Vibration Techniques
Thorough compaction and
thus the removal of air is paramount for concrete to
cure to full strength and therefore durability.
Currently the most effective way of achieving this is
the induction of vibration into the concrete. Vibration
can be induced either by a traditional poker device or
via our new vibratory free screeding tools that
eliminate the need for a poker.
Concrete should be placed
in layers no more than 450mm deep. Each layer should be
vibrated before the next layer is placed. This ensures
the air bubbles can escape to the surface and don't get
trapped. The next layer has to be vibrated before the
previous layer has hardened. The vibration should
penetrate the first layer by about 100mm to ensure a
good bond between the two layers.
When using a poker
only a small area
around the poker will be compacted to an appropriate
degree. The size of
this area depends on a number of factors; size of the
poker head, frequency and amplitude of the vibration,
slump of the concrete, aggregate and admixtures, amount
and size of reinforcement bars, distance from the
formwork.
Watch the surface around the
poker, the size of the
of the compaction circle can be determined by the 'fat'
that rises to the surface. This 'fat' aids in providing
a final finish to the concrete. For complete compaction the poker should be inserted at intervals so
these circles overlap.
Choosing a vibrator
The size of the job and
the power supplies available on site will determine
which type of poker to use.
-
Hand held, small jobs powered by mains electric or a
generator
-
Backpack pokers, powered by small backpack mounted
Honda engine
-
Electric high frequency
The selection of head size
is determined by the application. Small diameters for
small concrete volumes, and narrow areas, larger
diameters increase productivity on large pours. Rubber
coated heads are also available that protected Epoxy
coated rebar.
Caution!
Do not drag the poker
through the concrete as pockets of air are likely to be
trapped
Do not over vibrate, holder
the poker in place for too long will cause the
aggregate, sand and cement to separate out and reduce
the strength of the concrete
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