Playing a pivotal role in the construction of one of Gauteng’s largest and most technical complex water towers, construction materials supplier AfriSam is supplying specially designed readymix concrete to meet both structural and seismic performance requirements.

Located near Main Reef road south of Johannesburg, the 43-m-high water tower will store 3.2-million litres of water to support the new Goudrand megacity development.

With construction led by construction company Murray & Dickinson (M&D) Construction and engineering design by civil engineering company SCIP Engineering Group, the project has demanded highly customised concrete solutions from AfriSam.

The structure is located in a seismically active zone and required additional reinforcement in the lower section of the shaft to withstand ground acceleration above 0.1 g.

This called for increased steel density and a concrete mix that could deliver strength, flowability and controlled heat of hydration.

AfriSam product technical team leader Mduduzi Ndlovu explains that the concrete mix was developed with a high proportion of supplementary cementitious materials (SCMs) to reduce the heat generated during curing.

“The base mix comprised 70% ground granulated blast furnace slag (GGBS) and 30% AfriSam High Strength Cement, reducing the ordinary Portland cement (OPC) content to just 20%,” states Ndlovu.

Despite the low OPC content, Ndlovu explains that the mix exceeded expectations, achieving the target strength of 51 MPa in only 28 days compared with the designed 56-day requirement.

The construction process placed high demands on the readymix in terms of both slump control and delivery precision. With over 210 kg of rebar per cubic metre in some sections, AfriSam developed a high slump pump mix for vertical pours, while limiting slump to 130 mm for slanted sections to avoid concrete sliding off shuttering.

M&D Construction contracts manager Sheldon Temlett highlights the importance of this mix performance.

“With such dense steel and complex geometry, AfriSam’s mix gave us the workability we needed without compromising quality. ”

AfriSam territory manager Toni Williams adds that logistics were carefully aligned with construction progress to avoid delays.

“Coordination was key to supporting M&D’s controlled rise rate of 1 m/h, especially as the concrete had to partially set before each formwork lift could proceed,” states Williams.

Construction of the Main Reef water tower began in September 2024 and is scheduled for completion in April 2026.

Once commissioned, it will  supply about 20 000 homes in the Goudrand housing development – a major project spearheaded by the Gauteng Department of Housing, the City of Johannesburg and Blue Print Housing.