Portland Cement Chemistry – Compounds Responsible for Early Strength In ordinary Portland cement hydration, which compound is primarily responsible for developing the early strength (notably within the first week)?

Introduction:
Understanding the roles of clinker phases is central to predicting strength gain in concrete. While several compounds hydrate, early strength in ordinary Portland cement is dominated by one phase that reacts comparatively rapidly and yields high-strength hydrates.

Given Data / Assumptions:

• Ordinary Portland cement composition includes C3S, C2S, C3A, and C4AF with added gypsum.
• “Early” here refers to strength in roughly 1–7 days of curing at standard conditions.
• Hydration products include C-S-H gel and calcium hydroxide from silicates.

Concept / Approach:

C3S hydrates more rapidly than C2S and contributes most to early compressive strength by forming C-S-H gel. C3A reacts very quickly but its primary role is in setting/ettringite formation; it does not dominate compressive strength development beyond the initial period.

Step-by-Step Solution:

Verification / Alternative check:

Strength-vs-time curves from cement chemistry show higher early strengths with higher C3S content; C2S contributes more to later strength (beyond 7–28 days).

Why Other Options Are Wrong:

C4AF: minor contributor to strength; affects color and heat. C3A: rapid reaction but not principal early strength provider. C2S: slower, contributes later. Gypsum: regulator of set, not a strength phase.

Common Pitfalls:

Confusing “earliest reaction” (C3A) with “early strength” (C3S-driven C-S-H formation).

Final Answer:

Tricalcium silicate (C3S)