By Jaco de Bruin and Willie de Jager
Constructing a large reservoir in record time is an achievement in its own right. This is especially when the South African construction industry like so many countries in other parts of the world is grappling with a severe shortage of high-level skills that are required to efficiently manage large civil-engineering projects. An absence of skilled labour in the country is also placing further strain on the ability of engineers, technicians and general foremen to efficiently deliver this infrastructure.
The successful completion of large water-retaining structures, such as the 50ML Mafenya, 50ML Krugersburg and 45ML Longridge reservoirs with only minor delays is testament to the skills and capabilities of the professional teams involved. These projects also demonstrate the efficacy of incorporating precast-concrete elements into the design of complex structures. This method has significantly reduced construction periods and helped to maintain consistently high-quality controls throughout the works programme.
On some of these projects, this “out-of-box” thinking resulted in a solution that was up to three times faster than in-situ methods, considering the standardisation and repetition of processes, components and methods.
High levels of quality were also maintained throughout because of the controls that the precast-concrete system provided, spanning manufacture through to the installation of the many elements on site.
Constructing the roof of a reservoir is the most expensive and time-consuming aspect of these projects. Mistakes on this aspect of the works programme will, therefore, have potentially disastrous consequences.
Using cast-in-place methods, onerous demands are placed on professional teams to plan and manage the various aspects of the construction of the roof, which is undertaken once the wall has reached its final height as part of the final components of the works programme.
This includes the erection and dismantling of tons of scaffolding inside of the reservoir to support the forms for the construction of the large overhead structure. It, in turn, is supported by in-situ concrete columns inside the reservoir that are cast while the wall begins to climb from the ground. In addition to the extensive formwork, there is very little scope for error in the placement of the tons of reinforcement and extensive concrete works involved in constructing these large overhead structures.
The quicker installation of a precast-concrete roof system can be programmed at any stage of the reservoir construction project and as early as the earthworks phases.
This process starts with the placement and grouting of the precast-concrete columns onto the in-situ stubs. They, in turn, support the precast-concrete beams and hollow-core slabs (HCS) that serve as roof planks. The HCS are stitched together and covered with a grout to form a monolithic slab and a precast-concrete coping is then installed as a finish to complete the structure.
Coreslab and Corestruc oversee the entire construction of the precast-concrete roof system, while the main contractor proceeds with the construction of the wall and other aspects of the project to mitigate delays. The companies have acquired and refined this capability over the many years that they have been designing, manufacturing and constructing precast-concrete roof systems. This institutional knowledge is being deployed on reservoir projects throughout the country to provide enhanced programme monitoring for delivery certainty.
However, there are many more benefits of this hybrid approach that incorporates best practice in in-situ construction and precast-concrete technologies.
This includes a noticeable reduction in the delivery of construction materials to site, over-and-above eliminating the need for extensive temporary works. On all the company’s projects, this method has provided a visibly clean and clear working area.
With the various elements produced in a controlled environment and dispatched to site according to the construction programme, the precast-concrete roof system also enables the introduction of greater health and safety (H&S) protocol on projects. These are incorporated in the precast-concrete factory and then on-site during the construction of the roof by a team with extensive experience installing these elements.
Coreslab and Corestruc are constantly innovating to take precast concrete to the next level. A case in point is an innovative reservoir wall system that now provides a complete precast-concrete solution for these projects.
Jaco de Bruin is Managing Director of Coreslab and Willie de Jager is Managing Director of Corestruc