Compaction Equipment

Most of the concrete now placed in building  construction is consolidated by vibration. Compaction of concrete by vibration has completely revolutionized the concrete technology. It is now possible to use low slump stiff mixes for production of high  quality concrete with desired strength and impermeability. A concrete with about 4 cm slump can be placed and compacted fully in a heavily reinforced concrete work which is not at all possible  with hand compaction where a slump of about 12 cm may be required.  Actually the action of vibration is to set the particles of  fresh concrete in motion, reducing the function between then and effecting a temporary qualification of concrete which enables easy settlement. The concrete  flows or liabilities under the shear forces accompanying the vibration and the concrete is compacted  away from the vibrator. Vibration by itself dtms not affect the  strength of concrete which is controlled by amercement ratio. But by permitting  use of less water, i.e, concrete of higher strength  and better quality can be made for a given cement factor. All the potential  advantages of.vibration can he fully  harnessed if proper  control is exercised 111 the design and manufacturer of concrete and the type of vibrator required and its correct use is made. We will now discussion different  kinds of  vibrator which are available and how ad where they should  be used. 

Internal Vibrator 

This is the most commonly used  vibrator on construction  sites. It is also known  by other nannies like Needle  Vibrator, Immersion Vibrator and Pocker Vibrator. Its major components are. a power unit, a flexible shaft and needle. The power  unit  may be electrically  driven, operated by  petrol engine or air compressor. The internal vibrator  produces  vibrations by eccentric weights attached to the shaft or to the rotor of a vibrating element. Electromagnetic pulsating equipment is also  available. The frequency of vibration  varies from 400 to  12000 revolutions per Nimitz. An average frequency of 3500 to 5000 has been normally  used. The needle driveler the internal  vibrator  varies from 20 to 75  and its length  varies from 25 cin to 90 cm. The bigger needle sizes are used in mass concrete construction like dam. The internal vibrator are portable and can be moved very easily to different locations and  easy to operate. 

External Vibrator 

The external  vibrator is also called as formwork shutter vibrator. It is used for concreting beams, columns, thin  walls or in the casting  of pre-cast units. The vibrator is clamped to the external surface of the formwork. The vibration is imparted to in situations where congested reinforcement, arrow spaces, curved sections or slip forming do not permit use of internal vibrator. The use of external  vibrator imparts a good finish to the concrete surface. Since the vibration is given  indirectly to the concrete through the formwork, this vibrator consumes more power  and its efficiency  is lower than  that of internal  vibrator.  An  important  point to note by you js  that since vibration is imparted to the formwork by external vibrator therefore formwork must be ngid and strong and watertight and preferably it should be steel formwork. 

Screed Board  Vibrator 

This is a small  vibrator  placed on the screed board  thus  providing an effective method of levelling and compacting of thin concrete members like flax slabs, root slabs and pavement. These members being thin the internal vibrator cannot be effectively employed. It is seen that screed vibrators are effective in members of depth upto 15 cm only. Sometimes the concrete is also vibrated by using vibratory roller which is moved on the surface as  in road slabs. 

Table and Platform  Vibrator 

The table vibrator is also a special case of external or formwork vibrator, except that here the vibrator is clamped to the table on which the article to be  vibrated is pared. This is  used in laboratories for precise casting of small RCC members. The platform vibrator is a larger version of table vibrator. 11 is used in the manufacture of large prefabricated elements like electric  poles, railway sleepers and roofing elements. Sometimes il is also couples with a jerking or shock giving  arrangement to achieve thorough compaction.