Tuesday, 1 March 2016

Tests For Aggregates (Elongation and Flakiness Tests)

Tests For Aggregates 

1) Determination Of Flakiness Index

The flakiness index of aggregate is the percentage by weight of particles in it whose least
dimension (thickness) is less than three-fifths of their mean dimension. The test is not applicable
to sizes smaller than 6.3 mm.
This test is conducted by using a metal thickness gauge, of the description shown in below fig A sufficient quantity of aggregate is taken such that a minimum number of 200 pieces of any fraction can be tested. Each fraction is gauged in turn for thickness on the metal gauge. The total amount passing in the guage is weighed to an accuracy of 0.1 per cent of the weight of the samples taken. The flakiness index is taken as the total weight of the material passing the various thickness gauges expressed as a percentage of the total weight of the sample taken. Table 3.18 shows the standard dimensions of thickness and length gauges.

2) Determination Of Elongation Index

The elongation index on an aggregate is the percentage by weight of particles whose
greatest dimension (length) is greater than 1.8 times their mean dimension. The elongation
index is not applicable to sizes smaller than 6.3 mm.
This test is conducted by using metal length gauge of the description shown in below fig
A sufficient quantity of aggregate is taken to provide a minimum number of 200 pieces of any
fraction to be tested. Each fraction shall be gauged individually for length on the metal guage.
The guage length used shall be that specified in column of 4 of Table 3.18 for the appropriate
size of material. The total amount retained by the guage length shall be weighed to an
accuracy of at least 0.1 per cent of the weight of the test samples taken. 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. The presence of elongated particles in
excess of 10 to 15 per cent is generally considered undesirable, but no recoganised limits are
laid down.



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