Building Materials, Third Edition

196 Building Materials

For fine aggregate, the dried sample is cooled to room temperature and then sieved over
a 300 micron IS sieve until less than 1% of the retained material passes the sieve in one minute
of continuous sieving. Weigh the material coarser than 300 micron IS sieve and introduce it
into heavy liquid in a suitable container, the volume of liquid being at least three times the
absolute volume of the aggregate. The liquid is poured into another container, passing it
through the skimmer in a way that only floating pieces are poured off with the liquid. The
liquid collected in the second container is returned to the first container, agitate the sample
by stirring and repeat the process until the sample is free of floating pieces. The decanted
pieces are washed in carbon tetrachloride, until the heavy liquid is removed and then these
are dried in an oven at 105°C. The decanted pieces are brushed and weighed. The percentage
of light weight pieces, L is given by

L=^1

2

W

100

W

¥

In case of coarse aggregate, the dried sample is cooled to room temperature and sieved over
a 4.75 mm IS sieve. The material coarser than 4.75 mm IS sieve is weighted. It is then
introduced into the heavy liquid in a suitable container, the volume of liquid being at least
three times the absolute volume of the aggregate. The pieces that rise to the surface are
removed by skimmer and sieved. The remaining pieces are agitated repeatedly and floating
pieces are removed until no additional pieces rise to the surface. The decanted pieces are
washed with carbon tetrachloride until all of the heavy liquid is removed and are allowed to
dry. The percentage of light weight pieces, L is given by

L=^1

3

W

100

W

¥

Where W 1 = dry weight (g), of decanted pieces

W 2 = dry weight (g), of portion of sample coarser than 300-micron IS sieve

W 3 = dry weight (g), of portion of sample coarser than 4. 75-mm IS sieve

These impurities should not exceed 1% for fine and coarse aggregates (IS: 383)

Determination of soft particles in coarse aggregate

The sample size for the test should be as follows.

Sieve size (mm) sample weight (g)

(square opening sieves)

over 10 to 12.5 200

over 12.5 to 20 600

over 20 to 25 1500

over 25 to 40 4500

over 40 to 50 12, 000

Note:If the sample contains less than 10 per cent of any of the sizes as above, the size should not be tested
but, for the purpose of calculating the test results, it should be considered to contain the same
percentage of the soft particles as the average of next smaller and the next larger size. If one of these
sizes is absent, it should be considered to have the same percentage of soft particles as the next larger
or next smaller size, whichever is present. Each particle of the aggregate under test is scratched with
a brass rod (1.6 mm diameter) with a pressure of 1 kg. Particles are considered to be soft if a groove
is made without deposition of metal from the brass rod or if separate particles are detached from the
roke mass.