comparative study of different test methods for reinforced
TRANSCRIPT
ORIGINAL ARTICLE
Comparative study of different test methods for reinforcedconcrete durability assessment in marine environment
Miguel Angel Bermudez Odriozola ÆPilar Alaejos Gutierrez
Received: 4 October 2006 / Accepted: 11 May 2007 / Published online: 14 June 2007
� RILEM 2007
Abstract There are many different test methods to
assess reinforced concrete durability. As in marine
environment reinforcement corrosion due to chloride
attack is the most important degradation process,
chloride penetration rate has been compared with
different durability tests results (concrete strength,
porosity, water absorption, water penetration depth
under pressure, capillarity, water and oxygen perme-
ability) carried out on concrete cores obtained from
the caissons of seven Spanish wharves. Data have
been studied separately, depending on concrete
location (chloride penetration rate is faster in
submerged concretes than in tidal zone concretes)
and cement type (mineral admixtures reduce perme-
ation rate due to pore size refinement). Results show
that it is advisable to control concrete water tightness
through water penetration under pressure test; addi-
tionally, in order to make sure a slow corrosion rate,
it should be advisable to control oxygen permeability
in tidal zone concretes.
Keywords Marine environment � Reinforced
concrete corrosion � Chloride ingress � Durability
tests � Cement type
1 Introduction
Nowadays, concrete structures are designed under
international technical standards, the Structural Con-
crete Instruction (EHE [1]) in Spain. The aim of these
standards is to guarantee that structures comply with
certain stability and resistance requirements, and
keep them during design working life.
For concrete durability control, Eurocode 2 [2]
requires a minimum compressive strength related to
the exposure environment, while ACI 318R [3] also
establishes a minimum w/c ratio, but also only
compressive strength tests are required. In Spain,
the Structural Concrete Instruction (EHE [1]) uses
water penetration depth under pressure test (UNE
83309:90 EX) as hardened concrete durability con-
trol. Depending on environmental conditions, there
are also some requirements related to concrete
composition (maximum w/c ratio and minimum
cement content).
Although not included in Spanish or international
standards, there can be found many test methods to
M. A. Bermudez Odriozola
Concrete Durability Division, Structures and Materials
Laboratory, CEDEX, Ministry of Public Works, Madrid,
Spain
P. Alaejos Gutierrez
Materials Science Program, Structures and Materials
Laboratory, CEDEX, Ministry of Public Works, Madrid,
Spain
M. A. Bermudez Odriozola (&)
Laboratorio Central de Estructuras y Materiales, CEDEX,
C/ Alfonso XII, 3 y 5, Madrid 28014, Spain
e-mail: [email protected]
Materials and Structures (2008) 41:527–541
DOI 10.1617/s11527-007-9263-8
assess concrete durability, which are representative of
different transport mechanisms in concrete: water
permeability, gas permeability, absorption, capillar-
ity, etc., but there is no agreement about which one is
the most suitable test to control durability of concrete.
The main objective of this study is to select a
durability test which guarantees the designed service
life of reinforced concrete structures located in tidal
zone, i.e., a durability test whose results were linked
to chloride penetration rate.
In order to select the appropriate test method for
reinforced concrete in marine environment, it must be
considered that there are different chloride penetra-
tion mechanisms overlapping depending on marine
exposure conditions: diffusion, capillarity, etc. [4, 5];
nevertheless, Fick’s second law is used to model
chloride penetration due to the different interacting
mechanisms (absorption, diffusion, chloride binding)
in marine environment, but then D is not a ‘‘true’’
diffusion coefficient and should be considered as an
‘‘apparent’’ diffusion coefficient [6, 7].
In this article, it has been compared the experi-
mental results from several durability tests with
chloride penetration rates measured in seven marine
structures (named Wharf A to Wharf G) of different
concrete quality and exposure times, to select the
most appropriate test methods to assess reinforced
concrete behaviour in full-scale structures. These test
results may be used to assess the effectiveness of
actual quality control standards requirements, i.e.
EHE Instruction, or the need to adopt new quality
control methods.
Then these are the objectives of this research
programme: to compare the effectiveness of labora-
tory test methods to assess the durability of concrete
marine structures; and to select the test method that
better assesses the real behaviour of concrete in
marine exposure.
2 Methodology
Methodology consisted of the following steps:
2.1 Data collection
Information was obtained from the wharves construc-
tion’s projects about the characteristics of the caissons
(dimensions, typology, reinforcement geometry, etc)
and the concrete used for construction (design cylinder
strength, w/c, etc).
Also the documents from the quality control
carried out during construction of the caissons have
been reviewed. Data on compressive strength of
concrete corresponding to the layers where cores
were drilled in this study have been collected and
compared with actual measured strengths; these data
have been used to select the caissons where cores had
to be extracted: one high strength caisson, one low
strength caisson and one or two average strength
caissons in each wharf were selected. When no data
on concrete quality were available, the caissons have
been selected from ultrasonic wave transmission test
results, carried out on all caissons of the wharf.
Finally, only in Wharf A the initial content of
chloride in concrete was known. Summary of all
these data can be seen in Table 1.
2.2 Drilling of concrete cores
Two different procedures of drilling the cores have
been followed, depending on concrete location:
permanently submerged (wharves A and B) or in
tidal zone (wharves C, D, E, F and G).
2.2.1 Submerged concrete
Concrete is permanently submerged in these caissons,
so just the concrete slab on them is over the sea level,
but it wasn’t the objective of this investigation. As it
is hard to drill concrete cores under the sea, it was
planned to drill two vertical borings from the
concrete slab per caisson.
Following this procedure, double concrete corings
were drilled in two wharves (A and B). Three
caissons were investigated per wharf, so finally 12
cores were extracted to study permanently submerged
concretes.
Moreover, concrete specimens (150 mm cubes and
150 · 150 · 300 mm prisms) were cast in laboratory
with different mix designs (see Table 2) and
submerged in seawater for 1 year, measuring chloride
penetration at different times (7, 28 and 119 days).
One group of specimens was cured in standard
conditions (for 7 or 28 days) before ponding in
seawater, while the second group was directly
submerged in seawater after removing from the
moulds (at 1 day). Chloride penetration depths were
528 Materials and Structures (2008) 41:527–541
Ta
ble
1D
ata
coll
ecti
on
of
cais
son
s
Wh
arf
AW
har
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Wh
arf
CW
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arf
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arf
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e(y
ears
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on
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iter
ran
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ean
Med
iter
ran
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anti
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bri
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anta
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c
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relo
cati
on
hei
gh
to
ver
low
tid
e
lev
el/t
idal
ran
ge
(m)
�0
.1/0
.8�
0.1
/0.4
+0
.5/0
.7+
2.5
/4.0
+3
.5/4
.5+
2.0
–3
.5/5
.4+
1.3
/4.5
Ex
po
sure
env
iro
nm
ent
Su
bm
erg
edS
ub
mer
ged
Tid
alzo
ne
Tid
alzo
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alzo
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ign
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ncr
ete
(N/m
m2)
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-25
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-25
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-30
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-30
–
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3)
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n(q
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(N/m
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sA
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.4B
1-2
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.8C
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.5
Materials and Structures (2008) 41:527–541 529
measured by means of splitting 5 cm thick slices from
the specimens and spraying the freshly fractured
concrete face with an AgNO3 solution at each
exposure age. Then the split surface of concrete
was waterproofed with a bituminous mixture and the
specimen returned to the seawater tank.
Results from cores and laboratory specimens were
analysed together as all of them were exposed to the
same environmental conditions and then their behav-
iour was quite similar.
2.2.2 Tidal zone concrete
The day of drilling was chosen to coincide with
minimum low tide level. Concrete cores were drilled
horizontally from the front face of the caissons.
Following this procedure, concrete cores were
extracted in five wharves (C, D, E, F and G) Several
caissons (3–5) were selected per wharf, so finally 20
cores were extracted to study concrete exposed to
tidal zone.
2.3 Selection of tests
The tests carried out to characterise physical
and mechanical properties of concrete cores have
been:
– Compressive strength (Spanish standard UNE
83.304/84, similar to European EN 12390-3).
– Ultrasonic pulse velocity (Spanish standard UNE
83-308-93, similar to European EN 12504-4).
– Water penetration under pressure depth (Spanish
standard UNE 83.309-90, similar to ISO (DIS)
7031).
– Water porosity (RILEM CPC 11.3).
– Water absorption (BS1881: Part 122).
– Capillarity (RILEM CPC 11.2).
– Oxygen permeability (CEMBUREAU method).
– Permeability coefficient was estimated by substi-
tuting the maximum water penetration depth and
concrete porosity data obtained in the equation
developed by Valenta [8]: k = Px2/2 ht, where
‘‘k’’ is the permeability coefficient, ‘‘P’’ is
porosity, ‘‘x’’ is water penetration depth, ‘‘h’’ is
hydraulic pressure and ‘‘t’’ is the time the
pressure is applied.
– Acid-soluble chloride penetration profile was
obtained through chemical analysis (as described
in standard ASTM C1152) of chloride content of
concrete samples 10 mm thick at different depths.
These tests aim to control the different chloride
transport mechanisms into concrete in marine envi-
ronment, as well as oxygen availability for corrosion
propagation: water and oxygen permeability, capil-
larity, absorption and diffusion.
2.4 Specimen distribution
Figure 1a and b shows typical specimen distribution
for wharves A and B cores (vertical borings in
submerged caissons), while Fig. 2 shows correspond-
ing distribution for wharves C, D, E, F and G cores
(horizontal drilling in tidal zone concretes).
As can be seen in Fig. 1a, a 100 mm height
specimen was cut from wharves A and B cores to
conduct the chloride tests. These specimens (Fig. 1b)
were sliced to obtain four samples 20 mm thick and
100 mm long, which were used for the chemical
analyses.
Figure 2 show typical specimen distribution for
wharves C, D, E, F and G cores. The first 95 mm of
the specimen were used to obtain the chloride
penetration profile, by means of several 10 mm thick
slices.
Table 2 Mix proportions, size and curing time of concrete specimens
Concrete 1 Concrete 2 Concrete 3 Concrete 4
Specimen size (mm) 150 · 150 · 150 150 · 150 · 300 150 · 150 · 300 150 · 150 · 300
Standard curing time (days) 7 28 28 28
Water/binder ratio 0.45 0.45 0.40 0.36
Cement content (kg/m3) 395 400 400 396
Silica fume (kg/m3) – – – 44
Type of cement CEM I 42.5N/SR CEM I 42.5R/SR CEM I 42.5R/SR CEM I 42.5R/SR
530 Materials and Structures (2008) 41:527–541
2.5 Chloride diffusion coefficient calculation
Chloride penetration rate is often described by an
error function model, which fulfils the condition of
Fick’s second law of diffusion [9]:
Cx � Cb ¼ Cs � Cbð Þ � 1� erfx
2ffiffiffiffiffiffiffiffiffiffi
D � tp
� �
;
where:
Cx = chloride content (% by concrete weight) at
depth x (cm).
Cs = chloride concentration at the concrete surface
(% by concrete weight).
Cb = initial chloride content (% by concrete
weight).
D = effective diffusion coefficient (cm2/s).
t = exposure time (seconds).
erf = error function.
Fig. 1 (a) Sketch of typical
specimen distribution for
testing. Wharves A and B.
Elevation view. (b)
Specimen for chloride
analysis. Wharves A and B.
Plan view
Fig. 2 Sketch of typical
specimen distribution for
testing. Wharves C, D, E, F
and G. Elevation view
WHARF A (4.5 years) - Submerged
y = -0.027x + 0.5315R2 = 0.9396
y = -0.0178x + 0.4064R2 = 0.9183
y = -0.0138x + 0.2666R2 = 0.9934
0.0
0.2
0.4
0.6
0.
SQ
.RO
OT
(%
CH
LO
R-
BY
CO
NC
RE
TE
WT
) 8
0 5 10 15 20 25DEPTH (cm)
Caisson A1-A2 Caisson A3-A4 Caisson A5-A6
Fig. 3 Chloride penetration profile of Wharf A cores (sample
depth versus square root of chloride concentration)
WHARF B (6.5 years) - Submerged
y = -0.0232x + 0.4796
R2 = 0.692
y = -0.0371x + 0.7591
R2 = 0.8577
y = -0.0245x + 0.5892
R2 = 0.9452
0.0
0.2
0.4
0.6
0.8
0 5 10 15 20 25DEPTH (cm)
Caisson B1-B2 Caisson B3 Caisson B4-B5
SQ
.RO
OT
(%
CH
LO
R-
BY
CO
NC
RE
TE
WT
)
Fig. 4 Chloride penetration profile of Wharf B cores (sample
depth versus square root of chloride concentration)
Materials and Structures (2008) 41:527–541 531
This formula may be simplified by using a parabola
function [10]:
Cx � Cb ¼ Cs � Cbð Þ � 1� x
2ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
3 � D � tp
� �2
The diffusion coefficient after an exposure time
‘‘t’’ has been obtained from core’s chloride penetra-
tion profiles. Experimental results are plotted in
Figs. 3–9 (expressed as square root of chloride
content). Finally, a linear regression is adjusted for all
the wharves, as can be seen in the same figures.
The chloride concentration has been corrected
subtracting the chloride content measured at the end
of the core, which corresponds to initial chloride
concentration of concrete. So the ‘‘Cx�Cb’’ values
(expressed as square root of chloride content) have
been plotted.
From the linear regressions adjusted (y = mx + b),
chloride concentration at concrete surface is obtained
from the formula b ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Cs � Cb
pand diffusion coef-
ficient D at time ‘‘t’’ (wharf age) is calculated from:
m ¼ffiffiffiffiffiffiffiffiffiffi
Cs�Cb
pffiffiffiffiffiffiffiffiffiffiffi
12�D�tp .
Also must be taken into account that chloride
diffusion coefficient changes with time, according to
[11]: D(t) = D1*t�0.5; where ‘‘D(t)’’ is the diffusion
coefficient after an exposure time ‘‘t’’ and ‘‘D1’’ is
the diffusion coefficient after 1 year, if ‘‘t’’ is in
years. D1 values have been obtained from this
formula to compare the diffusion coefficients of the
seven wharves.
WHARF G (31years) - Tidal zone
y = -0.0617x + 0.7466
R2 = 0.7633
y = -0.0999x + 0.9494
R2 = 0.9633
y = -0.0784x + 0.8935
R2 = 0.9949-0.2
0.0
0.2
0.4
0.6
0.8
1.0
0 5 10 15 20 25DEPTH (cm)
Caisson G1 Caisson G3 Caisson G4 Caisson G5
y = -0.0813x + 0.7788
R2 = 0.9999
SQ
.RO
OT
(%
CH
LO
R. B
Y
C
ON
CR
ET
E W
T)
Fig. 9 Chloride penetration profile of Wharf G cores (sample
depth versus square root of chloride concentration)
WHARF D (5 years) -Tidal zoney = -0.0224x + 0.5697
R2 = 0.9313
y = -0.0165x + 0.441
R2 = 0.7181
y = -0.0226x + 0.5894
R2 = 0.9244
0.0
0.2
0.4
0.6
0.8
1.0
0 5 10 15 20 25
DEPTH (cm)
Caisson D1 Caisson D2 Caisson D3 Caisson D4
y = -0.0225x + 0.5145
R2 = 0.9872
SQ
.RO
OT
(%
CH
LO
R-
BY
CO
NC
RE
TE
WT
)
Fig. 6 Chloride penetration profile of Wharf D cores (sample
depth versus square root of chloride concentration)
WHARF C (7.5 years) - Tidal zone
y = -0.0319x + 0.6484
R2 = 0.9428
y = -0.0613x + 0.7327
R2 = 0.999
y = -0.0288x + 0.6141
R2 = 0.80310.0
0.2
0.4
0.6
0.8
1.0
0 5 10 15 20 25
DEPTH (cm)
Caisson C1 Caisson C2 Caisson C3
SQ
.RO
OT
(%
CH
LO
R-
BY
CO
NC
RE
TE
WT
)
Fig. 5 Chloride penetration profile of Wharf C cores (sample
depth versus square root of chloride concentration)
WHARF E (2years) - Tidal zone
y = -0.0854x + 0.6817
R2 = 0.9314
y = -0.2461x + 0.9332
R2 = 0.9859
y = -0.2552x + 0.8677
R2 = 0.9978
0.0
0.2
0.4
0.6
0.8
1.0
0 5 10 15 20 25DEPTH (cm)
Caisson E1 Caisson E2 Caisson E3 Caisson E4
y = -0.1835x + 0.7295
R2 = 0.9748
SQ
.RO
OT
(%
CH
LO
R-
BY
CO
NC
RE
TE
WT
)
Fig. 7 Chloride penetration profile of Wharf E cores (sample
depth versus square root of chloride concentration)
WHARF F (2 years) -Tidalzone
y = -0.1302x + 0.8321
R2 = 0.9804
y = -0.1384x + 0.7182
R2 = 0.799
y = -0.1516x + 0.7941
R2 = 0.9907
0.00.20.40.60.81.0
0 5 10 15 20 25DEPTH (cm)
Caisson F1 Caisson F2 Caisson F3 Caisson F4
y = -0.1201x + 0.6345
R2 = 0.9838
SQ
.RO
OT
(%
CH
LO
R-
BY
CO
NC
RE
TE
WT
)
Fig. 8 Chloride penetration profile of Wharf F cores (sample
depth versus square root of chloride concentration)
532 Materials and Structures (2008) 41:527–541
3 Results
Figures 3–9 show the chloride penetration profiles
(3–5 caissons) of the seven wharves. In these figures,
square root of acid-soluble chloride content (% by
concrete weight) as a function of depth is presented
graphically, as well as the linear regressions fitted for
all the profiles.
Analysing each wharf separately, it can be seen that
all the caissons show a very similar chloride penetra-
tion profile, except for some particular cores. In these
cases, the differences may be due to a better or worse
quality concrete used in particular caissons, what is
also reflected in the other concrete properties tested.
Comparing the chloride profiles obtained in the
different wharves, it can be seen that, despite using
similar mixes (see Table 1), wharves have been built
with different durability concretes, resulting in chlo-
ride penetration profiles very different too. So, except
for Wharves E and F (exposed to seawater just for
2 years), high chloride contents at rebar level have
been measured, despite concretes had a w/c ratio of
0.5 and cement contents of 300 kg/m3. When drilling
the cores some steel rebars were cut, which some-
times showed corrosion symptoms. The corroded bars
belong to tidal zone concretes (Wharves C and G, the
first one exposed to seawater just for 5 years, see
Fig. 10), while permanently submerged concretes
showed rebars without corrosion symptoms (Wharves
A and B, see Fig. 11). These observations point out that
although standards (EHE, BS 8110) establish a chloride
threshold for corrosion of 0.4% by cement weight, this
value depends on many parameters, as type of steel, type
of cement and, overall, exposure conditions.
Table 3 shows diffusion coefficients calculated
(actual D values and those corresponding to one year
exposure D1) for all the cores analysed, obtained
from linear regressions plotted in Figs. 3–9, as
explained in Sect. 2.5.
On the other hand, experimental results of com-
pressive strength, water penetration, porosity, water
permeability (estimated according to Valenta method
[8]), absorption, capillarity and oxygen permeability
tests are shown in Figs. 12–19, and will be discussed
in next section.
4 Discussion
Chloride diffusion coefficient has been taken as
reference parameter because it is representative of
‘‘global’’ penetration rate in marine environment as it
was explained in Sect. 1. Introduction. This param-
eter has been compared with the different durability
tests results, to evaluate their effectiveness.
Figures 12–19 show correlations between chloride
diffusion coefficient (1 year exposure value, mea-
sured in m2/s · 10�12) and all the tests results
measured in concrete cores of the seven wharves and
in laboratory specimens submerged in seawater.
Correlation coefficients obtained are considered good
enough in most cases, taking into account that they
come from the analysis of real structures built with
cast in place concretes, so chloride penetration rates
are representative of natural exposure conditions along
service life. Linear regressions were fitted as they
showed the highest correlation coefficient values.
Themainparametersaffectingconcretebehaviourare
the exposure conditions and the use of mineral admix-
tures (blended cements), as it is described as follows.
Fig. 10 Corroded bar, tidal zone concrete exposed for 5 years.
Chloride concentration at rebar level: 1.43% of cement weight.
Wharf C
Fig. 11 Not corroded bar, submerged concrete exposed for
4.5 years. Chloride concentration at rebar level: 1.49% of
cement weight. Wharf A
Materials and Structures (2008) 41:527–541 533
Table 3 Diffusion
coefficients calculated for all
the cores of the seven
wharves
Wharf Core Time (years) Diffusion D (*10�8 cm2/s) Diffusion D1 (*10�8 cm2/s)
A A1–A2 4.5 22.8 48.4
A3–A4 4.5 30.6 64.9
A5–A6 4.5 21.9 45.8
B B1–B2 6.5 17.4 44.4
B3 6.5 17.0 43.3
B4–B5 6.5 23.5 59.9
C C1 7.5 14.0 38.3
C2 7.5 6.7 18.4
C3 7.5 14.4 39.4
D D1 5 34.2 76.5
D2 5 37.8 84.5
D3 5 35.9 80.3
D4 5 27.6 61.7
E E1 2 8.4 11.9
E2 2 1.9 2.7
E3 2 1.5 2.2
E4 2 2.1 3.0
F F1 2 5.4 7.6
F2 2 3.6 5.0
F3 2 3.6 5.1
F4 2 3.7 5.2
G G1 31 1.3 7.0
G3 31 0.9 5.2
G4 31 1.1 6.1
G5 31 1.1 6.2
STRENGTH-DIFFUSION
y = -0,4421x + 69,021
R2 = 0,5006
y = -0,1045x + 40,221
R2 = 0,1206
0
20
40
60
80
100
C-S
TR
EN
GT
H (
N/m
m2 )
0 50
DIFFUSION COEF.(x10-12 m2/s)
100
opc-submerged admixt.-submerged
opc-tidal zone admixt.-tidal zone
Fig. 12 Chloride diffusion coefficient versus compressive
strength
POROSITY-DIFFUSION
PO
RO
SIT
Y (
%)
y = 0,1108x + 11,005
R2 = 0,6747
y = -0,007x + 17,052
R2 = 0,011
0
4
8
12
16
20
24
0 50DIFFUSION COEF. (x10-12m2/s)
100
opc-submerged admixt.-submerged
opc-tidal zone admixt.-tidal zone
Fig. 13 Chloride diffusion coefficient versus porosity
534 Materials and Structures (2008) 41:527–541
4.1 Influence of marine exposure conditions
Data have been separated in two different regres-
sions, depending on concrete location: submerged or
tidal zone (Figs. 12–18): chloride penetration rate for
similar quality concretes must be different in both
environments as the transport mechanisms are dif-
ferent too (see Sect. 1. Introduction). Besides, it has
been plotted separately data from ordinary portland
cement concretes (full shapes) and from blended
cement mixes (empty shapes).
Chloride penetration rate is faster in submerged
concretes than in tidal zone concretes, which is
clearly pointed out on figures with good correlation
coefficients (Figs. 12, 15–18). This behaviour has
also been confirmed by other marine structures data
collected from bibliography and can be explained
because chloride penetration rate in submerged
environments is mainly controlled by a very slow
but permanent pure diffusion transport mechanism
due to total water saturation of concrete. On the
other hand, capillarity is the main transport
W. PERMEABILITY-DIFFUSIONW
. PE
RM
. (×1
0-12
m/s
)
y = 0,2988x + 1,4138
R2 = 0,7438
y = 0,0956x- 0,156
R2 = 0,5747
0
10
20
30
40
0 50DIFFUSION COEF. (x10-12m2/s)
100
opc-submerged admixt.-submerged
opc-tidal zone admixt.-tidal zone
Fig. 17 Chloride diffusion coefficient versus water perme-
ability
ABSORPTION-DIFFUSIONA
BS
OR
PT
ION
(%
)
y = 0,0318x + 1,9147
R2 = 0,7925
y = -0,0022x + 3,5246
R2 = 0,0284
0
1
2
3
4
5
0 50DIFFUSION COEF. (x10-12 m2/s)
100
opc-ssubmerged admixt.-submerged
opc-tidal zone admixt.-tidal zone
Fig. 14 Chloride diffusion coefficient versus water absorption
MAX. DEPTH-DIFFUSION
MA
XIM
UM
DE
PT
H (
mm
)
y = 0,4111x + 16,521
R2 = 0,4861
y = 0,873x + 22,39
R2 = 0,7349
0
20
40
60
80
100
120
0 50DIFFUSION COEF. (x10-12 m2/s)
100
opc-submerged admixt.-submerged
opc-tidal zone admixt.-tidal zone
Fig. 15 Chloride diffusion coefficient versus maximum
penetration depth
AVER. DEPTH-DIFFUSION
AV
ER
AG
E D
EP
TH
(m
m)
y = 0, 346x + 5 , 8446
R 2 = 0 , 53 77
y = 0 , 9826x + 1 0 , 898
R 2 = 0, 8392
0
20
40
60
80
100
120
0 5 0 DIFFUSION COEF. (x10-12 m2/s)
100
opc-submerged admixt.-submerged
opc-tidal zone admixt.-tidal zone
Fig. 16 Chloride diffusion coefficient versus average penetra-
tion depth
Materials and Structures (2008) 41:527–541 535
mechanism in tidal zone (a very fast mechanism, but
interrupted by wetting-drying cycles), overlapped
with a pure diffusion much slower than in submerged
zone. Additionally, in tidal zone chloride ions
may also diffuse outward to the concrete surface,
due to the external washing out of chlorides in
concrete subjected to cyclic wetting and drying. Final
balance of these complex mechanisms shows
an apparent diffusion rate in tidal zone slower than
in submerged zone.
Another interesting point is that apparent diffusion
rates are as much different in both environments as
poorer is concrete quality. Chloride diffusion rate for
submerged concretes of high permeability is extre-
mely high (Fig. 17). However, apparent diffusion rate
for good quality concretes come closer for both
exposure conditions.
4.2 Influence of cement type
Related to the effect of using mineral admixtures, it is
very important on concrete behaviour, changing its
micro-structure with different results on concrete
properties. To analyse this effect, it must be consid-
ered that mineral admixtures (GGBS, fly ashes and
silica fume) cause concrete pore refinement, reducing
small size pores volume [12]. This effect may not
have an important influence on total porosity (and
consequently on absorption and compressive
strength, see Figs. 12–14), but drastically decrease
permeation rate into concrete: capillarity, permeabil-
ity and water penetration are reduced due to pore size
refinement (see Figs. 15–18). Moreover, as can be
seen in all the figures (12–18), blended cement
concretes results (hollow symbols) are grouped in the
low diffusion coefficients area, highlighting this
effect.
Now results obtained on different concrete prop-
erties tests are going to be analysed separately.
4.3 Diffusion coefficient—compressive strength
Figure 12 shows correlations between chloride diffu-
sion coefficient and compressive strengths (in N/
mm2).
Tendencies obtained in linear regressions are as
expected: higher strength concretes show lower
diffusion coefficients. Related to the effect of mineral
admixtures on both properties, it can be seen that it
almost doesn’t affect the concrete strength but it
really does on chloride penetration rate. In submerged
environment, diffusion rate is faster, and increasing
as the concrete strength decreases.
However, concrete strength is not suitable to
control durability, as the graph shows similar strength
concretes with very different diffusion coefficients, in
the same exposure conditions. Furthermore, the effect
of adding mineral admixtures on concrete strength is
much smaller than on chloride penetration rate, so
strength test does not control properly their beneficial
effect on concrete durability.
OXYGEN PERM.-DIFFUSION
OX
YG
EN
PE
RM
. (x1
0-16
m2 ) y = -0,0348x + 4,6754
R2 = 0,0543
0
4
8
12
16
20
0 20 40 60 80 100
DIFFUSION COEF. (x10-12 m2/s)
opc-tidal zone admixt.-tidal zone
Fig. 19 Chloride diffusion coefficient versus oxygen perme-
ability
CAPILLARITY-DIFFUSIONC
AP
ILL
AR
ITY
(m
m/m
in0.
5 )
y = 0,0002x + 0,1525
R2 = 0,0205
y = 0,0019x + 0,1287
R2 = 0,7189
0,00
0,05
0,10
0,15
0,20
0,25
0,30
0,35
0 20 40 60 80 100
DIFFUSION COEF. (x10-12 m2/s)
opc-submerged opc-tidal zone admixt.-tidal zone
Fig. 18 Chloride diffusion coefficient versus water capillarity
536 Materials and Structures (2008) 41:527–541
4.4 Diffusion coefficient—porosity
Figure 13 shows correlations between chloride diffu-
sion coefficient and porosity (in %).
Linear regressions adjusted show a very poor
correlation coefficient for tidal zone concretes, while
quite a high one for submerged concretes. The
beneficial effect of fly ashes and GGBS on the
reduction of chloride penetration rate is not followed
by porosity test results. So, it can be seen that blended
cements results (hollow symbols) distort the regres-
sion adjusted for tidal zone concretes. Nevertheless,
these high porosity concretes have very low diffusion
coefficients, due to the typical pore distribution of
blended cement concretes, as explained: although the
effect of mineral admixtures on concrete total poros-
ity is not remarkable, they originate a pore size
refinement, reducing the chloride penetration rate. In
submerged silica fume concretes, initial porosity was
really low (w/c = 0.36), so pore size refinement was
smaller and linear regression fitted show high corre-
lation coefficient (triangular symbols).
Finally, analysing only full shaped data (OPC
concretes), no clear distinction between both different
environments results appears, as total porosity test
gives partial information about concrete durability,
because it doesn’t assess pore distribution.
In terms of durability control test, due to these
disagreements (not properly taking into account
mineral admixtures effect and no distinction of
different exposure conditions), total porosity is not
considered an appropriate concrete property to con-
trol the chloride permeation resistance.
4.5 Diffusion coefficient—absorption
Figure 14 shows correlations between chloride diffu-
sion coefficient and absorption (in %).
Absorption results are influenced by total pore
volume, so it is the same case as explained for
porosity test, where blended cement (fly ashes and
GGBS) concretes results distorted the linear regres-
sion fitted for tidal zone concretes. So, it can be seen
in Fig. 14 that both parameters correlate bad for tidal
zone concretes due to the beneficial effect of mineral
admixtures on concrete porosity, not reflected by
absorption test. In submerged concretes, linear
regression fitted well because blended cement con-
cretes correspond with very low w/c ratio mixes.
Similarly, considering only data from OPC concretes
(full symbols) submerged or tidal zone exposure
cannot be distinguished.
For these reasons, water absorption is not consid-
ered an appropriate test to control the chloride
permeation resistance of concrete in marine environ-
ment (tidal and submerged zones). Nevertheless, in
submerged zone absorption test results show the best
correlation coefficient, meaning that this transport
mechanism is significant in this exposure conditions.
4.6 Diffusion coefficient—water penetration
depth
Figures 15 and 16 show correlations between chloride
diffusion coefficient and water penetration depth
under pressure (maximum and average depths, in
mm).
Related to global results analysis, tendency
obtained is as expected: lower water penetration
depth concretes have lower diffusion coefficients too,
and submerged concretes show higher chloride
penetration rates. Also, in both exposure conditions
good correlation are obtained for both maximum and
average penetration depths.
In this case, it is clearly shown the extremely
beneficial effect of adding mineral admixtures on
reducing different transport mechanisms rate into
concrete: both chloride diffusion and water penetra-
tion are reduced; moreover, this test distinguish
between diffusion rates corresponding to different
exposure conditions, so water penetration depth
under pressure is considered an appropriate concrete
test to control the chloride permeation resistance, and
so on the durability of reinforced concrete in marine
environment.
4.7 Diffusion coefficient—water permeability
Figure 17 shows correlations between chloride diffu-
sion coefficient and water permeability (estimated
from water penetration depth and porosity test results,
in m/s · 10�12).
Water penetration depth test results are even
slightly improved by water permeability results:
higher correlation coefficients are achieved, showing
a good sensitivity to control the chloride diffusion.
Besides, it takes into account properly the beneficial
effect of adding mineral admixtures (results are
Materials and Structures (2008) 41:527–541 537
grouped in the area next to zero point) and distin-
guishes between different exposure conditions (both
linear regressions are clearly different). Tendency
obtained is as expected too: higher water permeabil-
ity concretes have higher diffusion coefficients, and
submerged concretes show higher chloride penetra-
tion rates. Similarly, when adding mineral admixtures
to cement, both transport mechanisms (water perme-
ability and chloride diffusion) are reduced.
Main disadvantage is due to the fact that water
permeability results are estimated from two tests
(water penetration depth and porosity), and it
improves just slightly the linear regressions obtained
with water penetration depth test. On the other hand,
the possibility of carrying out a water permeability
test instead of its calculation is not considered good,
as high quality concretes are studied, where it is very
difficult to carry out this test.
4.8 Diffusion coefficient—capillarity
Figure 18 shows correlations between chloride diffu-
sion coefficient and water capillarity (in mm/min0.5)
measured in concrete cores of the seven wharves and
in some laboratory specimens submerged in seawater.
In tidal zone concretes, tendency obtained in linear
regression is as expected (the higher the capillarity,
the higher the diffusion coefficient, showing high
correlation coefficient) and takes into account prop-
erly the effect of adding mineral admixtures. As
capillarity is the dominant transport mechanism in
this type of exposure conditions, the linear regression
shows a high correlation coefficient, so capillarity
reflects well the changes in chloride penetration rate.
However, in permanently submerged concretes the
dominant transport mechanism is diffusion and the
influence of other mechanism as capillarity is small
on apparent diffusion, so the linear regression
obtained shows worse correlation coefficient; the
effect of high initial permeation by capillarity seems
to vanish at later ages because of diffusion.
Due to its poor sensitivity in permanently sub-
merged environment, water capillarity is not consid-
ered an appropriate concrete property to control the
chloride permeation resistance in marine environment
(tidal and submerged zones). Nevertheless, in tidal
zone capillarity test results show almost the best
correlation coefficient, meaning that this transport
mechanism is significant in this exposure conditions.
4.9 Diffusion coefficient—oxygen permeability
Figure 19 shows the correlation between chloride
diffusion coefficient and oxygen permeability (in
m2 · 10�16) measured in concrete cores of five
wharves. There are not results corresponding to
submerged concretes because the cores were obtained
by drilling vertically the concrete caisson and using
this procedure the diameter of the cores were so small
to carry out the oxygen permeability test.
Linear regression fitted shows a very poor corre-
lation coefficient and oxygen permeability test results
don’t take into account properly the effect of adding
mineral admixtures, so this test is not considered an
appropriate concrete property to control the chloride
permeation resistance, during the corrosion initiation
period.
However, from a theoretical point of view, this test
could be useful to assess the corrosion propagation
period, which starts once the rebars are depassivated
due to chloride penetration, and depends only on the
presence of water and oxygen around the rebar.
Therefore, in permanently submerged and tidal zone
environments, where relative humidity is high, rebar
corrosion rate will depend mainly on concrete oxygen
permeability.
Figure 20 shows concrete oxygen permeability test
results versus chloride concentration (in % of cement
weight) at rebar level. Corroded and not corroded
bars results are plotted in different shapes. As can be
seen, low values of oxygen permeability (below
4 · 10�16 m2) reduce the risk of corrosion, at least till
CHLORIDES-OXYGEN PERMEABILITY
0
4
8
12
16
20
0 1 2 3 4 5CHLORIDES AT REBAR LEVEL
(% cement weigth)
YXO
P NEG
.MRE
01x(
1-
6m
2)
Corroded bars Not corroded bars
Fig. 20 Risk of corrosion depending on concrete oxygen
permeability
538 Materials and Structures (2008) 41:527–541
chloride concentration at rebar level is very high
(more than 2% by cement weight, approximately).
From a conservative point of view, the couple of
values oxygen permeability-chloride concentration
that can origin a significant corrosion rate (line
plotted in Fig. 20) can be estimated.
4.10 Overall analysis of results
Correlation coefficients obtained can be classified
into two groups:
• R-squared values lower than 0.20: very poor
coefficients, meaning that they are not-significant
values (porosity and absorption in tidal zone;
capillarity in submerged zone).
• Rest of correlation coefficients. These coefficients
may not be considered so poor (R2 over 0.50),
taking into account that they are not laboratory
concretes but they come from the analysis of real
structures made of cast in place concretes (in situ
curing and consolidation, etc), built in different
areas, with different materials and separately in
time (concrete technology has changed so much);
so they may be considered significant values.
These significant correlation coefficients can be
analysed in terms of ‘‘relevance’’ of results: in tidal
zone, capillarity is the main transport mechanism [4]
(and consequently shows a high correlation coeffi-
cient: R2 = 0.72), while water penetration under
pressure and water permeability are not the main
transport mechanisms, but show high correlation
coefficients (R2 > 0.70). Compressive strength,
porosity and absorption are not significant
(R2 < 0.2). Capillarity should be the selected dura-
bility test in tidal zone.
In submerged zone, absorption is the main trans-
port mechanism (R2 = 0.79), while compressive
strength, porosity, water penetration under pressure
and water permeability are not the main transport
mechanisms, but show high correlation coefficients
(R2 > 0.50). Capillarity is not significant (R2 < 0.2).
Absorption should be the selected durability test in
submerged zone.
Water penetration under pressure is not the main
transport mechanism in any of both marine zones, but
correlation coefficients obtained are good enough in
both exposure conditions (R2 = 0.84 and 0.54,
respectively). So, from a practical point of view, it
may be selected as the only durability test to control
concrete durability in marine environment.
5 Conclusions
Based on the result obtained from this study, the
following conclusions may be drawn:
(1) In marine environment, reinforced concrete
durability depends mainly on the risk of rebar
corrosion due to chloride penetration.
(2) The experimental study carried out has com-
pared the sensitivity of different durability test
methods to predict chloride penetration into
concrete, using chloride diffusion rates ob-
tained from seven concrete structures. To
evaluate these test methods, it has been taken
into account if they properly reflect the effect
of adding mineral admixtures (and its effect on
pore size distribution) and if they distinguish
between permanently submerged and tidal
zone exposure results.
(3) Chloride penetration rate is higher in perma-
nently submerged concretes than in tidal zone
concretes, considering similar quality con-
cretes. Moreover, apparent diffusion rates are
as much different in both environments as
poorer is concrete quality.
(4) Adding mineral admixtures has a beneficial
effect on concrete quality, as they decrease
permeation rate: capillarity, diffusion, perme-
ability and water penetration are reduced due
to pore size refinement.
(5) Concrete durability control must be carried out
by means of specific tests, and compressive
strength test results must be considered just as
indicative values, as this test doesn’t reflect
properly the beneficial effect of adding min-
eral admixtures on concrete durability.
(6) Porosity and absorption test are not considered
appropriate to assess chloride permeation
resistance of concrete, as they don’t show
properly the effect of adding mineral admix-
tures and neither distinguish properly chloride
permeation rates in concretes exposed to
different marine environments.
(7) Capillarity test can distinguish between differ-
ent marine environments permeation rates
Materials and Structures (2008) 41:527–541 539
(permanently submerged and tidal zone), as well
as properly assess the effect of adding mineral
admixtures. However, it shows a very poor
sensitivity in permanently submerged concretes,
as in this environment capillarity is much less
important than diffusion and then it can’t eval-
uate properly global chloride penetration rate.
(8) Oxygen permeability test is not appropriate to
assess corrosion initiation period as it doesn’t
show properly chloride penetration rate, nei-
ther the effect of adding mineral admixtures,
but it is valid to evaluate corrosion propaga-
tion period, especially in permanently sub-
merged and tidal zone environments, where
relative humidity is high and corrosion rate is
controlled by oxygen availability.
(9) Water penetration depth and water permeabil-
ity tests are considered to assess properly
chloride permeation resistance of concrete, as
they show high correlation coefficients, which
proves their sensitivity to assess apparent
diffusion rates in tidal zone and permanently
submerged concretes. Moreover, these tests
take into account properly the effect of adding
mineral admixtures and distinguish between
chloride penetration rates in concretes exposed
to different marine environments. Water per-
meability coefficient is harder to obtain, as it
requires carrying out two tests: water penetra-
tion depth and porosity, so water penetration
depth test is considered the most suitable test.
(10) Finally, results show that it is advisable to
control concrete water tightness through
water penetration under pressure test, in
compliance with UNE 83.309-90 standard
(similar to ISO (DIS) 7031). Additionally, in
order to make sure an slow corrosion rate, it
should be advisable to control oxygen per-
meability in tidal zone concretes, by means
of Cembureau method [13], consisting of
measuring oxygen flux through a 5 cm thick
concrete disk, preconditioned at 20 ± 28C and
65 ± 5% RH for 28 days.
6 Future research
This article shows results obtained in the study of
concrete behaviour in marine environment (perma-
nently submerged and tidal zones). However, this
investigation is continuing with the following
objectives:
– Calculation of mineral admixtures efficiency
coefficient, in terms of chloride penetration
permeability.
– Modelling chloride diffusion for concretes (made
of OPC or blended cements) located in perma-
nently submerged or tidal zones, from chloride
profiles measures in full-scale structures.
– Assessing the influence of curing concrete with
seawater on its properties, especially on chloride
penetration rate.
Acknowledgements The authors wish to thank the financial
support given by Ports of Spain. Thanks to General Directionsof CEDEX for initiatives to promote postgraduate training and
development of doctoral thesis. Thanks to College of CivilEngineer for all the support at all stages during the preparation
of this experimental study.
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