Reservoir construction showcases best practice in precast concrete

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Reservoir construction showcases best practice in precast concrete

A reservoir construction site in Bundu is showcasing the many benefits of building with precast-concrete technologies.

Using a unique modular reservoir wall and roof system, Thembisile Hani Local Municipality will be able to complete the 10 Ml structure in a significantly shorter period of time than would be possible using a more conventional approach to constructing the structure.

The municipality is already reaping the benefits of its decision considering the extremely complex ground conditions in which the structure in being built.

Located in very rocky terrain, Mbako Projects & Trading, the main contractor, has had to undertake extensive and time-consuming blasting just to establish the platform of the reservoir.

It has also encountered similar ground conditions along most of the entire length of the 2,5 km pipeline.

While work forges ahead on this component of the work scope, the walls of the structure are being manufactured at a state-of-the-art precast-concrete factory.

They are being transported to the site and then installed in half the time that it would take to build the water-retaining walls using cast-in-place methods.

Certainly, the high levels of efficiencies and accuracies achievable using precast-concrete technologies can already be evidenced by the centre portion of the roof structure on site that was completed in record time.

The structure, comprising precast-concrete columns, beams and hollow-core slabs, was built by Corestruc in only four days.

Corestruc’s reservoir roof system has been used on many other projects to significantly accelerate water delivery and was adapted for this build together with input from Monde Consulting Engineers & Project Managers.

This is only the second project in the country to also incorporate Corestruc’s new modular precast-concrete wall system to further accelerate the build.

Sefiso Mdingi, Monde Consulting Engineers & Project Managers’ civil-engineering technologist, lauds the municipality for its willingness to test new technology on its important water projects.

“Water is a basic human right, and the local authority was, therefore, willing to take the lead by being the first to use new state-of-the-art technology that will help it significantly accelerate the delivery of water to this area of the province,” Mdingi says.

The 60 wall panels and four buttress panels, all no less than 80 MPa, are being accurately placed on the steel fixing on the ring beam that was constructed by the main contractor as part of its work scope.

Rudie Bezuidenhout, senior foreman of Mbako Projects & Trading, says that the contractor maintained close contact with Corestruc throughout to ensure accuracy ahead of the arrival of the precast-concrete panels.

“They are being lifted and placed as they arrive by Corestruc’s team and, in so doing, negating many of the challenges associated with building these walls using conventional cast-in-place techniques. This includes the establishment of tonnes of formwork and co-ordinating the various teams, counting the steel fixers, shutter hands and concrete gangs, on site,” Bezuidenhout says.

The wall panels each weigh eight tons and are 9,8 m in length and 16,4 m in width and were produced by Corestruc using forms that were designed and manufactured specifically for this project.

Many hours were also invested in the design of four buttresses, which contain numerous cast-in components that were manufactured in-house using computer-numerically controlled machines.

The voids between the panels are sealed using a specially-designed grout that is pumped between the precast-concrete wall slabs.

It was designed to reach a compressive strength of 100 MPa within four days and to further react when it comes into contact with water.

About 6,6 km of PVC post-tensioning ducts and cables are being installed by hand between the joints of the wall panels, before the grout is pumped around the circumference of the reservoir.

Works started on the foundations and bases for the columns of the roof structure which, once completed, was followed by the ring beam and the walls, and will end with the floor of the structure.

By constructing the wall in this manner, the critical path of the programme runs through the earthworks and foundations.

“The construction of the floor slabs overlaps the installation of the walls and roof on the works programme. We are able to construct the walls and roof in as little as two to three months on site, while the manufacture of the structure takes place at our factory during the earthworks and construction of the foundations,” says Willie de Jager, managing director of Corestruc.

De Jager says that it is an achievement to be associated with a visionary client, such as Thembisile Hani Local Municipality, while noting the large role that Monde Engineering & Project Managers is playing in driving innovation in service delivery.

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