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Technical Details
Right after placement, concrete contains up to
20% entrapped air. The amount varies according
to the type of mix and its
slump, the placement
method, form size, and the
amount of reinforcing steel
used. Concrete vibration can
improve the compressive
strength of the concrete by
about 3% to 5% for each
percent of air removed.
Vibration consolidates
concrete in two stages: first
by moving the concrete
particles, then by removing
entrapped air.
Vibration settles the concrete
by subjecting the individual
particles to a rapid succession of impulses, causing
differential motion (each particle moving
independently of the other). The particles consolidate
as trapped air are forced to the surface, allowing the concrete to flow into corners,
around rebar and flush against the form face.
This eliminates voids (honeycombing) and brings
paste to the surface to assist in finishing. Since
concrete flows better with vibration, the mix can
contain less water, thereby providing greater
strength for the finished product.
Until both vibration stages are complete, the
concrete isn’t fully consolidated. If the vibrator is
removed too soon, some of the smaller bubbles
don’t have enough time to move to the surface. |
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