In civil engineering works, why is sea sand generally avoided for concrete and masonry? Identify the most likely consequences when chloride- and sulphate-laden sea sand is used in structural work.

Introduction / Context:
Aggregates and sand quality critically affect durability of concrete and masonry. Sea sand naturally contains soluble salts such as chlorides and sulphates. This question examines the practical problems that arise when such contaminated sand is used without proper treatment.

Given Data / Assumptions:

• Sea sand contains chlorides/sulphates even after casual washing.
• Concrete and masonry components may be exposed to moisture cycles.
• Reinforcement in concrete is susceptible to corrosion from chlorides.

Concept / Approach:
Chlorides accelerate steel corrosion; sulphates react with cement hydrates to form expansive products that crack the matrix. In walls, soluble salts migrate with moisture and crystallize near surfaces, creating efflorescence and attracting dampness by hygroscopic action, compounding deterioration.

Step-by-Step Solution:

Verification / Alternative check:
Durability specifications often cap chloride and sulphate contents in fine aggregates; desalination or prohibition of sea sand is commonly mandated unless rigorous washing and testing are performed.

Why Other Options Are Wrong:

• A/B/C individually capture only part of the problem; the comprehensive, correct impact is all of them together.

Common Pitfalls:
Assuming a single freshwater rinse removes salts; neglecting long-term migration and crystallization; ignoring code limits for chloride content in reinforced concrete.

Final Answer:
All of these