Chloride Ion Ingress of Concrete the Influence of Increased Levels of Limestone Mineral Addition

Transcription

1 Chloride Ion Ingress of Concrete the Influence of Increased Levels of Limestone Mineral Addition B. Tom Benn 1, Daksh Baweja 2 and Julie E. Mills 3 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 , 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 (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.

2 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 (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 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 (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 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.

3 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 & ASTM C 150) Property Units Type GP (AS 3972) CEM I N (EN 197-1) CEM I N (EN 197-1) Type I (ASTM C 150) Mineral addition % 7.5 max 5 max 5 max 5 max Minor additional constituents % 5 % of mineral addition Considered a mineral addition not specified Initial setting time minutes Final setting time hours 6 not specified not specified 6.25 Soundness mm 5 (Le Chatelier) 10 (Le Chatelier) 10 (Le Chatelier) 0.80 (autoclave expansion) MgO % (in clinker) Chloride ion content % not specified SO 3 content % (C 3A 8%) 3.5 (C 3A 8%) Loss on ignition % not specified Insoluble residue % not specified days compressive MPa not specified not specified 10.0 not specified 3-days compressive MPa not specified not specified not specified 12.0 (50 mm cubes) 7-days compressive MPa 35.0 (ISO prisms) 16.0 (ISO prisms) not specified 19.0 (50 mm cubes) 28-days compressive MPa 45.0 (ISO prisms) (ISO prisms) (ISO prisms) 28.0 optional (50 mm cubes) 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 (5): The limestone must be a natural inorganic mineral material. It shall contain not less than 75% by mass of calcium oxide (CaO 3 ). If the CaO 3 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.

4 If the CaO 3 content is 80% or greater no additional testing is required. The Canadian Standard CSA A3001 (6) has a minimum limit on the CaO 3 of 75% in the limestone and ASTM C 150 (10) has a requirement of at least 70% by mass of the CaO 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 Tidal Splash and spray Coastal Basement exterior walls or transport tunnel liners below low tide. Liquid containing structures. Substructures and superstructures in tidal zone. Superstructures above high tide in the open sea. Land based structures in coastal area or superstructures above high tide in river estuary or body of water in coastal area. Permeation, diffusion and possibly wick action Capillary absorption and diffusion Capillary absorption and diffusion (also carbonation) 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.

5 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 Long term At constant temperature Affected by conductors in concrete Approximate duration Salt ponding AASHTO T259 Yes Yes No 90 days after curing and conditioning Bulk Diffusion NT Build 443 ASTM C 1556 Short term Rapid chloride penetration Electrical migration AASHTO T 277 ASTM C 1202 Rapid Migration NT Build 492 AASHTO TP 64 Resistivity Cores Wenner probe Pressure penetration Colorimetric chloride penetration Other Yes Yes No days after curing and conditioning No No Yes 6 hours Yes Yes Yes Depends on Voltage & Concrete Yes Yes Yes 8 hours No Yes Yes 30 minutes None quoted Yes Yes No Depends on pressure & concrete None quoted Yes Yes No Depends on concrete Sorptivity - Lab None quoted No Yes No 1 week including conditioning Sorptivity - field None quoted No Yes No 30 minutes Propan-2-ol counter diffusion None quoted No Yes No 14 days with thin paste samples Gas diffusion None quoted No Yes No 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 No No No Up to 4 days 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.

6 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 Cement Cement Fly ash w/c ratio limestone fineness % m 2 /kg kg/m 3 kg/m 3 C08/ C08/ C08/ C08/ C08/ C08/ C10/ C10/ C10/ C10/ C10/ C10/ C10/ C10/ C10/ CF10/ CF10/ CF10/ CF10/ CF10/ CF10/ CF10/ CF10/ CF10/ 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 The

7 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 Compressive 28 days Total charge passed mm MPa MPa MPa MPa Coulombs Coulombs Coulombs Jones & Moran 2008 (17) C08/ * C08/ * C08/ * C08/ * C08/ * C08/ * Gaboyo, Tang et al (18) C10/ C10/ C10/ C10/ C10/ C10/ C10/ C10/ C10/ Laudato, Patel et al (19) CF10/ CF10/ CF10/ CF10/ CF10/ CF10/ CF10/ CF10/ CF10/ 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.

8 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 % Fineness m 2 /kg Total cementitious kg/m Cement content ( 80%) kg/m Fly ash content ( 20%) kg/m w/c ratio day compressive strength MPa ASTM C at 30 days Coulombs 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 300 kg/m 3 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 Cement 70% Fly ash 30% Cement 70% Fly ash 30% Cement 70% Fly ash 20% Silica fume 8% Limestone % Fineness of cement m 2 /kg Total cementitious kg/m Cement content kg/m fly ash content kg/m Silica fume content kg/m 3 36 w/c ratio day compressive strength MPa ASTM C at 28 days Coulombs 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 In their report Hooton and Nokken (7) interpreting the results of Tsivilis and Batis et al.

9 (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 % Fineness m 2 /kg Cement content kg/m w/c ratio day compressive strength MPa ASTM C at 28 days Coulombs 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 Series B Series C Limestone % Fineness m 2 /kg Total cementitious kg/m Cement content kg/m Fly ash content kg/m Slag content kg/m w/c ratio day compressive strength MPa RCPT at 28 days Coulombs RCPT at 56 days Coulombs 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 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

10 investigated by determining if there any changes to the heat of hydration with time using the test method AS (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. References 1. Standards Association of Australia, General purpose and blended cements, (AS ), Standards Australia, 2010, Sydney. 2. NordTest, Concrete, Hardened: Accelerated chloride penetration, (NT Build 443), NordTest method, 1995, Espoo, Finland. 3. American Society for Testing and Materials, Standard Test Method for Electrical Indication of Concrete s Ability to Resist Chloride Ion Penetration, (ASTM C ), ASTM International, 2007, West Conshohocken, PA. 4. Standards Association of Australia, Portland and blended cements, (AS ), Standards Australia, 1991, Sydney. 5. European Committee for Standardization, Cement composition, specification and conformity criteria: Common cements, (EN 197-1), 2000, Brussels, Belgium. 6. Canadian Standards Association, Cementitious Materials for Use in Concrete, (CAN/CSA A ), CSA, 2008, Mississauga, Ontario, Canada. 7. Hooton, R.D., Nokken, M. et al., Portland-Limestone Cement: State-of-the-Art Report and Gap Analysis for CSA A 3000, Report prepared for St. Lawrence Cement, Cement Association of Canada, 2007, Ottawa, Ontario, Canada. 8. Canadian Standards Association, Portland cement, (CAN/CSA-A5, 1983), CSA, 1983, Mississauga, Ontario, Canada. 9. South African Bureau of Standards, Portland Cement (ordinary, rapid-hardening and sulphate resisting), (SABS , as amended 1973, 1981 & 1982), SABS, 1982, Pretoria, South Africa. 10. American Society for Testing and Materials, Standard Specification for Portland Cement, (ASTM C )", ASTM International, 2005, West Conshohocken, PA. 11. Neville, A.M., Properties of Concrete, 4 th Edition, Addison Wesley Longman Ltd, Harlow, England, Daugherty, E.D., & Funnel, J.E., The Incorporation of Low Levels of By-Products in Portland/Cement and the Effects on Cement Quality, Cement, Concrete and Aggregates, American Society for Testing and Materials, Philadelphia, Pennsylvania, USA, vol. 5, no Adaska, W.S., & Taubert, D.S., Proceedings of IEEE/PCA 50 th Cement Industry Technical Conference: Beneficial uses of Cement Kiln Dust, Miami, Florida, Hamilton, H.R., Boyd, A., et al., Permeability of Concrete Comparison of Conductivity and Diffusion Methods, UF Project No: , Department of Civil and Coastal Eng., University of Florida, Cement Concrete & Aggregates Australia, Report, Chloride Resistance of Concrete, Cement Concrete & Aggregates Australia (CCAA), 2009, Sydney, Australia.

11 16. Stanish, K.D., Hooton, R.D., et al., Testing the Chloride Penetration Resistance of Concrete: A Literature Review, Federal Highway Administration (FHWA), Contract DTFJ61-97-R-00022, 1997, McLean, Virginia, USA. 17. Jones, A., & Moran, J., The Impact of Increasing Limestone, the Preferred Mineral Addition, from 5% to 10% on the Properties of Type GP Cement in Concrete, Final year Civil Engineering Research Investigation Report, School of Natural and Built Environments, University of South Australia, 2008, Adelaide, Australia. Unpublished. 18. Gaboyo, E., Tang, et al., The effect of different Limestone Mineral Addition Levels in Type GP Cement on the Compressive Strength of Concrete, Final year Civil Engineering Research Investigation Report, School of Natural and Built Environments, University of South Australia, 2010, Adelaide, Australia. Unpublished. 19. Laudato, C., Patel, K., et al., The effect of Limestone Mineral Addition in Type GP Cement when used in conjunction with Fly Ash", Final year Civil Engineering Research Investigation Report, School of Natural and Built Environments, University of South Australia, 2010, Adelaide, Australia. Unpublished. 20. Tennis, P.D., Thomas, M.D.A., et al., State-of-the-Art Report on Use of Limestone in Cements at Levels of up to 15%, 2011, SN3148, Portland Cement Association, Skokie, Illinois, USA. 21. Tsivilis, S., Batis, G., et al., Properties and behavior of limestone cement concrete and mortar, 2000, Cement and Concrete Research, vol. 30 no. 10, pp Thomas, M.D.A., Cail, K., et al., Equivalent Performance with Half the Clinker Content using PLC and SCM, 2010 Sustainability Conference, National Ready Mixed Concrete Association, 2010b, Tempe, Arizona, USA. 23. Standards Association of Australia, Methods for Testing Portland and Blended Cements Heat of Hydration of Portland Cement (AS ), Standards Australia, 2010, Sydney.