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Concrete In Australia : March 2012
Concrete in Australia Vol 38 No 1 15 million t/a or around 25% of the total supply of cementitious binder.3 Limestone as a mineral addition in the production of cement is now making a significant and growing contribution to clinker substitution. e Australian Cement Standard allows up to 7.5% addition of limestone and there is strong evidence that addition rates up to 10% are possible with no detrimental impact upon cement properties. If the 10% addition is fully realised, a carbon dioxide emission reduction of up to 750,000 t/a is possible with limestone addition coupled with reductions in energy and raw material use. 4.0 ALTERNATIVE MATERIALS Over 30 years the global cement industry has demonstrated its capacity to reuse materials previously considered waste as sources of raw materials and energy in the manufacture of cement. e cement manufacturing process provides a controlled environment in which the hydrocarbon component of waste materials are converted to useful energy, any acid gases are scrubbed in the alkaline raw material and the heavy metals are locked up in the clinker mineral phases. e progress in moving from traditional raw materials and fossil fuels to waste derived materials has not been uniform. e European industry has achieved around 25% average substitution. Some European countries have demonstrated yearly average substitution rates of more than 50% and up to 80% can be achievable at single cement plants.4 e growth in Australia has been modest by comparison with current substitution rates running at 7%. e materials used as fuels and raw materials in Australia include timber, tyres, solvents, waste oil, animal fats, carbon waste from the aluminium industry, catalyst waste from oil refining, gypsum produced from scrubbing sulfur dioxide flue gas and waste foundry sands. e slower take up of alternative fuels by the Australian industry has been a consequence of a range of factors specific to jurisdictions and geographical location, including the relatively low cost of energy and the low cost of waste disposal, community opposition, regulatory inconsistency and the logistics of collection and processing the waste. Several projects remain under consideration by the industry including the use of sewage and commercial and industrial waste as fuels. ese projects not only have the advantage of better managing waste but contain high biogenic fuel components that will allow reductions in carbon dioxide emissions. 5.0 CONCLUSION ere are better ways to manage our use of raw materials, energy and waste to bring about real and lasting change in the building and construction industry. e use of extenders and alternative fuels in the manufacture of cement are just two examples.It does require each contributor to the building and construction process to re-examine the way things are done, find better ways and educate themselves, their peers and the general population in the advantages of doing things differently. REFERENCES 1. Horne, Grant, Verghese, Life Cycle Assessment: Principles, Practice and Prospects, CSIRO Publishing 2009. 2. WBCSD and IEA, Cement Technology Roadmap 2009 Carbon Emission Reductions up to 2050. 3. Personal communication, Cement Industry Federation 2011. 4. CSI/ECRA, Development of State of the Art Techniques in Cement Manufacturing: Trying to look ahead. Geneva, 2009. n r r r L n u n n pr u n S g u n n pr u n F y h u n n pr u n Figure 3. Raw material and energy inputs and waste produced in cement manufacture. Figure 4. Cement extenders used in cement production and sold for concrete production (million tonnes). GRAPHIC: CEMENT INDUSTRY FEDERATION 2011 Figure 5. Alternative fuel use as a percentage of total thermal energy use. GRAPHIC: CEMENT INDUSTRY FEDERATION 2011 0.9 tonne carbon dioxide Raw Materials Grinding Pre-heater/ Kiln Clinker Storage Cement Bulk Storage Storage Calciner Cooler Grinding & Loading 0.1 tonne coal eq 1.6 tonne raw material