Cement chemistry — composition linked to rapid-hardening cement Rapid hardening cement is characterised primarily by a higher content of which clinker compound?

Difficulty: Easy

Correct Answer: Tri-calcium silicate (C3S)

Explanation:


Introduction / Context:
Rapid hardening cement (RHC) is specified where early strength is required, such as precast elements and urgent repairs. Its chemistry is tuned to accelerate strength gain in the first 1–7 days.


Given Data / Assumptions:

  • Clinker phases: C3S, C2S, C3A, C4AF, with gypsum added at grinding.
  • Early strength is closely related to C3S content and fineness.
  • Normal curing conditions are assumed.


Concept / Approach:
Increasing tri-calcium silicate (C3S) and grinding fineness enhances hydration rate, producing more calcium-silicate-hydrate quickly, hence higher early compressive strength. C2S contributes later-age strength; C3A affects setting and heat evolution.


Step-by-Step Solution:

Target property → early strength development.Link to phase → higher C3S raises early strength.Cross-check → RHC often has finer grinding to further accelerate hydration.


Verification / Alternative check:
Strength–age curves in cement handbooks show RHC surpassing OPC at early ages due to elevated C3S and fineness.


Why Other Options Are Wrong:

  • C3A (B): influences set/heat; excessive C3A can cause sulfate issues.
  • C4AF (C): minor effect on strength; affects colour and some reactions.
  • C2S (D): contributes mainly to later strengths, not rapid hardening.


Common Pitfalls:
Confusing rapid-hardening with quick-setting cement; the former focuses on early strength, the latter on accelerated set.


Final Answer:

Tri-calcium silicate (C3S)

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