BENEFICIATION
This is an extrusion line for hollow-core slab manufacture. With their tubular voids extending the full length of the element, hollow-core slabs are
significantly lighter than a large solid concrete floor slab of equal thickness or strength. This lowers the cost of manufacture by reducing raw materials, as
well as their transportation to site where they are lifted and placed, levelled and grouted to complete the floor structure.
capabilities to install rib-and-block which
requires more work by the contractor
pouring concrete. With hollow-core slabs,
we are appointed to manufacture and
install the elements — there will always
be room for both.” Nonetheless, 80% of
CoreSlab’s production comprises hollow-
core slabs because De Bruin explains that
construction techniques are following
technology towards “easier and faster
applications”.
The primary reason why hollow-core
slab is not chosen is where the contractor
is confident about its capabilities to
install rib-and-block systems, he says.
“However, it is costlier and more time-
consuming, considering the shuttering,
the rebar, the concrete, and the labour
involved. The decision to use hollow-core
slabs on a typical residential project is,
therefore, usually made at a level above
the contractor, although not all of these
projects would be suited to hollow-core
slabs.”
30_QUARRY SA | MAY/JUNE 2019
Precast hollow-core slabs are typically
used for the construction of suspended
slabs in multistorey residential complexes
and property developments. Once the
bearing walls have been built, the hollow-
core slabs are placed directly from a trailer
onto a mortar bedding to rapidly create
the division between two floors. “You can’t
compare it to rib-and-block slabs in terms
of speed on site (it’s much faster) and
consequently the demand for hollow slab
is growing every day.” He says the biggest
projects that CoreSlab has supplied have
been for the expansion of residences at the
University of Venda and the University of
Limpopo. Through its associate company
Corestruc, the group also does the
installation, which enables the contractor
to continue with its own work on site,
whereas it would traditionally be unable to
work while concrete is laid and curing.
De Bruin explains that the residential
construction market is not as sophisticated
as other markets, so hollow-core slabs
offer the homebuilder and its professional
team peace of mind. “Work which would
otherwise be done in situ is now done in a
controlled environment in the factory.”
The process
CoreSlab gets all its washed aggregate
from a single source — Roodepoort
Crusher, less than one kilometre down
a gravel road — which is processed into
concrete at a batch plant on site, separately
managed by operational manager Martin
Potgieter.
Both wet and dry processing are
employed on the site. The dry mix
comprises a small amount of water added
in the batch plant, is placed in a bucket
and transported by forklift direct to the
mould for manufacturing the hollow-
core slabs. Wet mix is used for bridge
beams as well as stadia and reservoir
slabs, and the process is the same except
for the amount of water added. “We only
use self-compacting concrete (SCC) for
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