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Concrete In Australia : September 2013
34 Concrete in Australia Vol 39 No 3 Field application of geopolymer concrete: a measure towards reducing carbon dioxide emission Ahmad Shayan* and Aimin Xu, ARRB Group Ltd, Melbourne Fred Andrews-Phaedonos, VicRoads, Technical Consulting, Melbourne * Corresponding Author Ordinary Portland Cement (OPC) is an energy-intensive material, requiring large amounts of heat in its production. Moreover, manufacture of this material involves burning of limestone, and each tonne of Portland cement releases almost one tone of CO2 into the atmosphere. Incorporation of supplementary cementitious and pozzolanic materials, as partial replacement of Portland cement in concrete, is a measure for reducing the utilisation of Portland cement in concrete and reduction in CO2 emission. Another benefit of these materials is improvement in the durability of concrete structures. However, geopolymer concrete does not use Portland cement and relies on reactions between industrial by-products and highly alkaline solutions to generate its binding properties in hardened state. Such materials are, therefore, environmentally friendly and their use in concrete structures is encouraged, where possible. VicRoads recently used a geopolymer concrete, manufactured from blast furnace slag, for the construction of retaining walls around one abutment of a bridge in the Melbourne Area. e present work involved electrochemical measurements carried out on the geopolymer components, as well as laboratory testing and examination of the concrete to determine its properties with respect to strength, durability, chemical composition and microstructure. 1.0 INTRODUCTION Geopolymer is a generic name for a range of synthetic alumino-silicate products which are manufactured through a wide range of recipes, utilising a variety of curing conditions, and for numerous applications, including construction. Two factors are identified as the main drivers for the development of geopolymer concrete as an alternative to traditional concrete, both of which have environmental significance. One factor concerns the utilisation of waste materials and surplus industrial by-products in the manufacture of geopolymers, which will conserve virgin materials and divert materials from the waste stream, freeing landfill spaces for more urgent issues. e other factor concerns manufacture of geopolymers as potential replacement for Portland cement, which is the main ingredient of traditional OPC-based concrete. e process of Portland cement production generates the greenhouse gas CO2 according to the following reaction, which generates approximately 0.55 tonne of CO2 through burning of lime. 5 CaCO3 + 2 SiO2 → (3CaO.SiO2) + (2CaO.SiO2) + 5 CO2 In addition, production of one tonne of OPC requires burning of fuel which generates about 0.4 tonne of CO2 per tonne of cement (Davidovits, 1994), i.e. manufacture of one tonne of cement causes emission of about one tonne of CO2 into the atmosphere. Davidovits (1994) presented statistics showing that world production of OPC was about 300 million tonnes in 1960, and projected to reach around 2000 million tonnes in year 2000 and 3500 million tonnes in 2015, based on 5% growth per year. However, a Google search revealed information, dated 7 November 2012, from a site called http:// earlywarn.blogspot.com.au/2012/11/cement-production-china- and-elsewhere.html , which shows that the projected level of OPC production for 2015 was already reached in 2011. is is an environmentally alarming trend with respect to global warming and needs to be addressed. e chemistry of geopolymer production (Davidovits, 1991) does not involve direct emission of CO2, which is an advantage, besides the alleged superior quality of geopolymer products compared to corresponding Portland cement-based products. Davidovits (1994) stated that replacement of Portland cement by geopolymers could reduce the CO2 emission by 80-90%, although widely different estimations, ranging from 9% to 64% have also been reported (Stengel et al., 2009; McLellan et al., 2011; Habert et al., 2011; Turner and Collins, 2012). Geopolymers are sensitive to changes in compositional parameters and manufacturing processes, and these can result in variable performance of geopolymer concrete (Lee and Van Deventer 2002a, b; 2004 & 2007; Hardjito, et al., 2002; 2004a, b; Duxson, et al., 2005, 2007; Weng et al., 2005; van Deventer, et al. (2007, 2012); Steveson and Sagoe-Crentsil, 2005a, 2005b; Provis et al., 2005a; Kobera, et al., 2011). Technically, many investigations have shown that correctly manufactured geopolymer concretes perform well with respect to mechanical properties and durability parameters such as drying shrinkage, acid attack, and sulfate attack, although resistance to carbonation is uncertain, probably because the available test method may not be applicable to geopolymer concrete. However, application of geopolymer concrete for structural