV

Fast cooled clinker with euhedralalite and rounded belite crystals.

0.05mm

Klinker production

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 40: Portland Cement

Normative mineralogy of clinker I

Klinker production

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 41: Portland Cement

Normative mineralogy of clinker II

Klinker production

Minor elements in the main klinker phases in cements ofdifferent cement factories. Most cements contain 5wt% and more minor elements which introduces considerable errors when using Bogues original formula,

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 42: Portland Cement

Normative mineralogy of clinker III

Klinker production

Corrected Bogue equation

0.05mm

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

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 43: Portland Cement

Normative mineralogy of clinker IV

Klinker production

0.05mm

Difference in calculated alite and belite content using the original(top) and the corrected (bottom) Bogue formula

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 44: Portland Cement

Energy balance in clinker productionTemp range

20-450°Cwet 100°Cca. 450°C450-900°Cca. 900°Cca. 900°C900-1400°C900-1400°Cca. 1300°C1400-20°C900-20°C450-20°C

Process

Heating of the materialEvaporation of free H2ORemoval of H2O from clayheating of the materialDissociation of calciteCrystallisation of dehydrated clayHeating of the decarbonated materialHeat of formation of clinker mineralsMelting of liquid phasesCooling of clinkerCooling of CO2Cooling of H2OTotal

Heat exchange kJ/kg clinker 710(1800) 170 820 2000 -40 525

-420 100

-1510 -500

-85 4325 -2555

Klinker production

Institut de Minéralogie et PétrographieUniversité de Fribourg

Technische MineralogieETHZ IMP 2008

Page 45: Portland Cement

Energy costs of cement production

Process

QuarryCrushersPrehomoginizing and transportRaw millRaw meal siloKiln feederKiln and coolerCoal millCement millPacking plantOther total

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

Klinker production

Dry process cement plant 5000t/day

Institut de Minéralogie et PétrographieUniversité de Fribourg

Technische MineralogieETHZ IMP 2008

Page 46: Portland Cement

- use of alternative raw materials

- increasing the burning rate

- lowering the melting point of the system.

- use of alternative raw materials

- increasing the burning rate

Mineralized cement

Improvements in klinker manufacturing

1. Energy savings through:

- better insulation, improved heat exchanger etc.

2. Reduction of CO2 ,SO3 NOx etc output through:

Technische MineralogieETHZ IMP 2008

Institut de Minéralogie et PétrographieUniversité de Fribourg

Page 47: Portland Cement

- use of alternative raw materials

- increasing the burning rate

- lowering the melting point of the system.

- use of alternative raw materials

- increasing the burning rate

Mineralized cement

Improvements in klinker manufacturing

1. Energy savings through:

- better insulation, improved heat exchanger etc.

2. Reduction of CO2 ,SO3 NOx etc output through:

Cours bloc 2006Institut de Minéralogie et PétrographieUniversité de Fribourg

Page 48: Portland Cement

Bulk composition and mineralogy of mineralized clinkers

M (wt%) in clinker

M(w

t%) i

n si

licat

es0.0 0.5 1.0 1.5 2.0 2.5

0.0

0.5

1.0

1.5

2.0

F

3.0

Partitioning of SO3 and F between silicates and other phases

SO3

SiO2Al2O3Fe2O3CaOMgOSO3FK 2 ONa 2 O

C2SC3SC3AC4AFproduced in 3500tpd precalciner kiln.(Herfort et al., 1997, Shen et al., 1995)

22.44.43.4

65.80.70.80.10.80.4

33.349.5

4.97.7

21.54.63.6

65.60.72.00.20.80.4

34.846.9

4.08.5

normal PC mineralized

Mineralized cement

Cours bloc 2006Institut de Minéralogie et PétrographieUniversité de Fribourg

Page 49: Portland Cement

Mineralizer used in klinker manufacturing:

Fluorite CaF2 = CFGypsum CaSO4

.2H2O = CS

Mineralizer

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%

Mineralized cement

Cours bloc 2006Institut de Minéralogie et PétrographieUniversité de Fribourg

Page 50: Portland Cement

Effect of mineralizer concentration on clinker mineralogy

clin

ker

min

eral

(wt%

)

0.0 2.0 4.0 6.0 8.00.0

20

40

60

80

SO3 (wt%)

clin

ker

min

eral

(wt%

)0.0 0.25 0.5 0.75 1.0

0.0

20

40

60

80alite

belite

F (wt%)

Herford et al. 1997 (contained < 0.2wt%F) Shen et al., 1995 (contained 2wt% SO3 )

Mineralized cement

Cours bloc 2006Institut de Minéralogie et PétrographieUniversité de Fribourg

Page 51: Portland Cement

The system Ca2SiO5 - CaO - CaF2

first melt appearance: 1113°C

Mineralized cement

Cours bloc 2006Institut de Minéralogie et PétrographieUniversité de Fribourg

Page 52: Portland Cement

0.05mm

Mineralized klinker with langbeinitefilling interstitial space

Microstructures I

Mineralized klinker rich in alite whichremained in the hexagonal modification

Mineralized cement

Cours bloc 2006Institut de Minéralogie et PétrographieUniversité de Fribourg

Page 53: Portland Cement

Mechanisms enhancing clinker formation I

With the addition of gypsum and fluorite intermediate fluor-ellestadite (Ca10 Si3 O32 (SO4 )3 F2 is formed, whichdecomposes to belite and liquid at 1113°C.

Mineralized cement

Cours bloc 2006Institut de Minéralogie et PétrographieUniversité de Fribourg

Page 54: Portland Cement

Mineralizer lower the melting point. Even earlybelite formation happens in the present of a liquid phase. Transport of matter is by fast diffusion through the liquid phase.

The reactions producing belite and too a smaller extent alite in an ordinary PC klinkercomposition occur in the solid state. Matter is tranported by slow, solid state diffusion

Mechanisms enhancing clinker formation II

Consequences: - increased number of belite nuclei- faster growth kinetic of belite- in presence of fluorine, faster reaction rates for the transformationbelite -> alite

Mineralized cement

Cours bloc 2006Institut de Minéralogie et PétrographieUniversité de Fribourg

Page 55: Portland Cement

Problems with mineralized cement I

High gaseous alkali- and sulfatespecies can condensate in towards the outlet. Klinker particle coalesceon the wet kiln surface and lead toring formation.

Fine grained belite and alite lead to excessive dusting in the kiln

0. 2mm

Mineralized cement

Cours bloc 2006Institut de Minéralogie et PétrographieUniversité de Fribourg

Page 56: Portland Cement

Problems with mineralized cement II

Anhydrite inclusions in belite crystals. (6.4 wt% total SO3 )

Activation of sulfur dissolvedin silicates or present as sulfateinclusions:Late ettringite formation causingdeterioration of mechanical properties.

Mineralized cement

Cours bloc 2006Institut de Minéralogie et PétrographieUniversité de Fribourg

Page 57: Portland Cement

Pro and cons of mineralized klinker

- lowering of burning temperature- increase of alite content - formation of the rhombohedral, hydraulic more active polymorph of alite- stabilization of the hydraulic more active phase of belite

Pro:

- Ring formation and excessive dusting in the kiln- with too low fluorine content: increase in belite content- Presence of phases deletrious to mechanical properties

Cons:

Mineralized cement

Cours bloc 2006Institut de Minéralogie et PétrographieUniversité de Fribourg

Page 58: Portland Cement

Rapid burning

Consequences of steep temperature ramps:

- Decomposition and new phase formation occur simultaneously

- New phases are formed through metastable reactions having larger reaction free energies

- Decomposition products are much smaller and have a higher surface activity

Rapid burning

Cours bloc 2006Institut de Minéralogie et PétrographieUniversité de Fribourg

Page 59: Portland Cement

Grain size of decomposition products

diam

eter

(Å)

0.0 5 10 15 200.0

500

1000

1500

2000

t (min)25

800 °C/min 5 °C/min

T(max): 1300°C

CaO

Rapid burning

Cours bloc 2006Institut de Minéralogie et PétrographieUniversité de Fribourg

Page 60: Portland Cement

Rapid burning

Free energy of formation for C2S and C3S

G (K

J/m

ol)

800 900 1000 1100 1200-200

-100

0

100

200

t (min)

1300

3CaCO3 +SiO2 = Ca3SiO5 + 3CO22CaCO3 +SiO2 = Ca2SiO4 + 2CO23CaO +SiO2 = Ca3SiO52CaO +SiO2 = Ca2SiO4

Above 1100° the direct reactions of calcite with silica to form CS-phases have more negative Gf andare favoured over the reactioninvolving lime.

Cours bloc 2006Institut de Minéralogie et PétrographieUniversité de Fribourg

Page 61: Portland Cement

Batch production of PC klinker

Rotary kiln- continous process- steady speed

Batch production- heating and cooling speeds can be enhanced and adapted

Burning technique:- Batches of raw meal is fed into a furnace with circulating air at reaction temperature such as to form a gaseous suspension.- Reaction occurs at contact pointsbetween suspended particles

Feeder

Collector

Rapid burning

Cours bloc 2006Institut de Minéralogie et PétrographieUniversité de Fribourg

Page 62: Portland Cement

Proportioning of raw materials II

Lime saturation factor (cont.)The actual lime saturation of a raw material mix is given by the ratio

CaO2.8 SiO2 + 1.2Al2O3 + 0.65Fe2O3

The LSF is in the ideal case 1.0, but often the reaction time in the kilnis not sufficient to bind all the CaO.

Free limeThe free lime is the leftover CaO which did not react to form silicates. Anacceptable free lime content is more important than an LSF of 1.0.

LSF =

Raw materials

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 63: Portland Cement

Proportioning of raw materials III

Silica and alumina ratios The silica and alumina ratios are defined as

SiO2 Al2O3Al2O3 + Fe2O3 Fe2O3

Hydraulic index

SR = AR =

Raw materials

IH =CaO + MgO

SiO2 + Al2O3 + Fe2O3

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 64: Portland Cement

Proportioning of raw materials IVExample

Raw materials Chalk wt% Clay wt% Loam wt% Ash wt%

S 2.5 50.0 84.0 48.0A 0.5 22.0 6.0 29.0F 0.2 9.0 3.0 10.0C 54.0 2.5 1.0 8.0Res. 42.8 16.5 6.0 5.0

From trials we know that to keep the free lime at an acceptable value the LSF must not be higher than 0.96. The lime required to saturate the oxides to this level is:

CaO = 0.96 (2.8 SiO2 + 1.2Al2O3 + 0.65Fe2O3 )

Raw materials

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 65: Portland Cement

Proportioning of raw materials V

Example (cont.)

1. lime required to saturate acidic oxide in chalk: 7.42.lime required to saturate acidic oxides in clay: 164.9 3. lime available in chalk 54.03. lime available in clay 2.54. net lime required for clay 164.9 - 2.5 = 162.45. net lime available from chalk 54.0 - 7.4 = 46.6

To get the right mix A, clay and chalk have to be mixed at the ratio

chalk 46.6clay 162.4= = 3.49

Raw materials

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008

Page 66: Portland Cement

Proportioning of raw materials VI

Example (cont.)The SR of this mix is however too low and has to be adjusted using a mix B between chalk and loam with an LSF of 0.96. The final mix C, with an LSF of0.96 and a SR of 3.0 can be obtained by blending mix A and B together.

Mixes Mix A wt% Mix B wt% Mix C wt%

S 13.9 16.1 14.5A 5.3 1.4 3.4F 2.2 0.7 1.4C 42.5 45.0 43.7 Res. 36.9 36.8 36.8

Raw materials

Technical MineralogyDepartment of Geosciences Technische Mineralogie

ETHZ IMP 2008