ETHtechMin Portland Cement 2012

7/28/2019 ETHtechMin Portland Cement 2012

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Prof. Grobty B., Inst. de Minralogie et Ptrographie, Univ. de Fribourg

Technical MineralogyDepartment of Geosciences

Technische MineralogieETHZ 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 amortar mix of 1 part of lime and4 part of sand. Examples:193 BC: Porticu House, Amaelia,200 AD: Pantheon, Rome

(www.romanconcrete.com)

Introduction



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 resembledthe stone quarried on the Isle of Portland off the British coast.

Historical background II

Introduction


Portland cement. This was the namegiven by Joseph Aspdin to the productconsisting of limestone and clay, on whichhe took out a patent in 1824: "Portland",owing to the similarity to the buildingstone 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 materialcomposed of calcium silicates and aluminates, and a smallamount of added gypsum/anhydrite. The clinker is made byburning 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. Themechanical strength can be reinforced by the insertionof 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 hydratesHCP = hydrated cement pastePFA = pulverized fuel ashPC = Portland cementOPC = Ordinary Portland cement

Chemical notation

Introduction




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Portland Cement I

Chemical compositionThe composition of PortlandCements and puzzolanicadditives cover a certain range.

Introduction



Portland cement II

Name + Chem. Comp Approx. % in OPC Properties

Belite C2S 20 Slow strength gain, responsiblefor long term strength

Alite C3S 55 Rapid strength gain, responsiblefor 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 graycolor 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 siloShipping by ship

Introduction




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Introduction



World cement productions(minerals.usgs.gov/minerals/pubs/commodity/cementWorld cement production 2000 (thousand of tons):United States (includes Puerto Rico) 92,300Brazil 41,500China 576,000Egypt 23,000France 24,000Germany 38,099India 95,000Indonesia 27,000Italy 36,000Japan 77,500Korea, Republic of 50,000

Mexico 30,000Russia 30,000Spain 30,000Taiwan 19,000Thailand 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




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Swiss cement industry (www.cemsuisse.ch)Cement plants in Switzerland

cement plant

klinker mills

1 Eclpens2 Cornaux3 Reuchenette4 Wildegg5 Siggenthal6 Thayngen7 Brunnen8 Untervaz

Total production1987: 4478000 t1989: 5461000 t2000: 3715908 t

Introduction



Raw materials

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

Corrective constituents

Shales: - clay rich, usually dominated by illite, smectite andkaolinite. 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 beintroduced through impurities in the fuel. Up of 30% of ash is producedby the firing of brown coal.

Raw materials




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Composition of ordinary Portland cements

SiO2 Al2O3Fe2O3CaOMgOK2ONa2OSO3 LOI (H

2O+CO

2)

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 applicationis 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



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 differentoxide 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 pof mix A and 1-pof mix B to get an SR of 3.0 can beobtained through following consideration:

The value acan be obtained from

S 13.1p + 16.1(1-p)A+F 7.5p + 2.1(1-p)

- SR = = 3.0

- Mix A MixBS 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 RT: triclinic M: monoclinic R: rhombohedral

620C 920C 980C 990C 1060C 1070C

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

orthosilicate0.71nm

R- C3S projectedalong the c-axis

SiO4

Ca

O

Klinker production




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Klinker phases II

2. Belite Ca2SiO4 = C2S

Polymorphic transformations:

O1() M1() M2(L) O2(H) H1()

O: orthorhombic M: monoclinic H: hexagonal


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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% ofsubstituting elements: Mg, Al, Fe, Si

C3S early crystallized small crystals rich in substitutes: M3 late crystallizedlarge crystals: M2 (single twins), rarely T1 (polysynthetic twins)3-4% of substituting elements, mainly Mg, Al and Fe

C2S usually only in the M1() polymorph with parallel twin lamellae M2(L) hastypical crossed twin lamellae. The transformation M2() M() sho


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

Klinker production



Klinker reactions below 1300C

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

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

Temp. range products

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

Formation of first melt phases: > 1000C

Drying 100C free water evaporates100 - 300C 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[ ]CaCO

3[ ]= 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 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)



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( )1

3 = kta

t

reaction progress a

Klinker production




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Belite formation

1. Formation of belite throughsolid state reaction

quartz

amorphous material

belite

2. Transformation of the beliteshells to belite crystal clusters

lime

Klinker production



Appearance of first melts

2. C-S-A melts: lowesteutecticum 1170

1. Alkali and sulfate melts

Klinker production




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P: typical bulk composition of Portland cement klinkers

First melt appearance: 1455C

Phase diagram

Klinker production



Klinker reactions between 1300C and 1450C

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

alite3. 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 1450C 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

Liquidphase(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 thecontacts between belite cluster and lime

3. Recrystallized and new formed alitereplaces lime crystals

Klinker production




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Microtextures I (all pictures FL Smidth review 25)

0.05mmAlite wall separating CaO and abelite cluster

alite melt phase (aluminates,ferrites)belite lime

Belite clusters replacing previousquartz grains.

0.1mm

Klinker production



Alite crystallizing at the expense oflime and belite

0.3mm

Microtextures II

lime belite

alite

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

pores

0.2mm

Klinker production




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Klinker reactions during cooling

1. Crystallization of the restitic melt. Products: aluminates (C3A) andferrites (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 beliteplus lime in a belite poor clinker(fast cooling).

0.04mm

beliterims

Etched thin section showing thetransformation twins in belite.

0.02mm

Klinker production




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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



Normative mineralogy of clinker I

Klinker production




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Normative mineralogyof clinker II

Klinker production

Minor elements in the mainklinker phases in cements ofdifferent cement factories.Most cements contain 5wt% andmore minor elements whichintroduces considerable errorswhen 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 OclinkerC2 Scorr = C2 Sbogue - 1.5 MgOclinker - 2.2 K2 OclinkerC3 Acorr = C3 Abogue + 7.8 Na2O + 1.5 AR - 2.1 S3O - 5.0C4 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 thecorrected (bottom) Bogue formula



Energy balance in clinker production

Temp range

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

900-1400Cca. 1300C1400-20C900-20C450-20C

Process

Heating of the materialEvaporation of free H2ORemoval of H2O from clayheating of the materialDissociation of calciteCrystallisation of dehydrated clayHeating of the decarbonated material

Heat of formation of clinker mineralsMelting of liquid phasesCooling of clinkerCooling of CO2Cooling of H2OTotal

Heat exchangekJ/kg clinker

710(1800)

170820

2000-40

525

-420100

-1510-500-85

4325 -2555

Klinker production

Institut de Minralogie et PtrographieUniversit de Fribourg



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Energy costs of cement production

Process

QuarryCrushersPrehomoginizing and transportRaw millRaw meal siloKiln feederKiln and cooler

Coal millCement millPacking plantOthertotal

Fuel Electricity Cost($/day)kcal/kg cement kwh/ton cement

0 02.5 6001.5 360

0-100 27.0 98131.5 3601.5 360

700 23.0 28853

2.5 60030.0 72001.0 2404.5 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 thesystem.



Mineralized cement

Improvements in klinker manufacturing

1. Energy savings through:

- better insulation, improvedheat exchanger etc.

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




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- lowering the melting point of thesystem.



Mineralized cement

Improvements in klinker manufacturing

1. Energy savings through:

- better insulation, improvedheat exchanger etc.

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

Cours bloc 2006Institut de Minralogie et PtrographieUniversit de Fribourg

Bulk composition and mineralogy of mineralized clinkers

M (wt%) in clinker

M

(wt%)insilicates

0.0 0.5 1.0 1.5 2.0 2.50.00.5

1.0

1.5

2.0F

3.0Partitioning of SO3 and F betweensilicates and other phases

SO3

SiO2 Al2O3 Fe2O3 CaOMgOSO3FK 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

33.349.54.97.7

21.54.63.6

65.60.72.00.20.80.4

34.846.94.08.5

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 ofreactant phases

Energy savings: 105 - 630kJ/kg = 3 - 20%

Mineralized cement


Effect of mineralizer concentration on clinker mineralogy

clinkerm

ineral(wt%)

0.0 2.0 4.0 6.0 8.00.0

20

40

60

80

SO3 (wt%)

clinkerm

ineral(wt%)

0.0 0.25 0.5 0.75 1.00.0

20

40

60

80alite

belite

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

Mineralized cement



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The system Ca2SiO5 - CaO - CaF2

first melt appearance: 1113C

Mineralized cement


0.05mmMineralized klinker with langbeinitefilling interstitial space

Microstructures I

Mineralized klinker rich in alite whichremained in the hexagonal modification

Mineralized cement



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Mechanisms enhancing clinker formation I

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

Mineralized cement


Mineralizer lower the melting point. Even earlybelite formation happens in the present of a

liquid phase. Transport of matter is by fastdiffusion through the liquid phase.

The reactions producing belite and too asmaller extent alite in an ordinary PC klinkercomposition occur in the solid state. Matteris 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, fasterreaction rates for the transformationbelite -> alite

Mineralized cement



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Problems with mineralized cement I

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

Fine grained belite and alite lead toexcessive 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 dissolvedin silicates or present as sulfateinclusions:Late ettringite formation causingdeterioration 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 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 occursimultaneously

- New phases are formed through metastablereactions having larger reaction free energies

- Decomposition products are much smallerand have a higher surface activity

Rapid burning



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Grain size of decomposition products

diameter()

0.0 5 10 15 200.0

500

1000

1500

2000

t (min) 25

800 C/min5 C/min

T(max): 1300C

CaO

Rapid burning


Rapid burning

Free energy of formation for C2S and C3S

G(KJ/mol)

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 directreactions of calcite withsilica to form CS-phaseshave more negative Gf andare favoured over the reactioninvolving lime.



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Batch production of PC klinker

Rotary kiln- continous process- steady speed

Batch production- heating and cooling speedscan be enhanced and adapted

Burning technique:- Batches of raw meal is fed into

a furnace with circulating air atreaction temperature such as toform a gaseous suspension.- Reaction occurs at contact pointsbetween 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

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




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Proportioning of raw materials III

Silica and alumina ratiosThe silica and alumina ratios are defined as

SiO2 Al2O3Al2O3 + Fe2O3 Fe2O3

Hydraulic index

SR = AR =

Raw materials

IH =CaO + MgO

SiO2 + Al2O3 + Fe2O3



Proportioning of raw materials IV

Example

Raw materialsChalk 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 theLSF must not be higher than 0.96. The lime required to saturate the oxidesto this level is:

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

Raw materials




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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: 164.93. 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



Proportioning of raw materials VI

Example (cont.)The SR of this mix is however too low and has to be adjusted using a mix Bbetween 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.

MixesMix A wt% Mix B wt% Mix C wt%

S 13.9 16.1 14.5

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

Raw materials



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ETHtechMin Portland Cement 2012