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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.