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Chloride penetration into concrete – Comparison of results from field exposure tests and laboratory tests

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Abstract and Figures

Femern A/S, the Owner of the coming Fehmarnbelt Fixed Link, has built a marine field exposure site in the harbour of Roedbyhavn as a part of the preparations for the coming 17.6 km long immersed tunnel between Denmark and Germany, which will be the longest combined rail and road tunnel to date. A total of 15 large concrete blocks (2 x 1 x 0.2 m) with different concrete mix designs and 15 small concrete blocks (1 x 1 x 0.2 m) with concrete mix designs matching the large blocks were produced in 2010 by the Danish Technological Institute (DTI is external concrete laboratory for Femern A/S). The large blocks were placed partly submerged in seawater in Roedbyhavn field exposure site and the small blocks were placed outside the laboratory. The 15 mix designs include concrete with three different cement types (two Portland cements and one blast furnace cement) and three different pozzolans (silica fume, fly ash and blast furnace slag). The field exposed concrete blocks will be monitored at least until the end of the construction period (2021). Chloride penetration profiles have already been measured after ½ years and 2 years field exposure in immersed zone and in splash zone. The results are presented and compared to results from accelerated laboratory testing of samples from the small blocks by the chloride migration test according to NT BUILD 492 at the maturity age of 1 month and 6 months.
Content may be subject to copyright.
CHLORIDE PENETRATION INTO CONCRETE COMPARISON OF
RESULTS FROM FIELD EXPOSURE TESTS AND LABORATORY TESTS
Henrik Erndahl SØRENSEN Ulf JÖNSSON Christian MUNCH-PETERSEN
Danish Technological Institute Femern A/S Emcon A/S
Taastrup, Denmark Copenhagen, Denmark Charlottenlund, Denmark
hks@dti.dk ujo@femern.dk cmp@emcon.dk
ABSTRACT
Femern A/S, the Owner of the coming Fehmarnbelt Fixed Link, has built a marine field exposure site in
the harbour of Roedbyhavn as a part of the preparations for the coming 17.6 km long immersed tunnel
between Denmark and Germany, which will be the longest combined rail and road tunnel to date.
A total of 15 large concrete blocks (2 x 1 x 0.2 m) with different concrete mix designs and 15 small
concrete blocks (1 x 1 x 0.2 m) with concrete mix designs matching the large blocks were produced in
2010 by the Danish Technological Institute (DTI is external concrete laboratory for Femern A/S). The
large blocks were placed partly submerged in seawater in Roedbyhavn field exposure site and the small
blocks were placed outside the laboratory. The 15 mix designs include concrete with three different
cement types (two Portland cements and one blast furnace cement) and three different pozzolans (silica
fume, fly ash and blast furnace slag).
The field exposed concrete blocks will be monitored at least until the end of the construction period
(2021). Chloride penetration profiles have already been measured after ½ years and 2 years field
exposure in immersed zone and in splash zone. The results are presented and compared to results from
accelerated laboratory testing of samples from the small blocks by the chloride migration test according
to NT BUILD 492 at the maturity age of 1 month and 6 months.
Key-words: Concrete, Chloride penetration, Durability, Field exposure, Laboratory tests.
INTRODUCTION
Since the 1980-ies it has been common to specify an extended required service life for new large
concrete infrastructures compared to the 50 years which is incorporated in the general standards for
concrete construction. In Denmark, such requirements have been applied in several major bridges and
tunnels, e.g. the Great Belt Link, the Öresund Link, and the Copenhagen Metro. The required service
life for the coming Fehmarnbelt Fixed Link is specified to be minimum 120 years.
The decisive parameter regarding service life for concrete infrastructures is typically chloride
penetration when the structures are built in marine environment or inland environment with cold
winters. Therefore, the service life models used for these structures are based on the prediction of
chloride penetration into concrete. It is common that these models operate with input parameters
obtained from observations on field exposed concrete. However, observations from accelerated testing
are often used as input parameters to the service life models due to lack of data from long-term exposure
of relevant concrete types, e.g. in fib Model Code 2010 [1] where the chloride migration coefficient
Dnssm from accelerated testing acc. to NT BUILD 492 [6] is used when no relevant observations from
field exposed concrete are available.
The ongoing field exposure in Roedbyhavn of 15 large concrete blocks with different concrete mix
designs will produce high quality chloride penetration data for future service life modelling. New
measurements will be performed after 5 and 10 years exposure in 2015 and 2020, respectively. If
relevant, parallel testing is possible on 15 small concrete blocks exposed outside the laboratory.
DESIGN AND PRODUCTION OF CONCRETE BLOCKS
Based on experience from former field exposure tests in Sweden [2] and Denmark [3] it was decided
that all the large concrete blocks should be produced with dimensions of 2 x 1 x 0.2 m (H x W x D).
This size should allow long-term exposure in a marine environment without any interaction between the
chloride penetration from the two opposite exposed faces. Furthermore, the large exposed area allows
many samples to be taken from a concrete specimen with an operational size and weight. Each large
concrete block has a ring reinforcement of stainless steel, which also forms two eyebolts on top of the
block. The stainless steel ring reinforcement used in all large blocks is made from Ø10 mm ribbed rebar
grade 1.4362 (duplex). The small concrete blocks of dimensions of 1 x 1 x 0.2 m (H x W x D) have no
reinforcement. Detailed information regarding mix design and production is given in the following
subsections.
Concrete mix designs
A total of 15 different concrete mix designs were composed by combinations of three different cements
and three different mineral additives (pozzolans). The cements are a) Low alkali sulphate resistant
Portland cement CEM I 42.5 N - SR5 EA, b) Rapid hardening ordinary Portland cement CEM I 52.5 N,
and c) Blast furnace cement CEM III/B 42.5 N (slag cement). The mineral additives are d) Fly ash, e)
Silica fume slurry (micro silica), and f) Ground granulated blast furnace slag. The chemical composition
of the cements and mineral additives are shown in Table 1. The binder composition and identification of
the 15 different mix designs are shown in table 2.
The nominal compositions of constituent materials in the 15 concrete mix designs are shown in table 3.
The concrete types A-G and J-O all had a nominal eqv. w/c ratio of 0.400, whereas concrete type H had
an eqv. w/c-ratio of 0.450 and concrete type I had an eqv. w/c ratio of 0.350. The nominal target air
content was 4.5 % for air entrained concrete and 2.0 % for non air entrained concrete. The target
consistency was 160 mm for slump concrete types and 580 mm slump flow for the SCC types.
Table 1 - Chemical composition of cements and mineral additives.
*)Bogue composition is calculated on the clinker part of CEM III/B.
Category
CEM I
42.5 N
CEM I
52.5 N
CEM
III/B
SF
FA
Slag
SiO2 (%)
24.8
20.0
95,4
60,3
34.87
Al2O3 (%)
2.9
5.34
-
20,5
12.95
Fe2O3 (%)
2.3
3.78
-
7,4
0.40
CaO (%)
65,6
63.40
0,3
1,6
40.09
MgO (%)
0,8
0.86
-
-
8.09
SO3 (%)
2,2
3.29
0,2
0,5
2.72
TiO2 (%)
0,1
0.31
-
-
-
P2O5 (%)
0,2
0.29
-
-
-
CO2 (%)
0,2
1.30
-
-
0.52
Loss on ignition (%)
0,7
2.24
1,3
3,2
0.27
Eq. Na2O (%)
0,7
0.61
0,7
2,8
0.78
Blaine (m2/kg)
366
452
-
-
-
C3S (Bogue)
49,0
55.37
-
-
-
C2S (Bogue)
34,4
15.65
-
-
-
C3A (Bogue)
3,8
7.77
-
-
-
C4AF (Bogue)
6,8
11.49
-
-
-
28 days strength
(MPa)
55,2
66.4
-
-
-
Table 2 Identification and binder composition of the 15 different mix designs.
The activity factors used to calculate the equivalent w/c-ratio are 2.0 for silica fume and 0.5 for fly ash.
ID
Powder/variant
Cement description
A
100SRPC
Portland low alkali cement (CEM I 42.5 N - SR5 EA). Equivalent w/c=0.40
B
85SRPC + 15FA
As A with 15 % fly ash (Emineral). Equivalent w/c=0.40
C
75SRPC + 25FA
As A with 25 % fly ash (Emineral). Equivalent w/c=0.40
D
75SRPC + 25FA SCC
As C but as SCC. Equivalent w/c=0.40
E
96SRPC + 4SF
As A with 4 % micro silica (Elkem). Equivalent w/c=0.40
F
84SRPC + 4SF +12FA
As A with 12 % fly ash and 4% micro silica. Equivalent w/c=0.40
G
84SRPC + 4SF +12FA / no air
As F but without air entrainment. Equivalent w/c=0.40
H
84SRPC + 4SF +12FA / 0.45w/c
As F but with Equivalent w/c=0.45
I
84SRPC + 4SF +12FA / 0.35w/c
As F but with Equivalent w/c=0.35
J
84SRPC + 4SF +12FA / SCC
As F but as SCC. Equivalent w/c=0.40
K
100SLAGPC
Traditional blast furnace cement (CEM III/B). Equivalent w/c=0.40
L
100SLAGPC / no air
As K but without air entrainment. Equivalent w/c=0.40
M
100SLAGPC / SCC
As K but as SCC. Equivalent w/c=0.40.
N
30OPC + 70GGBFS
70 % slag mixed with 30 % Portland cement (CEM I 52.5 N). Eq. w/c=0.40
O
96SRPC + 4SF / SAP
As E with superabsorbing polymers. Equivalent w/c=0.40
Table 3a - Mix designs for concrete blocks.
The activity factors used to calculate the equivalent w/c-ratio are 2.0 for silica fume and 0.5 for fly ash.
Concrete ID:
A
B
C
D
E
F
G
H
Powder
composition %-
wt
Low alkali SR cement
CEM I 42.5 N
100
85
75
75
96
84
84
84
Rapid hardening cement
CEM I 52.5 N
Blast furnace cement
CEM III/B 42.5 N
Fly ash
EN 450-1 N
15
25
25
12
12
12
Silica fume
50 %-wt slurry
4
4
4
4
GG blast furnace slag
EN 15167-1
Concrete composition
Cement
kg/m3
365
322
300
336
340
300
310
276
Fly ash
kg/m3
57
100
112
43
44
39
Silica fume, solid matter
kg/m3
14
14
15
13
GGBFS
kg/m3
Water content
l/m3
146
140
140
157
147
140
145
145
Aggregate 0/2
kg/m3
695
671
642
678
695
677
731
700
Aggregate 4/8
kg/m3
377
374
367
349
377
377
386
380
Aggregate 8/16
kg/m3
266
270
271
704
266
272
266
268
Aggregate 16/22
kg/m3
529
538
541
529
543
530
534
Air entraining agent
kg/m3
1.7
1.7
2.3
4.0
0.7
1.6
0.0
1.5
Superplasticizer 1
kg/m3
3.8
Superplasticizer 2
kg/m3
2.3
2.2
Superplasticizer 3
kg/m3
2.8
2.9
2.7
2.9
2.6
Table 3b - Mix designs for concrete blocks.
The activity factors used to calculate the equivalent w/c-ratio are 2.0 for silica fume and 0.5 for fly ash.
Concrete ID:
I
J
K
L
M
N
O
Powder
composition %-
wt
Low alkali SR cement
CEM I 42.5 N
84
84
96
Rapid hardening cement
CEM 1 52.5 N
30
Slag cement
CEM III/B 42.5 N
100
100
100
Fly ash
EN 450-1 N
12
12
Silica fume
50 %-wt slurry
4
4
4
GG blast furnace slag
EN 15167-1
70
Concrete composition
Cement
kg/m3
330
350
360
375
410
108
340
Fly ash
kg/m3
47
50
Silica fume, solid matter
kg/m3
16
17
14
GGBFS
kg/m3
252
Water content
l/m3
135
163
144
150
164
144
147
Aggregate 0/2
kg/m3
671
687
689
702
686
689
695
Aggregate 4/8
kg/m3
374
354
373
381
353
374
377
Aggregate 8/16
kg/m3
270
713
263
269
712
263
266
Aggregate 16/22
kg/m3
538
525
535
525
529
Air entraining agent
kg/m3
2.3
2.2
0.8
0.0
1-6
1.0
0.0
Superplasticizer 1
kg/m3
Superplasticizer 2
kg/m3
Superplasticizer 3
kg/m3
3.6
3.4
2.3
2.6
2.9
2.9
3.7
Mixing and casting
The concrete was produced using the concrete mixing station at the DTI laboratories. The main
challenge of the concrete production was to comply with the predefined requirement of less than 1%
batching deviation on the individual constituent. In particular the water content was a challenge and a
special procedure for controlling aggregate moisture content was established. In connection with the
production of each batch of concrete the moisture content in the individual aggregate fraction was
determined by micro wave drying on three samples of approximate 1 kg each taken directly from the
material actually batched, i.e. from the material on the conveyor belt. The adopted procedure also
allowed to batch exactly the nominal amount of aggregate as material could be added or removed from
the conveyor belt to equal precisely the desired amount. The total time required to obtain the moisture
content of four aggregate fractions was approximately 25 minutes. During this time the aggregate was
resting in the closed confines of the mixer, i.e. no moisture loss took place. From the measured moisture
contents the exact amount of water needed to obtain the w/c ratio was calculated and subsequently
batched. All materials were batched based on weight.
The applied mixing sequence was:
The aggregate was mixed for 30 seconds
Powder was added from the powder pre-silo and mixing continued to a total of 60 seconds
Water and silica fume slurry was added over a period of 30 seconds while mixing
Air entraining agent was added and with a 30 second delay the superplasticizer was added
Mixing was continued for 120 seconds after addition of superplasticizer to a total of 240 seconds.
The fresh concrete properties were then tested and if in accordance with target ranges the concrete was
discharged to a 500 liter crane bucket, and used to cast test cylinders and cubes or one small concrete
block of 1 x 1 x 0.2 m. For the production of one large concrete block of 1 x 2 x 0.2 m two batches of
concrete were required. For SCC both batches had to meet fresh concrete requirements, while for slump
concrete the two batches had to be homogenized and the combined batch had to meet the fresh concrete
requirements. Homogenization was performed in a 500 liter pan mixer discharging the concrete back
into the crane bucket.
Casting of slump concrete was performed in layers of 30 - 40 cm. Each layer was poker vibrated
according to the Danish HETEK guideline [4]. SCC was cast at a target rate of 20 m/hr corresponding
to a casting time of 6 minutes pr. element.
The formwork was made from plywood. All blocks were cast in an upright position, i.e. a height of 1 or
2 meters for small and large concrete blocks, respectively.
CURING
The concrete blocks were cured using the following procedure:
The concrete blocks were demoulded at an age corresponding to minimum 24 maturity hours.
Immediately after demoulding the blocks was wrapped in plastic, i.e. a thick large PE plastic bag
was pulled down over the concrete block and another bag was pulled up over the concrete block.
The plastic bags were secured tightly around the concrete with tape. The plastic remained on the
blocks until they were placed at the exposure site in Roedbyhavn harbour (large blocks) or to core
drilling for testing at approx. 1 months maturity (small blocks).
Each concrete block remained indoors until the block had reached minimum 14 maturity days.
Hereafter the blocks could be moved outside if required to control maturity gain.
The exact maturity of the concrete blocks was monitored closely using temperature sensors cast
into the concrete.
EXPOSURE
The small concrete blocks were plastic sealed and stored in temperature controlled laboratory conditions
until the first core drilling at a maturity of 30-34 days. Then they were stored uncovered outside the DTI
laboratory until the second core drilling at a maturity of 176-186 days. The large concrete blocks were
plastic sealed and stored in temperature controlled laboratory conditions until they were exposed to
seawater in the field exposure site in Roedbyhavn harbour at a maturity of 43-49 -days. The blocks are
placed partly immersed in seawater with the upper 70 cm above normal water level, refer to figure 1.
Figure 1 Large concrete blocks exposed to sea water in Roedbyhavn field exposure site.
The water in Roedbyhavn is generally quite calm, because the harbour is protected by two long piers.
The regular tide is only 0.1 m, but normal water level variations are ±1.1 m and extreme variations are
±2.0 m. The chloride content of the seawater is approx. 0.7% Cl [5] and annual temperature variations
of the seawater are typically in the range -1°C to 20°C.
SAMPLING
Two cores for determination of chloride migration coefficients were drilled from each small concrete
block at approximately 1 month maturity and again at approximately 6 months maturity.
Two cores for determination of chloride penetration parameters were drilled from each large concrete
block, i.e. one core from the immersed zone and one core from the splash zone, after approximately 6
months (203 days) of exposure to the marine environment and again after approximately 2 years (735
days) of exposure.
TESTING AND TEST RESULTS
Chloride migration coefficients
The determination of chloride migration coefficients acc. NT BUILD 492 [6] were performed on three
subsamples containing the outmost part of the small concrete blocks. The maturity at testing after
approx. 1 month was between 30 and 34 days, and at testing after approx. 6 months it was between 174
and 186 days. The test results are shown in table 4.
Table 4 Test results for choride migration coefficients at approx. 1 month and 6 months maturity.
ID
Powder/variant
Dnssm [x10-12 m2/s] 1 month
Dnssm [x10-12 m2/s] 6 months
A
B
C
Mean
A
B
C
Mean
A
100SRPC
16.6
16.6
15.7
16.3
9.1
9.5
10.4
9.7
B
85SRPC + 15FA
24.4
20.6
22.0
22.3
5.0
4.3
4.4
4.5
C
75SRPC + 25FA
27.0
27.7
27.7
27.5
1.6
2.1
3.3
2.3
D
75SRPC + 25FA SCC
25.1
24.7
20.0
23.3
2.4
3.0
3.3
2.9
E
96SRPC + 4SF
11.6
11.7
11.6
11.6
5.2
5.5
7.0
5.9
F
84SRPC + 4SF +12FA
9.2
9.7
10.3
9.7
2.7
3.2
2.4
2.8
G
84SRPC + 4SF +12FA / no air
10.3
9.1
9.4
9.6
2.0
2.7
2.1
2.3
H
84SRPC + 4SF +12FA / 0.45w/c
14.7
14.6
13.9
14.4
4.6
3.4
3.6
3.8
I
84SRPC + 4SF +12FA / 0.35w/c
9.8
8.0
10.3
9.4
2.4
2.0
1.9
2.1
J
84SRPC + 4SF +12FA / SCC
10.0
9.8
10.0
9.9
3.3
2.8
3.2
3.1
K
100SLAGPC
2.5
2.8
2.3
2.5
1.4
1.2
1.3
1.3
L
100SLAGPC / no air
2.5
3.1
2.8
2.8
1.4
1.8
1.1
1.4
M
100SLAGPC / SCC
2.3
2.4
2.3
2.3
0.8
1.0
1.1
1.0
N
30OPC + 70GGBFS
3.8
4.5
4.2
4.1
1.5
1.6
1.7
1.6
O
96SRPC + 4SF / SAP
10.5
12.3
12.1
11.6
4.9
4.7
5.6
5.0
Chloride penetration parameters after marine field exposure
The determination of chloride penetration parameters were performed on the cores from the large
concrete blocks exposed in Roedbyhavn field exposure site for 6 months and 2 years, respectively.
Initially, chloride and calcium profiles were determined on all the drilled cores from the field exposure
site. Subsamples for chloride and calcium analyses were obtained by applying the profile grinding
method described in NT BUILD 443:1995 [6]. The chloride content were measured according to the test
method DS 423.28:1984, which corresponds to NT BUILD 208.1984 [6]. The calcium content were
measured according to APM 214:1995 (in Danish) [6]. All chloride and calcium profiles and other
supplementary details can be found at the homepage of the Danish Expert Centre for Infrastructure
Constructions [7].
Experience from earlier work (e.g. Träslövläge field exposure site in Sweden [2]) shows that the amount
of cement paste in the extracted concrete cores can vary substantially from core to core, even when the
cores are extracted from the same concrete block. Furthermore, the paste content will increase towards
the exposed surface from a depth of approx. half the maximum aggregate size due to the wall effect. In
order to facilitate comparison between cores extracted from the same concrete block at different
exposure times and to eliminate the wall effect, it is often the chloride content measured as acid-soluble
chloride by mass of binder, which has been calculated, used for comparison between different
concretes, and used as input for service life models.
The aggregates used for the concretes in the blocks exposed in Roedbyhavn contain no or reasonable
small amounts of acid-soluble calcium. Therefore, the calcium content measured by acid extraction acc.
to APM 214:1995 can be used as a measure of the paste content of the concrete. Examples of calcium
profiles measured on concrete cores extracted after 24 months exposure of concrete type D are shown in
figure 2.
Figure 2 Calcium content in two cores extracted from block D after 2 years exposure.
As discussed above, a correction for the variations in paste content is needed in order to be able to
compare the chloride profiles measured on different cores. The solid lines in figure 3 show the
calculated chloride contents, when they have been corrected according to the measured calcium contents
shown in figure 2. The correction has been done separately for each layer in the chloride profile by
multiplying a scaling factor Cat/Cam(n), where Cat is the theoretical mean acid-soluble calcium content
calculated from the content of calcium in all binder materials, and Cam(n) is the measured calcium
content in the actual layer n of the profile. The corrected chloride profile represents the situation where
the paste content in each layer of the profile corresponds to the theoretical mean value calculated from
the mix proportions, assuming that the measured acid-soluble calcium content corresponds to the
theoretical calcium content of the binder materials in each of the concrete mixes. They are shown in
table 5 together with the binder contents and concrete densities.
Figure 3 Chloride content in two cores extracted from block D after 2 years exposure.
Dotted lines: Measured values. Solid lines: Corrected values.
Table 5 Theoretical data for binder content, concrete density, and acid-soluble calcium content.
The values are calculated from the mix proportioning sheets.
ID
Powder/variant
Binder
[kg/m3]
Concrete density
[kg/m3]
Ca content
[wt% of binder]
Ca content
[wt% of concrete]
A
100SRPC
360.2
2346
46.89
7.20
B
85SRPC + 15FA
374.9
2351
40.07
6.39
C
75SRPC + 25FA
397.6
2337
35.53
6.04
D
75SRPC + 25FA SCC
448.9
2339
35.51
6.81
E
96SRPC + 4SF
353.6
2361
45.03
6.74
F
84SRPC + 4SF +12FA
352.8
2353
39.60
5.94
G
84SRPC + 4SF +12FA / no air
332.3
2429
43.05
5.89
H
84SRPC + 4SF +12FA / 0.45w/c
323.9
2350
39.55
5.45
I
84SRPC + 4SF +12FA / 0.35w/c
387.2
2352
39.58
6.52
J
84SRPC + 4SF +12FA / SCC
421.2
2357
39.56
7.07
K
100SLAGPC
359.0
2347
34.16
5.22
L
100SLAGPC / no air
380.1
2440
34.16
5.32
M
100SLAGPC / SCC
408.6
2317
34.16
6.02
N
30OPC + 70GGBFS
353.3
2316
33.64
5.13
O
96SRPC + 4SF / SAP
354.7
2399
45.02
6.66
The following evaluation of the chloride penetration into the 15 large concrete blocks are based on
analyses of the corrected chloride profiles. A simple way to describe the chloride penetration is to
measure the penetration depth of a reference chloride concentration. Table 6 shows the penetration
depth of a reference chloride concentration of 0.05 %Cl by weight of concrete for all measured chloride
profiles. The penetration depths are calculated from the corrected chloride profiles by interpolation and
in a few cases also extrapolation.
Table 6 Chloride penetration depths of a reference chloride concentration of 0.05 %Cl by weight of
concrete. In some cases the chloride penetration depth after two years exposure is equal to or less than
after 6 months exposure (red numbers).
ID
Powder/variant
Submerged zone
Chloride penetration depth
x0.05 [mm]
Splash zone
Chloride penetration depth
x0.05 [mm]
6 months
2 years
difference
6 months
2 years
difference
A
100SRPC
18.3
18.6
0.3
19.3
30.1
10.8
B
85SRPC + 15FA
15.8
23.6
7.9
16.2
22.5
6.3
C
75SRPC + 25FA
15.4
9.7
-5.7
16.2
19.2
3.0
D
75SRPC + 25FA SCC
12.9
17.1
4.1
16.0
20.2
4.2
E
96SRPC + 4SF
11.5
21.6
10.1
15.7
23.9
8.2
F
84SRPC + 4SF +12FA
14.3
19.8
5.5
14.4
13.9
-0.5
G
84SRPC + 4SF +12FA / no air
12.9
17.0
4.1
13.2
18.1
4.8
H
84SRPC + 4SF +12FA / 0.45w/c
15.7
21.4
5.7
16.6
23.1
6.5
I
84SRPC + 4SF +12FA / 0.35w/c
11.2
16.2
5.1
12.4
16.1
3.7
J
84SRPC + 4SF +12FA / SCC
12.9
18.7
5.7
12.9
18.6
5.7
K
100SLAGPC
5.9
9.2
3.3
6.9
8.7
1.9
L
100SLAGPC / no air
6.0
9.4
3.4
6.4
9.5
3.1
M
100SLAGPC / SCC
4.2
9.7
5.5
4.9
10.1
5.2
N
30OPC + 70GGBFS
6.4
7.7
1.4
6.7
10.1
3.4
O
96SRPC + 4SF / SAP
15.3
13.2
-2.1
16.2
26.5
10.3
The chloride penetration parameters Ci, Cs, Dapp, and Kcr are often used to describe measured chloride
profiles, because it makes comparison between profiles from different exposure times easier, and the
parameters can also be used as input to several service life models. The calculation of these parameters
is performed by curve-fitting of the error function solution to Ficks 2nd law of diffusion on the corrected
chloride profiles acc. to the principles described in NT BUILD 443:1995 [6]. The calculation is
performed on the part of the profile, where the outmost points of the profile are omitted until the point
with the maximum chloride content is reached. An example of this calculation is shown in figure 4.
Figure 4 Calculation of chloride penetration parameters on corrected chloride profile data from a
core drilled from concrete type D after 24 months exposure.
Red marks: Measured values. Marks in brackets are omitted. Solid line: Calculated curve fit.
The results from the calculation of chloride penetration parameters an all cores from the 15 different
concrete mix designs are shown in table 7 and table 8. A reference chloride concentration of 0.05 %wt
of concrete has been used for the calculation of Kcr.
Dapp 9.62E-13 m2/s
Dapp 30.3 mm2/yr
Cs 0.803 wt% Cl
Ci 0.000 wt% Cl
t 2.01 yr
Kcr 14.5 mm/yr½
( )
( )
Table 7 Calculated chloride penetration parameters for large concrete blocks exposed in the
submerged zone for 6 months and 2 years. A reference chloride concentration of 0.05 %wt of concrete
has been used for the calculation of Kcr. Data from suspect chloride profiles are marked with red color.
ID
Powder/variant
Submerged zone
Chloride penetration
parameters 6 months
Submerged zone
Chloride penetration
parameters 2 years
Cs
%wt Co
Dapp
10-12 m2/s
K0.05
mm/yr½
Cs
%wt Co
Dapp
10-12 m2/s
K0.05
mm/yr½
A
100SRPC
0.418
5.36
28.7
0.329
1.39
13.4
B
85SRPC + 15FA
0.313
4.41
23.4
0.639
2.06
20.1
C
75SRPC + 25FA
0.347
2.93
19.9
0.765
0.28
7.7
D
75SRPC + 25FA SCC
0.404
3.11
21.6
0.803
0.96
14.5
E
96SRPC + 4SF
0.240
3.03
17.4
0.547
1.75
17.7
F
84SRPC + 4SF +12FA
0.442
2.76
20.9
0.599
1.39
16.2
G
84SRPC + 4SF +12FA / no air
0.400
2.15
17.9
0.564
1.21
14.8
H
84SRPC + 4SF +12FA / 0.45w/c
0.469
2.94
22.0
0.518
1.62
16.8
I
84SRPC + 4SF +12FA / 0.35w/c
0.511
1.50
16.1
0.633
0.91
13.3
J
84SRPC + 4SF +12FA / SCC
0.459
1.68
16.6
0.637
1.18
15.2
K
100SLAGPC
0.291
0.61
8.5
0.633
0.24
6.9
L
100SLAGPC / no air
0.275
0.58
8.1
0.597
0.30
7.5
M
100SLAGPC / SCC
0.311
0.33
6.4
0.775
0.29
8.0
N
30OPC + 70GGBFS
(0.154)
(1.11)
(8.2)
0.414
0.21
5.7
O
96SRPC + 4SF / SAP
0.319
3.53
21.2
0.293
0.74
9.4
Table 8 Calculated chloride penetration parameters for large concrete blocks exposed in the splash
zone for 6 months and 2 years. A reference chloride concentration of 0.05 %wt of concrete has been
used for the calculation of Kcr. Data from suspect chloride profiles are marked with red color.
ID
Powder/variant
Splash zone
Chloride penetration
parameters 6 months
Splash zone
Chloride penetration
parameters 2 years
Cs
%wt Co
Dapp
10-12 m2/s
K0.05
mm/yr½
Cs
%wt Co
Dapp
10-12 m2/s
K0.05
mm/yr½
A
100SRPC
0.349
7.50
31.9
0.468
4.24
26.4
B
85SRPC + 15FA
0.430
4.03
25.0
0.613
1.70
18.1
C
75SRPC + 25FA
0.496
4.04
20.4
0.689
1.72
18.8
D
75SRPC + 25FA SCC
0.579
3.15
24.2
0.762
1.60
18.5
E
96SRPC + 4SF
0.340
3.55
21.7
0.499
2.43
20.3
F
84SRPC + 4SF +12FA
0.449
2.83
21.3
0.280
1.09
11.1
G
84SRPC + 4SF +12FA / no air
0.387
2.44
18.8
0.517
0.82
12.0
H
84SRPC + 4SF +12FA / 0.45w/c
0.450
3.23
22.7
0.577
2.01
19.3
I
84SRPC + 4SF +12FA / 0.35w/c
0.399
2.05
17.4
0.621
0.98
13.7
J
84SRPC + 4SF +12FA / SCC
0.436
1.93
17.5
0.737
1.18
15.8
K
100SLAGPC
0.317
0.77
9.9
0.602
0.23
6.6
L
100SLAGPC / no air
0.429
0.49
8.7
0.377
0.45
8.0
M
100SLAGPC / SCC
0.112
0.83
5.6
0.804
0.32
8.4
N
30OPC + 70GGBFS
0.497
0.48
9.1
0.565
0.43
8.9
O
96SRPC + 4SF / SAP
0.357
5.72
28.1
0.541
2.26
20.1
DISCUSSION
Chloride migration coefficients
A compilation of the measured chloride migration coefficients on all 15 different concrete mix designs
is given in figure 5 where test results for 1 month maturity is compared to test results for 6 months
maturity.
Figure 5 Chloride migration coefficient, Dnssm, of the different concrete types measured according to
NT Build 492 at 1 months and 6 months maturity, respectively.
At 1 months maturity there seems to be a clear trend that the blast furnace slag based concretes have the
lowest chloride migration coefficients of the tested concrete compositions. Likewise, 3-powder
compositions (cement, fly ash and silica fume) have lower coefficients than silica fume concrete
(type E & O) followed by pure Portland cement mixtures, while fly ash concrete has the highest
chloride migration coefficient.
At 6 months maturity the ranking according to chloride migration coefficients between the different
binder composition has changed dramatically. Pure Portland cement concrete (type A) has the highest
migration coefficient followed by silica fume concrete (type E & O), fly ash concrete and 3-powder
concrete at about the same level, and blast furnace slag based concrete with the lowest coefficients.
The observation that fly ash concrete performs poorly in the early age (lowest ranking of all binder
compositions at 1 month maturity) and much better at a later stage (rank no. 2 following close to blast
furnace slag based concretes) has also been reported elsewhere, e.g. [8]. This fact has to be considered
when the chloride migration coefficient Dnssm is used as input to service life models, because the Dnssm
values is often measured at 28 days maturity before the late hydration of fly ash has taken place.
The uncertainty of the chloride migration results determined in the DTI laboratory is:
For average values Xave < 10 (x 10-12 m2/s): Variation coefficient V = 30 1.5 x Xave %.
For average values Xave ≥ 10 (x 10-12 m2/s): Variation coefficient V = 15 %.
Chloride penetration parameters
The chloride penetration depths x0.05 in all the corrected chloride profiles are shown in figure 6. A few
chloride profiles measured after two years exposure had less or equal chloride penetration compared to
the measurements on the same concrete blocks after ½ year exposure. These concrete blocks (marked
with red in table 6) are A, C and O in submerged zone and F in splash zone. This observation of rather
large variation emphasises the importance of having more than one single sample for each situation,
which unfortunately not have been the case in the present study.
Figure 6 Comparison of chloride penetration depths (x0.05) for all measured chloride profiles. The two
brown colored columns are penetration depths after the first ½ years exposure. The blue colored
columns are the additional penetration depths in the period from the first ½ years exposure until 2 years
exposure.
As seen in figure 6 the major part of the chloride ingress during the first two years exposure has
occurred in the early period just after immersion of the concrete blocks. The penetration depth during
the first 6 months are generally about 2/3 of the total penetration depth during the first 2 years exposure,
with the tendency that fly ash blended binders to be even higher (3/4 in the first 6 months).
In general the variation in penetration depth between the two different exposure situations do not differ
much for each concrete type. There seems to be a slightly higher penetration in the splash zone, which
could be due to a contribution from repeated wetting and drying of the outer concrete layer.
Figure 7 and figure 8 presents a summary of the calculated penetration parameters Dapp and K0.05,
respectively. As seen for the chloride penetration depth (x0.05) the values for the two chloride
penetration parameters are not showing much variation between the two different exposure situations.
Figure 7 Calculated apparent chloride diffusion coefficients. Please note that values for concrete
types A, C and O in submerged zone and F in splash zone are uncertian due to suspect chloride profiles.
Figure 8 Calculated chloride penetration parameters. Please note that values for concrete types A, C
and O in submerged zone and F in splash zone are uncertian due to suspect chloride profiles.
Comparison between accelerated laboratories tests and field exposure observations
The ranking of concrete types (excluding the reference A type) from chloride migration testing at 1
month maturity is similar to the ranking from the early chloride penetration measurements after ½ year
field exposure, where the relative performance against chloride ingress is: Blast furnace slag concrete <
3-powder concrete < silica fume concrete < fly ash concrete.
The change in ranking from chloride migration testing at 6 months maturity, where fly ash concrete
performs much better is also observed in the field exposed concretes, when the increment in chloride
penetration depth (x0.05) from ½ year to 2 years exposure is considered. Here is the performance of the
3-powder concrete and the fly ash concrete at the same level and better than silica fume concrete. This
results in the following ranking regarding relative performance against chloride ingress:
Blast furnace slag concrete < 3-powder concrete & fly ash concrete < silica fume concrete.
The correlation between the chloride migration coefficients (Dnssm) at 1 months maturity and the
apparent chloride diffusion coefficients (Dapp) after 2 years exposure is poor. A better correlation exists
between Dnssm at 6 months maturity and Dapp after 2 years exposure, see figure 9.
Figure 9 Correlation between the chloride migration coefficient (Dnssm) measured at 1 months
maturity and the apparent diffusion coefficient after 2 years exposure. Please note that values for
concrete types A, C and O in submerged zone and F in splash zone are omited due to suspect chloride
profiles.
The best correlation between the produced test results from accelerated laboratory testing and test
results from marine field exposure is observed between the chloride migration coefficient (Dnssm) at 6
months maturity and the increment in chloride penetration depth (x0.05) from ½ year exposure to 2 years
exposure, see figure 10.
Figure 10 Correlation between the chloride migration coefficient (Dnssm) measured at 6 months
maturity and the increment in chloride penetration depth (x0.05) between ½ year and 2 years exposure.
Please note that values for concrete types A, C and O in submerged zone and F in splash zone are
omited due to suspect chloride profiles.
CONCLUSIONS
A study of chloride penetration into 15 different concrete mix designs after 2 years natural marine
exposure in Roedbyhavn field exposure site has given the following result in ranking regarding relative
performance against chloride ingress:
1) Blast furnace slag concrete
2) 3-powder concrete & fly ash concrete
3) Silica fume concrete
4) Ordinary Portland cement concrete.
Concrete types made from binder systems composed of Portland cement and fly ash are generally quite
permeable in the early age due to slow hydration of fly ash. However, during the first half year these
concrete types will have potential to develop a very dense matrix with low permeability not far from
concrete made from binders with blast furnace slag.
The use of chloride migration coefficients (Dnssm) as input parameters to service life modelling instead
of data from natural long-time exposure should be performed with some caution. In many cases the use
of Dnssm values measured at 28 days maturity will not be able to predict the long-time permeability of
the tested concrete when blended binders and fly ash are used.
Special precautions could be applied to minimize the relatively high chloride ingress in the beginning of
the exposure of young fly ash concretes. The initial chloride ingress might be reduced by e.g. wet curing
before chloride exposure in order to minimise or eliminate capillary suction, by prolonged curing
allowing the concrete to gain more maturity and thereby less permeability giving a better resistance
against chloride penetration, or by the use of cements which develop high hydroxide concentrations in
the pore water in order to speed up the hydration of fly ash.
REFERENCES
1. fib Bulletin 65, “Model Code 2010. Final draft. Volume 1”, International Federation for Structural Concrete,
Bulletin 65, Lausanne, Switzerland, 2012, 311 pp. ISBN 978-2-88394-105-2
2. SANDBERG, P., “Recurrent studies of chloride ingress in uncracked marine concrete at various exposure times and
–elevations”, Div. of Building Materials LTH, Lund University, Report TVBM-3080, 1998, 48 pages.
ISSN: 0348-7911
3. BAGER, D.H. “Aalborg Portlands’ durability project – 25 years judgement”. Proc. of Nordic Miniseminar on
Nordic Exposure Sites - input to revision of EN 206-1. Hirtshals, November 12-14, 2008, pp. 119-135.
NCR workshop-proceeding No. 8. ISBN 978-82-8208-013-2
4. ANDERSEN, O.V.; Et al., “HETEK. Stavvibrering. Højkvalitetsbeton. Entreprenørens teknologi – Anvisning
(Poker vibration. High Quality Concrete. Contractors Technology – Guideline)”. The Danish Road Directorate,
Report No. 74, 1997. Available at http://www.hetek.teknologisk.dk/16228
5. ANDERSEN, I. “Salt- og temperaturforhold i de indre danske farvande (Salt and temperature conditions in the inner
Danish waters)”. Danish Meteorological Institute, Copenhagen, Technical Report No. 94-4, 1994
6. FREDERIKSEN, J.M. “HETEK, Chloride Penetration into Concrete, Relevant test methods”. The Danish Road
Directorate, Report No. 53, 1997. ISBN 87-7491-804-4. Available at www.hetek.teknologisk.dk/english/16507
7. DANISH EXPERT CENTRE FOR INFRASTRUCTURE CONSTRUCTIONS, www.concreteexpertcentre
8. BAROGNEL-BOUNY, V.; KINOMURA, K; THIERY, M.; MOSCARDELLI, S. “Easy assessment of durability
indicators for service life prediction or quality control of concretes with high volumes of supplementary
cementitious materials”, Cement and Concrete Composites, Vol. 33, No. 8, September 2011, pages 832847
... [1] and [2]. ...
... Calculated values of D a , C s and K Cr are given in Table 2 Values for D a and C s were obtained from chloride profiles measured on cores drilled from the submerged zone of the exposed concrete blocks. Similar data determined after 0.5 and 2 years of exposure [2] are shown as well for comparison. ...
... The improved resistance against chloride ingress as a result of using mineral addition such as slag, fly ash or silica fume has previously been confirmed in numerous studies (e.g. [2] and [6]). ...
Conference Paper
Full-text available
This paper presents new results from a long-running study following the chloride ingress in concrete blocks exposed at the marine exposure site located at Rødbyhavn harbour in Denmark. The site was established in 2010 as part of the preparatory work for the planned Fehmarnbelt fixed link between Denmark and Germany. Chloride profiles have previously been measured on cores extracted from the blocks after 0.5 and 2 years of exposure to seawater-and now after 5 years. The studied blocks represent 15 different concrete mixes produced using a variety of binder types. The chloride ingress in the blocks have been investigated for both submerged and splash zone exposure conditions. Chloride transport parameters such as the achieved chloride diffusion coefficient (D_a), surface chloride concentration (C s) and the penetration parameter K_Cr were determined by fitting the error function solution to Fick's 2nd law to the measured profiles. Results from the Rødbyhavn exposure site are also compared to chloride data from the field exposure site in Träslövsläge, Sweden. Based on the findings from Rødbyhavn and chloride data from the literature, a simplified chloride penetration model for long-term marine exposure is proposed and discussed.
... The types of cement have notable impact on the concrete resistance to chloride ingress: slag cement [ fly ash (FA) cement [ silica fume (SF) cement [ ordinary Portland cement [42]. The apparent chloride diffusion coefficient and the critical chloride content for corrosion initiation decrease with increasing FA content in the binder [43]. ...
Article
This paper reviews the technical aspects related to the long-term field exposure practice in marine environments, based on the return of experiences of major marine exposure sites in world-wide scope. The long-term exposure practice helps both the research on durability mechanisms of structural concretes under real environments and the calibration of durability models to support the life-cycle management of concrete structures. The presentation of the field exposure data can be categorized into the information relevant to exposure sites, the data related to the exposed materials and specimens, the information of environmental actions, and the data related to the performance of materials. A standardized presentation of these data can help the efficiency of data sharing and exploitation. The exploitation of exposure data employs various models to represent the chloride ingress and the induced corrosion risk of the embedded steel bars. There are needs for models addressing the strong environment-material interactions, and simple yet reliable durability indicators for engineering use. The design and operation of exposure stations need the careful choice of exposure sites and specimens, the appropriate scheme for monitoring and inspection of exposed specimens, the systematic recording and management of exposure data, and the regular maintenance of exposure facilities. The support of exposure data for life-cycle management is demonstrated through the durability planning of a real project case. The good practice of long-term field exposure is summarized in the end.
Chapter
Service life modelling for concrete structures exposed to severe environments has been developed and used for several years. The upcoming revision of the Eurocode 2 for concrete structures is incorporating service life design (SLD) based on performance based models as an alternative to the more common concept of deemed-to-satisfy material requirements. The performance based approach is generally recognised to have a more sustainable profile than the traditional prescriptive one.
Article
This paper investigates whether durability indicators (DIs), more specifically transport properties, can be assessed by simple methods, e.g. direct experimental methods or indirect methods based on analytical formulas, for every type of concrete. First the results of electrical resistivity and apparent chloride diffusion coefficient obtained by direct measurement on a broad range of materials, particularly on high-volume supplementary cementitious materials (SCM) mixtures, are discussed. Then, various methods, in particular methods based on these last parameters, are compared for the assessment of effective chloride diffusion coefficient and “intrinsic” liquid water permeability, including for the latter a sophisticated method based on numerical inverse analysis. The good agreement observed between the various methods points out that simple methods can allow DI assessment with sufficient accuracy. Moreover, the available values of electrical resistivity, effective/apparent chloride diffusion coefficients and “intrinsic” liquid water permeability can be included in a database. Throughout the paper, the specificities of high-volume SCM mixtures are highlighted.
Article
Uncracked reinforced concrete slabs were field exposed mounted on a floating pontoon and partly submerged for 5 years at the Swedish west coast. The total chloride ingress was analysed at various exposure times at 3 elevations representing a submerged, a splash, and an atmospheric exposure zone. The concrete mixtures varied in w/c ratio, type of cement, and amount and type of pozzolan used in the binder. The data is unique as it represents recurrently measured total chloride penetration profiles at various exposure ages, providing a foundation for the prediction of chloride ingress in concrete in a given environment. The results after 5 years of exposure confirmed the expected inverse relationship between water-to-binder ratio and chloride ingress. The use of 5–10% silica fume in the binder had a very positive effect on reducing the chloride ingress, but little or no benefit at all was found for concrete with fly ash in the binder as compared to the use of 5% silica fume. The chloride penetration rate as expressed by a calculated effective chloride diffusivity has a tendency to decrease over time. High- performance concrete with w/c ≤ 0.4 and a minimum of 5% silica fume added as a well dispersed slurry exhibited an effective chloride diffusivity in the range of 1 × 10−13 to 5 × 10−13 m2/s after 5 years exposure in the splash zone.
Model Code 2010. Final draft
fib Bulletin 65, "Model Code 2010. Final draft. Volume 1", International Federation for Structural Concrete, Bulletin 65, Lausanne, Switzerland, 2012, 311 pp. ISBN 978-2-88394-105-2
Aalborg Portlands' durability project -25 years judgement
  • D H Bager
BAGER, D.H. "Aalborg Portlands' durability project -25 years judgement". Proc. of Nordic Miniseminar on Nordic Exposure Sites -input to revision of EN 206-1. Hirtshals, November 12-14, 2008, pp. 119-135. NCR workshop-proceeding No. 8. ISBN 978-82-8208-013-2
High Quality Concrete. Contractors Technology-Guideline)". The Danish Road Directorate
ANDERSEN, O.V.; Et al., "HETEK. Stavvibrering. Højkvalitetsbeton. Entreprenørens teknologi-Anvisning (Poker vibration. High Quality Concrete. Contractors Technology-Guideline)". The Danish Road Directorate, Report No. 74, 1997. Available at http://www.hetek.teknologisk.dk/16228
Salt-og temperaturforhold i de indre danske farvande (Salt and temperature conditions in the inner Danish waters
  • I Andersen
ANDERSEN, I. "Salt-og temperaturforhold i de indre danske farvande (Salt and temperature conditions in the inner Danish waters)". Danish Meteorological Institute, Copenhagen, Technical Report No. 94-4, 1994
HETEK, Chloride Penetration into Concrete, Relevant test methods
  • J Frederiksen
FREDERIKSEN, J.M. "HETEK, Chloride Penetration into Concrete, Relevant test methods". The Danish Road Directorate, Report No. 53, 1997. ISBN 87-7491-804-4. Available at www.hetek.teknologisk.dk/english/16507