Sand for Concrete – washing and chloride concerns Which of the following statements about sand sources and their suitability for concrete is correct under typical site practice?

Introduction / Context:
Aggregate cleanliness directly affects concrete durability and appearance. Clay and silt increase water demand and reduce bond; chlorides promote steel corrosion and surface efflorescence. Source selection and washing requirements should be understood before batching.

Given Data / Assumptions:

• Pit sand may be dry or from flooded pits/quarries.
• Sea-shore sand and shingle can be contaminated with soluble salts, especially chlorides.
• Concrete permeability strongly influences corrosion risk.

Concept / Approach:

Dry pit sands often carry dust, silt, and clay that must be washed out. Flooded-pit sands are partially washed by nature and may need less treatment but still require checks for impurities. Marine sands contain chlorides; even after washing, residual salts can remain and lead to efflorescence and corrosion if concrete remains permeable. A dense, low w/c concrete with adequate cover mitigates but does not eliminate risks; many specifications restrict or prohibit unprocessed sea sand.

Step-by-Step Solution:

Verification / Alternative check:

Specifications typically limit acid-soluble chloride content in aggregates and fresh concrete and require silt content checks (for example, by decantation or turbidity tests).

Why Other Options Are Wrong:

Since A–D are valid, none of them is incorrect, and E best captures the full picture.

Common Pitfalls:

Assuming marine sand is safe after superficial rinsing; ignoring chloride limits; failing to verify silt/clay content for pit sands.

Final Answer:

All of the above