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PERFORMANCE OF CONCRETE CONTAINING
T E R N A R Y BINDERS IN C H L O R I D E - L A D E N E N V I R O N M E N T S
B J Magee
Purdue University
United States of America
M R Jones
R K Dhir
University of Dundee
United Kingdom
A B S T R A C T . Based on the premise that if one additional binder material in concrete
provides improved performance, then further benefits are likely when using two, this study
was carried out to examine selected properties of ternary binder concrete (TBC). Various
fresh concrete properties were considered as well as strength development and chloride
resistance of TBC. In addition, the nature of the near surface pore structure of the concrete
has been inferred from its initial surface absorption. Performance in all instances was
compared to PC and binary PC/PFA concrete of equivalent 28-day cube strengths of 20, 40
and 60 N/mm2. In general, no practical dissimilarity existed between TBC, PC and PC/PFA
mixtures in terms of fresh concrete properties. When designed for equivalent 28-day strength,
TBC exhibited lower strengths than the controls. Equations enabling estimates of strength
reductions are proposed. Improved long-term strength was achieved by TBC, with PC
replacement levels of around 60% by mass identified as an optimum. Using accelerated
electrochemical and penetration test methods, it has been shown that the chloride resistance
of all the ternary binder concrete (TBC) is significantly higher than corresponding PC and
PC/PFA mixes.
This improved performance is attributed mainly to the improved
microstructure of TBC mixes.
Keywords: Ternary binder concrete, PFA, GBS, SF, Mix handling/placing/finishing
characteristics, Strength development, Chloride ingress.
D r B r y a n J Magee is currently a post-doctoral research associate at the School of Civil
Engineering, Purdue University, Indiana, USA. Prior to this appointment, he held a similar
position at the Department of Civil Engineering, University of Cape Town, South Africa. He
received his BSc(Eng) and PhD degrees from the University of Dundee, Scotland. His
research interests include cement and concrete technology, with emphasis on the use of
supplementary cementitious materials and the issue of long-term durability
D r R o d Jones is a chartered civil engineer and senior lecturer in the Concrete Technology
Unit in the Department of Civil Engineering at the University of Dundee. His research
focuses mainly on binder technology, concrete durability and repair and maintenance.
Professor R a v i n d r a D h i r is the Director of the Concrete Technology Unit and Professor of
Concrete Technology at the University of Dundee. He is a member of numerous national and
international technical committees and has published extensively on many aspects of concrete
technology, binder science, durability and construction methods.
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228
Magee, Jones, Dhir
INTRODUCTION
Premature corrosion damage of embedded reinforcement in concrete continues to present one
of the most serious durability problems facing engineers. Although it is established [1-3] that
improved resistance to corrosion damage is achievable through the use of materials such as
pulverised-fuel ash (PFA), granulated blastfurnace slag (GBS) and silica fume (SF) in binary
blends, case studies indicate that many existing structures continue to suffer [4].
Encouragingly, recent research [5,6] indicates that ternary blended binders in concrete allow
high levels of durability to be achieved, particularly with respect to chloride ingress. These
findings assume particular significance with the adoption of the cement standard ENV 197-1
(1996), which presents European engineers with the opportunity to tailor concrete for high
levels of durability via binder optimisation. Indeed, ENV 197-1 allows cocktails of three or
more binder materials to be prescribed for any given concrete mix. The value of using
ternary binder concrete (TBC) has already been realised in many countries, with its
advantages exploited for some major infrastructure projects. For example, the Great Belt
Link in Denmark was constructed using a PC/PFA/SF blend [7]. In this case, TBC was used
as an integral component of a multistage protection strategy designed to provide a service life
of 100 years.
this study was undertaken to examine both the practicality and performance of TBC.
Although the main focus of the study was the chloride resistance of TBC, selected fresh
properties and strength development were additionally considered. Despite ENV 197-1
identifying a total of 25 types of cement (of which Types II-N and V allow ternary blended
binders) based around 8 different additional materials, only those of immediate relevance to
the UK were considered. Combinations of Portland cement (PC) to BS 12 (1991), PFA to
BS EN 450 (1995), GBS to BS 6699 (1991) and SF were, therefore, considered within the
scope of this work, used in combinations based on the requirements of ENV 197-1.
EXPERIMENTAL MIX PROPORTIONS
On a practical basis and in order to limit large numbers of possible binder combinations,
additional materials were proportioned based on replacement levels similar to those used in
typical binary mixes. Such binder proportions were also considered suitable due to their
potential to provide practical mixes with high levels of chloride resistance [1-3]. Using a mix
design method developed at the University of Dundee [8], TBC mix proportions were
selected to give standard 28-day cube strengths of 20, 40 and 60 N/mm . The control mixes
were PC and PC/30% PFA concrete of equal cube strengths. The mix proportions used are
given in Table 1, which additionally includes a binder proportion summary where each binder
material is represented as a percentage of the total binder content by mass.
2
Performance of each binder combination chosen was highlighted by maintaining fixed free
water and coarse aggregate contents (185 1/m and 1200 kg/m respectively). Unit volumes
of the mixes were subsequently achieved by varying the fine aggregate contents. It should be
noted that with the free water content selected, 28-day cube strengths of 60 N/mm were not
achievable with the PC/PFA/GBS blends. All mixes obtained a nominal slump of 75 mm
without the need for a plasticising chemical admixture except for those using SF, where the
very cohesive nature of the concrete required the use of a minimal dosage of superplasticiser
(see Table 2 for details). All concrete specimens were standard water cured for 28-days and
all tests were initiated at that time.
3
3
2
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Ternary Binder Concrete 229
[able 1 Summary of concrete mix proportions
28-DAY
CUBE
STRENGTH,
N/mm
MIX
CODE
CONST 1 IT I'NT M A T E R I A L S , kg/m'
Binder
2
PC
PFA
PC control
C1
C2
C 3
20
40
60
225
325
430
-
PC/PFA
C4
C 5
C6
20
40
60
PC/PFA/GBS
TBC 1
TBC 2
TBC 3
TBC 4
TBC 5
TBC 6
TBC 7
GBS
S
F
Fine
Aggregate
BINDER
PROPORTION,
% BY M A S S
-
820
745
630
100/0/0
100/0/0
220
270
405
95
115
175
600
540
360
70/30/0
70/30/0
70/30/0
20
20
20
20
40
40
40
140
100
195
85
230
155
155
50
120
70
150
55
175
90
595
565
475
475
545
425
330
42.5/15/42.5
32.5/35/32.5
25/15/60
20/35/45
60/15/25
32.5/35/32.5
25/15/60
PC/PFA/SF
TBC 8
TBC 9
TBC 10
TBC 11
TBC 12
20
20
40
40
60
180
140
250
220
265
20
140
30
220
265
20
30
30
45
65
725
580
615
410
355
80/10/10
45/45/10
80/10/10
45/45/10
45/45/10
PC/GBS/SF
TBC 13
TBC 14
TBC 15
TBC 16
40
40
40
60
195
155
105
160
25
35
35
50
625
580
545
370
65/25/10
45/45/10
25/65/10
25/65/10
1 ooo/o/
control
140
100
195
195
100
155
370
85
155
245
370
FRESH PROPERTIES
Mix Observations
Owing to the unfamiliarity of TBC, qualitative observations for ease of compaction,
cohesiveness, colour and finishing characteristics were initially documented, see Table 2.
Clearly, TBC mixes exhibited no visual dissimilarity to good quality PC concrete. In fact,
with regards to fresh properties, TBC was generally of higher quality than the PC and
PC/PFA controls. Of practical significance, TBC was easily compacted, exhibited no visible
bleeding and produced an excellent surface finish.
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230 Magee, Jones, Dhir
Table 2 Fresh properties and visual observations of TBC
MIX
SLUMP, mm
CODE
PC
SP
DOSAGE
AIR
1
C O N T E N T , O B S E R V A T I O N S OF MIX H A N D L I N G
%
CHARACTERISTICS
control
C 1
85
-
1.2
Normal m i x appearance.
C2
75
-
1.1
Normal m i x appearance.
C3
60
-
1.1
Normal m i x appearance.
G o o d w o r k a b i l i t y and c o m p a c t i o n .
Slight bleeding.
G o o d w o r k a b i l i t y and c o m p a c t i o n .
PC/PFA
control
C4
90
-
1.0
Normal m i x appearance.
C5
75
-
1.2
Normal m i x appearance.
C6
65
-
1.1
Normal m i x appearance.
Very workable, easy compaction.
G o o d c o h e s i o n and compaction.
H a n d l i n g and c o m p a c t i o n g o o d .
PC/PFA/GBS
TBC 1
75
-
1.1
Normal m i x appearance, with g o o d
TBC 2
65
-
1.3
Normal m i x appearance.
TBC 3
80
-
1.2
Normal m i x appearance, no bleeding, good
TBC 4
60
-
1.1
G o o d w o r k a b i l i t y , c o m p a c t i o n and
TBC 5
60
-
1.1
N o r m a l m i x a p p e a r a n c e , quite stiff, n o
TBC 6
50
-
1.0
Normal m i x appearance.
TBC 7
50
-
1.3
Normal mix, g o o d workability,
w o r k a b i l i t y , c o m p a c t i o n a n d finish
G o o d workability, slight bleeding.
c o h e s i o n and s u r f a c e finish.
cohesion. Appeared normal.
bleeding, good cohesion.
c o m p a c t i o n , finish and c o h e s i o n .
PC/PFA/SF
TBC 8
65
0.7 (7.0)
0.9
TBC 9
60
0.9 (9.0)
0.8
A v e r a g e w o r k a b i l i t y but m i x e a s i l y
c o m p a c t e d . D a r k in a p p e a r a n c e .
Fairly harsh m i x , n o b l e e d i n g .
E a s y c o n c r e t e c o m p a c t i o n . D a r k grey.
T B C 10
60
0.9 (9.0)
0.6
M i x appeared normal.
G o o d w o r k a b i l i t y , e a s y h a n d l i n g and
workability.
T B C 11
55
1.1 ( 1 7 . 0 )
0.9
M i x stiff, w i t h l o w s l u m p .
C o m p a c t i o n a c h i e v e d . V e r y dark c o l o u r .
T B C 12
50
1.5(13.0)
0.9
M i x stiff, w i t h l o w s l u m p .
C o m p a c t i o n a c h i e v e d . V e r y dark c o l o u r .
PC/GBS/SF
T B C 13
75
1.0(12.0)
0.8
Discolouration, average workability, mix
c o m p a c t e d satisfactorily.
T B C 14
70
1.0(10.0)
0.9
H a r s h , stiff m i x but g o o d c o m p a c t i o n .
No
bleeding, discolouration.
T B C 15
70
1.1 ( 1 2 . 0 )
0.7
T B C 16
65
1.4(16.0)
0.9
M i x appeared normal. G o o d workability,
h a n d l i n g and c o m p a c t i o n .
Stiff, harsh m i x . N o b l e e d i n g , h i g h
cohesion. Slight discolouration.
1
Superplasticiser dosage as % of total binder content (and SF content) by mass
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Ternary Binder Concrete
231
However, there was some variation in the colour of TBC when assessed at 28 days. Mixes
rich in GBS and PFA tended to range from lighter shades of grey to typical shades.
Alternatively, and due to the nature of the slurry used, mixes rich in SF ranged from darker
shades of grey to almost black.
Entrapped Air Contents
As the potential for TBC to entrap air was uncertain, all concrete was tested in compliance
with BS 1881: Part 106 (1983) after undergoing full compaction. As shown in Table 2,
results indicate minor differences existing between the controls and PC/PFA/GBS mixes. In
contrast, entrapped air contents obtained for all TBC mixes containing SF were on average
30% lower than the controls. Why the observed reduction in entrapped air occurs is unclear,
although some hypotheses have been described for binary mixes. As superplasticisers are
dispersants they tend to repel air that has become, in part, stabilised by orientation of the
surfactant. For this reason, high workability concrete containing superplasticisers are often
characterised by foam, caused by a rapid release of entrapped air [9]. As all TBC mixes
inclusive of SF contained superplasticiser, this theory may, in part, explain the reduced air
contents recorded.
STRENGTH DEVELOPMENT
Specimens (100 mm cubes) were tested at intervals up to 180-days in accordance with BS
1881: Part 116 (1983). TBC mixes generally exhibited lower early strength development
than PC and PC/PFA control concrete. Indeed, at 1 and 3-days, respective TBC strengths
were on average 50% and 30% lower than PC concrete, and 25% and 15% lower than
PC/PFA concrete. These strength differences decreased with time, however, and by 90 days
the TBC strengths were on average 25% and 20% higher than the PC and PC/PFA concrete
respectively. This level of strength improvement was maintained up to 180 days.
Cube strengths obtained for TBC mixes at 1, 3, 90 and 180 days are given in Figure 1,
expressed as a percentage of PC control results and plotted with respect to the percentage of
PC replacement used for each mix.
20
100
60
40
170
6
H
(a)
Y = -[0.4X + 9.3]
-20
'ex..
w
PQ
U
U
150
A
A
-40
x
oo -60
Y = - [ 0 . 7 X + 15.5]
A*
o \
o
o
O
O 90-day
A
A
A
(b)
A 180-day
-80
130
o
A
0
A
b-,.o
A
<=>R
o
110
\
x
O1-day
0
A 3-day
90
-100
0
20
40
60
% O F PC REPLACEMENT, by mass
Figure 1 Relationship between TBC strength and percentage
of PC replacement used
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100
232
Magee, Jones, Dhir
Figure 1(a) indicates that as PC replacement in the TBC mixes increased, strength
development at 1 and 3 days decreased with respect to the PC control. By calculating the
equations of the best-fit lines shown, it is possible to estimate early strength development of
TBC.
For example, consider a TBC mix with a PC replacement of X%. Strength at 1 and 3 days
would be approximately [0.7 X + 15.5]% ± 9.0% (at a 90% confidence) and [0.4 X + 9.3]% ±
8.0% (at a 90% confidence) lower than a typical PC mix respectively.
In contrast, the relationship between improved TBC strength and PC replacement at 90 and
180-days was not consistent. Indeed, Figure 1(b) indicates that an optimum PC replacement
exists, in terms of ultimate strength development, of around 60% by mass. Beyond this level,
it is likely that Ca(OH)2 available for pozzolanic reactions may be limited. It should be
recognised, however, that as all concrete specimens were standard water cured until the
required test age, continued pozzolanic activity was not prevented.
ACCELERATED CHLORIDE RESISTANCE TESTS
E l e c t r o c h e m i c a l C h l o r i d e Ingress
Predicting a potentially high chloride ingress resistance of the TBC mixes, an accelerated 14day electrochemical chloride transmission test [10] using 12V DC potential difference (PD)
was initially adopted. PD indices were subsequently calculated using Fick's First Law and
these are compared for all mixes in Figure 2.
Figure 2 Comparison of PD indices obtained for control and TBC mixes
In comparison to both the PC and PC/PFA control mixes, the use of ternary blended binders
resulted in a dramatic reduction in PD index. Considering the 20 N/mm mixes for example,
PD indices obtained for TBC were on average 90% and 85% lower than those obtained for
the control PC and PC/PFA concrete respectively.
2
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Ternary Binder Concrete
233
The degree of improved performance decreased slightly with an increase of concrete strength
to 40 N/mm and corresponding reductions for these TBC mixes were on average 89% and
82%. At the conclusion of the 14-day test period no chloride transmission was measured for
either of the 60 N/mm TBC mixes considered.
2
2
Comparing the PD indices obtained it is evident that only minor differences existed (results
ranged from between 0.30 to 0.90), irrespective of the concrete strength or the binder
combination used. These variations are, in fact, within the accuracy of the test method and
may, therefore, not be significant [10]. This trend most likely reflects equally very high
levels of chloride resistance for all TBC. It is interesting that as the level of PC replacement
ranged from between 20 to 80% by mass, the results from this test method suggest that no
optimum PC replacement exists in order to achieve maximum chloride resistance.
Chloride P e n e t r a t i o n
Owing to the rapid nature of the electrochemical chloride transmission test and the resulting
likelihood of limited chloride binding [11], a restricted series (i.e. mixes TBC 13-16 omitted)
of chloride immersion testing was additionally carried out. All test specimens (75 x 75 x
300 mm prisms) were immersed in 5 M. NaCl solution and sealed on 5 faces to give uniaxial
chloride penetration. After an immersion period of 28, 56 and 91 days, powder samples were
obtained by incremental drilling at depths of 0-5 mm, 6-15 mm and 16-30 mm from the ascast surface. X-ray fluorescence was subsequently used to analyse these samples for their
total chloride content.
Using results obtained after 91 days of immersion, chloride profiles were constructed as
shown in Figure 3.
Figure 3 Chloride profiles constructed from 91 day accelerated
chloride penetration results
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234
Magee, Jones, Dhir
The significant advantage of using TBC mixes is, once again, clearly apparent. For example,
considering the 16-30 mm results collectively over the range of 28 day strengths, the TBC
mixes had on average 80% lower chloride concentration than the PC/PFA controls. As
would be expected due to shorter exposure periods, increasingly lower chloride levels, in
comparison to Figure 3, were obtained for all mixes at 56 and 28 days. However, profiles
constructed from results at each of these ages produced very similar trends to those shown in
Figure 3, with TBC outperforming the controls in all instances.
CHLORIDE DIFFUSION COEFFICIENTS
Owing to the accelerated nature of the chloride tests considered, the results obtained (PD
indices and percentages of total chlorides by mass of concrete for the electrochemical and
penetration tests respectively) are not comparable and cannot easily be used to evaluate
concrete's resistance to chloride ingress. For this reason, coefficients of chloride diffusion
were estimated or calculated from the results obtained from each test.
Curves have been reported in the literature [10], correlating values of PD index and
coefficients of chloride diffusion for PC and PC/30% PFA concrete. As no established
relationship exist between coefficients of diffusion and PD indices for TBC, the curves given
for the PC/30%) PFA concrete were adopted for both the PFA control and TBC mixes. Using
these curves, coefficients of chloride diffusion have been estimated as shown in Table 3. It is
recognised that further research is merited in this area, to establish relationships between
coefficients of diffusion and PD indices for various TBC mixture combinations.
Alternatively, coefficients of chloride diffusion were calculated from the chloride profiles
shown in Figure 3, using Fick's Second Law. Clearly from Table 3, and most likely
reflecting the assumptions made when estimating values from the electrochemical test data,
variations existed in coefficients of chloride diffusion obtained from the two accelerated test
methods.
The results again illustrate, however, the greatly increased performance of TBC in
comparison to the controls. Nomograms enabling estimates of service life for a given set of
conditions have been established [12] and indicate that poor, good, very good and excellent
performance is likely for coefficients of chloride diffusion in the ranges >10.0, 5.0-10.0, 1.05.0 and <1.0 x 10" cm /sec respectively. From this study, TBC mixes indicate the likelihood
of very good and excellent performance in all cases, whereas only 60 N/mm PC/PFA
concrete achieves very good performance. The PC control concrete results indicate the
probability of poor performance at strengths up to 40 N/mm . The 60 N/mm PC concrete
achieves only good performance status.
9
2
2
2
2
DISCUSSION OF TEST RESULTS
Fresh Concrete
From the qualitative analysis carried out, the use of ternary blended binders in concrete
presents no immediate technical difficulties. Indeed, the compaction, cohesiveness, and
finishing characteristics of TBC were all favourable. However, the colour variability noted
has aesthetic implications, for example, in structures where selected elements use TBC with
conventional or binary mixes in close proximity. TBC that is almost black in colour is not
likely to be practicable in many cases and probable application for such mixes is limited to
underground works. For structures where aesthetics are critical, suitable materials and
material combinations should be chosen and trial mixed.
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Ternary Binder Concrete
235
Table 3 Coefficients of chloride diffusion calculated or estimated from accelerated tests
2
MIX
CODE
9
COEFFICIENT OF CHLORIDE DIFFUSION, cm x 10"
Calculated from accelerated Estimated from accelerated
chloride penetration test
electrochemical chloride test
1
2
PC control
C1
C2
C3
PC/PFA
65.0
25.0
9.5
95.0
40.0
11.0
15.0
8.5
5.5
35.0
17.0
11.0
2.0
1.0
1.0
1.7
0.5
1.0
1.1
4.0
4.0
5.0
5.5
3.5
3.5
2.0
2.1
3.0
0.5
0.4
0.4
3.5
5.5
4.0
2.0
0
control
C4
C5
C6
PC/PFA/GBS
TBC 1
TBC 2
TBC 3
TBC 4
TBC 5
TBC 6
TBC 7
PC/PFA/SF
TBC 8
TBC 9
TBC 10
TBC 11
TBC 12
1
Calculated using Fick's Second Law.
Estimated using established relationships between PD-index and coefficient of chloride
diffusion, with relationship for PC/30%PFA assumed to be valid for TBC mixes.
2
S t r e n g t h Development
The inherent low strength development of TBC mixes at early ages may have to be accounted
for in practice, particularly if designing for applied pre-stressing forces, formwork pressures
and stripping times etc. In addition to estimating early strength reductions using the
equations proposed, it is likely that this drawback might be minimised by using accelerating
admixtures, raised curing temperatures or by reducing the level of PC replacement. In
adopting the latter course of action, however, the producer may sacrifice longer-term concrete
performance, particularly with respect to durability.
Clearly, the results indicate an optimum PC replacement level with respect to the longer-term
strength development of TBC. It is likely that optimum performance in terms of durability
may also be achieved using this PC replacement level (around 60% by mass).
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236 Magee, Jones, Dhir
In many cases, however, achieving maximum strength development may not be the main
design criterion and factors such as cost, heat evolution etc. may be the controlling parameter.
This may result in selecting a TBC mix for a minimum total binder content or a minimum PC
content.
Chloride Resistance
In terms of chloride resistance and due to either physical and/or chemical influences [5], the
improved TBC performance is striking, with 20 N/mm TBC mixes outperforming 60 N/mm
controls in many cases. Physically, pozzolanic reactions associated with additional materials
are likely to refine the microstructure of concrete [12]. The results recorded after 10 minutes
(IS AT-10 results) indicated a large reduction of TBC surface absorption in comparison to the
controls. ISAT-10 values of 75.0, 55.0 and 40.0 ml/m /sec x 10' were obtained for the 20,
40 and 60 N/mm PC concrete respectively, with reductions of 14%, 18% and 50% noted for
the corresponding PC/PFA mixes. In contrast, average reductions in ISAT-10 values for the
TBC mixes were 63%, 67%) and 80% at each strength grade respectively. This trend
essentially mirrors that obtained for chloride resistance, as given in Figure 2.
2
2
2
2
2
It has been reported [11] that some aluminate phases in concrete may play a role in the
binding of chloride ions. Although the bulk AI2O3 content may be a relatively poor estimate
of the actual amount of chloride binding sites available, it is at least generally indicative.
Despite variations in total binder content existing between mixes, calculations indicated that
the quantity of AI2O3 (per kg/m ) in the majority of TBC mixes was not significantly
different than that in the PC/30% PFA controls and indeed in many cases was lower, in
particular for the SF mixes. This suggests that overall it is probably the improved
microstructure of TBC that has the dominant effect on increased chloride resistance.
3
CONCLUSIONS
1. In terms of the fresh properties examined, no practical difference existed between TBC,
PC and PC/PFA mixes. TBC was, however, very cohesive but easily compacted and
produced a high quality surface finish. The use of superplasticiser was found necessary
in all TBC mixes containing SF. TBC containing PC/PFA/GBS entrapped similar
quantities of air to PC and PC/PFA control mixes. All TBC containing SF entrapped on
average 30% less air than control mixes. TBC had a wide range of colours, ranging from
light grey to almost black, depending on the combinations of binder materials used.
2. When designed for equivalent 28-day strength, TBC exhibited on average 50% and 30%
lower strength than PC control concrete and 1 and 3 days. These differences reduced
with time, however, and the TBC strength results were on average 25% higher than the
PC control at 90 and 180 days. For optimum long-term strength development, PC
replacement levels of around 60% by mass were identified for TBC.
3. The results obtained from both the electrochemical ingress and penetration tests indicated
that the chloride resistance of TBC was significantly better than both the PC and PC/PFA
control mixes. The initial surface absorption of TBC was reduced in comparison to the
controls. Since there were only minor differences in bulk AI2O3 content, this suggests
that the chloride resistance of TBC is mainly the result of microstructural refinement. No
optimum replacement levels for PC or combinations of binder materials for chloride
resistance were found and it is recommended, therefore, that mix proportions are chosen
to maximise strength development (i.e. by selecting a PC replacement of around 60%).
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Ternary Binder Concrete
237
REFERENCES
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