Which among the following are essential constituents of Portland cement ?

Portland cement is a hydraulic cement produced by heating a mixture of raw materials to form a clinker, which is then ground into a fine powder. The three primary chemical constituents essential for its manufacture are:

• Lime (Calcium Oxide, CaO): The most significant component, usually comprising 60-67% of the cement. It is typically derived from limestone.
• Silica (Silicon Dioxide, SiO₂): Making up about 17-25%, it reacts with lime to form dicalcium and tricalcium silicates, which provide strength.
• Alumina (Aluminium Oxide, Al₂O₃): Comprising 3-8%, it acts as a flux, lowering the clinkering temperature during manufacture.

While clay is a common raw material used in the process, it is valued specifically for providing the silica and alumina. Other minor constituents include iron oxide and gypsum. Graphite and graphene are not standard constituents of Portland cement.