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

􀀁 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”
􀀁 “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)
􀀁 LOCATION
􀀁 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

 

BE AWARE OF THIS

􀀁 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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