Reinforcement of concrete in contact with internal vibrators 

At the time of concreting, if internal vibrators are placed accidentally in contact with some of the reinforcement bars, some undesirable effects can result. The most obvious one is that reinforcement bars can become displaced or damaged if loosely tied.  

Air bubbles are likely to move towards the source of vibration. For poker vibrators touching the reinforcement bars, air pockets can be trapped in the vicinity of the reinforcement since vibration produced by internal vibrators attracts these air bubbles. Therefore the bond between the surrounding and reinforcement concrete would be impaired.

To attain good surface finish close to densely-packed reinforcement cage, workers can insert poker vibrators in the gap between reinforcement cage and formwork since reinforcement cage tend to damp down the vibration effect when vibrators are located at a distance from the formwork. Though concentrated vibration within the cover region causes migration of finer cement mortar to this area and leads to changes in concrete colour. If concrete cover is small, chance of getting the poker vibrators jammed in the gap is high and formwork is tends to be damaged by vibrators.