Determining Flakiness Index of Aggregates

  Flakiness Index of Aggregates (IS:2386 part 1)

Aggregate particles are classified as flaky when they have a thickness (smallest dimension) of less than 0.6 of their mean sieve size. The flakiness index of an aggregate sample is found by separating the flaky particles and expressing their mass as a percentage of the mass of the sample tested. This test is not applicable to aggregate passing 6.30mm sieve and retained as 63.0mm sieve. Flaky particles are considered to be unsuitable for the pavement materials. Flaky particles tends to get broken as the impact loading of vehicles passing over the road.

Apparatus

Sample,Weighing machine, Thickness gauge,Is Sieves of sizes 63mm, 50mm, 40mm, 31.5mm, 25mm, 20mm, 16mm, 10mm and 6.3mm.

Thickness Gauge

Test Procedure

1. Take the aggregate sample having at least 200 pieces of different sized aggregates.
2. Sieve the sample through mentioned sieves i.e., from 63mm to 6.3mm sieves.
3. Aggregates retained on 63 mm and passing 6.3mm are discarded.
4. Now weigh aggregate retained on different sieve and note down the total weight as “W1”
5. The aggregate particles from each of the size range is taken and passed through corresponding gauge of thickness gauge or flakiness gauge with its thinnest side facing the slot thickness  of gauge.
6. Each gauge length is 0.6 times the mean dimension of aggregate size range. If particle retained on 16mm and passed through 20mm size is taken, then it should pass through 10.8 mm slot of gauge which is 0.6 times the mean of 16mm and 20 mm.(i.e. [{0.6*(16+20)}/2]=10.8 mm
7. The particles that were passing through the length gauge are weighed which is “W2”.
8. Now calculate the flakiness index which is the ratio of weight of particles passed through thickness gauge to the total weight of the sample gauged and it is expressed in percentage.

Calculations:

Elongation index =(W2/W1) X 100

W1= Weight passed of aggregates through thickness gauge
W2= Total sample weight.
Flakiness Index should not more than 15 %  for pavement aggregates material.