They tell us how irregularly shaped the coarse aggregates are — especially how thin (flaky) or long (elongated) they are relative to their width.
If thickness < 0.6 × mean size, the particle is too thin. Such particles are unstable under traffic loads and tend to snap or wear out.
If length > 1.8 × mean size, the particle is too long and slender. These can bend, twist, or crush under compaction and live loads.
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