Constitutional compounds of portland cement

• The properties of cement depend upon the relative proportion of the constitutional compounds present and each of them has different characteristics.
• When cement comes in contact with water, its constitutional compounds undergo hydration at different rate.

Tricalcium aluminate (C₃A) 10%
When cements come in contact with H₂O, C₃A undergoes hydration very fastly. It is responsible for initial set of paste of cement or flash set. The early strength is good but the ultimate (overall) strength is quite low. Its heat of hydration is about 880 KJ/kg.

Tricalcium silicate (C₃S) 45%
Its rate of hydration is medium. It develops very high strength quite early and the ultimate strength is also the highest. Its heat of hydration is about 502 KJ/Kg.

Tetra calcium alumina ferrite (C₄AF) 10%
Its rate of hydration is slow. It provide very less strength to the cement concrete as compared to the other constitutional compounds of the cement. Its heat of hydration is about 418 KJ/kg.

Dicalcium silicate (C₂S) 25%
Its rate of hydration is very slow.It develops low eary strength of cement paste but develops ultimate strength same as that of C₃S. Its heat of hydrations is the lowest i.e. 251 KJ/kg.