Kariba dam plunge pool stabilised

An ambitious project at Kariba dam will see the building of a temporary coffer dam downstream of the main wall, allowing the deep plunge pool at the base of the Kariba dam to be drained, reshaped and stabilised.

The aim of the project is to reduce the backward scour in the pool, created by water released by sluices in the dam wall, in an effort to address the concern that this scouring is edging towards the dam foundations.

The multi-million Euro engineering project to reshape the plunge pool incorporates the use of CHRYSO concrete admixtures. Working with main contractor Razel-Bec is Mart Solutions, the Zambian distributor for CHRYSO Southern Africa.

According to Mart Solutions, collaboration on the project started about two years before the concrete work began in October 2019, with the companies working together to ensure that the specified concrete mixes are achieved to the consultants’ required standards.

The specialised admixture Aquabeton ZA is seen as key in allowing concrete to be placed underwater, to create a foundation for the coffer dam’s seven piers. The admixture assists in minimising washout and segregation of fresh concrete when placed underwater.

Among the range of CHRYSO products provided by Mart Solutions is its Omega 162 superplasticer, which reduces the need to add extra water and so increases the durability of concrete. The admixture also improves cohesion and lowers viscosity in the concrete mix, leading to improved homogeneity and off-shutter finishes, explains the company.

The large pier structures will range from 250 t to 700 t in weight. The first of these, currently under construction, will measure 5.5 m tall when complete.

CHRYSO Fuge B, which is a pore-blocking permeability reducer for mass concrete, is also being used. The product reduces the size of the capillaries, aimed at almost eliminating the penetration of water under pressure. This is seen as important for the piers, as they are constantly in contact with water.

The piers are being slip-formed as hollow structures, from a specially-built rig in the Zambezi river. When the piers have achieved the minimum required height, they are floated into position, secured to the foundation and filled with concrete.

Facilitating the release of formwork from the concrete piers is CHRYSO DEM S, a mould-release oil for timber or steel. Mart Solutions is also supplying the Kariba project with construction chemicals from the company’s a.b.e. range. The polymer bonding liquid a.b.e. Duralatex is applied to the cone holes in the piers and the holes are then filled with a.b.e. Duragrout, which is a non-shrink grout for sealing.