ELONGATION INDEX



DETERMINATION OF ELONGATION INDEX OF COARSE AGGREGATE 

IS: 2386 - Part 1 

1. Introduction

This method of test covers the procedure for determining the Elongation Index of coarse aggregate. Elongation index is not applicable to aggregate size smaller than 6.3 mm.

2. Apparatus

(i) Metal gauge of the pattern shown in the figure

(ii) A balance of sufficient capacity and sensitivity with accuracy of at least 0.1 percent of the total weight of the sample tested.

(iii)  IS test sieves of sizes shown in the table below for sieving the aggregates.

3. Sample preparation

Sufficient quantity of aggregate shall be taken to provide a minimum number of 200 pieces of each fraction for gauging. 

Passing IS sieve mm Retained on IS sieve mm Length of gauge mm
50 40 81
40 25 58.5
25 20 40.5
20 16 32.4
16 12.5 25.6
12.5 10 20.2
10 6.3 14.7

4. Procedure

a) The sample shall be first sieved through the required sieves given in the table above. (The dimension of the thickness gauge for each size of aggregate is also indicated in the table).

b) The weight of each fraction retained, W1, W2, W3…etc are determined to the accuracy of 0.1% of the total weight of the test sample. The sum of these will be the total weight of the test sample (W).

c) W1, W2, W3… etc are then gauged through the appropriate slot of the length gauge, one by one.

d) The weight of the aggregates not passing each slot (Elongated particles) Y1, Y2….etc are determined. 

e) In case where sieves with slots are used in place of gauge, the fraction of the sample retained on each sieve is sieved through the slotted sieves in full, instead of checking the aggregate pieces individually.

5. Calculation

e) The percentage by weight of particles retained on each sieve, w1, w2, w3 ….etc of the total weight of the aggregates tested (W) are then calculated to the accuracy of 0.1 percent of the weight of test sample.  i.e., w1 = W1/W, w2 = W2/W, w3 = W3/W…. etc. The sum of this should be 100%.

f) The % by weight of particles not passing each slot (Elongated particles) say, y1, y2, y3 ….etc are then calculated.  i.e., y1 = Y1/W1, y2 = Y2/W2, y3 = Y3/W3…. etc

g) The Elongation Index is the total weighted fraction of the material retained on the slots or sieves, expressed as a percentage.

Elongation Index in percentage = (x1y1 + x2y2 + x3y3 ……)/100. 

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