Innovation trends
Reduce water – add another step to sustainability
R
esponsible contractors have realised the growing strain on South Africa’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 in the province of Mpumalanga. This is probably one of the largest cylindrical posttensioned concrete reservoirs in the world, with an inner diameter of 154 metres and a heavily reinforced 11,8 metre 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,” says Flannigan. “It can also increase the slump – or flow – without affecting the water content of the mix.” The Vlakfontein Reservoir has a ground water drainage system constructed with three layers of 5 MPa no-fines concrete. The 8 000 m3 of no-fines concrete comprises a 50 mm thick layer of 9,5 mm stone mix, followed by a 245 mm and 125 mm layer of 19 mm aggregate. To facilitate consistency and ensure the aggregate would bind mechanically and hydraulically, CHRYSO® Easydrain was introduced to these mixes to the cement paste. This specialised admixture fluidises the concrete, assists with a homogenous
Evaporation was controlled using CHRYSO Profilm 19 evaporation reducer at the Khutsong reservoir project mix and improves curing to reduce the chance of cracking. The bonded aggregates, once dried, will not loosen. An additional drainage layer of around 2 200 m3 of no-fines concrete will be poured around the reservoir.
Khutsong Reservoir – the first time a pre-tensioned floor was used for a reservoir in Africa
Concrete Trends Issue 4 2021
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