Water storage solution specialist Aquadam, under licence to European company Farmitec, will soon introduce what it believes to be the first and only prestressed and post-tensioned reservoir, the Muleby system tank IA, onto the South African market.

The Muleby tank is a cylindrical reservoir of prestressed precast concrete elements, for the storage of fluids. The design conforms to the requirements for the highest classification of water tightness in the new European standard, Eurocode 2, Part 3: Liquid retaining and containment structures.

Different types of fluids, including drinking water, sewage, molasses and certain chemi- cals, can be contained in these reservoirs.

The reservoirs can be constructed with volumes of between 174 m3 and 5 765 m3 in different configurations between 8.6 m × 3 m and 32.7 m × 7 m. Bigger structures are in the planning phase. Each structure is designed and manufactured according to the specific requirements of the client.

The panels are longitudinally prestressed, enabling the reservoir to resist different load cases without cracking.

Each element is 1 575 mm wide and between 130 mm and 160 mm thick. The elements are erected in circles of 15 to 68.

Assembly of the reservoir is safe, quick and efficient. “Having already cast the concrete floor, the concrete slabs are individually erected. A structure of up to 5.7 Mℓ may take up to two days to erect. A further week is needed for curing of the joints and an additional day is required to do post- tensioning on it,” explains Aquadam product manager Anton Liebenberg.

After the erection process is complete, a cable, comprising mono strands, is run through the elements and post-tensioned to take up the hoop tension and keep the joints compressed.

The prestressing of the panels and the post-tensioning of the joints ensure that the reservoir is stressed vertically and circumferentially.

The technology behind the reservoirs is used widely in civil construction, but the combination is a first in South Africa, states Liebenberg.

Because of the prestressing technology used, the structure is thinner and lighter than the conventional concrete structures that we are used to in South Africa.

The concrete elements are produced locally under controlled conditions at Aquadam’s factory, in Pretoria. This allows for strict quality control and fast and efficient service delivery. “Prestress elements can be transported over long distances, without damage. No more struggling in getting the right aggregates, like when casting on site,” he says.

The controlled environment offered by Aquadam during the production process guarantees high-quality products, efficient production and a short construction time once on site. The installation of the reservoir is less labour intensive, which ensures safety in the workplace and better service delivery, Liebenberg adds.

“Poor quality has become a menace in the South African market. There is a high demand for quality and safety. To work on scaffolding and erecting steel shutters and reinforcing, 7 m up in the air, is dangerous. With this product, the elements are placed by crane and there is almost no one working at height,” he says.

Liebenberg highlights that this new technology also allows for cheaper installation than with the conventional con- crete method and can even compete with steel tanks. It is also more durable since it is designed at 35 MPa to 45 MPa con- crete but with the precasting ends above 60 MPa.

This makes it suitable for treatment plants and application in adverse conditions. It has a life span of more than 50 years, he adds.

Limited maintenance of the structure is required. “If you are storing heavily corrosive materials inside the tank, there will eventually be a need to recoat the inside of the tank,” says Liebenberg.

The reservoir can be closed off should there be a need. Aquadam provides roofs that are made from steel, polyvinyl chloride or prefabricated concrete. Roofs can even be cast in situ should the client require it.

Liebenberg says industries are still a bit sceptical about the product, as it is a slender element compared with conver- sional methods. He expects to see more demand for this product as industries start understanding the product.

“For its safe working environment and cost savings, some of the big role-players in the industry have already shown a keen interest in the product,” he adds.

Author: Nomvelo Buthelezi