Cementitous materials Inorganic cements - SGTK · Mortar: Mixture of Portland cement, ... - Silica...

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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

Introduction

Cementitous materials

Definition: 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



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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

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



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.

Historical background II

Introduction


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.


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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.

Introduction



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 hydrates HCP = hydrated cement paste PFA = pulverized fuel ash PC = Portland cement OPC = Ordinary Portland cement

Chemical notation

Introduction



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Portland Cement I Chemical composition The composition of Portland Cements and puzzolanic additives cover a certain range.

Introduction



Portland cement II

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

Main mineralogical components

Introduction



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Portland Cement III

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

Quarrying chalk in northern Jutland (Aalborg Cement)

Introduction



Portland Cement IV

Chalk slurry tank (Aalborg cement)

Main production steps (cont.)

Introduction



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Portland Cement V


Preheater, rotary kilns and storage silos

Introduction



Portland Cement VI


Cement silo Shipping by ship

Introduction



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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

Introduction

China 576,000 China produces one third of the world cement output!

World total (rounded) 1,700,000



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Swiss cement industry (www.cemsuisse.ch)

Cement plants in Switzerland

cement plant

klinker mills

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

Introduction



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 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.

Raw materials



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Composition of ordinary Portland cements

SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O SO3 LOI (H2O+CO2)

Minor components and traces (deleterious) few %: MgO, SrO2 few tenth of a %: P2O5, CaF2 , alkalis traces: 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 - 23.0 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

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

Proportioning of raw materials

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

Raw materials



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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 16.1 A+F 7.5 2.1

S A +F

= 3.0 = ⇒ p = 0.51

Raw materials



Klinker phases I

1. Alite Ca3SiO5 = C3S

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

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

orthosilicate 0.71nm

R- C3S projected along the c-axis

SiO4

Ca

O

Klinker production



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Klinker phases II

2. Belite Ca2SiO4 = C2S

Polymorphic transformations: O1(γ) M1(β) M2(αL ’) O2(αH’) H1(α)

O: orthorhombic M: monoclinic H: hexagonal

<500°C 630°C 1160°C 1425°

Max. concentration of impurities: 4.0-6.0wt% Al2O3+ Fe2O3 impurities stabilize the β-phase

orthosilicate

0.55nm α - C2S proj. down c-axis

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

Klinker production



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Klinker phases IV Polymorphs 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 Fe

C2S usually only in the M1(β) polymorph with parallel twin lamellae M2(αL ’) has typical crossed twin lamellae. The transformation M2(β) ⇒M(γ) 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



Klinker phases V Etched microstructures of the different klinker polymorphs

Alite crystals with both single and polysynthetic twins

Klinker production

Belite crystals with complex twin lamellae (M2(αL ’) polymorph)

Belite crystals with paralllel twin lamellae (M(β) polymorph)

Belite crystals with crack formation along lamellae boundaries (M(β) ⇒(M(β) transf.)



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Rotary kiln Without preheater/precalciner the kiln aspect ratio is about 30

Klinker production



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



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Decomposition of carbonate phases I

Decomposition reaction: CaCO3 = CaO + CO2

K =CaO[ ] CO2[ ]CaCO3[ ]

= pCO2

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 temperature As function of CO2 partial pressure

0.0

0.25

0.5

0.75

1.0

750 800 850 900

890°C

T(°C)

P(CO2)



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 ?

1! a( )13 = kt

a

t

reaction progress a

Klinker production



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Belite formation

1. Formation of belite through solid state reaction

quartz amorphous material

belite

2. Transformation of the belite shells to belite crystal clusters

lime

Klinker production



Appearance of first melts

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

1. Alkali and sulfate melts

Klinker production



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

Phase diagram

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)

Klinker production



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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

(wt

%)

3.5



Formation and recrystallization of alite

amorphous material

lime

belite

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

Klinker production



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Microtextures I (all pictures FL Smidth review 25)

0.05mm

Alite wall separating CaO and a belite cluster

alite melt phase (aluminates,ferrites) belite lime

Belite clusters replacing previous quartz grains.

0.1mm

Klinker production



Alite crystallizing at the expense of lime and belite

0.3mm

Microtextures II

lime belite

alite

Well crystallized, homogeneous clinker. The raw mix contained few quartz grains and a well controlled carbonate grain size.

pores

0.2mm

Klinker production



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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



Microtextures III

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

0.04mm

belite rims

Etched thin section showing the transformation twins in belite.

0.02mm

Klinker production



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Slowly cooled clinker with corroded alite phase and recrystallized belite grains.

0.05mm

Microtextures IV

Fast cooled clinker with euhedral alite and rounded belite crystals.

0.05mm

Klinker production



Normative mineralogy of clinker I

Klinker production



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Normative mineralogy of clinker II

Klinker production

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,



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



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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



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

Klinker production

Institut de Minéralogie et Pétrographie Université de Fribourg


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Energy costs of cement production

Process Quarry Crushers Prehomoginizing and transport Raw mill Raw meal silo Kiln feeder Kiln and cooler Coal mill Cement mill Packing plant Other 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



- use of alternative raw materials

- increasing the burning rate

- lowering the melting point of the system.



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:



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- lowering the melting point of the system.



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 2006 Institut de Minéralogie et Pétrographie Université de Fribourg

Bulk composition and mineralogy of mineralized clinkers

M (wt%) in clinker

M(w

t%) i

n sil

icat

es

0.0 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

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)

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

normal PC mineralized

Mineralized cement


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Mineralizer used in klinker manufacturing: Fluorite CaF2 = CF Gypsum 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


Effect of mineralizer concentration on clinker mineralogy

clin

ker m

iner

al (w

t%)

0.0 2.0 4.0 6.0 8.0 0.0

20

40

60

80

SO3 (wt%)

clin

ker m

iner

al (w

t%)

0.0 0.25 0.5 0.75 1.0 0.0

20

40

60

80 alite

belite

F (wt%)

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

Mineralized cement


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The system Ca2SiO5 - CaO - CaF2

first melt appearance: 1113°C

Mineralized cement


0.05mm

Mineralized klinker with langbeinite filling interstitial space

Microstructures I

Mineralized klinker rich in alite which remained in the hexagonal modification

Mineralized cement


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Mechanisms enhancing clinker formation I

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

Mineralized cement


Mineralizer lower the melting point. Even early belite 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 klinker composition 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 transformation belite -> alite

Mineralized cement


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Problems with mineralized cement I

High gaseous alkali- and sulfate species can condensate in towards the outlet. Klinker particle coalesce on the wet kiln surface and lead to ring formation.

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

0. 2mm

Mineralized cement


Problems with mineralized cement II

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

Activation of sulfur dissolved in silicates or present as sulfate inclusions: Late ettringite formation causing deterioration of mechanical properties.

Mineralized cement


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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 α 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


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


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Grain size of decomposition products

diam

eter

(Å)

0.0 5 10 15 20 0.0

500

1000

1500

2000

t (min) 25

800 °C/min 5 °C/min

T(max): 1300°C

CaO

Rapid burning


Rapid burning

Free energy of formation for C2S and C3S

ΔG

(KJ/

mol

)

800 900 1000 1100 1200 -200

-100

0

100

200

t (min)

1300

3CaCO3 +SiO2 = Ca3SiO5 + 3CO2 2CaCO3 +SiO2 = Ca2SiO4 + 2CO2 3CaO +SiO2 = Ca3SiO5 2CaO +SiO2 = Ca2SiO4

Above 1100° the direct reactions of calcite with silica to form CS-phases have more negative ΔGf and are favoured over the reaction involving lime.


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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 points between suspended particles

Feeder

Collector

Rapid burning


Proportioning of raw materials II

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

CaO 2.8 SiO2 + 1.2Al2O3 + 0.65Fe2O3

The LSF is in the ideal case 1.0, but often the reaction time in the kiln is not sufficient to bind all the CaO. Free lime The free lime is the leftover CaO which did not react to form silicates. An acceptable free lime content is more important than an LSF of 1.0.

LSF =

Raw materials



32

Proportioning of raw materials III

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

SiO2 Al2O3 Al2O3 + Fe2O3 Fe2O3

Hydraulic index

SR = AR =

Raw materials

IH = CaO + MgO

SiO2 + Al2O3 + Fe2O3



Proportioning of raw materials IV Example Raw materials

Chalk wt% Clay wt% Loam wt% Ash wt% S 2.5 50.0 84.0 48.0 A 0.5 22.0 6.0 29.0 F 0.2 9.0 3.0 10.0 C 54.0 2.5 1.0 8.0 Res. 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



33

Proportioning of raw materials V

Example (cont.) 1. lime required to saturate acidic oxide in chalk: 7.4 2.lime required to saturate acidic oxides in clay: 164.9 3. lime available in chalk 54.0 3. lime available in clay 2.5 4. net lime required for clay 164.9 - 2.5 = 162.4 5. 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 46.6 clay 162.4

= = 3.49

Raw materials



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 of 0.96 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 14.5 A 5.3 1.4 3.4 F 2.2 0.7 1.4 C 42.5 45.0 43.7 Res. 36.9 36.8 36.8

Raw materials



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