Civil Engineering Reference
In-Depth Information
Table 11-1. Range of Characteristics, Performance, and Applications of Internal* Vibrators
Suggested values of
Approximate values of
Recommended
Eccentric
Rate of
Diameter
frequency,
moment,
Average
Centrifugal
Radius of
concrete
of head,
vibrations
mm-kg
amplitude,
force,
action,
†
placement,
Group
mm (in.)
per minute**
in.-lb (10
-3
)
mm (in.)
kg (lb)
mm (in.)
m
3
/h (yd
3
/h)
‡
Application
Plastic and flowing concrete in very thin
members and confined places. May be
used to supplement larger vibrators,
20-40
3.5-12
0.4-0.8
45-180
80-150
0.8-4
1
9000-15,000
especially in prestressed work where
(
3
⁄
4
-1
1
⁄
2
)
(0.03-0.10)
(0.015-0.03)
(100-400)
(3-6)
(1-5)
cables and ducts cause congestion in
forms. Also used for fabricating laboratory
test specimens.
Plastic concrete in thin walls, columns,
30-60
9-29
0.5-1.0
140-400
130-250
2.3-8
beams, precast piles, thin slabs, and along
2
8500-12,500
(1
1
⁄
4
-2
1
⁄
2
)
(0.08-0.25)
(0.02-0.04)
(300-900)
(5-10)
(3-10)
construction joints. May be used to supple-
ment larger vibrators in confined areas.
Stiff plastic concrete (less than 80-mm
[3-in.] slump) in general construction
such as walls, columns, beams, pre-
50-90
23-81
0.6-1.3
320-900
180-360
4.6-15
stressed piles, and heavy slabs. Auxiliary
3
8000-12,000
(2-3
1
⁄
2
)
(0.20-0.70)
(0.025-0.05)
(700-2000)
(7-14)
(6-20)
vibration adjacent to forms of mass con-
crete and pavements. May be gang
mounted to provide full-width internal
vibration of pavement slabs.
Mass and structural concrete of 0 to 50-mm
(2-in.) slump deposited in quantities up
to 3 m
3
(4 yd
3
) in relatively open forms of
80-150
8-290
0.8-1.5
680-1800
300-510
11-31
heavy construction (powerhouses, heavy
4
7000-10,500
(3-6)
(0.70-2.5)
(0.03-0.06)
(1500-4000)
(12-20)
(15-40)
bridge piers, and foundations). Also used
for auxiliary vibration in dam construction
near forms and around embedded items
and reinforcing steel.
Mass concrete in gravity dams, large piers,
massive walls, etc. Two or more vibrators
130-150
260-400
1.0-2.0
1100-2700
400-610
19-38
will be required to operate simultaneously
5
5500-8500
(5-6)
(2.25-3.50)
(0.04-0.08)
(2500-6000)
(16-24)
(25-50)
to mix and consolidate quantities of con-
crete of 3 m
3
(4 yd
3
) or more deposited at
one time into the form.
* Generally, extremely dry or very stiff concrete does not respond well to internal vibrators.
** While vibrator is operating in concrete.
† Distance over which concrete is fully consolidated.
‡
Assumes the insertion spacing is 1
1
⁄
2
times the radius of action, and that vibrator operates two-thirds of time concrete is being placed. These
ranges reflect not only the capability of the vibrator but also differences in workability of the mix, degree of deaeration desired, and other
conditions experienced in construction.
Adapted from
ACI 309
.
grade. The distance between insertions should be about
1
1
⁄
2
times the radius of action so that the area visibly
affected by the vibrator overlaps the adjacent previously
vibrated area by a few centimeters (inches).
The vibrator should be held stationary until adequate
consolidation is attained and then slowly withdrawn. An
insertion time of 5 to 15 seconds will usually provide ade-
quate consolidation. The concrete should move to fill the
hole left by the vibrator on withdrawal. If the hole does
not refill, reinsertion of the vibrator at a nearby point
should solve the problem.
Adequacy of internal vibration is judged by experi-
ence and by changes in the surface appearance of the con-
crete. Changes to watch for are the embedment of large
aggregate particles,general batch leveling, the appearance
of a thin film of mortar on the top surface, and the cessa-
tion of large bubbles of entrapped air escaping at the sur-
face. Internal vibration may significantly affect the
entrained-air-void system in concrete (
Stark 1986
, and
Hover 2001
). Detailed guidance for proper vibration
should be followed (
ACI Committee 309
).
Allowing a vibrator to remain immersed in concrete
after paste accumulates over the head is bad practice and
can result in nonuniformity. The length of time that a
vibrator should be left in the concrete will depend on the
workability of the concrete, the power of the vibrator, and
the nature of the section being consolidated.
In heavily-reinforced sections where an internal vi-
brator cannot be inserted, it is sometimes helpful to
vibrate the reinforcing bars by attaching a form vibrator to
