CONCRETE LIBRARY OF JSCE NO. 33, JUNE 1999
RESEARCH ON SELF-OOMPACTABILITY OF HIGH-FLUIDITY CONCRETE
(Translation from Proceedings of JSCE, No.571/V-36, August 1997)
Hiromi FUJIWARA
Shigeyoshi NAGATAKI
Akito DOZONO
Akira OBATAKE
High-fluidity concrete is a concrete that is expected to self-fill (or self-compact) within
formwork. The realization of such concrete makes possible the mechanization of concrete work.
This study aims to propose method of predicting the degree of self-compaction in formworks .
Some factors which have some effects on the self-compactability, such as surface resistance
on formworks , internal friction angle, resistance due to_steel reinforcing bars ware estimated
and a method of predicting was constructed by comb:i.ning these factors . ‘This method was verified
experimentally and the validity was con:E:L'|:med.
Keywords: Iiigz-fluidilj/concrete, self-cmpactabili £3/, sun!-‘ace resistance, internal friction
angle, resistance due to steel reizzforaing bars
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Hiromi Fujiwara is a Manager and Chief Research Engineer at CEREFO Research in Tokyo. He
obtained his D.Eng. from Tokyo Institute of Technology in 1996 . He has been engaged in
fundamental research in the field of cement and admixture. He has been also engaged in
developing new concrete products . He is a member of JSCE.
Shigeyoshi Nagataki is a Professor in the Department of Civil Engineering and Architecture
at Niigata University and an Emeritus Professor at Tokyo Institute of Technology. He obtained
his D.Eng. from the University of Tokyo in 1966 . He is a member of JSCE and a past Vice President
of JSCE. He has written many papers on concrete. He is a Fellow of both JSCE and ACI.
Akito Dozono is a research engineer at Taiheiyo Cement C0. . He obtained his M.Eng. from
Hiroshima University in 1992 . He has been engaged in fundamental research in the field of
cement and admixture. He is a member of JSCE.
Akita Obatake is a research engineer at Taiheiyo Cement C0. . He obtained his B.Eng. from
Okayama University in 1994 . He has been engaged :i.n deneloping new concrete products . He is
a member of JSCE.
1
. INTRODUCTION
High-fluidity
concrete is a concrete that is expected to self-fill
(or self-compact) within
formwork. The realization
of such concrete makes possible the mechanization of concrete work.
The basic requirement of high-fluidity
concrete is to ensure non-segregation of the materials
while maintaining high-fluidity,
and to achieve this yield point of the concrete must be set
greater than a certain value. Since this is not a Newtonianfluid like water, a limit exists
naturally on its self-compactability.
In cases where high-fluidity
concrete is placed in
locations where confirmation of self-compacting is not possible by eye with overconfidence.
The possibility
exists of serious error as a result of inferior compacting.
The purpose of this research is to construct a model of the self-compacting mechanism and
verify its conformity. Wewill then propose a method of predicting the degree of compaction
as a wayto increase the reliability
of self-compacting high-fluidity
concrete.
2. SYNOPSIS OF RESEARCH
The compaction of high-fluidity
concrete in formwork as considered in this research takes
place under conditions where the top surface of the concrete is not observable as in the case
of a box culvert. Compaction under conditions where the top surface is open is treated
separately.
The first step in the research wasto construct a self-compacting mechanismunderthe assumption
that the determinants of compaction are three: a)surface resistance between concrete and
formwork,b) internal friction angle of the concrete , and c)resistance
due to steel reinforcing
bars. These factors were then evaluated quantitatively
and formulas were prepared for
estimating them from the mix proportion of the concrete and the conditions under which work
is executed. Finally, the compacting properties of high-fluidity
concrete are measured by
actually placing concrete into model forms and actual box culverts, using the results to
demonstrate the validity of the compaction model. Based on the results , a method of predicting
self-compacting properties is proposed.
3.
CONSTRUCTION OF SELF-C30MPACTION
3. 1 Definition
MODEL
of Factors
The factors which determine the self-compactability
of high-fluidity
concrete (surface
resistance between the concrete and formwork; resistance due to steel reinforcing bars ; and
internal friction
angle of the concrete) are defined as follows.
Surface resistance
(r h) and resistance(r)
due to steel
reinforcing
bars are
defined by formulae (1) , which gives the balance of power under conditions
where
the concrete is suspended in a pipe duct in which steel
reinforcing
bars are
arranged shown in Fig-1.
Fig-1
Power Balance of Concrete at Suspension
Condition
in Pipe Duct with Steel
Reinforcing
Bars
-28
-
d(P+p
2 7trl+rX7tr2
à"gà"z)X7Tr2
(1)
dx
Where, P: Ps-Pe; p: density;
r: radius
of pipe;
1: length
g: acceleration
of pipe.
due to gravity,-
Internal
friction
angle (<J>) appears
as a phenomenon in which concrete
internal
pressure
in the vertical
direction
{ a j falls
below the pressure
in the
pressurizing
direction
(crj,
resulting
in loss of fluidity
at the corners of
the formwork. This internal
friction
angle is defined
by formulae
(2),
which
is derived from the yield conditions
of Mohr-Coulomb. This formulae ignores the
adhesive
property
of concrete.
It is reasonable
to do so because,
in the case
of high-fluidity
concrete whose slump flow is greater
than 500mm, adhesion
(the
yield
point)
is quite
small.
OJOV=tan2(45°
-0/2)
(2)
3
.2 Self-compacting
Mechanism
The self-compactability
of high-fluidity
concrete is assumed to be determined
by how the pressure
generated
by placement
height
is transmitted
to the tip of
concrete flow without
loss.
It is further
assumed that only loss of pressure results
from surface resistance
on formwork, resistance
due to steel reinforcing
bars, and the internal
friction
angle of concrete,
as previously
mentioned.
Namely, it is considered
that
the stop of flow is caused by a phenomenon in
which the pressure
generated
by placing
height
balances
the pressure
loss due
to surface resistance,
resistance
due to steel reinforcing
bars, and the internal
friction
angle as shown in Fig-2.
In this figure,
it is assumed that length of a wall member is sufficiently
great
compared with the thickness
of a wall member (wx« b),
and that
the steel
reinforcing
bars are arranged at regular
interval.
The mechanism of pressure loss is now explained.
In this explanation,
the model
formwork is of U shape (gutter
shape),
as shown in Fig-3,
and the concrete is
placed from the wall member on one side.
R
esistance
due to
steel bars
Pressure loss at
second corner
Fig-2
Pressure loss at
first corner
Power Balance in U-Shaped
(Gutter
Shaped)
Formwork
Fig-3
-29
-
Model
of
Formwork
a) Incipient
pressure
resulting
in fluidity
The fluidity
of concrete in the formwork derived from the height of placed concrete
in the wall member. The incipient
pressure (P0:Pa)
is expressed by formulae (3)
in terms of height
from the formwork bottom to the placing
position
(h0 : cm)
and concrete
density
(p c:g/cm3)
as follows.
P0
= (p0-h0-gjXicr1
(3)
Where, g: acceleration
due to gravity
(980cm/s2)
b) Loss of fluidity
due to resistance
of wall member in which concrete is placed
Some of the incipient
pressure obtained
as in a) above is to surface resistance
in the formwork and to resistance
due to the steel
reinforcing
bars.
This loss (Px:Pa)
is expressed
by formulae (4) in terms of surface resistance
stress
(rh : Pa), resistance
due to the steel
reinforcing
bars in a closed path
(r:Pa),
the number of layers of steel reinforcing
bars crossing
the wall (nh),
the thickness
of the wall member (w^cm) , and the thickness
of the bottom member
(w2:cm).
Pi={2(r
h/Wl)
à" (h0-w2/2)+T
'nh}
c) Loss
of fluidity
at
first
corner
Concrete
placed
into
the wall loses
internal
friction
angle.(<f>:°
). This
terms of P0 and Px.
(4)
pressure
loss(P2:Pa)
at
is
the first
expressed
P2=(P0-P1)-{l-tan2(45-<|)/2)}
(5)
d) Loss of pressure
due to resistance
at formwork bottom
As with b) above, the pressure loss (P3:Pa)
given by formulae
bottom.
P3=((?h
/
corner
due to the
by formula
(5) in
w2)à"(21b-w1-w3)
+7
'^}
(6)
occurs
at the
(6)
Where, nx: number of layer of steel
reinforcing
bars passing
the bottom;
lb: length of bottom member (cm);
and w3: thickness
member at opposite
side(cm).
through
of wall
If the inequality
(7) holds
true, the concrete rises in the wall facing the wall
where concrete is placed.
But if not hold true, the concrete stops at the bottom.
P1+P2+P3^
P0
(7)
That is, suppose inequality
(7) does not hold true, this means that the incipient
pressure is balanced by the total resistance,
and in this case the distance
(1J
of the concrete tip from the wall where it is placed is expressed by formulae
(8).
!1=l(P0-P1-P2)/{(2(
Where,
r
1 : interval
e) Loss amount at
If inequality
(7)
it is placed,
and
generated
at the
h
/w2)
à"1+T)}+wx
between
(8)
steel
reinforcing
bars
the second corner
hold true,
concrete
rises
in the wall facing
the one where
in this case the loss (P4:Pa)
expressed
by formulae
(9) is
second corner.
P4=(P0-P1-P2-P3){l-tan2(45-d)/2)}
f) Resistance
The pressure
(cm).
(9)
of opposite
wall
available
to push the concrete
-30
-
up in the opposite
wall
(P5:Pa)
is
expressed
by formulae
P5
=
(10).
P0-Pi-P2-P3-P4
(10)
The concrete stops at the position
where this pressure is balanced by the surface
resistance
of the formwork, the resistance
due to the steel reinforcing
bars,
and the dead load of the concrete.
In this case the rise height
(h^cm)
is expressed
by formulae (ll).
h
ai-
w3-P5+w2-rh-n2-w3-y
~
2Th +pcà"W3
;
(ll)
à"gx10
Where, n2: number of layer
the rise portion
4.
Evaluation
4.1
Outline
of Surface
of
of steel
Resistance
of
reinforcing
bars
passing
through
Formwork
Experiment
An experiment was carried out to obtain the surface resistance
by measuring the
displacement
and load against
a test plate as it was drawn out of fresh concrete.
a) Materials
used for the experiment
Cement (NC) :Ordinary
portland
cement (specific
gravity
3.15)
Fine aggregate
(S) :Crushed
sand produced from Mizuho (F.M =2.90. , specific
gravity
2.61)
Coarse aggregate
(G):Crushed
stone produced from Ome (Max. size 20mm,
specific
gravity
2.64,
solid
content
59.8%)
Superplasticizer(Sp)
: 0- Naphthalene
sulfonic
acid salt
Viscosity-controlling
admixture (HF) :Acrylic-based
water-soluble
polymer
b) Experimental
conditions
As mix proportion
factors,
the volumetric
ratio
of coarse aggregate
in the
concrete (X^) and its rheological
properties
(yield
point and plastic
viscosity)
were
adopted.
Four
in order to change
HF were used:
1.3,
levels
of
X,,,
the rheological
2.0 and 2.7%
As composition
of mortar portion
referring
to the mix proportion
Cement : Water
: Fine
0%,
25.0%,
30.0%,
and
35.0%
properties
at X^SO.0%,
of the weight
of cement.
were
three
adopted
mix ratios
and
of
following
constant
mix proportion
was adopted
of ordinary
high-fluidity
concrete [1].
aggregate
= 20.6
: 27.1
: 52.3
(volume
ratio)
Sp was added at the ratio of 3% liquid
weight to cement weight. The mix proportions
are shown in Table-1.
Test plates
of two materials
were used, i. e. steel
plates
and plastic
plates
(of vinyl
chloride),
with the latter
softer
than the former.
Further,
in order to investigate
the effects
of withdrawal
rate and concrete
pressure on surface resistance,
the withdrawal
rate of the test plate
and the
depth
to which it was inserted
were taken up as factors
and studied.
The
combinations
of these factors
are shown in Table-2.
Tests were carried
out after wiping away surface dirt using acetone.
In order
to study the effects
of a surface treated
with mold lubricant,
the combinations
marked with an asterisk
in Table-2 were treated
with oleaginous
and aqueous mold
lubricant.
c)Mixing
method
A pan-type mixer of capacity
O.lm3 was used. Cement, SP, water, fine aggregate,
and HF were fed into the mixer and the mortar portion was mixed for two minutes'.
The rheological
properties
of the mortar were then measured. Next, the coarse
aggregate
was fed into the mixer and the concrete was mixed another two minutes.
-31
-
Table-1
M ix
p r o pN oo r .t i o n
Mix Proportion,
* xv
%
Rheological
HF
m i x in g
r at io
% )
Sp
ad d it io n
r a ti o
%
Un i t
Properties
W ei gh t
(k g / m 3 )
NC
w
s
and Slump Flow
Rn e o lo g ic a l
p r op e rt i es of
m o r ta r
S lu m p
fl ow
(ra m )
fl pI
G
* t
Pa
P a 's
ﾖ
0 .0
2 .0
3 .0
65 0
2 70
1 36 5
0
2 4 .5
l l .2
ｩ
2 5 .0
2 .0
3 .0
47 4
1 98
99 6
6 59
2 4 .5
l l .2
6 30
9 .8
8 .2
6 60
2 4 .5
l l .2
6 00
4 1 .2
1 4 .4
5 20
2 4 .5
l l .2
5 25
ﾖ
1 .3
ｩ
3 0 .0
2 .0
ｩ
3 .0
441
1 84
92 8
7 91
2 .7
ｩ
3 5 .0
2 .0
>& Volumetric
ratio
3 .0
409
of coarse
Table-2
1 71
86 0
aggregate
Experimental
9 23
in concrete
Combinations
M a te r ia l
Mix
p r op o rt io n
No .
S te e l
i n s e r t (c m )
40
60
20
W i t h d r a w a l v e l o c i t y (m m / m i n )
5 .0
1 0 .0
1 .0
20
1 .0
(D
ｩ
ﾖ
ﾖ
ｩ
ｩ
P la s t ic
De p th
o
o*
o
^ Oleaginous
o
o
o
o*
o
o
o
o
o
of
o
o
o
o
o
o*
o
and a q u e o u s mold lubricant
o
o
o
o
o
40
60
1 .0
o
o
o
o
o
o
o
o
o
o
applied.
d)Test
items
©Yield point and plastic
viscosity
of mortar
A SOOcc mortar sample w a s taken immediately after m o r t a r mixing of w a s f i n i s h e d
and its plastic
viscosity
(77 pl) and yield point (t f) were m e a s u r e d using a
revolving viscometer (with an outer revolving cylinder).
It was confirmed at
this time that no slipping had taken place on the cylindrical
wall surface and
the sample w a s fully flowing.
After m e a s u r e m e n tsample was returned to the mixer.
©Slump flow of concrete
In a c c o r d a n c e with JIS A1101 (slump test)
the slump flow w a s m e a s u r e das the
diameter of spread.
©Surface resistance o n f o r m w o r k
The equipment used to m e a s u r e s u r f a c e
L oad cell
resistance is shown in Fig-4.
The test
plate was inserted into the concrete and
I IT
then d r a w n up at a constant speed while
measuring displacement and load. The load
P la te b o ard
(T h ickn ess
w a s increased sharply as the test plate
. 0 .2 m m ) 60
w a s d r a w nup and the m a x i m u m
value over
the displacement from 2 to 10mm was
'0
recorded.
Surface
resistance
was
obtained by subtracting the value (weight
k - zo - ;
of test
platebuoyancy) from the
m a x i m uvm
a l u e a n d dividing it by all the
U
s u r f a c e a r e a of the test plate in contact
nit: cm
30
with the concrete at the start
of
withdrawal.
Fig-4 Measuring
Equipment
of
Surface Resistance
-32
-
Table-3
Measurement Results
for
Surface
Resistance
M at er i al
Mix
p r op or t i on
No .
S te e l
D e p t h o f i n s e r t (c m )
40
60
20
W i t h d r a w a l v e l o c i t y (m m / m i n )
5 .0
1 0 .0
1 .0
M e a su re
20
-m e rit
1 .0
ﾖ
(2 )
Su r f ac e
r e si st a nc e
6 .9
9 .8
l l .7
l l .7
1 .0
20 .5
1 7 .6
1 8 .6
9 .8
2 1 .5
2 1 .5
1 9 .6
l l .7
( 1 5 . 6 1* 1
(l l .7 )* 2
ll .7
(l l .7 }* 1
( 9 .8 * 2
1 2 .7
l l .7
( 1 5 .6 ) * 1
( 1 0 .7 )* 2
2 1 .5
2 1 .5
1 9 .6
23 .5
2 2 .5
20 .5
2 8 .4
2 5 .4
22 .5
13 .7
mold lubricant
1 4 .7
ll .7
1 9 .6
1 9 .6
l l .7
1 3 .7
: Oleaginous
60
8 .8
ｩ
ｩ
*1
5 .9
40
8 .8
ﾖ
<D
3 .9
P l a st ic
applied
Aqueous mold lubricant
applied
Results
of
Experiment
and
Consideration
O
Measurements of rheological
properties
: Ste l
20
D : Plastic
and slump flow are shown in Table-1. All
«/
mix conditions
yielded
a slump flow of
at least
500mm and were highly
fluid.
Table-3
shows the
measurements
of
surface resistance.
These results
prove
10
that surface resistance
was quite small,
Depth of insert : 40(cm)
reaching
at most about 28Pa.
HF mixing ratio : 2.0(%)
In
Fig-5 ,
the
relation
between
Withdrawal speed : 1.0(mm/min)
volumetric
ratio
of coarse aggregate
0
20
40
(Xy) and surface
resistance
is shown.
Volumetric ratio of
The surface resistance
increased
with
coarse aggregate Xv(%)
Xy. This seems due to the increase
in
Fig-5 Result of Surface Resistance
to
the
amount of coarse
aggregate
in
Volumetric
Ratio of Coarse Aggregate
contact
with the test plate.
In cases where the plate material
was
the softer
plastic,
the surface resistance
was higher.
The reason for this is
thought to be the following.
In the case of a smooth, hard surface,
the surface
resistance
is controlled
by a thin boundary layer,
whereas if the surface
is
coarse or soft,
the fine aggregate
is first
retained
and then later
the coarse
aggregate,
thus leading
to a higher
surface resistance.
As to the other factors,
no difference
in surface resistance
was observed among
the various levels.
Regression
formulae in which the surface resistance
( r h:Pa)
is adopted as the object
variable
and Xv(%) as the predictor
variable
are given
\
4. 2
below.
Using these formulas,
estimated
from Xv.
©Steel
plate
= 0.39XV
©Plastic
surface
of the
formwork can easily
- 0.02
(12)
+
(13)
2.13
. EVALUATION OF INTERNAL
5.1
resistance
plate
= 0.65XV
5
the
Outline
The evaluation
high-fluidity
of
FRICTION
ANGLE OF CONCRETE
Experiment
of internal
friction
angle was implemented
as follows.
First
concrete
was placed
into a column-shaped
form, and the pressure
-33
-
be
Table-4
Mix Proportions,
Rheological
Properties,
and Slump Flow
R ne ol og ic al
H F
Xv
%
m ix
r a tio
% )
Sp
ad di ti on
ra ti o (% )
U n it
w e i g h t (k g / m 3)
pr op er ti es
o f
mo r tar
N C
w
s
G
?
t
Pa )
Pa
pi
s )
Slu mp
f lo w
(m m )
2 6 .0
2 .0
46 7
6 .5
67 0
45 4
98 3
95 6
l l .3
2 .0
1 95
1 89
68 6
2 8 .0
7 39
l l .1
9 .8
7 .9
6 .2
63 0
66 0
44 1
1 84
92 8
7 91
1 4 .5
8 .2
60 0
2 2 .3
9 .4
58 0
1 .3
3 0 .0
2 .0
3 .0
2 .7
3 2 .0
3 4 .0
2 .0
2 .0
42 8
41 5
1 79
1 73
90 1
8 45
l l .8
6 .9
61 5
8 74
8 98
1 2 .3
6 .9
61 0
distribution
in the horizontal
direction
on the sides of the formwork was measured.
The results
were compared with a calculated
value of pressure assuming a liquid.
a)Materials
used for experiment
The same materials
as used in Section
4 were adopted.
b)Experimental
conditions
As a factor indicating
of concrete properties,
Xywas set at five levels:
26.0,
28.0,
case
30.0,
32.0
and34.0.
TheratioofHFwas
when the three
levels
1.3,
2.0,
set at 2.0%,
except
2.7% were adopted.
and
intheXv=30.0%
The basic composition
of the mortar portion was the same as that used in Section
4. A 3% ratio of SP to cement weight was used. The mix proportions
of respective
concretes
are shown in Table-4.
c)Mixing
method
The same mixing method applied
in Section
4 was applied.
d)Test
items
ÖRheological
properties
of mortar
The yield point and plastic
viscosity
were measured using the method described
in Section
4.
©Slump flow of concrete
The method described
in Section
4 was used.
ÖInternal
friction
angle of concrete
The shape of the formwork and pressure sensor locations
used for evaluating
the
internal
friction
angle are shown in Fig-6.
Ten pressure
sensors were used to
measure pressure
in the transverse
direction.
While filling
the formworkwith concrete,
it was desired to avoid the transmission
of vibration
to the formwork as much as
possible.
Consequently,
the concrete
was filled
gently downward with a small
cup.
Immediately
after
compaction,
a
pressure in the transverse
direction
D
(a h) on the side faces of the formwork
D
was measured. The pressure
of liquid
m
o
D
pressure
distribution
(a v) was then
(/)
q
10@ 10
calculated
for the depth of each sensor
<u
D
C
O
10
0)
and using
the specific
gravity
of
D
9
concrete.
The internal
friction
angle
<CnO
m<U
($)
was obtained
using formulae (2).
D
FM
5
.2 Consideration
Experimental
Results
D
and
15
The measured rheological
properties
of
the mortar and the slump flow are shown
in Table-4.
All mix proportions
-34
15
u
Fig-6 Equipment for
Internal
Friction
-
it :cm
Evaluating
Angle
30000,
30000i
Liquid pressure
distrib utio n
£
PL(
V
V
fe 20000!
: Liquid pressure
distrib utio n
&
20000i
2 loooof
ioooob
P
0
SO
M
100
0
50
Depth of concrete (cm)
Fig-
7 Relation
Depth
between
and
-
100
Depth of concrete (cm)
Concrete
8 Relation
Fig-
a h(Xv=26.0%)
Depth
between
Concrete
and a h(Xv=28.0%)
30000i
30000,
&
aoooop
T OOOOffM
0
100
D
Fig-9
Relation
Depth
and.
between
Concrete
Fig-10
CTh(Xv=30.0%)
yielded
slump flows of more than 500mm
and exhibited
high-fluidity.
In Figs-7
~11,
the relations
between depth
of
concrete
and a h for each Xy are shown.
(In case of Xv = 30.0%,the
mix ratio
of
HF
50
1 00
Depth of concrete (cm)
epth of concrete (cm)
Relation
between Concrete
Depth and a h(Xv=32.0%)
30000,
= 2.0%)
The pressure distribution
was nearly
proportional
to the depth of concrete,
but it was observed that the ratio
of
pressure in the transverse
direction
to
calculated
liquid
pressure
( a h/a v)
became small as ^ increased.
This seems
to be because the effect
of coarse
aggregate
meshing
becomes
more
significant
as Xy becomes large.
Next, the relation
between mix ratio of
HF (atXv=
in Fig-12.
observable
Next,
the
30.0%)
and (ah/av)
is shown
Almost
no difference
is
with a change in HF ratio.
relation
between internal
-35
S
P
10000t
4
0
50
100
Depth of concrete (cm)
Fig-ll
Relation
between Concrete
Depth and ah(Xv=34.0%)
4
à"6-
¥
1
O
r.
b
X Ov : 30 .0
(% r, )
_o
tj
n
74
Relation
and ah/av
friction
analysis
predictor
between
this
32
36
HF Mix Ratio
Fig-13
Relation
Internal
between Xv and
Friction
Angle
angle of concrete
(<f>:°
) and Xv is shown in Fig-13.
A single
regression
using internal
friction
angle as the object
variable
and ^ as the
variable
was carried out, yielding
the following
regression
formulae:
= 0.025X/-
Using
28
Volumetric ratio of
coarse aggregate Xv(%)
HF mix ratio (%)
Fig-12
3
<u
"5b
ca
c
2
D
b
formulae,
l.SVXv
the
+
internal
(14)
20.9
friction
angle
can easily
be estimated
from
Xv.
6
.EVALUATION
6.1
Experiment
OF RESISTANCE
DUE TO STEEL
REINFORCING
BARS.
Planning
A quantitative
evaluation
of the resistance
imposed by steel reinforcing
bars
when high-fluidity
concrete flows into formwork was carried out. Twocases were
considered:
a relatively
large section
in which concrete can pass all clearance
between the steel
reinforcing
bars and between steel
reinforcing
bars and
formwork surface,
and a situation
in which concrete is blocked between steel
reinforcing
bars and formwork surface as it passes between two steel reinforcing
bars. In the latter
case, the fact that concrete
cannot pass between steel
reinforcing
bars and formwork surface means the space of it causes the loss of
sectional
area for passing
and so great resistance
was expected to occur. The
resistance
due to steel reinforcing
bars in these two cases was evaluated
in
separate
experiments.
6
.2 Experiment
I
Resistance
due to Steel
when Concrete
Passes
Evaluation
Reinforcing
All Clearances
of
Bars
a)Outline
of experiment
Test apparatus
A, as shown in Fig-14,
was used
for the test and the clearance
of steel bars
and loss ratio of sectional
area for passing
due to steel bars were varied by altering
the
number of steel bars in the section
and their
diameter,
as shown in Table-5.
The steel bars
were arranged
longitudinally
at
equal
intervals.
The left-hand
chamber was filled
up to the top with concrete,
and the gate was
opened. When the movement of concrete had
-36
-
MO
_.i,_
_HO
Unit (mm)
Fig-14
Test
i^
'200_
Passing section
Apparatus
A
Table-5
Combinations
of Steel
Bars,
and Loss Ratio of Sectional
D i a m e t e r
o f
N o .
s t e e l
b a r s
o f
3
4 3 .3
1 3 .5
1 3
4 0 .3
1 9 .5
H F
mi x
r at io
% )
Xv (% )
.0
.0
.0
.0
s te e l
o f
5 8 .0
1 3 .0
(nun )
L o s s
r at io
ar e a
fo r
o f
R e si s ta n ce
d u e to st ee l
b a r s
s ec ti on a l
p a ss in g
X v
%
(P a )
s t e e l
mm)
b a r s
2
1
1 9 . 0
8 7 .5
1 2 .5
8 1 .0
3 8
1 9 .0
and Slump Flow of Concrete
NC
4
4
4
4
Stage,
5 4 . 0
U n it w e igh t
(k g /m j)
w
53
41
28
16
Resistance
b ar s
(m m )
Cl e ar an c e
9 3 . 5
6 .5
3 .0
b ar s
st ee l
o f
3
2 5
Sp
ad di ti on
ra ti o
% )
2 .2
N o .
s t e e l
b a r s
1 9m m
Mix Proportions
Table-7
o f
o f
6 . 0
9
Di am e t er
D i a m e t e r
1
6 2 .7
Table-6
N o .
b a r s
2
6 m m
2 6
28
30
32
s t e e l
Clearances
of Steel Bars (Upper
Area for passing
(Lower Stage,
20
20
19
18
s
7
1
5
9
due to Steel
S lum p
fl ow
(m m )
G
96 4
93 7
910
8 84
6
7
7
8
reinforcing
86
39
91
45
61
59
60
57
5
0
7
1
'
bars
2
1
3
2
1
3
2
1
6 .0
13 .0
9 .0
13 .0
2 5 .0
13 .0
1 9 .0
3 8 .0
St a nd a rd
6 2 .7
9 3 .5
4 3 .3
58 .0
8 7 .5
40 .3
5 4 .0
8 1 .0
v a lu e
Pa
1 9 .0
6 .0
6 .5
1 3 .5
13 .0
1 2 .5
19 .5
1 9 .0
26 .0
49
4 9
88
8 8
49
12 0
11 8
9 8
28 .0
3 43
24 5
10 3 0
34 3
2 1 6
98 0
4 0 0
29 4
5 7 8
30 .0
1 02 9
19 6
48 0
1 96
4 8 0
2 8 4
1 24 5
1 6 80
8 79
1 60 8
1 50 1
1 52 1
(% )
3 2 .0
B lo ck in g
B lo ck in g
B lo ck -
4 5 1
in g
B l o ck in g
B l o ck in g
2 2 5
stopped,
the height
of concrete
in the left
and right
chambers was measured.
The pressure
difference
was then calculated
from the specific
gravity
of the
concrete.
The pressure difference
was also measuredwith
no steel bars in place,
and this value was used as the standard
value.
The resistance
due to the steel
bars was evaluated by subtracting
the standard value from the pressure difference
under each respective
condition.
The materials
used in the experiment
were the same as described
in Section
4.
The Xvvalue of the concretewas
set at four levels:
26.0,
28.0,
30.0,
and 32.0%.
The composition
of mortar portion
was: cement : water : fine aggregate
= 20.0 :
28.7
: 51.3
(by volume).
This composition
was kept constant
throughout
the
experiment.
The mix ratio of HFwas 2.2%. The Mixproportions
are shown in Table-6.
The slump flow of concrete
was measured by the same method as used in Section
4.
b)Experimental
results
and consideration
In Table-6,
the slump flow results
are shown together
with the concrete
mix
proportion.
All mixes exhibited
high-fluidity.
Table-7
shows the measured
resistance
due to steel
bars. Ignoring
situation
where blocking
occurred,
the
results
were subjected
to multiple
regression
analysis
in which the object
variable
was resistance,
and the regression
formulae obtained
is shown below.
In this
case, a predictor
variable
with a 5% of significance
level was chosen.
r
o = 183.6
Xy
-
ll.3L
-
(15)
3982
-37
-
Where, r 0: resistance
due to steelreinforcingbars
ratio
of coarse aggregate
(%);
L: clearance
(Pa)
of steel
; Xv: volumetric
bars (mm).
Based on this formulae,
it is clear that within the range of this experiment,
the resistance
increased by about 180Pa for every 1% increase in Xv and decreased
by about 10 Pa for every 1mmincrease
of clearance
steel bars. This formulae
makes possible
the estimation
of resistance
value based on mix proportion
and
steel
bar arrangement.
6.3 Experiment
n ; Evaluation
Blockage
Occurs between
Steel
of Resistance
due to Steel
Bars and Formwork Surface
Bars
When
a)Outline
of experiment
In this experiment,
test apparatus
A was used in conjunction
with apparatus
B
and C, as shown in Figs-15
and 16 respectively.
The section between steel bars
and formwork surface (less
than 35mm) which was considered
to cause blockage
and steel reinforcing
bars was lost sectional
area forpassing
as shown in Fig-17
and the resistance
due to steel
bars was evaluated.
In this experiment the
diameter of steel bars was assumed to be 13mmand the clearance between steel
bars and formwork surface was to be three levels:
25, 30, and 35mm. Each of
lost sectional
area for passing was set in the experiment apparatus
using wooden
plate.
Arrangement directionwas
to be two levels of longitudinal
and transverse.
The Xv value of the concrete was set at six levels:
24.0 to 34.0%.
The experimental
conditions
are
shown inTable-8.
The resistancewas
evaluated using the same procedure as
in experiment I. The slump flow of the
concrete
was measured in parallel
with the experiment.
The materials
used and the basic composition
of the
mortar portion
were the same as in
experiment I. The Addition
ratio of
Sp was 3% and the mix ratio of HF was
2.2%.
The mixes proportion
of the
concrete
are shown in Table-9..
b)Experimental
results
The
measured
s lump
flow
and
resistance
due to steel
reinforcing
bars are shown in Table-10.
Based on
U
nit(mm)
Passingsection
these results,
multiple
regression
analysis
was
conducted
using
Fig-15
Test Apparatus
B
resistance
as the object variable
and
Lost sectional
3
area for passing
13
: H
H W
^- Steel bars -^
S
U
Fig-16
nit (mm)
Passing
Test
Apparatus
ection between steel
bars and formwork surface
section
C
Fig-17
-38
-
Passing
Section
Table-8
Xv
2
2
2
3
3
3
4
6
8
0
2
4
Combinations
25
B
.0
.0
.0
.0
.0
.0
A : t es t
app ar at us
A , C
c
A , C
c
A , C
app ar a tu s B ; C : t es t
A ; B : te st
Mix Proportions
H F
Sp
m ix
r at io
% )
a dd iti on
r at io
(%
A , C
A
app ar at us
C .
w e igh t
(k g /nr )
w
s
G
2 4 .0
4 66
2 12
45 3
2 07
99 1
964
6 33
2 6 .0
44 1
42 8
2 01
93 7
910
73 9
79 1
41 6
1 95
18 9
40 3
18 4
2 .2
T ab le -10
3 .0
Sl ump
Fl ow
an d
R e si stan ce
Am o un t
Xv
%
S lu m p
fl
ow
(m m )
Cl e ar an c e
(m m )
T e st
a pp a r at u s
D ir ec t io n o f
a rr a n gem e n t
2 4 .0
6 80
25
B
Lo n gi tu d i na l
Lo n gi tu d i na l
T r an sv e r se
Lo n gx tu d in a l
L o ng i tu d in a l
L o ng i tu d in a l
T ra n sv er se
L on g x tu d in a l
Tr a n sv er se
L on g i tu d in a l
Tr a n sv er s e
L on g it u di n a l
Tr a n sv er s e
L on g it ud i n al
L on g it ud i n al
T r an s ve r se
Lo n g it ud i na l
Lo n gi tu d i na l
T r an sv e r se
Lo n gi tu d in a l
Lo n gi tu d in a l
6 45
c
30
26 .0
64 0
62 5
35
A
A
30
c
25
25
B
c
63 0
3 2 .0
A
of Concrete
U ni t
3 2 .0
3 4 .0
3 0 .0
35
N C
2 8 .0
3 0 .0
28 .0
H
30
B
c
B
Table-9
Xv
in Experiment
C l e a r a n c e b e t w e e n s t e e l b a r s a n d f o r m w o r k s u r f a c e (m m )
c
30
620
A
c
A
630
620
35
6 20
30
c
25
B
6 00
c
30
34 .0
6 00
A
A
35
Xv, clearance,
bar arrangement
of sectional
area as predictor
choosing
a predictor
variable
T
0
= 3.15
V
-
12.7L
du e
68 6
8 84
8 57
to
S tee l
Pa s si n g
se ct i on
w id th
(m m )
75
16 4
1 14
10 4
16 4
75
17 4
16 4
11 4
154
104
1 64
75
1 64
1 14
1 04
84 5
89 8
re in for c ing
R e s is ta n ce
d u e to st ee l
b a rs
Pa
50
0
0
46
18 5
0
0
32 1
30 2
11 6
256
256
325
465
3 50
3 03
23 7 2
3 04
5 38
11 69
36 30
b ar s
S ta nd a rd
v a lu e
Pa )
60
11 5
254
116
135
1 63
3 02
1 63
30 2
23 3
25 6
28 1
35 1
direction,
width of passing
section,
lost ratio
variables.
The regression
formulae obtained
by
with a 5% significance
level is shown below.
-
(16)
565
Where, r 0: resistance
due to steel bars (Pa);
y^ : volumetric
aggregate
(%);
L: passing
section
width
(mm).
ratio
of coarse
Using this formulae,
it is possible
to estimate
the resistance
due to steel bars
based on the arrangement of bars and the mix proportion
under conditions
in which
blockage
occurred between steel
bars and formwork surface.
-39
-
7
. EXPERIMENTAL
MODEL
FORMWORK VERIFICATION
OF SELF-COMPACTING
MECHANISM MODEL USING
7.1
Outline
of Experiment
Here, high-fluidity
concrete
was filled
into model formwork containing
steel
bars in a real arrangement,
and compactability
was evaluated.
The results
were
analyzed based on the compaction model developed in Section
3 using the measured
value of each factor.
This confirmed
the validity
of the model.
a)Model
formwork
The model formwork used in this experiment
is shown in Fig-18.
The steel
bar
arrangement placed in the formwork corresponded
to that used for box culvert
and clearance between steel
bars was 75mm.
b)Materials
used
The same materials
as used in Section
4 were used.
c)Mix proportions
As a concrete
mix factor,
X^ was set at three levels:
24.0,
28.0,
and 32.0%.
The concrete mix proportions
are shown in Table-ll.
HF was used at a ratio of
2.2% to cement weight and 3.0% of Sp was added.
d)Mixing
method
The same method was used as in Section
4.
e)Test
items
(DSlump
flow of concrete
The method described
in Section
4 was used.
(DCompactability
of concrete
It had been confirmed
in a preliminary
experiment
that,
when high-fluidity
concrete is placed
from the position
shown in Fig-19,
it first
flows down to
the bottom as shown in the figure
(closed
route flow) and then rises up the wall
facing the wall where filling
takes place.
When the concrete
stops rising,
it
flows along the wall (open route flow).
From this result,
the compactability
was evaluated
by measuring the concrete surface height
at the placing
position
(hsc)and
the concrete
height
at the facing wall (hc) both at the time when the
flow of concrete
through
the bottom part came to a halt,
as shown in Fig-20.
7.2
Experimental
Results
and Analysis
a)Experimental
results
The measured results
of concrete
slump flow are shown in Table-ll
together
for
the various
mix proportions.
As these
results
show all mixes of exhibited
sufficiently
high-fluidity.
The measurements of compacting
condition
of the
concrete are shown in Table-12.
Under the conditions
of Xv = 24.0 and 28.0,
the
concrete rose in the facing wall section,
whereas under with
X^ = 32.0% it was
unable to rise up in the facing
wall.
U
15 0 ,
m
1 "
31 31
C
oncrete placing
ｧoo
., position
utline
Fig-18
i S'lr
D
H
Elevation
Drawing
S te e l b a r
( <P 1 3 )
H
Hu
ｧo
O
I
nit (mm)
900_
(A-A' Section)
Model
-40
Formworks
-
Steel bar
(* 13)
Plan (B-B'
12
If
Section)
12
Concrete placing
Concrete placing
position
position
o\°
Fig-19
Behavior
^°
of Concrete
Fig-20
Compactability
Position
Measuring
b )Analysis
The value of each factor was calculated
using the formulae obtained
in Sections
4 to 6 from the respective
mix proportions,
and these values were substituted
into the formulae for the compacting mechanism established
in Section
3. The
results
are shown in Table-13.
In this case, it was assumed that P0 the incipient
pressure,
is given by the
height
of the concrete from the bottom to the placing
position
at the time when
concrete placing
was completed.
Also, analytical
values of compactability
are
compared with measured values in Fig-21.
This comparison confirms that,
as
regards the rise height in the facing wall, the analytical
value agrees closely
with
the
measured
value
for
that the concrete dose not
stopping
position
almost
results.
It is considered
of high-fluidity
concrete
internal
friction
angle
substantiated.
Xv = 24.0%
Table-ll
HF
Xv
(% )
m ix
r a %t i o
Sp
ad di ti on
r a %t i o
2 4 .0
2 8 .0
3 2 .0
2 .2
3 .0
Table-12
X v (% )
h s c (c m )
h e (c m )
*N
na l
sto pp in g
and 28.0%.
With
X,, = 32.0,
it
is
confirmed
rise up but stops in the bottom section;
the calculated
agrees closely
with the measured value. From these
that, the assumption in which the self-compactability
is determined
by surface resistance
on formswork,
and resistance
due to steel
reinforcing
bars is
Mix Proportion
and Slump Flow
U n it w e i gh t
(k g / nr )
NC
w
s
G
4 74
4 48
4 28
2 16
1 97
18 6
99 4
97 9
92 4
62 9
73 9
84 5
Compactability
2 4 .0
4 7 .0
2 5 .0
di st anc e on b ot tom
6 47
5 80
5 50
Measurements
from
-41
Slu mp
flow
(m m )
-
2 8 .0
7 0 .0
3 0 .0
w al l w he re
3 2 .0
8 0 .0
0 ( 9 0 .0 * )
c on cr et e w a s p i
a ce a
Table-13
Results
It em
of Analysis
? h (P a )
0 (
T
)
(Pa
P o (P a
P i (P a
P 2 (P a
P 3 (P a
P 4 (P a
P 5 (P a
l i (c m
h , (c m
a n avlayltuiec a l
)
)
)
)
)
)
)
)
3 2 .0
2 .32
2 .3 8
2 .40
1 3
1 9 .8
2 0 .4
2 3 .0
1 4
1 .74
2 .26
2 .78
1 6 )
2 97
952
17 09
10 68 6
6 93
100 7
193 5
4 15
6 63 6
1 632 7
30 46
930
49 89
5 59
68 03
2 6 .0
2 6 .0
18 81 6
708 2
105 5
8 80 0
1 73
170 6
90 .0
0
3 )
4
5
6
(9
1 0
8 )
l l
X v = 2 4 .0 %
<u
2
"3
>
t3
CD
g
to
<a
0>
2
Fig-21
80
J5 H
-9 0 -
0
J
80
70
/k 7
y ¥
i I/ / X / / S ¥ 1
-90 -
-9 0 -
Comparison of Measured
(Model Formworks )
of
S
90-
. EXPERIMENTAL VERIFICATION
ACTUAL STRUCTURE
Outline
X v = 3 2 .0 %
T0
-9 0 -
8
8.1
r
90
& J H
0)
3
-3
>
ca
rt
So 2TJ / L
ed
3
X v = 2 8 .0 %
n
Formwork)
2 4 .0
P o (g / c m 3 )
M ea su re d
fac tor
(Model
X v (% )
2 8 .0
For mu l ae
-9 0 -
and Analytical
Compactability
OF SELF-COMPACTING
Values
MECHANISM MODEL USING
Experiment
This experiment
was carried
out on an actual concrete
structure.
High-fluidity
concrete
was placed
into
plant-fabricated
formwork for a box culvert
and
compactability
was measured. This experiment
also verified
the compacting
mechanism model.
a)Box culvert
used for verification
Fig-22
shows the box culvert
used for the experiment.
This box culvert
is a
design actually
used for water channels,
etc. , and the formwork is made of steel.
The clearance
of steel
reinforcing
bars is 52mm for wall members and 43.5mm for
the bottom member. The concrete
cover is more than 35mm for both members.
b)Material
used
Cement (VC) : High-early-strength
portland
cement (specific
gravity
2.71)
Fine aggregate
(S):
River sand produced from Atsuma, Hokkaido (F.M. 2.81;
specific
gravity
2.71)
Coarse aggregate
(G) : Crushed
stone produced from Fukagawa Otoe, Hokkaido
(max. size 20mm; specific
gravity
2.72)
-42
-
2 3 00
i3 1 o JI
m m
m
<N
m
¥
i
50
C oncrete p lacing
position
O
TIO
H I
d
nｫ a
m
h-^
G002
H
｣ra｣
B00J
Einl
m
m
(N
13
｣S
m
WfSSL
5
-1
X
5 285
K B *!
-1
5@ 300
Table-14
Xv
%
3 0 .0
3 2 .0
3 4 .0
2000
6@ 205=1230
T
35
80
la
35
HlU L
m
mu
ar
001
0
ii _ ｣cmo2T ｱ
0
50
1500
mm
LO
ta
m
m
CO
mm
K
CM
E
/r
^B jm i BS
uoE
285 65
-"5 r03
-15 0 0
r
35 120
4o _L
y
15 0
Unit
Fig-22
Box Culvert
Used for
Mixing
Proportion,
Slum Flow and Compactibility
HF
m ix ing
ra ti o
%
Sp
add in g
0 .9
3 .0
r at io
(% )
Un i t w e igh t
vc
45 0
450
450
w
18 5
18 5
18 5
Experiment
(k g /m 3 )
s
9 48
8 94
84 0
G
8 13
8 67
9 21
fa r t
Slum p
f low
Com p ac tab i lity
(m m )
hs
he
5 70
19 8
1 76
60 5
198
16 3
58 0
192
13 2
Superplasticizer(Sp)
: j3- Naphthalene
sulfonic
acid salt
Viscosity-controlling
admixture (HF) : Acrylic-based
water-soluble
polymer
c)Mix proportions
As a concrete mix factor,
Xv was again set at three levels
of 30.0,
32.0,
and
34. 0%. The concrete mix proportions
used in this experiment are shown in Table-14.
HF was used at a ratio
of 0.9% to cement weight and 3.0% of Sp was added.
d)Mixing
method
The materials
were fed en-masse into a pan-type mixer of 1m3 capacity
and mixed
for 90 seconds.
e)Test
items
©Slump flow of concrete
The method described
in Section
4 was used.
(DCompactability
of concrete
Concrete was placed from the position
shown in Fig-22,
and this placing
position
did not change until the concrete lost its fluidity.
Compactability
was evaluated
by measuring the surface height
of the concrete at the placing
position
(hs)
and its rise height
(he) in the facing wall at the time when the concrete flow
came to a halt.
8.2
Experimental
Results
and Analysis
The measured results
of concrete
slump flow and the corresponding
compaction
are shown in Table-14,
together
with the mix proportions.
As these results
show
all mixes of concrete had a slump flow of about 600mm, and therefore
exhibited
sufficient
fluidity
to be classified
as high-fluidity
concrete.
Concrete rose
up in the facing wall in every case.
The value of each factor was calculated
using the formulas obtained
in sections
-43
-
4 to 6 from the respective
mix proportions
and then substituted
into the formulae
for the compacting mechanism established
in Section
3. The results
of analysis
are shown in Table-15.
In this case, as in Section
7, it was assumed that the incipient
pressure
Po
was given by the height
at the placing position
(hs) of concrete from the bottom
at the time when the placingwas
completed.
The resistance
due to steel reinforcing
bars was obtained using formulae (15)
with clearance
of steel reinforcing
bars
of 52mm for wall member and 43.5mm for bottom member for the following
reasons.
ÖThe concrete cover is more than 35mmand so the concrete can pass between steel
bars and formwork surface.
©The clearance of steel
reinforcing
bars is larger than the clearance
between
steel bars and formwork surface,
and it is considered
that the stop of concrete
flow is caused when blockage
occurs at the gap with maximumwidth.
Table-15
Results
Ite m
of Analysis
X v (% )
3 2 .0
3 4 .0
2 .4 0
2 .4 0
2 .40
12
l l .7
12 .5
1 3 .3
14
2 .5 2
2 .78
3 .04
16 72
P o (g / c m 3 )
M e asu re d
f ac tor
A n av layltuiec a l
*1
*2
:
:
* h (P a
4> r
)
(Box Culvert)
3 0 .0
For mu l ae
T
, ( P a )* l
(15
93 8
130 5
T
2 (P a )* 2
(15
1 034
14 01
P
P
P
P
P
P
H
o( P
i( P
2( P
3( P
4( P
,( P
i ic
Re si st anc e
Re si st anc e
a
a
a
a
a
a
m
)
)
)
)
)
)
)
du e
du e
to
to
3
4
5
6
9
10
ll
s tee l
s tee l
4 6
5
3
6
2
2 8
5 70
92 5
25 2
53 9
5 91
2 63
I l l
re in for c in g
re in for c in g
46
8
3
8
2
23
b ar s
b a r s
5
1
4
7
4
7
7 0
47
56
64
37
6 6
8 9
in the
in the
17 68
4 51
10 3
3 4
1 09
2 0
1 82
58
59
7 9
89
5 3
78
7 7
w al l m em b er
b ot tom m em b e:
The analytical
values of compactability
obtained
from the formulas are compared
with actually
measured values in Fig-23.
This confirms that the measured rise
was about 60cm higher than the analytical
value.
The following
explanations
are proposed
for this result.
©The box culverts
have hunches at the corners and this reduced the pressure
loss at the corner.
(D Since the actual
box culvert
was much wider than that of the test
at the
laboratory
level,
the concrete flow was two-dimensional
in the laboratory
case
while it was three-dimensional
in the actual culvert
and the freedom of flow
was higher. As a result,
the resistance
due to steel reinforcing
bars was reduced.
Accordingly,
the rise was calculated
once again, this time assuming that the
pressure
loss at the corners was as zero. The results
(analysis
value 2) are
also shown in Fig-23.
The difference
between the analytical
and measured values
was some 40cm in this
case.
As the result of this study, it was clarified
that the model constructed
in Section
3 is able to explain
the self-compactability
of high-fluidity
concrete
in
formwork to a certain
extent at the model level,
but actual compactability
is
somewhat better
than estimated
using the model.
Efforts
now need to focus an increasing
the accuracy of the compaction
model
by studying
the effects
of corner shape, formwork dimensions,
and concrete flow
velocity,
etc.
-44
-
Fig-23
Comparison
of Measured
and Analytical
Culvert)
9. PROPOSED METHOD OF PREDICTING
FLUIDITY
CONCRETE
9.1
Values
of Compactability
OF SELF-COMPARABILITY
(Box
OF HIGH-
Outline
According to the research carried out so far, it is clear that in the model formwork
level the compactabiity
of high-fluidity
concrete can be largely
explained
in
terms of the surface resistance
of the forms, the internal
frictional
angle of
the concrete,
and the resistance
due to steel reinforcing
bars.
Also, although
further
study is required
in future,
compactability
can be explained
to some
degree for an actual
structure.
Thus, a prediction
method for compactability
is proposed based on these factors
as determined
by work execution
conditions
and concrete
mix proportions.
Work execution
conditions
Mix proportions
Shape of formwork;
material
of
formwork; steel
bars arrangement
(concrete
cover, clearance
of
steel
reinforcing
bars)
Volumetric
ratio
of
coarse aggregate
(Xv) ;specific
gravity
of concrete
Estimation
factors
Surface
resistance
Internal
angle
Tip
Fig-24
Prediction
friction
position
concrete
of Compactability
-45
of
Resistance
steel
bars
due to
of
of High-Fluidity
Concrete
9
.2 Prediction
Method for Self
Compactability
In this research,
the prediction
of compactability
entails
estimating
the the
final
configuration
of high-fluidity
concrete.
According to the procedure laid
out in Fig-24,
the following
process
can be used to predict
compactability.
a)Collection
of data required
for prediction
When prediction
is required,
the following
data must first
be collected.
©Data on formwork
Shape of formwork, such as the number of corners, width, etc. and the formmaterial,
etc.
©Data on steel
bar arrangement
Clearance of steel reinforcing
bars in the of concrete flow section,
concrete
cover, number of layer of arranged steel reinforcing
bars, etc.
©Data on concrete properties
Xv and specific
gravity
of concrete
b)Estimation
of factors
which affect
compactability
©Estimation
of surface resistance
of formwork
The surface
resistance
is estimated
using data on formwork and conctrete
properties
by applying
formulae (12)
or formulae (13).
©Estimation
of internal
friction
angle of concrete
The internal
friction
angle is estimated
using data on concrete properties
by
applying
formulae (14).
©Estimation
of resistance
due to steel
reinforcing
bars
The resistance
due to steel reinforcing
bars is estimated
using data on concrete
properties
and the steel
bars arrangement by applying
formulae (15)
in a case
where concrete can pass through all the gaps of steel
bars due to relatively
large section and formulae (16)
in a case where the concrete is blocked between
steel
bars and formwork surface,
etc. due to relatively
small section.
c)Prediction
of final
position
of concrete
(final
raise position)
The incipient
pressure Po is calculated
from the concrete placing
height based
on the working plan and the specific
gravity of concrete. Then the final position
is predicted
according
to the procedure described
in Section
3.
By applying this method, the risk of serious error, such as inferior
compacting,
before placing
high-fluidity
concrete
in formwork.
10.
CONCLUSION
A method of the concrete compaction mechanism was constructed
after clarifying
that the self-compactability
of high-fluidity
concrete in forwork is determined
by the surface resistance
of the form, the internal
friction
angle of the concrete,
and the resistance
due to steel reinforcing
bars. A quantitative
evaluation
of
these factors
which seemed to have an effect
on compactaility
was conducted.
Using the model, self-compactability
in model formwork -and in an actual concrete
structure
was predicted,
thus providing
verification
of the compaction model.
As a result,
the following
points were clarified:
(l)The
surface
resistance,.
( r h:Pa)
of formwork can be estimated
using the
following
formulae from the form material
and the volumetric
ratio
(Xv:%)
of
coarse aggregate:
©In the case of steel
plate
forms
rhs
©In
case of plastic
rhp
(2)The
using
= 0.39
plate
=
0.65
Xv-0.02
forms
Xv+2.13
internal
friction
angle ( <f> :° ) of high-fluidity
the following
formulae from the volumetric
&=0.025Xv2-l.37XV+20.9
-46
-
concrete can be estimated
ratio
of coarse aggregate:
(3)The
resistance
(r c.ro
: Pa) due to steel reinforcing
using the following
formulae from the volumetric
ratio
the clearance
width (L:mm) :
©Where concrete can pass between steel
bars
Tc
= 183.6
Xv-ll.SL-3982
(DWhere concrete is blocked
covering portion).
7
0=
3.15
bars can be estimated
of coarse aggregate
and
between steel
bars
and formwork surface
(concrete
Xv2-12.7L-565
(4)The
self-compactability
of high-fluidity
concrete
can be estimated
in the
case of model formwork from the surface resistance
on the formwork, the internal
friction
angle of the concrete,
the resistance
due to steel
reinforcing
bars,
the shape of the formwork, and the steel
bars arrangement.
In the case of an
actual structure,
the actual compactability
is somewhat better
than the value
estimated
using this method.
Based on these
findings,
a prediction
method for the compactability
of
high-fluidity
concrete
is proposed on the basis work execution conditions
and
concrete mix proportions.
Although further
study is required
to improve the
accuracy of this prediction,
even at its present level of accuracy it can, before
high-fluidity
concrete is placed,
reduce the possibility
of serious errors such
as inferior
compaction.
This will
increase
the reliability
of work with
high-fluidity
concrete.
References
[l]Fujiwara,
H.,
Shimoyama,
Y., Tomita,
R.,
Kubota,
H., "Fundamental
Study
on
the Self-Compacting
Property
of the High Fluid
Concrete",
Proc.
Of JCI,
Vol.14,
No.l,
pp.27-32,
1992(in
Japanese)
[2]Hannah,
C., Fujiwara,
H., Shimoyama,
Y., Douzono,
A., "Surface
Resistance
and Pressure
Distribution
of High FluidityConcrete",
Proc. Of JCI, Vol. 15, No.1,
pp.1223-1228,
1993
[3]Kawai,
T., Kuroda,
Y. , Mukawa, Y. , "An Experimental
Study on the Properties
of Highly
Flowable.Concrete
Using
Low Heat Generating
Cement",
Proc.
Of JSCE,
N0.462/VI-18,
pplll-120,
1993(in
Japanese)
[4]Fujiwara,
H., Nagataki,
S.,
Ohtsuki,
N., Yora, Y., "A Study
on the Ability
to Pass between
Bars of High Fluidity
Concrete",
Proc.
Of JCI,
Vol.17,
No.l,
pp.17-22,
1995(in
Japanese)
47 -