Main properties of dicalcium silicate (C2S) in Portland cement Considering early heat, rate of hydration, strength development, and chemical durability, which statement correctly describes C2S?

Introduction / Context:
Portland cement clinker contains several principal phases: tricalcium silicate (C3S), dicalcium silicate (C2S), tricalcium aluminate (C3A), and tetracalcium aluminoferrite (C4AF). Each phase affects heat evolution, strength development, and durability differently. Recognizing the role of C2S is essential for mass concrete and long-term performance considerations.

Given Data / Assumptions:

• C2S reacts more slowly than C3S.
• Mass concrete benefits from lower heat of hydration.
• Durability in sulphate environments is influenced mainly by low C3A and suitable C2S/C3S balance.

Concept / Approach:
C2S hydrates more slowly than C3S, thus producing lower early heat and strength. However, it contributes significantly to strength at later ages. Because the rapid-release heat source is smaller, mixes richer in C2S are often preferred for mass placements to reduce thermal gradients. C2S does not inherently have poorer sulphate resistance; problems in sulphate exposure are mostly tied to C3A content and ettringite formation. Therefore, the defining, correct statement here is that C2S generates less heat of hydration compared with C3S.

Step-by-Step Solution:

Verification / Alternative check:
Heat-of-hydration curves consistently show reduced early peaks for cements with higher C2S, corroborating the selected statement.

Why Other Options Are Wrong:

• (a) and (c) claim rapid hydration/rapid hardening, which is characteristic of C3S, not C2S.
• (d) C2S contributes significantly to later-age strength; the statement is misleading.
• (e) Sulphate attack is more a function of C3A; C2S is not the primary problem.

Common Pitfalls:
Assuming “less heat” means “less strength overall.” C2S supports long-term strength while reducing early heat, a benefit in mass concrete.

Final Answer:
Generates less heat of hydration