Fine aggregate grading — which IS sand zone typically demands a higher water–cement ratio? According to standard Indian grading zones for fine aggregates, sand that requires a relatively higher water–cement ratio for similar workability belongs to:

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:

  • IS grading zones I (coarse) to IV (very fine) for natural sand.
  • Targeting equal workability (slump) without altering admixture dosage.
  • Other constituents held constant to isolate grading effects.


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:

Relate grading → specific surface → water demand.Zone IV is finest → highest water demand → higher w/c if unchanged.Therefore, choose Zone IV.


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:

  • Zones I–III are progressively coarser than IV and generally demand less water.


Common Pitfalls:

  • Failing to re-balance fines or use water-reducers when switching to finer sands.


Final Answer:

Zone IV (finer sand).

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