Question

Statement (I): Admixture in concrete is an essential constituent of concrete.

Statement (II): Admixture helps in improving or modifying specific qualities in concrete. 
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 4 : Statement (I) is false but Statement (II) is true

Statement I: False and Statement II: True

Anything apart from fine aggregates, coarse aggregates, cement, sand, and water is added in concrete in order to modify its properties is called admixture.  They are not the essential constituents in concrete.

The different type of admixtures helps in improving different properties of concrete as shown below in tabulated form:

Type of Admixture	Property  Modified
Plasticizers and Super plasticizers	They improve the plasticity of fresh concrete by improving the workability for given water –cement ratio and maintain workability with a reduced amount of water.
Air Entrainers	They reduce the segregation and bleeding in concrete and increase the resistance against chemical attack. But they reduce the compressive strength of concrete due to presence of air bubbles in it.
Accelerators	They speed up the chemical reaction of cement and water and so accelerate the rate of setting and hence, help in early gain of strength.
Retarders	They slow the chemical reaction of cement with water lading to longer setting time and slower initial strength gain.