Cement Storage – Effect of Aging on Strength When ordinary Portland cement is stored for extended periods under average site conditions, what typically happens to its potential strength?

Introduction:
Cement is hygroscopic. With time, especially in humid climates, it reacts slowly with atmospheric moisture and carbon dioxide even inside bags. This premature reaction reduces reactivity during actual mixing and lowers the achievable strength of mortar and concrete made from aged cement.

Given Data / Assumptions:

• Storage is in typical warehouses where some humidity exposure is inevitable.
• No special vacuum packing or desiccation is assumed.
• Strength refers to standardized test strength achievable at equal water content.

Concept / Approach:

Partial hydration and carbonation of clinker compounds occur during storage. These irreversible changes consume reactive phases and create agglomerates that do not fully participate in later hydration, lowering ultimate strength. Hence, specifications often limit storage time or require re-testing before use.

Step-by-Step Solution:

Verification / Alternative check:

Standards require periodic re-testing of stored cement and recommend first-in-first-out usage to mitigate strength loss.

Why Other Options Are Wrong:

Increase in strength does not occur in sealed bags; exact sameness is unrealistic; 'none' and 'random oscillation' ignore known chemistry.

Common Pitfalls:

Using old cement without re-testing; ignoring the need to adjust water demand due to caking and reduced reactivity.

Final Answer:

It decreases as the cement partially reacts with moisture and carbon dioxide