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Q: Which of the following compounds is responsible for slow hardening, less heat of hydration, and greater resistance to the chemical attack in OPC Cement?
  • A. C₃S
  • B. C₃A
  • C. C₄AF
  • D. C₂S
Correct Answer: Option D - Dicalcium silicate (C₂S)–It is about 25-40% of cement. It hydrates and hardens slowly and takes long time to add to the strength (after a year or more). It imparts resistance to chemical attack. Raising of C2S content renders clinker harder to grind, reduces early strength, decreases resistance to freezing and thawing at early ages and decreases heat of hydration. The heat of hydration is 260 J/g.
D. Dicalcium silicate (C₂S)–It is about 25-40% of cement. It hydrates and hardens slowly and takes long time to add to the strength (after a year or more). It imparts resistance to chemical attack. Raising of C2S content renders clinker harder to grind, reduces early strength, decreases resistance to freezing and thawing at early ages and decreases heat of hydration. The heat of hydration is 260 J/g.

Explanations:

Dicalcium silicate (C₂S)–It is about 25-40% of cement. It hydrates and hardens slowly and takes long time to add to the strength (after a year or more). It imparts resistance to chemical attack. Raising of C2S content renders clinker harder to grind, reduces early strength, decreases resistance to freezing and thawing at early ages and decreases heat of hydration. The heat of hydration is 260 J/g.