Construction World April 2023

COVER STORY

The readymix is a 30% replacement of cement making it a green star mix (three or four stars).

Major South African construction company Concor is currently building a super-basement in Sunnyside, Pretoria as the first phase of the Trevenna Office Campus. It is part of a larger venture driven by the Public Investment Corporation (PIC). This expansive 68 000 m 2 basement will service the future three A-grade office buildings of this campus. AfriSam, a leading supplier of superior quality construction materials and technical solutions, is supplying the readymix concrete for the second half of this project. Construction World recently visited the bustling urban site where readymix deliveries must be timed meticulously to suit the construction programme. AFRISAM READYMIX FOR SUNNYSIDE’S NEW SUPER-BASEMENT

M artin Muller, Senior Contracts Manager at Concor, says that the basement is 20 metres below ground level. “The scope of the project is to build a 68 000 m 2 super-basement structure of five levels of reinforced concrete slabs which will form parking for the overall Trevenna campus. It ties into the existing campus which already has three buildings. “The super-basement that we are building in this multi phase development has the capacity to facilitate another three office buildings on top of it. Concor is responsible for the extensive underground services such as sewer and stormwater infrastructure, electrical reticulation, lifts to the ground floor and access control,” says Muller. Trevenna’s challenges Muller says that apart from meticulous planning and management of logistics because of the site’s urban location, the ingress from surface and groundwater and rock conditions posed challenges. “The site is below the water table and we therefore had to contend with large volumes of groundwater when we started with the bases. “Water had to be pumped out of the worksite and into the stormwater system,” says Muller. “The client has a water usage licence and on average, since bulk earthworks started, some 40 million litres have already been pumped out.” The blasting was done by the bulk earthworks contractor

and once this portion of the contract had been done, Concor moved onto site in February 2022. “This was a phased handover of the basement because of the amount of work and the challenges experienced by the bulk earthworks contractor with the hard rock – up to 250 MPa - and groundwater,” Muller says. The basement is constructed off conventional bases on this hard rock as it is sufficient to support the structure with no piling required,” says Muller. “The way in which we have managed these potential risks showcase Concor’s experience and expertise on functioning on complicated projects to be able to meet the client’s deliverables,” adds Muller. The limited working space necessitates that the rebar and formwork are stacked on the deck itself that has already been completed. The footprint of the basement extends across almost the entire site. “Logistics, material handling and deliveries are critical and require careful and meticulous project planning to ensure that materials arrive in line with the construction programme, which relates directly to AfriSam’s - the readymix supplier - deliveries,” says Muller. In-situ construction of post-tensioned beams All the beams used for the super-basement are post tensioned. This enables the use of thinner slabs that use less

20 CONSTRUCTION WORLD APRIL 2023