Global Manufacturing, Inc
®
800.551.3569
TOLL FREE USA & CANADA
1801 East 22nd Street
501.374.7416
TEL
501.376.7147
FAX
Little Rock, AR 72206 USA
w w w. G l o b a l M a n u f a c t u r i n g . c o m
9
Tips for using External Vibrators for
concrete consolidation
:
Proper placement of the external vibrators is critical
to ensure that the vibration is distributed over the
desired area of the concrete. Depending on the
concrete consistency, density of embedments and
the quality of the mounting, External Vibrators
produce an Area-of-Influence determined by the
force and frequency of the vibrator and the duration
of the vibrating time.
The following guidelines for spacing External
Vibrators have been developed, but contractors
should determine specific spacing requirements
for each project to ensure complete coverage of
vibration and successful consolidation.
Vibrator Spacing
for Concrete Consolidation
Consistency
Slump
Distance
between
Vibrators
Very stiff or
stiff concrete
< 1.0"
< 25 mm
5' Apart
1524 mm
Stiff plastic
concrete
1.0 − 2.0"
25 − 50 mm
6' Apart
1828 mm
Plastic
concrete
2.0 − 5.0"
50 − 127 mm
7' Apart
2134 mm
Flowing
concrete
> 5.0"
> 127 mm
8' Apart
2438 mm
Vibrating times for external vibrators may be
longer than for immersed internal vibrators. Most
operators will initially vibrate for approximately
two minutes per lift, and increase or decrease
vibrating times as needed. Note that the same
criteria should be used to determine when the
consolidation is complete (no air bubbles at the top
surface, a thin film of mortar on the top surface
and a stabilization of the speed of the vibrator).
Pour concrete into the forms in evenly dispersed
layers (lifts). Do not exceed a 20" lift height
otherwise the weight of the concrete can prevent
the entrapped air from escaping. Operate vibrators
in conjunction with each lift until the concrete is
fully consolidated. As each subsequent lift is placed,
locate additional vibrators for operation (or move
them from the previous level). Some operators
prefer to operate the previous lift’s vibrators for
a short period of time to promote “knitting” of the
two layers together.
Important!
If the thickness of the concrete to be consolidated
is greater than the area of influence of the vibrator,
or if a higher-quality finished surface is required on
both sides, the contractor should locate alternate
vibrators on opposite form walls. For instance, the
first vibrator is placed on the front wall and the
next is 5' (1.5 m) away but on the back wall. See
illustration below.
Alternating the vibrators on a concrete form
In some cases, when the thickness of the concrete
to be consolidated is extraordinarily large,
contractors may choose to use Internal Vibrators
in the center section, with External Vibrators used
simultaneously along the outer edges.
Forms should be well made to withstand the
strains of vibration.
1. If using wooden forms, use screws instead of
nails (which may back out with vibration).
2. Forms need to be well braced to prevent bulging.
3. Joints need to be closely fit to prevent leaking.
4. Monitor forms during placement of concrete.
Tighten as needed.
Vibrators on the opposite
side of the form.
Vibrators on the near
side of the form.
