DIFFERENT TYPES OF VIBRATORS USED IN CONSTRUCTION INDUSTRY

DIFFERENT TYPES OF VIBRATORSLASU JOSEM Tech 1st YearNEED OF VIBRATORSStrength of the hand compacted concrete will be less because of the higher W/C ratio required for full compaction.

For high strength concrete W/C ratio should be kept minimum.

To compact such type of concrete, vibratory equipment has to be used.

How Do Vibrators Work?Vibrators impart a vibratory force into the concrete through a combination of frequency and amplitude.

Frequency is the number of vibration cycles per minute, and is expressed as rpm .

Vibration of fresh concrete reduces its internal shear strength and enables the concrete to temporarily liquefy- facilitating the consolidation process.

Amplitude is the peak force.

It is more effective with a heavier mass of concrete. It moves the rocks and determines the radius of action.

For a thin concrete layer , vibration has to be given at a high frequency and low amplitude.

DIFFERENT TYPES OF VIBRATORInternal Vibrator (needle vibrator)

Form work Vibrator (External)

Table Vibrator

Platform Vibrator

Surface Vibrator

Vibratory Rollers

Needle VibratorThis is the most commonly used vibratorThis mainly consists of :Power unitFlexible shaftNeedle

The power unit may be electrically driven or operated by petrol engine or air compressor

DIFFERENT TYPES OF NEEDLE VIBRATORS

Pneumatic needle vibrator

Use Of needle vibratorExternal VibratorThese type of vibrator s are mainly used for concreting of columns, thin walls or in the casting of precast units

The machine is clamped on to the external wall surface of the form work.

The vibration is given to the form work so that the concrete in the vicinity gets vibrated.

These type of vibration is adopted when reinforcement, lateral ties and spacers interfere too much with vibrator .

Use of formwork vibrators will produce a good finish to concrete surface.

Since the vibration is given to the concrete indirectly through the formwork, they consume more power.

Efficiency of external vibrator is less comparing with needle vibrator.Table VibratorThis is a special case of form work vibrator.

The vibrator is clamped to the table which is mounted on springs.

Anything kept on the table gets vibrated.

These are mainly used for vibrating concrete cubes.

TABLE VIBRATORSpringsMotorPlatform VibratorPlatform vibrator is a table vibrator but it is larger in size.

These are mainly used in the manufacture of large prefabricate concrete elements.

PLATFORM VIBRATORSurface VibratorThese are also known as Screed board Vibrators

These are mainly used for slabs and road surface.

As the slabs are thin, it is very difficult to use internal vibrators. In such cases we can use surface vibrators.

These are not efficient beyond about 15cm.

SURFACE VIBRATORScreed PaverScreed Paver is a dual purpose concrete finishing machine.

Consisting of a vibrator and screed finisher in one unit.

It is light in weight, portable and gives higher production and greater accuracy.

Guidelines For The Use Of VibratorsCare shall be taken to avoid the collision of vibrating head with any hard objects.

Otherwise the impact may damage the bearings.

When the space for vibrator is narrow , it should be switched on only after the vibrator head has been introduced .

Strength of form work has to be more, comparing with form work for ordinary hand compacted concrete.

Factors to be Considered Height of Concrete layer

Depth of immersion of Vibrator

Spacing and No of insertion positions

Speed of insertion and withdrawal of the vibrating head

Duration of vibrationHeight of ConcreteUsually thickness of concrete layer should not be more than 60cm.

On intial placing it should not be more than 15 cm.

The superimposed load increases with the height of layer will favour the action of vibration. But thick layers may get entrapped with more air. Depth of immersion of vibratorActive part of the vibrator should be completely immersed in the concrete.

The direction of vibrator should be perpendicular.Spacing and no of insertion pointsThe points of insertion of vibrator in the concrete should be spaced such that range of action should overlap.

For concrete of workability 0.75 to 0.8 CF, spacing should be 35 to 90 cm .Speed on insertion and withdrawal of Vibrating HeadVibrating head should be inserted regularly and uniformly.

Usually a speed of 3cm/s gives sufficient consolidation.Duration Of VibrationDuration of vibration required depends upon the thickness of layer , characteristics of vibrator and workability of the mix.

The degree of compaction can be recoganised from the rising air bubbles and the formation of thin shining film around the vibrating head.

Effects Of Over vibrationOver vibration leads to segregation

It separates lighter and smaller constituents (mortar) of the mix to the surface.

Leads to leakage of mortar through the defective joints of form work.

Reduces the strength and durability of concrete.REFERENCESwww.JBformworks.comwww.mcmagazine.comwww.wikipeida.comwww.houstonvibrator.comConcrete Technology, M S Shetty, S.Chand &company, New Delhi.