FLAKINESS INDEX



DETERMINATION OF FLAKINESS INDEX OF COARSE AGGREGATE 

IS: 2386 - Part 1 

1. Introduction

This method of test covers the procedure for determining the Flakiness Index of coarse aggregate in the size range from 63 mm to 6.3 mm.

2. Apparatus

(i) Metal gauge of the pattern shown in the figure.

(ii) A balance of sufficient capacity and sensitivity with accuracy of at least 0.1 percent of the total weight of the sample tested.

(ii)  IS test sieves of sizes shown in the table 1 below for sieving the aggregates.

3. Sample preparation

Sufficient quantity of aggregate shall be taken to provide a minimum number of 200 pieces of each fraction for gauging

Passing IS sieve mm Retained on IS sieve mm Thickness of gauge  mm
63 50 33.9
50 40 27
40 31.5 21.5
31.5 25 16.95
25 20 13.5
20 16 10.8
16 12.5 8.55
12.5 10 6.75
10 6.3 4.89

4. Procedure

a) The sample shall be first sieved through the required sieves given in the table 1 above. The dimension of the thickness gauge to be used to test aggregate of each size range is also indicated in the table.

b) The weight of each fraction retained in the sieves, W1, W2, W3 …..etc is determined. The sum of these will be the weight of sample tested (W).

c) The fraction retained in each sieve is then gauged through the appropriate slot of the thickness gauge, one by one.

d) The weight of material passing each slot is determined as Y1, Y2, Y3 etc, which constitute the flaky particles.

e) In case where sieves with slots are used in place of gauge, the fraction of the sample retained on each sieve is sieved through each of the slotted sieves in full, instead of checking the aggregate pieces individually.  

5. Calculation

a) The percentage by weight retained on each sieve, x1, x2, x3 ….etc of the total weight of the aggregates tested (W) are then calculated to the accuracy of 0.1 percent of the weight of test sample.

i.e., x1 = W1/W, x2 = W2/W, x3 = W3/W…. etc. The sum of this should be 100%.

b) The percentage of particles passing each slot say, y1, y2, y3 ….etc are then calculated.  i.e., y1 = Y1/W1, y2 = Y2/W2, y3 = Y3/W3…. etc

c) The weighted % of aggregates passing each slot is determined by multiplying x1 by y1, x2 by y2….etc  d) The Flakiness Index is the % total weighted mass of the material passing the gauges or sieves expressed as a percentage of the total weight of the sample tested.  Flakiness Index in percentage = (x1y1 + x2y2 + x3y3 ……)/100.

6. Combined Flakiness and Elongation Indices

Some specifications insist on combined Flakiness and Elongation Indices (Total). This combined value is determined as follows:

a) The Flakiness Index of the sample passing 63 mm IS sieve and retaining on 6.3 mm IS sieve is first determined.

b) The flaky particles are then separated out from the sample.

c) From the remaining non-flaky material, elongated particles are separated.

d) The Elongation Index is then calculated from the weight of the non-flaky part.

e) The value of Flakiness Index and Elongation Index thus computed is added up to give the combined Flakiness and Elongation Indices (Total). 

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