Building Materials, Third Edition

Materials for Making Concrete-II Aggregates 201

Vd = the weight of the sample divided by the specific gravity on saturated and

surface-dry basis determined as prescribed

Ms = weight in g of the sample

P 2 = percentage surface moisture in terms of the weight of wet fine aggregate

Note:The surface moisture in the fine aggregate should be reported to the nearest one per cent, and also
that whether it is by weight or by volume.

Bulking Test for Fine Aggregate (IS: 2386 (Part III))

Fine aggregate (sand) has a tendency to increase in volume (bulk) depending upon the
moisture present in it. In making concrete mix, if the batching in done by volume, the actual
quantity of sand in each batch will be less than the recommended volume and actual quantity
of sand in each batch will be less than the recommended volume and consequently the mix will
be rich in cement, i.e. the proportions of cement and sand will be different to be provided. This
will result in uneconomy and may affect adversely teh concrete also. Therefore, the amount
of sand will have to be increased by percentage bulking (B).
The field method of determination of bulking is explained in Sec. 6.3. In the laboratory test
sufficient quantity of oven dried sand is filled in graduated cylinder up to a certain fixed mark.
The sand is emptied in a container and the weigh of dry sand is determined 1% water is added
in the sand mixed thoroughly and filled in the graduated cylinder. The volume of sand will
be found to increase. The process is repeated by increasing the percentage of water in steps
of 1% each time till a decrease in the volume of sand is observed. Still this addition of water
is continued till the volume of sand comes back to the original volume (fully saturated).
A graph is plotted between moisture content and percentage increase in volume. The graph
will be of the shape as shown in Fig. 6.2. The percentage bulking is given by,

B =

bulked volume dry volume

100

dry volume

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Crushing Value Test (IS: 2386 (Part IV))

The material for the test should consist of aggregate passing 12.5 mm sieve and retained on
10 mm sieve. For other sizes, the materials are separated on the appropriate sieves given in
Table 6.6.

Table 6.6 Details of Aggregate Crushing Test for Non-standard Sizes of Aggregate

Nominal sizes Diameter of cylinder Size of sieve for

to be used (cm) separating fines

Passing through Retained on

(mm) (mm)

25.00 20.00 15.0 4.75 mm

20.00 12.50 15.0 3.35 mm

10.00 6.30 15.0 or 7.5 1.70 mm

6.3 4.75 15.0 or 7.5 1.18 mm

4.75 3.35 15.0 or 7.5 850 micron

3.35 2.36 15.0 or 7.5 600 micron

Note:About 6500 g of natural aggregate is required to provide samples for the 150 mm cylinder, or about
1000 g for the 75 mm cylinder.