Quarry Southern Africa May 2019 - Page 32

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 www.quarryonline.co.za