Building Materials, Third Edition

Materials for Making Concrete-II Aggregates 199

occasionally to facilitate drying. It is then cooled in the air-tight container and weighed
(weight D).

Specific gravity =

D

A(BC)--

Apparent specific gravity =

D

D(BC)--

Water absorption (per cent of dry weight) =

AD

100

D

• ¥
  Where A =weight in g of saturated surface-dry sample
  B = weight in g of pycnometer or gas jar containing sample and filled with
  distilled water
  C = weight in g of pycnometer or gas jar filled with distilled water only
  D = weight in g of oven-dried sample

Determination of Bulk Density and Voids (IS: 2386 (Part III))

The bulk density, measured in kilograms per litre is affected by several factors, including the
amount of moisture present and the amount of effort introduced in filling the measure. This
is laboratory test intended for comparing properties of different aggregates. It is not generally
suitable for use as a basis for quoting mix design conversion factors.
The test is carried out on dry material when determining the voids, but when bulking tests
are required material with a given percentage of moisture may be used.
The measure is filled with thoroughly mixed aggregate to about one-third and tamped with
25 strokes of the rounded end of the tamping rod. A further similar quantity of aggregate is
added with a further tamping of 25 times and the surplus aggregate is struck off, using the
tamping rod as a straight edge. The net weight of the aggregate in the measure is determined
and the bulk density is calculated.
The measure is then filled to overflowing by means of a shovel or scoop, the aggregate being
discharged from a height not exceeding 50 mm above the top of the measure. The surface of
the aggregate is then levelled with a straight edge. The net weight of the aggregate in the
measure is determined and the bulk density is calculated.
The percentage of voids are calculated as follows:

Percentage of voids = s

s

G

100

G

-g

¥

where GS = specific gravity of the aggregate

g = bulk density in kg/litre

Necessary adjustment for bulking of fine aggregate (Field method)

I Method: Sufficient quantity of the sand is put loosely into a container until it is about two-
third full. The sand is levelled off and a steel rule is pushed vertically down through the sand
at the middle to the bottom and the height is measured (say h mm).
The sand is transferred into another container. The first container is half filled with water
and about half the sand is put back and rammed with a steel rod (about 6 mm in diameter)
so that its volume is reduced to a minimum. Then the remainder of the sand is added and
rammed in the same way. The depth is measured at the middle with the steel rule (say h¢ mm).