CONCRETE LIBRARY OF JSCE NO. 36, DECEMBER 2000
AN EXPERIMENTAL
STUDY ON IMPROVEMENT
AND REPAIR
EFFECTS
USING
ELECTROCHEMICAL
(Translation
from Proceedings
of JSCE,
No.641/V-4§
OF CONCRETE
METHODS
february
2000 )
^à"\
"à"f
Yukio
II
KITAGO,
Masanobu
ASHIDA,
Norihiro
KIKUTA,
Toyoaki
MIYAGAWA
An experimental
study
was carried
out to find
the threshold
value
of the chloride
ionto
hydroxy
ion ratio
([Cf]/
[OH]:
mol ratio)
fortheonset
of reinforcing
steel
corrosion
in
concrete.
After
application
of
an electrochemical
concrete
improvement
method
(desalination
and realkalizaton)
to specimens,
a five-year
follow-up
survey
was made to check
the
effectiveness
of the
rehabilitation
method.
The results
of tests
showed
that reinforcing
steel
did not corrode
when pH value
was 12 or higher
and
Cl'/OH"
ratio
was 1 or lower.
Rehabilitation
using
the
desalination
and realkalizatiou
method
increased
pH value
to between
12.6
and
13.2
and reduced
water-soluble
chloride
content
to 0.47
to 0.56
kg/m
around
reinforcing
bars in concrete
of existing
structures.
Almost
no rediffusion
of chloride
ions into
concrete
around
reinforcing
bars was
detected
in the five-year
follow-up
survey,
and the presence
of clear
shadow
spots
behind
the reinforcement
was not noted.
Key Words:
desalination,
corrosion
realkalization
of
reinforcing
steel,
Yukio Kitago is a director of Civil Engineering
design
research interests relate to the technology of rehabilitating
JSCE.
threshold
of
[Cl]/[OH],
repair,
in the JR West Japan Consultants
Company. His
concrete structures. He is a member of the JCI and
Masanobu Ashida is a manager in the technical division of the Special Cement Additives Department at Denki
Kagaku Kogyo Kabushiki Kaisha Co., Ltd., Japan. He received his doctorate in engineering
from Kyoto
University in 2000. His research interests relate to the technology of rehabilitating
concrete structures. He is a
memberof the JSMS, JCI and JSCE.
Norihiro Kikuta is a manager in the department of structual maintenance at the West Japan Railway Company.
He inspects concrete structures of SANYO SHINKANSEN in Hiroshima district.
He is a member of the JCI
and JSCE.
Toyo Miyagawa is a professor in the Department of Civil Engineering,
Kyoto University,
Kyoto, Japan. He
received his doctorate in engineering
from Kyoto University in 1985. He is the author of a number of papers
dealing
with the durability,
maintenance
and repair of reinforced
concrete structures. He is a member of the
ACI, RILEM,
CEB, JSMS,
JCI and JSCE.
-227-
1.
INTRODUCTION
Concrete
is known as a material
of excellent
durability.
Not a few concrete
structures
have
been
in service
for long
periods
and even now remain in
satisfactory
functional
condition.
However,
it is also
a fact
that
certain
structures
have
deteriorated
for various
reasons,
and concrete,
which
had
been thought
of as a maintenance-free
material,
was found actually
not to be
so.In
fact,
durability
cannot
be attained
unless
proper
maintenance
is carried
out,
and in a sense,
what
should
have
been obvious
is only
now beginning
to be recognized.
Many
of the
changes
seen
in railway
structures,
of which
rigid-frame
viaducts
are representative,
are caused
by corrosion
of reinforcing
steel.
Where
such deteriorated
structures
are located
in normal environments,
they
are often
treated
by the
" lining
method",
which
entails
giving
a surface
coating
to the concrete.
Results
of previous
investigationsC
|) C 3 suggest
that
the
causes
of reinforcing
bar corrosion
are chlorides
and carbonation
due to inadequate
chloride
removal
from fine
aggregate,
particularly
the
latter.
The actual
situation
is that,
in application
of the lining
method,
there
were many places
where
the
chloride
content
of concrete
had not
been measured,
and that
when chloride
content
was high,
repairs
by lining
and similar
methods
were not necessarily
done
after
having
removed
the
chloride.
Recognizing
that
there
are limits
to the
durability
of lining
materials
themselves,
a method
that
improves
the quality
of concrete
itself
through
realkalization
(after
desalination)
by an electrochemical
method
has been tried
in recent
years
as a radical
alternative
to the lining
method.
In this
case,
it is necessary-to
clearly
determine
the chloride
content
and
the alkaline
environment
after
desalination
and realkalizaton,
which
will
ensure
that
subsequent
reinforcing
bar corrosion
will
not occur.
However, it
has
not
necessarily
been
made
clear
what
influences
chlorides
and
carbonation,
respectively,
have on reinforcing
bar corrosion.
In this
possibility
hydroxy
quality
desalination
follow-up
study,
an attempt
is made at the
laboratory
level
to quantify
the
reinforcing
bar corrosion
in concrete
with
the chloride
ion to
ion
ratio
([C1"J/[OH"])
as a parameter.
The way in which
the
of
concrete
in
an actual
structure
was
improved
through
and
realkalizaton
are
also
discussed.
The
results
of a
survey
made over aperiod
offive
yearsare
reported.
of
2. INFLUENCE
ON REINFORCING
OF
CHLORIDE
ION-HYDROXY
STEEL
CORROSION
The
results
of a previous
surveyC3)
normal
environment,
when carbonation
far as reinforcing
steel,
noprominentcorrosion
in agreement
with
the thinking
that,
ions
(Cl~),
the presence
of hydroxy
ions
accelerates
the formation
of a passive
thus
repairing
any passive
film,
which
words,
whether
or not reinforcing
steel
influenced
by
the
[C1"]/[OH"]
ratio
hydroxy
ion concentration
in the steel's
should
exist.
The results
of past
studiesare
ION
RATIO
(rcn/fOH'1)
suggest
that,
with
a structure
in a
of concrete
has not progressed
as
of the steel
is seen.
This
is
even though
there
may be chloride
(OH)
above
certain
concentration
film
on the reinforcing
bar surface,
may have
been
broken.
In other
corrosion
occurs
should
be greatly
of
chloride
ion
concentration
to
environment.
Also threshold
value
given
in Table
1.
225
Table
1
Threshold
pH
values
E x p e rim e n ta l c o n d itio n s
H au sm am i
l l .6
1 2 .4
1 3 .2
0 .5
0 .6 1
0 .8 3
S t e e l in
a lk a li n e s o lu tio n
G ou d a &
D iam o n d
l l .8
12 .1
1 2 .6
1 3 .0
1 3 .3
0 .5 7
0 .4 8
0 .2 9
0 .2 7
0 .3 0
S te e l in
a lk a lin e s o lu tio n
P ag e
1 3 .9 1
0 .5 4
S te e l in
c em
62
cS ot ne te a li n i ni ng
HP aagv ed a&h l
Y o ii e z a w a ,
V .A s h w o rt h ,R .P .M .
P ro c te r
S .E . H u s s a i n
et al.
(l)Threshold
[C1']/[OH']
[c r /O H ]
Value
L
1
M
1
for
ess
3 .3
o re
3 .3
th a n
th a n
was considered
as being
measurement.
Hausmann's
of [CT]/[OH']
with
pH
increase,
it is approximately
3 0c %e m s ei lni ct a fp u am s et e
5
S te e l in
c e m e n t m o rta r
1 .1
2 .0
1 .2 8
1 .8 6
S t e e l in
c e m e n t m o r ta r
Reinforcing
Hausmann's
value
of [C1"]/[OH"]
for
reinforcing
steel
corrosion
that
when
pHvalueswere
ll.6,
[C1"]/[OH']
values
were
0.5,
e n t p a st e
Steel
Corrosion
0 0.6CO
is
in an alkaline
12.4,and
13.2,
0.61,
and
0.83,
in
Alkaline
well
known
solution.
corrosionwould
respectively.
Solution
as the threshold
Hausmann
found
not occurif
The
0.83
value
of poor
reliability
because
of difficulties
met in
conclusion
was that
although
the threshold
value
in the
range
of ll.6
to 12.4
shows
a trend
of
0.6.
Gouda
studied
alkaline
solutions
with
pH values
from
ll.75
to more than
135 C5}.
Diamond
modified
Gouda's
results
using
the activity
coefficient
of NaOH to estimate
hydroxy
ion concentration
from
pH value.
A check
of
the
results
reveals
that
the threshold
[C1"]/[OH]
value
decreases
as pH
value
increases.
In a range
of pH ll.8
to 12.1,
there
is good
agreement
with
Hausmann's
value
of 0.60.
Further,
HausmannC0
holds
that
these
values
are influenced
by the
amount
of oxygen
supply.
He reports
that,
consequently,
the
threshold
value
increases
if
the
concrete
is
fully
saturated
with
water.
(2)
Threshold
Value
for
Reinforcing
Steel
Corrosion
in
Cement
Paste
Page
et al.C7}
C8}
, in tests
using
reinforcing
bars
embedded
in cement
paste,
foundthatwhenthepHvalue
of pore
waterand
[Cl]/[OH]
are 13.91
and 0.54,
respectively,the
steel
is inactive.
Thisvalue
of0.54
at a pHof
13.91
is more than
double
the [C1"]/[OK]
= 0.23,the
value
estimated
from
Gouda'
s results.
Therefore,
in case
of steel
embedded
in cement
paste,
[C1"]/[OH~]
as the threshold
value
is thought
to be a value
far higher
than
that
in an alkaline
solution.
Page
et al.CS}
found
that
steel
embedded
in
hardened
cementpasteisinactiveup
to a [CI]/[OH]
valueof62.
(3)
In
Threshold
cement
Value
mortar,
for
the
Reinforcing
conditions
Steel
are
-229-
still
Corrosion
more
in
lenient,
Cement
and
Mortar
YonezawaC
9
et al. obtained
a threshold
on the
characteristics
of
adherence
between
steelbar
steel
a) Filter
paper
embedded
b)
bar
Steel
Yonezawa
steel
bars
compared
of
separating
embedded
[CT]/[OH"]i
bar corrosion
and mortar,
a)
directly
in
found
that
the threshold
embedded
in cement
withthat
in an alkaline
steel
approx.
for
and b)
bar
5. They
two different
as defined
also
reported
states
of
below.
and mortar
mortar
value
mortar
solution.
of [CI]/[OH]
under
both
was far
adherence
higher
for
conditions
The reportby
S.E. Hussaineta1.C10)
concerns
corrosion
of steel
inmortar
with
a water-cement
ratio
of 0.55.
Although
hydroxy
ion
concentrations
were varied
in the comparatively
narrow
range
of pH 13.26
to 13.36,
the
threshold
value
of
[C1"]/[OH"]
decreased
with
increasing
hydroxy
ion
concentration.
For example,
at hydroxy
ion concentrations
of pH 13.30
and
under,
the
threshold
values
of [CT]/[OH]
were
in a range
of 1.7 to 2.0,
while
at hydroxy
ion concentrations
above
pH 13.30,the
threshold
values
of
[Cr]/[OH']
were in arange
of1.28to
1.86.
(4)
Threshold
Value
for
Reinforcing
Steel
Corrosion
in
Concrete
With
regard
to the
above
reports,
Glass
and BuenfeldC11}
studied
the
proposed
[C1"]/[OH']
threshold
value
and chloride
threshold
value
based
on
published
data.
The
objects
of
examination
were
reinforced
concrete
structures;
concrete
specimens
exposed
to an outdoor
environment;
concrete,
mortar,
and
cement
paste
specimens
in a laboratory
environment;
and
simulatedpore
water.
The study
also
included
parts
of(1)
to (3)
above.
A summary of the examination
results
follows.
à" Regarding
the
method
of defining
threshold
value
as the
ratio
chloride
content
or
water-soluble
chloride
content
to
hydroxy
concentration,
the
effectiveness
of such a definition
cannot
be verified
the data
available.
à" Initial
oxidation
at the
anode
increases
local
activity
of chlorides
accelerate
the release
of bound
chlorides.
à" Even
though
chlorides
are
bound,
there
exists
a risk
of corrosion
occurring.
à" The most
important
corrosion-prevention
property
of cement
is that
restrictingpHvalue
from declining
locally
to below
12.6.
à"Regarding
the threshold
value
for steel
corrosion
in concrete,
it is best
to indicate
the total
chloride
content
byweight
of cement.
The maximum
and minimum
compiled
in Table
2. Threshold
by weight
of cement.
Table
2 Threshold
values
threshold
values
for
values
for
are given
concrete
as total
of steel
in concrete
corrosion
T h r e s h o l d v a lu e s o f t o t a l
c h lo r id e io n s f o r st e e l
c o r r o s i o n ( C l 'w t % C e m )
C o n c re te s tru c tu re
0 .1 7
2 .2
(4 )
C o n c r e te s p e c im e n
(o u t d o o r e x p o s u re )
0 .3 2 -
1 .9
(4 )
( lCa ob on rc ar te ot er y )s p e c i m e n
0 .5
( l aM b o r at at or r y s)p e c i m e n
0 .2 5 ^
Figures
in ( ) indicate
-230-
2 .5
1 .6
numbers
(4 )
(2 )
of references
and
chloride
of
by
to
of
mortar
are
content
and mortar
3.
EXPERIMENTS
REINFORCING
STEEL
ON
THRESHOLD
CORROSION
IN
Experiments
were conducted
steel
in cement
mortar.
(1)
Experimental
[Cr]/[OH']
CEMENT
MORTAR
on threshold
[Cl]/[OH
a) Materials
Reinforcing
steel:
steel
form polished
bars
(0
results
oftension
tests
0.14%,
] values
for
Si
=
bars
for reinforcement
13 mm x 100mm).
of the original
bars
0.18%,
Mn
= 0.49%,
P
=0.017%,
and
of
[Cl]/[OH]
reinforcing
S
were of the
[C1']/[OH"],
kinds
two
Table
was JIS
proportions
indicated
ofeachkindbeing
3
Varieties
pH
1 2 .0
[c iy
o JT ]
0
2 .0
standard
percubic
1 2 .5
0 .1
3 .0
= 0.011%,
1 3 .5
1 .0
7 .5
yieldpoint=
= 29%
strength
of
forpH
10
3, with
made.
molecularweight
ofmortaris
251
can be determined
10cm,
with
of cover
19
using
epoxy
was zero.
1.
4 levels
of
pH
ratio
ofO.50.The
and
le v e l s
a water-cement
given
in Table
4.
of mortar
5 0 2 k g /m
1 5 0 7 k g /m 3
2 5 1 k g /m J
= 13.0
and [C1']/[OH']
1.0
from
pH
= 13.0,
= 1.0,
[CT]
of chlorine),
and since
the
kg, the quantity
of chloride
by the followingequation:
water
ions
=
as
3.16
The
pH values
were
set up by adjusting
the
amount
water.
However,
apH
of12.0
was considered
to mean
solution,
and noadjustment
with
NaOH was node.
Forexample,
and
[Cr]/[OHT]
cement"
4 l e v e ls
1 .5
10
mortar
with
meter are
Table 4 Mixture proportions
W a te r
Table
to
and
of specimens
1 3 .0
0 .5
5 .0
O rd in a ry p o rtla n d c e m e n t
S ta n d a rd sa n d
in
placed
in the
were shaved
composition
b) Specimens
Cylindrical
mortar
specimens
of
diameter
5 cm,
height
reinforcing
bars
embedded
at centers
were made with
thickness
mm. The bars
were bonded
to the
bottom
surfaces
of molds
resin
before
casting
the mortar.
Cover
at the
ends
of specimens
The appearance
and dimensionsofaspecimen
are shownin
Fig.
Mortar
mixture
reinforcing
values,
bars
(JIS
G 3112)
The chemical
are as follows:
330 N/mm2,
tensile
strength
= 472 N/mrn , elongation
Sand:
standard
sand
("standard
sand
for
testing
specified
in JIS R 5201),
specific
gravity:
2.64
Cement:
ordinary
portland
cement,
specific
gravity:
Alkali:
sodium
hydroxide
Chloride:
commercial
table
salt,
NaCl:
99%
Specimens
10 levelsof
FOR
Method
Mortar
specimens
were made withvarying
pH
in a desiccator,
and whether
or not corrosion
specimens
had occurred
was investigated.
C=
VALUES
since
=0.1mol/l
of NaOH
a saturated
[OH']
content
ofa
used
in the
=
in
= 0.1
3.55g/l
mixing
calcium
mol/1
(V
cubic
meter
experiments
231
3.55(g/1)
The
X
251
(1/m3)=891
(g/m')
amounts
of chloride
ionsused
in the experiments
are given
in Table
Table 5 [Cl-]/[OH-]
when placing mortar, total chlorides in mortar [g/m3], and percentage
of total chlorides by weight ofcement [wt%]
5
pH
C l
7o H
13 .5
1 3 .0
1 2 .5
1 2 .0
0
0
(0 )
0
(0 )
0
(0 )
0
(0 )
0 .1
2 8 5 .1
(0 .0 5 7 )
8 9 .1
(0 .0 1 8 )
2 6 .7
(0 .0 0 5 )
8 .9
(0 .0 0 2 )
0 .5
1 4 2 5 .7
(0 .2 8 4 )
4 4 5 .5
(0 .0 8 9 )
1 3 3 .7
(0 .0 2 7 )
4 4 .5
(0 .0 0 9 )
1
2 8 5 1 .4
(0 .5 6 8 )
8 9 1 .0
[0 .1 7 7 )
2 6 7 .3
(0 .0 5 3 )
8 9 .0
(0 .0 1 8 )
1 .5
4 2 .8
(0
7;:
4 0 1 .0
(0 .0 8 0 )
1 3 3 .5
(0 .0 2 7 )
2
5 7 0 2 .8
(1 .1 3 6 )
1 7 8 2 .0
(0 .3 5 5 )
5 3 4 .6
(0 . 1 0 6 )
3
8 5 5 4 .2
(1 .7 0 4 )
2 6 7 3 .0
(0 .5 3 2 )
8 0 1 .9
(0 .1 6 0 )
5
7 .5
10
'ｫｻ ｻ
I
II
II
m
m
Figures in ( ) indicate percentages of total chlorides
Shaded portions indicate corroded parts.
c) Environmental
The experimental
Figs.
2.1
to
2.3.
Conditions
apparatus
for
by weight of cement (wt%).
accelerating
G a s m ix tu re
corrosion
of
steel
is
shown
in
L a b o r ato ry
N28oVJ0xiia
i%ty UgrllA
oe ngU Ue Cn
S tpep alym
su
I^
I
o f B ud bi sbt il lle
i n gc
I
r > ｫ ^ :ｫ ｫ ^ .
W jM H U U M j
w ate r
D is ti ll e d w a t e r h e a t e d w it h
chw o antttearia nnireo rt f(inrho omct o an irtoa uca t)
tns di d ed i's tgillle
a si
D e s ic c a to r
(sp e c im e n )
ftn ^a Bm H a I
L^
0 ::: J .- .T S
F ig . 2 .1
O u t l in e
232
Gas m ixture
lind f
I
"
¥
I
0
I'wDbgai.sbttbe!irliniegd
Gas exhaust
0«siccator
Fig.2,2
Schematic
of
experimental
apparatus
spediman
In order to'prevent
progress
of carbonation,
a gas mixture of 20% oxygen
and 80% nitrogen
(free of c a r b o n dioxide)
was passed through
distilled
water and conducted
into the desiccator
in which specimens w e r e r e s t i n g .
The specimens
in the desiccator
w e r e in a moist but not dripping
condition.
Temperature
and
humidity
were
measured
using
an automatic
temperature-humidity
recorder. Testing
w a s performed up to the age of 115
d a y s . H o w e v e r , b e c a u s e o f t h e possibility
that corrosion
of steel would not
o c c u r e v e n o v e r this length of time, parts of the experimental
environment
w e r e changed. To elaborate,
the conditions
between 4days
and 33days
of
age were temperatures
f r o m 20 to 3 0 ° C and relativehumidities
from 80 to
9 0 % . T h e n , later,
the conditions
were changed to temperatures
from 20 to
3 0 ° C a n d relativehumidities
from 80 to 90%upto
90days
of age, withthe
bottom 2cm ofmortarspecimens
immersed in an aqueous solution.
Also, it
w a s decided
t o w a r m t h e distilled
water used for bubbling.
Thereafter,
the
ambient
temperature
w a s m a d e 6 0 ° C u p to llSdays
of age. The rates of
absorption
in mortar portions
of specimens w e r e m e a s u r e d after completion
of the experiments.
Absorption
was measured
by following
-233-
JIS
A 1110
and the procedure
below
was used.
Absorption
by mortar
specimens
was allowed
to proceed
for
24 hours
in
water
at a temperature
of20±
2°c . Upon removal
from thewater,
surface
water
was wiped
off
with
an absorbent
cloth
to obtain
a saturated
surface-dry
condition,
after
which
the mass (m)
was immediately
measured.
Upon
determination
100-110°C
and,
measured.
The
absorption
of
after
of
mass
cooling
specimens
Q = ms - mo
where,
(m),
to
was
/ me
Q: absorption
(%)
ms: mass of sample
me: mass of sample
X
specimens
were
room
temperature,
calculated
by
the
dried
the
for
24 hours
mass
(m>)
following
at
was
equation:
100
in saturated
after
drying
surface-dry
(g)
(2)
Experimental
Results
The temperatures
and humidities
in the dessicator
set
up.
Reinforcing
bars
were
taken
out at the
degrees
of corrosion
were investigated.
The results
state
(g)
satisfied
the conditions
age of 115days
and
are shown in Photo.
the
1.
The results
of determining
whether
or not corrosion
had occurred
are given
in Table
5. The shaded
portions
of the table
indicate
specimens,
which
had
corroded.
Since
cover
at ends
of specimens
was zero,
there
were some
specimens
in which
corrosion
appeared
to have progressed
from the ends.
Here,
the
effects
of cracking
and inadequate
cover
frequently
seen
in
actual
structures
were taken
into
consideration,
and these
specimens
were
included
among cases of corrosion
to be on the conservative
side.
The absorption
of mortar
portions
of specimens
was indicated
as 7.6 wt%
as a result
of measurements.
The unit
mass
of mortar
was 2050
kg/m.
Portions
of cement
paste
which
had been
in direct
contact
with
reinforcing
bar
surfaces,
where
specimens
had
been
split
and
bars
removed,
were
sampled
and X-ray
diffraction
was performed.
Distinct
peaks
of Friedel's
salt-were
not seen in the results.
Given
the
[C1~]/[OH"]
experiments,
[Cl'J/fOIT]
results
of the experiments,
conditions
initially
set up
pH values
of mortar
valuesof
0.1,
1.5,
and since
it was expected
that
would
change
during
the course
of
in the specimens
were
measured
the
the
for
and2.0.
The method
of measurement
was as follows:
© Drymortarfor7daysinadryerat60°C.
0) Coarsely
grind
the
dried
mortar
followed
by fine
pulverization
mortar
andpestleto
88JLL
m andunder.
d) Add40
gofdistilledwaterto
100gofthefinelypulverizedmortarand
storeinadesiccaator(filledwithN*
gas)at
20°C
for7days.
(D
Using
the
suction
filtering
method,
separate
moisture
finely-divided
mortar
to which
distilled
water
had been added.
0) Measure
the separated
moisture
by pH electrode.
(D [OH']/40g
x1000g=[OH']mol
0) [OH"]
mol x moisture
content
of mortar
The results
are given
in Table
6. It may
solution
had
changed
because
temperature
during
the
testing
period.
For
example,
considered
a saturated
calcium
solution
and
-234-
be considered
conditions
the
solution
adjustment
with
from
that
had
of
with
a
the
pH of the
been
altered
pH 12.0
was
NaOH was not
pH=13.5
pH=12.0
pH=12.5
pH=13.0
à".o
ot-yoM-^a
0.1
à"12.0
C1'/OH-»0.»
0.5
r>H-13:S
C1
/OH-0,S
o
o
r
1.0
3.0
.8
C»
/OM
I8,0
"3-0
C1
/OHn}.0
5.0
7.5
35>ptioli.i.
0"
/3H
«T.»
10.0
Corroded bar
( Legend)
Photo 1
Corroded
-255-
conditions
of reinforcing
bars
made. Since
thepH
at 20°C
was 12.6,
and at 60°C
itwas
ll.4,
pH during
the experiments
varied
in a range
of ll.4
to 12.6.
However,
the differences
between
pH values
at completion
of the experiments
and the originally
set
pH valuewere
0.07to
0.1,
close
tothevalue
initially
targeted.
Table
6 Values of pH after completion
of tests
pH
[c kr ] ]
[o
1 3 .5
1 3 .0
1 2 .5
1 2 .0
1 .0
1 3 .0 7
(13 .5 8 )
1 2 .4 6
(1 2 .9 7 )
1 2 .0 7
(1 2 .5 8 )
l l .5 6
(1 2 .0 7 )
1 .5
12 .5 6
( 13 .0 7 )
1 2 .2 7
(1 2 .7 8 )
l l .9 6
(1 2 .4 7 )
l l .5 7
(1 2 .0 8 )
2 .0
13 .1 0
(1 3 .6 1 )
1 2 .4 1
(1 2 .9 2 )
1 2 .1 8
(1 2 .6 9 )
l l .5 9
( 1 2 .1 0 )
Upper tier: measured
Lower tier: calculated
Even when NaOH had been
added,
solution
varied
depending
on
between
pH values
at completion
ranged
from 0.03
to 0.43,
indicating
(3)
Discussion
The testing
and it may
solution.
environment
be assumed
that
it may be considered
temperature
conditions.
of experiments
and
considerable
scatter.
ensured
that
specimens
all pores
(=voids)
were in
were close
that
The
initial
the
pH of the
differences
pH values
a saturated
to full
with
state
pore
Though
pore
solution
is consumed
by the
hydratiou
reaction,
since
the
testing
environment
ensured
an adequate
moisture
supply,
it was assumed
that
Cl" and OH" in the pore
solutionwould
not become
concentrated.Also,
although
pH varied
because
of changing
temperature,
and
pH values
at
completion
showed
considerable
scatter,
it
is
assumed
here
that
the
[C1']/[OH']
ratio
did
not
vary
and that the
initially
set pH value
remained
unchanged.
As already
noted
the shaded
portions
of table
5 indicate
specimens
in which
corrosion
was recognized.
Although
comparatively
on the conservative
side,
these
results
indicate
that
if pH is 12.0
or higher
and
[CI]/[OH]
is 1.0 or
lower,
steel
does
not
corrode.
Further,
although
judged
as corroded
in
case pH was 13.5
or higher
and [C1"]/[OH']
was 1.5,
and in case
pH was
13.0
and [C1']/[OH]
was 1.5,
it is possible
from the conditions
of adjacent
specimens
that
the results
had been
of special
nature,
and it is considered
that
further
studies
are
still
required
to
be
made.
This
result
is
considerably
different
from
the
threshold
value
in an alkaline
solution.
That
is, thethreshold
value
in mortar,
at pHof12.0
to 13.0,
is higher
than
in an alkaline
solution,
while
at pH of 13.5
they
are approximately
equal.
The value
is small
compared
with
the results
obtained
by Yonezawa
et a1,
and this
is thought
to have
been
because
of the
lack
of cover
at the
specimens
ends and the
considerable
influence
of differences
in oxygen
supply
conditions.
So far as can be judged
pH, and it appears
that
express
the
threshold
total
chloride
content
from Table
5, corrosion
of steel
is influenced
what
Glass
and Buenfeld
have said
that
it is bestto
value
for corrosion
of steel
in concrete
in terms
by weight
of cement
is notnecessarily
true.
-236
-
by
of
Further,
the
limit
value
of
[C1']/[OH'J
was
studied
using
polished
reinforcing
bars.
It is known
that
limit
values
of [C1]/[OH]
differ
for
polished
bars
and bars
with
mill
scale
on their
surface.The
experiments
in
this
case were carried
out strictly
with
the
aim of gaining
basic
knowledge,
andthe
influence
of mill
scale
is amatterforfuture
study.
The
absorption
at the
mortar
portion
of
measured
and was found
to be 7.6 wt%.
measured
and it was 2,050
kg/m3.
Therefore,
2,050kg/m3
and
the
pores
On the
concrete
provided
to the
Therefore,
evaluation
x7.6wt%=155.8kg/m'
involved
in
absorption
were
approximately
15.6
other
hand,
absorption
of concrete
cores
structures
(number
of samples.-38)
indicated
that
the unit
mass
of concrete
assumed
to
absorption
of the
mortar
specimens
used
it is considered
that
the
results
obtained
of actual
structures.
In measuring
pore
structure
not carbonated.
of
is
moisture
altered
4. IMPROVEMENT
ELECTRO-CHEMICAL
by
contents
of
carbonation,
OF CONCRETE
TECHNIQUES
Improvement
of way concrete
in
realkalizalion
will
be described,
survey
carried
out over
a period
was also
done
on adjacent
structures
of this
treatment
and
the
results
described.
(1)
Structures
Treated
The
structures
tested
rigid-frame
viaducts,
These
chlorides
due to
a specimen
after
testing
The
unit
mass
of mortar
the absorption
in mortarwas
as
were
shown
vol%.
sampled
from
actual
7 wt% (= 16.1vo1%,
be 2,300
kg/rn
), close
in these
experiments.
here
can be used
in
actual
structures,
sampling
was
IN
was
was
ACTUAL
done
since
it is said
from portions
STRUCTURES
BY
an actual
structure
by desalination
and
along
with
the
results
of a follow-up
of five
years
after
treatment.
Treatment
using
realkalization
only.
The effects
of a one-year
follow-up
survey
are
single-line,
in Fig.3.
single-column
beam-and-slab
viaducts
were constructed
at a time
when regulations
concerning
in concrete
were not clear-cut,
and the chloride
content
was high
the use of marine
sand.
Asaresult,
carbonation
had progressed.
The mixture
proportions
givenin
Table
7. Whether
Table 7
Estimated
s(k
D tgre f/c
esnimggt)hn M a x . siz e S(cmlu )m p
c o amrs)e a g g ,
(m
24 0
25
of the concrete
at the time
admixtures
had beenused
specified
A ir
(% )
1 2 ｱ 2 4 .5 ｱ 1
were
as
mix of concrete
w )/ c
(%
U n it c o n te n t (k g /m )
W a te r
53
157
C em en t
2 97
Admixture:
Test
treatments
were applied
to
Prior
to treatment,
the
structures
investigation,
and the results,
are
of construction
is not known.
columns,
were
described
257
beams,
examined,
below.
-
F in e ag g . C o a rs e a g g .
699
115 8
AE water-reducing
agent
and cantilevered
slabs.
detail
and
methods
of
f e vv
r~B
DesaIinatIon
+
reafkal1rat1en
,treatment
$ection
R6 re»Ikailzation
treatment
section
r-A.
Star
t
po in't
st
$outh
sid
No r t h
s i de
IOOE
d«
NJLSJUS.
.CantiIever
tIab
South
s i de
Nor th
s i de
We s t
face
jSBJsH
PoI4riza11on
curve
core
sampling
l.R..9..?J.l?_G
//
//.
a)Visual
Inspection
3, Structure
numeraI:Msaturernent
l-ocation
CoIumn
Fig,
0ireIed
Unit:mm
tested
of Appearance
Visual
inspections
of overall
appearance
ware carried
out, but
no prominent
cracking
was recognized.
Cores
sampled
from columns
and beams were split
in half
longitudinally,and
the
fractured
surfaces
were visually
inspected,
but
no cracks
or leaching
of gel-like
substances
were noted
from
either
columns
or beams.
Not did
coarse
aggregate
particles
show
signs
cracking
or reaction
rings.
b)
Measurement
Carbonation
Concrete
reinforcing
same time,
of
Reinforcing
cover
was
bars
judged
measurements
Bar
Corrosion,
Cover,
removed
by
chipping
and
the
according
to the grading
given
were made of cover
and carbonation
Table 8 Corrosion
C orro sio n deg ree
0
and
corroded
in Table
depth.
degrees
V isu ally o bserv ed state
I
C o n d ition at tim e of co n stru ctio n m ain tain ed , w ith n
su bsequ en t c o rro sio n n o ticeab le
C o rro sion in p arts seen L ig ht co rrosio n
II
cG ro
reate
ss se
r pction
art o fb ro
su ke
rface
n off
c orro
in pd arts
ed
Ill
C ro ss se ction b rok en o ff ov er entire c ircu m ferenc e o
re inforcin g b ar
IV
C ross sectio n o f reinfo rcin g b ar ab ou t 1/6 to 1/3 m issin g
-238-
Depth
state
8. At
of
of
the
The
method
of measuring
carbonation
depth
is
as described
below.
After
chipping,
any powdered
concrete
on the
surface
was removed
by
means of a blower
or similar
apparatus,
anda
1% phenolphthalein
solution
was sprayed
on the chipped
surface.
The distance
from the concrete
surface
to the portion
turned
red was measured
using
calipers.
Measurements
were
made at roughly
20 equidistant
points
around
the
circumference
of the
chipped
portion
and the average
was taken
as the carbonation
depth.
The
resultsaregiven
inTable
9.
Table 9 Reinforcement corrosion degree, cover,
and carbonation depth investigation
results
P ar t
R e in fo rc e
B ar
C o rro s io n
d ia m e te r
d e g re e
m e u t ty p e
0
C o lu m n M a in re in fo rc e m e n
D 32
( wc e e)ｮsA
fa
0
9
II
H o o p re in fo r ce m e n t
0
B e a m M a in re iu fo rc e m e n
D 32
c(ae ron tu en r d)
6 13
II
S tirru p
The
results
given
in
of
carbonation
Table
10.
Table
10
Core
P art
cB ee na tme r) ( a r o u n d
carbonation
Chloride
Content
Table
ll
carried
out
on
sampled
cores
are
tests
23
28
26
28
2 6 .8
22
19
20
23
25
2 1.8
B e a m
of Test
of total
chloride
contents
of the
analysis
results
were determined
meter
of concrete
was 2,300
kg.
JCI-SC4,
"Method
of Analysis
Chloride
quantity
n
days
cores
sampled
are
on the hypothesis
Chloride
analysis
for
Chlorides
conerete(kg/m)
f r o m
0
15
3 0
4 5
60
75
15
30
45
60
75
90
1 .0 0
2 .5 1
3 .3 0
2 .8 5
1 .9 0
2 .0 6
1 .0 6
2 .5 1
4 .5 3
4 .0 0
3 .0 1
2 .5 4
Treatment
treatment
consisted
and realkalization
realkalization
only
The desalination
current
for 60
in
Ds u e rp f ta hc e o (fm ms )a m p l i n g
C o l u m
The
test
desalination
after
which
2 2 .1
19
Analysis
P a r t
Details
52
44
29
The results
of analyses
given
in Table
ll.
The
that
the mass per cubic
was performed
following
Contained
in Concrete."
(2)
tests
62
C a rb o n atio n
d e p th (m m )
3 3 .6
C a r b o n a t i o n A v . c a r b o n a ti o n
d e p t h (m m )
d e p th (m m )
ｩ
ｮ
(D <D
ｩ
sC iod elu/ wm ens t f( ae ca es )t
c)
depth
C o v e r(m m )
+ realkalization
for desalination,
firstly
of
(= desalination
wasperformed
procedure
then
-239-
carrying
out
+ realkalization),
on an adjacent
consisted
carrying
out
a
process
of
four years
viaduct.
of applying
realkalization
electric
for
a
further
15 days.
The anode
for the desalination
+ realkalization
procedure
consisted
of pneumatically
applying
fibers
of cellulose
nature
together
with
the
specified
electrolytic
solution
(saturated
calcium
hydroxide
solution)
to the
concrete
surface,
fixing
a titanium
mesh
over this,
and
then
applying
one
more
layer
of
fibers
and
electrolytic
solution.
Maintaining
the anode
in a moist
condition,
reinforcing
steel
embedded
in
the structure
was made the cathode,
and direct
current
was applied
for 60
days
to achieve
desalination.
The current
density
was 1 A per square
meter
of concrete
surface.
Realkalization
was by a method
called
electroendosmosis
in which
a
lithium-based
alkali
metal
salt
(lithium
carbonate)
is introduced
from the
concrete
surface
to the vicinity
of reinforcing
steel
aim of restoring
the
alkalinity
of the
carbonated
concrete.
More specifically,
alkalization
was achieved
by maintaining
the
anode
used
in desalination
in a moist
condition
with
a solution
containing
a combination
sodium
carbonate
plus
lithium
carbonate
solution
(Li/Na
mol ratio
= 0.1).
After
applying
electric
current
for desalination,
the electric
current
was applied
for 15 days
for
realkalization.
In cases
applied
where
for 15
realkalization
days;
however,
only
that
was carried
in this
case
out,
steel
current
mesh
was similarly
was used as the
treatment,
+ realkalization
at 3, 6,
anode.
(3)
Confirmation
of
Effect
survey,
out
In the
locations
follow-up
were
carried
12,
24,
and
18,
36,
60
investigations
a total
of
of desalination
times
after
eight
Where realkalization
only
was implemented,
out three
times,
at 3, 6, and 12 months.
made against
the state
before
application
completing
treatment.
a)
Chloride
Analysis
Concrete
cores
sampled
before
of electric
current
were used
and thereby
ascertain
the effects
3.5
"E 3
s 2.5
-+t01-> 02
c 1.5
n
l
-o0>
o
4
Total
treatment
and periodically
to measure
the chloride
of desalination.
¥
V
X
m
application
of concrete
-Before treatment
一* treatment
2 days after
3 months aft er
一*- 6 months aft er
-9 months aft er
BIT looitfcn
/
/
after
content
X
:.> a
- 0 --
1 2 m o n t h s af te r
".--
1 8 m o n t h s a ft e r
W .i
0 .5
0
Fig.
follow-up
surveys
were carried
In both
cases,
comparisons
were
of electric
current
two days
after
of Concrete
o
9,
months.
in
T^ｻ
chloride
o
n
m)
m
*t
oJ
o
(o
u*s
m
r^
o}
o
0 >
in¥
o
c*4
i-i
o
in
t?
o
m
i-?
o
-rCMI
o
*f
CMI
o
t CMI
o
Q
CO
I
i-
W
n -
tO
I^ -
ｫO
O
CM
O
IO
O
cO
TO -
TO J-
O r-
^
T-
i-
CM
CM
CM
content
(desalination
-240-
- 2 4 m o n t h s a ft e r
3 6 m o n t h s a ft e r
6 0 m o n t h s a ft e r
+ realkalization)coliimn(D
With
regard
to changes
with
time
in chloride
subjected
to the
desalination
+ realkalization
contents
are shownin
Fig. 4 andsolublechloride
1.8
Bir [octtlcci
^
y
1.6
T
¥
V.E 1.1.42
/
¥
¥x
3ce 1 /
S o.8 / x T
I) 0.6 T ^ 2 i8S
0. ^ s ^
/
<O p r
go 0-4 1
0.2
0
contents
of
procedure,
contentsinFig.5.
.'/ .'
^!
Fig.
5
Soluble
c *j
I
**
I
to
J
r ^
o
cN
I
^ -
co
-a-
CD
r-
o
chloride
in
I
oo
I
^
I
^
J
r^
I
o
I
oc j
<D e pt h (m m )
ion
i-
oc o
-
o*一
cs
o* *
CM
or- ｫ
es
content
Chloride
Chloride
Ion
Selective
Contained
seen iu both
while
hardly
months
after
total
chloride
any
increase
treatment.
" ｻ
0 .8
0 .7
o .6
¥
0 .5
"<V
N X
:i o .4
l_
E 0 .3
0 .2
0 .1
w
O
+ realkalization)
column®
centers
and measurements
were
contents.
Chloride
content
was
Difference
Titration
Using
in JCI-SC4,
"Method
of Analysis
for
Concrete."
Significant
reductions
were
soluble
chloride
contents
after
treatment,
seen in chloride
content
even at 60
and
was
indicate
reinforcing
bar
ions
into
the surrounding
shadow
spots
behind
locations
concrete
reinforcing
where
took
bars
¥
¥
/*
/
/
/
vt
m
TI
O
- 3 6 m o nt h s af te r
column
chloride
of Potential
The broken
lines
in the
figures
almost
no rediffusion
of chloride
place,
while
it appears
prominent
were not recognizable.
-o
o
-C0
I
- Before treatment
-2 days aft er
treatment
. 3 m onths after
it.- -6 m onths after
-JK- -9 m onths after
-12 m onths after
一?- 18 m onths after
-24 m onths after
to
Electrode"
Hardened
in
portions
chloride
6 0 m o n t h s a f te r
(desalination
At 36 months,
coring
was done
made of total
chloride
and soluble
measured
according
to "Method
column
total
I
I
o
co
I
in
I
m
**
I
O
CO
I
o
co
I
m
Tf
I
10
rI
O
o
as
I
tr>
- Before treatm ent
-2 days aft er treatm ent
-3 m onths after
-6 m onths after
- OK- 9 m onths aft er
一 - 12 m onths after
- 18 m onths aft er
24 m onths after
- 36 m onths after
一-<>- 60 m onths after
Depth(mm)
Fig.
6
Percentage
of soluble
chlorides
(desalination
+ realkalization)
The
ratios
of soluble
to total
chloride
contents
are shown
in Fig.6.
Immediately
after
treatment,
the ratio
at a point
15 mm from the surface
was zero,
and this
was due to both
total
and soluble
chloride
contents
being
practically
zero.
To around
30 mm from the surface,
portions
with
-241
-
high
soluble
chloride
that
had been carbonated.
portions
that
had been
Below
30
50% even
The soluble
is thought
totalchloride
content
ratios
Apparently,
carbonated.
more
or
chlorides
with
areas
form in
mm, where
carbonatioii
had
not
occurred,
the
ratio
was around
after
60 months
had elapsed,
and no great
variation
was seen.
chloride
content
was reduced
by desalination
treatment,
but it
fixed
chloride
became
soluble
so the ratio
of soluble
chloride
to
didnotvary
to any greatextent.
Regarding
changes
with
lime
in chloride
contents
had been
implemented,
total
chloride
contents
soluble
chloride
contents
in Fig.
8. Compared
treatment,
there
was little
change
in eithertotal
chloride
content.
J
2 .5
･c
m
/ * ^
where
realkalization
are shown
in Fig.
with
the situation
chloride
content
or
3 .
2
ｫ *s ^ W
0
c 1 .5
o
o
-a<D l
1_
-2 0 .5
o
0
Fig.
treatment
-*-2 days after
^
7
treatme nt
m
T?
o
c s
I
if )
ｫ!*
I
o
co
I
to
r
I
o
0 1
I
O
ID
T-
O
co
LO
**
O
co
IO
r-
Total
chlorides
I.D
1 .4
1 .2
(realkalization
^
" 0 .6
0 .4
0 .2
0
Measurement
8
of pH,
Concrete
cores
were split,
in concrete
were soaked
and alkali
blue
(pH
test
alkalinity
was
maintained
¥¥
¥ ¥
0 ^ *S SSi=
Z w
¥
/
-x-12 months
after
-*Before
treatment
-«2 days
afte r
tre
atment
---*-3 months
afte r
m
i-I
o
Fig.
-&-3months
afte r
only)
/ A
<o
3+ｫ8O3> ^fr-^E 0 -81
o
only
7 and
before
soluble
-+~
Before
5
Depth(mm)
b)
less
overlapped
existed
in soluble
o
COI
10
Y-
Soluble
m
o
I
I
o
in
CO
TtD e p th (m m )
chlorides
Confirmation
to
I
o
CO
o
I
m
f
(realkalization
ofAlkalinity
and the concrete
surface
with
alizarin
yellow
(pH
paper,
pH ll.0-13.6)
to
after
realkalizaton;
-242-
-x12 months
afte r
only)
Maintenance
sides
and Reinforcement
testpaper,
pH 10.0-12.0)
judge
how well
concrete
note,
however,
that
this
method
using
pH test
paper
only
allowedjudgments
in terms
of ranges
such
as iO.2
to 0.4.
It must
also
be noted
that
even
a single
split
surface
exhibited
scatter,
such
as for example
pH = 12.8-13.6.
Therefore,
it was
decided
to
express
results
as average
pH values
obtained
by
adding
together
maximum
and minimum
values
and dividing
by two.
The average
pH values
of cores
before
treatment,
two
days
after
completion
of
treatment,
and 6, 12, 24, 36, and 60 months
after
treatment,
are shown in
Fig.
9.
14
- D esalin atio n -frea lkalization co lum n^
s urf
"" "^ "" " D e salin atio n +
rea lkalization co lum n (5
rein for
O
U n tre ate d s ection
c olum n(6)su rfa ce
13
12
ll
> K V/
c- & - y - X
X
o
o
10
X- X - X O
Q
ｩ
- X - U ntreate d se ction
c olum n(D reinfo rce m e nt
9
8
- R e alka liz ation se ction
co lu m n ｮ surfac e
^^ V,/ o^f><^<o * /o^^ 9 .^ /o^^< l^ /0<>
>?rJ^NV /o^^^ ^o^^j f o^
/ /^ /o^^
,
X
R ea lka liz atlon se ction
co lu m n ｮ re in forc e m en t
^ &6^^ jr
Fig.
9
At locations
where
desalination
period
between
treatment
and
so it
For
parts
reinforcement
treatment.
at concrete
isclearthat
that
60
+ realkalization
months
after
surfaces
and
12.8-13.6
there
were stable
alkaline
underwent
in treated
parts
realkalization
had pH
in
was
treatment,
implemented,
pH values
vicinities
zones.
of
only,
the
of 13.0-13.6,12
values
x-s 30
J25
£20
<D
T3
c 15
o
2 10
o
ll.2-12.0
bars,
AveragepHofcores
^
Fig.10
Results
of carbonation
-243
T^
CJ
depth measurements
-
in
the
were
reinforcing
surroundings
months
of
after
Carbonation
depths
were measured
spraying
1% phenolphthalein
solution
on
concrete
cores.
The results
of these
measurements
are shown
in Fig.
10.
Immediately
after
treatment,
the carbonation
depth
became
0 mm, while
even at 60 months
after
treatment,
it remained0
mm.
c)
Measurement
Measurements
below.
Copper
Sections
Measured
Examples
of Spontaneous
Potential
of spontaneous
sulfate
electrodes
potentials
were
used
were
made
as reference
treated
with
desalination
+ realkalization:
0) cantilever
slab,
undersurface
(north
side)
0) cantilever
slab,
undersurface
(south
side)
(D beam,
undersurface
0) column,
side
surface
Untreated
sections
of the same viaduct
("untreated
0) beam, undersurface
0) column,
side
surface
sections
of adjacent
viaduct
("outside
treated
CD slab,
undersurface
(south
side)
0) beam,
undersurface
0) column,
side
surface
of spontaneous
potential
sections,inFig.llfor(D,inFig.
measurement
B efore treatment
2 days after treatment
3 mont
6 mont
9 mont
12
18
24
36
60
months
months
months
months
months
Fig.
m
m
® -200>E^-350mv
Spontaneous
measurement
ll
nO
listed
span"):
are
shown
13for®
.
1 00%
>0 ?:* VO
lim iiim"^m m Sn riSK｣m !
aftei
aftei
aftei
aftei
aftei
0 E^-200mV
80%
40%
the
parts
electrodes.
locations"):
results
12ford),andinFig.
20%
at
!V 4H ^ H
H ^ H
40%
H
M ^ B H
e ;il
H -350mV>E
potential
(beam
results/(desalination
20%
H
60%
undersurface(S)
)
+ realkalization)
80%
1 00%
Before treatment (j
2 days after treatment
3 mont
6 mont
9 mont
12
18
24
36
60
months
months
months
months
months
aftei
aftei
aftei
aftei
aftei
0 E^-200mV
Fig.
12
H -200>E^-350mv
Spontaneous
measurement
H -350mV>E
potential
(beam
results/untreated
-244-
undersurface(5)
part
)
for
beam
20%
40%
B efore treatment
2 days after treatment
3 mont
6 mont
9 mont
12 months after
18 months after
24 months after
36 months after
60 months after
!s ^ ^ = s s^ ^ ^ ^ a f
D E ^ - 20 0m V m - 200 > E ^ - 350 m v
Fig.
13
100%
60%
Spontaneous
measurement
potential
results/outside
- 3 50m V > E
(beam
undersurface®
treated
span
)
For desalination
+ realkalization
sections,
months
after
treatment
was little
different
treatment,
but
the
potential
distributions
shifted
in the noble
direction.
the
potential
compared
with
at 24,
36,
and
Meanwhile,
at untreated
shift
in the
noble
direction,
were recognized.
treated
spans,
there
was some
no large
changes
in potential
Variations
in potential
in Fig.
14.
The effectwas
which
were comparatively
initially
to
the
base
direction.
parts
and
but
outside
as a whole,
at parts
treated
with
that
ofrealkalization
on the noble
side.
side
after
treatment
20%
40%
realkalization
only
havingbeendone
It can be seen that
shifted
later
in
18
after
had
are shown
onparts,
what
went
the
noble
1 00%
60%
m
Before
treatme nt
distribution
12 months
60 months
;!:9P
m
2 days after
tre atment
5|
3 mont
61
12 months after
d E^-200mV
Fig.
Spontaneous
ASTM are
14
potentials
giveninTable
il
H -200>E^-350mv
Spontaneous
measurement
B -350mV>E
potential
(column
results/realkalization
and corrosion
l2.
probability
member^
only
assessments
according
to
Looking
at Fig.13,
on comparing
the
results
of
spontaneous
potential
measurements
on the
undersurfaces
of beams
before
treatment
and
60
months
after
desalination
+ realkalization
treatment
following
ASTM
C
876-87,
what
were 0% of Rank
I in corrosion
activity
(E > -200
mV) or
"90%
or higher
probability
of no corrosion"
were 97% 60 months
after
-245-
treatment.
"indeterminate,"
What
Table
12
were
were,
56%
reduced
Spontaneous
of
to
potential
C o r r o s io n S p o n t a n e o u s
c t i v i t y vp so ctes En t i a l (m V )
ra n k
I
E > -20 0
90 %
corrosion
In d e te r m in a t e
Ill
-35 0 ^ E > -50 0
9 0 %
-50 0 > E
were
44%
or higher
of
be seen that,
after
treatment.
as
III
a whole,
Similar
results
were
obtained
(north
side),
slab
undersurface
it may be thought
permissible
stable
spontaneous
potential
reinforcing
bars in concrete.
In contrast,
and side
potential
there
of
Anode
ap p ro x im ate ly
shift
was
to
o ne
60
the
h alf
(-350mV^
months
noble
Polarization
of beams
outside
changes
were seen
Curve
of
of
E),
after
side
at other
treated
parts,
"slab
undersurface
(south
side),
side
surface
of column,"
to consider
that
a shift
had been made
zone
where
a passive
film
was formed
with
regard
to undersurfaces
surfaces
of columns,
hardly
any
measurement
results.
d)
Measurement
(Laboratory)
mV),
probability
IV ill corrosion
activity
corrosion,"
were
0%
and
of
-350
o r h i g h e r p ro b a b il it y o f c o r ro s io n
C r a c k in g in
s p e c im e n s
Ranks
probability
>
o r h i g h e r p r o b a b il it y o f n o c o r ro s i o n
-20 0 ^ E > -3 50
It can
months
Anode
concrete
between
potential,
formed
and
mV ^ E
after
treatment.
C o r r o s io n p r o b a b i lit y
II
IV
What
"90%
treatment.
Rank
II
(-200
3% 60 months
60
and
to a
on
treated
spans
in spontaneous
Reinforcing
Steel
polarization
curves
of
reinforcing
bars
were
measured
using
cores
with
hoop
reinforcement.
The maximum current
density
Imax
+200
mV and +600
mV was determined
from
the spontaneous
and it was attempted
to judge
whether
or not passive
films
are
on reinforcing
bars
in concrete.
Core samples
obtained
from
"column®
" of the
column
portion
of the
desalination
+ realkalization
section
and
"column
© " of the
column
portion
of the untreated
section
for comparison
were used,
and polarization
curves
of reinforcing
bars
were measured.
The cores
were collected
in a
form that
ensured
parts
of hoop
reinforcement
would
be included.
Values
realkalizatiou
section
At 18
indicated
A/cm2.
Evaluation
of
are
Imax up
section
plottedinFig.
to
60 months
after
and Imax up to 12
15.
treatment
months
in
in
the
the
desalination
realkalization
months
after
treatment
the
desalination
+ realkalization
a slight
increase
to 17 JUL A/cm,
but by 60 months
It is considered
that
apassive
state
had been reproduced.
criteria
for
anode
polarization
-246
curves
-
are
given
it
in Table
+
only
section
was 5jU.
13.
IUU
90
80
70
60
50
40
30
20
10
0
"E
o
^
y
/
./
ｫ
A
¥
¥
^ 1
H t_.
. ^ " ---. ..一 - "
...f x g - ** ***^ c^ ,^ｫ ｰ & "> N,
^J- * ;&.
s* */&jf /^
f^> ^0<^0* <
Fig.
15
Desalination
+
realkalizat
lumnｮ
/
/J ^ /-<^ /-o^ /-<^ ^J ? /&
Results
of
anode
Untreated
section
ilum nｩ
0?
- Realkalizatio
n section
colum nｮ
polarization!
tests
(Imax)
Imax where
desalination
+ realkalization
had
been
performed
was 29jU.
A/cm'
and
in the
zone
of Grade
1, "Incomplete
but
some
amount
of
passivity"
before
treatment.
Contractedly,
at 60 months
after
treatment,
it
was5
0A/cm2
andhadshiftedto
aGrade2or3
zone,
inthedirectionof
forming
passive
films
on bar surfaces.
Table
13
Evaluation
criteria
G ra d e
for
anode
E v a lu a tio n
polarization
c r it e r i o n
0
(C c u o r mr ep nl et t e dl ye n n s oi t py a s es ix v c iet ey d) s
1
aC mu or rue nn tt o d f e pn as si ts yi v il tO y ) 1 0 0 jU . A /c m
2
iC n u c rlru e d n et d d ie n n sG i rt ya d ee xs c Oe ,e d1 s o lr O 3o
3
C u rr e n t d e n s it y
4
iC n u c r lru e dn et d d i.en ii Gs i rt ay d ee sx cO e , e 1d ,s 2 I, jU o. rA /c3 m
5
C u r r e n t d e n s it y
p a s s iv it y )
At sections
of realkalization
14 JUL A/cm2 was indicated
same
as for
locations
performed
l
curvesC13}
1 00 /Z
A /c m
(t h o u g h
A /c m
a t
le a s t
o n c e
i n c o m p le t e ,s o m
a t le a s t o n c e , b u t n o
1 0 fJ. A /c m
d o e s
n o t
only,
current
12 months
after
where
desalination
e x c ee d
a t
le a s t o n c e , b u t
I jU
A /c m
(v e ry
density
became
90jU
treatment,
a value
+ realkalization
n o
g o o
A/cm
roughly
had
, but
the
been
The maximum current
density
in the anode
polarization
curve
for untreated
sections,
which
was 31JLL A/cm2
before
treatment,
was 38JLL A/cm
60
months
after
treatment,
indicating
hardly
any change.
If remained
in the
zone of Grade
1, "Incomplete
but some amounts
of passivity."
Anode
concrete
resistance
potential
passive
values
gradient
polarization
curves
of
reinforcing
bars
were
measured
using
cores
taken
to include
hoop
reinforcement,
and
polarization
from the
anode
polarization
curve
gradient
at a spontaneous
plus
50 mV. From this,
it was attempted
to judge
whether
or not
films
would
be formed
on reinforcing
steel
in the
concrete.
The
of polarization
resistance
obtained
from
the
polarization
curve
before
treatment
and 60 months
after
treatment
are shown in Fig.
-247-
16.
Criteria
for
corrosion
evaluation
from
polarization
resistance
are
given
in
14.
<fO
40
35
30
25
20
15
10
5
0
o
Table
ci
j*
>Xo
.4
J^
^ /
O ir
x^
i tr
1
K
/
A .
*
¥ /
- D esalination
+
realkalizat
colum nｮ
v
- -S&- " U ntreated
section
)lum n(D
? ^-F^c> </F^^ ><>F <^^S </^^ i
<<>,fVb^^-/<b^</"F^->^<^O<^NV </o ^NS>
-R ealkalization
section
colum nｮ
JsO<J<t> & &
Fig.
Table
14
Criteria
16
for
Polarization
corrosion
resistance
evaluation
by
polarization
resistanceC
10*)
P o la ri z a t io n C o r r o s i o n e v a lu a t io n
re s is t a n c e
L e s s t h a n 4 k cZ oo rnr oe s ioo fn g w r ie tah t or ce ci un fr ro er nc ce em e on ft
!) -c m
c ra c k in e
Z o n e
o f m e d iu m
re in f o r c e m e n
4
8k (! -c m
c o r ro s i o n
Z o n e
o f m e d iu m
re in f o rc e m e n t
8
12 k fi -c m
c o r ro s i o n
M o r e
Z o n e o f n o r e in f o r c e m e n t c o r ro s io i
t h a n 12 k Q c m
o r z o n e o f m i n u t e c o r ro s io n
R an k
I
n
Ill
IV
The polarization
resistance
of a part
where
desalination
+realkalization
was performed,
16.7
kQà"cm2
before
treatment,
became
35.7
kQà" cni
24
months
after
treatment
but by 60 months
it had declined
slightly.
However,
it was of Rank IV, "Zone
of no reinforcement
corrosion
or zone of minute
corrosion"
(12.kQà"cm2
or
higher),
and
it
may
be
considered
that
polarization
resistance
is increased
by desalination
+à"realkalization
and
there is a shift
toward
passive
film
formation.
At the
realkalization
only
section,
a value
slightly
lower
than
where
desalination
+ realkalization
had
been
carried
out
was
indicated
immediately
after
treatment,
but
12 months
after
treatment
it was 20 kQ à"
cm2, roughly
the same as where desalination
-f realkalizatiou
had been done.
Polarization
resistance
outside
the
treated
span,
which
was 14.7
kQ à" cm
before
treatment,
became
7.7 kQ à" cm.2 60 months
after
treatment,
RankII,
"Medium
reinforcingsteelcorrosion
zone"
(4-8
kQ à" cm).
(4)
Summary
The following
realkalization
summarized
and realkalizatiou
a)
of
Application
Desalination
the
effects
only
of test
treatments
application
on actual
of desalination
structures:
+
+ Realkalization
248-
1)
Evaluations
of
spontaneous
potential,
resistance,
indicate
passive
films
tendedto
corrosion
activity
of
anode
polarization
that,
for
the period
up
be formed
on reinforcing
2) The alkalinity
of the concrete
paper
and
1% phenolphthalein
months
after
treatment.
3) The chloride
distribution
there
was no rediffusion
of
even 60 months
after
treatment.
4) The
ratio
parts
extremely
major
changes
in the
chloride
of
soluble
chlorides
near the surface,
were noted.
5)
Noclearshadow
b)
Application
spots
could
of
test
reinforcing
of13.0-13.6
and realkalization
results
and
to
as measured
found
to be
after
the
treatment
vicinity
behind
after
usingpH
test
stable
even
60
of
Table
desalination
1.28
and
15
indicated
reinforcement
reinforcing
polarization
to
bars
were
cases
resistance
where
in treated
indicated.
TEST
were
measurements
ChangesinpH
+ realkalization
parts
RESULTS
evaluated
on actual
and
pH
[C1"]/[OH"]
12 months
desalination
12
months
T o t a l
c(k hg l /ir
o f r )i d e s
6 0 m o n t h s
a fte r
through
structures.
S o l u b l e
c h (kl go /n
r i )d e s
application
[ c l-]
C o H -]
45
60
1 0 .4
1 0 .8
2 .8 5
(0 .9 6 )
1 .4 4
(0 .4 8 )
7 9 0 .8
1 9 8 8 .0
60 -
75
1 0 .4
1 0 .8
1 .9 0
(0 . 6 4 )
0 .8 0
(0 .2 7 )
5 2 6 .1
1 3 2 2 .7
45
60
1 2 .6
1 3 .2
1 .2 5
(0 .4 2 )
0 .5 6
(0 .1 9 )
1 .3 8 5 .4 9
60
75
1 2 .6
1 3 .2
1 .1 6
(0 .3 9 )
0 .4 7
(0 .1 6 )
1 .2 8
5 .1 0
-249-
after
+
after
AND MEASUREMENTS
dueto
(m m )
B e fo re
tre atm e n t
at
no
bars,
a comparison
of
realkalization
be identified
application
of
reinforcement
while
soluble
pores
in
would
be
5.49.
D e p th
that
remained
except
60 months,
and
Changes
in pH and Cl'/OH"
after
application
of desalination
+
are summarized
in Table
15. Specific
values
of pH could
not
because
of problems
with
measurement
techniques,
but the
desalination
+ realkalization
resulted
in pH values
around
being
improved
to 12.6-13.2
60 months
after
treatment,
chlorides
were
also
reduced
to
0.47-0.56kg/rn
. Considering
concrete
as amounting
to 16.1vo1%
of total
volume,
[Cl]/[OH]
between
on
Only
5.COMPARISON
OF LABORATORY
ON ACTUAL STRUCTURES
Desalination
laboratory
concrete
ions
be seen
polarization
curves
and
were
roughly
equivalent
was applied.
vicinities
pHvalues
treatment,
was
to total
chlorides
around
50% even
of Realkalization
1) Anode
treatment
realkalization
2)
In
treatment
after
solution,
reinforcing
steel
based
curves,
and
polar-ization
to 60 months
after
treatment,
steel.
of
Note)
pH values
for reinforcement
parts
in treated
portion
@
Calculation
of [C1]/[OH]
performed
for total
chlorides
withquantity
pores
inconcrete
taken
as 16.1
vol%
of total
volume.
Figures
in ()ratios
(%)of
chloride
ion quantity
to unitcementcontent
The conclusion
treatment
tests
mortar
used
in
structures
were
pHis
12orhigherand
be applied
without
pH, but not with
drawn
from laboratory
on structures
based
tests
and
laboratory
tests
approximately
equal
[C1']/[OH~]is
modification,
regard
to [C1"]/[OH"].
it
tests
carried
out in tandem
with
on the fact
that
moisture
contents
of
concrete
cores
collected
from actual
was that
steel
does not corrode
when
1.0orunder.
would
Changes
in pH and [C1']/[OH"]
after
application
summarizedin
Table
16. Through
application
the vicinity
of reinforcement
was improved
[Crj/[OH']
wasbetween
0.76
and 3.41.
Table
16
ChangesinpHand
realkalization
[C1']/[OH"]
Ifthisconditionwereto
satisfactory
with
be
of
to
dueto
regard
to
of realkalization
only
are
realkalization
only,
pH in
a range
of 13.0-13.6,
while
applicationof
only
D e p th
(m m )
12 m o n th s 45
a f t e r
t re a t m e n t
60
Note)
of
pH values
forreinforcement
Calculation
of [C1"]/[OH"]
pores
in concrete
taken
Figures
in ()ratios
(%)
pH
[ c r]
/
[ o H ]
T o t a l
S o l u b le
c h lo r i d e s c h l o r id e s
(k g A n ')
(k g A n )
6 0 1 3 .0
1 3 .6
1 .9 5
(0 .6 6 )
0 .6 0
(0 .2 0 )
0 .8 6
3 .4 1
7 5 1 3 .0
1 3 .6
1 .7 4
(0 .5 9 )
0 .5 3
(0 .1 8 )
0 .7 6
3 .0 4
parts
in treated
portion
®
performed
for total
chlorides
with
as 16.1
vol%
oftotalvolume.
of chloride
ion quantity
to unitcementcontent.
In this
case,
to pH, while
not more than
strong
alkali
logarithmic,
the conditions
with
regard
to
1.0.
Thereduction
direction)
both
the contribution
for preventing
steel
[C1']/[OH"]
also,
in chloride
contribute
to the
due to risein
pH
The relationship
1.0 and 1.3
between
pH and total
chloride
and with pH in the range
12.6-13.6
corrosion
are satisfied
there
is a possibility
ions andtheincrease
fall
in [Cl]/[OH],
is claminant.
content
for
as obtained
quantity
of
with
respect
that
it will
be
in pH (shift
in
but since
pH is
[Cl]/[OH]
in treatment
values
of
is shown
25
ill
Fig.
17.
With
the
threshold
value
of reinforcing
t
steel
corrosion
I
3 .5
^
A
3
E 2 .5
*s :i
C c i- ] /
[ O H - ] = 1 .0
A
*o
A
- L l .5
o
1
- - - A - - - [ OC l-H -] ]/ = 1 .3
A '
0 .5
0
12
Fig.
[C1']/[OH"]
^ 1.0,
below
the
solid
"not
corroded."
as
line
Considering
that
film
after
application
^ 1.3 is allowed
line
in the figure
an
The past
value
of
notedby
of1.7-2.0,
18,
based
relationship
17
12.5ph|3
13.5
Corrosion
obtained
in the
from
figure
threshold
the
is
actual
structure
of desalination
onthethreshold
from
isthe
range,whichmay
value
resultsoflaboratory
the
range
which
may
tests,
be
the
part
considered
shift
toward
formation
of a passive
+ realkalization
if up to [Cl]/[OH]
Table
14, the
part
below
the
broken
be considered
"not
corroded."
research
summarized
in Chapter
2 indicates
that
the
threshold
[C1"]/[OH"]
for
corrosion
of reinforcing
steel
in cement
mortar
S.E.Hussainetal.C10)
atapHoflessthan13.30isinarange
while
for pH greater
than
13.30,
the range
is 1.28-1.86.
In Fig.
on these
values,
and with
a pore
volume
of 16.1
vol%,
the
with
total
chloride
is shown,
further
superimposing
Fig.
17.
Fig.
It can be seen
value
is obtained.
that
18
even
Corrosion
threshold
S.E. Hussain
et a1.
with
[C1"]/[OHT]i
values
according
and accordingto
1.3,
a relatively
to
thisstudy
conservative
6. CONCLUSIONS
This
investigation
(1)
Experiments
[C1"]/[OH"]
is
judged
by the
leads
to the
with
mortar
1.0
or less,
steel
results
of these
following
conclusions:
indicate
that
if pH
is
12 or higher
reinforcement
will
not corrode.
So
experiments,
whether
corrosion
occurs
-257
-
far
or
and
as
not
steel
is greatly
influenced
by pH. From the results
of experiments
actual
structures,
it isconcludedthat
steel
will
not corrode
if [Cl]/[OH]
1.3 orunder.
This result
isin
conformity
with
results
of past
research.
(2)
By
carrying
out
desalination
+
realkalizalion,
pH
values
on
is
around
reinforcing
steel
in structures
were improved
to 12.6-13.2
60 months
after
treatment,
while
soluble
chlorides
were
reduced
to 0.47-0.56
kg/m
. Even
60
months
after
treatment,
practically
no changes
were
noted
in
the
alkalinity
and chloride
content
of the concrete,
while
there
was hardly
any
rediffusion
of chloride
ions
around
reinforcing
bars.
No prominent
shadow
spots
were seen behind
reinforcing
bars
either.
(3)
The
ratio
of soluble
chlorides
about
50%
after
the
elapse
of
surface,
and no large
variations
to total
60 months,
were seen.
chlorides
except
was
extremely
(4)
Where
realkalization
only
was carried
out as treatment,
pH values
around
reinforcement
in structures
had improved
months
later,
while
[C1']/[OH"]
values
were between
0.76
there
is a possibility
that
the threshold
[C1']/[OH]
value
through
application
ofrealkalization
only.
estimated
close
to
be
the
to
after
treatment,
to 13.0-13.6,12
and 3.41.
Hence,
will
be satisfied
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1)
Ishibashi,
Applied
to
9th
Annual
pp.429-434,
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Kitago,
Y.:
"Effects
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1984
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Materials
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V.K.:
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Materials
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Havdahl,
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Chloride
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1986(in
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Hussain,
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