27 August 2019

There is increasing interest in Corestruc’s
reservoir system as more of the country’s municipalities and water authorities
prioritise South Africa’s water infrastructure backlog.

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

The company recently constructed two 10-Ml reservoirs
in only six weeks using its sophisticated precast system.

Willie de Jager, MD of Corestruc, says that it would
have taken four to six months to only construct the reservoir walls using
conventional in-situ techniques.

“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 construction of the roof, which entails erecting and installing
tons of scaffolding and formwork inside the structure. On most of these
projects, work can only take place at one or two faces at any given point in
time. Our modular system enables the construction of the floor, walls and roof
simultaneously to deliver the infrastructure in a fraction of the time it would
using conventional methods,” says De Jager.

The roof and wall systems are manufactured at the
company’s state-of-the-art factory while the principal contractor completes the
earthworks and the reservoir floor.

Corestruc first installs the centre portion of the
roof system, comprising precast columns, beams and hollow-core slabs.

It took the company only four working days to build
the centre portion of the roof structures for the two 10-Ml reservoirs in

Once the ring beam has been completed by the main
contractor, Corestruc started dispatching the wall panels to the construction
site on a just-in-time basis.

They were lifted directly from the truck trailers
and placed on top of the ring beam using a mobile crane. The first panel is
supported by props that are removed once it has set and the remaining precast
elements are then placed against the other to complete the reservoir wall.

Corestruc’s installation team uses a Total Station
technology to precisely install each panel, maintaining tolerances of about 5

The walls of the two 10-Ml reservoirs comprise as
many as 60 panels, each weighing 8t, 9,8 m in length and 1,9 m in width, as
well as the four 11,7-ton buttresses that reinforce the structure.

Corestruc is able to manufacture up to 10 reservoir
wall panels of various widths and lengths at a time at its factories using
specialised forms designed and developed by the company’s own engineering

The various concrete elements that make up the entire
wall and roof system are manufactured in a controlled environment, far removed
from the many variables encountered on a conventional construction site.

Every 70 to 80 MPa wall panel has its own technical
drawing and documentation, which includes detailed specifications and a
thorough account of the pre- and post-inspections.

The extensive quality controls in place at the
factory were a major selling point for the civil engineers who promoted the
system to municipal officials for use on the two 10-Ml reservoirs.

The extremely remote locations of the two
construction sites obviated servicing by readymix producers and on-site
batching of concrete for the walls and roof would have required extensive
quality controls and careful coordination of the various materials.

De Jager says that meticulous attention was also
paid to the design and development of the grouting and post-tensioning process
to overcome the many limitations of other precast reservoir wall systems in the

Tian de Jager, technical director of Corestruc,
researched the leading international precast reservoir wall technologies
available. This was refined and modified for the African environment.

Notably, Corestruc uses 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 6,6 km of post-tensioning ducts and cables
were installed by hand between the joints of the wall panels in preparation for
the grouting.

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.

The grout must be extremely flowable so that it can
be pumped through all the post-tensioning ducts from a single position using
two pumps, and its working time is extended by cooling it down to 7°C.

It took 40 hours in a continuous process to pump the
grout around the entire circumference of the two 10-Ml reservoirs.

The grout underwent extensive testing ahead of its
application and Corestruc even brought its own water to site to ensure that the
medium achieved the desired reaction.

While the cost of the system is comparable to in-situ
techniques on smaller structures, it provides a more affordable means of
constructing larger reservoirs.

De Jager says: “The need to innovate to improve
infrastructure delivery is also reiterated in the latest Municipal
Infrastructure Grant guidelines. Municipalities, especially those in the B and
C categories, need to consider innovation in the full spectrum of
infrastructure technologies and associated operations and maintenance
solutions. Corestruc is contractually responsible for the performance of all of
its systems, allaying any concerns regarding the deployment of new technology
on municipal projects.”

He adds that public-sector client bodies are also
increasingly realising that precast concrete technologies complement their
labour-based construction policies.

Precast factories provide many long-term and secure
jobs, as opposed to only temporary employment prospects during the construction

Notably, the main contractors also met all of the
municipality’s stringent socio-economic targets during the construction of the
two 10 Ml reservoirs.

This focus included ensuring that ample opportunity
for employment, as well as skills development and training was created for
members of local surrounding communities.

Piping and construction materials were also procured
from local small black-owned businesses in the vicinity. 

Both sites were completely free of safety incidents despite
teams working at heights.

More information at

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