New precast concrete wall system accelerates water delivery in Mpumalanga

A
new precast concrete reservoir wall system has been successfully deployed on
two water schemes that will significantly strengthen drinking water supply to
areas of Mpumalanga.

Both
project sites provided an ideal opportunity to refine the system ahead of its
commercial launch by Corestruc, a leading South African precast concrete
specialist.

The
first 10 Ml command reservoir was built by Corestruc in KwaMhlanga and the
second such structure in Bundu. In both instances, the new precast concrete
wall technology was used in combination with the company’s tried-and-tested modular
roof structure.

Notably, this is the first time that a South African municipality has used Corestruc’s precast concrete wall system, based on what is considered to be international best practice and adapted to unique local conditions.

Monde
Consulting Engineers and Ceenex motivated the use of the new technology to
representatives of Thembisile Hani Local Municipality to significantly accelerate
the construction of the two structures as vital components of the water schemes.

Using
the system, a reservoir wall for a structure of this size can be built in as
little as five to six weeks, while also providing significant cost-savings in
the construction of larger reservoirs.

Meanwhile,
Corestruc is contractually liable for the performance of all its systems, which
helped allay any initial concerns regarding the use of the new technology on
these important projects.

The
walls of both structures comprise 60 precast concrete panels, each weighing
eight tons, and are 9,8 m in length and 16,4 m in width.

Manufactured at Corestruc’s factory, they are
transported to site and then placed on top of the ring-beam that is built by the main
contractor once the centre portion of the structure, comprising precast
concrete columns, beams and hollow-core slabs, has been completed.

The precast concrete wall panels, as well as the four buttress panels were manufactured using specialised forms that were designed and produced by CoreEngineering.

As
essential components of Corestruc’s post-tensioning system that assist in
reinforcing the walls both vertically and horizontally, the buttress panels
contain many cast-in components that were all manufactured by the company’s own
engineering department.

CoreEngineering
also designed the three-dimensional prints that are used to secure the rubber
cast that serves as a temporary shutter for the grout.

Ceenex
and Monde Consulting Engineers worked closely with Corestruc to refine the
system for these two projects.

Special
attention was also given to the grouting process, the most time-consuming and
intensive process of the entire construction phase.

At
both structures, about 6,6 km of post-tensioning ducts and cables were
installed by hand between the joints of the wall panels, before the grout could
be pumped around the circumference of the reservoir.

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.

Designed
by Corestruc, it is blended and packaged by Epoxerite, a leading South African
construction chemicals specialist.

As
part of the service offering, the company also undertakes regular testing of
the material to ensure a consistent high quality of supply.

The
grout underwent extensive testing ahead of its application, and Corestruc even
brought its own water to the first construction site in KwaMhlangu to ensure it
achieved the desired reaction.

Importantly,
the grout has to be very flowable to be pumped through all of the
post-tensioning ducts from a single position using two pumps in a process that
takes up to two days to complete.

It is pumped in a controlled manner and the working time of the grout is extended by cooling it down to seven degrees Celsius.

Willie de Jager, managing director of
Corestruc, concludes that he is proud to be associated with Ceenex and Monde
Consulting Engineers, both respected participants in water infrastructure, and
lauds Thembisile
Hani Local Municipality for its visionary approach to service
delivery.

More information from Corestruc, Tel: +27(0)87 232 2462 / www.corestruc.co.za

Corestruc is able to construct the walls and roof in as little as three months on site, while the manufacture of the structure takes place at the factory during the earthworks and construction of the foundations