Experiment No. 5:
Standard test method for the determination of Bulk Density (i.e. unit weight and the voids in aggregates). (ASTM C-29/C-29M)
Scope & Significance:
- This test method is used to determine the bulk density of the given fine grained specimen.
- During the concrete mix design, when the aggregate is to be batched by volume or by weight, then it becomes necessary to know the mass of the aggregates that will fill the container of unit volume. If we know the bulk density of the aggregate material then we can easily determine the mass required to fill a unit volume container.
- Bulk density also indicates the percentage of voids present in the aggregate material. This percentage of voids affects the grading of the aggregates which is important in high strength concrete.
- Bulk density also indicates the compactive effort required to compact the concrete.
Related Theory:
Bulk Density
It is the mass of the unit volume of bulk aggregate material. The term volume includes the volume of the individual particles and the volume of the voids between the particles.Bulk density is used in weight and volume batching.
Voids
It is the space between the individual particles in a unit volume of the aggregate mass and is not occupied by the solid mineral matter.Voids within the particles, either permeable or impermeable are not included in the voids for the determination of bulk density by this method.
Absolute Density
It is the mass per unit volume of the individual particles only.
Did You Know?
Bulk density is the weight of soil for a given volume. It is used to measure compaction. In general, the greater the density, the less pore space for water movement, root growth and penetration, an seedling germination.
Facts About Bulk Density
Bulk-density depends upon how densely the aggregate is packed. It also depends upon the size, distribution and shape of the particles. If the particles are of the same size, then it can be packed to a limited extent but when the smaller particles are added, the voids get filled with them and thus the bulk density increases. For a coarse aggregate, a higher bulk density means that there are few voids which are to be filled by the fine aggregate and cement. Thus bulk density also depends upon the degree of packing.
Note: Moreover, the bulk density as determined in our lab is not directly suitable for the conversion of mass to volume of the aggregates for the purpose of volume batching as the degree of compaction in the lab and at the site may not be the same.
Apparatus:
- Balance
- Temping rod
- Measuring Cylinder
- Shovel or Scoop
Procedure:
Note down the dimensions and empty weight of the measuring contai 
ner and compute its volume. For the determination of the loose bulk density, fill the container with the aggregate material by means of a shovel and level its top surface. Weigh the container filled with the aggregate and note down its reading. Then the loose bulk density of the aggregate material can be computed by using the relation;
Now for the determination of the compacted bulk density, the only difference is in filling the container. In this case, the container is filled in three equal layers. Fill the container about one-third full and level the surface with the fingers. Rod the layer of the aggregate with 25 strokes of the temping rod evenly distributed over the surface. Next fill the container two-third full and again rod it with 25 strokes of the temping rod. Finally, fill the container to overflowing and rod again in the manner previously mentioned. Now level the top surface and weigh the container. Calculate the compacted bulk density by using the relation;
Observations & Calculations:
Measuring Cylinder For Coarse Aggregate
Diameter =…25.5 cm = 0.225 m…… Height =.…26.9 cm = 0.269 m…
Volume =……0.0107 m3…
Measuring Cylinder For Fine Aggregate
Diameter =……15.5 cm = 0.155 m…… Height =…15.2 cm = 0.152 m…
Volume =………0.0028 m3……
|
Sample |
Weight of |
Volume of |
Weight of |
Weight of |
Bulk |
|
|
State |
Container |
Container |
Agg. + Cont. |
Aggregate |
Density |
|
|
|
(kg) |
(m3) |
(kg) |
(kg) |
(kg/m3) |
|
|
Coarse Aggregate |
||||||
|
MARGALA CRUSH |
||||||
|
Loose |
7.4 |
0.01374 |
26.6 |
19.2 |
1397.38 |
|
|
Compacted |
7.4 |
0.01374 |
29 |
21.6 |
1572.05 |
|
|
|
SARGODHA CRUSH |
|||||
|
Loose |
7.4 |
0.01374 |
27.4 |
20 |
1455.60 |
|
|
Compacted |
7.4 |
0.01374 |
29.9 |
22.5 |
1637.55 |
|
|
Fine Aggregate |
||||||
|
CHENAB SAND |
||||||
|
Loose |
2.6 |
0.00287 |
6.4 |
3.8 |
1324.04 |
|
|
Compacted |
2.6 |
0.00287 |
6.9 |
4.3 |
1498.26 |
|
|
|
LAWRENCEPURE SAND |
|||||
|
Loose |
2.6 |
0.00287 |
6.8 |
4.2 |
1463.41 |
|
|
Compacted |
2.6 |
0.00287 |
7.15 |
4.55 |
1585.36 |
|
Comparison Table:
|
Sr.No |
Sample Name |
Loose Bulk Density |
Compacted Bulk Density |
Increase in Bulk Density |
% Increase |
|
1 |
MARGALA CRUSH |
1397.38 |
1572.05 |
174.67 |
12.5 |
|
2 |
SARGODHA CRUSH |
1455.60 |
1637.55 |
181.95 |
12.5 |
|
3 |
CHENAB SAND |
1324.04 |
1498.26 |
174.22 |
13.16 |
|
4 |
LAWRENCEPURE SAND |
1463.41 |
1585.36 |
121.95 |
8.33 |
Comments:
From the experiment performed we came to know that the bulk-density of a material in compacted form is greater than the bulk-density of a material in loose form. The percentage increase in the bulk density of Lawrence pure sand is 8.33 and the percentage increase in the bulk-density of Sargodha crush is 12.5. So the percentage increase in the Bulk-density of Chenab sand is 13.16 and is greater than all of the samples. The greater the bulk-density the less are the voids present and the more is the compactive effort required.
The greater the bulk-density the less are the voids present and the more is the compactive effort required.
plz explain how ?
i guess we need less compactive effort…
Compaction means to reduce the air voids by some mechanical process. When the voids are already less, means material already compacted to some extend and required less compaction effort to achieve desired compaction.
How do you determine or calculate the loose aggregate at a loose bulk density if it’s not given. Thank you!