Acceptable pH of mixing water for concrete production What is the general minimum pH requirement for water used in concrete so that it does not adversely affect cement hydration or durability?

Introduction:
Water quality directly affects cement hydration and the long-term durability of concrete. Highly acidic or contaminated water can delay setting, reduce strength, and cause corrosion issues. This question focuses on the commonly adopted lower bound for pH of mixing water in concrete.

Given Data / Assumptions:

• Normal potable-quality water is preferred for concrete.
• No special chemical admixtures requiring different limits are considered.
• Concrete is for typical structural applications.

Concept / Approach:

Concrete is alkaline, and extremely acidic water can disrupt hydration and leach calcium hydroxide, impairing strength gain. A practical and code-aligned guideline is to ensure that pH of mixing water is not less than 6, roughly in the neutral-to-alkaline range, avoiding aggressive acidity.

Step-by-Step Solution:

Verification / Alternative check:

If water is safe to drink, it is generally suitable for mixing concrete. When in doubt, compressive strength comparison tests with distilled water batches can verify acceptability.

Why Other Options Are Wrong:

Options A and D use “not more than” and are directionally incorrect for a minimum threshold. Option C allows pH 5, which is too acidic. Option E (not less than 7) is stricter than necessary and may reject otherwise acceptable water.

Common Pitfalls:

Ignoring chemical contaminants (sugars, chlorides, sulfates) even if pH seems acceptable; not accounting for admixture compatibility.

Final Answer:

not less than 6