Elongation Index
The presence of elongated aggregates in a mixture can disrupt the arrangement of particles and increase the space between them. This can cause a reduction in the workability of concrete as elongated particles have a higher surface area to volume ratio. If elongated particles are used in the construction of pavement base courses, they may break down easily under heavy loads and cause damage to the pavement. Therefore, it is essential to determine the elongation index of the aggregate mix to ensure its suitability for use in construction projects.
Apparatus
The apparatus required for determining the Elongation Index of coarse aggregates includes:
Aggregate sample
Digital balance
Elongation gauge or length gauge
Test sieves in the following sizes: 63mm, 50mm, 40mm, 31.5mm, 25mm, 20mm, 16mm, 10mm, and 6.3mm
Test method
The following steps are involved in the elongation index test procedure:
Take a representative aggregate sample containing a minimum of 200 particles of any fraction.
Sieve the aggregate sample through the specified sieves, ranging from 63mm to 6.3mm.
Disregard the aggregate retained on 63mm sieve and that which passes through the 6.3mm sieve.
Weigh the aggregate retained on each sieve and record the total weight as "W1".
Take the aggregate particles from each size range and pass them through the corresponding length gauge or elongation gauge with their longest side. Each gauge length should be 1.8 times the mean dimension of the aggregate size range. To eliminate testing bias, the particle should be passed multiple times with different facings.
Weigh the particles that are not passed or retained on the length gauge and record the weight as "W2".
Calculate the elongation index as the ratio of weight of particles retained on the length gauge to the total weight of the sample gauged, expressed as a percentage.
Elongation Calculation
The elongation index of aggregate is calculated as a percentage using the following formula:
Elongation index = (W1 / W2) x 100%
Where W1 is the weight of particles retained in the length gauge in grams, and W2 is the weight of the total sample taken for the test in grams.