Effect of sand grading — which properties vary significantly? Variation in the grading (particle size distribution) of fine aggregate (sand) most strongly affects which aspects of concrete performance and handling?

Introduction / Context:
Fine aggregate grading controls paste demand, packing density, and bleeding/segregation tendencies. Consequently, it influences fresh properties and the hardened performance of concrete, especially when water–cement ratio is adjusted to maintain workability.

Given Data / Assumptions:

• Only sand grading varies; other materials and proportions are otherwise comparable.
• Mix adjustments may be made to achieve target slump.
• Normal Portland cement concrete is considered.

Concept / Approach:
Well-graded sand reduces voids and paste demand, improving workability without excessive water, which supports higher strength and improved durability (lower permeability). Poorly graded or overly fine sands increase water demand for the same workability, raising w/c ratio, which reduces strength and durability. Extremely gap-graded sands increase segregation and finishing difficulties, complicating handling and placing.

Step-by-Step Solution:

Verification / Alternative check:
Empirical mix design charts show clear links between sand fineness modulus and water demand; durability indicators (e.g., rapid chloride permeability) correlate with paste content and w/c ratio affected by grading.

Why Other Options Are Wrong:

• Choosing only one or two properties overlooks the coupled impact of grading on both fresh and hardened characteristics.

Common Pitfalls:
Compensating poor grading with excess cement rather than optimized gradation; ignoring variability in sand source leading to day-to-day changes in slump.

Final Answer:
All the above