Kariba Dam rehabilitation project progresses

The stabilisation and reshaping of the plunge pool at the foot of Kariba Dam’s 138 m high wall is using vast quantities of concrete in a range of applications.

“Among the first challenges we faced was in the construction of piers for the temporary coffer dam, where concrete had to be poured underwater to create a foundation,” says Martie Coulson of Mart Solutions, Chryso Southern Africa’s Zambian distributor.

Mart Solutions has been one of the key suppliers of construction chemicals to main contractor Razel-Bec since the beginning of the project.

“Difficulties in finding bedrock for piers 7, 8 and 9 – as well as for the dam’s right bank – meant that 22 000 m3 of concrete had to be placed underwater,” Coulson explains.

This arduous process – which took six months and was completed in September 2022 – involved pumping concrete to a depth of 25 m, with divers handling the 125 mm diameter pipe to place the concrete. Adding to the complexity was the movement of water from Zimbabwe’s nearby hydro-electric turbine outlet.

“This raised the risk of the cement being washed out of the mix, leaving the aggregate behind, as well as further reducing visibility for the divers. The Chryso Aquabeton product played a critical role as an anti-washout admixture that increases the cohesion of the concrete mix,” she explains, adding that this allowed the placement of a concrete base for the three piers, measuring some 15 m wide and 20 m deep.

Repairing a rock fault

Another important aspect of the project is repairing a fault in the rock at the foot of the Kariba Dam wall. Here, some 7 071 m3 of specialised concrete will be used for the large 90 m high, 45 m wide and 2.5 m thick wall, which will be built in front of the fault as a protective shield. This will be fixed onto the 12 m long, 40 mm diameter anchors in the wall, which will in turn be secured 10 m into the rock.

A combination of Chryso Omega 162 and Chryso Fluid Optima 206 will be used in conjunction with densified silica fume and fly ash in the concrete mix for the wall to assist in preventing the temperature rise in the concrete during placement and to avoid cracking. This is important due to the high ambient temperatures of up to 40°C.