The Civil Engineering Contractor June 2019 | Page 24

ON SITE
The precision achieved by AJ King.
support the ribs of the canopy. Each
individual rib was laser cut and no two
are the same. The shutter ply was then
placed and fastened to the support
structure. At all times strict health
and safety was maintained. A blinding
layer of shotcrete was then put down
so as not to use ‘spacers’ that would
have negatively affected the smooth
finish required by the architect.
Shotcreting
“It would not have been possible to
cast the concrete in the conventional
method of closing up the vertical
faces. An alternative approach was
needed and the casting of concrete
by shotcrete with a controlled water
cement ratio was the key to success.
The canopy is asymmetric in terms
of every formed surface and the
development of the formwork had
to be done off a 3D model. Some of
the formed elements, like the curved
stop ends had to be built in place by
AJ King and his team,” says Middel.
The design and fixing of the rebar
was also a challenge and a hands-on
approach was the only way to get
the job done.
“From my personal point of view,
I would say that this project was a
question of complete commitment
from all involved and required clear
vision from the architect in terms
of what had to be achieved. The
progress meetings we had required
22 | CEC June 2019
detailed technical discussions and the
various trades worked much closer
together than normal,” says Middel.
“The steel bending schedule was
very complicated and required many
clarification meetings to ensure it was
designed and installed correctly.”
Shotcrete’s King says, “Every aspect
of the project has been a challenge.
Everything changes everywhere –
there is no duplication anywhere.” In
fact, the Shotcrete application turned
out to be the most simple aspect of
this build.
Shotcrete Africa SCP is a specialist
shotcrete contractor and has been
involved in the construction of
many concrete structures where the
speed of construction and minimal
formwork requirements offered
by the wet-shotcrete method of
placing concrete, have accelerated
their clients’ programme leading to
significant time and cost savings.
“Wet Shotcrete is just a method
of placing concrete,” says MD and
founder, Dustin Strever. “We have
invested heavily in best of breed REED
shotcrete equipment that enables us
to tackle landmark projects such as
this one. With our pumps capable
of 145 bar of pumping pressure at
the piston, there is not much these
pumps can’t push.
“The mix design was critical to
achieve an ideal slump that enabled
us to shoot the 800mm thick columns
through two layers of heavy rebar
with a minimum of rebound and
excellent encapsulation of the rebar.
The addition of Penetron to the mix
will ensure a very durable concrete
structure that lasts,” he says.
Unlike many construction projects,
the job was internal and had no impact
on surrounding roads and communities
other than the need to implement a
traffic go/stop system in the access
roads to the GeoSciences building. The
construction also did not affect the
landscape – all the trees were left in
space with abundant gardens. nn
List of professionals
Client:
GeoSciences
Main contractor: Bhekanani
Engineers: SCIP
Formwork design and shuttering:
Peri
Concrete work: Shotcrete Africa SCP
Concrete supplier: Metier
Architect: Pieter Breytenbach
Steel:
Piovesan
www.civilsonline.co.za