Composition of cement and functions of various ingredients of cement | Cement Chemistry

Lecture-6: Composition of cement and functions of various ingredients of cement | Properties of Cement Compounds by Dr. K. Mohan.
Dr K Mohan is an internationally renowned and an acclaimed cement scientist. He is a former Director General of National Council for Cement and Building Materials (NCCBM).
He holds a Ph.D. degree in Cement Chemistry from University of Aberdeen, Scotland, U.K.
Cement chemistry notation i.e., abbreviations used in cement chemistry.
 C = CaO
 S = SiO2
 A = Al2O3
 F = Fe2O3
 M = MgO
 S= SO3
 H = H20
So on and so forth.
 Cement consists mainly of Lime (Calcium Oxide) (CaO), Silica (SiO2), Alumina (Al2O3) and Iron Oxide (Fe2O3). Apart from these, fairly significant proportions of Magnesium Oxide (MgO) and Sulphur Trioxide (SO3) are also present.
Oxide Composition of Cement:
Oxide Common Name Composition Range (%)
CaO Lime 60 ~ 67
SiO2 Silica 17 ~ 25
Al2O3 Alumina 3 ~ 8
Fe2O3 Iron Oxide 4 ~ 6
MgO Magnesia 1 ~ 5
SO3 Sulphur Trioxide 2 ~ 3.5
• Small amounts of free lime, alkalis (Na2O & K2O) and minor amounts of other elements are also present.
Phase Composition (Compound Composition) of Cement:
C3S 3CaO. SiO2 Tricalcium Silicate
(Alite) 45 ~ 60 %
C2S 2CaO. SiO2 Dicalcium Silicate
(Belite) 15 ~ 35 %
C3A 3CaO. Al2O3 Tricalcium Aluminate
(Aluminate/ Celite) 5 ~ 12 %
C4AF 4CaO. Al2O3. Fe2O3 Tetra calcium Alumino Ferrite
(Ferrite) 10 ~ 14 %
Functions of Various Cement Ingredients:
1. Lime (CaO):
• This is the important ingredient of cement and its proportion is to be carefully maintained.
• Sufficient quantity of lime forms tricalcium silicate (C3S) and dicalcium silicate (C2S).
• The lime in excess makes the cement unsound and cause the expansion and disintegration of the cement.
• On the other hand, if the lime is deficient, it will decrease the strength of the cement and will cause it to set quickly.
2. Silica (SiO2):
• It imparts strength to the cement due to formation of dicalcium silicate and tricalcium silicate.
• If silica is present in excess quantity setting time of cement is prolonged.
3. Alumina (Al2O3):
• Alumina imparts quick setting property to the cement.
• It acts as a flux and it lowers the clinkering temperature.
• Alumina in excess reduces the strength of cement.
4. Iron Oxide (Fe2O3):
• Iron oxide imparts colour, hardness and strength to cement.
5. Magnesia (MgO):
• Magnesia, if present in small amount, imparts hardness and colour to the cement.
• A high content of magnesia makes the cement unsound.
6. Calcium Sulphate (CaSO4):
• Calcium sulphate is in the form of gypsum and its function is to increase the initial setting time of cement.
7. Sulphur (S):
• A very small amount of sulphur is useful in making sound cement. If it is in excess, it causes cement to become unsound.
8. Alkalies:
• Most of the alkalies present in raw materials are carried away by the flue gases during heating and the cement contains only a small amount of alkalies.
• If they are in excess in cement, they cause a number of troubles such as alkali-aggregate reaction, efflorescence and staining when used in concrete, brickwork or masonry mortar.
Properties of cement compounds?
Tricalcium Silicate (C3S)
• Hydrates and hardens rapidly.
• Largely responsible for initial set and early strength(upto 7 days).
• Portland cements with higher percentages of C3S will exhibit higher early strength.
• Produces more heat of hydration.
Dicalcium Silicate (C2S)
• Hydrates and hardens slowly.
• Largely responsible for strength increase beyond 7 days.
• Produces much of ultimate strength.
• Produces less heat of hydration.
Tricalcium Aluminate (C3A)
• Hydrates and hardens the quickest.
• Liberates a large amount of heat almost immediately.
• Contributes somewhat to early strength, especially 1day strength.
• Gypsum is added to retard C3A hydration. Without gypsum C3A hydration would cause cement to set almost immediately after adding water. (Flash set)
• Cement with Low C3A are more resistant to sulphate attack.
Tetra calcium Alumino Ferrite (C4AF)
• Hydrates rapidly but contributes very little to strength.
• The presence of iron oxide lowers clinkerisation temperature.
• Colour effects (grey colour) are due to C4AF.
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[@VishnuSharma-cj2qt]

good knowledgeable vedio

[@kamalrout4822]

What about flyash and slag,is it mixed or not, some cement bag mentioned regarding mixing of above-mentioned ingredients

[@manjunathjakkaraddi3132]

Good work

[@chandrabhushanvishwakarma797]

Very useful & informative video ..
R/sir...
It is request to you kindly explained the Free lime (Caof).how will be formation of free lime & what is the advantage and disadvantages of the same??
Rads.
CB vishwakarma.

[@biseswarnayak4577]

Today's market in PSC cement slag% have very high 60 to 70 %.its mean 30 to 35 kg add in slag in 1 pkt cement. Can it's use to good for construction.in another case PPC cement have 35 ℅ flyash added in cement bag . Which cement is better use for construction work in costal area. Please replay sir

[@cementpdm]

PSC Portland Slag cement

[@biseswarnayak4577]

@@cementpdm ?

[@cementpdm]

@@biseswarnayak4577 Slag have already reach % of calcium oxide, which is part of making good cement..

[@biseswarnayak4577]

Thank you so much sir your valuable comment 🙏

[@sachindrasingh7685]

Please share about brown core clinker problem

[@rameshgourshete1500]

Sir what should be the recepie for the composite cement used in paver block and cement frames?

[@arvindgolhani1650]

Good video sir