Building Materials, Third Edition

Materials for Making Concrete-II Aggregates 195

Table 6.5 Weights of Sample

Max. size present in substantial Proportion (mm) Approximate sample weight (g)

63 to 25 6000

20 to 12.5 1000

10 to 6.3 500

4.75 or smaller 300

For testing fine aggregate for clay, fine silt and dust weight approximately 300g of the air
dried sample, passing the 4.75 mm IS sieve, and place it in the screw-topped glass jar, together
with 300 ml of diluted sodium oxalate solution. The jar is then rotated about its long axis (with
this axis horizontal) at a speed of 80 rpm for 15 minutes. The suspension is then poured into
1000 ml measuring cylinder and the residue washed by gentle swirling and decantation of
successive 150 ml portions of sodium oxalate solution, the washings being added to the
cylinder until the volume is made up to 1000 ml.

For coarse aggregate the sample is placed in a suitable container, covered with a measured
volume of sodium oxalate solution (0.8 g/l), agitated vigorously and the liquid suspension
transferred to the 1000 ml measuring cylinder. The process is repeated until all clayey material
is transferred to the cylinder. The volume is made upto 1000 ml with sodium oxalate solution.

The percentage of fine clay, silt and dust, A, is determined by the folliwng fomula

A =

ʈ-

Á ̃Ë ̄

2

1

100 1000 W
0.8
WV
Where W 1 = weight of original sample (g)
W 2 = weight of dried sample (g)
V = volume of the pepette (ml)
0.8 = weight of sodium oxalate (g) in one litre of the dilute solution.
Note:These impurities should not exceed 3% for fine and coarse aggregates except for crushed fine
aggregate for which the limit is 15% (IS:383).

Determination of Light-weight pieces (coal and lignite)

The percentage of light-weight pieces are determined by means of sink-float separation in a
heavy liquid of suitable specific gravity. The approximate volumes of materials to be combined
to produce a mixture of the desired specific gravity may be computed from the following sp.
gr. of the different liquids used to form the heavy liquid of sp. gr. 2± 0.01.

Liquid sp. gr.

1, 1, 2, 2 - Tetra bromoethane 2.97

Benzene 0.88

Bromoform 2.88

Carbon tetra chloride 1.58

Monobromobenzene 1.49

The minimum size of test sample should be as follows.

Max. size of aggregate (mm) Min. weight of sample (g)

6.3 (fine aggregate) 200

20 3000

40 5000

80 10000