MINERAL PHASES OF PORTLAND CEMENTCLINKER

For optimum clinker quality

• The kiln feed chemistry must be of low variability ( must be good uniformity)

• The raw meal must be adequately ground

• The coal ash must be uniformly incorporated into the clinker

• The clinker must be rapidly cooled from the burning zone temperature.

CHEMICAL COMPOSITION OF CLINKER

*

COMPOSITION NORMAL RANGE CONTENT SiO2 - (S) Al2O3 - (A) Fe2O3 - (F) CaO - ( C)

20-22 % 5-6 % 3-4 %

63-66 %

‘main element’. This 4 oxide

containing 95% chemical composition in clinker

MgO SO3 K2O Na2O

Loss on ignition

0.5-3.0 % 0.3-1.0 % 0.3-1.0 %

0.05-0.3 % 0.4-0.7 %

‘minor element’ Containing 5

% from overall clinker composition

TiO2 Mn2O3 Chloride Florine Cr2O3

0.1-0.5 % 0.01-0.10 % 0.01-0.10 % 0.01-0.05 % 0.01-0.05 %

‘traces element’

During burning process the four main constituent of clinker aresuccessively formed

1. C3A

2. C4AF

3. C2S

4. C3S

Temperature bet 1260 0C – 1338 0C

Temperature bet 1260 0C – 1338 0C

Temperature bet 1338 0C – 1420 0C

Temperature bet 1338 0C – 14200C

BOGUE FORMULA

C3S = 4.07C-7.6S-6.72A-1.47F

C2S = 2.867S-0.754C3S

C3A = 2.65A-1.69F

C4AF = 3.04 F

Where C = total CaO-free CaO-0.7SO3

S = total SiO2-Insoluble residue

CLINKER MINERALOGY

• Alite for C3S-tricalcium silicate 3CaO+SiO2 Ca3SiO5• Belite for C2S-Dicalcium silicate 2CaO +Al2O3 Ca2SiO4 • Aluminate for C3A-Tricalcium aluminate 3CaO+Al2O3 C3A• Ferrite for C4AF- Tetracalcium alumino ferrite 4CaO+Al2O3+Fe2O3 Ca4Al2O10

Major compounds

CLINKER MINERALOGY

• Minor compounds

- CaSO4

- K2SO4

- KCl

- Na2SO4

- NaCl

- MgO

NAME SHORT NAME

‘MINERAL NAME

PROPORTION NORMAL RANGE*

PROPERTIES (CLINKER+ GYPSUM)

Tricalcium silicate C3S Alite 16 parts 50-62 Strength 28 days

Dicalsium silicate C2S Belite 2 parts 10-24 Long term strength Tricalcium aluminate C3A Aluminate 1 parts 5-12 Setting time, early

strength Tetracalcium aluminaferrite

C4AF Ferrite 1 parts 7-12 No effect on strength but gives a dark color

4 MAJOR COMPOUNDS IN CLINKER

* Depend on type of cement produce

By Bogue calculation only give potential clinker phase but by microscopic canDetermine the real clinker phase.

C3S (Alite Properties)

• Main strength constituent in cement

• Higher initial strength and good final strength

• Rapid hydration

• Contains impurities: Mg, Al, Fe

• Typically 50-62 % of clinker

• Difficult to burn kiln feed if C3S >65%

C2S (Belite) properties

• Low early strength but good final strength

• Slow hydration

• Contains impurerities:alkalis,Al,Fe,flouride

• Typically 16-24 % of clinker

• Clinker grindability adversely impacted by higher C2S.

C3A Properties

• Rapid hydration- gypsum added to control rate

• Early strength

• Typically 5-12 % of clinker

• Importance impact on clinker quality:

-Plasticity/workability

-Resistance to sulfate in soil/water exposure.

C4AF Properties

• Governs the color of cement i.e

higher C4AF = darker cement

• Hardly any strength development

• Slow to moderate hydration

• Typically 7- 12 %

Alkali Equivalent (NaEq)Na2O+0.658K2O

• Combines both alkalis expressed to equivalent Na

• Importance for product specification• Influence cement performance• Setting time decrease with increase the alkali

sulfate. -can lead to flowability problem -can react with same aggregates and lead to

concrete durability problems• Influence kiln stability as volatile compounds

• Diagrammatic representation of the major constituents of clinker

THE REAL CLINKER MINERALS/PHASE

GOOD CLINKER FORMATION

HARD BURNING CLINKER- VERY BIG ALITE CRYSTAL-LOWER28 DAYS STRENGTH

OVER BURN-HIGH TEMPERATURE OR LONG FLAME

16/5/03-X50 Alite sixe 138 um

5/5/03-X50 Alite sixe 53 um-dusty clinker23/10/0-X50 PC 100 %- Alite sixe 138 um

1 2

3Photo1: Large fused alite crystal due to slow passage athighTemp. Through burning zone & Reducing condition

Photo2: dusty clinker product -due to raw mix difficult to burn thetemperature in burning zone very high and too long, in sufficient nodulation taken place

Photo3: Large alite cystal size, hard burning.

Large free lime cluster due to coarse limestone particle in raw feed

RAW MIX FINENESS

RAW FEED FINENESS AND HOMOGENITY

Coarse quartz particle

Belite surrounded by large alite crystalThis is due to high max. temperature.

Slow Cooling rate

periclase

Belite crystal- fringe

FREE LIME CRYSTAL

• Yellow banding typical of reduction

REDUCING/OXIDISING

• Reducing condition if:

- Lack of Oxygen

- Poor mix of fuel and fuel

- Coarse of fuel particles• Symptoms:

- CO2

- SO2

- Volatilization

• Oxidizing condition if:

- Enough oxygen

- Good Mix (burner)

- Fine Fuel• Signs:

- Stable O2

-Reduced amount of build-up

- improve kiln stability

Factors effecting clinker reactivity

• CHEMICAL COMPOSITION -C3S, C2S, C3A, C4AF, SO3, ALKALIS, FREE LIME.

• PARTICLE SIZE DISTRIBUTION OF RAW MEAL 200UM, 90UM, 63UM

• MINEROLOGY FORMATION C3S- CRYSTAL SIZE, BIGGER/SMALLER SHAPE-ROUND OR SHARP EDGE C3A- ORTHOROMBIC - CUBIC (if more soluble alkali-sulfate) - Periclase

FACTORS INFLUENCING CLINKER TEXTURE

Influence parameters Specific factor

Raw mix properties -chemical composition, major & minor elements

-fineness and Mineralogy

-homogeneity

Fuel type - Coal ash

Burning condition -burning time/temperature

- Kiln atmosphere O2(reducing condition), NOX

Cooling condition -rate of cooling

HOW TO INCREASE CLINKER REACTIVITY?

• Increase the C3S ( but not more than 65%)• Fast cooling rate• Fast heating rate, need short flame & hot• Ovoid over burning to control alite size max

40um• Control the SO3/Alkali >1• Optimize the PSD of raw meal• Homogenity of raw meal• Avoid reducing condition environment inside kiln.