Question

Which of the following statements is/are correct regarding the strength of cement?

1) Particle sizes less than 3 μm increase the viscous nature of the cement.

2) Finer particles in cement can be replaced by fly-ash to improve the strength.
1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2

Answer 1

Correct Answer - Option 3 : Both 1 and 2

Statement I - True

When cement and water is mixed, the cement slurry formed is fluid and becomes progressively more viscous as the cement hydrates as a function of time. After a few hours, it will set and behave as a solid with increasing strength. As size of cement particles decreases, rate of hydration increases and hence, cement becomes solid early and its viscosity decreases.

Statement II - True

Fly ash reacts with available lime and alkali in cement, producing additional cementitious compounds as calcium silicate hydrate (C–S–H) gel. This additional binder produced by fly ash allows fly ash cement to gain strength over time. This will ultimately increases the strength of cement containing fly-ash.

Note:

Materials that can be replaced by cement other than fly ash:

1. Blast furnace Slag

2. Rice husk ash

3. Surkhi (Brick Powder)

4. Charcoal