Calculator
Ref: IS 2386 (Part 1) – 1963
Aim
To Determine Flakiness Index and Elongation Index of Aggregates
Theory
- The particle shape of aggregate can be described by the percentage of how flaky or how elongated the aggregate is.
- For base course and construction of bituminous and cement concrete type, the presence of flaky and elongated particles are considered undesirable as they may cause inherent weakness with possibilities of breaking down under heavy loads. This test is not applicable to sizes smaller than 6.3mm.
- An aggregate is said to be flaky if its least lateral dimension is less than 0.6 times the mean dimension.
- An aggregate is said to be elongated if its largest lateral dimension is greater than 1.8 times the mean dimension.
Apparatus
Standard I.S. sieves 63,50,40,30,20,16,12.5,10 & 6.3mm
Flakiness gauge
Elongation gauge
Electronic weigh balance
Procedure
Flakiness Index
- Sample is sieved using standard sieves.
- Weight on each sieve is noted as ‘weight on sieve’.
- The samples passing through each sieve are then passed through the flakiness gauge.
- The sample passing through this gauge is noted as ‘Weight passing gauge’.
- Flakiness index is expressed as percentage of weight of aggregates passed through the gauge to the weight of sample in sieves.
- \text { Flakiness Index }=\frac{\text { Total weight passing gauge }}{\text { Total weight on sieves }} * 100
Elongation Index
- Sample is sieved using standard sieves.
- Weight on each sieve is noted as ‘weight on sieve’.
- The samples passing through each sieve are then passed through the elongation gauge.
- The sample retained on this gauge is noted as ‘Weight retained on gauge’.
- Elongation index is expressed as percentage of weight of aggregates passed retained on the gauge to the weight of sample in sieves.
- \text { Elongation Index }=\frac{\text { Total weight retained on gauge }}{\text { Total weight on sieves }} * 100
Desirable values
- Flakiness index below 15% is desirable and in no case should it be greater than 25%.
- Elongation index in excess of 10 to 15 % is generally considered undesirable.
