Question

Blow holes in concreting are result of
1. Excess water-cement ratio
2. Insufficient workability
3. Improper design of shuttering
4. None of the above

Answer 1

Correct Answer - Option 3 : Improper design of shuttering

Explanation

(i) Blow holes are cavities on the vertical surface of the concrete. These are caused by air in concrete being trapped against the form face or sometimes due to insufficient vibration.

(ii) The occurrence of blowholes can be minimized by the use of a suitable air release agent on the surface of the formwork or by providing adequate vibrations. In addition to this concrete should have adequate workability. Blows holes does not affect the long-term performance of the concrete structures.

(iii) Improper design of shuttering may cause trapping of air against form face which can lead to blow holes.