Concrete Vibrator

A concrete vibrator is used to ensure that the concrete becomes compact while putting concrete i.e. the concrete is placed without the inclusion of air bubbles which can affect its strength and it is necessary in most cases because the fluidity of concrete is limited by the amount of water used in the mixture.

Certain types of liquid concrete mixes (self compacting concrete) do not require a vibrator.

Types of concrete vibrator:

1. Needle Vibration:

Needle vibrators are also referred to as internal vibrators, immersion vibrators, and poker vibrators, the various components of a needle vibrator are power, flexible shafts, and needles.

The needle is usually chosen on the basis of concreting work i.e. large needle is chosen for large scale concreting work, sometimes the needle is replaced with a blade of the same length.

This blade helps to vibrate and compact the concrete in congested reinforcements, where the needle is not possible to move and vibrate.

They are portable and lightweight in weight and are commonly used for compaction of concrete.

Vibrations are caused by eccentric loads associated with the rotor, shaft, or any vibrating element and their vibration frequency is up to 12000 per minute, but usually a frequency of 3500 to 5000 per minute is used.

The diameter of the needle varies from 20 mm to 75 mm and its length varies from 25 cm to 90 cm.

The bigger needles are used extensively in concreting, this needle can be replaced by a blade to facilitate vibrating in congested reinforcement.

2. Surface Vibrators or Screed Vibrator:

A small vibrator placed on a screw board offers an efficient method to compact and level the skinny concrete members such as ground slabs, roof slabs and street surfaces.

Mostly, floor and ceiling slabs are so thin that a needle or any other vibrator cannot be used easily.

In such cases, surface vibrators can be used effectively.

3. External Vibrator or formwork Vibrator:

An external vibrator is a more suitable vibrator for concreting the column in casting thin walls or precast members, it gives a good finish to the concrete surface.

Compaction by an external vibrator or formwork vibrator is particularly used for the area where reinforcement, lateral ties, and spacer become more congested and give more interfere to the internal vibrator.

The external vibrator consumes more power than the internal vibrator because the concrete is vibrated indirectly through the formwork.

Surface vibrators are also known as screw board vibrators or pan vibrators used where condensation is to be done.

These are small vibrators mounted on a screw board, these screw vibrators are not more effective than 15 cm.

4. Table Vibrator:

This is a type of formwork vibrator, where the vibrator is placed on a table and any object placed on the desk will get vibrated.

It is mainly adopted in laboratories in making small but precise prefabricated RCC members.

Advantages of concrete vibrator:

1. The honeycomb structure can be avoided.
2. Structure with heavy reinforcement can be easily compacted.
3. The structure prepared by the vibrators is dense and watertight.
4. Low water-cement ratio can be used.
5. Work speed increases.
6. High aggregate cement ratio can be used.

Disadvantages of concrete Vibrator:

1. If the concrete mixture is designed with low workability, the over vibration causes additional power consumption, resulting in energy dissipation.

Precautions to be taken for Compaction of Concrete by using concrete vibrator:

1. Concrete should be compacted into layers with a thickness of 20 to 50 cm.

2. The vibrator should be inserted vertically in sufficient number of steps to achieve complete compaction of all concrete.

3. The formwork should be tight and strong to avoid leakage of the motor.

4. Vibration should be stopped when the cement slurry starts appearing on the surface.

5. Over vibration should never be used.

6. The vibrator should never be used to move concrete mix laterally to avoid segregation of concrete.

7. Vibrators should not be allowed to touch the formwork to avoid any damage.

8. The vibrator should be withdrawn slowly and it should be kept operating while being withdrawn to avoid weep holes in the concrete.

9. Re-vibration of concrete is not harmful unless the concrete is well established that it does not become plastic again by vibration.

Also read: Concrete Mixer, Concrete Finishing Tools & Concrete Grinder

Conclusion:

Even though there are hand compaction techniques available, they are comparatively less effective when used for insignificant tasks.

In a concrete vibrator, a concrete of sufficient workability and a low water-cement ratio is expected, while compaction of concrete can also be done for stiff concrete.