Correct Answer: (e) None of the above/More than one of the above
Solution:Cement is made with limestone, silica clay, and marl as the main raw materials. Lime is the main ingredient of cement, accounting for about 60-65% of total cement weight. Silica is the second major ingredient of cement and about 17 to 25% of cement ingredients is silica. Cement (OPC) is made by heating limestone (calcium carbonate) with other materials (such as clay) to 1,450°C (2,640°F) in a kiln, a process known as calcination that liberates a molecule of carbon dioxide from the calcium carbonate to form calcium oxide CaO, or quicklime, which then chemically combines with the other materials in the mix to form calcium silicates and other cementitious compounds. The resulting hard substance, called 'clinker', is then ground with a small amount of gypsum (CaSO. 2H₂O) into a powder to make ordinary Portland cement, the most commonly used type of cement (often referred to as OPC).
