Concrete shrinkage — key dependencies and time effect Which of the following general statements about drying shrinkage of concrete are true?

Introduction / Context:Drying shrinkage is a volumetric reduction due to moisture loss from hardened cement paste. Excess shrinkage causes cracking and serviceability problems. Understanding the main influencers helps in proportioning mixes and detailing joints and reinforcement for crack control.

Given Data / Assumptions:

• Ordinary concretes without special expansive agents.
• Comparable aggregate types and environmental conditions.
• Focus on qualitative dependencies rather than exact magnitudes.

Concept / Approach:

Shrinkage largely originates in the paste fraction. More mixing water (and higher w/c) leaves a more connected capillary network, allowing greater drying shrinkage. For the same workability, higher cement content increases paste volume relative to aggregate, often increasing shrinkage. Over time, shrinkage accumulates and asymptotically approaches a final value; the rate decreases with age, but the total amount increases with time of drying.

Step-by-Step Solution:

Verification / Alternative check:

Empirical models (e.g., code shrinkage equations) reflect dependence on paste content, w/c, member size, and time of drying, confirming these trends.

Why Other Options Are Wrong:

• “None of the above” contradicts well-established mechanisms.

Common Pitfalls:

• Ignoring the strong restraining role of aggregate; richer mixes with the same w/c can still shrink more due to higher paste fraction.

Final Answer:

All of the above.