Why cement is grey ?

Colour of Cement .

Cement has become the basic and important part in the Feild of construction. Earlier Egyptians used calcined gypsum as cement and greeks and Roman used lime made by heating limestone and added mortar with coarsar stones for concrete. And then finally in cement was discovered in 1824 by burning finely ground chalk and clay until carbon dioxide is removed.
Now cement and its composition is well known by anyone .

But how many of them know why cement is grey in colour ?

Generally cement is not fully grey in colour. Instead it also consists whitish grey colours also . This whitish Grey colour of the cement is due to the presence of iron in the cement. This is because to make white cement, we need ingredients which donot dicolour it. The primary culprit is Fe2O3 . In the other ingredients (limestone , clay and little gypsum ). Chromium and Manganese are also a source of discoloration.

However, making white cement requires sintering into clinker at around 1600C. Which is expensive, in part because of the need to make it that hot, and also because the lining for the kiln is also more expensive. By adding Fe2O3, or by using ingredients yielding around 3% Fe2O3, the required temperature drops to 1450C. The iron oxide, along with aluminium oxide and magnesium oxide act as a flux, lowering the required temperature, but not helping in the strength inducing properties of the cement.

So this the reason for the cement to be grey in colour. However nowadays there are best alternative to cement such as Geopolymer , Cemfree etc .

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