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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
MANUFACTURE OF PORTLAND CEMENT
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
CHEMICAL AND MINERALOGICAL COMPOSITION OF CLINKER
GRINDING OF CEMENT
RAW MATERIALS
MANUFACTURE OF PORTLAND CEMENT
BURNING OF PORTLAND CLINKER
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
BURNING OF PORTLAND CLINKER
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
MANUFACTURE OF PORTLAND CEMENT
CHEMICAL AND MINERALOGICAL COMPOSITION OF CLINKER
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
MANUFACTURE OF PORTLAND CEMENT
FIRING OF PORTLAND CLINKER
CHEMICAL AND MINERALOGICAL COMPOSITION OF CLINKER
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 (%)
CHEMICAL AND MINERALOGICAL COMPOSITION OF CLINKER
GRINDING OF CEMENT
RAW MATERIALS
MANUFACTURE OF PORTLAND CEMENT
FIRING OF PORTLAND CLINKER
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.
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