CEMENT MADE SIMPLE
Cement is a fine grey powder that is mixed with gravel, sand, and water to form concrete, the most widely used construction material in the world. Cement and supplementary cementing materials (SCMs) are the critical ingredients that lock sand and gravel together into an inert concrete matrix. They typically represent 10% to 15% of a concrete mix. On average, concrete has a greenhouse gas emissions intensity equal to 1/9 that of cement. Each of the six types of cement manufactured in Canada meets technical specifications established by the Canadian Standards Association.
In simple terms, cement is manufactured by heating a precise mixture of finely ground limestone, clay and sand in a rotating kiln to temperatures reaching 1450 ºC. This results in the production of cement clinker, an intermediate product in the manufacture of cement. The cement clinker emerges from the kiln, is cooled, and then finely ground to produce portland cement. Portland cement may also be interground with supplementary cementing materials for their environmental benefits and to meet product specifications.Portland cement is a precisely controlled chemical combination of calcium, silicon, aluminum, iron and small amounts of other ingredients. Gypsum is added in the final grinding process to regulate the setting time of the concrete. Lime and silica make up about 85% of the mass. Common among the materials used in its manufacture are limestone, shells, and chalk or marl, combined with shale, clay, slate or blast furnace slag, silica sand, and iron ore.
The precision required to manufacture portland cement involves approximately 80 separate and continuous operations, the use of heavy machinery and equipment, and large amounts of heat and energy. The capital investment per worker in the cement industry is among the highest of all manufacturing industries.
Each step in the manufacturing process of portland cement is checked by frequent chemical and physical tests in plant laboratories. The finished product is also analyzed and tested to ensure that it complies with all specifications.
THE MANUFACTURING PROCESS
This graphic shows an overview of the major manufacturing processes in the production of cement: