Cement
(Chemical Composition and Hydration)
Oxide Composition of Portland cement:
•
Portland cement is composed of four major oxides: lime (CaO), silica (SiO2),
alumina (Al2O3), and iron (Fe2O3).
•
Also Portland cement contains small amount of magnesia (MgO), alkalis (Na2O
and K2O ), and sulfuric anhydrite ( SO3 ).
Approximate Composition Limits of Oxides in Portland cement:
Oxide
Common Name
Content, %
CaO
Lime
60-67
SiO2
Silica
17-25
Al2O3
Alumina
3-8
Fe2O3
Iron
0,5-6
MgO
Magnesia
0,1-4
Na2O and K2O
Alkalies
0,2-1,3
SO3
Sulfuric anhydride
1-3
Oxide Composition:
Mass Percentage
Oxide
Cement 1
Cement 2
Cement 3
CaO
66
63
66
SiO2
20
22
20
Al2O3
7
7.7
5.5
Fe2O3
3
3.3
4.5
Others
4
4
4
Major Compounds of Portland Cement (Bogue’s Compound Composition):
Name
Chemical formula
Abbreviation
Tricalcium silicate
3CaO.SiO2
C3 S
2. Dicalcium silicate
3. Tricalcium aluminate
2CaO.SiO2
C2 S
3CaO.Al2O3
C3 A
4. Tetracalcium alumino
ferrite
4CaO.Al2O3.Fe2O3
C4AF
1.
Bogue’s Compound Composition:
•
C3S=4.07(CaO)-7.6(SiO2)- 6.72(Al2O3)-1.43(Fe2O3 ) – 2.85( SO3 )
•
C2S= 2.87 (SiO2) - 0.75( 3Cao. SiO2)
•
C3A= 2.65(Al2O3) – 1.69 (Fe2O3 )
•
C4AF = 3.04 (Fe2O3 )
Significance of Compound Composition
Mass Percentage
Compound
Cement 1
Cement 2
Cement 3
C3S
65
33
73
C2S
8
38
2
C3A
14
15
7
C4AF
4
10
14
Hydration of cement
 When Portland cement is mixed with water its chemical compound constituents
undergo a series of chemical reactions that cause it to harden. This chemical
reaction with water is called "hydration". Each one of these reactions occurs at a