Step 1: Understanding the Question:
The question asks to identify the major chemical phase in Portland cement (Bogue's compounds) that is primarily responsible for the development of its strength.
Step 2: Detailed Explanation:
Bogue's Compounds: Portland cement consists primarily of four phases:
1. Tricalcium Silicate ($C_3S$, Alite): Makes up $50-70%$ of the cement.
2. Dicalcium Silicate ($C_2S$, Belite): Makes up $15-30%$.
3. Tricalcium Aluminate ($C_3A$).
4. Tetracalcium Aluminoferrite ($C_4AF$).
Role of $C_3S$ (Tricalcium Silicate): This is the most important component for strength. It reacts rapidly with water (hydration) to form C-S-H gel. It is responsible for the early strength (the first 7 days) and the overall hardening of the concrete. High $C_3S$ content leads to "Rapid Hardening" cement.
Analyzing Other Options:
- $C_2S$ (A): Hydrates slowly and is responsible for the "late strength" (after 28 days and up to a year).
- $C_3A$ (B): Reacts instantly and is responsible for "flash set" and heat generation, but contributes little to final strength.
- $C_4AF$ (D): Acts primarily as a flux during manufacturing and has negligible contribution to strength.
Step 3: Final Answer:
Tricalcium Silicate ($C_3S$) is the primary phase responsible for the hardening and early strength of cement. Therefore, option (C) is correct.