Compaction method: steel fibres and aggregates (standard)
Compaction is more effective on the packing density of fibres and irregular aggregates
than on spherical particles [Hoy, 1998]. At a low compaction level the porosity between
the fibres is high; the change in packing density is relatively larger at increasing
compacting level compared with round grains. Hoy performed experiments according
to the British Standard [BS 812: Part 2, 1975]. He found that the variation of this
method was lower compared to pouring or vibrating. Still, the single results of his
measurement showed significant scatter; to minimise the scatter a higher level of
compaction energy was adopted. The applied compaction method was the following:
First, a container (volume: 8.67 litres; to measure the Vebe-time) was filled in three
equal layers; each layer was tamped 30 times by a rod. The falling height of the rod was
50 mm. This compaction method is similar to that of British Standard [BS 812: Part 2,
1975]; the size of the container differed. Next, two additional minutes of vibration
(Vebe-instrument) with a compression force of 14 kg were applied. The weight was
imposed by a second container (container: NEN 5961, 1988), which covered the
complete surface. The surplus of solids was removed by striking up the top with the rod.
The fibres (tests with fibres alone) were carefully removed by hand not to disturb the
packing.