Jobsite description

In November 2020 started the construction in South Africa of the Vlakfontein reservoir in Benoni, Gauteng.
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.

The concrete reservoir is due for completion in the first half of 2023.
The circular post-tensioned reservoir, which will store 213.4 million litres of potable water, is the country’s largest cylindrical post-tensioned concrete reservoir, one of the biggest in the world. Due to its enormous size, it may also be classified as a dam.

CHRYSO expertise

The reservoir has a ground water drainage system which is constructed with 3 layers of 5 MPa no-fines concrete. The 8000m3 of no-fines concrete started with a 50mm thick layer of 9.5mm stone mix, following a 245mm and 125mm layer of 19mm size stone mix. These mixes were challenging, CHRYSO introduced CHRYSO®Easydrain solution.
CHRYSO®Easydrain mechanically and hydraulically binds the aggregates with the cement paste. It fluidizes the concrete, assisting with a homogeneous mix and improves the curing to reduce the chances of cracking.
Once completed an additional drainage layer of around 2200m3 of no-fines concrete was poured around the reservoir.

Once the no-fines concrete was completed, a layer of 200mm, 35MPa concrete was pumped in 13 pours of approximately 250m3 each. This mix has been designed with a shrinkage reducing admixture CHRYSO®Serenis.
CHRYSO®Omega 178 superplasticiser was combined to reduce water and assist with workability.

All reinforced concrete structures are water-retaining,  CHRYSO®CWA 10 crystalline waterproofing agent was used in the concrete walls and floor, to prevent water penetration into the concrete and protects the concrete and reinforcement against corrosive ground water, chemicals etc.


  • CHRYSO®Omega 178
  • CHRYSO®Serenis
  • CHRYSO®Easydrain

Project technical challenges

This project is significant in its innovative use of concrete and for the large volume of concrete used. Additionally, the challenges created by the variations in climatic conditions between summer and winter. High ambient temperatures were a particular constraint, as were the strict slump requirements specified.
This exceptional structure is a bold and overt statement of the strength and robustness of concrete. Due to the fact that it must resist large compression forces of water, no other modern construction material is better suited to this task than concrete.

Project participants

Client: Rand Water
Concrete supplier:
PPC/Pronto RMX Benoni
Admixture Supplier:


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