All about civil construction knowledge- PARAM VISIONS

Flakiness index test for coarse aggregates.

 Apparatus & items required:

 1. Weighing scale. 

 2. Tray.

 3. Aggregate sample.

 4. Metal thickness gauge.

 5. Set of sieves.

 6. Record sheet.


As per IS-2386, certain conditions to be followed while doing the flakiness index test are as below.

1. The flakiness index test is not applicable to the coarse aggregates retained over 63mm. sieve & passing through the 6.3mm. sieve.

2. The minimum weight of the sample to be taken for the particular size of aggregates are as below.

3. A number of aggregates retained over any sieve size should be at least 200 pieces for good results of the flakiness index test.

Go through the article 👇

👀. What is the flakiness index test of coarse aggregates?


1. Let us take approx. 6kg of 20mm. aggregate sample for the test procedure.

2. Set the sieves in increasing order so that the smaller one is placed at the bottom and the larger-sized sieve is placed at the top. The different sizes of sieves are shown below.

3. Now, we have to put the aggregate at the top sieve and shake them well. We can use a mechanical sieve shaker for good results, & if it is not available we can do the sieving manually. 

4. After the sieving action is complete, the fraction of aggregates of different sizes is retained over the particular sieves. The aggregates will pass through the 1st 5 sieves (63mm to 25mm.) & the fraction of the sample starts retaining from 20mm. sieve. 

5. We have to collect the sample of aggregates retained over the individual sieves separately. The collected samples should be kept on the floor in descending order one beside the another.

 That means the samples retained over 20mm, 16mm, 12.5mm.,10mm., & 6.3mm. sieve should be kept separately.

6. We have to take the total weight of samples retained over the individual sieve separately & record them before passing through the thickness gauge (As shown in the below table at 9.).

7. Now, we have to pass the aggregates of individual sieve samples through the corresponding slots of the thickness gauge.

As you can observe in the above image, all the aggregate samples retained over 16mm. sieve should be passed through slot J(20 to 16). The sample pieces passing through slot J & retained over the slot should be bifurcated separately.

The same procedure should be carried out for all the sieve samples by selecting the respective slots as per the aggregate sieve size.

8. The passed & retained stones for all the sieve samples are separated from each other.

9. Now, one by one the aggregates passed through the thickness gauge are weighed & the wt. is recorded in the sheet in descending order as shown below.

10. We have to add the total sample wt. & the weight of the fraction passed through the thickness gauge. Let the weight be W1 & W2 respectively.

11. Flakiness index 

= [total wt. of sample passing through various thickness gauges.÷ total wt. of an aggregate sample]х100

FI = [W2 ÷ W1] х 100

 The flakiness index should be within 35% for building concrete.


Flakiness index

 = [560gm.  ÷ 5980gm.] х 100

   FI = 9.36 ✔ OK

11. The same procedure is carried out for the aggregate of the same lot and the average of the two is considered the final flakiness index.


For concrete<35%

For BTSD (bituminous surface dressing) < 25% 

For BTBM (bituminous bond macadam) < 15% 

For pavement construction < 15%

Combined FI + EI < 30%

FI 👉 Flakiness index.

EI 👉 Elongation index.

Thank you for going through this test procedure. Have a good day 😄.


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