Construction World July 2020

PROJECTS & CONTRACTS

Hollow-core slabs are manufactured to size in a controlled factory environment and installed by a specialist team.

A decision to use hollow-core slabs (HCS) on a large residential project freed up necessary space in an extremely built-up environment, while also reducing construction costs and enabling the property developer, as well as its professional team to significantly accelerate the build. FAST-TRACKING HOUSING DEVELOPMENT

T he eight-bedroom house is being constructed in Nirvana, which is a residential area of Polokwane, Limpopo that is home to a YLEUDQW DQG DͧXHQW 0XVOLP SRSXODWLRQ Initially, Bendor Builders, the principal contractor, intended using rib-and-block technology to construct the 583 m 2 ͤUVW ͥRRU VODE RI the house. Comprising rectangular-shaped reinforced or pre-stressed SUHFDVW FRQFUHWH ULEV VXSSRUWLQJ UHEDWHG ͤOOHU EORFNV ULE DQG EORFN technology is extremely labour-intensive and, therefore, a more RQHURXV PHDQV RI FRQVWUXFWLQJ FRQFUHWH ͥRRU VODEV It is also costlier than HCS considering the additional consumables and materials, such as propping and concrete, required for their installation. $OWHUQDWLYHO\ +&6 DUH PDQXIDFWXUHG WR VL]H LQ D FRQWUROOHG IDFWRU\ environment to extremely high accuracy levels. ,QVWDOOHG E\ D VSHFLDOLVW WHDP IXUWKHU SUHFLVLRQ DQG HͦFLHQFLHV are possible than rib-and-block technologies and conventional in-situ techniques considering the many variables encountered on a traditional construction site. This approach, therefore, eliminates the potential risk of wastage and delays as a result of having to redo work. Placed on a thin layer of mortar bedding and then levelled and grouted in place, work can commence almost immediately at the QH[W OHYHO DQG EHORZ WR VLJQLͤFDQWO\ DFFHOHUDWH WKH SURMHFW +RZHYHU RQH RI WKH VLJQLͤFDQW DGYDQWDJHV RI +&6 RQ WKLV construction project is the role that it played in freeing up available space in an extremely built-up environment. The concrete ‘planks’ were transported to site on a just- in-time basis and then lifted directly from the specialised trailer and placed on the load bearing walls using an 80 t mobile crane. Strategically positioned on one side of the development and with a maximum reach of 25 m, the crane was able to lift and place the elements, including the heaviest 4,9 t slab, which is 320 m and spans 10 m, with minimal effort. ̸:H ZHUH DEOH WR LQVWDOO DQ HQWLUH ͥRRU LQ DV OLWWOH DV WZR days. This included mobilising the crane to site early in the morning to commence installing the elements, the bulk of which weighed 2,3 t and were 150 m to 250 m in length,” Johan Muller, Project Manager of CoreSlab, which was

between every six and seven minutes. This is considered an optimal production rate by the precast concrete specialist and an impressive feat that has also been made possible by using innovative equipment. A case in point is the specialised lifting tackle that has EHHQ GHVLJQHG E\ &RUH6ODE̵V HQJLQHHULQJ WHDP WR HͦFLHQWO\ DQG safely handle its HCS. This is over-and-above the skills and capabilities of the installation team, which comprises seven people, including the crane operator and truck driver who transported the HCS to site. Bendor Builders owner, Nicky Booysen, praises CoreSlab’s high level of workmanship. “This is an extremely complex project, considering the number of changes that have been made to the original architectural design since we commenced working on the project. There is, therefore, very little room for error. Certainly, working with a competent sub- contractor, such as CoreSlab, has helped mitigate some of the risk for this discerning client,” Booysen says. The precast-concrete specialist is closely associated with many DͧXHQW KRXVLQJ SURMHFWV LQ DQG DURXQG WKH JURZLQJ 3RORNZDQH central-business district. “Working with Bendor Builders and VBL Consulting Engineers on this prestigious project has been an absolute pleasure. We remain very proud of the role that we have played in promoting the use of HCS, especially in the home-building market,” Jaco de Bruin, Managing Director of CoreSlab, concludes. ƒ

The entire floor structure was installed in only two days.

appointed to manufacture and install the HCS, says. The precast-concrete specialist installs an element

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CONSTRUCTION WORLD JULY 2020