How to do compaction of concrete

- Each layer of Fresh Concrete shall be thoroughly compacted by vibrators to the minimum practicable consolidated volume.

- The concrete to be vibrated shall be placed in position in level layers of suitable thickness not greater than the effective length of the vibrating needle. It is advisable to have concrete layer thickness not more than 600mm(in vertical members) for effective vibration.

- Vibrator needle shall be inserted vertically inside the Concrete and shall be allowed to penetrate through by its own weight. Vibration shall not be stopped when needle is immersed in Concrete.- The vibrator shall penetrate fully into the layer being placed and also penetrate about 100 to 200 mm in the already consolidated lower layer for good bond and homogeneity between the two layers and to prevent the formation of cold joints. The vibrators shall be withdrawn slowly out of the concrete so as to allow the concrete to flow back into the hole behind the vibrator.

- The spacing of insertion shall be at intervals of about 450 mm to 700 mm depending upon the mix. The specified spacing between the inserting positions shall be maintained uniformly throughout the surface of concrete so that the concrete is uniformly vibrated.

- The spacing shall provide some overlapping of the area vibrated at each insertion. It is better to insert the vibrating head at a number of places than to leave it at one place for a long
time.

- The range of action & degree of consolidation can be recognized from the rising air bubbles & the formation of a smooth textured surface around the vibrating head.

- Vibrator needle shall be kept clear from forms at least by 100 mm. Vibrator shall be prevented from coming into contact with the reinforcement bars, embedded parts. Over vibration shall be avoided.Compaction of concrete at junctions with hardened concrete:

-The hardened concrete surface shall be prepared by hacking or roughening & removing laitance, greasy matter & loose particles.

- The cleaned surface shall be wetted. Cement – sand grout of proportion 1:1 & of creamy consistency shall then be applied to the wet surface of old concrete. & fresh concrete vibrated against it.