Portland (constructional) cement is a fine powder mixture of various minerals. It is produced by mixing calcareous minerals such as chalk, limestone containing silica and alumina and heating it to 1450 deg c when it cools a clinker is formed.
This clinker is then finely ground and mixed with small quantity 3-5% of gypsum which has calcium sulphate in it. The amount of gypsum controls the physical properties of the eventual concrete. Sometimes very minute quantities of pigments are also added. Cement producing processes do however vary.
TYPES OF CEMENT	:	- opc ordinary portland cement - rapid hardening portland cement - sulphate resisting portland cement - low heat portland cement - white portland cement - other cements based on portland: -waterproof & water repellent cement    -masonry cement    -hydrophobic cement    -blast-furnace cement
PACKING	:	- 50 bags (paper or poly bags) - 1.5 tonne bags - 2 tonne bags - bulk/loose - some manufacturers are now supplying 10 tonne bags
COUNTRY OF ORIGIN	:	(at buyer's choice) - china - india - indonesia - iran - italy - russia - others