This standard prescribes the methods of test for determining the particle size distribution (sieve analysis) and shape characteristics (flakiness, elongation, and angularity) of aggregates. These properties are critical for determining the workability of fresh concrete and the durability of hardened concrete.
Covers methods for determining particle size and shape of aggregates, including grading and flakiness index.
Quick Reference Values
flakiness thresholdless than 0.6 times the mean dimension
elongation thresholdgreater than 1.8 times the mean dimension
min aggregate size for shape tests6.3 mm
angularity number range0 to 11
washing sieve size75-micron IS Sieve
Key Formulas
Flakiness Index = (Weight of material passing thickness gauges / Total weight of sample) x 100
Elongation Index = (Weight of material retained on length gauges / Total weight of sample) x 100
Angularity Number = 67 - (100 x W / (C x GA))
Practical Notes
Flakiness and elongation indices tests are not applicable to aggregate sizes smaller than 6.3 mm.
Highly flaky or elongated aggregates increase the water demand of concrete and reduce its compressive strength.
Do not overload sieves during sieve analysis to avoid inaccurate gradation curves; use appropriate sample weights as per Table 3.