Aggregates – criterion for a flaky particle According to standard definitions, an aggregate particle is termed “flaky” if its least dimension (thickness) is less than what fraction of its mean size?

Introduction / Context:
Shape characteristics of aggregates—particularly flakiness and elongation—affect workability, compaction, and the mechanical interlock in concrete and bituminous mixes. Excess flaky particles increase surface area, demand more paste/bitumen, and can reduce strength and durability.

Given Data / Assumptions:

• Mean size is the average of the sieve size through which the particle passes and the sieve size on which it is retained.
• “Least dimension” means thickness of the particle.
• Standard test equipment (flakiness gauge) is assumed.

Concept / Approach:
Standards define a particle as flaky if thickness < 0.6 * mean size. The factor 0.6 corresponds to 3/5. Limits on the percentage by mass of flaky particles are specified to maintain desirable aggregate skeleton.

Step-by-Step Solution:
Compute threshold: thickness limit = 0.6 * mean size.Convert 0.6 to a rational fraction: 3/5.Select the matching option: 3/5 of the mean size.

Verification / Alternative check:
Flakiness index testing uses slot widths equal to 0.6 times the mean sieve size for each fraction; particles passing are counted as flaky.

Why Other Options Are Wrong:

• 2/3 (0.667), 3/4 (0.75), 5/8 (0.625) do not match the codal threshold of 0.6.
• “None of these” is incorrect because 3/5 is correct.

Common Pitfalls:
Confusing flakiness (thickness) with elongation (length); both must be controlled but use different gauges and limits.

Final Answer:
3/5 of the mean size