Difficulty: Easy
Correct Answer: Zone IV (finer sand)
Explanation:
Introduction / Context:
Workability and water demand of concrete are sensitive to fine aggregate grading. Finer sands increase specific surface area, which raises paste demand and typically increases required water for a given slump unless adjustments are made.
Given Data / Assumptions:
Concept / Approach:
As sand becomes finer (toward Zone IV), its specific surface area increases. More paste is required to coat particles and fill voids, leading to higher water demand at constant cement content. Coarser sands (Zone I) generally need less water for the same slump. Hence sands in Zone IV tend to require a higher water–cement ratio unless compensated by admixtures or mix redesign.
Step-by-Step Solution:
Verification / Alternative check:
Mix design guidance routinely flags fine Zone IV sands as increasing water requirement and shrinkage risk if not properly adjusted.
Why Other Options Are Wrong:
Common Pitfalls:
Final Answer:
Zone IV (finer sand).
Discussion & Comments