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| HeidelbergCement develops alternative binders  The cement industry is the source of about 5 per cent of the global anthropogenic CO2 emissions. On average, the production of one tonne of cement clinker generates around 800 kg of CO2. From this amount, about 40 per cent is due to the energy-intensive burning process; 60 per cent is attributed to raw materials in the course of limestone decarbonisation. By using alternative fuels such as tires, meat and bone meal, or sewage sludge, among other measures, HeidelbergCement has succeeded in reducing the specific CO2 emissions to 0.621 tonnes of CO2 per tonne of cement. A further reduction through process-related measures and the use of alternative fuels is only possible to a very limited extent.Additives can be used, however, to further improve the CO2 balance of products based on Portland cement. These alternative substances are by-products from steel manufacturing or coal-fired power plants, and serve as source materials for composite cements. Portland cement clinker is partly replaced, for example, by blast furnace slag, fly ash, or silica fume, whereby the specific use of these additives often even improves the properties of the cement product. However, this is only possible to a certain extent because of the limited availability of high-quality raw materials. The HeidelbergCement Technology Center (HTC) goes one step further: In an effort to tap the further potential for CO2 reduction, HTC has been working on the development of alternative binders that work more or less without conventional clinker for several years. Since the beginning of 2010, new staff has been hired at the HTC Global research centre in Leimen, Germany, to develop concepts for alternative clinker. A previous internal study from 2009 systematically analysed all of the concepts known at the time. One of the most promising concepts in this study was a calcium sulfoaluminate-belite binder (CSAB). Calcium sulfoaluminate (CSA) cements have been produced for use in building chemicals for a long time, especially in China. They are mainly used in screeds, tile glues, and special products. A characteristic feature is that they form ettringite very quickly and therefore exhibit a very high early strength. Experiments have already been performed with a view to use these cements for construction purposes, but their durability has not yet been sufficient. The advantages of ternesite containing clinker are obvious: Because of its chemical composition and manufacturing at lower temperatures, the new product generates up to 30 per cent less CO2 than normal Portland cement clinker. There is also an improvement in energy efficiency, as the burning temperature is 150 to 200°C lower and the fuel consumption is reduced by about 10 per cent. The electricity costs for the manufacturing process are likewise lowered by about 15 per cent, because less energy is required, particularly for the grinding process. The first large-scale trial is planned for this year in one of the German HeidelbergCement plants, where the new products are to be manufactured for the first time with the existing plant technology. write your comments about the article :: © 2013 Construction News :: home page |