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AIV, AAV, ACV and flakiness/elongation

Short answer

Aggregate Impact Value measures toughness by 15 hammer blows, % passing 2.36 mm. Los Angeles Abrasion Value measures hardness by 500 revolutions, % passing 1.7 mm. Aggregate Crushing Value measures strength under 40 t load, % passing 2.36 mm. Flakiness and elongation indices limit weak, poorly interlocking particles that reduce stability and increase binder demand.

Distinguish between Aggregate Impact Value, Aggregate Abrasion Value and Aggregate Crushing Value. Why is it necessary to determine flakiness and elongation indices of an aggregate sample?

Distinguishing the three values

PointAggregate Impact Value (AIV)Aggregate Abrasion Value (LAAV)Aggregate Crushing Value (ACV)
Property measuredToughness: resistance to sudden impactHardness: resistance to wear by abrasion and impactStrength: resistance to gradually applied compressive load
TestImpact machine, 14 kg hammer, 380 mm fall, 15 blowsLos Angeles machine, steel balls, 500 revolutions at 30-33 rpmCylinder, 40 t load in 10 min
Sample10-12.5 mm, 3 layers 25 tamps5 or 10 kg of graded aggregate10-12.5 mm, 3 layers 25 tamps
Result% fines passing 2.36 mm% passing 1.7 mm% fines passing 2.36 mm
FormulaW2/W1×100W_2/W_1 \times 100(W1−W2)/W1×100(W_1 - W_2)/W_1 \times 100W2/W1×100W_2/W_1\times 100
Typical limitNot more than 30% (surface), 45% (base)Not more than 30% (surface), 40-50% (base)Not more than 30% (surface), 45% (base)

Good aggregates give low values in all three tests.

Why flakiness and elongation indices are needed

  • Flaky particles (least dimension less than 0.6 times the mean size) and elongated particles (length more than 1.8 times the mean size) have a poor shape.
  • They are weak and break easily under rollers and traffic, which changes the grading.
  • They do not interlock or pack well, leaving more voids and giving lower stability and poorer compaction.
  • They tend to orient in the same direction, creating weak planes.
  • They need more binder for coating in bituminous mixes.

So their quantity is controlled (combined flakiness and elongation index not more than about 30-35%) by determining these indices.

✓ Answer checked by Claude Opus 5.5 (high effort)

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