Everything you need to know about Cements – Composition, Types

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Cements – Composition, Types


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? Finish up cement manufacture
? Properties of component phases
? Types of cements

Summary of Kiln Reactions


? Clinker is what comes out of the kiln
? 3 to 25 mm in diameter
? 20-25% Molten

Compound Composition of Clinker / Cement

? Four major compounds formed from the oxides under high temperature in the kiln
? Name (Oxide Notation) – Shorthand
? Tricalcium silicate (3 CaO. SiO2) – C3S
? Dicalcium silicate (2 CaO. SiO2) – C2S
? Tricalcium aluminate (3 CaO. Al2O3) – C3A
? Tetracalcium aluminoferrite (4 CaO. Al2O3. Fe2O3) – C4AF

Summary of Cement Compounds

Implications of compound composition

? Determines the physical and mechanical characteristics of the cement
? Determines its chemical activity
? Determines its scope of use
? Determines the cost

Contributions of Compounds to Strength

C3S contributes to high early strength – tomake high early strength concrete, higher
C3S proportions needed

C2S contributes to later age strength –defines the long term strength

C3A reacts immediately with water – defines set

In the absence of gypsum, C3A causes flash set

Compressive strength development of pure cement compounds

? C3A reacts instantaneously
? Final strength determined by C3S and C2S
? Increase C3S for high early strength

Making Life Harder – I

? Remember the compound name, oxide notation, and the shorthand notation…
? Just to make sure that cement and concrete is complicated, tricalcium silicate in its impure form in clinker is historically called Alite
? Even more complication arises – various crystalline polymorphs of tricalcium silicates exist
? Similar troubles for other compounds also

Making Life Harder – II

? Not all cement components can be expressed by the oxide formulae and shorthand notation
? Chlorides, Fluorides etc
? Expressed using normal chemical formulae
? Mineral names are commonly used for raw materials (calcite, quartz) and for some cement hydration products (ettringite, portlandite etc)

Beware of “LIME”

? Be clear what you mean when you say
? “Lime” can be used for CaO, either by itself or in combination with other components
? “Lime” can be used for Calcium hydroxide (also called portlandite, abbreviated as CH)
? “Lime” is sometimes used for limestone rock or its major chemical component calcium carbonate

Manufacturing control criteria in the Kiln

Bogue’s Equations – Compound composition

To calculate the amounts of C3S, C2S, C3A, and C4AF in clinker (or the cement) from its chemical analysis (from the mill certificate)

? Assumptions in calculations
? Chemical equilibrium established at the clinkering temperature
? Components maintained unchanged through the rapid cooling period
? Compounds are “pure”

Bogue’s Equations

? Case 1 : A/F >=0.64
? C3S = 4.071C – 7.6S – 6.718A – 1.43F – 2.852S
? C2S = 2.867S – 0.7544C3S
? C3A = 2.65A – 1.692F
? C4AF = 3.043Fv

? Case 1 : A/F >=0.64
? C3S = 4.071C – 7.6S – 6.718A – 1.43F – 2.852S
? C2S = 2.867S – 0.7544C3S
? C3A = 2.65A – 1.692F
? C4AF = 3.043F

Clinker components and Temperature

Summary of Kiln Reactions

Clinker Microstructure

SchematicMill of a Grinding 

Grinding Mill


Fineness of cement

? Grinding is the last step in processing
? Measures of fineness
? Specific surface
? Particle size distribution
? Blaine’s fineness
? Measure of air permeability
? Typical surface areas
? ~ 350 m2 / kg (Normal cements)
? ~ 500 m2 / kg (High early strength cements)

PSD of cement


Significance of fineness

? Finer cement = Faster reaction
? Finer cement = Higher heat of hydration
? Large particles do not react with water completely
? Higher fineness
? Higher shrinkage
? Reduced bleeding
? Reduced durability
? More gypsum needed

Summary of the Cement Making Process

Some practical issues about cement making

? Scale of the business (local / national)
? Plant operations
? Wet versus Dry process
? Energy savings – Preheaters, Dust
? Energy and fuels
? Environment

The economics of cement making

? Transportation costs – when shipped further than ~ 200 miles
? About 175 plants nationwide
? Cost of maintenance – plant and the environment
? Rising fuel costs – raw material quality and fuel dependence
? Continuous operability

Portland Cement Types (ASTM C 150)

? ASTM C 150 (AASHTO M 85)
? 5 types in general – types I to V
? Type I – Normal (OPC)
? Type II – Moderate Sulfate Resistance
? Type III – High early Strength
? Type IV – Low heat of hydration
? Type V – High Sulfate Resistance
? Chemical compositions different

Other special Types

? Not very commonly used or manufactured
? Type IA – Normal (OPC) – air entraining
? Type IIA – Moderate sulfate resistance –air entraining
? Type IIIA- High early strength – air entraining

Typical Compositions

Applications of Type- I cement

Applications of Type II and IV



? Type of cement is no guarantee against other bad concreting practices
? To be durable, you have to get the basics right: the cement type is just an aid
? Water-cement ratio is key
? Top picture – w/c 0.69, Type V
? Bottom picture – w/c 0.35, Type V


Applications of Type III (High early strength)

Applications of Type IV (Low Heat)

White Portland Cement


Blended Hydraulic Cements

? ASTM C 595 (AASHTO M 240)
? Blending supplementary materials into OPC
? Improves properties (we will see in detail how this is effected)
? Reduces cost – materials like fly ash are waste products from other industries
? Environmental effects –concrete acts as a sink to hazardous products

Blended Cements

? Type IS –Portland blast furnace slag cement
? Type IP, Type P – Portland Pozzolan cement
? Type I(PM) – Pozzolan modified Portland cement
? Type S –slag cement
? Type I (SM) – Slag modified pozzolan cement

Other Hydraulic Cements

? ASTM C 1157 – 6 types
? Type GU – General Use
? Type HE – High early strength
? Type MS –Moderate sulfate resistance
? Type HS – High sulfate resistance
? Type LH – Low heat of hydration

? Type MH – Moderate heat of hydration


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