Civil Engineering March 2022 | Vol 30 No 2

Civil Engineering March 2022 45 bar size and placement are also verified as part of the quality control procedures at the factory. These steps are complemented by the checks and balances introduced by Corestruc ahead of mobilising on site to commence with erecting the structure. Corestruc manages the setting out and installation of the column anchors for the precast concrete roof. By confirming the dimensional accuracies before erection, the company ensures that the beams of the roof structure fit the first-time round. The precast concrete wall panels are placed and positioned in a similar manner with the assistance of permanent locating plates that are fixed to the ring foundation. STRUCTURE OVERVIEW The Pam Brink reservoir has an inside di- ameter of 65.2 m and water height of 7.8 m. The roof column grids for the roof slab and beam span are 10.87 m × 10.87 m. The roof structure consists of hol- lowcore slabs that are placed on precast concrete beams, which are supported by prefabricated columns. They are connected to the in-situ bases by components that are cast into the precast concrete columns, also referred to as “column shoes”. Similar to the construction of a conventional steel structure, the precast concrete columns are connected to hold- down bolts in the base. Suspended precast concrete beams are then installed onto the columns. They are secured with dowels that protrude from the columns. The hollowcore slabs are then in- stalled onto the beams and secured into place. This is achieved by tying the steel reinforcing and placing in-situ concrete into the cores of the prefabricated slabs. Stirrups protruding from the precast con- crete beam act as a mechanical interlock to form a composite mechanism with infill concrete. The circular wall comprises 170 mm thick precast concrete panels that have been prestressed vertically. They feature 32 mm diameter polyvinyl chloride sleeves that have been positioned ac- cording to the post-tensioning design. The panels are placed into position and then supported by push-pull props and steel brackets at the top of each. Unbonded cables are then pushed through the sleeves which are then grouted mono- lithically with the joints of the panels. The grout is poured continuously in between the wall panels and horizontal cable sleeves. It is important to achieve a high-strength, high-flow grout with an extended pot-life, free of segregation. To achieve this, the water-to-cement ratio of 0:37 is manipulated with the use of admixtures and the water temperature is reduced and controlled to act as a chiller in the mix. Furthermore, only cement is used in the grout mix, which also contains an un-hydrated cement that reacts with water and seals possible leaks. After the grout has cured to a strength of 80 MPa, the cables are stressed to 75% via six precast concrete buttress panels that have been spaced along the perimeter of the reservoir. The wall is then pinned by casting a 200 mm to 250 mm high reinforced kicker on the wall footing on both sides of each panel. Joints between the panels are grouted with a high-flow, high-strength Learn more at mapei.co.za Tel: +27 11 552 8476 Email: info@mapei.co.za As MAPEI celebrates 85 years of teamwork , we acknowledge all of our clients, stakeholders and staff with whom we have shared challenges, innovation, passion and respect for people and the environment in construction. We have so much more to build, let’s continue to do this together.