CoreCivils’
unique precast concrete system has enabled the Johannesburg Roads Agency (JRA)
and its professional team to significantly accelerate the construction of a
pedestrian bridge in Kaalfontein, Gauteng.
Crossing
a stream that traverses the community, the 100-m-long and 3,5-m-wide bridge
will help authorities evacuate residents during flood conditions, while also
significantly improving mobility by providing a direct connection between
Flashlight Fish and Trout Fish Streets.
CoreCivils’
system comprises conventionally reinforced precast beams and hollow-core slabs
e supported by two in-situ concrete
piers.
The
company proposed the use of hollow-core slabs rather than rib-and-block slabs
between the precast beams to provide a faster and more accurate means of
constructing the superstructure.
These
modifications were accepted by the design engineer, BMK Consulting Engineers,
which is also overseeing the construction programme on behalf of the JRA.
Jaco
de Bruin, MD of CoreCivils, says that the company installed the beams and
hollow-core slabs in only a day.
“The
hollow-core slabs were manufactured and cut to size at our factory so that they
could be placed directly on top of the precast beams. This eliminated the need
to first install extensive propping before being able to cast the rib-and-block
slabs. Meanwhile, our approach was also better suited to working in an
extremely built-up environment and mitigating the need to coordinate construction
materials to the site via a very narrow gravel road that services the
community,” De Bruin says.
CoreCivils
mobilised to site once Axton Matrix’s team had built the two in-situ concrete
piers and abutments, as well as the approach ramps and their walls.
The
precast elements were dispatched from the company’s factory and lifted directly
from the truck trailers using a mobile crane positioned on the north-facing
side of the bridge.
Working
in very marshy terrain, Axton Matrix had to first construct a secure platform
for the crane. It comprised 700-mm-thick G5 material sufficiently compacted to
provide the stability needed to lift and place the heavy precast elements.
These included the 14 precast beams, two per span and each 15 m long and weighing
four tons.
Axton
Matrix was able to commence working on the remaining portion of the
superstructure immediately after CoreSlab had installed the hollow-core slabs.
The
hollow-core slabs are first covered with polystyrene moulds with voids to
reduce the load of the 150-mm-thick final concrete slab on the precast beams.
Services are then installed on top and covered with a steel mesh to reinforce
the final slab.
The
in-situ works, including the sides of the structure, are extremely labour
intensive and about 17 members of the community had the opportunity to work
alongside Axton Matrix’s team on this project.
Meanwhile,
an additional 20 people will be employed to work on the extended work scope,
which includes constructing 70 m of asphalt roads and sidewalks and installing
storm-water drainage, curbing and wing walls.
The
project is, another example of the complementary role precast concrete can play
in traditional labour-based Expanded Public Works Programme projects.
Notably,
there have also been no safety or injury-related incidents on this project,
despite working at heights and in close proximity to many dwellings.
Valued
at more than R13-million, the project is one of numerous pedestrian bridges
that are currently being built by the JRA in the
larger Midrand area as part of the City of Johannesburg’s R103,4-million investment into low-income communities.
CoreCivils
is also working with Axton Matrix on the construction of another similar
pedestrian bridge in Diepsloot, Gauteng.
More
information from www.corecivil.co.za
