The Civil Engineering Contractor May 2019 | Page 24

ON SITE: PROJECT 2
Precast concrete slabs were manufactured by CoreSlab.
de Bruin, MD of CoreSlab, explains
that the company manufactured
I-type beams for the project, with
installation done by Corestruc once
the bearings were installed. Corestruc
is the installation arm of CoreSlab.
“We supplied 210 precast-concrete
beams for the bridge, and each span
comprises 21 beams.”
Delivery of the 210 beams was a
logistical challenge, considering space
constraints on site. Katzke explains
that they were, therefore, supplied
on a just-in-time basis rather than
being offloaded all at one go, as the
bearings on which they rest were
consecutively completed. “They were
consequently stored at CoreSlab’s
factory and installed as the bearings
were completed.
“The beams consequently are
conventionally transported straight
from factory to site and lifted directly
from the truck trailers using a mobile
crane from CoreHire. There are five
beams per load, each beam weighing
2.8t, enabling us to complete two
spans a day. Once all the beams
are laid, we will pour concrete on
the central slab, which will facilitate
access to the bridge at that level,
22 | CEC May 2019
enabling us to easily construct the
barrier wall side section, drainage
pipes, and service ducts. The side
section can be done with the precast
acting as shuttering. This is more
efficient and will ensure the accuracy
required for this component of the
work,” says Katzke. He notes that
the project demands the same high
standards as South Africa. SABS
standards are applied throughout and
the FIDIC Red Book form of contract
is being used on this project. “We are
close to South Africa in this regard.”
The bridge site has its own
batching plant, with aggregate for the
concrete sourced from a crusher in
Selebi Phikwe, which recycles mine
waste rock on site. This was more
economic, as only tertiary crushing
and screening was necessary, while
also mitigating the need to open
borrow pits. “Aggregate and sand
were stockpiled here for batching on
the Botswana side, as a contingency
for flooding. The concrete batching
plant has a capacity of between
200m 3 and 300m 3 a day for a 15MPa
blinding material and 35MPa material
for structural requirements. An
independent laboratory was operated
The old bridge alongside the new one being built.
by the client to test the concrete.
On every pour, we do a slump
test, something which was possible
considering the smaller pours.”
Truck-mounted booms assist with
pouring at that level, enabling one
section to be completed each day in
continuous pour.
The relief culverts were to be
done in situ, but the design opted
for prefabricated units from Rocla on
both sides.
Project challenges
Like any project, Platjan Bridge came
with its challenges, says Katzke. The
Limpopo’s watershed area extends
as far as Johannesburg, which saw a
huge amount of rain flooding into the
Crocodile River and hence into the
Limpopo. “We struggled at the start
due to flooding during wet season
— February 2018 saw a massive
flood on the river. We had to use
large pumps to remove water and
isolate the pier bases at that time.
Thereafter, we built a coffer dam
that also served as a platform for the
mobile crane, as the existing bridge
was too small for the machine with its
outriggers fully extended. Once the
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