Compaction of concrete can be done in two ways
1. Hand compaction
2. Machine compaction (by vibrators)
1. Hand compaction
- Hand compaction is obtained for small quantities of concrete.
- We use hand compaction when Vibrators are not available on site.
- It results in inefficient compaction.
- Hand compaction requires high water content.
- It can be done by Tamping, Ramming and Rodding.
Methods Of Hand Compaction :-
1. RODDING 2. RAMMING 3. TAMPING
1. Rodding :-
It is a method of poking with 2m long, 16 mm diameter rod at sharp corners and edges. The thickness of layers for rodding should be 15 to 20 cm.
A piece of bamboo maybe used for rodding the concrete.
It is generally used for compaction on ground in plain concrete. It is not used either in RCC or on upper floors.
It is adopting in compacting roof or floor or road pavements where the thickness of concrete is comparatively less and surface to be finished smooth and level.
For Tamping concrete a wooden beam of cross section 10cm*10cm is used.
2. Machine compaction (by Vibrators)
In machine compaction we compact the concrete by using vibrators.
Following vibrators can be used for compaction.
- Internal vibrators
- Surface vibrators
- Formwork vibrators
- Platform vibrators
1. Formwork Vibrator:-
Formwork vibrator is used for the concreting columns , thin walls or in the casting of precast units. The machine is clamped onto the external walls surface of the formwork. The vibration is given to the formwork so that the concrete in the vicinity of the shutter gets vibrated. This method of vibrating concrete is particularly useful and adopted where reinforcement, lateral ties and spaces interfere too much with the internal vibrator.
Use of formwork vibrator will produce a good finish to the concrete surface. Since the vibration is given to the concrete indirectly through the formwork, they consume more power and the efficiency of internal vibrator.
2. Table Vibrator:-
This is the special case of formwork vibrator, where the vibrator is clamped to the table or table is mounted on springs which are vibrated transferring the vibration to the table. They are commonly used for vibrating concrete cubes. Any article kept on the table gets vibrated. This is adopted mostly in the laboratories and in making small but precise prefabricated R.C.C. members.
3. Platform Vibrator:-
Platform vibrator is nothing but a table vibrator, but it is larger in size. This is used in the manufacture of large prefabricated concrete elements such as electric pole ,railway sleepers, prefabricated roofing elements etc. Sometimes, the platform vibrator is also coupled with jerking or shock giving arrangement such that a through compaction is given to the concrete.
4. Surface Vibrator:-
Surface vibrator is sometimes knows as, “Screed Board Vibrator”. A small vibrator is placed on the screed board gives an effective method of compacting and levelling of thin concrete members, such as floor slab , roof slab and road surface. Mostly , floor slabs and roof slabs are so thin that vibrator or any other type of vibrator cannot be easily employed. In such cases , surface vibrator can be effectively used. In general, surface vibrator are not effective beyond about 15 cm. In the modern construction practices like vaccum dewatering technique, or slip-form paving technique , the use of screed board vibrator are common feature. In the above situations double beam screed board vibrator are often used.
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