Question

Early attainment of strength in rapid hardening cement is mainly due to:
1. Tricalcium silicate
2. Tri-calcium aluminate
3. Finer grinding
4. Gypsum

Answer 1

Correct Answer - Option 3 : Finer grinding

Concept:

Rapid hardening cement:

• It is also called high early strength cement.
• It attains due to a larger proportion of lime grinded finer than normal cement.
• It has a high specific surface area.
• Contains a high percentage of Tri-calcium silicate(C3S) and the low percentage of Di-calcium silicate(C2S).
• Suitable for road repairing work and in structures where the load is applied in a short time
• Unsuitable for mass concreting work, such as bridges, dams, etc

Explanation:

• Early attainment of strength in rapid hardening cement is mainly due to finer grinding.
• A high percentage of Tri-calcium silicate(C3S) and the low percentage of Di-calcium silicate(C2S) is also helpful to attain rapid hardening cement
• Tricalcium aluminate is helpful for decrease the initial setting time cement.
• Gypsum is added to increase the initial setting time of cement.

Major compounds of cement clinker (also known as Bogues compounds) are:   

Bogues compounds	Properties
Tetra-calcium alumino-ferrite(C4AF)	Formed within 24 hours of the addition of water The High heat of hydration in initial periods
Tri-calcium aluminates(C3A)	Formed in 24 hours of the addition of water Max. evolution of heat of hydration Reduce the setting time of cement
Di-calcium silicate(C2S)	Last compound formed during the hydration of cement Responsible for progressive later stage strength The Proportion of this increase in hydraulic structures, bridges, etc.
Tri-calcium silicate(C3S)	Formed within a week Responsible for initial strength of cement Contribute about 50-60% in cement