Hi smithy,
You seem confused.
We are concerned with the amount of "free CaO" available in our bag of finest Grey cement, NOT the amount of CaO that is used to produce the cement.
Burning in a kiln – formation of cement clinker
Solid state reaction zone (900˚ - 1300˚)
CaO and reactive silica combine to form small crystals of belite, one of the four main cement minerals.
Clinkering zone (1300˚C – 1550˚C)
Inside the liquid phase, Alite forms by reaction between Belite crystals and CaO.
Crystals of solid Alite grow within the liquid, while crystals of Belite formed earlier decrease in number but grow in size.
The clinkering process is complete when all of silica is in the Alite and Belite crystals and the amount of free lime (CaO) is reduced to a minimal level (<1%).
Chemical composition of clinker
The cement clinker formed has the following typical composition:
Compound Formula Shorthand form % by weight1 Tricalcium aluminate Ca3Al2O6 C3A 10 Tetracalcium aluminoferrite Ca4Al2Fe2O10 C4AF 8 Belite or dicalcium silicate Ca2SiO5 C2S 20 Alite or tricalcium silicate Ca3SiO4 C3S 55 Sodium oxide Na2O N ) )Up to 2 Potassium oxide K2O K Gypsum CaSO4.2H2O CSH2 5
Think of making glass
While you start out with mostly sand in the furnace, there is very little sand left when you finish
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