What is bulk density?
The bulk density is
the weight of material in a given volume. It is measured in kilograms per miter
cube but for the purpose of this standard it is measured in kilograms per
litre.
Who
affects bulk density of aggregate?
The bulk density of
an aggregate is affected by several factors, including the amount of moisture
present and the amount of effort introduced in filling the measures.
What
is bulking of sand?
The increase in
volume of sand (or aggregate) due to presence of moisture is known as bulking
of sand.
What
is the reason behind bulking of sand?
The bulking of sand
is due to the formation of thin film of water around the sand grains and the
interlocking of air in between the sand grains and the film of water.
When more water is
added a sand particle got submerged and volume again becomes equal to dry
volume of sand. To compensate the bulking effect extra sand is added in the
concrete so that the ration of coarse to fine aggregate will not change from
the specified value. Fine sand shows greater percentage of bulking than coarse
sand with equal percentage of moisture.
Bulk Density and Voids in Aggregate asper IS: 2386-3 (1963)
Hi friends, you are
welcomed in the world of Civil Allied Gyan. “Read here definition, apparatus,
IS code, test procedure, formula, result and lab report for bulk density and voids in aggregate as per
IS: 2386-3 (1963).”
Important:- This
method of test covers the procedure for determining unit weight or bulk density
and void of aggregates.
Note-1: It
is emphasized that this is a 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.
Note-2:
Considerably
more compactive effort is used in the determination of angularity number [as
per IS: 2336 (Part 1)-1963] than in this test, and hence the values for bulk
density and voids are different.
IS Code of Bulk Density and Voids in Aggregate:-
IS: 2386 (Part
III)-1963, Methods for specific gravity, density, voids, absorption and bulking
of aggregates.
Apparatus
Required for Determination of Bulk
Density and Voids in Aggregate:-
- Balance: A balance sensitive to 0.5 % of the weight of the given sample.
- Tamping Rod: A straight metal tamping rod of cylindrical cross-section 16 mm in diameter and 60 cm long and rounded at one end.
- Special Vessel for unit volume
- Tray
- Cylindrical Metal Containers: See below table.
Table-1: Size of Container for Bulk Density Test
Calibration:- The measure shall be calibrated by determining the weight of water at 27°C required to fill it such that no meniscus is present above the rim of the container. The capacity in litres shall be obtained by dividing the weight of water in kilograms required to fill the container at 27°C by the weight of water in 1 litre at 27°C, which may be taken as 1 kg.
Procedure for Determination of Bulk Density and Voids in Aggregate:-
- Condition
of Specimen:- For the determination of the voids the dry
material may normally be used, but
when bulking tests are required, then the material with a given percentage of
moisture may be used.
- Take the appropriate
container and weight it (M₁).
- Then fill the cylindrical metal container about one-third full with thoroughly mixed aggregate and tamped with 25 strokes of the rounded end of the tamping rod.
- Add further similar quantity (one-third of measure) of aggregate and tamped with 25 strokes of the rounded end of the tamping rod again.
- Finally fill the measure to over-flowing, tamped with 25 times of the rounded end of the tamping rod again and struck off the surplus aggregate using the tamping rod as a straightedge.
- Then weight the
container with sample (M₂)
and determine the net weight of the aggregate in the measure (M₂−M₁), which is called rodded or
compacted weight.
- Calculate the bulk density of sample aggregate in kilograms per litre (the formula is given below in calculations).
- Now fill the measure to over-flowing by means of a shovel or scoop, discharge the aggregate from a height not exceeding 5 cm above the top of the measure.
- Care shall be taken to prevent, as far as possible, segregation of the particle sizes of which the sample is composed.
- Level the surface of the aggregate using the tamping rod as a straightedge.
- Then weight the
container with sample (M₃)
and determine the net weight of the aggregate in the measure (M₃−M₁), which is called loose
weight.
- Calculate the bulk density of sample aggregate in kilograms per litre (the formula is given below in calculations).
Calculations:-
Calculation of Bulk Density: The bulk density of aggregate will be calculated as follows:
Where;
M₁ = Weight of container in kg,
M₂ = Weight of container and sample in kg,
M₃ = Weight of container and sample in kg,
V = Volume of container
in L,
Compacted weight = M₂−M₁ and
Loose weight = M₃−M₁.
Calculation
of Voids: The percentage of voids will be calculated as follows:
Where,
Gs = Specific
gravity of the aggregate, and
Î¥ = Bulk density in kg/litre.
Reporting of Results:–
The bulk density of
aggregate will be reported in kg/litre to the nearest 0.01 kg/L.
The voids in aggregate
will be reported as a percentage to the nearest whole number.
The condition of sample
aggregate at the time of test shall be stated, that is (a) oven dry, (b)
saturated and surface dry, or (c) with a given percentage of moisture.
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