Basic Cement Chemistry

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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
  • 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

Elemental Composition (weight – %)

raw meal

Chemical Composition

  • 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

L.o.I. (Loss on ignition) SiO2 Al2O3 Fe2O3 CaO MgO SO3 K2O Na2O TiO2 Mn2O3 P2O5 Cl F

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

Chemical Formula

  • 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)

Chemical Formulae

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

Mineralogical Composition

Composition of material, expressed in weight-percentage of the occurring minerals

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%

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%

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

Lime Saturation

LS=2.80 SiO2 + 1.18 Al2O3 + 0.65 Fe2O3 or

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.

Applied for:

Raw meal

Clinker

Cement:  neat OPC only

CaO = CaO(total) – 0.7 SO3

Usual range in clinker: 85 – 100

Note:  The influence of MgO can be accounted for

CaO + 0.75 MgO) x 100

Max. 2% MgO may be introduced in formula (not applied in cement specifications)

Silica Ratio

Al2O3 + Fe2O3

Applied for:

Siliceous-argillaceous raw   components

Raw Meal

Clinker

Cement

Usual range in clinker: 1.8 – 3.6

Alumina Ratio

ar

Applied for:

Siliceous-argillaceous raw   components

Raw Meal

Clinker

Cement

Usual range in clinker: 1 – 3

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

Moduli of Main Clinkers in Holcim group

Alumina Ratio - Silica ratio

Moduli of Main Clinkers

Lime Saturation - silica ratio

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.

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

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

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.)

  • 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%

Clinker Minerals as Function of LS

Clinker Minerals as Function of LS

Clinker Minerals as Function of SR

Clinker Minerals as Function of SR

Clinker Minerals as Function of SR

Clinker Minerals as Function of AR

Clinker Minerals as Function of AR

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Posted in Cement Chemistry, Cement chemistry, Process Engineering.

13 Comments

  1. I am Hendy Alheety director of quality control at the Kubaisa cement plant very interested in scientific bullentins and hop that I receive constantly …… thanks

  2. As per quality checks there are several factors involved in Cement chemist in that mainly Cement strength ex- for OPC – one day strength should be 18 to 20 MPA A as per BIS (Bureau of Indian standard) for 7 days it should be 46 to 48 MPA and for 28 days it should be 53 MPA minimum etc

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