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Why are limestone and clay commonly used to make portland cement?
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Cement
The cement-making process, from crushing and grinding of raw materials, through roasting of the ground and mixed ingredients, to final cooling and storing of the finished product.
Limestone and clay are used to manufacture portland cement because they provide the essential chemical compounds required for the material's composition.1
Portland cement is primarily composed of lime (calcium oxide), silica, and alumina. These ingredients are sourced from two distinct types of raw materials:1
- Calcareous materials: Limestone (or chalk) serves as the primary source of lime.1
- Argillaceous materials: Clay (or shale and slate) provides the necessary silica and alumina.1
During the manufacturing process, these materials are blended in specific proportions and heated in a kiln to fuse them together. This chemical reaction produces clinker, the fundamental glassy product that is subsequently ground into the final cement powder. By combining these specific natural materials, manufacturers can achieve the precise chemical balance needed for the cement to set and harden effectively.2314