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Concrete In Australia : March 2012
20 Concrete in Australia Vol 38 No 1 1.0 INTRODUCTION e cement industry in Australia has for a number of years been engaged in a program to reduce the level of greenhouse gas emissions embodied in its products. e potential introduction of a carbon tax, first mooted in 2007, provided further motivation for the industry to commence an investigation to increase the level of limestone mineral addition (LMA) above 5%. Concurrently with the testing carried out by the cement manufacturing companies a literature review was carried out on the international experience. is paper broadly examines the performance of concrete made with cements containing limestone mineral additions greater than 5% based on published international literature. In addition, the results obtained between 2007 and 2009 during the course of the Australian investigation have been included in the appropriate sections for comparison. 2.0 INTERNATIONAL HISTORY e incorporation of different amounts of limestone in the final cement product commenced in a number of countries (Hooton et al, 2007) well before EN197-1 (2000) was adopted. Europe in particular has a long history of limestone use, with Spain commencing in 1960 (Tennis et al, 2011), Germany in 1965 (Schmidt, 1992) where Heidelberg Cement produced limestone cement with a 20% addition, and France in the 1970s (Hooton et al, 2007). Other countries including South Africa in 1982 (SABS471-1971 amended 1982) and Canada in 1983 (CAN/CSA A5, 1983) adopted the use of limestone in cement quite early. e ENV197-1 (1992) standard allowed higher proportions of limestone, up to 35%, but accommodated this cement as a separate category called "Portland limestone cements" (PLC). New Zealand in 1991 permitted up to 15% in their Portland- limestone-filler cement (NZS 3125, 1991) and in 2010 amended the cement standard (NZS 3122, 2009) to allow up to 10% limestone mineral addition in the Portland and blended cements. 3.0 AUSTRALIAN HISTORY In 1991, the Australian cement standard "Portland and blended cements" (AS 3972-1991) allowed the inclusion of up to 5% mineral additions which could be limestone, fly ash or granulated iron blastfurnace slag or combinations of these materials. In 2007, the Cement Technical Committee of the Cement Concrete & Aggregates Australia (CCAA) commenced an investigation program to assess the impact of increasing the limestone mineral addition to 10%. Several trials were carried out independently at eight cement manufacturing plants and tested under laboratory conditions for compliance to AS 3972-1997. Once the results indicated that the cement capable of delivering parity performance with the existing Type GP cements, further field trials were carried out. e results of all the laboratory and field trials were collated by the CCAA and are reported in this article. Based on the data obtained, in 2010 a revised edition of AS 3972 was adopted with the following major changes: • e title was changed to "General purpose and blended cements". • e allowable mineral addition was increased to 7.5%. • Up to 5% of minor additional constituents (eg cement kiln dust) can be added. • General purpose limestone cement, Type GL, was added to the standard. • A maximum chloride content was included as a specified requirement. 4.0 EFFECTS ON CONCRETE PROPERTIES All of the cements used in the CCAA investigation between the second half of 2007 and the end of 2009 satisfied the Type GP requirements of AS 3972-2007, except the limestone mineral addition was greater than 5%. e limestone content of the trial cements varied between 8% and 13% compared to the "Control" Type GP cement in which the limestone content varied from 3.5% to 5%. e results obtained have been reported as percentage of control (either Type GP or Type SL) as each of the participating laboratories used local aggregates in their standard laboratory mix. e trends of the results have been compared to the results reported in the international literature. 4.1 Workability ere are conflicting reports in the literature on the effect of limestone on the workability of concrete. Matthews (1994) reported that the water/cement (w/c) ratio had to be increased by 0.01 for limestone additions of less than 5% and by Properties of concrete made with cement containing increased level of limestone addition: The Australian experience BT (Tom) Benn -- Technical Services Manager, Adelaide Brighton Cement WA (Tony) Thomas -- Chief Engineer, Concrete, Boral Construction Materials