cement production basic knowledge-shang

8/7/2019 Cement Production Basic Knowledge-Shang

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Cementproductionbasicknowledge

1Cement:

In the most general sense of the word, a cement is a binder, a substancewhich sets and hardens independently, and can bind other materials

together. The word "cement" traces to the Romans, who used the term "opus

caementicium" to describe masonry which resembled concrete and was made

from crushed rock with burnt lime as binder. The volcanic ash and

pulverized brick additives which were added to the burnt lime to obtain

a hydraulic binder were later referred to as cementum, cimentum, cment

and cement. Cements used in construction are characterized as hydraulicor non-hydraulic.

The most important use of cement is the production of mortar andconcretethe bonding of natural or artificial aggregates to form a strong

building material which is durable in the face of normal environmental

effects.

Concrete should not be confused with cement because the term cementrefers

only to the dry powder substance used to bind the aggregate materials of

concrete. Upon the addition of water and/or additives the cement mixture

is referred to as concrete, especially if aggregates have been added.

Portland cement (often referred to as OPC, from Ordinary Portland Cement)is the most common type of cement in general use around the world, because

it is a basic ingredient of concrete, mortar, stucco and most

non-specialty grout. It is a fine powder produced by grinding Portland

cement clinker (more than 90%), a limited amount of calcium sulfate which

controls the set time, and up to 5% minor constituents (as allowed by

various standards).

As defined by the European Standard EN197.1:

Portland cement clinker is a hydraulic material which shall consist of

at least two-thirds by mass of calcium silicates(3CaO.SiO2 and 2CaO.SiO2),

the remainder consisting of aluminium- and iron-containing clinker phases

and other compounds. The ratio of CaO to SiO2 shall not be less than 2.0.

The magnesium content (MgO) shall not exceed 5.0% by mass.

Portland cementPortland cement clinker is made by heating, in a kiln, a homogeneous

mixture of raw materials to a sintering temperature, which is about1450 C for modern cements. The aluminium oxide and iron oxide are present


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as a flux and contribute little to the strength. For special cements, such

as Low Heat (LH) and Sulfate Resistant (SR) types, it is necessary to limit

the amount of tricalcium aluminate (3CaO.Al2O3) formed. The major raw

material for the clinker-making is usually limestone (CaCO3) mixed with

a second material containing clay as source of alumino-silicate. Normally,

an impure limestone which contains clay or SiO2 is used. The CaCO3 content

of these limestones can be as low as 80%. Second raw materials (materials

in the rawmix other than limestone) depend on the purity of the limestone.

Some of the second raw materials used are: clay, shale, sand, iron ore,

bauxite, fly ash and slag. When a cement kiln is fired by coal, the ash

of the coal acts as a secondary raw material.

2.History:

History of the origin of cementEarly usesIt is uncertain where it was first discovered that a combination of

hydrated non-hydraulic lime and a pozzolan produces a hydraulic mixture

(see also: Pozzolanic reaction), but concrete made from such mixtures was

first used on a large scale by Roman engineers.[1]

They used both natural

pozzolans (trass or pumice)a local name of volcanic tuff. and (ground

brick or pottery) in these concretes. Many excellent examples of

structures made from these concretes are still standing, notably the huge

monolithic dome of the Pantheon in Rome and the massive Baths of

Caracalla.[2]

The vast system of Roman aqueducts also made extensive use

of hydraulic cement.[3]

The use disappeared in medieval Europe, although

weak pozzolanic concretes continued to be used as a core fill in stone

walls and columns.

Modern cement

Modern hydraulic cements began to be developed from the start of theIndustrial Revolution (around 1800), driven by three main needs:

Hydraulic renders for finishing brick buildings in wet climates

Hydraulic mortars for masonry construction of harbor works etc, in

contact with sea water.

Development of strong concretes.

In Britain particularly, good quality building stone became ever more

expensive during a period of rapid growth, and it became a common practice

to construct prestige buildings from the new industrial bricks, and tofinish them with a stucco to imitate stone. Hydraulic limes were favored


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for this, but the need for a fast set time encouraged the development of

new cements. Most famous was Parker's "Roman cement."[4]

This was developed

by James Parker in the 1780s, and finally patented in 1796. It was, in

fact, nothing like any material used by the Romans, but was a "Natural

cement" made by burning septaria - nodules that are found in certain clay

deposits, and that contain both clay minerals and calcium carbonate. The

burnt nodules were ground to a fine powder. This product, made into a

mortar with sand, set in 515 minutes. The success of "Roman Cement" led

other manufacturers to develop rival products by burning artificial

mixtures of clay and chalk.

John Smeaton made an important contribution to the development of cements

when he was planning the construction of the third Eddystone Lighthouse

(1755-9) in the English Channel. He needed a hydraulic mortar that would

set and develop some strength in the twelve hour period between successivehigh tides. He performed an exhaustive market research on the available

hydraulic limes, visiting their production sites, and noted that the

"hydraulicity" of the lime was directly related to the clay content of

the limestone from which it was made. Smeaton was a civil engineer by

profession, and took the idea no further. Apparently unaware of Smeaton's

work, the same principle was identified by Louis Vicat in the first decade

of the nineteenth century. Vicat went on to devise a method of combining

chalk and clay into an intimate mixture, and, burning this, produced an

"artificial cement" in 1817. James Frost,[5]

working in Britain, produced

what he called "British cement" in a similar manner around the same time,

but did not obtain a patent until 1822. In 1824, Joseph Aspdin patented

a similar material, which he called Portland cement, because the render

made from it was in color similar to the prestigious Portland stone.

All the above products could not compete with lime/pozzolan concretes

because of fast-setting (giving insufficient time for placement) and low

early strengths (requiring a delay of many weeks before formwork could

be removed). Hydraulic limes, "natural" cements and "artificial" cements

all rely upon their belite content for strength development. Belitedevelops strength slowly. Because they were burned at temperatures below

1250 C, they contained no alite, which is responsible for early strength

in modern cements. The first cement to consistently contain alite was made

by Joseph Aspdin's son William in the early 1840s. This was what we call

today "modern" Portland cement. Because of the air of mystery with which

William Aspdin surrounded his product, others (e.g. Vicat and I C Johnson)

have claimed precedence in this invention, but recent analysis[6]

of both

his concrete and raw cement have shown that William Aspdin's product made

at Northfleet, Kent was a true alite-based cement. However, Aspdin's

methods were "rule-of-thumb": Vicat is responsible for establishing the


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chemical basis of these cements, and Johnson established the importance

of sintering the mix in the kiln.

William Aspdin's innovation was counter-intuitive for manufacturers of

"artificial cements", because they required more lime in the mix (a

problem for his father), because they required a much higher kiln

temperature (and therefore more fuel) and because the resulting clinker

was very hard and rapidly wore down the millstones which were the only

available grinding technology of the time. Manufacturing costs were

therefore considerably higher, but the product set reasonably slowly and

developed strength quickly, thus opening up a market for use in concrete.

The use of concrete in construction grew rapidly from 1850 onwards, and

was soon the dominant use for cements. Thus Portland cement began its

predominant role.

3.Production

TherearethreefundamentalstagesintheproductionofPortlandcement:

(1) Preparation of the raw mixture

(2) Production of the clinler

(3) Cement grinding

Rawmix preparation

A limestone prehomogenization pile being built by a boom stacker


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A completed limestone prehomogenization pile

The raw materials for Portland cement production are a mixture (as fine

powder in the 'Dry process' or in the form of a slurry in the 'Wet process')

of minerals containing calcium oxide, silicon oxide, aluminium oxide,

ferric oxide, and magnesium oxide. The raw materials are usually quarried

from local rock, which in some places is already practically the desiredcomposition and in other places requires the addition of clay and

limestone, as well as iron ore, bauxite or recycled materials. The

individual raw materials are first crushed, typically to below 50 mm. In

many plants, some or all of the raw materials are then roughly blended

in a "prehomogenization pile." The raw materials are next ground together

in a rawmill. Silos of individual raw materials are arranged over the feed

conveyor belt. Accurately controlled proportions of each material are

delivered onto the belt by weigh-feeders. Passing into the rawmill, the

mixture is ground to rawmix. The fineness of rawmix is specified in terms

of the size of the largest particles, and is usually controlled so that

there are less than 5%-15% by mass of particles exceeding 90 m in

diameter. It is important that the rawmix contains no large particles in

order to complete the chemical reactions in the kiln, and to ensure the

mix is chemically homogenous. In the case of a dry process, the rawmill

also dries the raw materials, usually by passing hot exhaust gases from

the kiln through the mill, so that the rawmix emerges as a fine powder.

This is conveyed to the blending system by conveyor belt or by a powder

pump. In the case of wet process, water is added to the rawmill feed, and

the mill product is a slurry with moisture content usually in the range25-45% by mass. This slurry is conveyed to the blending system by

conventional liquid pumps.

Rawmix blendingThe rawmix is formulated to a very tight chemical specification. Typically,

the content of individual components in the rawmix must be controlled

within 0.1% or better. Calcium and silicon are present in order to form

the strength-producing calcium silicates. Aluminium and iron are used inorder to produce liquid ("flux") in the kiln burning zone. The liquid acts


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as a solvent for the silicate-forming reactions, and allows these to occur

at an economically low temperature. Insufficient aluminium and iron lead

to difficult burning of the clinker, while excessive amounts lead to low

strength due to dilution of the silicates by aluminates and ferrites. Very

small changes in calcium content lead to large changes in the ratio of

alite to belite in the clinker, and to corresponding changes in the

cement's strength-growth characteristics. The relative amounts of each

oxide are therefore kept constant in order to maintain steady conditions

in the kiln, and to maintain constant product properties. In practice,

the rawmix is controlled by frequent chemical analysis (hourly by X-Ray

fluorescence analysis, or every three minutes by prompt gamma neutron

activation analysis). The analysis data is used to make automatic

adjustments to raw material feed rates. Remaining chemical variation is

minimized by passing the raw mix through a blending system that

homogenizes up to a day's supply of rawmix (15,000 tonnes in the case ofa large kiln).

Formation of clinker

Precalciner kiln


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Typical clinker nodules

The raw mixture is heated in a cement kiln, a slowly rotating and sloped

cylinder, with temperatures increasing over the length of the cylinder

up to a peak temperature of 1400-1450 . A complex succession of chemicalreactions take place (see cement kiln) as the temperature rises. The peak

temperature is regulated so that the product contains sintered but not

fused lumps. Sintering consists of the melting of 25-30% of the mass of

the material. The resulting liquid draws the remaining solid particles

together by surface tension, and acts as a solvent for the final chemical

reaction in which alite is formed. Too low a temperature causes

insufficient sintering and incomplete reaction, but too high a

temperature results in a molten mass or glass, destruction of the kiln

lining, and waste of fuel. When all goes to plan, the resulting material

is clinker. On cooling, it is conveyed to storage. Some effort is usually

made to blend the clinker, because although the chemistry of the rawmix

may have been tightly controlled, the kiln process potentially introduces

new sources of chemical variability. The clinker can be stored for a number

of years before use. Prolonged exposure to water decreases the reactivity

of cement produced from weathered clinker.

The enthalpy of formation of clinker from calcium carbonate and clay

minerals is about 1700 kJ/kg. However, because of heat loss during

production, actual values can be much higher. The high energy requirementsand the release of significant amounts of carbon dioxide makes cement

production a concern for global warming. See "Environmental effects"

below.

Cement grinding


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A 10 MW cement mill, producing cement at 270 tonnes per hour

In order to achieve the desired setting qualities in the finished product,

a quantity (2-8%, but typically 5%) of calcium sulfate (usually gypsum

or anhydrite) is added to the clinker and the mixture is finely ground

to form the finished cement powder. This is achieved in a cement mill.The grinding process is controlled to obtain a powder with a broad particle

size range, in which typically 15% by mass consists of particles below

5 m diameter, and 5% of particles above 45 m. The measure of fineness

usually used is the "specific surface", which is the total particle

surface area of a unit mass of cement. The rate of initial reaction (up

to 24 hours) of the cement on addition of water is directly proportional

to the specific surface. Typical values are 320-380 m2kg

1for general

purpose cements, and 450-650 m2kg

1for "rapid hardening" cements. The

cement is conveyed by belt or powder pump to a silo for storage. Cement

plants normally have sufficient silo space for 120 weeks production,

depending upon local demand cycles. The cement is delivered to end-users

either in bags or as bulk powder blown from a pressure vehicle into the

customer's silo. In developed countries, 80% or more of cement is

delivered in bulk, and many cement plants have no bag-packing facility.

In poorcountries,bags are the normal mode of delivery.

4 Performanceindex

4.1 The main technical index of cement

1specific gravity and bulk density: The specific gravity of Portland cement

is 3:1, and the bulk density is usually 1300kg/M3.

2finenessCement fineness refers to the granularity of cement particle. More

fine of the particle, the faster of the hardening, and the higher of early strength.

3setting timethe needed time for cement from mixing with water to starting

primary coagulation is called initial setting time. The needed time for cement

from mixing with water to finish coagulation is called final setting time. For

Portland cement, the initial time should not less than 45 min and final setting

time should not over 12 hours.

4strengthStrength of cement should match National Standard.


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5volume stability: It refers to the equality of vo lume changing during cement

hardening, if there are more impurity in the cement, it will cause irregular

deformation.

6heat of hydration: Mix cement with water will cause exothermic reaction,

during hardening of cement, continuous release the heat is called heat of

hydration.

7standard consistency: It refers to the consistency of cement paste when it

has certain resistance to normal testing bars sinking inside of cement paste.

5.Basicknowledgeofcementchemistry

Gelled materialpeople use it since ancient times(e.g the pyramid, theColosseum3000yearsago).Therearemainlytwokindsofbuildinggelledmaterials:

nonhydraulic gelled materialwhich cant get hardened in water(see the table

below),and hydraulicgelledmaterial.

Nonhydraulic gelled material was

widelyusedduringtheancienttimes.

High solubility of Calvital and

plaster means that they will get

worsened quickly under humid

circumstances.AncientRomanpeople

made good use of limebase gelled material and its mortar( gelled

material+sand).Theyusewetnetpasteasbaseto formsuperficial layerwithhigh

density. Whenthenetpastemeetswiththeair,itwillform outersurface with

calcspar,whichhas lowpermeability.Thisouter surfacewillprotectCa(OH)under

it,eventoday wecanfindtheexampleofRomanlimemortarin HadriansWall.

Notuntilrecentlyislimemortarusedindomesticbuildings.Naturalmaterialsneed

warmingprocess.Suchasnaturalplasters segmentaldehydration(200oC),the

calcinations of calcspar (850oC). hydraulic gelledmaterialcan last formuchmoretime.Itshydrousproductisinsolubleindeedgelledmaterialthatcangethardened inwater. The earliest systematic development is owed to the Roman

people.Theyusedlimestonewithsiliconandaluminum,besidestheyput volcanic

ashsoilasadditive intolimestonethathadbeenburnedearlier.Thisisregardedas

nonhydraulicgelledmaterial,forexample:

(i)anhydrite(CaSO4.1/2H2O)

CaSO4.1/2H2O+1

1/2H2OCaSO4.2H2O(plaster)

(ii)limebase gelledmaterial(CaO)

CaO+H2OCa(OH)2 +CO2CaCO3(calcite)


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the precursorofmodernportlandcement.

PortlandcementwasinventedbyJosephAspdininthemiddleof19thcentury.

It

is

the

product

of

burned

mixture

of

crumble

limestone

and

fine

clay,

containing

65%70% CaO, 1824% SiO2, 38% Fe2O3, 38% Al2O3and a small quantity ofsecondaryoxide e.gNa2O,K2O,MgOetc.)Muchmoreeffectivemanufacturingprocess isused in moderncementplant.Peoplecangetthat cement through

materials in a right proportion,which obtains prospective scale of intensity and

durability.


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li

c

s

o

p

II

thr

and

Rawmatermestonehalkellarlitebtainingirrobably c

Theforma

ughsolidafterward

ialusedincla

sch

ka

ot

nalumin

halybeate

ionof cli

tatereactiitwillbes

modernceistliner silicatumcorrectiv

nkerminer

onandsintent forp

mentplant

e minera

materials

al

Thehomog

driedprehea

mixtur

burned

tempe

firingering. Vilverizing

ls

ey is eenizing ofand dehter and pr materi in roature comone of kicoolingprithplaster.

fective praw matydrated icalcinator,

l(raw maary kiln.es up toln ),materiocesswec

lverizingrial. Theyn suspen after thatterial) willWhen

1500oC(at

als haveanget cli

andgetsionthebethetheonenker


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Theformationof clinkermineral

1Dehydrationanddecomposeofrawmaterial

Withthedehydration,decompositionandactivationofinsertedwaterandclay

mineral

)()( 21002 steamOHterinsertedwaOH

+ OHSiOOAOHSiOOA

2232

600450

223222l22l

2322322l2l SiOOASiOOA +

2Decompositionofcarbonate

Whenthetemperatureisabove600,thecarbonateofrawmaterialbeginsto

decompose.Whenthetemperatureisaround750,MgCO3 decomposes

acutelyandquickly CaCO3 decomposesquicklyatthetemperatureof 900,

andstopsdecomposingat1000.

+ 2

750

3M COgOMgCO

about

+ 2

910

3COCaOCaCO

about

3Solidphasereaction

Duetothedehydrationofclaydecompositionofcarbonateetc, SiO2Al2O3


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Fe2O3CaOcomeintobeing intherawmaterial,theyareactiveanddoexist

separately.Theystartthe combinationreactionwitheachother,andthereaction

speedgetsfastergraduallywiththe temperatureincrement.Thesolidphase

reaction,whichoccurs among themotesbymutualcontact,is polystage

reaction,anditsmuchcomplicated.Thereactingprocessisasfollows:

8009003232

OFeCaOOFeCaO +

3232OAlCaOOAlCaO +

90010003232

352)(3 OAlCaOCaOOAlCaO +

22 22 SiOCaOSiOCaO +

32322 OFeCaOCaOOFeCaO +

theformationreactionofC2Sstopsatabout1200

10001200 )3(34353232

OAlCaOCaOOAlCaO +

)4(3)2(33532323232

OFeOAlCaOCaOOFeCaOOAlCaO ++

4Thefiring ofclinker

Whenthetemperaturecomesupto1300,C3AandC4AFgetfused,and

liquidoidappearsinthematerials.AbsorbingCaOintheliquidoid,C2SbecomesC3S

22 32 SiOCaOCaOSiOCaO +

Thisiscalledlimeabsorbingprocess.Inrealmanufacturingprocessthe

temperatureofmaterialsiscontrolledabove1300,usuallybetween 1350

1500,thisscopeiscalled firing

temperature.

5. Thecoolingofclinker

Burnedclinkerneedstobecooled.thespeedofcoolinghavemucheffectonthe

qualityofclinker.Fastcoolingcanprevent SC2 withgoodhydraulicity

turninginto SC2 thathardlyhasanyhydraulicity.Fastcoolingstillcanprevent

liquatedMgO CaOf fromcrystallizing,butexistingincementinglassstate,so


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thestabilityisimproved.Fastcoolingalsocanpreventclinkermineralcrystalfrom

becomingbiggerorfullycrystallizing,whichcangetcement hydratedeasily.

IIIThecomponentofclinker1ChemicalcomponentofPortlandcementclinker

ThemaincomponentofPortlandcementclinkerisCaOSiO2Al2O3Fe2O3etc

they takesupmore than95% inclinker.besides thereareother fewoxide, suchas

MgOSO3P2O5K2ONa2Oetcwhichtakesuplessthan5%ofclinker.

Accordingtostatistics,usuallythewaverangeoffouroxidesinPortlandcement

clinkeris:

CaO 62%67%

SiO2 20%24%

Al2O3 4%7%

Fe2O3 2.5%6%

2ThePortlandcementclinkermineralcomponent

InthecompositionofPortlandcementclinkerCaOSiO2AI2O3Fe2O3andso

onitisnotonlyexistencebytheindependentoxidecompound,butbytwokindsor

twoaboveoxidecompoundsrespondedthatcombinestoplantthedifferentoxide

compoundtheaggregate,namelyexistenceshapebymanykindsofchamotte

mineral.Thesechamottemineralcrystalistiny.So,wemaythinkthatthePortland

cementchamotteiscomposedofakindofmineralconstituent,andthecrystaltiny

manmaderock..

InthePortlandcementclinkeringredient'sessentialmineralhasthefollowing

fourkinds:

calciumsilicate: 3CaOSiO2, theabbreviationis C3S;

dicalciumsilicate: 2CaOSiO2, theabbreviationis C3S;

tricalciumaluminate; 3CaOAl2O3, theabbreviationis C3A

4CaOAl2O3Fe2O, theabbreviationis C4AF


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Diffe

rentiatesC3S C2S C3A C4AF

C3S+

C2S

C3A+

C4AF

rota

rykiln

42

60

15

32

4

11

10

18

72

78

20

24

Inaddition,includeslitterfCaO,crystallizationmagnesia(MgO),

cholinergicbearingmineral,vitreousbodyandsoon..

Thesameasportlandcementclinker,buttherewillbequitedifferentsinthe

mainmineralcontent,becauseoftheproductionclinker'stechnologicalconditions

aredifferentorClinkerperformancerequirementsofthedifferentingredients

chosenbythedifferentprogrammes.

Thefourmajormineralshavetheirowncharacteristics,thuscalcinedclinker

andcementalsoaffectthequalityofagreaterdifference.

1C3SisthemostimportantmineralcompositioninPortlandcementclinker.Its

contentapproximatelycomposesthechamotteabove50%.IntheC3Scrystaloften

includesfewoxidecompoundsandsoonMgOandAl2O3,thesematerialsformthe

solidsolution,bynamedAlite,theabbreviationisAore.Addingwatertoreconcile

C3S,Thesettingtimeisnormal,Thehydratedisquickly,earlyinthehighintensity,

intensityprogressionrateisbig.Its28daysofintensities,1yearintensityishighestin

4kindofminerals,itsvolumeairshrinkageissmally,anditsfrostresistanceiegreat.

Therefore,wehopehavemoreC3Singredientsintheclinkertogenerally.Butits

hydrationheatishighly,thewaterresistingpropertyisbadly,antisulfateetching

powerisbadlytoo.Moreover,incalcineprocess,weneedsthehighlyfiring

temperatureandthelonglyfiringtimecanformtheC3S,thiscausesthechamotte

thecalcineoperationbecomesdifficultly.So,intheactualproductionwehasno

alternativebuttocutpursuestheC3Squantity,otherwiseharmfulingredientfCaO

willbetoincrease,Causestoreducetheclinkerquality.


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2WhenC2Sfunctionwithwater,thehydratedspeedisslowly,intensityislowly

inearlytime,buttheintensitystillfastergrowthafter28dayslater,itsmayapproach

C3Sayearlater.Itshydrationheatislowly,itdosenthavevolumeairshrinkage,the

waterresistingpropertyandtheantisulfateetchingpowerisstrong.Itsformation

temperatureislowingenerally,absoluteC2Seasytohavethemulticrystalseed

transformationbelowin1450 ,especiallywhenislowerthan500,when C2S

transformsinto C2S,itsdensityismoresmaller,activenessisverylow,andits

Volumeexpansion10%,Leadtotheclinkerdusting,andcausesthechamotte

intensitytoreducegreatly.Thiskindofphenomenonhappenedcomparativelymuch

inwhichverticalkilnproductionthatbadlyventilates,fewliquidphasequantity,the

reducingatmosphereismorethickerandcool(ing)downisslowly.Firingatahigher

temperature,rapidcoolingoftheclinker,asC2Sinthesolutionintoasmallamount

ofAl2O3Fe2O3MgO,usuallycanbemaintained .Thisiscalled C2SBelite,

theabbreviationisBore.

C3SandC2Sgenerictermissilicatemineral.Theclinkermainlycomposedof

them,theyoccupytheclinkeringredientabove70%,Istheclinkerintensity

importantsource.Portlandcement.ThisisthePortlandcementnameorigin.

3C3AAftercombinedwithwaterhydrationismorefasterthecongealment

hardeningisveryquickifdoesnotaddretardersandsoongypsum,easytocause

thecementflashset.Itsintensityishighinearlytimes,however,littlegrowthinthe

latterpartofintensity,evenshrinksbutactually.Itsheatofhydrationishigh,theair

shrinkagedistortsinabigway,theantisulfatecorrodesandthealkaliresistancetobe

bad..It'salsobrittle,poorwearresistance.InC3Amaymeltoxidecompoundsandso

onfewSiO2,Fe2O3,MgO.

4C4AFthehydratedhardeningspeedisquickly,thustheearlystrengthishigh,

isonlyinferiortoC3A..ItslongtermstrengthisalsohighlikeC3S,differentwithC3A.

It's

hydration

heat

low,

the

air

shrinkage

distortsu

is

small,

the

anti

impact

and

the

antisulfatecorrodestobegood.


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Infact,C4AFistheC2FC8A3continualsolidsolution,ingeneralinPortland

cementclinker,thiskindofcontinualsolidsolution'schemicalcomposition

approachesinC4AF,so,representsinthechamottebyC4AFthehardaluminate

mineral,IscalledonlythenRitter(Celite),orCore.Inthemineraldissolveshasfew

oxidecompoundsandsoonMgOSiO2.TheCoreassumesthewhiteunderthe

emittinglight,thereforeiscalledthewhiteintermediatephase.

C3AandC4AFandclinkerinthecompositionofthevitreousandvolatile

compounds,suchasalkalithenPackingbetweenC3SandC2Sarecalledforthe

intermediatephaseIntermediatephasecalcintocertaintemperatureinchamotte

fusestheliquidphaseLiquidisthereactionofthenecessaryconditionsforC3S

FormstheessentialmineralC3Sessentialcertainliquidphasequantityandthelow

liquidphaseviscosityTherefore,inordinarycircumstanceswemusthavecertain

quantityofC3AandC4AF,thusguaranteescertainliquidphasequantity;atthesame

timetheC3Aquantitycannotbeexcessivelymorenotonlythisconsideredthatit

somebadcharacteristicswhichrevealsinthehydratedprocessitalsoliesinthe

formationoflargeliquidviscositydoesnotfavoressentialmineralC3Sthe

productionOfcourse,tothegeneraltechnologicalconditions'cementkiln,has

certainamountC3Aregardingthekilnskin(revolvingfurnace)isalsonecessary..

3Clinkerratevalueandsignificance

Cementclinkerisacollectionofmanyfossils,Butthesemineralsarealso

combinedfromthemainoxidecompoundchemicalcombinations.So, Inproduction

control,weshouldnotonlytocontroltheclinkerintheoxidecontent,shouldalso

controltheoxiderateistheratiobetweenthevalue.Likethis,mayexpressbetween

thechemicalcompositionandthemineralconstituentrelationsquiteconveniently,

itscanexpressexplicitlytocementclinker'sperformanceandthecalcine

influence.So,inproduction,theratewasasaproductionvalueofthecontrolofa

target.

The

people

were

engaged

in

the

cement

production

the

experience

to

summarizethechamotteratethevalueforalongtime.Inthecontroloftheclinker


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productionratethanthevalueoftheabsolutecontroloftheoxideismoreimportant,

butalsomoreconvenient.Therateofrawmaterialisalsothebasisforthe

ingredients.Variouscountriesrecognizeseveralkindofcommonlyusedratevalue

formulashavefourkinds.

In1868,germanMishowEllisfirstproposedthehydraulicindex(Hydraulic

Modulus)takesthecontrolchamottebeingsuitablelimecontentacoefficient.

Calciumoxideandtheacidoxidesuminchamottemasspercentratio,indicatedby

HMorm.Itsformulaisasfollows:

32322 OFeOAlSiO ++=

CaOHM

Intheformula:CaO,SiO2 Al2O3 Fe2O3separatelyonbehalfofchamottein

variousoxidecompoundsmasspercent.

Usuallyhydraulicindexfluctuationbetween1.8~2.4.Theaboveequation

supposesthecalciumoxidequantitywhichvariousacidoxidesunifyisthesame,in

factwhenvariousacidoxidesproportionhasbeenchanged,althoughthesumtotal

wasinvariable,butneedsthecalciumoxidequantitynottobethesame..So,although

hydraulicindexcomputationissimply,ifonlycontrolsthesimilarhydraulicindex,thus

hasthedisadvantageousinfluencetothechamottequalityandthecalcine.Onlythen

simultaneouslycontrolsbetweenvariousacidoxidestheproportion,wecan

guaranteethechamotteingredientthestability

Afterward,keerproposedthatinthechamottebetweentheacidoxiderelates

ratethevalue,namely:Siliconrate,alsocallsthesilicamodulus,IndicatedbySMorn:

aluminumrate,alsocallstheIronModulusoraluminarate,IndicatedbyIMorp.Its

formula

is

as

follows:


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3232

2

OFeOAl

SiO)SM(n

+=

32

32)(OFe

OAlpIM =

Informula:CaO,SiO2 Al2O3 Fe2O3separatelyonbehalfofchamotteinvarious

oxidecompoundsmasspercent.

Usually,portlandcementclinkersiliconratebetween1.7~2.7,aluminumrate

between0.8~1.7.Somespeciessiliconratecanbeashighasabout4.0suchaswhite

Portlandcementclinker,buttheantisulfatecementorcementoflowheatof

hydration'saluminumratemaylowerto0.7.

Thesiliconrateisexpressesintheclinkerthesilicacontentandthealuminum

oxide,theferricoxidesumofmassratio,alsoexpressedthesilicatemineralandthe

meltingagentmineralproportionintheclinker.Whenthealuminumrateisbigger

than0.64,mathematicstypewhichandthemineralconstituentrelatesafterbetween

theinferentialreasoningsiliconrateis:

SM=C3S 1.325C2S

1.434C3A 2.046C4AF

Informula:C3S C2SC3A C4AFseparatelyonbehalfofchamotteinvarious

oxidecompoundsmasspercent.

Obviously,thesiliconrateoffluctuatesratioofalongwiththesilicatemineral

andthemeltingagentmineral..Ifthesiliconrateistoohigherintheclinker,when

calcine,becausetheliquidphasequantityobviouslyhasreducesd,thechamotte

calcineisdifficulties;Especiallywhenthecalciumoxidecontenttobelower,the

contentofcalciumsilicateishigher,theclinkeriseasytopulverizethesilicontolead


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excessivelylowly,thesilicatemineralaretoofewintheclinkerandaffectsthe

strengthofcement,becauseandtheliquidphasecontentisexcessivelyhigh,easyto

appearcongealsthebulk,theknotaccretions,theknotcircleandsoon,affectskiln's

operation.


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cement production basic knowledge-shang

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