English
عربىThere are several different types of vibrators. These include internal, external and shutter vibrators.
An internal or needle vibrator, aka a poker, is the most common and most popular type of vibrator for use with poured concrete. It is a small, portable machine that includes an electric motor and a long tube on which a vibrating head is attached.
It is typically used to compact concrete just after placement, particularly along slab edges and around columns / pits etc. The vibrator should be inserted vertically into the concrete and then slowly withdrawn.
This is usually done at about one inch per second. This is a good rate because it allows the air bubbles to rise up unimpeded by a slopping vibrator.
Another important tip is to insert the poker vertically so that the air bubbles can rise up under its weight. This minimises voids created when the poker is inserted horizontally, and makes it easier for the vibrator to get into the lower layers of the concrete under its own weight.
Using an internal or needle vibrator to consolidate concrete is an essential step in creating a properly-bonded, cohesive concrete mass that meets its strength requirements and is suitable for construction purposes. It can help create a smoother surface, reduce the amount of cement required, and improve the bonding with reinforcement steel, leading to improved strength.
To be effective, an internal or needle vibrator needs to be inserted at regular intervals to ensure the entire surface of concrete is consolidated. The points of insertion should be spaced no more than 10 times the diameter of the poker head.
Incorrect placement of a vibrator can result in under-vibration (withdrawing too fast) or over-vibration (withdrawing too slow). Both techniques can cause the concrete to become bulged, deformed or even fail to meet its designated strength requirements.
An internal or needle vibrator must be inserted into the concrete and then withdrawn at a slow rate of 1 inch per second or less to ensure that the concrete is free of air bubbles. As a result, the vibration is most effective when the head is penetrated into the concrete for about 15 seconds.
When the head is withdrawn, large air bubbles should be released from the concrete and smaller aggregate particles embedded within it. As a result, a thin film of glistening mortar should appear on the surface and cement paste will rise to meet the formwork where the concrete is in contact with it.
Depending on the size of the concrete, it can take anywhere from 15-20 seconds to fully consolidate. This is dependent on the amount of rebar in the concrete and whether the concrete is poured in multiple lifts or a single lift.
