opc cement

Portland cement is manufactured from calcium carbonate in the form of crushed limestone or chalk and an argillaceous material such as clay, marl or shale. Currently, approximately two-thirds of UK Portland cement production is based on limestone, with the remainder from chalk in the south and east of the country. Minor constituents such as iron oxide or sand may be added depending upon the composition of the raw materials and the exact product required.

In principle, the process involves the decarbonisation of calcium carbonate (chalk or limestone) by expulsion of the carbon dioxide, and sintering, at the point of incipient fusion, the resulting calcium oxide (lime) with the clay and iron oxide. Depending on the raw materials used and their water content at extraction, three key variations in the manufacturing process are currently in use. These are the semi-wet, semi-dry and dry processes. The UK produces over 10 million tonnes of Portland cement each year.

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