The standard “ISO 6782 Aggregates for concrete - Determination of bulk density” developed by the International Organization for Standardization (ISO) describes a test method for determining the bulk density of dry or moist aggregates (normal or lightweight) for concrete in loose or compacted state.
This standard references the “ISO 4847, Concrete - Sieve analysis of aggregates” standard.
For the purposes of this standard, bulk density is the ratio of the mass of a sample of aggregate filling a given container to its volume. It is expressed as mass per unit volume, i.e. kilograms per cubic metre.
The main equipment used in these tests includes:
During the preparation phase for the tests, a sample is taken from the aggregate according to the ISO 4847 standard. If the determination is to be made on aggregates, the sample is dried to a constant mass at a temperature of 105 degrees plus/minus 5 degrees and thoroughly mixed. If the determination is to be made on moist aggregates, the moisture content is determined as a percentage of the dry mass and this is stated in the test report. If the homogeneity of a fraction needs to be checked, large-sized aggregates should be separated from small-sized aggregates by sieving.
Before starting the test, the container must be calibrated. To do this, the container is filled with water at 20 degrees plus/minus 2 degrees and covered with a glass plate to eliminate bubbles and excess water, and the mass of the water is calibrated to an accuracy of 0,2 percent. The actual volume of the container is obtained in cubic meters, then the mass of the water, in kilograms, is divided by 1000.
To determine the uncompacted bulk density, the container is filled with thoroughly mixed aggregate by shovel or ladle and the aggregate is discharged from a height of not more than 50 mm above the top of the container. Care is taken, as far as possible, to avoid segregation of the particle sizes of which the sample is composed. The container is filled to overflowing and excess aggregate is removed by rolling the tamping rod over the top of the container and in contact with it, any aggregate which impedes its progress is removed by hand and aggregate is added to fill any obvious depressions. For aggregates of 5 mm or less, the surface may be scraped using the tamping rod as a ruler. The aggregate and container are weighed to an accuracy of 0,2 per cent.
Compacted bulk density.
When compacting by rodding, the aggregate is transferred to the container until it is approximately one-third full, as described above. The surface is leveled by hand and the aggregate layer is rodded by the required number of strokes of the tamping rod evenly distributed over the surface. More aggregate is placed in the container until it is approximately two-thirds full, and it is leveled and rodded again as before. Finally, the container is filled to overflowing and rodded again as before. When rodding the first layer, the rod is not allowed to strike the bottom of the container with force. When rodding the second and third layers, only sufficient force is used to ensure that the tamping rod penetrates the previous layer of aggregate. Any damage to the aggregate should be avoided. Finally, the surface of the aggregate is leveled and the aggregate and the container are weighed to an accuracy of 0,2 per cent.
Other compaction methods such as vibration or jigging may be used to compact the aggregate in the container and, if used, should be detailed in the test report.
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