Question

Statement (I): Air-entraining cement has a higher initial setting time than O.P.C and resists frost action better.

Statement (II): Air-entraining cement has a longer final setting time compared to O.P.C 

1. Both Statement (I) and Statement (II) are individually true and Statement (II) is the correct explanation of Statement (I)
2. Both Statement (I) and Statement (II) are individually true but Statement (II) is not the correct explanation of Statement (I)
3. Statement (I) is true but Statement (II) is false 
4. Statement (I) is false but Statement (II) is true 

Answer 1

Correct Answer - Option 3 : Statement (I) is true but Statement (II) is false 

Concept:

In the cold environment, due to low temperature, the water inside the concrete gets freezed and expands. The use of this cement provides the required space for the water to expand and thus doesn’t let the concrete to rupture.

However, entrained air bubbles serve as reservoirs for the expanded water, thereby relieving expansion pressure and preventing concrete damage.

The advantages of air-entrained concrete are:

1. Workability of concrete increases.

2. Use of air-entraining agents reduces the effect of freezing and thawing.

3. Bleeding, segregation, and laitance in concrete reduces.

4. Entrained air improves the sulphate resisting capacity of concrete.

5. Reduces the possibility of shrinkage and crack formation in the concrete surface.

6. Final setting time of air entraining cement is less than the setting time of O.P.C.