Department of Civil Engineering
Bangladesh University of Engineering and Technology
Unit Weight:
✓ weight of aggregate in a unit volume
✓ used for determining mass/volume relationships for
conversions
✓ used to determine bulk density values necessary for
selecting proportions for concrete mixtures
✓ used for calculating the percentages of voids in
aggregates
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Unit Weight:
Affected by:
✓ moisture in aggregate,
✓ degree of compaction,
✓ aggregate gradation etc.
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Void content:
✓ Affects the amount of cement paste required for the mix
✓ Angularity of aggregates increase the void content
✓ Larger sizes and improved gradation of aggregate
decrease the void content
✓ Voids within particles, either permeable or
impermeable, are not included
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3 different procedures:
✓ Shoveling– measures aggregate unit weight in loose
condition.
✓ Rodding- used for determination of compacted unit
weight of aggregates having a nominal maximum size of
1.5 in (37.5 mm) or less
✓ Jigging- used for determination of compacted unit weight
of aggregates having a nominal maximum size greater
than 1.5 in (37.5 mm) & not exceeding 6 inch (150 mm)
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Code:
✓ ASTM specification C29/C29M − 17a
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• Apparatus
✓ Balance
✓ Tamping rod
✓ Calibration equipment
✓ Measure (Container)
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Size of measure is determined based on the nominal
maximum size of aggregate:
The indicated size of measure used to test aggregates of a nominal maximum size equal to or smaller than that
listed. The actual volume of the measure should be at least 95 % of the nominal volume listed
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Sampling:
✓ The size of the sample should be approximately 125 to
200% of the quantity required to fill the specified
measure, and should be handled in a manner to avoid
segregation.
✓ Dry the aggregate sample to essentially constant mass,
preferably in an oven at 230 ± 9°F [110 ± 5°C]
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Calibration of Measure:
✓ Fill the measure with water at room temperature and
cover with a piece of plate glass in such a way as to
eliminate bubbles and excess water.
✓ Determine the mass of the water in the measure using
the balance.
✓ Measure the temperature of the water and determine
its density by interpolating (from Table-2) if necessary.
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Calibration of Measure:
✓ Calculate the volume V, of the measure by dividing
the mass of the water required to fill the measure by
its density.
✓ If this calibrated volume of the measure is within
±5.0% variation of corresponding standard volume of
the measure (in table -1) use standard volume for
calculation, otherwise use the calibrated volume for
calculating unit weights of aggregates
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Shovelling:
✓ Fill the measure to overflowing by means of a shovel
or scoop, discharging the aggregate from a height not
exceeding 2 inch (50 mm) above the top of the
measure. Exercise care to prevent, so far as possible,
segregation of the particle sizes of which the sample is
composed.
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✓ Level the surface of the aggregate with the fingers (for
coarse aggregate) in such a way that any slight
projections of the larger pieces of the coarse aggregate
approximately balance the larger voids in the surface
below the top of the measure or with a straightedge
(for fine aggregate) .
✓ Determine the mass of the measure plus its contents,
and the mass of the measure alone, and record the
values to the nearest 0.1 lb (0.05 kg).
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Rodding:
✓ Fill the measure one-third full and level the surface
with the fingers.
✓ Rod the layer of aggregate with 25 strokes of the
tamping rod evenly distributed over the surface. Do
not allow the rod to strike the bottom of the measure
forcibly.
✓ Fill the measure two-thirds full and again level and
rod as above.
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✓ Finally, fill the measure to overflowing and rod again
in the manner previously mentioned.
✓ Level the surface of the aggregate with the fingers (for
coarse aggregate) in such a way that any slight
projections of the larger pieces of the coarse aggregate
approximately balance the larger voids in the surface
below the top of the measure or with a straightedge
(for fine aggregate) .
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✓ In rodding the second and third layers, use vigorous
effort, but do not apply such a force as to cause the
tamping rod to penetrate to the previous layer of
aggregate.
✓ Determine the mass of the measure plus its contents,
and the mass of the measure alone, and record the
values to the nearest 0.1 lb (0.05 kg).
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Jigging:
✓ Fill the measure in three approximately equal layers
as described previously, compacting each layer by
placing the measure on a firm base such as a cementconcrete floor, raising the opposite sides alternately
about 2 inch (50 mm), and allowing the measure to
drop in such a manner as to hit with a sharp, slapping
blow. The aggregate particles, by this procedure, will
arrange themselves in a densely compacted condition.
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✓ Compact each layer by dropping the measure 50 times in
the manner described, 25 times on each side.
✓ Level the surface of the aggregate with the fingers (for
coarse aggregate) in such a way that any slight projections
of the larger pieces of the coarse aggregate approximately
balance the larger voids in the surface below the top of the
measure or with a straightedge (for fine aggregate) .
✓ Determine the mass of the measure plus its contents, and
the mass of the measure alone, and record the values to the
nearest 0.1 lb (0.05 kg).
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• Calculation
✓ Calculate the unit weight as follows:
M = unit weight of the aggregate, lb/ft3(kg/m3),
G = mass of the aggregate plus the measure, lb(kg),
T = mass of the measure, lb(kg),
V = volume of the measure, ft3(m3) [calibrated / standard]
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✓ The unit weight determined by this test method is for
aggregate in an oven-dry condition. If the unit weight in terms
of saturated-surface-dry (SSD) condition is desired, use the
exact procedure in this test method, and then calculate the SSD
unit weight using the following formula:
𝑀𝑆𝑆𝐷 = unit weight of aggregate in SSD condition, lb/ft3 (kg/m3)
A = absorption capacity in aggregate (%)
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• Calculate the void content in the aggregate using the
corresponding unit weight:
M = unit weight of the aggregate, lb/ft3 (kg/m3)
S = bulk specific gravity (O-D basis) as determined in
accordance with test method C127 or C 128 (Exp. No. - 9)
W = density of water, lb/ft3 (kg/m3)
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• Reporting
✓ Report the results for the unit weight to the nearest 1
lb/ft3 (10 kg/m3)
✓ Report the results for the void content to the nearest 1%
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