Difficulty: Easy
Correct Answer: Limestone and clay
Explanation:
Introduction / Context:
Ordinary Portland cement is produced by forming clinker in a rotary kiln at high temperature and then inter-grinding it with a small amount of gypsum to control setting. Knowing the basic raw materials helps distinguish OPC from blended cements.
Given Data / Assumptions:
Concept / Approach:
Limestone supplies calcium carbonate (CaCO3 → CaO), while clay provides silica, alumina, and iron oxides. The kiln burning forms clinker phases (alite, belite, aluminate, ferrite). Gypsum is subsequently inter-ground to regulate set; pozzolana is not part of OPC but of blended cements like PPC.
Step-by-Step Solution:
Identify calcareous source → limestone.Identify argillaceous source → clay/shale.Therefore OPC clinker is made from limestone and clay, then ground with gypsum.
Verification / Alternative check:
Material balance in kiln feed confirms dominant CaO from limestone and the remainder from clayey components; minor correctives (iron ore, bauxite, sand) fine-tune the chemistry.
Why Other Options Are Wrong:
Gypsum and lime: gypsum is not kiln-burned as a major CaO source; it is a set regulator at grinding.Pozzolana options describe blended cements, not OPC.
Common Pitfalls:
Confusing OPC raw feed with PPC/PSC constituents; assuming gypsum is a primary feed for CaO.
Final Answer:
Limestone and clay.
Discussion & Comments