Cement soundness — oxides that cause deleterious expansion Cement may become unsound due to the presence of excessive amounts of which constituents?

Introduction / Context:
Soundness refers to the ability of a hardened cement paste to retain volume stability. Excess slowly hydrating or reactive oxides can cause late expansion, cracking, and failure—vital considerations in structural durability.

Given Data / Assumptions:

• Typical Portland clinker contains CaO (lime), MgO (magnesia), and controlled SO3 from gypsum.
• Standards limit free CaO and MgO to prevent delayed expansion.
• Sulphur (as SO3) must be balanced with C3A to avoid deleterious sulfate reactions.

Concept / Approach:
Excess free lime (CaO) or magnesia (MgO) can hydrate slowly after set, expanding and disrupting the hardened matrix. Imbalance or excess sulphate can also lead to expansive ettringite formation. Hence, quality control enforces strict oxide limits and soundness tests (e.g., Le Chatelier, autoclave).

Step-by-Step Solution:

Verification / Alternative check:
Specification limits (e.g., MgO typically < 5%, SO3 within narrow range) are industry norms to prevent late expansion; autoclave expansion limits verify soundness.

Why Other Options Are Wrong:

• Each of A, B, C alone highlights a single cause; the comprehensive and safest choice is D.

Common Pitfalls:
Assuming only MgO causes unsoundness; free CaO and sulphate imbalance can be equally problematic. Always review mill certificates and compliance tests.

Final Answer: