|Internal Poker Vibrators|
Mechanical internal 'poker' vibrators1 are the most commonly used, and the most versatile, of all vibration equipment. They can be powered by electricity, petrol engine or compressed air.
While their length is generally fixed at around a foot-and-a-half, the girth and cycle speed (vibrations per minute) varies.
Smaller sizes, say 20mm to 60mm diameter, are most commonly used for general purposes, and typically vibrate between 150 and 250 cycles per second.
Larger vibrators, up to say 180mm diameter, vibrate more slowly, say between 90 and 140 cycles per second, and are used for large-scale jobs. One of these will probably require two men to operate it, and for really big jobs (say six cubic metres plus), two can be operated in tandem to achieve 'melt down'.
The whole length of an internal vibrator should be immersed.
Vibrators should be inserted vertically.
Vibrators should not be allowed to touch the sides.
Withdrawal should be undertaken slowly and carefully to ensure that all holes close up.
Vibrators should only be used for compaction of wet concrete. They should not be used to move or transport concrete laterally.
1 The operation of mixing and pouring concrete inevitably introduces and entraps air bubbles in the wet concrete. These air bubbles are detrimental to the strength of the concrete as they have no inherent strength. It is therefore necessary to remove them from the concrete before the mixture hardens. The most common and effective method is to vibrate the wet concrete, and this is usually performed by immersion of an internal poker vibrator into the wet mix. Rapid agitation of the mix encourages air-bubbles to merge and then rise to the surface. It is like burping a baby. As the air is expelled, the volume of the concrete visibly reduces, hence the term 'meltdown'.
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