ELONGATION INDEX
The elongation index of an aggregate is the percentage by weight of particles whose greatest dimension (length) is greater than one and four fifth times (1.8 times) their mean dimension. The elongation test is not applicable to sizes smaller than 6.3 mm.
APPARATUS
The apparatus consists of the length gauge, sieves of the sizes specified in Table 15.1 and a balance.
PROCEDURE
The sample is sieved through the IS sieves specified in Table 15.1. A minimum of 200 pieces of each fraction is taken and weighed.
In order to separate elongated material, each fraction is then gauged individually for length in a length gauge (see fig. 15.2).
The gauge length used should be those specified in column 4 of the Table for the appropriate material.
The pieces of aggregates from each fraction tested which could not pass through the specified gauge length with its long side are elongated particles and are collected separately to find the total weight of aggregate retained on the length gauge from each fraction.
The total amounts of elongated material retained by the length gauge are weighed to an accuracy of at least 0.1 percent of the weight of the test sample.
CALCULATION AND RESULT
In order to calculate the elongation index of the entire sample of aggregates, the weight of aggregates which is retained on the specified gauge length from each fraction is noted.
As an example, let 200 pieces of the aggregate passing 40 mm sieve and retained 25 mm sieve W1 g.
Each piece of these are tried to be passed through the specified gauge length of length gauge, which in this example is (40+25)/2 x 1.8 = 58.5 mm with its longest side and those elongated pieces which do not pass the gauge are separated and the total weight determined = w1 g.
Similarly the weight of each fraction of aggregate passing and retaining on specified sieves sizes are found, W1, W2, W3… and the total weight sample determined = W1+ W2 +W3 + … = Wg.
Also the weight of material from each fraction retained on the specified gauge length are found = x1, x2, x3… and the total weight retained determined = x1+x2+x3+…= Xg.
The elongation index is the total weight of the material retained on the various length gauges, expressed as a percentage of the total weight of the sample gauged.
Elongation Index = (Xg / Wg) x 100%
The elongation index of an aggregate is the percentage by weight of particles whose greatest dimension (length) is greater than one and four fifth times (1.8 times) their mean dimension. The elongation test is not applicable to sizes smaller than 6.3 mm.
APPARATUS
The apparatus consists of the length gauge, sieves of the sizes specified in Table 15.1 and a balance.
PROCEDURE
The sample is sieved through the IS sieves specified in Table 15.1. A minimum of 200 pieces of each fraction is taken and weighed.
In order to separate elongated material, each fraction is then gauged individually for length in a length gauge (see fig. 15.2).
The gauge length used should be those specified in column 4 of the Table for the appropriate material.
The pieces of aggregates from each fraction tested which could not pass through the specified gauge length with its long side are elongated particles and are collected separately to find the total weight of aggregate retained on the length gauge from each fraction.
The total amounts of elongated material retained by the length gauge are weighed to an accuracy of at least 0.1 percent of the weight of the test sample.
CALCULATION AND RESULT
In order to calculate the elongation index of the entire sample of aggregates, the weight of aggregates which is retained on the specified gauge length from each fraction is noted.
As an example, let 200 pieces of the aggregate passing 40 mm sieve and retained 25 mm sieve W1 g.
Each piece of these are tried to be passed through the specified gauge length of length gauge, which in this example is (40+25)/2 x 1.8 = 58.5 mm with its longest side and those elongated pieces which do not pass the gauge are separated and the total weight determined = w1 g.
Similarly the weight of each fraction of aggregate passing and retaining on specified sieves sizes are found, W1, W2, W3… and the total weight sample determined = W1+ W2 +W3 + … = Wg.
Also the weight of material from each fraction retained on the specified gauge length are found = x1, x2, x3… and the total weight retained determined = x1+x2+x3+…= Xg.
The elongation index is the total weight of the material retained on the various length gauges, expressed as a percentage of the total weight of the sample gauged.
Elongation Index = (Xg / Wg) x 100%
