Construction World August 2022

PROJECT PROFILE

60 MPa and require a special concrete mix to reach full strength after seven days. “The sheer walls are 40 MPa and the slabs 25 MPa,” says Ngobese. Part of the project specifications was the removal of back propping on the slabs. “It works on a 100, 75 and 25% back propping ratio. When we are busy with a l ive deck, 100% of back propping remains on that floor for four days after casting or until it reaches 60% of the required 25 MPa as specified by the structural engineer. We can then reduce the slab back propping to the two floors below to 75% and 25% respectively and only then can we commence with brickwork.” Some 1,5 mill ion bricks (including face bricks) will be required by the project. Steel fixing has to be done in the small the lay down area on Enoch Sontonga Avenue. “The project requires 960 tons of steel. Normally we pour our columns from floor to floor, but on this project it was an engineering specification that all our columns had to be double l ift – two floors. This saves us a day on steel fixing and also reduces the slab pouring time. It is also cost saving as it reduces the amount of spl icing on the columns,” Ngobese explains. Two of Concor ’s tower cranes have been erected on site to help deal with space constraints and to expedite the movement of materials in the interests of the fast pace of construction. The bigger of the two has a 60 m j ib and can reach right around the site. The smaller crane has a 40 m j ib and is used predominantly to l ift material onto floors. Both these cranes can only move materials within the constraint of the footprint of the site. Since March these cranes are operated 24/7. “The nightshift team loads the materials that will be needed

the scope for the foundations. “The pile caps had to be bigger than what we had tendered for and the piles had to reach depths of between 3 and 5 metres (as opposed to the expected 1,5 m) which caused delays.” To mitigate this delay Ngobese says that Concor doubled its resources on site for the foundations. Overcoming the location challenges The project borders the M1 highway to the west. “This is a high risk area and the site is in close proximity to it. As a result, all our work started from the western façade. We installed our brickwork scaffolding early, something we do at a later stage on less risky projects. It offers protection between the perimeter of the building and the M1 highway,” Ngobese elaborates. Shade netting covers the entire western façade as a safety precaution to prevent matter from fall ing onto this M1. “Shade netting comes in 3 m sections and these were stitched together. The practice was used to great effect on some of Concor ’s other projects.” In addition, the heavily trafficked Enoch Sontonga Avenue and De Korte Streets border the site to the north and east. “This necessitated extra flagmen to assist with del iveries and traffic control. We have wayleaves on De Korte Street and on Enoch Sontonga Avenue.” The importance of sequencing Ngobese explains that concrete is poured daily for columns and sheer walls. “At least two floor slabs are poured per week. Our turnaround time for these pours was 11 days, but it has been brought down to eight days.” Lafarge is supplying the 6 200 m 3 of concrete that is required by the project. The columns have a strength of

North view – façade brickwork in progress.

36 CONSTRUCTION WORLD AUGUST 2022