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How Cement is Made

Cement is manufactured by thermally treating a mineral mixture of limestone, sandstone and shale, with some minor raw materials, allowing Exshaw to serve the community by using waste products that would otherwise be landfilled. Raw materials for cement production include: limestone, which is quarried from immediately north of the Plant; shale, quarried near Seebe; and sandstone, which is quarried near Yamnuska Mountain. Exshaw also consumes waste glass from the Bow Valley, soils from an industrial site in Calgary and iron waste from a rolling mill. These raw materials are extracted from the quarries, crushed to a very fine powder and then blended in the correct proportion to achieve the proper chemistry. This blended raw material is called ‘raw feed' or ‘kiln feed' and is heated in a rotary kiln where it reaches a temperature of about 1,400-1,500°C. In its simplest form, the rotary kiln is a tube approximately 200 m long and approximately 6 m in diameter, with a long flame (coal or natural gas) at one end. The raw feed enters the cool end of the kiln, gradually passes down to the hot end, then descends out of the kiln and cools down. The material formed in the kiln is called ‘clinker'. After cooling, the clinker may be stored temporarily in the clinker storage hall, or it may pass directly to the cement mill, which grinds the clinker to a fine powder. A small amount of gypsum is ground up with the clinker to control the setting properties of the cement when water is added. Exshaw makes cement primarily for the Prairies construction industry, but also produces special cement for oil and gas well cementing.