Raw materials for Ordinary Portland Cement (OPC): OPC clinker is primarily manufactured by burning a proportioned mix of which natural materials in the kiln, followed by inter-grinding with gypsum?

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:

  • Main oxides needed: CaO, SiO2, Al2O3, Fe2O3.
  • Raw mix sources: calcareous and argillaceous materials.
  • Gypsum added later (not a primary kiln feed component providing CaO).



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.

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