A concrete vibrator is a construction tool typically used on concrete pouring sites. These machines and an assortment of attachments are designed for multiple applications built by a variety of manufacturers. The vibrators are used to ensure that the pour is free of air bubbles and are even. This is so that the concrete remains strong and has a smooth finish even after removal of the form work. It is not exactly necessary for small jobs but it can be essential for large load bearing projects.
The machines range in sizes from small battery powered wands to larger plug in versions that are used on very deep pours. A concrete vibrator can reach to the bottom of the pouring forms should be used in all cases. This ensures even treatment during the entire concrete pour process. Attachments are selected on the basis of depth and type of concrete used during the concrete pour.
A typical concrete vibrator utilizes an off-center weight that spins at 10000 times a minute. This results in a large air pocket within the concrete to disperse as the concrete is being gradually shaken. Especially in the concrete pours of low slump concrete that uses minimal amount of water. The use of a vibrator is essential in order to ensure that the concrete does not form bubbles or holes. In cases where consumers look at the finished concrete, this tool will help to create an even and attractive surface instead of one that is ragged filled with bubbles on the surface. It is commonly seen in schools of design where they usually employ concrete counters and floorings to be done.
The proper use of a concrete vibrator would require some form of training. The head should be slowly lowered then pulled out gradually to avoid the formation of an air pocket in the pour. The tool should also never be dragged through a pour. This will leave a groove in the concrete behind it. The time required varies and is dependent on the mix. That being said, the mix should not take more than 30 seconds to settle the concrete sufficiently moving on to the next section of the concrete.
If the concrete vibrator is being used incorrectly on a concrete mix that has a wide range of material sizes, this can cause the larger rocks to settle at the bottom which then makes the concrete weaker. Additionally, the tool can push rock and gravel away from the area that is being shaken. This causes the weaker concrete paste to fill the area. This again may result in instability. The main goal is to build a strong matrix of material that could withstand the many years of usage. However, if it is being used correctly, the operator will be able to see large bubbles floating towards the surface of the concrete pour. A layer of mortar will also appear on the surface. This is to indicate that the concrete is mixed evenly and is unlikely to have honeycombing and air pockets.
The first thing to take into consideration when choosing a concrete vibrator would be the size of it. The size depends on how much concrete you will need to vibrate. When considering this, it is crucial to think whether the concrete has to be vibrated quickly or some time allowance is provided. It is advised to spend a little extra on a vibrator that has a lot of horsepower if speed is a large considering factor. On top of that, there are also external and internal concrete vibrators to choose from. However, the latter is the more commonly used option for many projects these days.
TYPES OF VIBRATORS USED FOR CONCRETE COMPACTION
- Internal or Immersion or Poker or Needle Type Vibrator
- Shutter form or External Type Vibrator
- Surface or Screed or Pan Type Vibrators
- Vibrating Tables
1. Internal or Immersion or Poker or Needle Type Vibrator
These concrete vibrators are also referred to as poker or immersion vibrator. These are extensively used in building industry. A needle vibrator consists of a cylindrical casing made of steel and is vibrated by means of a flexible drive with an outer tube run from an operating machine which can be run by electricity, petrol, diesel or compresses air. The frequency of vibrations of an immersion vibrator is very important as higher frequency gives better compaction. It varies from 3500 to 12000 cycles per minute. Frequencies below 3500 cycles per minute are inefficient for concrete compaction. The diameter of the vibrating part varies from 20 to 75 mm and its length varies from 25 to 90 cm.
2. Shutter form or External Type Vibrator
3. Surface or Screed or Pan Type Vibrators
They are also called screed or pan vibrators.They are clamped to the screed.Very dry mixes can be most effectively compacted with surface vibrators. They vibrate the concrete from the surface at the time when screeding (striking off) of the concrete is carried out. They are effective only if depth of concrete is upto 20 cm. if the depth is more they can be used in combination with internal vibrators. They are used for long horizontal surfaces such as pavements and slabs.The operating frequency is about 4000 rpm at an acceleration of 4g to 9g.4. Vibrating Tables
The vibrating table consists of a rigidly built steel platform mounted on flexible springs and is driven by an electric motor.The normal frequency of vibration is 4000 rpm at an acceleration of 4g to 7g.
The concrete is placed in moulds mounted on the platforms and securely clamped to the vibrating table, so that mould and concrete vibrate in union.
The vibrating tables are very efficient in compacting stiff and harsh concrete mixes required for manufacture of precast elements in the factories and test specimens in laboratories.
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