Flakiness and Elongation Index Test

Flakiness and Elongation Index Test of Coarse Aggregate

Flakiness and Elongation Index Test are very important tests to be performed on aggregate in the laboratory. This test gives the percentage of flaky and elongate aggregate present in the total aggregate sample.

Aggregate shape, size, and surface texture majorly affect the properties of freshly mixed concrete more than the properties of hardened concrete. 

Angular, flaky, rough-textured, and elongated aggregate particles require more water to produce workable concrete than the smooth, rounded compact aggregate. Also, such irregular-shaped aggregate cement content must also be increased to maintain the water-cement ratio.

Elongated and flaky aggregate, when used in the construction of pavement may result in failure of the pavement due to their random position under repeated loading and vibration.

It is important to keep the amount of flaky and elongated aggregate within permissible levels. Generally, flaky and elongated aggregate are avoided or are limited to about 15 % by weight of the total aggregate.

Read More: Aggregate Impact Value Test, Procedure, Result & Standards


What is Flakiness Index?

“The flakiness index of aggregate is the % by weight of the particles (aggregates) whose thickness is less than 3/5th(0.6 times) of their mean dimension.”


What is Elongation Index?

“The Elongation index of aggregate is the % by weight of the particles (aggregates) whose length is greater than 1 and 4/5th (1.8 times) of their mean dimension.”


Objectives

This method uses to measure the Flakiness Index and Elongation index of aggregate use in the construction of Highway pavement and concrete structure.

Reference:- IS 2386 (Part 1) – 1963 PDF.


Apparatus

  1. Balance:-

The balance used to measure the aggregate has sufficient capacity. It accuracy is 0.1% of the weight of the test sample.

  1. Metal gauge:-

The metal gauge used to measure the thickness/elongation is looks like this figure shown below:

Flakiness and Elongation Index Test of Coarse Aggregate

The IS Sieves: 63 mm, 50 mm, 40 mm, 31.5 mm, 25 mm, 20 mm, 16 mm, 12.5 mm, 10 mm, 6.3 mm.

SIZE OF AGGREGATES
PASSING THROUGH IS SIEVESRETAINED ON IS SIEVETHICKNESS GAUGE LENGTH GAUGE
1234
63 MM50 MM33.90 MM0
50 MM40 MM27.00 MM81.0 MM
40 MM31.5 MM19.50 MM58.5 MM
31.5 MM25 MM16.95 MM0
25 MM20 MM13.50 MM40.5 MM
20 MM16 MM10.80 MM32.4 MM
16 MM12.5 MM08.55MM25.6 MM
12.5 MM10 MM06.75 MM20.2 MM
10 MM6.3 MM04.89 MM14.7 MM
Flakiness and Elongation Index
Flakiness Index Gauge
Flakiness and Elongation Index Test of Coarse Aggregate
Elongation Index Gauge
  • The Dimension shown in thickness gauge is equal to 0.6 times the mean sieve size.
  • The Dimension shown in length gauge is equal to 1.8 times the mean sieve size

Read More: Aggregate Crushing Value Test – Procedure and Result


Preparation of Sample For Flakiness and Elongation Index Test

Sample Preparation:

Flakiness and Elongation Index Test of Coarse Aggregate
IS Sieve
  • Prepare aggregate sample for the test by sieving between IS sieve 6.3 mm size at the bottom and 63 mm IS sieve at top.
  • Separate sample retains on each sieve.
  • The collected aggregate sample should have at least 200 numbers of individual aggregate for accurate test results from each range of IS sieve.
  • We take a range of aggregate samples retained on 6.3 mm IS Sieve. (Separate test can be conducted on each range of Sieve).
  • Take the weight of the total aggregate sample collected for tests as W1.

Note: Test can be conducted for each range of Flakiness gauge slot.


Test Procedure for Flakiness Index

Separation of Flaky Material:

Flakiness and Elongation Index
Flakiness Test
  • Try to pass the aggregate width-wise through the slot of 10mm to 6.3 mm on a flakiness gauge.
  • Separate sample passed through this slot and weight it(W2)

Note: Test can be conducted for each range of Flakiness gauge slot.

Observation Table

Passing through IS sieve
(mm)
Retained on IS sieves
(mm)
Flakiness Gauge
(mm)
Weight passing on
Flakiness Gauge (W1)
63MM50MM33.90MM 
50MM40MM27.00MM 
40MM31.5MM19.50MM 
31.5MM25MM16.95MM 
25MM20MM13.50MM 
20MM16MM10.80MM 
16MM12.5MM08.55MM 
12.5MM10MM06.75MM 
10MM6.3MM04.89MM 
  Total 

Flakiness Index = Weight of aggregate passed through width gauge 10 mm to 6.3 mm (W2) /     Total weight of aggregate sample taken (W1)

                            = (W2/W1) x 100

For example, Weight of aggregate passed through width gauge of 10 mm to 6.3mm(W2) = 200 gm and Total weight of aggregate sample = 1000 gm

Flakiness Index = (200 gm / 1000 gm) x 100 = 20%


Result  

Percentage of flaky aggregate in the range of 10 mm to 6.3 mm is 20%.

Read More: Abrasion Test on Aggregate (Los Angeles Test)


Test Procedure for Elongation Index

The Following is procedure for elongation index,

Separation of Elongation Material

  • Try to pass the aggregate length wise through slot of 10mm to 6.3 mm on length gauge.
  • Separate sample retain on this slot and weight it(W2).

Note: Test can be conducted for each range of elongation gauge slot.


Observation Table            

Passing through IS sieve
(mm)
Retained on IS sieves
(mm)
Elongation Gauge
(mm)
Weight retain on
length Gauge (W2)
63MM50MM0 
50MM40MM81.0MM 
40MM31.5MM58.5MM 
31.5MM25MM0 
25MM20MM40.5MM 
20MM16MM32.4MM 
16MM12.5MM25.6MM 
12.5MM10MM20.2MM 
10MM6.3MM14.7MM 
  Total 

Flakiness Index = weight of aggregate retained on length gauge of  10 mm to 6.3 mm (W2) / _ Total weight of aggregate sample taken (W1)

                             = (W2/W1) x 100

For example, Weight of aggregate retained on length gauge of 10 mm to 6.3mm(W2) = 150 gm and Total weight of aggregate sample = 1000 gm

Elongation Index = (150 gm / 1000 gm) x 100 = 15%


Result:

Percentage of flaky aggregate in the range of 10 mm to 6.3 mm is 15%.

IRC recommended the Flakiness Index Value

IRC recommended the Flakiness index value for the road construction is below 35%.

SR NO. TYPE OF CONSTRUCTIONALLOWABLE FLAKINESS INDEX
   
1 WBM construction 
  Wearing surface15%
  lower granular layer15%
2 Concrete construction 
3 Bituminous construction25%
4 Two coat bituminous surface dressing25%
5 Bituminous macadam 
  Base course25%
  Binder course25%
6 Dense bituminous macadam35%

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