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 3/5th(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 4/5th (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 structures.
Reference:- IS 2386 (Part 1) – 1963 PDF.
Apparatus
- Balance
The balance used to measure the aggregate has sufficient capacity. Its accuracy is 0.1% of the weight of the test sample.
- 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% |
FAQs
What is the Flakiness Index?
The Flakiness Index is the percentage of particles in a coarse aggregate sample that have a thickness less than three-fifths of their mean dimension. These particles are considered to be flaky, and can cause problems in concrete by reducing the workability and increasing the amount of voids in the mix.
What is the Elongation Index?
The Elongation Index is the percentage of particles in a coarse aggregate sample that have a length greater than one and a half times their width. These particles are considered to be elongated, and can cause problems in concrete by reducing the workability and increasing the amount of voids in the mix.
How is the Flakiness and Elongation Index Test performed?
The Flakiness and Elongation Index Test is performed by sieving a sample of coarse aggregate through a set of standardized sieves, and then measuring the percentage of particles that are either flaky or elongated.
You May Also Like
- Abrasion Test on Aggregate (Los Angeles Abrasion Test)
- Specific Gravity and Water Absorption Test of Coarse Aggregate
- Aggregate Impact Value Test, Procedure, Result & Standards
- Aggregate Testing | 7 Test On Aggregates | Coarse Aggregate Test
- Replacement of Coarse Aggregate In Concrete | Alternative Materials For Coarse Aggregate In Concrete
- Fineness Modulus of Sand | Fineness Modulus of Fine Aggregate
- All About Coarse Aggregate: Definition, Types, Properties, and Classification
