Cement storage quality – Moisture threshold beyond which cement becomes unusable During storage, cement may absorb atmospheric moisture. Beyond approximately what absorbed moisture content does cement generally become unfit (useless) for structural use?

Introduction / Context:
Cement is hygroscopic and readily absorbs moisture, which can lead to partial hydration, lump formation, and loss of strength development. Knowing the moisture threshold at which cement is considered unusable helps prevent compromised concrete quality on site.

Given Data / Assumptions:

• Ordinary Portland cement stored in bags under typical warehouse conditions.
• Moisture content refers to absorbed water in the powder, not free water addition in mixing.
• We focus on practical field acceptance thresholds used in many standards and textbooks.

Concept / Approach:
As moisture increases, early partial hydration consumes reactive clinker phases, reduces fineness effectiveness, and forms weak agglomerates. This reduces normal consistency and strength gain. Many practical guides treat cement as unserviceable for structural concrete when absorbed moisture approaches about 3% or more, due to unreliable setting and substantial strength loss.

Step-by-Step Solution:
Recognize moisture damages reactivity and fineness utilization.Threshold used in field acceptance ≈ 3% absorbed moisture for rejecting bags for structural work.Select 3% as the best answer.

Verification / Alternative check:
Cube strength tests with aged, moisture-contaminated cement typically show significant reductions relative to fresh cement even at 28 days, supporting the 3% rejection guidance.

Why Other Options Are Wrong:
Lower thresholds (1–2%) are overly conservative for all site conditions; higher thresholds (4–5%) often correspond to visibly lumpy, partially hydrated cement with severe quality loss.

Common Pitfalls:
Trying to crush lumps and reuse; once hydration has commenced, the lost reactivity cannot be restored. Always rotate stock (first-in, first-out) and store on raised wooden platforms with moisture barriers.

Final Answer:
3%