Flakiness index criterion: an aggregate particle is termed “flaky” if its least dimension is smaller than what fraction of its mean (nominal) size?

Introduction / Context:
Aggregate shape affects workability, strength, and durability. Standards define “flaky” and “elongated” particles because excessive amounts impair performance (higher water demand, poor packing). Field tests use simple gauges to classify particles by dimensional ratios.

Given Data / Assumptions:

• Mean (nominal) size refers to the mean of sieve apertures between which the particle is retained.
• We follow the common criterion used in Indian/British practice.
• We focus on the threshold fraction defining flakiness.

Concept / Approach:
A particle is deemed “flaky” if its least thickness is less than 0.6 of its mean size, i.e., less than 3/5 of the nominal size. Flaky particles have high surface area to volume and tend to align, harming workability and strength.

Step-by-Step Solution:
Recall standard threshold: least dimension < 0.6 × mean size.Express 0.6 as a fraction: 3/5.Select 3/5 of mean dimension.

Verification / Alternative check:
Flakiness index tests use a thickness gauge sized at 0.6 times the mean sieve size range; particles passing that slot are considered flaky.

Why Other Options Are Wrong:

• 1/5 or 2/5: far too restrictive (would classify too few as flaky).
• 4/5: too lenient (would classify many non-flaky as flaky).
• None: incorrect because a standard fraction exists.

Common Pitfalls:
Confusing flakiness with elongation (length > 1.8 times mean size); misusing nominal size instead of mean of the retained sieves.

Final Answer:
3/5 of mean dimension