FLAKINESS AND ELONGATION INDEX

FLAKINESS AND ELONGATION  TEST OF AGGREGATE

FLAKINESS INDEX: Percentage of aggregate by weight whose least dimension is less than 3/5 times of mean seive size is known as flakiness index

ELONGATION INDEX:Percentage of aggregate by weight whose greater dimension is more than 9/5 times of mean seive size is known as elongation index.

THIS TESTS IS NOT APPLICABLE FOR AGGREGATE SIZE LESS THAN 6.3 mm.

According To IS 383 :2016 COMBINED FLAKINESS AND ELONGATION VALUE IS NOT MORE THAN 40%.

PROCEDURE OF TEST IS GIVEN IN IS 2386 PART 1ST.

Meaning of 3/5 of mean seive size is:
mean seive size = aggregate passing from seive + aggregate retained on sieve ÷2

Then: 3/5× (20+16/2)= 10.8 mm

Here 20 mm is seive size where aggregate pass and 16 mm is seive where aggregate retained.


So here, when you see Flakiness gauge the gap between these particular seive 20 mm and 16 mm is 10.8 mm.
And in Elongation it is : 9/5× (20+16/2)= 32.4 mm.

Example for flakiness and elongation is given below:

Let we take 200 pieces of 20 mm after sampling and weight it
let it come : 2000 gm

seive size              Retained wt.          Passing
                                                             on gauge
                                     gm                        gm
20-16                          220                         21
16-12.5                       822                         220
12.5-10                       792                         190
10-6.3                         120                         16
                          Total  1954 gm               447 gm

% of Flakiness = 447/1954= 22.87%

Here 46 gm passing from 6.3 mm seive and retained on pan so it is not counted.


sieve size           Retained wt              Retained
                                                             on gauge

20-16                      199                         08
16-12.5                   602                         120
12.5-10                   602                         104
10-6.3                     104                         07
             Total        1507                         239

% Of Elongation = 15.85%


so combined Flakiness and Elongation value  : 22.87+15.85 = 38.72%