The objective of a vibrator is to compact concrete on the construction site easily and efficiently. At the time of vibration, compacting is influenced by cutback in internal friction among different particles of concrete because of oscillation of particles which lead to a solid and compact mass of concrete.
Vibrations can be accomplished in the following ways :-
a. Provided in the interior of the concrete with Internal vibrator, or
b. Provided in concrete by vibrating formwork with Shutter form vibrators, or
c. Provided on the surface of concrete with Surface vibrators, or
d. Provided in the total concrete mass with Vibrating table.
b. Provided in concrete by vibrating formwork with Shutter form vibrators, or
c. Provided on the surface of concrete with Surface vibrators, or
d. Provided in the total concrete mass with Vibrating table.
The following types of vibrators are generally found for compaction :-
1. Internal or Immersion or Poker or Needle Type Vibrator
2. Shutter form or External Type Vibrator
3. Surface or Screed or Pan Type Vibrators
4. Vibrating Tables
2. Shutter form or External Type Vibrator
3. Surface or Screed or Pan Type Vibrators
4. Vibrating Tables
1. Internal Vibrators: These are also known as immersion, poker or needle vibrators. They basically comprise of a power unit and a long adjustable tube, at the end of which a vibrating head is connected. Power is supplied through electric motor, compressed air or petrol engine. The long tube comprises of a flexible shaft that revolves an eccentric weight inside the vibrating head. The frequency of the vibrator remains approximately 700 cycles per minute.
The vibrating head is included in the concrete. They are very useful since the vibrating head gets in touch with concrete closely.
2. Form Vibrators: They are also known as external vibrators. They are secured with the formwork horizontally and vertically at exact distance not surpassing 90 cm in either direction.
With the advancement of the work progress they are transferred. They vibrate the concrete from the vibration of the forms and consequently lots of energy is exhausted.
Form vibrators will be applicable when the internal vibrators can’t be used in the case of thin and congested sections, arches and tunnel lining, etc.
3. Surface Vibrators: They are also known as screed or pan vibrators. They are secured to the screed. They vibrate the concrete from the surface while screeding (striking off) of the concrete is performed. They are useful when the depth of concrete remains up to 20 cm.
In case the depth is higher they should be utilized along with internal vibrators. They are suitable for long horizontal surfaces like pavements and slabs.
4. Vibrating Tables: These are inflexible and constructed with steel platforms secured on steel springs and operated by electric motors. The concrete is provided in moulds mounted on the platforms and firmly secured to the vibrating table, to facilitate mould and concrete vibration conjointly.
Vibrating tables are utilized for compacting hard and rough mixes utilized in precast structural members in factories and laboratory samples.
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