Construction World December 2017

KATLEHONG RESERVOIR The new 35 mega-litre reservoir in Palm Ridge, adjacent to the civic centre, was delivered by a professional team comprising consulting engineer, TLS Engineers & Project Managers, as well as civil- engineering contractors, Civcon and QC4 Civils.

contractor continued with the balance of the reservoir construction programme. Working alongside the main contractor, Corestruc installed a total of 2 000 square metres of precast concrete items in as little as eight working days. The main contracting team is now able to start water proofing the roof and covering it with a stone layer, as well as installing the tendons and tensioning, as well as grouting of the walls. This impressive productivity rate achieved by Corestruc on this site can be attributed to the extensive upfront planning implemented on all of its projects, as well as meticulous attention given to details such as the connection system as early as the design phases. Accuracies of the casting of each pre- cast component also contribute toward swift installation of the system. Manufactured in a controlled factory setting, all of the precast concrete items are no less than 55 MPa concrete – far exceeding the 40 MPa specification of the in-situ material. This contributes towards the overall performance of the asset, reducing maintenance requirements of the structure. Only washed aggregates and sand from reputable suppliers enter the production cycle, while silica fume supplements some of the cement content to create a denser micro-structure of the concrete.

Corestruc was appointed to design and install the structure’s precast concrete roof. The roof of the reservoir is the most complex and time-consuming aspect of any reservoir construction project. By building the roof of the structure using a modular precast concrete system, the professional team is able to accelerate the construction programme. In this instance, the system shaved as much as eight months off the programme. This is the first time that QC4 Civils has used a precast concrete system on any of its reservoir construction projects. One of the biggest advantages of the system is that it can be installed without the need to erect, dismantle and remove tons of supporting scaffolding, while the precast system can be programmed concurrently with other activities and, therefore, does not restrict multiple activities on the site. Corestruc became involved in this project early on during the design stages, working closely with the original design engineer, Aurecon. The decision to build the roof of the structure using a precast concrete roofing system was based on Corestruc’s previous track-record working with professional teams to accelerate the construction of reservoirs using the system.

The motivation was based on a string of successful projects undertaken by Corestruc since completing its first related project in 2011, namely the Krugersburg 50 mega litre reservoir. Corestruc’s precast concrete roof system comprises a total of 2 325 m 2 of hollow-core slabs, each up to 250 mm deep. They are supported by 16 precast concrete columns and 18 beams, weighing a total of 12,3 tons and 7,5 tons, respectively. The installation of the precast concrete roof of the structure can be programmed at any stage of the build. On this project, installation of the precast items started when 80% of the walls had been cast by the main contracting team. An opening in the wall was left just wide enough for Corestruc’s team to access the inside of the structure with a mobile crane to commence installing the precast concrete columns, working from centre outwards. Led by a seasoned surveyor equipped with a state-of-the-art theodolite, Corestruc’s team lifted and fastened the components into place, achieving tolerances of between about 20 mm at heights of 15 metres. The team averaged an impressive production rate of up to 12 columns and 20 beams in a single shift, while the main

PROJECT INFORMATION

• Company entering: Corestruc and Group Companies • Contract value: R5-million (Corestruc’s value) • Project team: QC4 Civils and TLS Engineers and Project Managers • Main contractor: QC4 Civils • Principal agent: TLS Engineers and Project Managers • Consulting engineer: TLS Engineers and Project Managers

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