Pratley Putty plays a key role in the rehabilitation of the Kariba Dam spillway


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Pratley Putty plays a key role in the rehabilitation of the Kariba Dam spillway. The hand-moldable, high-performance mastic-like adhesive has been identified by distributor Mart Solutions for use in the project’s cofferdam components.

“Pratley Putty is ideal for underwater use, but can also fill, seal, build and bond almost any rigid material,” notes Eldon Kruger, Marketing Director of Pratley.

Martie Coulson, owner of retailer Mart Solutions, says a similar product was initially tested, but it turned out to be too expensive and took a long time to get going. “Pratley Putty has proven to be the best quick-setting solution for holding the cofferdam components in place,” she points out.

The concrete dam wall has six gates that release water into Lake Kariba. Over time, the concrete has expanded slightly, affecting the proper functioning of the valves, which could lead to the valves sticking open or closed, posing a potential risk to people, animals and the environment .

The spillway gates are being renovated one by one as part of a long-term project that began in 2019 and is scheduled for completion in 2025. A consortium made up of GE Hydro France and Freyssinet International won the contract for the Zambezi River Authority (ZRA).

The first step is to fabricate key components like a new emergency door, motorized gantry crane and off-site cofferdam parts. These are transported to the site by boat and by road, reassembled and put in place.

The next step is to create a dry work space at each door so that it can be refurbished. This involves the construction of a small temporary cofferdam that clings to the dam wall at the edge of the lake. Experienced divers affix steel support members to the upstream face of the dam wall to allow the cofferdam to be put in place.

“As part of the work we do on site, we have to place and anchor the supporting metal pieces underwater. Then, it must be poured between these supports and the concrete structure of the cofferdam. Before pouring the grout, we put in place a wood and steel frame,” says Coulson.

The main application of Pratley Putty is to seal the framework to prevent leakage during pouring. In terms of the application process, the two components of Pratley Putty are mixed on the surface and then the mixture is taken underwater by a diver who applies it by hand.

A crane on the dam wall lowers the cofferdam pieces into place one by one. The water trapped between the cofferdam and the dam wall is pumped into the lake, creating the waterless space needed for the rehabilitation works.

Finally, a new self-propelled gantry crane will be installed which can move the emergency gate into position to close any of the sluice gates as needed. The spillway itself will be commissioned once the six gates have been renovated and the new gantry crane installed.

The Kariba Dam Rehabilitation Project (KDRP) is the latest unique application for Pratley Putty. Since the product’s launch in the early 1960s, Pratley Putty has become a household name, with myriad uses.

He secured coral fragments in a coral nursery project run by Oceans Without Borders in Zanzibar. A green sea turtle has had its damaged shell repaired with Pratley Putty, while researchers have used Pratley Putty to stick radio transmitters to the scales of pangolins while studying them in the wild. It was even used by the US space agency aboard its lunar Ranger spacecraft, gaining worldwide fame as the only South African manufactured product to go to the moon.

“The strength and reliability of Pratley Putty reinforces the company’s mantra of producing products that outperform all others in the global marketplace,” comments Kruger. Now the product has again proven its versatility with the tough engineering and construction work undertaken to rehabilitate the spillway.

The Kariba Dam has supplied the water needs of Zimbabwe and Zambia for over 60 years. The KDRP includes the remodeling of the deep basin, which is being undertaken by the French engineering company Razel-Bec, as well as the renovation of the spillway. This will ensure the long-term effectiveness of the dam in the future, reports the ZRA.

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