Flakiness and Elongation Index Test

1. Title

Determination of Flakiness Index and Elongation Index of Coarse Aggregates.

2. Objective

To determine the Flakiness Index (FI) and Elongation Index (EI) of a given sample of coarse aggregates to assess their suitability for road construction.

3. Apparatus Required

• Balance: A balance with sufficient capacity and accuracy (readable to 0.1% of the sample weight).
• IS Sieves: Standard sieves of sizes 63 mm, 50 mm, 40 mm, 31.5 mm, 25 mm, 20 mm, 16 mm, 12.5 mm, 10 mm, and 6.3 mm.
• Thickness Gauge (Flakiness Gauge): A metal plate with standard slots for determining the flakiness index.
• Length Gauge (Elongation Gauge): A metal base with fixed pins for determining the elongation index.
• Handling Equipment: Trays, scoops, and a brush.

4. Theory

Particle shape is a crucial property of aggregates used in pavement construction.

Flakiness Index: The Flakiness Index of an aggregate is the percentage by weight of particles in it whose least dimension (thickness) is less than 0.6 times their mean dimension. Flaky particles are detrimental as they tend to break under heavy loads.

Elongation Index: The Elongation Index of an aggregate is the percentage by weight of particles in it whose greatest dimension (length) is greater than 1.8 times their mean dimension. Elongated particles are prone to breaking during compaction and service.

Aggregates that are flaky or elongated reduce the workability of concrete and stability of bituminous mixes.

5. Procedure

The test was carried out using the following steps:

1. The sample was prepared by sieving the aggregates through IS sieves ranging from 63 mm to 6.3 mm.
2. From each size fraction, a minimum of 200 pieces were taken for testing.
3. Each individual particle was passed through the thickness gauge and the length gauge corresponding to its size fraction.
4. The weight of flaky aggregates (passing through the thickness gauge) and non-flaky aggregates (retained on the thickness gauge) were recorded separately ($w_1$).
5. The weight of elongated aggregates (retained on the length gauge) and non-elongated aggregates (passing through the length gauge) were recorded separately ($w_2$).

6. Observations and Calculations

Note: Due to time constraints, the class was divided into groups, with each group sieving a different fraction of the sample. Our group separated and tested the fraction passing 20 mm and retained on 16 mm, using a sample size of approximately 50 pieces of aggregate. The calculations below are based on these specific observations.

Table 1: Flakiness Index Observation

Size of Aggregate	Weight of Fraction ($W_1$) (g)
Passing (mm)	Retained (mm)
20	16	482.02
(Passing: 67.02 g + Retained: 415 g)
Total		$\sum W_1$ = 482.02 g

Weight of Passing (Flaky) ($w_1$): 67.02 g

Weight of Retained (Non-Flaky): 415.00 g

Table 2: Elongation Index Observation

Size of Aggregate	Weight of Fraction ($W_2$) (g)
Passing (mm)	Retained (mm)
20	16	482.02
(Passing: 349.25 g + Retained: 132.77 g)
Total		$\sum W_2$ = 482.02 g

Weight of Retained (Elongated) ($w_2$): 132.77 g

Weight of Passing (Non-Elongated): 349.25 g

Calculations

Flakiness Index (FI):

Elongation Index (EI):

7. Result

The Flakiness Index of the aggregate sample was found to be: 13.90%

The Elongation Index of the aggregate sample was found to be: 27.54%

8. Discussion and Conclusion

The aggregate sample tested yielded a Flakiness Index of 13.90% and an Elongation Index of 27.54%. The combined index is approximately 41.44%. Standard specifications (such as MORTH) generally recommend a combined index of less than 30% for high-quality pavement layers like bituminous concrete, though up to 35-40% may be permissible for sub-base layers.

While the Flakiness Index is relatively low and acceptable, the Elongation Index is quite high, indicating a significant presence of long, slender particles. Based on these observations, the aggregate is suitable for lower pavement layers (like GSB) but may need to be blended with better-shaped aggregates or crushed differently for use in surface courses to prevent breakage under traffic loads.

9. Precautions

• Sieving: Care should be taken to ensure distinct size fractions are isolated by proper sieving; clogged sieve openings must be cleaned.
• Gauging: Particles should be passed through the thickness and length gauges manually and gently; they must not be forced through the slots.
• Weighing: The balance should be leveled and checked for zero error before use to avoid parallax or measurement errors.
• Sampling: Since a limited sample size (approx. 50 pieces) is used due to time constraints, the results should be treated as indicative. Standard codes recommend a larger sample size for higher accuracy.