Laboratory: Unit Weight and Voids in Aggregate
Significance and Use
This test is to determine unit weights and voids in a sample of coarse, fine, or mixed aggregates.
Cylindrical measure container
Aggregate dried to constant weight, preferably in an oven at 110 +/-5 °C.
Find the empty weight of the measure.
2. Find the volume of the measure (V) by water displacement method. Calibrate the density of
water (W) with temperature according the table below:
3. Fill the measure one-third full with the dry sample.
4. Rod the layer of aggregate with 25 stokes.
5. Fill the measure two-thirds, level and rod 25 times.
6. Fill the measure overflowing and rod 25 times.
Level the surface of the aggregate with a finger and tamping rod such that any slight projection
of the larger pieces of the coarse aggregate approximately balances the larger voids in the surface
below the top of the measure.
8. Weight the measure with the aggregate and find the net weight of the aggregate: A.
9. Calculate the unit weight : B.
Unit weight of bulk density B.D = (A / V) lb/ft³ or kg/m³
10. Calculate the voids content or void percentage.
Void % = ( S.G - (B.D / W ) / S.G) * 100
Where S.G = Specific gravity of the aggregate
11. Repeat the above with a mixture of aggregate containing 35%, 40%, 45%, 50% fine aggregate,
and determine the void percentage, respectively.
The unit weight and void percentage for the coarse aggregate
The void percentage for aggregate mixture with 35%, 40%, 45%, and 50% fine aggregate,
Plot the void percentage vs. fine aggregate content and determine what aggregate mixture
(percentage of fine aggregate or sand ratio) to yield minimum void content.
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The objective of this experiment is used to determine unit weights and voids in a sample of fine, coarse or mixed aggregates. The unit density is not an intrinsic property of a material; it will change according to the material. The bulk density is used to determine the mass-volume relationship. The bulk density also indicates the percentage of voids present in the aggregate sample. This experiment will determine the percentage of voids by compacting the loose state and rodded state. The void content affects mortar requirements in mix design and mortar requirements tend to increase with an increase in aggregate void contents. In general, void contents range from 30-45% for coarse aggregates and 40-50% for fine aggregates. The procedure followed in this experiment is based on the specifications of the ASTM C 29-17 standard.
Unit weight or bulk density is defined as the ratio of mass to volume,...