The Cement & Concrete SA’s Inland Branch Committee hosted their first event for 2022 on 17th February, which was a site visit to the 210 Mℓ Vlakfontein concrete reservoir in Benoni, Gauteng.
It was a beautiful sunny morning when 28 industry colleagues gathered, eager to hear about the circular reservoir, which will store 213.4 million litres of potable water and is the country’s largest cylindrical post-tensioned concrete reservoir, if not in the world. Due to its enormous size, it may also be classified as a dam. This infrastructure development is part of the Gauteng Department of Water & Sanitation’s service delivery improvements to meet the increasing water demands of the area.
Erhard Kruger of HGK Consulting described the concrete requirements and construction of the reservoir: an 1800 m3 floor slab layer of 200 mm, 35 MPa concrete was pumped in 13 sequenced pours of approximately 250 – 360 m3 each. The post-tensioned 45 MPa outer concrete walls are 11.8 m high, like a three-story building. The walls are tapered from a thickness of 1 100 mm at the base to 300 mm at the top. It has an internal diameter of 154 m – the length of one and a half football fields – with 272 round reinforced 35 MPa concrete columns, 600 mm in diameter, to support the roof slab. The permeable groundwater drainage system is constructed with three layers of 15 MPa no-fines concrete. 8000 m3 of no-fines concrete was first placed with a 50 mm thick layer of 9.5 mm stone mix, following a 245 mm layer of 19 mm stone mix, and lastly, a 125 mm layer of 26 mm size stone mix.
Commissioned by Rand Water, the reservoir with a project value of up to R400 million, is under construction through a JV between WBHO Construction and the Motheo Construction Group. The structural designer is HGK Consulting, and the concrete supplier used is PPC Pronto Benoni.