Question

Why is super plasticizer added to concrete?

(i) To reduce the quantity of mixing water

(ii) To increase workability

(iii) To reduce the quantity of cement

(iv) To increase early age strength 

1. (i) and (iv)
2. (i), (ii) and (iv)
3.  (iii) and (iv)
4. (i), (ii), (iii) and (iv)

Answer 1

Correct Answer - Option 4 : (i), (ii), (iii) and (iv)

Explanation:

Super-plasticizers

They are admixtures that work on surfactant property, in which they disperse and deflocculate cement particles thus making concrete flowing, pourable, and easily placed.

Examples: Sulfonated Melamine formaldehyde resin, sulfonated naphthalene-formaldehyde resin, Mixtures of saccharates, and acid amides.

Note:

(Super-water reducers) - 15 to 30 % water reduction.

Purpose: 

1. To increase the workability of concrete without any change in the composition of the mix.

2. To reduce the water content of mixing water, to reduce the water/cement ratio resulting in the increase of strength and durability of concrete.

3. To reduce cement and water contents in the concrete to reduce the cost of production of concrete. The reduction in cement and water contents reduces the creep, shrinkage, and heat of hydration.

4. To slow the setting rate of the concrete while retaining the flowing properties of a concrete mixture and remove air bubbles.