Flakiness and Elongation Index Test of Coarse Aggregate

Flakiness and Elongation Index Test

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 the weight of the total aggregate.

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

Flakiness Index

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

Elongation Index

The Elongation index of aggregate is the % by weight of the particles (aggregates) whose length is greater than 1 and 4/5^th (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 structures.

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

Apparatus

1. Balance

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

2. Metal gauge

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

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 SIEVES	RETAINED ON IS SIEVE	THICKNESS GAUGE	LENGTH GAUGE
1	2	3	4
63 MM	50 MM	33.90 MM	0
50 MM	40 MM	27.00 MM	81.0 MM
40 MM	31.5 MM	19.50 MM	58.5 MM
31.5 MM	25 MM	16.95 MM	0
25 MM	20 MM	13.50 MM	40.5 MM
20 MM	16 MM	10.80 MM	32.4 MM
16 MM	12.5 MM	08.55MM	25.6 MM
12.5 MM	10 MM	06.75 MM	20.2 MM
10 MM	6.3 MM	04.89 MM	14.7 MM

The Dimension shown in the thickness gauge is equal to 0.6 times the mean sieve size.

The Dimension shown in the length gauge is equal to 1.8 times the mean sieve size

Read More: Aggregate Crushing Value Test – Procedure and Result

Flakiness and Elongation Test Procedure

Sample Preparation

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.

A 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

Try to pass the aggregate width-wise through the slot of 10mm to 6.3 mm on a flakiness gauge.

A separate sample passed through this slot and weight (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)
63MM	50MM	33.90MM
50MM	40MM	27.00MM
40MM	31.5MM	19.50MM
31.5MM	25MM	16.95MM
25MM	20MM	13.50MM
20MM	16MM	10.80MM
16MM	12.5MM	08.55MM
12.5MM	10MM	06.75MM
10MM	6.3MM	04.89MM

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  

The 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 the procedure for elongation index,

Separation of Elongation Material

Try to pass the aggregate length-wise through the slot of 10mm to 6.3 mm on the length gauge.

A separate sample retains on this slot and weighted 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)
63MM	50MM	0
50MM	40MM	81.0MM
40MM	31.5MM	58.5MM
31.5MM	25MM	0
25MM	20MM	40.5MM
20MM	16MM	32.4MM
16MM	12.5MM	25.6MM
12.5MM	10MM	20.2MM
10MM	6.3MM	14.7MM

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, the 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%

Read More: Aggregate Testing | 7 Test On Aggregates | Coarse Aggregate Test

Result

The 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 road construction be below 35%.

SR NO.	TYPE OF CONSTRUCTION	ALLOWABLE FLAKINESS INDEX
1	WBM construction
	Wearing surface	15%
	lower granular layer	15%
2	Concrete construction
3	Bituminous construction	25%
4	Two coat bituminous surface dressing	25%
5	Bituminous macadam
	Base course	25%
	Binder course	25%
6	Dense bituminous macadam	35%

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