Precast hollow core technology speeds up shopping centre construction

The use of Elematic prestressed hollow core concrete slabs has helped speed up construction on the Oakfields shopping centre in Benoni. The existing centre is undergoing a major extension which includes the construction of new premises for Pick 'n Pay, as well as the addition of several new line shops on a previously undeveloped portion of the site.

The new Pick 'n Pay will be some 3 300m2 in extent, while the line shops will take up an additional 1 300 m2 around the anchor tenant's position. Elematic hollow core slabs, which are manufactured and supplied in South Africa by Elematic SA (ESA), were used for the full 4 600m2 of floor area in the new structures.

Simon Griffiths, director at L&S Consulting and the design engineer on the project, explains that the Elematic slabs have been laid on top of castellated steel beams on a 7.5 metre grid to form the roof of the new 500 bay parking basement below Pick 'n Pay, as well as the mezzanine flooring for the line shops. "Considerations we took into account when specifying the Elematic slabs included the fact that the product was cost-effective for our purposes. The price of building materials, including steel, has come down, so we could use the two in combination successfully."

Griffiths adds that the main benefit of the product has been the speed with which construction can progress, due to the fact that the slabs are prefabricated off site. Construction commenced at the end of August, and the Pick 'n Pay component is expected to be open by the end of February. "This system has definitely saved us time in comparison to a conventional concrete slab. The slabs also result in a lighter structure, which is beneficial where the weight of the structure is important," says Griffiths.

Anver Arnolds of M&F Giuricich offers the contractor's point of view, and concurs about the time saving benefits of using Elematic slabs. He comments that the installation has gone smoothly and quickly, saying that the speed of using this system has saved time on site. "We also found ESA very accommodating and we worked well together. We got all the information we needed easily and communication was excellent at all times," he adds.

Griffiths also comments that ESA was very helpful in resolving any design queries with the engineers. Craig Webber, director at ESA, says that one of the challenges encountered was the fact that Pick 'n Pay requires a high loading tolerance on the slab. Charles van Wyk, ESA's design engineer, explains that Pick 'n Pay requires a loading tolerance of 7.5kN/m2 on the floor slab in the trading area, and 12kN/m2 in the storage and despatch area as a matter of course. There were also longer than average spans to be covered. The solution was to cast a 30MPa reinforced concrete structural screed 75mm thick on top of the 250mm Elematic slabs to create a floor that could withstand the specified loadings.

ESA manufactures its hollow core slabs using state of the art technology. It also has the R&D support of Elematic in Finland, which has a solid reputation based on five decades of experience. The benefits of using Elematic slabs include the fact that the prefabrication process under controlled conditions assures clients of consistent quality; the fact that the slabs can be installed quickly on site without the need for back-propping or curing time; and the fact that they typically require very little finishing once installed.

In conclusion, Griffiths notes: "We were already familiar with the generic system, but when ESA quoted on this job, we realised how cost effective it could be, and we have proposed its use on future projects."