Chloride Ion Ingress of Concrete – the Influence of Increased
Levels of Limestone Mineral Addition
1
2
3
B. Tom Benn , Daksh Baweja and Julie E. Mills
1
Lecturer, University of South Australia
2
Associate Professor, University of Technology Sydney
3
Professor of Engineering Education, University of South Australia
Abstract: This paper presents preliminary results of a research program that investigates chloride
ion ingress of concrete made with cement containing increased levels of limestone mineral addition.
Although the research program considers mineral additions based on limestone plus cement kiln dust,
this paper concentrates on the limestone mineral addition. For many years the cement industry has
been involved in test programs to reduce greenhouse gas levels and one method is to increase the
level of mineral addition, thus reducing the amount of clinker required to satisfy the country’s cement
demand.
The Australian cement standard, AS 3972-2010, permits a maximum mineral addition level of 7.5%
and further development work is underway to increase mineral addition above this level. The aim of
this research is to investigate the effect that levels of limestone mineral addition above 7.5% will have
on the chloride ion penetration into concrete. This paper discusses the preliminary results of chloride
penetration as measured by the Rapid Chloride Penetrability Test (RCPT) – ASTM C 1202, on a
range of concrete mixes made with both cement only and cement plus supplementary cementitious
materials. Some conclusions have been drawn and an outline of the future work is provided with
specific reference to mineral additions and minor additional constituents.
Keywords: Chloride ingress, concrete durability, limestone mineral addition, cement kiln dust.
1.
Introduction
This paper presents preliminary results of a research program that is investigating if increasing the
level of mineral addition (limestone in combination with cement kiln dust (CKD)), in Type GP cement
as defined in AS 3972-2010 (1) is likely to increase the rate of chloride ingress into concrete. The
research also investigates the effect that the use of fly ash and ground granulated blastfurnace slag,
when used as a partial replacement for the cement containing higher levels (i.e. >5%) of limestone
mineral additions plus CKD, will have on chloride penetration. The positive effect of fly ash and slag on
the ingress of chloride in concrete has been well documented by many researchers but there is little or
no published data on whether the combination of limestone and CKD is likely to alter this effect.
For many years the Australian cement industry has been involved in ongoing test programs to reduce
greenhouse gas levels. One method to achieve this goal is to increase the level of mineral addition,
thus reducing the amount of cement clinker needed to be manufactured in order to supply the volume
of cement required for the construction and building industries. Additional environmental benefits can
be achieved by incorporating minor additional constituents, such as cement kiln dust, as part of the
mineral addition, which in turn reduces the amount of kiln dust being sent to land fill.
The revision to Australian cement standard AS 3972 – General purpose and blended cements (1) in
2010, permitted the maximum level of mineral addition to increase from 5% to 7.5%. In addition two
other changes were incorporated:
 The use of minor additional constituents, defined as ‘specially selected, inorganic natural mineral
materials, or inorganic mineral materials derived from the clinker production process’ (1) up to a
maximum of 5 % of the mineral addition.
 The control of the chloride level in all cements was set at a maximum of 0.10 percent.
The paper considers briefly the background to the 2010 changes to the AS 3972 standard, the
materials used in the investigations and their influence on concrete. The paper discusses the various
test methods used to determine chloride ingress including the NordTest method: NT Build 443 –
Concrete, Hardened: Accelerated Chloride Penetration (2) and the American Society for Testing and
Materials (ASTM) method: ASTM C 1202 – Electrical Indication of Concrete’s Ability to Resist Chloride
Ion Penetration (3), that are the methods that have been selected for this research.
The results of the chloride penetration of concrete, based at this early stage of the research on
limestone additions only, using the ASTM method (3), are assessed and compared to published data
from both local and international sources. The next phase of the research, on the chloride ingress into
concrete, will concentrate in more detail on mineral additions made up of limestone plus CKD and on
the NT Build 443 test method to determine the chloride diffusion. In addition the effect of the partial
replacement of the cement by fly ash and slag will also be considered. To establish if the limestone
plus CKD addition is having any influence on the performance of the supplementary cementitious
materials (SCM) in the concrete, the hydration rate of the cementitious material will was also be
investigated during the course of the research program.
2.
Background
In 1991 the Australian cement standard, AS 3972 – Portland and blended cements (4) allowed the
inclusion of up to five percent mineral additions, which were defined as limestone, fly ash or ground
granulated iron blastfurnace slag or combinations of these materials. In 2007 the Cement Technical
Committee of Cement Concrete & Aggregates Australia (CCAA) commenced an investigation to
assess the impact of increasing the limestone mineral addition to 10%.
The results obtained culminated in 2010 with a comprehensive revision of the cement standard,
published as AS 3972 – General purpose and blended cements (1). In this revision the allowable
mineral addition was increased from 5% to 7.5% for all cement types in Australia. In addition, cement
kiln dust, defined as a ‘minor additional constituent’ was allowed at levels up to a maximum of five
percent of the total mineral addition. Furthermore the revised standard introduced a new type of
cement designated as Type GL, General purpose limestone cement, defined as cement with
limestone content of between 8% and 20%. This is different to other international practices. In the
European standard EN 197-1 (5), Portland limestone cements have limestone additions of between
5% and 20% or 21% and 35% and are called CEM II/A or CEM II/B respectively. The Canadian
cement standard, CSA A 3001 (6), designated this type of cement as Portland limestone cement
(PLC) with a maximum of 15% limestone.
Currently, under the auspices of the BD-10 Cement Committee of the Australian Standards
Organisation, a working group is undertaking an industry wide project to produce technical data on
fresh, hardened and durability properties of concrete made with cements containing limestone
additions of between 7.5% and 12.5%. The aim of the project is to support a proposal for an increase
in the limestone addition and it is expected that this work will be completed during the second half of
2013.
The paper will briefly outline the materials used and proposed test methods, it then will discuss the
data relating to the chloride ingress data obtained during the initial phase of the research program as
well as data from the Australian cement industry investigations and published international data.
3.
Materials
3.1
Cement
The incorporation of mineral additions, including limestone, into the Australia standard in 1991 (4),
was somewhat later than many other countries including Europe, where limestone had been used
from as early as 1965 (7). Limestone additions were allowed in Canada from 1983 (8) and South
Africa (9) from 1982, but the USA did not allow limestone additions until 2005 (10). The ENV 197-1 (5)
standard permits limestone additions of up to 35%, but accommodates these cements as a separate
category called Portland limestone cements.
The cement properties detailed in Table 1 below indicate that the AS 3972 cement (1), Type GP,
previously known as Ordinary or Normal Portland cement, is the equivalent to EN 197-1, CEM I 32.5N
(5) and ASTM C150 Type I cement (10). The CEM I 42.5N cement although defined by EN 197-1 as
an ordinary early strength cement, is more closely aligned to the AS 3972 Type HE cement and the
ATSM C 150 Type III cement. It must be noted that the Australian standard is now a performance
based standard while the ASTM is prescriptive and the EN standard can be considered somewhere inbetween.
3.2
Supplementary Cementitious Materials
Fly ash and ground granulated blastfurnace slag (GGBFS) are well established as supplementary
cementitious materials and their use in concrete has several advantages (11) including:
 Improved workability due to their influence on fine aggregate grading.
 Better cohesiveness and pumpability.



Significant and continuous compressive strength growth after 28-days.
Reduction in the potential for alkali silica reaction if there are reactive aggregates in the concrete.
Reduction in concrete drying shrinkage with fly ash and potentially reduced shrinkage with
GGBFS, which is dependent on mix proportions.
Reduced heat of hydration.
Reduced permeability and chloride ion penetration.
Better resistance to chemical attack, including sulfate attack.



Table 1: Comparison of Cement Requirements from Various Standards (AS 3792; EN 197-1 &
ASTM C 150)
Property
Units
Type GP
(AS 3972)
7.5 max
CEM I - 32.5N
(EN 197-1)
5 max
Mineral addition
%
Minor additional
constituents
Initial setting time
%
CEM I - 42.5N
(EN 197-1)
5 max
Considered a mineral addition
not specified
minutes
 5 % of mineral
addition
 45
 75
 75
 45
Final setting time
hours
6
not specified
not specified
 6.25
Soundness
mm
MgO
%
 10
(Le Chatelier)
 5.0
 10
(Le Chatelier)
 5.0
 0.80
(autoclave expansion)
 6.0
Chloride ion content
%
5
(Le Chatelier)
 4.5
(in clinker)
 0.10
 0.10
 0.10
not specified
SO3 content
%
 3.5
 3.5
 3.5
Loss on ignition
%
not specified
 5.0
 5.0
 3.0 (C3A  8%)
 3.5 (C3A  8%)
 3.0
Insoluble residue
%
not specified
 3.5
 3.5
 0.75
2-days compressive
MPa
not specified
not specified
 10.0
not specified
3-days compressive
MPa
not specified
not specified
not specified
7-days compressive
MPa
MPa
 16.0
(ISO prisms)
 32.5  52.5
(ISO prisms)
not specified
28-days compressive
 35.0
(ISO prisms)
 45.0
(ISO prisms)
12.0
(50 mm cubes)
19.0
(50 mm cubes)
28.0 optional
(50 mm cubes)
 42.5  62.5
(ISO prisms)
Type I
(ASTM C 150)
5 max
However, there are some important disadvantages (11) to be kept in mind when using these SCM:
 Longer concrete set times depending on the level of cement replacement.
 Lower early strengths that may affect formwork stripping times.
 Entrainment of air may be more difficult depending on the carbon content of fly ash.
 Undesired changes in fresh concrete properties where proper proportioning of SCM in concrete is
not carried out.
The advantages of improved impermeability and resistance to chemical attack, which are obtained
when using SCM, are of particular interest in this research.
3.3
Limestone
Fly ash and GGBFS are also used as mineral additions but the most common material is limestone
because it is the most economical and easiest material for the majority of cement manufacturers to
access. The quality of the limestone used for mineral addition at the cement mill is specified by the
various national cement standards. In AS 3972 (1), limestone must meet the following requirements,
which are very similar to European standard EN 197-1 (5):



The limestone must be a natural inorganic mineral material.
It shall contain not less than 75% by mass of calcium oxide (CaO3).
If the CaO3 content is between 75% and 80% the material is acceptable provided:
 The clay content determined using the methylene blue test is less than 1.20%.
 The total organic carbon content does not exceed 0.50% by mass.

If the CaO3 content is 80% or greater no additional testing is required.
The Canadian Standard CSA A3001 (6) has a minimum limit on the CaO3 of 75% in the limestone and
ASTM C 150 (10) has a requirement of at least 70% by mass of the CaO3.
3.4
Cement Kiln Dust
The dust created and extracted from the kiln during the burning process is often referred to as cement
kiln dust, but is also sometimes called by-pass dust. This can constitute as much as 20% by weight of
the clinker, but is typically between 7% and 15% in dry kiln operations. The two designations noted
above usually refer to where in the clinker manufacturing process the material is collected. The
collection points are usually exhaust gas dust control devices such as cyclones, electrostatic
precipitators and bag-house dust collectors. CKD is normally removed because it can cause one or
more of the following problems:
 Build-ups and rings in the kiln and/or preheater, due to a build-up of chlorine, sulphur and alkalis.
 Abnormal setting characteristics and strength development in the cement.
 High chloride content in the cement contributing to potentially increased chloride levels in
concrete.
 Cracking of concrete, due to an increased propensity for alkali silica reaction if reactive
aggregates are used in combination with cement containing high alkali levels.
CKD can be returned to the kiln as raw feed or be added to cement either at the milling stage or
blended with the cement after milling, provided regular testing indicates that it does not contain high
levels of chlorides and/or alkalis. Daugherty and Funnell (12) showed that up to 10% of interground
CKD had little influence on concrete set times and shrinkage. They however found that effects on
strength were variable due to the variability in the dust composition. Bhatty, cited by Adaska (13),
reported that where CKD was used to replace clinker the effect was decreased strength, an increased
water demand to maintain workability and retarded setting times. The drop in strength was attributed
to the alkalis in the CKD. However, according to Bhatty, the negative effect of the alkalis was negated
by using fly ash and/or slag.
4.
Chloride Ingress
4.1
Mechanism
Hamilton, Boyd et al. (14) describe essentially four modes of chloride ion transport through concrete,
but often more than one mechanism is involved at any one time, as summarised in Table 2.
Table 2: Chloride ion transport modes for various exposures (from 15)
Exposure
Type of structure
Primary chloride transport mode
Submerged
Substructure below low tide
Diffusion
Basement exterior walls or transport tunnel
liners below low tide. Liquid containing
structures.
Permeation, diffusion and possibly wick
action
Tidal
Substructures and superstructures in tidal
zone.
Capillary absorption and diffusion
Splash and spray
Superstructures above high tide in the
open sea.
Capillary absorption and diffusion (also
carbonation)
Coastal
Land based structures in coastal area or
superstructures above high tide in river
estuary or body of water in coastal area.
Capillary absorption (also carbonation)
The main modes as described in various publications (14, 15 & 16) are:
 Diffusion – transfer of mass free ions in the pore solution from high concentration to low
concentration regions.
 Capillary absorption – when moisture, perhaps laden with chloride ions, encounters the dry
surface of the concrete, it will be drawn into the pores by capillary suction. This often happens
where wetting and drying cycles are present.


Evaporative transport (also called wicking) – similar to absorption but where one surface is airexposed causing the moisture containing the chloride ions to be drawn from the wet surface to the
dry surface.
Hydrostatic pressure or permeation – where the hydraulic pressure on one side of the concrete
forces the liquid, containing the chloride ions, through the concrete matrix
Of these transport mechanisms diffusion, which is controlled by Fick’s Laws (16), is considered to be
the principal method of chloride ingress into concrete.
4.2
Test methods
Table 3, adapted from Standish and Hooton et al. (16), summarises the various methods available to
measure chloride penetration of concrete. The table also includes a summary of some aspects to be
considered when using a particular test, for example the duration and whether it measures the
chloride movement directly or indirectly.
Table 3: Summary of chloride penetration test methods
Test Method
Standard No.
Considers
chloride ion
movement
At constant
temperature
Affected by
conductors in
concrete
Approximate
duration
Long term
Salt ponding
AASHTO T259
Yes
Yes
No
90 days after
curing and
conditioning
40 – 120 days
after curing and
conditioning
Bulk Diffusion
NT Build 443
ASTM C 1556
Yes
Yes
No
Rapid chloride
penetration
Electrical
migration
AASHTO T 277
ASTM C 1202
No
No
Yes
6 hours
Yes
Yes
Yes
Rapid Migration
NT Build 492
AASHTO TP 64
Cores
Wenner probe
None quoted
Yes
Yes
Yes
Depends on
Voltage &
Concrete
8 hours
No
Yes
Yes
30 minutes
Yes
Yes
No
Colorimetric
chloride
penetration
Other
None quoted
Yes
Yes
No
Depends on
pressure &
concrete
Depends on
concrete
Sorptivity - Lab
None quoted
No
Yes
No
Sorptivity - field
None quoted
No
Yes
No
Propan-2-ol
counter diffusion
None quoted
No
Yes
No
Gas diffusion
None quoted
No
Yes
No
14 days with
thin paste
samples
2 – 3 hours
Impressed
current
Initial surface
absorption
Volume of
permeable voids
None quoted
Yes
Yes
Yes
Up to 120 days
BS 1881 part 5
No
Yes
No
Up to 2 hours
ASTM C 642
AS 1012.21
No
No
No
Up to 4 days
Short term
Resistivity
Pressure
penetration
1 week including
conditioning
30 minutes
Based on both the availability of equipment and international acceptance of tests method this research
will use the NT Build 443 (2) and ASTM C 1202 (3) to measure the chloride penetration of concrete.
The results detailed in the next section are of data obtained with increased levels of limestone mineral
addition only, using the ASTM C 1202 (3) test. Specimens are currently being exposed to the required
sodium chloride (NaCl) solution as part of the NT Build 443 (2) test.
5.
Test Methodology
At this stage of the research the results are based on samples made with the current cement
containing approximately 4% limestone mineral addition and samples made with increased levels of
limestone mineral additions. The research projects carried out at the University of South Australia
(UniSA) in 2008 and 2010 were carried out in parallel with the work being carried out at the time by the
Cement Industry. The aim of the projects was to assess the hardened properties, including the
resistance to chloride ingress as measured by the ASTM C 1202 method. Various grades of concrete
were made and tested and even though concrete mixes with w/c ratios of greater than 0.45 are not
used for durable concrete, the ASTM C 1202 test was carried out on all the mixes for comparative
purposes and the results incorporated in the paper.
In all of the projects dolomitic coarse and natural fine aggregates were sourced from a large local premix concrete supplier as these materials are typical of the materials used in the Adelaide region. A
normal water reducing admixture, Pozzolith 370, was used in all mixes. The control cement was the
local Type GP cement with limestone mineral addition typically around 4% and the trial cement was
cement manufactured for the Cement Industry trials with nominal limestone mineral additions of 6%
and 10% respectively as detailed in Table 4.
Table 4: Details of laboratory mixes
Mix code
Sample No
Nominal
limestone
%
4
10
4
10
4
10
Cement
fineness
2
m /kg
393
445
393
445
393
445
Cement
3
Fly ash
w/c ratio
3
kg/m
250
250
300
300
500
500
kg/m
-
0.74
0.71
0.61
0.60
0.40
0.40
C08/250-04
C08/250-10
C08/300-04
C08/300-10
C08/500-04
C08/500-10
7800
8387
7741
8373
7806
8395
C10/235-04
C10/235-06
C10/235-10
C10/285-04
C10/285-06
C10/285-10
C10/480-04
C10/480-06
C10/480-10
9271
9299
9312
9270
9300
9311
9269
9301
9313
4
6.5
10
4
6.5
10
4
6.5
10
435
395
420
435
395
420
435
395
420
235
235
235
285
285
285
480
480
480
-
0.83
0.84
0.87
0.67
0.65
0.65
0.42
0.41
0.42
CF10/235-04
CF10/235-06
CF10/235-10
CF10/285-04
CF10/285-06
CF10/285-10
CF10/480-04
CF10/480-06
CF10/480-10
9350
9403
9425
9351
9404
9426
9352
9405
9427
4
6.5
10
4
6.5
10
4
6.5
10
435
395
420
435
395
420
435
395
420
190
190
190
230
230
230
385
285
385
45
45
45
55
55
55
95
95
95
0.81
0.76
0.77
0.62
0.59
0.61
0.40
0.40
0.41
In the work by Jones and Moran (17) the hardened properties measured were the compressive
strength up to 56 days, the flexural strength at 7 and 28 days, the concrete shrinkage up to 56 days,
the water sorptivity and the potential for chloride ingress at 84 days. In the projects carried out by
Gaboyo and Tang et al. (18) and Laudato and Patel et al. (19) the compressive strength up to 56
days, the concrete shrinkage to 56 days, the water sorptivity and the potential for chloride ingress at
28 days was determined. In this paper only the slump, compressive strength at 28 days and the ASTM
C 1202 results are reported.
6.
Results and analysis
The results from the UniSA research projects are shown in Table 5, with the compressive strengths
being the average of two or three specimens as shown and the ASTM C 1202 results the average of
two samples. The ASTM C 1202 results of concrete with w/c ratios of greater than 0.45 have been
included in the paper to compare the performance of cements containing different limestone additions
even though durable concrete will normally be specified with w/c ratio not greater than 0.45. The
samples tested by Jones and Moran (17) were subject to the ASTM C 1202 test at 84 days as the test
was only included as part of the research late in the program, however the results do provide a
valuable comparison with the results for the 2010 research programs of Gaboyo, Tang et al. (18) and
Laudato, Patel et al. (19) that were tested at 28 days. All the ASTM C 1202 results shown in Table 5
were within the 42% precision for a single operator testing two samples made from the same materials
with the same dimensions.
Table 5: Results from UniSA research projects
Mix code
Sample
No
w/c
ratio
Slump
mm
Jones & Moran 2008 (17)
C08/250-04
7800
0.74
C08/250-10
8387
0.71
C08/300-04
7741
0.61
C08/300-10
8373
0.60
C08/500-04
7806
0.40
C08/500-10
8395
0.40
Gaboyo, Tang et al. 2010 (18)
C10/235-04
9271
0.83
C10/235-06
9299
0.84
C10/235-10
9312
0.87
C10/285-04
9270
0.67
C10/285-06
9300
0.65
C10/285-10
9311
0.65
C10/480-04
9269
0.42
C10/480-06
9301
0.41
C10/480-10
9313
0.42
Laudato, Patel et al. 2010 (19)
CF10/235-04
9350
0.81
CF10/235-06
9403
0.76
CF10/235-10
9425
0.77
CF10/285-04
9351
0.62
CF10/285-06
9404
0.59
CF10/285-10
9426
0.61
CF10/480-04
9352
0.40
CF10/480-06
9405
0.40
CF10/480-10
9427
0.41
Compressive strength
@ 28 days
MPa
MPa
MPa
MPa
Total charge passed
Coulombs
Coulombs
Coulombs
90
80
85
80
80
85
28.5
30.5
39.5
34.0
61.0
62.0
28.5
30.5
39.0
40.0
61.0
64.0
28.5
31.0
37.5
40.0
60.5
63.0
28.5
30.5
38.5
38.0
61.0
63.0
5155
5303
4348
5981
3246
3920
5204
5983
4217
5086
3060
3575
5180*
5643*
4283*
5534*
3153*
3748*
80
75
75
80
70
70
90
75
75
24.0
23.0
20.5
33.5
35.0
33.0
53.5
56.0
53.5
25.0
22.5
20.5
34.0
36.5
34.0
53.0
56.0
52.0
-
24.5
23.0
20.5
34.0
36.0
33.5
53.0
56.0
53.0
8758
10488
10326
4576
6901
6646
5058
6093
6548
3189†
9494
12631
6300
7926
7636
5026
6150
6652
8758
9991
11479
5438
7414
7141
5042
6122
6600
80
70
70
80
80
75
70
90
90
23.0
23.0
24.5
35.5
34.5
38.0
59.5
58.0
57.5
23.0
22.5
25.0
35.5
34.0
37.5
59.0
60.0
59.0
-
23.0
23.0
25.0
35.5
34.0
38.0
59.5
59.0
58.5
4980
6500
5235
5251
5242
4375
2985
2929
2671
5676
5259
4921
4188
6057
4359
2747
2955
2912
5328
5880
5078
4720
5650
4367
2866
2942
2792
NOTES: 1. * Indicates that the ASTM C 1202 test was carried out at 84 days
2. All other ASTM C 1202 test were carried out at 28 days
3. † Result rejected as typically too low for the grade of concrete
When considering the results of the cement only mixes the total charge passing increased as the
limestone mineral addition increased even up to 84 days of laboratory curing. The total charge
recorded after 84 days of curing was significantly lower than after 28 days of curing for all w/c ratios.
However, it was evident that where the w/c ratio was less than 0.45 the total charge was less than
4,000 Coulombs, putting those specimens into the moderate category for chloride ion penetrability as
defined by ASTM C 1202 (3) and indicating, as stated in the test method in Clause 4.4, that curing can
affect the results. All specimens where the w/c ratio was greater than 0.45 fell into the high range
(i.e. >4,000 Coulombs) of chloride ion penetrability, irrespective of whether the binder was cement
only or cement with 20% fly ash replacement.
Where the concrete was made with a 20% fly ash replacement of the cement the total charge passing
at 28 days was significantly lower than for the samples made with cement only, at the same age, for
all levels of limestone mineral addition. The charge transfers recorded for the former samples were
similar to those measured for the cement only mixes at 84 days, indicating again that curing can affect
the results. The charge passing the specimens containing 20% fly ash increased in the specimens
with 6% mineral addition, but was lower at the 10% limestone mineral addition level. This according to
Tennis and Thomas et al. (20) is due to the additional nucleation sites that limestone produces which
in turn promotes hydration products. The increase in hydration products will reduce the penetrability of
the concrete.
A statistical analysis based on the two tail t-test, normally used for a small number of samples,
indicated that there was no difference, at the 95% level of confidence, between the samples made
with 4% limestone mineral addition and the samples made with increased levels of mineral addition.
The t-test however did indicate that where the w/c ratio was less than 0.45, the binder was cement
only and only 28 days of curing had been achieved there was a statistical difference, at the 95% level
of confidence, between the 4% limestone mineral addition level and the higher mineral addition levels
up to 10%.
Table 6: Comparison of cement only and cement/fly ash mixes containing 10% limestone
addition to resist chloride ingress
Limestone
%
10
10
10
10
m /kg
445
410
445
410
3
300
300
300
300
3
300
300
240
240
60
60
2
Fineness
Total cementitious
kg/m
Cement content (≈ 80%)
kg/m
3
Fly ash content (≈ 20%)
kg/m
w/c ratio
0.62
0.62
0.58
0.56
28-day compressive strength
MPa
37.0
35.0
38.5
39.0
ASTM C 1202 - at 30 days
Coulombs
8143
8505
3995
4139
The results in Table 6 show the ASTM C 1202 test data generated from mixes made in the Adelaide
Brighton Cement laboratory, for submission to the Australian Standards committee, as part of the
initial Cement Industry investigation. A standard laboratory mix with a cementitious content of
3
300 kg/m was used. These results at w/c ratios of greater than 0.45 indicated a significant difference
between the concrete, with similar 28-day compressive strengths, made with cement only and the
concrete where the cement was partially replaced with 20% fly ash. These results confirm the trend
found between the cement only and cement and fly ash mixes tested in the investigations, carried out
at the University of South Australia, and shown in Table 5.
Table 7: Comparison of chloride penetration in mixes containing fly ash and silica fume
Mix details
Limestone
%
5
10
Cement 70%
Fly ash 20%
Silica fume 8%
10
Fineness of cement
m /kg
379
408
408
3
450
450
450
3
315
315
324
3
135
135
90
Total cementitious
Cement 70%
Fly ash 30%
2
kg/m
Cement content
kg/m
fly ash content
kg/m
Silica fume content
Cement 70%
Fly ash 30%
3
kg/m
w/c ratio
36
0.40
0.40
0.40
28-day compressive strength
MPa
57.5
54.0
52.0
ASTM C 1202 - at 28 days
Coulombs
1312
1472
2256
Recent trials carried out on behalf of the BD-10 working group, using cement samples from Adelaide
Brighton Cement, generated the results shown in Table 7. The mixes were based on proportions
considered, by the concrete industry, to be durable concrete mixes. The results indicate that there is
no significant difference between a mix made with up to a nominal 5% limestone and a mix made with
10% limestone. But where silica fume was included in the mix, there was a significant difference in the
Coulombs measured. This is not unexpected considering the effect silica fume has on the density of
the matrix of concrete, which is why silica fume is seldom used in concrete used where cathodic
protection is installed.
The results generated in the testing carried out at UniSA and on behalf of the Australian Cement
Industry are compared to results shown in Table 8, based on data published by Tsivilis and Batis et al.
(21) in 2000. In their report Hooton and Nokken (7) interpreting the results of Tsivilis and Batis et al.
(21) stated that there was ‘little significant impact due to increasing limestone content up to 15% to
20%. The mix with 35% limestone had a higher RCPT (3) value despite being cast with a lower w/c,
indicating that permeability increased at this level of limestone’.
Table 8: Effect of Limestone Additions on 28-day strength and charged passed (data from 21)
Limestone
%
2
Fineness
m /kg
3
Cement content
kg/m
w/c ratio
0
10
15
20
35
260
340
366
470
530
270
270
270
330
330
0.70
0.70
0.70
0.70
0.62
28-day compressive strength
MPa
31.9
27.4
27.3
28.0
26.6
ASTM C 1202 - at 28 days
Coulombs
6100
5800
6000
6400
6600
Thomas and Cail et al. (22), as cited by Tennis and Thomas et al. (20), generated the data shown in
Table 9, on the strength and durability in a series of three concrete mixes, Series A has not been
shown in Table 9 as no durability data was listed. The mixes were made with Portland cement (PC) at
4% and Portland limestone cement (PLC) at 12% limestone respectively. Based on results of the
ASTM C 1202 (3) Tennis and Thomas et al. (20) stated that the w/c ratio, the age of test and the
amount of SCM used can have a major impact on the permeability but that the impact of up to 12%
limestone mineral addition in the cement is not significant.
Table 9: Test Results for Concrete Produced with PC and PLC (adapted from table in 20)
Mix details
Limestone
Series B
%
2
Series C
4
12
4
12
4
12
4
12
Fineness
m /kg
380
500
380
500
380
500
380
500
Total cementitious
kg/m
3
354
358
355
356
358
358
409
413
3
345
358
230
231
286
287
409
413
72
71
125
125
Cement content
kg/m
3
Fly ash content
kg/m
Slag content
kg/m
3
w/c ratio
0.45
0.45
0.45
0.45
0.45
0.45
0.40
0.40
28-day compressive strength
MPa
39.4
44.8
44.9
50.4
43.4
43.6
54.6
57.3
RCPT 1202 - at 28 days
Coulombs
2610
2571
1016
925
1184
1433
2017
2048
RCPT 1202 - at 56 days
Coulombs
2344
2354
807
708
639
678
1716
1900
The interpretations given to the data in Table 8 and Table 9, by Tsivilis and Batis et al. (21) and
Thomas and Cail et al. (22) respectively, correlate with the findings of the Australian data detailed in
Tables 5, 6 and 7.
7.
Conclusions
At this early stage of the research it is clear that increasing the limestone mineral addition from around
the 5% limit to 10% will not adversely affect the performance of concrete with respect to chloride ion
penetration into the concrete as measured by the ASTM C1202 method. It is also clear that the use of
SCM will significantly improve the resistance of concrete to chloride ingress even where higher levels
of limestone mineral addition are present in the region of 10% by mass of cement, a value which is
higher than the current Australian Standard limit of 7.5% by mass of binder.
8.
Future work
Specimens to be assessed in the next phase of the research will be made with cement containing
limestone plus CKD as mineral addition and with cement partially replaced by fly ash and GGBFS.
The ability of these specimens to resist the ingress of chlorides will be assessed at various ages up to
and including two years using both the NT Build 443 (2) and ASTM C 1202 (3) test methods. The
research program will also include mathematical modelling of the early age data and will compare the
predicted penetration to actual chloride penetration measurements obtained on specimens that will be
exposed to the standard chloride solution for up to two years. In addition the influence of the mineral
addition, based on the combination of limestone and CKD, on the hydration of the cement will also be
investigated by determining if there any changes to the heat of hydration with time using the test
method AS 2350.7 (23).
9.
Acknowledgements
Mr Michael Miller of Adelaide Brighton Cement Ltd is acknowledged for ongoing support and allowing
the use of data generated during trials at Adelaide Brighton Cement in this paper.
The Cement Concrete and Aggregates Australia are acknowledged for allowing the use of data
generated during the Cement Industry investigations being used to support the setting of new limits for
limestone inclusion into cements.
The students of the University of South Australia are acknowledged for some of the data used in the
paper from their final year research projects under the supervision of the first author.
10.
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