SA Affordable Housing March - April 2020 // ISSUE: 81 | Page 21

despite it being more labour intensive and therefore time
consuming than HCS and CoreSlab continues to supply this
system to this market.
Unlike HCS, these suspended slab technologies are installed
by the contractor which also invests in the propping and raw
material, such as the concrete, required for their installation.
Generally, the floor system comprises rectangular-shaped
reinforced or pre-stressed precast-concrete ribs supporting
rebated filler blocks. In-situ concrete is then poured between
and over the blocks to form a single monolithic slab.
Slab depths vary between 170mm and 380mm with clear
span up to 10m. Beams with a width of between 100mm and
200mm and a minimum depth of 60mm are used with infill
blocks of between 200mm and 250mm in length, 440 to
485mm in width and 100mm to 355mm deep. Ribs are placed
on the masonry walls with a minimum bearing of 100mm at
approximate centres.
Their position is finally adjusted according to the width of
the filler block with a 35mm minimum bearing of block on rib.
Closed end filler blocks are then placed at the end of each
line and beams that do not exceed 1 800mm centres are
temporarily propped to a suitable level and camber.
Transverse stiffener ribs are also sometimes specified instead
of blocks to accommodate reinforcement and concrete.
Services are installed over the blocks and the specified mesh
placed throughout.
All rubble is removed and the blocks thoroughly wet, and a
minimum grade 25 concrete continuously cast. The temporary
CEMENT TESTING
results
PPC appointed, Beton-Lab, a South African National Accreditation System (SANAS)
accredited independent laboratory in September 2017 to prove intentional thwarting of
standards by cement producers who continuously supply the South African public with
sub-standard cement. The tests were done over a two year period.
It takes
up to
28
DAYS
1. Total
samples tested 2. Cement products
sold in retail:
274 =14
4. Amount of samples
failed = 5. One company
failure rate
= 33% = 73%
for cement to develop the
strength as indicated on
the bag.
3. Retesting
Products
= 31
(23%)
Duration of
test period
± 2 years
(total of all companies)
The data has been collated in a table below, which provides the totals for each cement
producer product tested. The SABS prescribed uncertainty of measurement allowance of
2.5% has been applied when analysing the resultant data allowing for some leniency.
www.saaffordablehousing.co.za
FEATURE
This development has used Corobrik’s Nebraska and Montanna
Travertine variations.
propping is removed once the compressive strength of the
in-situ concrete reaches 17MPa to avoid long-term deflections.
While there is still a strong market for RB, demand for HCS
continues to grow. This trend has gained momentum since
2008 when CoreSlab initially established its operation in
Polokwane to supply the domestic home-building market with
quality precast concrete technologies.
“We mainly started off by servicing the high demand for RB
systems in the area. However, over time, we increasingly
fielded more enquiries concerning our HCS offering. More
than ten years later, HCS have become our main product
offering, complementing our extensive range of other precast
concrete systems for an array of applications,” De Bruin says.
CLAY BRICKS LOOK GOOD IN AFFORDABLE HOUSING
Musa Shangase, Corobrik Commercial Director, says, “We are
able to supply the CoroJem as well as the traditional clay face
brick and non-face brick to the affordable housing space.
“When it comes to building homes, Corobrik understands
that this is more than just a place to sleep and store one’s
belongings. A home is an extension of the resident, a visual
representation of their place in society. This is why so many
developers are turning to Corobrik’s face brick range for the
affordable housing market. Clay bricks are available in a range
of earth tones and types, retaining their colour-fastness
despite intensive weathering. In addition to this aesthetic
appeal, there is no need for future maintenance related to
painting and plastering, which suits the budgetary constraints
of this particular sector.
“Joshco (Johannesburg Social Housing Company) is the City
of Johannesburg’s entity mandated to provide and manage
quality for affordable rental housing for the lower income
market. Committed to building ‘places people love to live’, they
prioritise quality, affordability and overall appeal, which is why
they have incorporated Corobrik’s face brick range for use in
many of the rental developments,” says Shangase.
Clay bricks have considerable advantages in terms of
long-term maintenance for residents, he says. “Fired clay
brick is robust and extremely durable which means it will not
require refurbishment and replacement at a later stage. In
addition, the colourfast properties of clay mitigate any need
for plastering and painting, making face brick one of the
biggest cost-savers for long-term maintenance. The clay from
which Corobrik’s face bricks are made offers a distinctive
range of colours, because the bricks are fired under high
temperatures. This means that they will not fade over time or
deteriorate in severe weather or harsh environments.”
MARCH - APRIL 2020
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