Cement chemistry (C3S) — identify the incorrect statement For ordinary Portland cement, consider the following statements about tricalcium silicate (C3S). Which one is NOT correct?

Introduction / Context:
Understanding the role of individual clinker phases in Portland cement is fundamental for predicting heat evolution, setting, strength development, and durability. Tricalcium silicate (C3S) and dicalcium silicate (C2S) dominate strength, while C3A strongly affects sulphate resistance.

Given Data / Assumptions:

• Ordinary Portland cement composition with typical C3S, C2S, C3A, and C4AF contents.
• Standard curing and no special sulphate-resisting modifications.
• General material behavior, not brand-specific variations.

Concept / Approach:

C3S hydrates relatively fast and delivers early strength; its hydration is exothermic and produces higher heat than C2S. Sulphate resistance of Portland cement systems is mainly compromised by higher C3A (which forms expansive ettringite in sulphate environments). Thus, attributing “more sulphate resistance” specifically to C3S is incorrect in this context.

Step-by-Step Solution:

Verification / Alternative check:

Durability guidance associates sulphate resistance with reduced C3A content or blended cements (e.g., PPC/SRPC), rather than with C3S dominance.

Why Other Options Are Wrong:

• Options (a), (b), and (c) reflect well-known C3S behavior and are correct.
• “None of these” is wrong because (d) is clearly incorrect.

Common Pitfalls:

• Confusing heat/strength effects of C3S with sulphate resistance, which is C3A-driven.

Final Answer:

Tricalcium silicate (C3S) has greater resistance to sulphate attack than other clinker phases.