The size of vibrators used to compact concrete should be suitable so it will be smoothly dipped between reinforcement bars, and between reinforcement and the side of shutter without disturbing reinforcement or shutter. The spacing between reinforcement will vary, for poker vibrators, the diameter should be less than the spacing between reinforcement or the spacing between reinforcement and form. We can check the contract drawing to determine the suitable size of vibrators for concreting a structure.
Using vibrators with bigger diameter can result in disturbing the reinforcement. The reinforcement may be displaced if loosely tied, the purpose of compacting or vibrating concrete is to expel the air bubbles and produce a dense concrete with low permeability, air bubbles tend to move towards vibration, therefore if the poker vibrator touches the reinforcement, this may result in the formation of air pockets near the reinforcement. The formation of air bubbles near the reinforcement has the potential to impair the bond of reinforcement and concrete. Concentrated vibration of concrete in the gape between the reinforcement and formworks will result in the migration of finer cement mortar to this area, and this may result in changing concrete color. The concentration vibration of this region may result in damaging the formwork for small concrete cover.