Cement Chemistry – effects of C3S and C2S contents on hardening and durability Which statements about the influence of tricalcium silicate (C3S) and dicalcium silicate (C2S) on Portland cement behavior are correct?

Difficulty: Easy

Correct Answer: All of the above

Explanation:


Introduction / Context:
The relative amounts of C3S and C2S in Portland cement clinker strongly influence rate of strength gain and durability in aggressive environments. Recognizing these trends helps in selecting cement types for specific site conditions (rapid construction, massive pours, sulphate exposure, etc.).


Given Data / Assumptions:

  • Cements compared are ordinary Portland types differing mainly in C3S/C2S proportions.
  • Other phases (C3A, C4AF) are not the focus of this question.
  • Standard curing and test conditions assumed.


Concept / Approach:

C3S hydrates relatively fast, producing early-age strength and more calcium hydroxide, while C2S hydrates more slowly, contributing to later strength and producing less calcium hydroxide. A higher C3S content thus accelerates hardening but can reduce chemical resistance because more free Ca(OH)2 is available for deleterious reactions (for example, sulphate attack). Conversely, higher C2S content slows early hardening and commonly improves chemical resistance due to lower Ca(OH)2 release and denser microstructure at later ages.


Step-by-Step Solution:

Option A: True—C3S drives rapid early strength.Option B: True—more Ca(OH)2 and higher permeability reduce chemical resistance.Option C: True—C2S contributes more slowly to strength.Option D: True—greater C2S typically improves resistance in many aggressive environments.


Verification / Alternative check:

Standard cement chemistry references show early-age strength correlating with C3S; durability often improves when C3S is moderated and C2S proportion is higher, especially when combined with SCMs.


Why Other Options Are Wrong:

Since A–D are correct, the best choice is “All of the above”.


Common Pitfalls:

Over-generalizing without considering C3A and permeability; assuming high early strength guarantees better durability.


Final Answer:

All of the above

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