Basic Cement Chemistry by .pdf

Cement Course 2002
Basic Cement Chemistry
Henry Salazar

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Cement Course-Chemistry.ppt
Holcim Group Support Basic Cement Chemistry
Learning Objectives
▪ Know the meaning and the way of presentation of
chemical and mineralogical composition of cement
specific materials
▪ Know the chemical moduli applied for cement specific
materials
▪ Know the Bogue-calculation for clinker mineral phases
and the relationship with chemical moduli

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Basic Cement Chemistry
▪ Chemical Composition
▪ Chemical Formulae
▪ Mineralogical Composition
▪ Chemical Parameters for Cement-Specific Materials
▪ Contents of Clinker Minerals According to Bogue
▪ Relationship between Chemical Moduli and Clinker
Mineral Contents
▪ Exercise for Calculation

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Elemental Composition (weight - %)
Raw Meal
O 48.4 K 0.52
Ca 30.0 Na 0.16
C 9.5 S 0.10
Si 6.7 Ti 0.10
Al 1.9 Mn 0.07
Fe 1.4 H 0.04
Mg 1.1 P 0.03
Cl 0.01

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Chemical Composition
L.o.I. (Loss on ignition)
SiO2
Al2O3
Fe2O3
CaO
MgO
SO3
K2O
Na2O
TiO2
Mn2O3
P2O5
Cl
F
Raw Mix
35.1
14.3
3.6
2.0
42.0
1.8
0.25
0.63
0.22
0.17
0.10
0.06
0.01
Total 100.24
▪ Elemental composition in
weight percentage.
By convention, the
elements are expressed
in form of their oxides
(exception; Cl, F).
▪ Usual sequence of
elements in cement
chemistry
▪ L.o.I.: e.g. at 1050 °C,
mainly due to CO2 and
H2O

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Chemical Composition - Examples
Limestone Clinker
L.o.l. 42.2 0.24
SiO2 1.9 22.7
Al2O3 0.81 5.7
Fe2O3 0.52 1.9
CaO 55.2 66.0
MgO 1.4 2.0
SO3 0.56 0.33
K2O 0.22 0.74
Na2O 0.08 0.09
TiO2 0.05 0.18
Cr2O3
Mn2O3 0.02 0.03
P2O5 0.01 0.05
Cl 0.01 0.01
F

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Chemical Formulae
▪ The chemical formula indicates the elements occurring in a
chemical compound:
 For a molecular compound, type and absolute number of
elements are given
H2O O2 C6H6
Water Oxygen Benzene
 For a mineralogical compound, type and relative number of
elements are given
SiO2 CaO CaCO3 Ca3SiO5
Quartz Lime Calcite Alite
Note: In mineralogical compounds, the elements need not
necessarily occur in simple numerical ratios (impurities,
solid solution)

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 In the cement chemistry, shorthand's are often used:
CaO SiO2 Al2O3 Fe2O3 SO3 H2O
C S A F S H
Examples:
C3S for Ca3SiO5 (Alite)
C2S for Ca2SiO4 (Belite)
C3A for Ca3Al2O6 (Aluminate)
C4AF for Ca4Al2Fe2O10 (Ferrite)
Chemical Formulae

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Mineralogical Composition
Composition of material, expressed in weight-percentage of the
occurring minerals
Examples:
Limestone Calcite CaCO3 90%
Dolomite CaMg(CO3)2 5%
Quartz SiO2 5%
Clinker Alite C3S 58%
Belite C2S 23%
Aluminate C3A 9%
Ferrite C4AF 7%
Periclase MgO 1%
Arcanite K2SO4 1%
Free lime CaO 1%

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Mineralogical Composition
Note: Difference between chemical and mineralogical
composition
Pure dolomite rock
Mineralogical composition: Chemical composition:
Dolomite CaMg(CO3)2: 100% L.o.l. (CO2): 47.7%
CaO: 30.4%
MgO: 21.9%

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Chemical Parameters for Cement-Specific Materials
Titration
Content of carbonates as determined by acid-base
titration, expressed as CaCO3
% Titration = 1.786 CaO + 2.48 MgO
Applied for: Limestone
Marl
Raw Meal

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Lime Saturation
LS =
2.80 SiO2 + 1.18 Al2O3 + 0.65 Fe2O3
or
LSF =
CaO x 100
CaO
2.80 SiO2 + 1.18 Al2O3 + 0.65 Fe2O3
The LS is a measure to which extent the CaO-richest compounds
C3S, C3A and C4AF can be formed without the necessary presence of
free lime. At LS > 100, free lime will unavoidably be present after
burning.

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Lime Saturation
Applied for: Raw meal
Clinker
Cement: neat OPC only
CaO = CaOtotal – 0.7 SO3
Usual range in clinker: 85 – 100
Note: The influence of MgO can be accounted for
LS =
Max. 2% MgO may be introduced in formula (not applied in cement
specifications)
(CaO + 0.75 MgO) x 100
2.80 SiO2 + 1.18 Al2O3 + 0.65 Fe2O3

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Silica Ratio
SR =
SiO2
Al2O3 + Fe2O3
Applied for: Siliceous-argillaceous raw
components
Raw Meal
Clinker
Cement
Usual range in clinker: 1.8 – 3.6

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Alumina Ratio
AR =
Al2O3
Fe2O3
Applied for: Siliceous-argillaceous raw
components
Raw Meal
Clinker
Cement
Usual range in clinker: 1 - 3

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Na2O-equivalent
Total alkali content, expressed as Na2O
Na2O-equivalent = Na2O + 0.658 K2O
Note: Limit for low alkali cement
Na2O-equivalent < 0.6 %
Applied for: Clinker
Cement

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Moduli of Main Clinkers in Holcim group
Alumina Ratio
Silica Ratio

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Moduli of Main Clinkers in Holcim Group
Lime
Saturation
Silica Ratio

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Content of clinker Minerals according to Bogue
▪ Percentage content of clinker minerals, assuming that
chemical equilibrium is attained, and that no impurities
are present.
C3S = 4.07 CaO – 7.6 SiO2 – 6.72 Al2O3 – 1.43 Fe2O3
C2S = 8.6 SiO2 + 5.07 Al2O3 + 2.08 Fe2O3 - 3.07 CaO
or 2.87 SiO2 – 0.754 C3S
C3A = 2.65 Al2O3 – 1.69 Fe2O3
C4AF = 3.04 Fe2O3
In reality, the mineralogical composition of industrial
clinkers differs to some extent from that calculated
according to Bogue.

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Contents of Clinker Minerals according to Bogue
Applied for Cement - OPC only (excl. blended cements)
- Correction for CaO in CaSO4:
CaO = CaOtot – 0.70 SO3
- For AASHTO: TiO2 and P2O5 to be
added to Al2O3 (no longer for ASTM)
Clinker - CaO can be corrected for free
lime; depending on objective of
calculation
CaO = CaOtot – CaOfree

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Significance of Clinker Minerals for Cement Properties
▪ C3S Contributes to early and late strength (1 d - …)
Increases heat of hydration
▪ C2S Contributes to late strength (28 d - …)
▪ C3A Contributes to early strength (1 – 3 d) Increases
heat of hydration
Impairs resistance to sulphate attack
▪ C4AF Little effect

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Significance of Clinker Minerals for ASTM Cement Types
▪ Type I Portland no restrictions regarding clinker
minerals
▪ Type II Portland with moderate sulphate resistance
(and moderate heat of hydration)
C3A max. 8 %
(C3S + C3A max. 58% for moderate
heat of hydration)
▪ Type III Portland with high early strength
C3A max. 15%
(C3A max. 8% for moderate sulphate resist.
C3A max. 5% for high sulphate resist.)

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Significance of Clinker Minerals for ASTM Cement Types
▪ Type IV Portland with low heat of hydration
C3S max. 35%
C2S min. 40%
C3A max. 7%
▪ Type V Portland with high sulphate resistance
C3A max. 5.0 %
C4AF + 2 C3A max. 25%
or
C4AF + 2 C2F max. 25%

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Clinker Minerals as Function of LS

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Clinker Minerals as Function of SR

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Clinker Minerals as Function of AR

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Exercise for Calculation
Raw Mix Potential clinker composition
L.o.I. 35.1 ………
SiO2 14.3 ………
Al2O3 3.6 ………
Fe2O3 2.0 ………
CaO 42.0 ………
MgO 1.8 ………
SO3 0.25 ………
K2O 0.63 ………
Na2O 0.22 ………
TiO2 0.17 ………
Mn2O3 0.10 ………
P2O5 0.06 ………
Cl 0.01 ………

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Exercise for Calculation
Raw Mix Potential clinker composition
Titration ………
LS ……… ………
SR ……… ………
AR ……… ………
Na2O-equiv. ………
C3S ………
C2S ………
C3A ………
C4AF ………

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