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The production of cement-clinker is an energy and carbon emissions intensive process. The main component of clinker (the semi-finished product that is ground to obtain cement) is calcium oxide. In nature, this element is found linked with CO2 in the form of calcium carbonate (usually as limestone) which makes up about 78% of the raw materials used to produce clinker. 60% of the direct CO2 emissions from cement manufacturing are generated by the limestone decarbonation, while 40% come from the combustion of fossil fuels used to reach the temperatures required for decarbonation to take place.
The most widely used cement type, Portland cement, is 95% cement clinker. However there is a range of other types of cement (called blended cements) which contain a variety of clinker substitutes to reduce the amount of clinker used, and therefore reduce carbon emissions per tonne of product.
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