Question

Which of the following is used to manufacture portland cement?
(A) Limestone, clay and sand
(B) Limestone, gypsum and sand
(C) Limestone, gypsum and alumina
(D) Limestone, clay and gypsum

Answer 1

In the above question, it is asked about the composition of Portland cement. Portland cement is used in construction sites because of their mechanical and hard structure. Portland cement contains alumina.

Complete step by step solution
In the above question, we are given limestone, clay, gypsum, sand and alumina as options. Hence, let us first look at the properties of these materials.
Limestone is a softer material than clinker and hence, it takes less energy to grind to the fine particles. In construction sites, this results in better particle size distribution in the cement and hence, enhances the particle packing and paste density in concrete.
Clay is added externally with Portland cement. The mechanical strength of cement depends upon the percentage of clay present in it.
Gypsum is chemically hydrated calcium sulfate. It plays an important role in hardening the cement. If gypsum is not added to the cement, then the cement will settle quickly leaving no time for concrete placing.
Sand, usually silica sand, is used in manufacturing to maintain the consistency of clay.
40-50% alumina is present in Portland cement as it forms ceramic bonds at high temperature and maintains its strength even after cooling.
Hence, we can conclude that the most important components required during manufacture of Portland cement is limestone, gypsum and alumina. Hence, the correct option is option C.

Note
Portland cement can be used in emergency construction and repairs, and construction of machine bases and gate installations.
Since Portland cement is used for construction purposes, it is not eco-friendly. It is caustic and hence, can cause chemical burns. The powder can cause irritation and severe exposure may lead to lung cancer. It also contributes towards global warming as it releases greenhouse gases.