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CONSTRUCTION WORLD
APRIL
2015
CEMENT AND CONCRETE TECHNOLOGY
The MTN Data Centre, Phase II,
which necessitated the addition
of a second floor to MTN’s Data
Centre in Louwlardia Centurion
using Echo prestressed slabs, is an example
of the latter.
Completed in February 2012, Phase I
comprised a ±3 000 m² single-storey struc-
ture which was roofed with Echo prestressed
slabs. Phase II, begun in January 2014,
entails the construction of a second storey
which is being built on the prestressed slab
roof of Phase I. Once again prestressed
hollow-core slabs, in this instance covering
an area ±2 600 m², was used for the roofing.
The main contractor on both phases was
Grinaker-LTA while DSM Consulting Engi-
neers was the engineering consultancy on
the second phase.
Morten Jerg, contracts director of
Grinaker-LTA, says that the benefit of using
precast slabs as opposed to in-situ concrete
is that it speeds up construction times and
causes minimal disruption.
“We have used Echo slabs on many occa-
sions. They enable us to do away with form-
work and propping, not to mention long
curing times, and in some instances, having
to pour concrete in wet weather. We also like
their smooth soffits.”
The prestressed roof slabs used on
both phases were 250 mm deep and
varied between spans of 2,2 m and 11,5 m.
They were designed to carry live loads of
10 kN/m² and dead loads of 2,5 kN/m² and
were mounted on precast inverted T-Beams
measuring 420 mm deep and 630 mm
wide. The design and manufacture of the
beams were outsourced by Echo. Andreas
Rehwinkel of ENCON did the design and
Civilcon handled the manufacturing.
The beams and the slabs were installed
by Echo using 80 and 200 ton cranes. The
former were placed on 6,5 m high reinforced
cast-in-situ concrete columns. Most of the
columns were cast with additional rebar
which protrudes ±1,5 m through the Echo’s
prestressed slab roof. These may be used at
SLABS
and
cell phone technology connect
The 21
st
century has seen South African construction
professionals making increasing use of precast hollow-core
slabs for the construction of multi-storey buildings and for
the extension of existing structures.
>
a later stage as stub columns for supporting
solar panels or other plant on a suspended
steel grid.
After all the slabs had been placed, a
lightweight politerm screed-to-falls, ranging
between 75-400 mm, was installed. It was
covered by a second 40 mm screed to take
a dual layer of water proofing. Once the new
roof was semi-sealed, Grinaker-LTA was able
to remove the screed on the roof of Phase I.
DSM
consulting
engineer,
Mike
Silberman, commented that the new roof
had been designed in close collaboration
with Echo Group engineer, Daniel Petrov,
who he said was extremely helpful in
ensuring the success of the project.
“Due to the amount of services and
penetrations through the new roof, an in-situ
concrete slab had been investigated as an
alternative to the prestressed slab solution.
“However, the amount of propping
required for an in-situ slab and the high
loading on the existing slab precluded
this choice and this is why we opted for
prestressed concrete slabs,” says Silberman.
Echo Group marketing director, Melinda
Esterhuizen, says precast hollow-core
slabs are to the construction industry
what cell phones are to modern commu-
nications – fast, flexible, multi-functional
and cost-effective.
ABOVE:
A workman finishes off one of the column/
beam joints at MNT’s data centre.
BELOW:
Phase II of
MTN’s Centurion data centre takes shape using Echo
prestressed slabs.
ABOVE:
Echo’s prestressed slabs are supported by
concrete columns and precast beams.
BELOW:
Some
of the installed Echo prestressed slabs of Phase II of
the MTN data centre switch roof project.
I