Elongation Index of Aggregates (IS:2386 part 1)
The elongation index of an aggregate is the percentage by weight of particles whose greatest dimension ( length ) is greater than 1.8 times their mean dimension.For this test aggregates passing 63 mm and retaining at 6.3 mm are taken.The elongation test is not applicable to sizes smaller than 6.3 mm. Elongated particles are considered unsuitable for the pavement. Elongated particles get broken when loaded vehicles pass over the pavement leading weakness of the structure.These particles also create problem in close packing of the aggregates leading to voids in concrete.Apparatus
Sample,Weighing machine, Length gauge,Is Sieves of sizes 63mm, 50mm, 40mm, 31.5mm, 25mm, 20mm, 16mm, 10mm and 6.3mm. |
| Length Gauge |
Test Procedure
- Take the aggregate sample having at least 200 pieces of different sized aggregates.
- Sieve the sample through mentioned sieves i.e., from 63mm to 6.3mm sieves.
- Aggregates retained on 63 mm and passing 6.3mm are discarded.
- Now weigh aggregate retained on different sieve and note down the total weight as “W1”
- The aggregate particles from each of the size range is taken and passed through corresponding gauge of length gauge or elongation gauge with its longest side facing the width of gauge.
- Each gauge length is 1.8 times the mean dimension of aggregate size range. If particle retained on 16mm and passed through 20mm size is taken, then it should pass through 32.4mm length gauge which is 1.8 times the mean of 16mm and 20 mm.(i.e. [{1.8*(16+20)}/2]=32.4 mm
- The particles that were retained on the length gauge are weighed which is “W2”.
- Now calculate the elongation index which is the ratio of weight of particle retained on length gauge to the total weight of the sample gauged and it is expressed in percentage.
Calculations:
Elongation index =(W2/W1) X 100W1= Weight retained of aggregates on length gauge
W2= Total sample weight.
Elongation Index should not more than 15 % for pavement aggregates material.
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