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Concrete In Australia : March 2012
38 Concrete in Australia Vol 38 No 1 suitable for precast concrete construction. Further studies of AAS concrete for compatibility for various admixtures (Bakharev et al, 2000), and long term durability against various attacks, such as alkali aggregate reaction (Bakharev et al, 2001b), sulfate attack (Bakharev et al, 2002) and carbonation (Bakharev et al, 2001c) ensure that AAS concrete is a viable alternative to the conventional Portland cement based concrete. e primary difference between geopolymer concrete and OPC concrete is its binder. e geopolymer binder is synthesised by alkali activation of aluminosilicate raw materials, which are transformed into reaction product by polymerisation in a high pH environment and hydrothermal conditions at relatively low temperatures (up to 120 °C). e reaction product is a polymer incorporating Al, Si and O, which is chemically very different from the hardened Portland cement which is calcium silicate hydrates (C-S-H) and calcium hydroxides. is difference in chemical structure gives geopolymer certain advantages over its OPC counterpart, such as a better strength performance when geopolymer materials are exposed to fire as seen in Figure 6 (Kong & Sanjayan, 2007, 2008, 2010; and Pan et al, 2009). Geopolymer also possesses excellent resistance to acid environments, similar to alkali activated slag concrete (Bakharev et al, 2003; Bakharev, 2005). is provides technical advantages in applications such as sewer pipes, dairy floors and other acid industrial applications where the conventional Portland cement concrete has long term durability problems because it does not possess sufficient acid resistance. High performance concrete made from Portland cement concrete suffer from explosive spalling when exposed to accidental fire (Sanjayan & Stocks, 1993). e widely suggested reason for this phenomenon is the high steam pressure development in the low permeable environment of high performance concrete. However, it has been found that the brittleness of the material (high performance concrete) and thermal incompatibilities between aggregate and paste also contribute to the spalling (Kong & Sanjayan, 2010). Geopolymer becomes a highly flexible material at a temperature around 700 °C, which allows the material to accommodate large strains without fracturing (Pan & Sanjayan, 2010). Further, hardened Portland cement pastes (C-S-H) dehydrate and disintegrate at high temperatures (>200 °C), whereas geopolymer gains strength when exposed to fire (Kong & Sanjayan, 2010). 4.0 CONCLUSIONS Fly ash and ground granulated slag are abundantly available in many parts of the world, far in excess of quantities needed to replace Portland cements as a construction material. Currently, they are used in limited quantities to partially replace Portland cement in concrete making. However, these industrial byproducts can potentially replace the entire Portland cement in concrete making by utilising the rapidly advancing technologies of geopolymer concrete and alkali activated slag concretes. ey have been shown to provide superior fire resistance and acid resistance. ere are also other materials currently in the research and development phase, such as finely ground waste glass and rice husk ash, which can potentially become more viable with the development of advancing technologies. Further incentives, such as price on carbon will trigger rapid advancement and use of these technologies in practice. ACKNOWLEDGEMENTS I acknowledge my PhD students for their contributions to the research and development of the alternative and blended cement systems, namely, Zhu Pan, Ren Zhao, Daniel Kong, Tarek Aly, Frank Collins, Tatiana Bakharev and Bill Sioulas. Some of their work is presented in this paper. REFERENCES Aly, T., and Sanjayan, J.G., (2008), "Factors Contributing to Early Age Shrinkage Cracking of Slag Concretes subjected to 7-days Moist Curing", Materials and Structures, Volume 41, Issue 4, pp. 633-642. Aly, T., and Sanjayan, J.G., (2009), "Development of Model Parameters for Early-age properties and Crack-width Prediction of Slag-concretes", Magazine of Concrete Research, Vol. 61, Issue 5, June, pp. 379-386. Bakharev, T., (2005), "Resistance of geopolymer materials to acid attack", Cement and Concrete Research, Volume 35, Issue 4, April 2005, pp. 658-670. Bakharev, T., Sanjayan, J. G., Cheng, Y. B., (1998), "Hydration of Slag Activated by Alkalis", Journal of the Australasian Ceramic Society, Vol. 34, No. 2, 1998, pp. 195- 200. Bakharev, T., Sanjayan, J. G., Cheng, Y. B., (1999a) "Alkali Activation of Australian Slag Cements", Cement and Concrete Research, January, 1999, Vol. 29, Issue 1, pp. 113-120. Bakharev, T., Sanjayan, J.G, Y.-B.Cheng, (2001a), "Microstructure and Properties of Alkali-Activated Slag Concrete", Journal of the Australasian Ceramic Society, 37(1), 2001, pp. 115-120, . Bakharev, T., Sanjayan, J.G, Y.-B.Cheng, (2002), "Sulphate Attack on Alkali Activated Slag Concrete", Cement and Concrete Research, Vol. 32 (2), pp. 211-216. Bakharev, T., Sanjayan, J.G., Cheng, Y.B., (1999b) "Effect of Elevated Temperature Curing on Properties of Alkali Activated Slag Concrete", Cement and Concrete Research, Vol. 29 (10), 1999, pp. 1619-1625. Bakharev, T., Sanjayan, J.G., Cheng, Y.B., (2000), "Effect of Admixtures on Properties of Activated Slag Concrete", Cement and Concrete Research, Vol. 30, Issue. 9, 2000, pp. 1367-1374. Bakharev, T., Sanjayan, J.G., Cheng, Y.-B., (2003) "Resistance of alkali activated slag concrete to acid attack", Cement and Concrete Research, Vol. 33, No.10, October, 2003, pp. 1607- 1611. Bakharev, T., Sanjayan, J.G., Y.-B.Cheng, (2001b), "Resistance of Alkali Activated Slag Concrete to Alkali Aggregate Reaction", Cement and Concrete Research, Vol. 31, Issue. 2, 2001, pp. 331-334. Bakharev, T., Sanjayan, J.G., Y.-B.Cheng, (2001c), "Resistance of Alkali Activated Slag Concrete to Carbonation", Cement