Handling of Vibrators:

Needle vibrators should be penetrated in vertical direction and vibrations should be transmitted till the concrete flattens and no entrapped air appears on the surface. The vibrator should be taken out of concrete slowly and carefully. Skilled workmen are essentially required for producing a uniform and well-compacted concrete. The correct placing and tamping of concrete mainly depends on the skill of the workmen and their experience. Vibration through unskilled persons is possibly more dangerous than hand tamping, since there is always a risk of either under- compaction or over-compaction of concrete. The equipment to be used for vibration must be kept clean and free from coatings of set concrete. Thus, the vibrators should be used very carefully in order to compact the concrete layer uniformly.

The subsequent steps should be observed in order to obtain good results by compacting concrete with vibrators.

(a) Vibrators should be controlled carefully through immersing the internal vibrator for 5 to 15 seconds at points 45 to 75 cm apart.

(b) The formworks shall be as tight as possible in order to prevent any leakage of mortar.

(c) The vibrator shall be inserted vertically otherwise it will not be possible to regulate the degree of compaction in all portions of concrete.

(d) The lift would not be less than 15 cm in order to avoid air being trapped.

(e) The vibrator should be immersed by the full depth of the freshly laid concrete. It should also be immersed within the lower layer if the concrete in that layer is still plastic.

(f) The vibrator should be withdrawn extremely slowly and should be allowed to penetrate of its own accord.

(g) The vibrator should not touch the form surface otherwise a sand streak is likely to occur. The surface of the formwork can also be damaged.

(h) The vibrator should just be used for compaction purposes. It should not be used for pushing the concrete laterally in the formworks, which would otherwise cause segregation.