Construction World February 2019

PROJECTS PROFILE

The project successfully managed to marry the in-situ system with the precast system.

Everyone working at height had to undergo a specific training course, with the main focus on securing edges.

Fourways Mall is set to become the country's largest precast concrete installation.

A benefit of a precast system is that the installation is much faster than in-situ concrete frames.

inverse serrations; this allowed the column to be socketed into the 1,4 metre wide base and then grouted together. The column was vertically aligned before grouting and was then stable without props. This efficient technique allowed for five to six towers had to be placed per day, with the pace of construction uninhibited by the traditional curing time of in-situ columns. Precision was also called for in the foundation excavations, as precast columns have set lengths; this is not always straightforward, given the varying geology of the site. In some cases, the columns had to be cut shorter, or further excavation conducted to place the beams in positions that ensured a level result. The innovation went beyond the precast system itself to the extensive quality assurance and quality control procedure applied by the contractor on site to ensure the safe installation and finishing of the concrete elements. At six tonnes each, the columns had to be navigated safely through the busy and confined site after delivery by flatbed trucks. Results in terms of concrete finish also exceeded expectations; while the project specification was for a Grade 2 finish, the use of MECSA’s steel

one opposite the construction site. The Laezonia yard used its own batch plant, while readymix supplier Scribante delivered concrete to the manufacturing yard opposite the construction site; in total, about 200 000 m 3 of concrete was supplied by MECSA and Scribante. Emphasis was on high-strength 65 MPa concrete that could attain early strength, as the elements were sizeable and had to be lifted and placed as soon as possible. This concrete was required to develop a 32 MPa strength specification at 18 hours, so the team worked with cement and additive experts to conduct trials on mixes and identify the best solution. AfriSam providing 42.5R cement which performed well in terms of the high early strength requirement. The company also contributed to conventional mixes (such as the 15 MPa and 30 MPa concretes) used for toppings on the fabricated slabs – with a waterproofing additive to waterproof the slabs. The overall quality of concrete accuracy for precast application was critical, as the columns had to fit exactly into a foundation socket. Column ends were designed with serration or tooth mechanisms, while the foundations had the ‘female’ or

24

CONSTRUCTION WORLD FEBRUARY 2019