Flakiness & Elongation Index

The flakiness index is the percentage by weight of aggregate particles whose least dimension (thickness) is less than 0.6 times their mean sieve size; the elongation index is the percentage whose greatest dimension (length) exceeds 1.8 times their mean size. Both are determined per IS 2386 Part 1 using a thickness gauge and a length gauge respectively.

Flaky and elongated particles are structurally weak (snap easily), pack poorly, increase voids and hence water/binder demand, and reduce workability and pavement stability. IS 383/MORTH typically limit the combined flakiness + elongation index to about ≤30-35% for concrete and ≤25-30% for bituminous wearing courses. Crushers producing excessive flaky material (impact vs cone crusher choice) are a common root cause and a quarry-acceptance flag.