Corestruc was one of the joint winners in the Specialist Contractor and Suppliers category of Construction World’s Best Projects of the Year Awards 2019.

The company received the award for its participation in the construction of a new 10Ml reservoir in Bundu on behalf of the Thembisile Hani Local Municipality.

Thembisile Hani Local Municipality is the first municipality in South Africa to use the company’s new precast-concrete system, which accelerates the construction of reservoirs.

“This achievement would not have been possible without the immense support from Thembisile Hani Local Municipality. This is in addition to its highly competent professional team, comprising consulting engineers, Ceenex Consulting Engineers and Mondeo Consulting, and main contractor, Mbako Projects & Trading,” Willie de Jager, Managing Director of Corestruc, says.

Using Corestruc’s technology, the construction of these structures can be significantly accelerated.

A 10Ml reservoir can be completed in only six weeks versus the four to six months it takes to only construct reservoir walls using conventional in-situ techniques, and this is without the risk of having to redo the work, considering the technically-complex nature of these construction projects.

Reservoirs are notoriously complicated and time-consuming structures to build. The construction of the wall demands absolute precision to ensure water-tightness. This slow and meticulous process is followed by the construction of the roof, which entails erecting and installing tons of scaffolding and formwork inside the structure. On most of these projects, work can, therefore, only take place at one or two faces at any given point in time.

Alternatively, Corestruc’s system enables the construction of the floor, walls and roof simultaneously to significantly accelerate the process.

The company builds the roof and wall at its factories while the principle contractor completes the earthworks and the reservoir floor. This means that the critical path of the programme runs through the earthworks and foundations.

Perfecting the design of the system took just more than five years from conception. It is based on what is considered to be best international practice that has been adapted for the unique African conditions.

Notably, Corestruc uses both vertical and horizontal tensioning to resist applied forces. This is opposed to conventional construction methods where reinforcing and post-tensioning is used to control applied forces.

About 6,6km of post-tensioning ducts and cables were installed by hand between the joints of the wall panels in preparation for the grouting on this project. This is in addition to the numerous three-dimensional printed components that were used to secure the rubber cast that acts as the temporary shutter.

Meanwhile, the grout has been designed to reach a compressive strength of 100 MPa within four days and to further react when the medium comes into contact with water when the reservoir is being filled.

It also has to be extremely flowable so that it can be pumped through all the post-tensioning ducts from a single position using two static pumps. The pumps deployed at Bundu could be quickly slowed down and accelerated to ensure that the correct quantity of grout was applied between the various panels. The working time of the grout was extended by cooling it down to seven degrees Celsius and it took up to 40 hours in a continuous process to pump it around the entire circumference of the two reservoirs.

The company then completed the construction of the outer section of the roof and ended with the stitching of the hollow-core slabs with a 35 MPa concrete to form a durable monolithic slab structure.

Corestruc is now preparing to manufacture another two 10 Ml precast-concrete reservoirs, and the company is hoping to be appointed to work on a 25 Ml reservoir project by a leading South African civil engineering contractor shortly. The principal contractor will undertake the earthworks, as well as construct the reservoir floor, pipeline and inlet works. Corestruc, as the specialist sub-contractor, will be tasked with the swift manufacture and installation of the wall and roof of the structure.