Almost everyone knows that cement is a substance used during construction that sticks to other materials to bind them together in an almost permanent bond. Cement is rarely used on its own but is used to bind sand and gravel together.
Cement mixed with a proportion of mortar for masonry, or with sand and gravel, produces concrete. Concrete is the globally most widely used material in existence and is only one step behind water as the planet’s most-consumed resource!
We know all that, but how many know how cement is made?
Cement is manufactured through a closely controlled chemical combination of calcium, silicon, aluminium, and iron among many other materials.
Some of the most common materials used to manufacture cement include limestone, shells, chalk, clay etc. These ingredients are treated with high temperatures which forms a rock-like substance that is ground into the fine powder – and that is what we commonly call ‘cement’.
Ingredients: Lime, Clay or Shale
Mix Ratio: Every company has its own ‘mix ratio’ with all companies competing to provide the best cement at the most competitive price.
Process: The above blend is known as the Raw Feed. This raw feed is pushed into a rotary kiln where the temperatures goes up to around 1400°C -1500°C. The kiln used to make cement is usually 200m long and 6m in diameter.
After the heating and combining, the material formed in the kiln is called ‘clinker’. It is typically in the form of 1 – 25mm spherical nodules between across.
After cooling, the clinker is pushed into a grinder producing the fine powder called Cement.
The cement used in construction sites is usually an inorganic, lime- or calcium silicate-based one which can be categorized into non-hydraulic or hydraulic cement based on the ability of the cement to set in the presence of water.
Non-hydraulic cement does not set in wet conditions or under treatment of water. Rather, it sets and hardens as it dries, reacting with the carbon dioxide present in the air. Once it has set, it is highly resistant to any chemicals.
Hydraulic cement sets and becomes adhesive due to a chemical reaction between the dry ingredients present in the cement and the treatment of water. The chemical reaction results in mineral hydrates which are in turn not very water-soluble, which makes this type of cement quite durable in water and safe from different forms of chemical attack.
This is all about how cement is made and the two important types of cement. In my next blog, I’ll be talking about the other materials used in construction.
Until then, stay home and be safe!