Cement composition effects: Which of the following statements about excess oxides in Portland cement are correct for field practice and durability?

Introduction / Context:
Cement chemistry directly governs setting, strength gain, and long-term soundness. Site engineers frequently diagnose failures by relating observed behavior to oxide composition. This question checks your recall of how excessive proportions of key oxides affect performance.

Given Data / Assumptions:

• Ordinary Portland cement considered under normal curing conditions.
• “Excess” means beyond the balanced clinker proportion needed for desired compounds.
• Soundness refers to the absence of late, disruptive expansion.

Concept / Approach:
Too much free lime causes expansive hydration and cracking. High silica slows reaction, delaying set and early strength. Excess alumina promotes very rapid reactions but lowers ultimate strength due to weaker hydration products. Free magnesium oxide hydrates slowly to magnesium hydroxide, causing delayed expansion and unsoundness. Each listed effect is a standard, well-known relationship in cement technology.

Step-by-Step Solution:
Map each oxide to its typical effect on hydration and microstructure.Confirm that all four statements are valid field-generalizations.Hence, the comprehensive correct choice is “All of the above”.

Verification / Alternative check:
Soundness tests (e.g., Le Chatelier, autoclave) specifically target excess free lime and MgO. Set time and strength trends corroborate the silica and alumina statements.

Why Other Options Are Wrong:
Any single-statement choice omits other equally true effects and is incomplete.

Common Pitfalls:
Confusing “fast set” with “high early strength” irrespective of durability; overlooking that unsoundness may appear late in service.

Final Answer:
All of the above.