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Concrete must be consolidated by rod, or by internal or external vibrators to
prevent stone pockets, honeycombs and entrapped air. Repeated spading
between the form and the concrete allows trapped air to escape and
keeps the coarse aggregate away from the forms. Internal vibrators
should be lowered vertically, at regular intervals under their own weight, into the concrete
layer or lift so that the vibrator penetrates 150
mm into the layer below it. A vibrator being inserted into thin slabs
should enter on an angle to keep the head submerged. Vibrators should
be held stationary in concrete for 5 to 10 seconds until consolidation
occurs. Vibration
is complete when the aggregate particles are embedded, the surface is
level, the vibrator head has a thin film of glistening paste around it,
and entrapped air ceases leaving the surface. Too much vibration
causes the concrete to segregate. |
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