Strength development of concrete with time — general trend under proper curing Under normal curing conditions, how does the compressive strength of concrete change with the passage of time after casting?

Introduction / Context:
Concrete hardens through hydration of cement, which is a time-dependent chemical process. Understanding how strength evolves with age is crucial for formwork removal, prestressing operations, load application, and long-term performance predictions.

Given Data / Assumptions:

• Normal ambient temperatures and adequate curing.
• Ordinary Portland or blended cements.
• No severe deterioration mechanisms active during early ages.

Concept / Approach:
As hydration proceeds, cement gel products fill pores and bond aggregates, reducing porosity and increasing strength. The rate of gain is rapid at early ages and slows progressively; however, strength continues to increase beyond 28 days, particularly for blended cements, as long as moisture and favorable temperatures persist.

Step-by-Step Solution:

Verification / Alternative check:
Standard strength development curves show typical gains from 7 to 28 days and continuing thereafter; long-term strengths can exceed 28-day values substantially, especially for SCM-rich mixes.

Why Other Options Are Wrong:

• (b) Decrease is associated with deterioration, not normal curing.
• (c) Random fluctuation does not represent hydration kinetics.
• (d) Constant strength contradicts continued hydration.

Common Pitfalls:
Assuming strength stops at 28 days; neglecting the role of curing in enabling continued hydration.

Final Answer:
Increases