Stud l6-1-cement-manufacture

The name "cement" goes back to the Romans who used the term "opus caementitium" to describe masonry which resembled concreteand was made from crushed rock with burnt lime as binder. Thevolcanic ash and pulverized brick additives which were added to theburnt lime to obtain a hydraulic binder were later referred to as cementum, cimentum, cäment and cement. Cements used in construction are characterized as hydraulic or non-hydraulic.

CEMENT

Examples of concrete constructions

Viaduct de Millau, France

reinforced concretesteel

Large Infrastructure Great Belt, Denmark

The Øresund bridge

History of Portland Cement

In 1824, Joseph Aspdin, a British stone mason, obtained a patent for a cement.

He heated a mixture of finely ground limestone and clay in stove and ground the mixture into a powder.He created a hydraulic cement - that hardens with the addition of water.

Aspdin named the product portland cement because it resembled a stone on the Isle of Portland, British Coast. With this invention, Aspdin laid the foundation for today's portland cement industry.

„Cement is a hydraulic binder, i.e. a finely ground inorganic material which, when mixed with water, forms a paste which sets and hardens by means of hydration reactions and processes and which, after hardening, retains its strength and stability even under water.“

„Cement conforming to EN 197-1, termed CEM cement, shall, when appropriately batched and mixed with aggregate and water, be capable of producing concrete or mortar which retains its workability for sufficient time and shall after defined periods attain specified strength levels and also possess long-term volume stability.“

Definition – part cited from European standard EN 197-1:

CEMENT

CEMENT (Portland cement and blended cements)

• is finely ground inorganic material

• is hydraulic binder. It sets and hardens by reactingchemically with water and is able to harden under water.

Setting and hardening is due to hydration reactions ofcompounds of cement (mainly calcium silicates, also calcium aluminates and -alumino ferites) with water. This is called hydraulic hardening.

• hardened cement paste (cement + water) is stable in water.

• cement paste acts as adhesive when is mixed with sand andaggregate (gravel,crushed rocks). Hardened cement paste - binds the particles of sand - CEMENT MORTAR- binds fine and coarse agregate - CONCRETE

Prepared cement concrete or mortar after mixing shall beworkable for sufficient time.

• CEM I Portland cement• CEM II Portland-composite cement• CEM III Blastfurnace cement• CEM IV Puzzolanic cement• CEM V Composite cement

COMMON CEMENTSCovered by European standard (STN) EN 197-1

EN 197-1 covers five main types of cement:

Blendedcements

PORTLAND CEMENT

PORTLAND CEMENT- is finely ground hydraulic binder

Portland cement clinker - is composed primarily of- calcium silicates- calcium aluminates and - calcium alumino-ferites

Main constituent:

It is produced by pulverizing clinker with calcium sulfate and eventually other compounds.

Calcium sulfate - usually gypsum (CaSO4.2H2O), or(3-5 %) - hemihydrate (CaSO4.1/2H2O), or

- anhydrite (CaSO4), oracts as set retarder - mixture of them

Set controlling admixture: controls setting of cement

CHEMICAL AND MINERALOGICAL COMPOSITION OF CLINKER

GRINDING OF CEMENT

RAW MATERIALS

MANUFACTURE OF PORTLAND CEMENT

BURNING OF PORTLAND CLINKER


Limestone

Mining (quarrying) of raw materials

Clay, shale, marl

grinding, blending, correctioning of composition of raw materials

burning (sintering) a raw mixture up to 1450oC into clinker - in cement kilns (mainly rotary kilns)

cooling of clinker - in a cooler

grinding of clinker with gypsum into cement

quality control of cement, packing and expedition

Iron ore

SCHEME OF DRY PROCESS

corrections

Argilaceous materials

quarry

crusher

conveyer

homogenizationand storage

Preheater (or precalciner) tower

grinding mill

Rotary kilncooler

Manufacture of cementAccording: Holcim Rohožník

F.PEŤKO, T.VINICKÝ , J. PETLUŠ

1450 oC

Limestone

Clay-pit:mining of clay

Burning of clinker

Grinding of clinker with gypsum and/or other materials to cement

Clinker silo (clinker storage)rotary ball mill

grinding of cement

cement silos

expedition

Clinker from the kiln

finely ground material

limestone

CaCO3 (MgCO3)Al2O3.2SiO2.2H2O

e.g. kaolinite

CaO (MgO) SiO2, Al2O3, Fe2O3

clay, shale....

Hydraulic oxides

marlSiO2 -quartz sandFe2O3 – iron oreAl2O3 - bauxite

RAW MIXTURE MIXTURE must have suitable chemical composition

ADDITIONAL (corrections)

32322 ++=

OFeOAlSiOCaOHM

HM = 1,9 - 2,4

RAW MATERIALS FOR PRODUCTION OF CLINKER

MAIN RAW MATERIALS

Generally, raw materials consist of combinations of limestone, shale, clay, sand, or iron ore. Most are mined from a quarry near the plant

Evaluated by hydraulic modulus

32322 ++=

OFeOAlSiOCaOHM

hydraulic modulus:HM = 1,9 - 2,4

3232

2+

= OFeOAlSiOSM

32

32= OFeOAlAMaluminate modulus

AM = 1,5 - 3,0

(chemical formulae represent weight percentages):

To evaluate suitable composition of raw materials mixture (clinker) - the values of following modules (parameters) are used

COMPOSITION OF MIX OF RAW MATERIALS

silicate modulusSM = 1,7-3,5

Oxide composition in raw materials for clinker is usually about

CaO MgO SiO2 Al2O3 Fe2O3 Na2O + K2O SO3

62-67 0,5-4 18-24 3-8 1,5-4,5 0,4 - 1,2 1,3

Limestone quarry – fy. Cement Hranice, a.s.

http://geologie.vsb.cz/loziska/suroviny/anorganicka_pojiva.html

Transport of limestone from a quarry

HOMOGENIZATION OF RAW MATERIALS

• limestone

• clay, shale

Correction of compositionof raw mix


GRINDING OF CEMENT

RAW MATERIALS



homogenizationand storage

Preheater (or precalciner) tower

grindingmill Rotary kiln

cooler

F.PEŤKO, T.VINICKÝ , J. PETLUŠ

1450 oC

Cyclones usewaste heat (air)

from the kiln

Clinkering zone

Burning of raw mixture in cement kilnsinto Portland clinker

Output ofclinker

Rawmix is fedinto preheater

Fig. According: Holcim Rohožník


CLINKER is made by burning of raw mixture in cement kilns

Rotary kilns Shaft kilnsBurning temperatureMax. 1450 °C

Process: dry (wet is not used today)

FUELS: pulverised coal, petroleum coke, waste oil, natural gas, spent tyres,

Steel tube - refractory lined Slope: 1 - 4°Length: 40 - 200 mDiameter: 3 - 7 mRotation: about 1 revolution / minRawmix is fed at the upper end and slowly moves downhill toward burner (counterflow movement)

Czech republic

Fuel used in cement

production

Coal

Other solid fuelsUsed tyres

RAW MATERIALS COMPOSITION



Portlandclinker

FIRING OF PORTLAND CLINKER

Burning changes raw mix into cement clinker. Produktsof reactions that compose Portland clinker are

• High-temperature reactions taking place in the kiln

CaO SiO2 Al2O3 Fe2O3

CaCO3 → CaO + CO2

Al2O3.2SiO2.2H2O → Al2O3.2SiO2 + 2H2O

• Decomposition of some raw materials(limestone, kaoline clay) in the preheater or the kiln

≤ 1450 °C

≤ 800 °C

PROCESSES DURING BURNING OF CLINKER

about 25 percent of the raw material mixture melts (partial fussion)

Minerals (compounds): Calcium silicates, calcium aluminates, and – alumino ferites

High-temperature reactions at clinker burning

2CaO + SiO2 → 2CaO.SiO2

2CaO.SiO2 + CaO → 3CaO.SiO2

CaCO3 → CaO + CO2

(CaCO3)CaO SiO2 + Al2O3 + Fe2O3

3CaO.SiO2

2CaO.SiO23CaO.Al2O3

4CaO. Al2O3.Fe2O3

3CaO + Al2O3 → 3CaO. Al2O3

4CaO + Al2O3 + Fe2O3 → 4CaO. Al2O3. Fe2O3

900 °C

≤ 1200 °C

1200 - 1450 °C

• 100-200°C - evaporation of physical water• 200-600 °C – releasing of water from clay minerals (dehydroxylation)• 600-800 °C – decomposition of MgCO3, formation of CA, C2F (C2S)• 800-900 °C – decomposition of CaCO3 (free CaO)• 900-1100 °C - formation and decomposition of C2AS,

- begining of formation of C3A and C4AF,- maximum content of free CaO (unbound)

•1100-1200 °C - most of C3A and C4AF is formed, - maximum content of C2S

• 1260 °C - occurs first partial fussion (melted material)• 1200-1450 °C - C3S forms

and content of free CaO therefore decreases

PROCESSES AND REACTIONS DURING BURNING OF CLINKER

CaO + 2SiO2→ 2CaO.SiO2

2CaO.SiO2 + CaO → 3CaO.SiO2

Informative scheme

Impure limestone, limestone-marl

Calcite Clay minerals

CaCO3 SiO2 + Al2O3 + Fe2O3 - CaO (free, quicklime)- calcium silicates (C2S)- calcium aluminates- calcium alumino-ferites

Hydraulic lime (naturalhydraulic lime)

COMPARRISON: HYDRAULIC LIME - PORTLAND CEMENT

burning

HYDRAULIC OXIDES

+

CaO CO2

1250 °C

Limestone + clay, shale

Calcite clay minerals

CaCO3 SiO2 + Al2O3 + Fe2O3- calcium silicates (C2S, C3S)- calcium aluminates (C3A)- calcium alumino-ferites

Portland clinkerburning

HYDRAULIC OXIDES

+

CaO CO2

1450 °C

almost any free CaO

Marl, limestone-marl

BURNING OF CLINKERRotary kiln

Mov

emen

t of c

linke

r

(raw

mat

erial

s)

Burner

Clinkerleavingthe kiln

Edison – patent 1905

Portland cement clinker

Clinker is discharged red-hot from the lower end of the kiln andtransferred to coolers to lower the clinker temperature

COOLING OF CLINKER

RAW MATERIALS




tricalcium silicate 3CaO.SiO2 (C3S)dicalcium silicate 2CaO.SiO2 (C2S)tricalcium aluminate 3CaO.Al2O3 (C3A) tetracalcium aluminoferite 4CaO.Al2O3.Fe2O3 (C4AF)

ALITE

BELITE

CELITE

Optical microscope imageof clinker minerals(polished sections)

Brown crystals - alite

blue crystals - belite

bright interstitial material - ferrite

small dark inclusions of aluminate

MAIN MINERALS IN PORTLAND CLINKER

http://www.understanding-cement.com/clinker.html

Is used to simplify the formulas are used mainly in chemistry ofcement. It is used for „short hand“ way of writing the chemicalformula of some oxides and water.

List of the abbreviations used:

ActualFormula

Abbr. ActualFormula

Abbr. ActualFormula

Abbr.

CaO C MgO M

KAT

H

SiO2 S K2O

H2O

CO2

SO3Al2O3 A Na2OFe2O3 F TiO2 - -

Conventional cement chemist notation

Examples: • 2CaO.SiO2 ≡ C2S; • Ca(OH)2 ≡ CH • 3CaO.Al2O3.13H2O ≡ C3AH13

tricalcium silicate 3CaO.SiO2 (C3S)

dicalcium silicate 2CaO.SiO2 (C2S)

tricalcium aluminate 3CaO.Al2O3 (C3A)

tetracalcium aluminoferite 4CaO.Al2O3.Fe2O3 (C4AF)

MAIN MINERALS IN PORTLAND CLINKER

ALITE

BELITE

CELITE

2CaO(Al2O3,Fe2O3)

Main products of high-temperature reactions in the kiln

C2(A,F)

CaO MgO SiO2 Al2O3 Fe2O3 Na2O + K2O SO3

62-67 0.5-4 19-24 4-8 1.5-4.5 0.4 – 1.1 0,3 - 1

3 CaO.SiO2 C3S 45 - 60 %2 CaO.SiO2 C2S 15 - 30 %3 CaO.Al2O3 C3A 3 - 15 % 4CaO.Al2O3.Fe2O3 C4AF 10 - 20 %free lime < 1.5 (2) %High content of unreacted oxides (CaO, MgO) can causeexpansion of cement (unsoundness) and affect setting time.- result of insufficient burning and high content of lime in clinker

CHEMICAL COMPOSITION OF PORTLAND CLINKER (%)

Dominantphases

MINERALOGICAL COMPOSITION OF PORTLAND CLINKER (%)


GRINDING OF CEMENT

RAW MATERIALS



Rotary ball millClinker

+ Gypsum

Portland cement

2.5-5 %

A 10 MW cement mill, producing cement at270 tonnes per hour. Wikipedia

GRINDING OF CEMENT

Fired clinker

Steel balls in the mill

GRINDING OF CEMENT AND DISPATCH

Clinker and 2,5-5 % of gypsum (or also other components) are finelyground together in rotary ball mills to form final cement product.- particles size of ground cement vary mostly from 1 - 200 μm (200 μm)

- blended cements contain, besides clinker and gypsum, also latenthydraulic or pozzolanic constituents

- cement is stored in an bulk silo until needed by the customer

Fineness of ground cement is evaluated by its specific surface. > 220 m2/kg according air permeability Blaine method

Fineness of cement affects almost all important properties of cement

- in bulk - by trucks, rail, or barge- in bugs - baged cement

www.gassmann-gmbh.com/frames.php?sprache=en

Expedition /dispatch of cement

Dispatch of cement

Výrobcovia cementu na Slovensku

1 - HOLCIM, a.s. Rohožník

2 - CEMMAC, a.s. Horné Srnie

3 - Cementáreň Turňa, a.s. Turňa nad Bodvou

4 - Považská cementáreň, a.s. Ladce

5 - Stredoslovenská cementáreň Banská Bystrica, a.s.

6 - ZEOCEM, s.r.o. Bystré

SETTING AND HARDENING OF PORTLAND CEMENT

(Cement mortars and concrete)

Hydration of clinker minerals

Reaction of cement with water

Setting and hardening

Release of heat

Structure development

SETTING AND HARDENING OF PORTLAND CEMENT

Is due to chemical reactions of cement with water

- consistency (fluidity) remains nearly constant for some time- mixture can be cast (placed) into different shapes

setting starts (initial set) 2 and 3 hours after mixingsetting develops until final set is obtainedhardening (strength gain) starts after final setstrength gain continues a long time with decreasing speed

Cement paste or slurry- is obtained by mixing of cement and water

Setting and hardening of cement paste

is stiffening of cement paste without significant development of compressive strength.

It typically occurs within a few hours.

Setting

Hardening is significant development of compressive strength

It is normally a slower processLea: p.113

- the reaction of cement with waterHydration of cement

chemical reaction accompanied by heat release

Hydration of cement is exotermic reaction

Exotermicreaction

definitions

Consistency

Strength development during hardening of cement paste C

ompr

essi

ve s

treng

th

[MP

a]

Time [days]

Strength development

Hydration of clinker minerals in cement paste is slow:e.g. 3 μm after 7 days → strength increses gradually

Hydration of cement grains with different size

Rate of heat evolution

Cement hydration

Contribution of Portlandcement minerals to strength of cement

(after Bogue and Lerch)

Cement hardening

setting → hardening

Reaction of cement with water (hydration of cement)

C3S C2S

C3A

C4AF

+ H2O

CaSO4.2H2O

Ca(OH)2 (portlandite)

3CaO.2SiO2.3H2O (CSH-gel)

3CaO.Al2O3.3CaSO4.32H2O

3CaO.Al2O3.CaSO4.12H2O4CaO.Al2O3.13H2O(3CaO.Al2O3. 6H2O)

gypsum

clinker

regulates the rate of setting

≅ 23 %

Cement + water → main hydration products

Calcium aluminate hydrates

Hydration of C3S a C3Sformation of hydrated reaction products

2(3CaO.SiO2) + 6H2O → 3CaO.2SiO2.3H2O + 3Ca(OH)2

2(2CaO.SiO2) + 4H2O → 3CaO.2SiO2.3H2O + Ca(OH)2

Calcium silica hydrates CSH gel or (C-S-H phase)

imperfect crystals, gel structure coloidal dimensions (1 - 500 nm)large surface area main contribution to strengthvery low solubility (hydrolysis)

Idealized ratio of CaO : SiO2 : H2O

Calcium hydroxide

relative large crystals low strength solubility 1.5 g/Leasily carbonatize

Ca(OH)2 + CO2 → CaCO3 + H2O

Main reaction products are:- calcium aluminate hydrates (C4AH13 or C4AH19, C3AH6) - complex calcium aluminate sulfate hydrates (ettringite, monosulfate)

1. Ettringite (trisulfate) forms by hydration of C3A in the presence of CaSO4(e.g.gypsum). Reaction takes place at beginning of hydration of cement.

3CaO.Al2O3 + 3 CaSO4 + 32 H2O → 3CaO.Al2O3.3CaSO4.32H2O

2(3CaO.Al2O3) + 3CaO.Al2O3.3CaSO4.32H2O + 4 H2O →→ 3(3CaO.Al2O3.CaSO4.12 H2O)

3CaO.Al2O3 + Ca(OH)2 + 18 H2O → 4CaO.Al2O3.19H2O

Hydration of C3A (similarly also C4AF)

2. After gypsum is consumed, C3A reacts with ettringite to form monosulfate:

3. Later C3A reacts with water to form mostly tetra calcium aluminate hydrate

Ca(OH)2 is formed at hydration of calcium silicates

Tricalcium silicate, C3S: • hydrates rapidly• strongly contributes to early and final strength of cement pastes • has high heat of hydration: (670 kJ/kg)

Dicalcium silicate, C2S: • hydrates slowly• strongly contributes to strength at later ages (> 1 week). • increases chemical resistance of cement• has low heat oh hydration: (350 kJ/kg)

Characteristic of clinker minerals – during hydration

Tricalcium Aluminate, C3A: • hydrates very rapidly; • contributes slightly to early strength development. • reduces chemical resistance of cement to sulfates (soils, waters) (low percentage of C3A is required for sulfate resisting cement).• large heat of hydration: (1060 kJ/kg), rapid during the first few days

Tetracalcium Aluminoferrite, C4AF: It contributes little to strength. (iron and aluminum in raw mixture reduce the clinkering temperature during clinker manufacture) and gives cement its gray color (Fe).Low heat of hydration:

STRUCTURE AND COMPOSITION OFHARDENED CEMENT PASTE

Hardened cement paste (HCP) is composed of:

• Pores in HCP are partially filled with pore solution. • Pore solution is saturated solution of Ca(OH)2

it contains also NaOH and KOH• pH is about 13 -13,5 (from PC; lower from blended cements)

• interlocked hydration products of cement (portlandite, C-S-H gel, hydrated calcium aluminates and - alumino ferites)

• unhydrated residual cement grains

• pores of various dimensions (characterized by pore size distribution)• gel pores in CSH gel < 3 nm• capillary pores -space between hydrating grains 10 nm – 1 000 nm• air pores or air voids > 50 μm up to about 2 mm.

Pore solution in hardened cement paste (HCP)

Soroka, 1979

Simplified scheme of hydrated cement paste microstructure

3. Capillary pores (capillarywater)

1. Unhydrated cement

2. C-S-H gel containing gelpores (interlayer water)

4. Hexagonal crystals of calciumhydroxide (portlandite)

Gel (or interlayer) pores havesize of 0.5-2.5 nm and occupyabout 28 vol. % of C-S-H gel

Capillary pores can have sizesfrom 10 to 1000 nm (1 μm) and even up to 5 μm. Volume and size depends on water/cement ratio and degree of hydration

Feldman-Sereda model for themicrostructure of C-S-HBlack lines: C-S-H sheet, Circles: Adsorbed water, Crosses: Interlayerwater

The flaky C-S-H crystalsgrown after 2 weeks ofhydration of C3S (W/C=0.8).The stoichiometric C/S ratio of C-S-H and morphology of its crystals in conventional cement systems dependon the curing condition.

http://www.cementlab.com/cement-art.htm

© 2010 Rouhollah Alizadeh, all rights reserved

Hydrated cement paste microstructure

C-S-H

7. Mehta, P.K. "Concrete Structures Properties and Materials", Prentice Hall, 19868. Feldman, F., and P.J. Sereda, Eng. J.. Vol 543, No. 8/9, 1970

Capillary pore in hydratedcement paste (8)The transition zone (Ref 7)

Simplified scheme of hydrated cement paste microstructure

Schematic representation of volumetric proportions in cement paste before and during hydration

Microstructureof cement paste

Influence of the water/cement ratio on the distribution of pore size in hydrated cement paste

40-60 %

50-70 %Portlandcement

Ions [mol/dm3]

Na+ + K+ 0,2 - 1

OH- 0,2 - 1

Ca2+ ≅ 0,001

SO42- 0,02

pH 13,4 - 14

Pore solution

0

0,01

0,02

0,03

0 0,4 0,8 1,2 NaOH (mol/l)

Ca2+

(mol

/l)

Na2OK2O

[ ] [ ]K Ca OHs = ±+ −γ 3 2 2

Solubility of Ca(OH)2 in the presence alkalies

CHEMICAL COMPOSITION OF PORE SOLUTION

Composition of pore solution is of prime importance for chemical properties of cement composites. Although solubility of Ca(OH)2 in water is about 0.02 mol.dm-3 at 20 °C and the pH value of saturated solution is about pH 12.5; these parameters are substantially affected by alkali metals. Alkali metals are released from cement during its hydration. Because they do not take part in the composition of the major cement hydration products they accumulate in the pore solution forming Na+, K+

and OH− ions, respectively. Increase in OH− ion concentration reduces significantly solubility of Ca(OH)2.

Pore solution in cement based composites therefore contains relatively high concentration of Na+, K+ and OH- ions (up to 1 mol.dm-3), but concentration of Ca2+ and also SO4

2- is considerably lower, for Ca2+ is often only about 1 mmol.dm-3. The pH-value of the pore fluids in cement composites (containing alkali metals) may well be greater than pH 12.5 in the case of Portland cement the pH can prevail pH 13.5.

Thank you

Stud l6-1-cement-manufacture

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