Cement Composition – major chemical ingredient by percentage Which oxide is present in the highest percentage in ordinary Portland cement (OPC) clinker chemistry?

Introduction / Context:
Understanding the principal oxides in cement is fundamental for predicting hydration behavior and performance. OPC clinker is chiefly composed of calcium oxide (lime), silica, alumina, and iron oxide, which combine to form clinker minerals such as C3S and C2S that control strength development.

Given Data / Assumptions:

• Ordinary Portland cement without special additions.
• Typical oxide ranges from standard cement chemistry references.

Concept / Approach:

Lime (CaO) is the dominant oxide, typically in the range of about 60–65% by mass. Silica (SiO2) commonly contributes around 17–25%, alumina roughly 3–8%, iron oxide about 1–5%, and magnesium oxide is usually limited to a few percent to avoid unsoundness. Since CaO is the highest, option D is correct.

Step-by-Step Solution:

Verification / Alternative check:

Oxide composition tables for OPC list CaO as the largest constituent, consistent with its role in forming C3S and C2S, the primary strength-giving phases.

Why Other Options Are Wrong:

Silica and alumina, while important, are present in smaller proportions; Fe2O3 and MgO are minor constituents with limits to prevent unsoundness.

Common Pitfalls:

Confusing oxide percentages with compound percentages (for example, C3S vs CaO); overlooking that excessive free lime (uncombined CaO) can cause expansion.

Final Answer:

Lime (CaO)