Precast • Issue 4 • 2021

Page 32

| TECHNICAL |

Responsible contractors have realised the growing strain on SA’s scarce water resources and a new admixture is geared to conservation efforts with its water-reducing admixtures for concrete. A recent example of this was in the construction of the Vlakfontein Reservoir near Standerton, Mpumalanga. This is probably one of the largest cylindrical post-tensioned concrete reservoirs in the world, with an inner diameter of 154m and a heavily reinforced 11,8m-high wall. A dynamic mix According to Patrick Flannigan, technical manager: concrete business unit at Chryso Southern Africa, the project made use of several admixtures to reduce water and improve workability. “One of these is our Plast Omega 178 plasticiser, which – when used in a concrete mix – permits a reduction in water content without affecting the consistency, also referred to as the workability,” he says. “It can also increase the slump – or flow – without affecting the water content of the mix.” The V la k fontein Reser voir has a groundwater drainage system constructed with three layers of 5MPa no-fines concrete. The 8 000m3 of no-fines concrete comprises a 50mm-thick layer of 9,5mm stone mix, followed by a 245mm and 125mm layer of 19mm aggregate. To facilitate consistency and ensure that the aggregate would bind mechanically and hydraulically, Chryso® Easydrain was introduced to these mixes for the cement paste. This specialised admixture fluidises the concrete, assists with a homogenous mix and improves curing to reduce the chance of cracking. The bonded aggregates, once (Above): The Khutsong Reservoir project marked the first time a pre-tensioned floor had been used for a reservoir in Africa.

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PRECAST | ISSUE FOUR | 2021

A WATER-WISE STEP ON YOUR WAY TO SUSTAINABILITY


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