PRECAST VOLUME THREE ISSUE 1 • JUNE 2009
• CRB walls – aiming for zero defects • Gautrain’s precast production facility • True modular construction can house the nation
contents 2
Message from the President
4
C&CI now has a dozen associate members
4
Mechanical paving machine available from Mondo Paving
5
eco-friendly road built with Terraforce hard lawn block
6
Hollow-core slab seminars being held nationally
7
New storm clip from Marley roofing
30
South Africa’s first permeable paving project using the Uni-ecolok system
34 Agrément approval for precast foundation beams
36 Infraset supplies concrete roof tiles for affordable housing project
40 CMA Membership list
PRECAST VOLUME THREE ISSUE 1 • JUNE 2009
8
New admixture counteracts efflorescence in pressed concrete products
8
Hytec expands product range
9
Challenging times for construction sector says C&CI
10 Mapei helps build Soccer City 10 CMA publishes sewer design manual
The underbelly of the Gautrain Project’s Viaduct Bridge-3, which spans 640m and crosses Allandale road just north of the Marlboro-based precast concrete production facility. Thirteen spans comprising between 15 and 18 viaducts per span were used in the bridge’s construction.
Gautrain Project’s Midrand-based precast concrete production facility has made significant gains in the MPa ratings of all the precast concrete elements it manufactures, while having simultaneously achieved considerable cost savings, especially on cement usage. A third gain, that of productivity, came as an unexpected fillip. All this and more was achieved within a context of a 100-year lifespan requirement, one of the world’s highest durability specifications for precast concrete. • CRB retaining walls – aiming for zero defects
• Gautrain’s precast yard - achieving more with less • True modular construction can house the nation
Prestressed hollow-core slabs used to
12 build security walls in Port elizabeth
CMA stages seminars on the design 14 of concrete outfall sewers Gautrain’s precast concrete production 16 facility - achieving more with less Hollow-core concrete slabs used on
20 medium-rise residential buildings 22
True modular construction can house the nation
24 CrB walls – aiming for zero defects 28
SA’s largest prestressed hollow-core concrete panel retaining wall project
PreCAST is the official journal of the Concrete Manufacturers Association (CMA). Block D, Lone Creek, Waterfall Office Park, Bekker road, Midrand. PO Box 168 Halfway House 1685 Tel: +27 11 805 6742, Fax: +27 86 524 9216 e-mail: main.cma@gmail.com website: www.cma.org.za editor: David Beer Tel: +27 11 478 0239, Fax: +27 11 678 0254 e-mail: bigsky@ibi.co.za Advertising: John Cairns Tel: +27 11 805 6742 email: main.cma@gmail.com Design, layout and production: Isikhova Publishing & Communications (Pty) Ltd, PO Box 651793, Benmore, 2010 Tel: +27 11 883 4627 e-mail: communications@isikhova.co.za The views and statements expressed in this publication are not necessarily those of the editor and neither he nor the CMA accept responsibility for them. No person connected with the publication of this journal will be liable for any loss or damage sustained as a result of action following any statements or opinions expressed herein.
2 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009
dams, bridges, roads and airports. Some of the initiatives already touted include retrofitting 75% of all federal buildings with energy saving devices; the installation of energy efficient windows, solar panels; and the building of green school buildings. Despite its third world status, South Africa is one of the countries in which green issues are taken seriously and there are countless initiatives aimed at reducing our collective carbon footprint. For instance, last year the CMA’s masonry division embarked on a programme to promote concrete masonry as a green construction material through conferences, exhibitions and the media. And on a wider front, the CMA is currently undertaking a survey to measure the carbon footprints of its producer members. The time is not far off when all activity, especially that of manufacturing, will be subject to some form of greening legislation. By pro-actively conducting its own carbon footprint survey, the CMA will be able
Message from the President - Green matters and SANS 204 Last year our previous president, Garth Gregory, used this column
to feed its results to bodies such as the SABS and CSIr and participate with them in the formulation of green standards for the manufacture of precast concrete. Further up the construction chain much work has already been undertaken in establishing a green standard for energy consumption in buildings, and last year the SABS published the SANS 204 standard. It was drafted following a directive from the Department of Mineral and energy Affairs and the Department of Housing several years ago. The standard aims to reduce energy consumption in new buildings by a considerable margin and, as SABS chairperson Bahle Sibisi says, it will eventually become mandatory.
to share some of his thinking on sustainability and green issues
Despite the good intent, in its current guise the document has
in the precast concrete industry. I would like to expand on this
some major shortcomings. For instance, it gives no indication as
theme here.
to the type of buildings to which it is it is referring; some of its
The world is a very different place today to what it was 15 months ago when the global growth juggernaut appeared unstoppable.
clauses are confusing and too vague to implement, and others are often at variance with local byelaws.
Had last year’s economic meltdown occurred a year later, the
Moreover, standards which encompass minimum specified
chances are we would have seen John McCain elected as the 44th
r-values for walling have been provided. Unlike Australia’s building
president of the United States. It didn’t and environmentalists took
code which provides the user with a variety of options to satisfy
heart when pro-green Barak Obama was elected instead.
the requirements, SANS 204-2 and SANS 204-3 prescribe that
Apart from his most urgent priority of re-vitalising America’s
all external walls with a density of less than 300 kg/m2, should
economy, the reduction of energy and carbon emissions is very
have r values of between 1.9 and 2.2, depending on the climate
much on the Obama agenda. During his first week in office he made
zone. This is far more stringent than the Australian standard and
clear his commitment to a cleaner, greener environment by allowing
quite unrealistic. The cost of masonry walling would most certainly
states such as California to introduce their own fuel-economy and
increase should the standards be applied in their current form.
emission controls. What, you may well ask, is the relevance of this to green issues in South Africa?
These and other omissions prompted the CMA to join several prominent construction-related associations in submitting a joint
As President Obama’s eco-friendly policies begin to take hold the
objection to the document last year. They include: Agrement South
spin-offs for the global consumer are likely be similar to those of the
Africa; Aluminium Federation of South Africa; Claybrick Association;
NASA space programme which, from the early 1960s, gave a kick-
Construction Industry Development Board. CSIr; Joint Civils
start to the electronic age which we currently take for granted.
Division of SAICe and ICe; Joint Structural Division of SAICe and
Similarly, some of the sustainable technologies which undoubtedly
IStructe; Southern African Institute of Steel Construction; and
will emerge from the US will hold great benefit for mankind. The
Technical Committee for National Building regulations.
Americans will also set their own greening standards, standards
It is gratifying to note that our objections and recommendations
which other countries might be obliged to adopt as greening
are being taken seriously and that SANS 204 is in the process of
benchmarks. As the US is one of our major trading partners we
revision. This standard is too important and the ramifications too
will probably fall into this category.
far reaching for South Africa to get it wrong.
Part of Obama’s $800 billion dollar recovery and reinvestment plan entails the repair and rebuilding of aging infrastructure such as
Silvio Ferraris, CMA President
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4 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009
C&CI now has a dozen associate members engineered Concrete Systems, southern African distribution
which aims to grow the market for concrete by providing information,
agent for international building products supplier, Mapei, has
technical, education, regulatory research and marketing services
become the 12th associate member of the Cement & Concrete
within the built environment in southern Africa.
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Institute (C&CI). Last year, engineered Concrete Systems launched Mapei’s comprehensive range of auxiliary and enhancement construction materials as part of the global group’s drive to participate in the substantial potential of the South African construction industry. Mapei products, which are currently being supplied locally, include admixtures for concrete, products for construction, and cementitious and resin floor coatings. John Sheath, marketing manager of C&CI, says associate membership of the Institute is reserved for companies involved in the manufacture or construction of concrete products or infrastructure, or suppliers of services or goods to the concrete product of concrete construction industry. The two other membership categories are producer members (cement manufacturers), and built environment professional members. Based in Midrand, C&CI is a technical marketing organisation
C&CI premises in Midrand. The Institute now has 12 associate members.
injuries associated with manual handling are eradicated. Skewed lines and varied heights are not on the agenda when using the Toro H 88, because the pavers, which are laid in batches measuring 1 200mm x 800mm, can only be installed in the precise positions in which they are manufactured. Direct cost savings can be as high as 19% although manufacturing costs can offset some of these savings. However, indirect savings such as improved site access, are also to be had. A variety of paving designs can be installed with the Toro H 88 and CBP manufacturer, Concor Technicrete, has the moulds to produce blocks in the following shapes and sizes: Satin Pave 205 x 105 Trojan 200 x 150 and 150 x 150 Bond Brick 100 x 200 Grassframe 400 x 600 Conleaf 200 x 200 The machine can pave any surface simply and quickly. Small,
Mechanical paving machine available from Mondo Paving
powerful and versatile, it paves small corners as effectively as large open spaces. Up to 1 700m² a day can be laid on a well organised site using just one operator and one assistant. The machine features a spacious cabin and an adjustable steering column. It is fully automatic and extremely manoueverable thanks to fifth wheel articulated steering. This reduces side shear on freshly installed paving surfaces. Various attachments offering other functionality are available.
Mondo Paving and retaining Walls, a Concrete Manufacturers
These include a joint filler, a vacuum unit with suction plates for
Association (CMA) member, is importing a mechanical concrete
lifting various concrete elements, a kerb clamp, hydraulically
block paving (CBP) machine, the Toro H 88.
operated sweepers and a mechanical screeding system. Kerbs
ease of installation, improved installation times, less wastage
can be laid at a rate of 70-100 linear metres per hour and the
and reduced overall costs, are some of the advantages which come
mechanical screeding system can produce a prepared bedding layer
the machine. Moreover, health and safety is another benefit, as the
of up to 2 000m² and hour.
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Retaining Wall Blocks (Gauteng based)
Eco-friendly road built with Terraforce hard lawn block January 2008 saw Pieter van rensburg,
pegs per block were used and only one
the manager at the Forest Hall Private
was used on level sections. Finally, the new
Nature reserve near the Crags, Plettenberg
tracks were covered with gravel on steep
Bay, take a decision to upgrade the
sections and top soil on level sections
reserve’s roads. Fire, erosion and alien
to encourage the growth of grass in the
plant control, were the main motivating
blocks. Where streams cross the road,
factors behind the decision. regular floods
the whole width of road was paved with
were washing away the existing roads
Terracrete and rip-rap erosion control was
and access to the reserve had become
installed on the downstream side.”
increasingly precarious.
The only problem encountered during
The 500 acre reserve boasts numerous
construction was that one section of the
trails through an indigenous forest, which
road passed through short stretches of
is home to an abundant array of birds and
soft ground. This entailed re-laying the
smaller mammals, including bushbuck,
blocks on a sub-base foundation. In general
monkeys, bush pigs, and baboons. The
though, repair and maintenance of the road
reserve also boasts its own stretch of
was kept relatively simple. When subjected
private coast-line.
to heavy loads, the occasional block cracks.
Tel: 011 393 5504 www.remacon.co.za In-House structural design service Manufacture, Supply & Design ProducT range ReMRock 220 - For garden landscaping walls less than 1,8m high. Sand colour rock face texture only. ReMblok 30 System - For most structural wall heights at 75° or less. Also available in sand colour and rock face ScoopLoc - Sc30 & Sc50
The roads were to be built without dis-
However, these can be left in place for a
Terraforce (Ethical Licencee)
turbing the indigenous forest and historical
while and still function perfectly until they
feel of the reserve
are replaced with new blocks.
L11 - For most structural wall heights at 90° or less, also available in sand colour and rock face
“We were looking for a green solution
In total eight kilometres of road were
to improve access to the reserve, and
upgr aded o v er nine mon ths and v an
one which would attract more interest
rensburg was very happy with the result.
in the area. This meant finding a product
“The products worked perfectly for
that would blend in with the look and feel
us. The blocks could be laid by hand and
of the old Manor House which was built in
not much of the surrounding forest was
the 1860s.”
disturbed by the construction process.
Af ter seeing an editorial on the
The road has been performing very well,
Terracrete block, a eco-friendly paving and
even coping with an eight ton concrete
hard lawn block designed by Terraforce,
truck and steep sections which were
the Cape Town based licensor of various
previously only accessible to heavy duty
precast concrete products, he decided
4x4 vehicles can now be negotiated with
that this product would work perfectly for
normal passenger cars.”
these circumstances and work commenced in February. Construction proved to be relatively straightforward and cost-effective.
For van rensburg the Terracrete block offered him a solution on all levels. “This block is great for anyone who needs to curb erosion on a road in an
“We use d our o w n t e am o f eigh t
ecologically sensitive area. I would like to
labourers to level the tracks and apply a
see more people use it. It is easy on the
sub-base topped with crusher dust onto
eye and does not make a big impact on the
which the blocks were laid. The blocks were
environment, unlike gravel and concrete
then each pinned with at least one 300
tracks which are often used in similar
mm long, Y12 reinforcement steel peg, to
circumstances. At the time of writing, the
prevent them from shifting.
blocks were almost completely covered
For steeper sections ± three steel
with grass.”
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L18 - For most structural walls, best suited where curves and terraced landscape features are required. Caps also available, rock face only 4X4 - For landscaping steps also used for stadium seating, amphitheaters Terracrete - Eco friendly grass block permeable pavers Terrafix 120 - Channel lining and erosion control
6 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009
The Concrete Manufacturers Association (CMA) is to stage three afternoon seminars on prestressed and reinforced precast concrete hollow-core slabs at different centres around the country during the coming months. Aimed principally at civil engineers, architects and property developers, the seminars will be held in: Durban in June; Bloemfontein in September, and Cape Town in October. They are being used as a forum to launch the CMA’s hollow-core slab information manual and to promote hollow-core slab technology as an alternative flooring material for multi-storey buildings. They will also demonstrate how to design insitu
Hollow-core slab seminars being held nationally
columns and beams in combination with precast hollow-core flooring and still
C air ns obser ves that hollow-cor e
achieve a monolithic, structural sound
slabs were originally developed as South
building, a process which is common to
Africa’s alternative to insitu concrete
many parts of the world.
floor panels for multi-story buildings some
Presenters will include: John Cairns,
25 years ago.
The Meridian, a 488 unit high density townhouse complex in Bedfordview, Gauteng, has demonstrated that pleasing and innovative architectural concepts can be both economical and simple to construct. Hollow-core concrete floor panels, manufactured by Echo Floors, were used to speed up construction. The developers, Baldwin Properties, broke their own records for construction speed with the first half of Phase 2 being completed three months ahead of the original target date.
CM A dir ec tor; Monique eggebeen,
“In many instances the hollow-core
managing director, echo Prestress; Daniel
slab is a preferable alternative to more
Petrov, technical director, echo Prestress;
conventional building methods. Besides
Victor Booth, consulting engineer; and
the obvious advantage of simpler, faster
“running to 36 pages, the CMA’s manual
Kgomotso Modise, operations manager,
construction, not to mention a more
addresses typical concerns about the
echo Prestress.
durable end product, the secret of applying
use of hollow-core slabs in medium-rise
The identical seminar was successfully
the material successfully is in the pre-
buildings and demonstrates the flexibility
presented to over 120 delegates at the
planning. Get one of our member companies
of hollow-core slabs as a flooring material.
By tes Conference Centre in Midrand,
involved at the conceptual stage and their
It covers aspects such as recommended
on March 31st. Topics covered were:
advice and input comes at no charge.
design loads f or common classes o f
history and design philosophy; general
“T he system was recently used in
buildings and includes various load span
design; composite floors; case studies;
the construction of two medium-rise
tables and prestressed concrete design
health and safety aspects; and alternative
apartment block developments in Gauteng.
details. Other items such as structural
applications such as, foundation systems,
Hollow-core slabs are widely used in europe
topping, and down-lighting are included.
security and retaining walls, attenuation
and North America on buildings as high as
tanks and reservoir roofs.
40 storeys.
The presenters of the CMA’s hollow-core slab seminars seen here during the first seminar at the Bytes Centre in Midrand. They are from left: John Cairns, CMA director; Kgomotso Modise, operations manager of Echo Prestress; Victor Booth, consulting engineer; Monique Eggebeen, managing director of Echo Prestress; and Daniel Petrov, technical director of Echo Prestress.
“Some o f the alter na ti v e uses o f hollow-cor e panels such as securit y
“Ignorance as to its true potential and
walling, warehouse walling, retaining walls,
the fear of using something unfamiliar has
suspended ground floor slabs, as well as
led to a reluctance to specify precast
walls and roofing for reservoirs, are also
slab technology locally, whereas insitu
covered,” observes Cairns.
construction is perceived by some engineers
The manual includes brief company
as more effective, mainly because labour is
profiles on those CMA member companies
considered cheap. However, no contractor
which produce hollow-core slabs. These
currently places a value on the lack of
are; echo Floors; echo Prestress; echo
productivity and re-work required due to
Prestress Durban; Fastfloor Botswana;
a lack of skills. Likewise, no value is placed
Shukuma Flooring Systems; Stabilan;
on using time-saving products such as
and Topfloor.
precast panels. Some of the advantages of precast flooring include speed, quality
The seminars have been registered with SAICe for CPD points.
of manufacture to the SANS 1879:2001
Anyone interested in attending the semi-
standard, a solution to the skills shortage
nars should contact Pam Zukor on (011) 805
and cost-effectiveness.
6742 or on main.cma@gmail.com.
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New storm clip from Marley Roofing Marley roofing has developed a new range of integrated storm clips, SoloFix, which, Marley claims, is far superior in function, durability and ease of installation to other roof fixing methods. The new range consists of four storm clips especially designed to fit the seven Marley roof tile profiles produced in South Africa as well as some imported Portuguese clay tiles. Solo-Fix storm clips secure roof tiles against wind uplif tment, even under extreme conditions. However, the right storm clip must be used on the right tile profile. Listed below is a guide for Solo-Fix applications. SOLO-FIX STOrM CLIPS PrODUCT CODe
FOr USe WITH
65/48S
• Ludlow • Modern
75/48S
• Double Roman • Mendip • Homestead
75/48r
• Double Roman Plus
85/48S
• Monarch • Portuguese Clay Tiles
Please use the product code above when ordering. The clips are packed in boxes, 500 per box. The boxes are clearly labelled as to which tile profile the clips are suited and each box carries detailed application instructions. Solo-Fix storm clips are manufactured from ZIAL®, a high quality material which is six times more corrosion resistant than galvanised steel, making them ideally suitable to coastal conditions. They are precision formed on high tech production machines, combining clips and nails in a single piece. The clips are rigorously tested strictly in accordance with DIN eN 14437 european standards. FIXING 1. Lay tiles in the normal manner, ensuring that vertical and horizontal alignment is maintained across the roof. 2. Locate the flattened hook of the clip onto the outer rib of the tile side-interlock. 3. ensure that the sharp point of the clip is located centrally in the back of the batten. 4. Hammer the serrated spike of the clip into the batten until the vertical section of the clip is located firmly against the tile beneath the min 20mm level.
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Y
CM
MY
CY CMY
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8 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009
New admixture counteracts efflorescence in pressed concrete products Chryso South Africa has launched a new silicone water repellant
basement walls, damp-coursing, any load-bearing blocks, as well
that virtually eliminates unsightly efflorescence in concrete
as pavers around swimming pools and other wet areas.
blocks, bricks and pavers.
“Tests have shown that Pareflo 15 reduces water absorption
The admixture, Chryso Pareflo 15, instills new pre-sealing
and efflorescence by over 80%. The degree of water resistance
technology to the manufacture of pressed concrete by boosting
can be varied simply by changing the dosage, and the admixture
the concrete’s resistance to water.
emits no hazardous material during its application. The product
“efflorescence appears because of the permeability of concrete blocks, bricks and pavers,” says Victor Boardman, Chryso SA’s
can easily be incorporated into any existing pressed concrete manufacturing procedure,” he adds.
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Technical Services Manager. “Based on the relatively new concept of pre-sealing concrete using silicone nano-technology, Pareflo 15 was developed in Australia and has been tested extensively by reputable bodies such as the Commonwealth Scientific and research Organisation (CSIrO), and the Australian Building Systems Appraisal Council (ABSAC).” Whereas traditional water repellant admixtures form insoluble fatty acid calcium salt deposits in the concrete matrix, the new silicone version forms poly-siloxane cross-linked network structures, chemically bonded to the concrete matrix. Traditional water-repelling admixtures contain fatty acid salt, physically which are deposited in the concrete and not chemically bonded as with Pareflo 15. The permanent chemical bonding now possible means that the admixture cannot be washed away by capillary water penetration. Fatty acid calcium salt deposits may also produce an oily surface, and are biodegradable. Pareflo 15, on the other hand, is both alkali- and biologically-stable, offering long-term durability, and not changing the appearance of the pressed concrete surfaces. Boardman says Pareflo 15 is suitable for pre-sealing coloured decorative walls and pavers, single leaf block walls, retaining and
Chryso’s new Pareflo 15 helps to eliminate efflorescence in pressed concrete products such as paving.
Hytec expands product range Hytec has announced the addition of the rexroth A4VTG Series
with the design including direct operated pressure relief valves for
33 of variable displacement pump to its product range. The
special resistance against contamination and internal gear pump
series features a closed circuit and swashplate design for easy
with geared contact area.
installation. The pumps have been specifically designed for use with drum drives on mobile concrete mixers. The A4VTG series features a high pressure level – rated pressure of 400
The line ports of the Series 33 pumps are the same as the Series 32, allowing for the models to be easly interchanged. The range of pumps is available in sizes 71 and 90, with coupling flanges provided on request for trouble-free
bar and maximum pressure of 450 bar – for a high
attachment of prop shafts. The pumps also feature a
power ratio, as well as stable electro proportional
stable SAe C 4-hole mounting flange for safe
control with mechanical manual override and robust
operation, and a port plate for high efficiencies
hydraulic mechanical servo control.
and service life.
The high pressure ports are unidirectional for an easy and cost-effective line arrangement,
Hytec is the sole sub-Saharan distributor of Bosch rexroth products.
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while the suction port is easy to assemble. The variable displacement pumps have been developed according to the highest quality standards
The Rexroth A4VTG Series 33, available from Hytec, has been specifically designed for use with drum drives on mobile concrete mixers.
PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009 9
Challenging times for construction sector says C&CI Tougher times lie ahead for the construction sector, although an improved inflation and interest rate outlook could bring some relief in the longer term, the Cement & Concrete Institute (C&CI), says in its Annual review for 2008. John Sheath, marketing manager of C&CI and author of the review, says affordability must improve and confidence levels be restored for the
John Sheath.
building industry to enjoy more prosperity. “If, as expected by a large number of economists, interest rates are lowered to around 12% during the course of 2009, then investor confidence will be boosted and economic growth stimulated. The expected positive impact on the building industry will, however, only be felt in 2010. “Only once interest rates have been lowered substantially, will the investment growth outlook for the residential market improve. The drop in house prices is expected to impact negatively on new residential developments and it can therefore be expected that construction activity in the residential sector will remain depressed for the next 12 to 18 months,” Sheath states. He says investment growth in non-residential construction looks slightly more positive as plans approved for this sector increased by 11% in 2008. “The actual building of these projects will, however, depend on an improved economic outlook and business confidence.” C&CI regards the outlook for the civil engineering industry as more promising. “Double-digit growth rates were experienced during the past few years, but may be replaced by more modest single-digit growth, provided local and provincial governments are able to implement budgetary allocations. The role of State-owned enterprises is very important and this is expected to continue in the near term,” Sheath adds. regarding cement demand last year, the review says the 14,7 million tons of cementitious products sold was 3,9% below that of 2007. This tonnage includes 1,4m tons of fly ash and slagment purchased for enhancing and extending concrete mixes. “It should also be noted that although 2008 sales showed a decline over the previous year, this follows a period of seven years of positive growth in the industry and – on more than occasion – at doubledigit levels,” he points out. Cement sales to the nine provinces in South Africa were down 4,6% with major reductions in demand in Gauteng (-11%) and Western Cape (-7,9%). Sales to neighbouring countries were 4,6% up on 2007 with growth in demand coming from only Botswana (+21%). Imports of both cement and clinker dropped last year in line with the drop in demand and introduction of new production capacity by local cement producers.
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10 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009
Mapei helps build Soccer City extensive use is being made of Mapei’s
adhesive used for structural bonding.
range of specialised concrete sealant,
Adesilex provides exceptional mechanical
adhesive and repair materials at
str eng th and adhesi v e capaci t y and
Soccer City, the stadium south west of
hardens into a shrink-free compound within
Johannesburg earmarked to host the
a few hours.
opening and final games of next year’s World Cup soccer competition.
Areas where corrosion and spalling occurred were scoured out and cleaned
Soccer City, Johannesburg, the World Cup stadium in which extensive use has been made of Mapei’s range of specialised concrete sealant, adhesive and repair materials. The insert shows a worker applying Mapei’s Planitop 100 skimming mortar to a repaired concrete surface and a steel bracket.
Mapei mor tar s ar e being supplied
with high-pressure water. If any reinforcing
by Sou th A f r ican Mapei distr ibu tor,
steel was exposed as a result of this
engineered Concrete Systems (eCS), to
process, it was treated with Mapefer 1K,
contractor Karrena Africa for repairing
an anti-corrosive cementitious mortar
sections of the old structure and for
which is applied with a brush. Thereafter
the enhancement, strengthening and
Mapegrout rapido, a very fast setting
Paul Niemandt, a site agent with
aesthetic finishing on some of the new
fibre reinforced shrinkage-compensated
Karrena Africa, says he is very impressed
portions of the stadium.
repair mortar was applied in layers ranging
with Mapei’s product range.
The Soccer City project involves a
from 25mm to 30mm. Mapegrout rapido
“The products offer exceptional quality
major upgrade of the old FNB Stadium and
sets within 15 minutes and reaches 10
and our workers like using them because
has entailed partial demolishing as well
MPa in three hours. After 24 hours it
they are easy to apply. Moreover, they
as fresh construction work, the latter
achieves a strength rating of 20 MPa, and
incur v er y low wast age, and all the
extending the stadium’s upper tier and
40-45 MPa is reached within 28 days.
packaging comes with instructions. Mapei
increasing seating capacity to 94 700.
eCS product manager, Pieter Aucamp,
also provides us with excellent back-up service,” notes Niemandt.
Karrena Africa has been responsible
observes that blow holes were dealt with
for a considerable portion of the repair
using a skimming mortar, Planitop 100,
T he f ollowing Mapei pr oducts and
and enhancement work, employing three
which is applied in layers up to 3mm thick.
quantities had been used at Soccer City
foremen and 65 workers on site. Much
This light-grey fast-setting fine mortar is
by the end of December 2008.
of the work has taken place in and around
applied with a trowel and smoothed off
• Mapegrout Rapido 12 500kg
the suites of the old stadium which, over
with a sponge.
• Planitop 100 20 000kg
the years, were subjected to weather and
Some of the vertical and horizontal
• Mapegrout Colabile 1 250kg
joints were sealed with Mapeflex PU
• Mapeflex PU 45 1 000 (600ml) sausages
Areas which required strengthening
45. Supplied in 600 ml sausages, it has
• Adesilex PG1 600kg
were repaired with steel brackets and
an expansion rate of around 10% and a
• Mapeband TPE 750 meters
Mapei’s Adesilex PG1, a thixotropic epoxy
Shore-A hardness of 40.
• Adesilex PG4 150kg.
water erosion.
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CMA publishes sewer design manual The Concrete Pipe, Infrastructural Products and
strengths and pipe loading, and field testing.
engineering Solutions (P.I.P.e.S.) Division of the
There is also a chapter on existing sewers and
Concrete Manufacturers Association (CMA),
how best to assess them.
has published the first edition of a design manual for concrete pipe outfall sewers.
“A ll the salient f ea tur es r equir ed f or selecting, specifying and testing concrete pipes
Aimed at specifiers, consulting engineers
are included. related topics such as sewer size
and contractors, the purpose of the manual
and jointing are also addressed and the chapter
is to provide the designer with the basic
sequence follows the typical design procedure
guidelines and tools needed for the cost-
used on a sewer project,” notes Cairns.
effective design of concrete sewers including
Much of the material included in the manual
the selection of the most appropriate
is scientifically researched, including a predic-
pipe materials.
tive theory, known as the Life Factor Model
CMA director, John Cairns, says although
(LFM), which was developed in the United
the containment of sewer corr osion and
States. The manual is available at no charge
corrosion assessment is its main focus, the
from the CMA. Call Pam on 011 805 6742 or
manual also covers hydraulic design, material
email her on main.cma@gmail.com.
P
Tel: 0861 33 5599
SUPPLIERS OF BEVEL AND INTERLOCK PAVING, STOCK AND SEMI-FACE BRICKS
Conframat was established in 1999 with its first brick plant becoming operational in May 2004. Conframat currently operates 3 plants in Vanderbijlpark Gauteng. Our main products include 55mm and 60mm bevel pavers, as well as 60mm and 80mm interlock pavers (pavelock). The standard colours are grey, charcoal, red, brown, tan and autumn multi-colour.
W W W . C O N F R A M A T. C O . Z A
We produce a high quality cement semi-face building brick (10.5 and 14 MPa) in various colours as well as 7 to
21 MPa non-ash stock bricks. Total capacity is currently more than 200 000 bricks per day and we maintain more than two million stock on our standard paving brick range to ensure stock availability. Conframat is renowned for their high quality and is accredited to supply bricks under the SABS mark warranty. Our transport fleet and production scheduling systems ensure that we deliver preordered loads on time every time. TM 5196
12 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009
Prestressed hollow-core slabs used to build security walls in Port Elizabeth
(Above): This security wall at Greenbushes Business Estate in Port Elizabeth is 2.75km long and 2.4m high. It was built with Shukuma Flooring Systems’ precast slabs and column blocks. (Left): The security wall at the Dora Nginza Hospital in Port Elizabeth which was built with precast hollow-core panels supplied by Shukuma Flooring Systems.
CMA member, Shukuma Flooring Systems, has supplied prestressed hollow-core slabs for the construction of two large security walls in Port elizabeth.
security wall.
The first wall is three metres high and
The second wall was erected around the
1.5km long, and was built around the Dora
Greenbushes Business estate which was
Nginza Hospital.
developed by Sweet equity. In this instance
It was designed by Ninham Shand/Hix
T he slabs were laid horizontally in
the wall was 2.75km long and 2,4m high. A
Architects and built by SBT Construction
stacks of three and were installed between
total of 916 panels measuring 6m x 1.2m x
for the Department of Public Works. A
in-situ cast reinforced columns, erected
120mm were used and supporting columns
total of 756 prestressed slabs were used
by SBT Construction. Only the bottom
were constructed using Shukuma column
on the project, each slab measuring 6m
half of the lowest panel in each section
blocks on reinforced foundations laid by
x 1.2m x 120mm and cast to a strength
is situated below ground level, a factor
SBT Construction.
rating of 50MPa.
which facilitated the creation of a high
C M A d i r e c t o r, J o h n C a i r n s s a y s increasing use is being made of prestressed hollow-core paneling for security walling. “There are several advantages to this type of walling, speed of erection being one of the major considerations, and a superior strength-to-weight ratio being another. “The current cost of building a precast security wall, say 3,0m high, is approximately half that of a wall offering the same properties using in-situ casting. Furthermore, it would take two to three times as long to build such a wall using in-situ casting, with no advantage in strength or durability. “In fact walls built with prestressed hollow-core slabs are exceptionally strong, far more so than walls of the same dimensions built with conventional masonry. The latter can be broken with a heavy-duty hammer and chisel, unlike prestressed
CMA MANAGEMENT CoMMITTEE The CMA’s 2009 management committee, which includes two new faces, Devi Lategan (standing right), vice president of the Masonry Division, and Chris Morgan (seated left), vice president of the Roof Tile Division. The remaining members are: Bryan Perrie (standing left), cement industry representative; John Simpson, treasurer; Taco Voogt, vice president, Paving Division; Monique Eggebeen, vice president floor slab division; Silvio Ferraris, CMA President and vice president of the Retaining Block Division; and John Cairns, CMA director. Pat Pretorius, vice president of the P.I.P.E.S Division, was not available for this photograph.
slab walls which require much greater, not to mention, noisy destructive force to break them. “A nother ad vantage is that being factory manufactured, precast concrete slabs are produced to a quality that is consistently high,” concludes Cairns.
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14 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009
CMA stages seminars on the design of concrete outfall sewers May saw the CMA hold four one-day seminars on the design of concrete outfall sewers at venues in Midrand, Port Elizabeth, KwaZulu-Natal and the Western Cape. The seminars were presented by well-known pipe expert, Alaster Goyns. A Pr eng with a Bsc Civil eng and an MBL. Goyns spent 21 years in the concrete pipe industry bef or e star ting his own consultancy some 10 years ago, specialising in gravity pipelines and trenchless rehabilitation. Goyns has written several papers on sewer corrosion and trenchless rehabilitation, having presented them both locally and internationally. Since 1999 he has managed the Virginia Sewer corrosion project on behalf of the concrete pipe industry. He was a founder member of the sewer study group initiated
A concrete pipe section which forms part of the Moreletaspruit outfall sewer expansion programme in Tshwane. The picture shows the long radius bends which have been used to reduce frictional losses and minimise hydraulic problems.
in 1987 that motivated the inclusion of
phases ha v e been moni tor ed by the
the results have been used in a design
this live experimental section during the
concrete pipe industry in conjunction with
manual for the prediction and control of
construction of this sewer.
the University of Cape Town.
corrosion in sewers. Copies of the manual
The implementation of this project and
A series of pipe materials were evaluated
were provided at the seminar. Some of
its monitoring over the first five years
over a 14 year period under extremely
the original samples are still in the sewer
was undertaken by the CSIr. Subsequent
aggressive conditions at Virginia and
and these, together with some recently installed cementitious samples, are being monitored on a regular basis. At the time of writing the first seminar had been held at the Bytes Conference Centre in Midrand and was attended by 75 delegates. The seminar generated considerable interest, so much so that a series of f ollow-up workshops has been proposed. As the workshops will entail working through examples they will be restricted to between 10 and 15 attendees each. A nominal charge of r600.00 will be levied to cover costs. Interested parties should contact Pam at the CMA on main.cma@gmail.com or on (011) 805-6742.
P
Alaster Goyns, independent consultant, seen here during his Midrand presentation on the design of outfall sewers.
16 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009
Gautrain’s precast concrete production facility achieving more with less A quality improvement in the production of any precast concrete product generally involves an increase in costs. So when better quality, which in this instance means strength, durability and impermeability, is achieved with a decrease in costs, the method by which this win/win situation is achieved bears close scrutiny. The Gautrain Project’s Midrand-based precast concrete production facility has made significant gains in the MPa ratings of all the precast concrete elements it manufactures, while having simultaneously achie v ed consider able cost sa v ings, especially on cement usage. Moreover, a third gain, that of productivity, came as an unexpected fillip. All this and more was achieved within a context of a 100year lifespan requirement, one of the world’s highest durability specifications for precast concrete. In this exclusive inter view with
Cyril Attwell is the concrete and
Precast’s David Beer, Cyril Attwell, chief
research manager of Murray & roberts
concrete technologist of Bombela, the
Construction.
company appointed for the design and construction of Gautrain, explains how the seemingly impossible was achieved. During the interview Attwell observed that there are fewer than 500 qualified
He studied analytical chemistry (Above): The underside of M-Beam Bridge-1 with the M-beams used in its construction clearly visible. (Below): The 175m M-Beam Bridge-1, which crosses the Jukskei river near Linbro Business Park.
at the Technikon Witwatersrand until 1995, a period during which he also worked at Fosroc, firstly as a quality control technician and then as a research and concrete technician. He joined Samson Construction P r o duc t s in 1996, ini tiall y as a research technician and later as a technical manager/consultant. While with SCP he consulted on several projects in Asia, (Philippines, Malaysia, Indonesia and Taiwan) and worked on numer ous pr ojec ts in A f r ica, designing concrete and consulting on construction practice. He passed his advanced concrete technology exams in 2005 and joined Murray & roberts Construction in 2006 as the chief concrete technologist on the Gautrain project.
18 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009
concrete technologists throughout the world and that a large proportion of them are South Africans. This led to another pleasantly surprising revelation, namely, that South African concrete technology is world class. The Midrand precast yard is producing viaduct segments weighing up to 58 tons each, M-beams of up to 40 tons apiece and several other precast elements. Approximately 100kg cement per cube has been saved on all of them since the first
A close-up of M-Beam-1 in which the precast sound protection barriers mounted on top of the viaducts are shown.
400 elements came off the production line. This saving is based on the simple fact that
the nett result being that we are achieving
when production began in April 2007, in
in excess of what we would have done had
excess of 400kg of cement in combination
we been using rapid hardening cement,”
with 100kg of fly ash per cube was used
observes Attwell.
to achieve the high early strengths.
ArC technology is based on the manner
T her eaf ter, mor e accurate str ength
in which cement, water, aggregates and
testing procedures and better mixes,
extenders such as fly ash react chemically.
meant that cement usage was reduced
The mineralogy of the aggregate in this
every single precast concrete element is
to 300kg with a minor 20kg increment in
process is critical.
key to this process.
fly ash usage, representing a significant overall saving.
A close-up of the underside of Viaduct Bridge-3.
Unlike past practice when aggregates
“When we began production we made a
were considered as a bulk material only,
corresponding set of test cubes measuring
Getting better usage out of a given
ArC uses them as a chemical component as
100mm x 100mm x 100mm for every
quantity of cement has been the key driver
well, and in so doing enhances the strength
concrete element produced. This gave us full
at the Midrand precast yard.
of the concrete substantially.
traceability. Cube tests were initially used
“We’ve achieved this by applying ArC
“We are using dolomitic crusher sand
for gauging early strength ratings so that
(advanced recrystallisation), a locally
in combination with the granite excavated
de-moulding could take place at the earliest
developed technology. The process first
from the Gautrain tunnel. Owing to the fact
possible moment. However, given that the
saw light of day at the Grootvlei Prison in
that less cement is being used (somewhere
actual segments were considerably larger
Bloemfontein where we achieved 12 MPa
between 65% and 75% of a normal precast
than the test cubes and, because of this,
in 12 hours at an average temperature of
yard) our carbon footprint has been lowered
had higher heat and strength ratings, we
-8ºC. By using ArC technology at Marlboro
accordingly. Moreover, the water used to
found it difficult to make accurate strength
we are averaging strengths of 74MPa
wash the trucks on site has a high dissolved
rating correlations between the two during
using a water/cement ratio of 0.45 with a
calcium content. It is collected in sumps
the first five days of curing.
fly ash replacement of 30%. We are also
and is re-used in the production of our
“It was for this reason that we decided
using a 42.5 Cem1 cement which is quite
concrete. It gives us an additional four
to opt for a maturity test for our early
unusual. Precast yards generally use a
to five MPa and provides further savings
age strength requirements and to use
rapid hardening, 52.5 Cem1, cement at a
per cube, simply because the high calcium
cube testing for the 28-day strength
rate of 400kg per cube to achieve a 74MPa
content water is being re-used.”
assessment only, which is when this test
While the saving of cement and lowering
gives a more realistic reading. The maturity
“The 42.5 Cem 1 is not as refined as the
of the carbon footprint could be regarded
test is based on measuring the heat
rapid-hardening cement. It also presents
as ‘nice-to-haves’ maintaining rigorous
generated within each precast element
a lower surface area and lower reactivity.
standards and best practice quality control
and gives us a far more accurate strength
South African fly ash has a very high
are considered essential to the overall
reading at any given time.
reactivity of 0.8 as opposed to european
success of the project. Measuring and
“We have produced over 3 000 precast
fly ashes which are generally rated at 0.4.,
maintaining consistent MPa ratings for
elements since we introduced the maturity
rating,” says Attwell.
test system and have not experienced
We have produced over 3 000 precast elements since we introduced the maturity test system and have not experienced a single breakage since then.
a single breakage since then. To put this into perspective, two breakages out of every 400 precast concrete elements is considered to be good by world standards, whereas maintaining a clean slate in the production of 3 000 elements, as we have
PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009 19
done, is quite exceptional.
maturity formulas available world-wide, we
bottleneck caused by this testing has
“Unlike cube tests which take place
did some research as to which one best
been eliminated. In fact we have actually
un der i de al t emp er a tur e c on di ti ons
matched the maturity (temperature/time)
reduced cube usage by some 60%. Many
of about 22ºC, the maturity test, is
functions of our concrete. We opted for
precast yards still use cubes and I believe
conducted in conditions of far greater
the Nurse-Saul function which accurately
this is the first time that maturity testing
thermal variance. For instance, we have
measures strength during the 5 hour to
has been used on such a large scale.”
experienced temperatures of -8ºC, and it is
24 day period. The reason for inserting
Permeability testing on all precast ele-
in extreme conditions such as these when
se v er al as opp o se d t o one ther mo -
ments is another quality requirement at
we need to know what is happening inside
couple into each element is because the
Marlboro. The 100-year durability speci-
each element. There is no point in testing
temperatures in a viaduct core are much
fication requires high levels of imperme-
a cube which is kept in relatively ideal
warmer than those in its wing areas.
ability in the concrete. Low permeability
conditions and then hoping that this will
So before the deviation gets too high
is achieved through high strength ratings
be representative of early-age strength.
we apply insulation formwork comprising
and good curing practice.
Maturity testing tells us with far more
polyurethane foam to the wing areas. It
Concrete erosion occurs when car-
accuracy when we can strip, move or de-
is simply sprayed onto the exterior of the
bon monoxide and water combine inside
tension and this alone has enabled us to
formwork and this gives us a five to six
a concrete structure to form carbonic
accelerate our M-beam production from
MPa boost within the first 24 hours.
acid. This lowers the Ph level of the con-
the original three-to-four day cycle to a
“T he increased production rate
crete and when it falls below nine, the
achieved through the maturity test has
passivation around the steel reinforcing
The maturity test involves inserting
more than offset the cost of the thermal
is eliminated. By increasing the imperme-
several thermo-couples into each pre-
couples. One of the reasons for this is
ability of the concrete the rate of carbon
cast element.
the fact that we no longer need cubes
monoxide diffusion through the concrete
for early age testing, and the production
is lowered.
36 hour cycle.”
“As there are in excess of 46 reliable
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20 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009
Hollow-core concrete slabs used on mediumrise residential buildings Hollow-core concrete slabs are finding increasing favour as a means of fasttracking the construction of medium-rise buildings in South Africa. Unlike in Europe and North America where it is the default system for such structures, the technology has been a slow-starter in SA, owing mainly to the conservative approach adopted by the local engineering fraternity. However, the time delays and rising costs attendant on insitu casting make precast flooring a more attractive proposition with each passing day.
weeks for each level. “Had we gone the cast in-situ route it would have taken about four weeks to complete each level,” he said. Quality consistency was another consideration. It is much easier to control the quality of slabs which are produced in a factory environment, than it is to achieve consistent quality levels using in-situ casting. Capital Hill was originally planned as a cast in-situ building. However, on reviewing the plans the developers decided that the design of the building was ideal for precast hollow-core slabs, and today they are very happy with that decision,” says Theron. The second to sixth floors (inclusive) at Capital Park, covering an area of 1 850m², were built using precast slabs, whereas at Bridgeview all five floors covering an area of 5 848m², were constructed with hollow-
Until recently four storeys was the high-
or seven storeys.
core slabs. echo Prestress supplied the
est level that buildings constructed with
CMA director, John Cairns, concurs,
slabs, which measured 120mm x 150mm
precast hollow-core slabs had reached.
saying that providing all the engineering
in lengths produced according to site
These included several high density housing
requirements are in place, such as a proper
dimensions, for both projects.
projects in the inner city of Johannesburg,
load-bearing walling system, there should
the Alexandra renewal project and the
be no height limit.
Witbank Presidential Housing project.
Mobile and tower cranes were used to hoist the slabs into position, and because
ehco Prestress technical director,
they were simply installed off the back of
That changed last year when Bridgeview,
Daniel Petrov, echo’s project manager on
echo delivery trucks, on-site storage space
a high-density load-bearing masonry apart-
Bridgeview, and an engineer with extensive
for the panels was never a requirement.
ment complex in Braamfontein, Johan-
international experience, notes that the
This makes them ideal for very restricted
nesburg, was constructed over five floors
use of panels is common in new high-rise
sites as well.
using echo Prestress hollow-core concrete
residential buildings in europe, some of
panels. And shortly thereafter Capital Hill
which reach heights of 16 storeys.
T he successful completion of both projects makes two important statements.
Apartments, a seven-storey residential
“Any system which can safely speed up
T h e f ir s t is th a t th e e ch o F l o o r ing
block of bachelor and one-bedroom flats
the delivery of homes is to be welcomed,”
prestressed hollow-core slab system is
in Arcadia, Pretoria, was completed with
observes Petrov.”
viable on medium-rise buildings and the
five of its floors having been erected using
Speed of construction, made possible by
second is the importance of team work,
concrete slab technology and the fact that
from the drawing board to completion. echo
Simon Knutton of Knutton Consulting,
no propping was required, was certainly
Prestress specialists worked closely with
the main engineer on Bridgeview, says the
the major feature on both projects. Floor-
the engineers, architects and contractors
trend is towards using hollow-core slab
to-floor turnaround on both projects was
on both projects.
flooring on structures of five floors and
particularly fast. For example, the five
higher especially in central urban areas
floors at Capital Park were completed in
where land is expensive. He says that
about three months.
echo’s precast hollow-core flooring.
hollow-core concrete flooring can certainly
Don Theron of DG Consulting engineers
be used for buildings at least as high as six
said that’s an average of about two-and-half
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(Above from left): A hollow-core concrete slab forms part of a partially completed floor at Bridgeview; a hollow-core concrete slab, manufactured by Echo Prestress, is lowered into position at Bridgeview, a medium-rise apartment block which was constructed last year in Braamfontein, Johannesburg.
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22 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2008
True modular construction can house the nation Modular construction, based on the use of concrete blocks as opposed to bricks, is an internationally proven masonry system, which if properly applied, can do much to alleviate South Africa’s housing shortage. However, this will require a change of attitude, as well as the re-introduction of genuine modular construction which proved so effective in the construction of affordable housing in the seventies and eighties.
addition, they offered training in modular construction and many of today’s highly skilled and efficient sub-contractors were recipients of that training. Koch observes that in those days the rate of housing delivery using modular block construction topped eighteen 6570m² houses a day during favourable summer months and 12 units a day during the remainder of the year. Some 35 000 houses were built in Mitchells Plain using Columbia DCM’s cavity wall construction system during that period. “We should be building at least 16 000 economic houses a year in the Western Cape alone where over 450 000 families are waiting for housing. As things stand now if we are building, say 5 000 35-40m² houses a year, it’s a lot. With the re-introduction of full and proper modular construction,
When first introduced by Concrete Manu-
incurred through chopping straight blocks
as well as improved economies of scale,
facturers Association (CMA ) member
to size is eliminated (and) laying is much
great progress would be made in housing
Columbia DCM in 1978, modular construc-
quicker. In fact the whole process is much
the homeless. All it takes is the will to do
tion was based on an international stand-
more economical than building the same
it and the discipline to follow though.
ard and was SABS approved. The system
sized structure using imperial-based
was similar to the child’s block building
brick masonry.
“Today uneconomic delivery of badly-built houses is the norm. One of the reasons
game, Lego, in that a complete range of
The CMA’s Cape representative, Günter
for this is that housing managers and
complementary blocks, such as corner,
Koch, says there were some notable
specifiers do not appear to understand
half and quarter units, were supplied in
successes in the early days of large scale
the economic advantages of modular
addition to the standard straight block.
housing delivery when the City of Cape Town
construction and therefore fail to insist on
Just as complementary blocks are an
issued several contracts, each of which
its full implementation i.e. the incorporation
essential ingredient to successful building
entailed building 5 000 economic houses.
of complementary masonry units in their
with straight Lego blocks, so it is with
These were built efficiently and on time
designs and specifications.
successful modular masonry. Wastage
by three large construction companies. In
“T his has led to the construction industry and block manufacturers abandoning true modular construction, replacing it with a crude and unproductive alter na ti v e which r elies on the sole use o f str aight blocks. e x per ienced building inspectors are a rarity and other supervisory organisations are not guiding or mentoring SMe builders in adhering to the correct procedures. “Not only is the current approach unproductive, the rate of construction, being far lower than that of truly modular masonry, but it is also a wasteful process. “I recently attended a ceremony at Taffelsigt on the Cape Flats in which Cape Town’s mayor, Helen Zille, presented keys for some economic houses built with modular concrete blocks. everyone was struck by
Visitors and children assemble in one of the halls of the MaAfrika Tikkun Child and Youth Development Centre in Diepsloot prior to the official opening of the community centre. The excellent concrete block masonry work is clearly visible. The blocks were manufactured by CMA member, Watson Concrete, and laid by Diepsloot community members.
the mess created by the discarded remains of broken and chopped blocks, and frankly speaking, it was embarrassing.
PreCAST VOLUME 3 • ISSUE 1 • JUNE 2008 23
“Moreover, the Council actually specified complementary blocks, yet only full blocks were ordered by the contractor, despite the fact that the company supplying the blocks had complementary blocks in stock. It would seem the main contractor simply could not be bothered to take advantage of the tremendous benefits to be gained by using complementary blocks. Instead, the sub-contractors were left to manage as best they could. “Property developers, builders and block manufacturers have forgotten, or chosen
True modular construction can be both practical and aesthetically pleasing, as this example clearly demonstrates at The MaAfrika Tikkun Child and Youth Development Centre in Diepsloot north of Johannesburg, where this créche was one of three buildings constructed with genuine modular block masonry.
to forget, that modular construction offers
material comprises nine core modules and
cost-effective masonry system, not only
considerable advantages. It also appears
120 credits. And as from the beginning
for economical housing, but for high-rise
as if today’s contractors don’t want the
of this year the CeTA will allow training
buildings, community centres, schools and
hassle of guiding and training workers to
providers to make use of the new training
shopping centres, as well as many other
use complementary units. Furthermore,
material and thereby treat brick and
structures.
modular construction entails applying a
block-laying as separate skills. A lengthy
“One of the other challenges we face
considerable degree of precision in the
process of obtaining SAQA certification
is for structural engineers to become
correct laying and placement of blocks for
still lies ahead of us. However, the fact
attuned to the significant benefits of
which bricklayers are either not prepared
that we can start using the training
modular construction. Most of them
nor able to apply.
material should do much to re-establishing
appear to have little knowledge on load-
modular block construction as the most
bearing masonry principles and practice,
“The CMA believes it is incumbent on national and local authorities to insist
and the assertion that South Africa lags
on the implementation of proper modular
50 years behind countries like the United
construction, not only at the tender
States and Australia in high-rise load-
process stage, but during the building
bearing structures is no exaggeration.
process through their own inspectors and
The fundamental problem appears to lie
with the assistance of NHBrC inspectors.
with the universities which, to the best of
Today’s building industry only needs to
my knowledge, do not include load-bearing
recall what it has forgotten and re-
masonry as part of the civil and structural
introduce building methodology which first
engineering curriculum. This could be
saw light of day 30 years ago. Productivity
overcome, however, with an additional FeT
will increase, wastage will be almost totally
programme.
eliminated, and most importantly, the
“Unlike some leading masonry construc-
quality of the finished product will be vastly
tion countries, South Africa makes little
improved,” observes Koch.
use of high rise modular construction, and
Another aspect contributing to the
when it does, it is often incorrectly de-
demise of modular construction is that
ployed. Not so in the United States, where
it has never been treated as a discrete
a 28 storey 4 000 room hotel was built in
skill by the South African Qualification
Las Vegas using the modular block system
Authorities (SAQA).
15 years ago. It is worth noting that steel
“Instead, it has been relegated to
usage on this project was significantly
Cinderella status and treated as an add-
less than an equivalent conventional frame
on to traditional brick laying courses. Over
would have required. The project took 29
the past 10 years the construction CeTA
weeks to build which is considerably faster
has failed to recognise the necessity to
than most other forms of construction.
separate brick laying from block laying.
There is no sound reason why this can’t
These are distinct skills and should be
be achieved locally as we certainly have the
treated as such.
brain-power. All it will take is the courage to
“This is about to change. Late last year the CMA took the initiative and developed trainee and facilitator training material for modular construction. The course
grasp the nettle and implement something new and profitable,” concludes Koch.
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(Left): The complete range of modular construction concrete blocks.
24 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009
Crb walls – aiming for zero defects Since they made their first appearance in South Africa some 26 years ago, concrete retaining block (CRB) walls have become a readily recognisable feature on the South African landscape. Used widely for residential, commercial and industrial applications, CRB’s favoured status among property owners and developers is owed in large measure to competitive advantages of low cost and fast construction.
• G e o t ex tile s (w her e r e quir e d ) no t inst alled cor r ec tl y or the incor r ec t products used. These of course are just the symptoms, the underlying cause being human error, either at the design stage but mainly during construction, or both. In many instances CrB walling forms the minor leg of a much larger project such as a shopping centre
An ability to follow any contour and a
percentage fail, usually within a year of
or office park, and as such it does not
suitability to greening are other factors
completion. However, no matter how few
receive the focused attention it deserves.
which contribute to their deployment. This
the failures, or how small the percentage,
But it is primarily a structural element and
success rests on sound design principals
the figure is still too high.
should be treated as such. However, unlike
and an adherence to correct construction
Some of the more common causes of
other areas of the construction industry
procedures. Given the relative simplicity
CrB wall failure are as follows:
where a philosophy of zero defect is or
of the entire process, nothing should go
• No engineering designs or drawing
should be rigorously applied, such as in
wrong. So why does it?
sections
the construction of bridges or dam walls,
• Inadequate foundation detail or no
CrB walling’s status often rates not much
Silvio Ferraris, president of the Concrete
foundations at all
higher than nuisance value. Little wonder
Manufacturers Association (CMA) and vice
• Wall slopes which are steeper than that
that errors and corner cutting exist.
president of its CrB Division, outlines his
allowed for in the design
reasons why CrB wall failures occur and
• Height of wall exceeds design and/or is
engineer, architect and quantity sur-
what can be done to avoid them.
too slender for wall height
veyor, have some responsibility for the
• Backfill material unsuitable
design and construction of CrB walls,
CrB walling is one of the construction
• Backfill insufficiently compacted – the
especially on large multi-faceted projects.
industry’s many success stories, with
major cause of most failures
They are the professionals at the top of
a proven capacity to provide innovative
• Deploying CRB blocks meant for low
the project chain responsible for assem-
and eco-friendly solutions to retaining
walls and landscaping purposes only in
bling tenders and bill of quantity docu-
wall challenges. Of the hundreds of CrB
structural applications
ments. The main contractor, CrB design
walls built every year only a very small
• No drainage detail
engineer and the CrB sub-contractor,
In this inter view with David Beer,
It should be stated at the outset that
Several professions such as the project
PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009 25
of services, and even basic essential
For those not sure what a comprehensive
surcharge loadings, wall height and angles.
sp e c i f i c a t i o n e n t a i l s, t h e C M A h a s
And more often than not no drawings are
published a CrB wall installation manual
supplied with the specifications.
which includes a typical bill of quantities
It is virtually impossible for the sub-
and covers most of the requirements
contractor and his design engineer to
for constructing a CrB wall. The CMA
second-guess, with a reasonable degree
has also produced a film (available on CD)
of accuracy, what the actual requirements
which provides step-by-step construction
are if the bill of quantities lacks relevant
guidelines, available at no charge.
details and drawings.
CrB wall specifiers can also refer to
CrB contractors generally react in one
two SABS standards, SANS 207:2006 for
of two ways to this type of specification.
the design and construction of reinforced
They can either make certain assumptions
soils and fills, and SANS 508 : 2007, the
in their own favour, one being the height
specification for retaining blocks, which
o f the wall, another the quantit y o f
was published in August 2008.
fill required, or, if the site is ready for
Despite having to work with inadequate
viewing, they can visit it, make more
bills of quantities and no drawings it is still
realistic assumptions, and quote more
the responsibility of the design engineer
appropriately. Although a higher quote
to see that walls are built according to
would reflect the actual requirements far
sound design and building principles. If
more accurately, the client generally opts
the original specification does not carry
for the lowest quote, which is when the
sufficient detail, either the CrB contractor
problems start.
or the design engineer must establish the
Then, when the winning CrB contractor Construction of a CRB wall in progress. This 6.8m high wall was built at 60° to within accuracy tolerances of +1˚, -2˚ as specified in the CMA’s Code of Practice for the construction of CRB walls.
theme of the overall project.
information such as soil parameters,
arrives on site he usually finds that the
parameters within which the wall must be designed and constructed.
project involves a higher wall as well as
This means sourcing the necessary
additional elements not dealt with in his
information from the project engineer, who
quote, such as poor access, more backfill,
because he is focused on the whole project,
who actually builds the walls, should work
fabric reinforcement, drains and stronger
is usually unable to provide it immediately.
closely with the professionals, but this is
foundations. So he either cuts corners,
For example, he may not have the soil
often not the case.
building a wall in which the risk of failure
parameters required to design walls as
The sub-contractor is usually
is high, or he revises his quotation, and
per SANS 207, and he may be uncertain of
responsible for the wall design and he
the project goes hopelessly over budget.
the loading, heights and angles, all of which
will use the services of a design engineer f or this purpose. However, the ini tial str uc tur al design specification and drawings, which are not meant to show much
There is no excuse for the submission of inadequate CRB wall specifications, and all CRB wall specifications should be accompanied by a set of drawings.
detail, are the domain
makes the design and pricing of the wall very difficult. The CrB design engineer also needs to know about ground water conditions and services such as water, sewerage and storm water pipes,
of the project engineer with additional
either way the project eventually ends up
not to mention irrigation systems and
input being made by the architect and
costing someone considerably more.
electrical reticulation details.
quantity surveyor. The project engineer is
There is no excuse for the submission
All these aspects ought to be taken
responsible for ensuring that the project
of inadequate CrB wall specifications,
into account before or during design to
fulfills the local by-law requirements,
and all CrB wall specifications should be
avoid the type of situation whereby once
such as reticulation, drainage, and road
accompanied by a set of drawings. These
a wall has been constructed, a services
levels, etc.
should also include a typical cross-section
trench is excavated, cutting into the
Problems can arise right at the outset
showing heights, wall angles, the quantity
geofabric and rendering it useless. Or an
when the project engineer’s CrB design
of concrete needed for the foundations,
irrigation system is installed with similar
specification and bills of quantity briefs
the drainage detail, the height of the wall
consequential damage.
lack essential information, which occurs
and the area it will cover. Furthermore,
Design flaws can also occur when the
frequently. Missing information typically
an architect should ensure that the wall
main contractor, who really acts as the
includes irrigation systems, the layout
doesn’t interfere with the architectural
interface between the project engineer and
26 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009
the sub-contractor, issues an instruction
quotation, whereas the main contractor
setting out the foundations is clearly most
to the sub-contractor which changes the
has all the site plans and surveyors at
appropriate and forms part of the CrB
original design without having informed or
their disposal to ensure precise setting
specialist’s terms and conditions.
consulted with the CrB design engineer.
out. This practice of the main contractor
T his could involve raising the wall or changing a kerb position, which can alter and ultimately compromise the safety and structural integrity of the wall. Furthermore, it is always the main contractor’s responsibility to set out the wall before the foundations are excavated, and this is not always done correctly. The reason for this is that the CrB specialist does not allow for surveyors in their
To avoid the scenarios sketched above, adherence to the SANS standards as
Most walls fail because their design or structural weaknesses make the fill prone to water saturation.
well as to the CMA manuals, available at no charge, comprising of “Installation manual”, “Code of Practice for Gravity Walls”, “Design of reinforced Walls” , “Design Check List” and various project reviews such as “Hydraulic Applications”, should be mandatory . It would remove the ambiguity as to where responsibility for design and construction procedure lies. One of the important rules covers design deviations and how best to handle them. In this instance, good liaison between the project engineer and CrB design engineer is a prerequisite. Most walls fail because their design or structural weaknesses make the fill prone to water saturation. Besides storm water, which is a cause of construction works in-progress failure, irrigation and storm water systems, which often leak and block with debris, can also undermine the integrity of a wall. It makes sense therefore for design engineers to be involved in the design and specification of irrigation systems as this would help lessen the threat of leaking. In an ideal world the backfill of CrB walls would contain a substantial percentage of
A failed CRB wall where a blocked storm water pipe and subsequent joint leakage meant that water permeated the soil under the roadbed, completely saturating the fill behind the CRB wall.
coarse material and a low percentage of fines (<15% passing a 75 micron sieve). This would reduce wall failure incidence dramatically, but importing selected fill is an expensive option, which is why soil found on site is generally selected. Before the engineer can design a wall he needs to know what the internal friction angle (Ø) of the soil is and its cohesion (c). To establish this information accurately, a shear box test is required. SANS 207 prescribes this test, yet on most retaining wall sites it is not undertaken. Instead, as a fallback measure, design engineers use the geotechnical report, which among others, includes results on the fines content of the soil. Geotechnical reports are mainly intended for piling and building foundation designs and almost never include shear box tests. This means
Photos such as this one should be taken at regular intervals during the construction of CRB walls as proof that design specifications are being followed.
that if a design engineer relies solely on a geotechnical report his assumptions can
PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009 27
be off the mark by a considerable margin.
take regular photos. This means that in the
The initial geotechnical investigation must
case of any comeback the contractor and
In summary, the causes of CrB wall
also include undisturbed shear box test
the design engineer will have proof that the
failures are many and prevention can take
results as per SANS 207 if the project is
wall was built according to design.
place from the beginning of a project,
to include a retaining wall element.
progress and performance.
DCP indicator tests should be
when the initial geotechnical investigation
Some design engineers insist on a
mandatory and should be conducted to
and specifications are drafted, or at the
tr oxler test, a nuclear dev ice which
check compaction up to the full height of
end when the integrity of a completed
tests compacted soil density. As this is
the fill at 1 000mm height intervals. Troxler
wall can be disturbed through unplanned
expensive and involves testing at every
tests can be done less frequently and the
and inappropriate inter vention, or at
300mm, it is generally called for when
results can be correlated with DCP results
any time between. If we are to achieve a
the walls are very high or when there is a
to ensure compaction uniformity.
situation of building CrB walls which are
substantial amount of fill.
A final note on storm water manage-
100% reliable i.e. built with zero defects,
As the compaction of back fill is a
ment responsibility during construction
a substantial change of attitude from
critical aspect, which if overlooked can lead
work. This is the joint overall responsibility
the professional project team down to
to wall failure, all CrB contractors should
of the professional team, project man-
the CrB sub-contractor will be required,
own a DCP compaction test kit. They
agers and the main contractor, as it is
an attitude which recognises that CrB
are inexpensive and pay for themselves
unreasonable to expect a sub-contractor
walls play an important structural role
many times over. Besides taking regular
to manage the other sub trades such
and that any wall failure will have serious
compaction tests before the placing of
as bulk ear thworks, plumbers, brick-
consequences, for both the client and the
foundations and during the construction
layers etc, who’s site works often have
project team. It is certainly an attainable
of walls, the CrB contractor should also
a direct impact on the CrB contractor’s
goal and one worth pursuing.
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28 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2008
SA’s largest prestressed hollow-core concrete panel retaining wall project The construction of The Houghton, a development comprising two luxury residential apartment blocks (Houghton 1 and Houghton 2) and a 180 room boutique hotel development (Houghton 3), has entailed South Africa’s largest deployment of prestressed hollow-core concrete panels as retaining walls to date.
varying in length from 3.2m to 5.0m. Panel thickness was a standard 150mm in most instances except where two slabs, one above of the other, were required to accommodate embankment depths of up to 10m, and in these instances panel thickness was increased to 250mm. The precast slabs used on Houghton 2 were between 3.2m to 4.1m, whereas in the cases of Houghton 1 (residential) and Houghton 3 (The Hotel), where the contours are more severe, there was a much greater variance in slab length.
Spanning approximately 2 000m at an
rogan Duffy of Pure Consulting, the
average height between 3.2m – 5.0m, the
consulting engineers responsible for the
panels are fulfilling a dual role of retaining
project’s structural engineering, says
embankment soil and providing walling for
that where possible the objective was
parking basements and below-ground level
to achieve as much standardisation as
service areas. Supplied by Concrete Manufacturers A s s o c i a t i o n ( C M A ) m e m b e r, e c h o Prestress, the prestressed panels were manufactured in standard 1.2m widths
The Houghton construction site, where two Echo prestressed hollow-core panels have been inserted into a foundation recess prior to the casting of a 300mm deep by 300mm wide surface bed edge on the right side of the channel.
PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009 29
possible in panel sizing to render their
poured, a steel reinforced cage and a metal
manufacture and on-site deployment as
wedge is inserted into the trench. Once the
simple as possible.
concrete sets the metal wedge is removed
F ounda tion supp or t f or the e cho panels is provided by 250mm deep footing
yielding a support channel with very smooth chamfered edges.
(Top from left): Prestressed hollow-core panels measuring 3.2m x 1.2m x 150mm shortly af ter offloading at The Houghton construction site; precast panels at Houghton 1 are supported by steel poles while the casting of the first floor slab is taking place; a parking basement at Houghton 2 clearly showing how the precast panels provide internal walling as well as retaining support; a completed section of precast panel walling at Houghton 1 in the process of being waterproofed.
channels. Additional lateral support is
“As with most building projects a key
achieved through thickening the edge of
objective was construction speed and in
the surface bed on the support side of the
this instance the use of precast panels
footing channel to 300mm, thereby lifting
meant that the retaining walls were
the height on that side of the channel to
generally erected three times faster
“In some instances we were unable to
550mm. Moreover, a fully cantilevered
than in situ construction would have
use the panels owing to on-site geometry.
application was avoided by bolting small
taken. We wanted to have the retaining
For example, on walls with tight radii, insitu
right-angled steel sections to the first
walls er ec ted be f or e the f ir st f loor
concrete or brickwork was chosen. As it
floor slabs. These provide the head of each
slabs were cast. This improved access
turned out brickwork was used in most of
panel with additional support.
for the main contractor, Murray and
these instances.
“In some instances we have done away with the steel angles and have allowed
roberts, and enabled it to work off the critical path.
comprised echo precast panels.
“Another advantage of echo’s panels is that they are very easy to cut, for example
the echo panels to rest against the first-
“As a result, Murray and roberts was
in creating space for the installation of
floor slabs. These receive no support from
able lay about eight linear metres of walling
air-conditioning units. The friction between
the panels and instead rest on concrete
a day in either brick or reinforced concrete,
the concrete and steel reinforcing in
columns situated inside the basements,”
and the panel contractor, echo Prestress,
a prestressed panel ensures that the
says Duffy.
has achieved in excess of 30m to 35m of
tension and structural integrity of the
“We are used footing channels for
prestressed paneling erected each day
panel is retained after cutting.
support because they were very cost-
without any significant involvement from
effective. They were very similar to the
Murray and roberts,” observes Duffy.
footings used for the project’s brick walls
Approximately 98% of the retaining
which, because they were curved, were
wall requirement on the Houghton project
“We have used echo panels on one other project and were very happy with their performance. This was why we chose the technology for this project,” says Duffy.
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not suitable for echo panels. Furthermore, by integrating the surface bed into the support channel, on-site productivity was significantly improved. “The channel or recess which provides foundation support for the panels was constructed in the same manner as any standard footing. Before the concrete is
The objective was to achieve as much standardisation as possible in panel sizing to render their manufacture and on-site deployment as simple as possible.
30 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009
South Africa’s first permeable paving project using the Uni-Ecolok system Twenty two Boeing Road East, Dunvegan, an address which at first glance appears like any other in this essentially residential suburb of Edenvale; with one striking exception, however. It will be remembered from here on as the site where the first permeable concrete block paving (PCBP) project using Infraset Landscape Products’ interlocking paving block system, Uni-Ecolok, took place. Much more is likely to be heard about the
development. It is also attractive and
Uni-ecolok paver in the years ahead as local
eliminates the need for surface run-off
governments increasingly stipulate some
measures.
form of storm water attenuation on new
T h e p r op er t y on 2 2 B o eing r o a d
and refurbished property developments.
has been conver ted f r om r esidential
Over-burdened storm water drainage, river
to commercial usage by M&F Giuricich
flooding and high river water temperatures
Developments and, in giving the make-
are the main motivating factors behind the
over plans the green light, the ekurhuleni
increasing usage of PCBP.
Council specified storm water attenuation
Attenuation is a process in which storm
In the metamorphosis from residential
or permeable paving systems, before
to office usage, the garden would be-
being released gradually and in manageable
come paved parking for cars and delivery
quantities into the existing storm water
vehicles. This meant that close on 95% of
drainage systems. It is a mechanism which
the 1,120 m² refurbished property would
can be used to relieve the storm water
be defined as run-off i.e. covered, either
run-off burden on existing storm water
by the house (offices) itself, or by paved
drainage systems, especially from new
surfaces. An increase in run-off area would
urban developments.
mean the discharging of higher volumes of
paving attenuation is that it eliminates
Bedding material 20mm thick is levelled out prior to the laying of the Uni-Ecolok blocks.
as one of the approval conditions.
water is held back, either in ponds, tanks
One of the advantages of permeable
The sub-base layer is compacted prior the laying of the first geofabric membrane.
storm water onto the roads and into the municipal storm water drains.
the need for collection sumps or ponds,
The Council accepted that permeable
thereby freeing up additional land for
paving offered an appropriate solution to
The Uni-Ecolok permeable paving block which is manufac t u red and supplied lo cally by Inf ras e t Landscape Products.
34786/E
www.ppc.co.za
18 000 000
16 000 000
14 000 000
Tons*
12 000 000
10 000 000
8 000 000
6 000 000
4 000 000
2 000 000
0
1892
1906
1920
*Total industry in South Africa.
1934
1948
1962
1976
Cement
While times have changed, our strength has not.
For 116 years, the South African market has continued to demand exceptional service and quality cement. And, through both trying economic circumstances and ever-increasing cement demands, PPC has played its part in giving South Africa the strength to progress and further develop our nationâ&#x20AC;&#x2122;s landscape.
1990
2008
32 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009
its attenuation requirements. The ensuing
T he parking area structure of the
design entailed laying a 480 m² permeable
Boeing road system, starting at the
paving system, 130 m² on the driveway
bottom and working up, comprises the
and 350 m² on its back yard. However,
following,: a 150mm insitu sub-grade
the council agreed that the front 135 m²
layer; a geofabric membrane supplied
section of the property, which comprises
by Kaytech; a combination of 13mm and
a portion of the driveway and the front
25mm aggregate forming a 200 mm sub-
yard, could be paved conventionally with
base layer; a second geofabric membrane;
an impermeable paved surface.
bedding material 20mm thick and Uni-
T h e P I C P d e sign w a s u n d e r t a k e n
ecolok paving blocks.
by Croswell engineers and one of its engineers, Steve Pearse, PrTech eng, saw the installation through to completion. In commenting on the project, Pearse noted that Infraset’s Uni-ecolok permeable paving blocks were specified because their L-shaped design offered exceptionally stable interlocking properties. They are especially appropriate in parking areas where there is a great deal of turning traffic, as is the case at Boeing road. The sub-base layer of any PICP system is as important as the paving block itself and its design depends on the manner in which the water is to be handled after infiltration has taken place. PICP designers have several options at their disposal. The water can either be
We struck a compromise between structural stability of the smaller stone on the one hand and creating enough capacity between the larger stones for water storage on the other.
stored in sub-surface tanks for re-use in gardens, washing vehicles and sanitary
T he insitu sub-grade layer was
parking area and the other on the lower
purposes or, as in suburban gardens or
compacted to 93% Mod. ASHTO. This layer
side of the driveway. Pearse estimates
any undeveloped land, it can infiltrate into
as well as the layers above it were laid at
that a possible 10 to 15 % of the infiltrated
the ground water system. At Boeing road
a gentle 0.5% cross-fall slope to ensure
water will penetrate the insitu soil and seep
the water infiltrates back into the ground
that any water which did not infiltrate into
beyond that into the underground water
beneath an insitu sub-base layer and any
the sub-grade layer would drain gradually
table. A layer of geofabric was laid on the
excess water is channeled into the street
towards the two 110mm PVC outlet pipes,
sub-grade layer before the stone sub-base
via two outlet pipes.
one positioned in the corner of the rear
was delivered.
Freshly laid permeable paving Uni-Ecolok blocks which were specified for their exceptionally stable interlocking properties.
PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009 33
(Clockwise from top right): A close up view of three of the sub-base layers at 22 Boeing Road, aggregate, geofabric membrane and bedding material, prior to the laying of the permeable paving Uni-Ecolok blocks; freshly laid permeable paving Uni-Ecolok blocks which were specified for their exceptionally stable interlocking properties; a worker pulls a section of geofabric membrane into position; the 200mm thick layer of aggregate comprising a combination of 13mm and 25mm stones, which was laid on the bottom layer of geofabric membrane.
International in collaboration with German universities, academics and engineers has produced permeable paving products which rank among the world’s best. “I n a d d i t i o n t o o f f e r i n g s u p e r i o r interlocking stability, the scientifically proven Uni-ecolok has enhanced permeable properties which means it is suitable for a wide range of local paving requirements. Moreover, it will conform to the new SANS 1058 standard when it is introduced later this year. The L-shape concrete block is ideal for driveways, car parks, residential streets and township roads, light and heavy duty industrial yards, as well as for bus terminals and through-roads in urban areas,” advises Stark. Germany is the world leader in permeable paving technology. Germany pioneered PCBP having introduced it some 20 plus years ago. One need look no further than Two sizes of aggregate were deployed
of up to 90% of pollutants from the
the recent flooding of Germany’s major
on this project because had stones of
infiltrated water is an important benefit.
rivers to understand why the Germans
25mm only been used they would have been
The sand, geotextile and stone act as a
take PCBP technology as seriously as they
unstable under loading.
trickle filter, retaining the hydrocarbons
do, so much so that they levy taxes on any
“The base of any paved surface, whether
which are digested by naturally occurring
non-permeable paved surface.
permeable or non-permeable, must be
microbes, and lowering of the water
With the unpr ecedented levels o f
stable or the whole system will fail,” says
temperature by as much as 30%. While
development which have taken place in
Pearse. “In this instance mixing in the
these advantages may seem of little
South Africa’s urban centres over the
smaller stones gave us the stability we
consequence given that this project can
past 10 years, increasing demands have
required. Similarly they could not be used
hardly make much of an impact on its
been placed on existing infrastructure
exclusively because the required water
own, as time goes by and additional PICP
systems, storm water drainage systems
storage volume of 30 to 35% would not
projects are brought on stream, the effect
being one of them.
have been achieved. So we struck a com-
will be cumulative.
This has meant that with the addition
promise between structural stability of the
“One has to start somewhere,” observes
of every new property development a
smaller stone on the one hand and creating
Infraset Landscape Products marketing
growing burden has been placed on existing
enough capacity between the larger stones
executive, earle Stark.
storm water drainage systems and the
for water storage on the other.” As in any PCBP system a second layer of geofabric was laid at Boeing road to prevent
Stark says that Infraset obtained the li-
threat of flooding increases with each
cense to manufacture the Uni-ecolok system
new development. The construction of
locally from Germany’s Uni-International.
new storm water drainage capacity is an
the bedding sand from infiltrating the ag-
“After thoroughly researching global
expensive and highly impractical remedy,
gregate layer and also as a leveling course.
mar ke ts f or the wor ld’s b es t P CBP
and this is why local governments are
It also acts as a filter, trapping most of the
solution, we chose Uni-ecolok, which
opting for local attenuation. It is far less
pollutants before the water infiltrates into
besides being scientifically researched
disruptive and the costs, which are lower
the layer of aggregate below.
and thoroughly tested, was suited to local
than new storm water drainage would be,
conditions. exhaustive research by Uni-
are borne by the developer.
Besides water attenuation, the removal
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34 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009
Agrément approval for precast foundation beams The Concrete Manufacturers Association (CMA) has been given the green light by Agrément South Africa to license its precast concrete slab producer members to manufacture precast concrete foundation beams for deployment in the construction of affordable single-storey houses.
the manufacturing process are required
Providing they comply with the speci-
security and retaining walls, warehouse
founding conditions are correctly classified
fications of Agrément Cer tificate No
walls, and walls and roofs for reservoirs.
and that any threat of under-scour, due to
to meet the following national standards: SANS 1083 for aggregates and sand; SANS eNV 197 for cement; and BS 5896 for prestressing steel. They also are obliged to ensure that the
2008/350, CMA member companies will
The foundation beam Agrément Cer-
water erosion adjacent to the foundation
be able to manufacture CMA Building
tificate specifies that the beams should
beams, is addressed. Adequate drainage
Foundation Beams, as they are to be
be 200mm wide by 400mm deep and
and the prevention of water ponding
known, for houses with maximum dimen-
a maximum length of 6.2 metres. Any
adjacent to the beams is another aspect
sions of 6.6 x 6.2 metres.
deviation from this specification is not
which requires the input of an engineer.
CMA Building Foundation Beams offer
permissable.
O ver and above Agr ément South
cer tain ad vantages over insitu built
The Certificate specifies further that
Africa’s performance criteria on durability
foundations. They are far quicker to install
the design, manufacture and installation
and quality management, the National Home
and therefore more cost effective. They are
of precast concrete beams should comply
Builders registration Council (NHBrC),
also ideal for supporting suspended flooring
with established manufacturing processes
which states that building sites should be
comprised of precast concrete slabs, thus
and codes and these should be under the
classified as either C or H in accordance
completely eliminating any ‘wet’ trades for
control of a professional engineer or other
foundations and ground floors.
approved competent person to ensure
CMA director, John Cairns, says that what this means is that yet another use has
that the requirements of the Certificate are met.
been found for the multi-faceted precast
Moreover, the Certificate holder’s quality
slab in South Africa which, besides its prime
management system needs to comply with
function as a precast flooring material, is
Agrément South Africa’s requirements.
being used in applications as diverse as
For instance, all the materials used in
(Top): One of 50 houses in the Bloemfontein township of Excelsior where Agrément SA approved CMA Building Foundation Beams were first tested. The actual foundation beams can’t be seen here, although one of the precast hollow-core floor slabs which they are supporting, is clearly visible. Those observing the house are Stoffel Botha (left), marketing director of Stabilan (Pty) Ltd, Jean du Plessis, technical marketing manager of Stabilan and Monique Eggebeen, managing director of Echo Prestress (Pty) Ltd.
PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009 35
with the Code of Pratice Foundations and Superstructures for single storey residential masonry buildings, must also be met. The accurate preparation of foundation trenches is another Agrément prerequisite.
• The uniformity or otherwise of the
Foundations other than the precast
founding soil conditions must also be
beams must also be properly designed and
assessed by the geotechnician
a building superstructure should under no
• Predicted differential foundation movement should not exceed 4mm
circum-stances exceed the performance criteria of their foundations.
• Soil bearing pressures must not
To ensure this, special attention must be
exceed the recommended limits as
MANUFACTUrING PrOCeSS
given to the training of workers. It is
set out in SANS 10161 Code of
L ike all pr ecast slabs, CM A Building
imperative that foundation beams rest
Practice for the design of foundations
Foundation Beams are cast in a continuous
on the same plane and the maximum
for buildings
process on prestressing beds. reinforcing
permissible variance is 15mm. The base of each foundation trench must also be horizontal with the maximum
• The possible effects of differential
steel, comprising 2 x 4 No. 7mm diameter
settlements in collapsible soils, must
strands, should be symmetrical at both the
be assessed.
top and bottom of the beam. The bed must
allowable ‘out of level’ tolerance being
• Matters pertaining to site drainage
be cleaned and lubricated prior to casting
+-15mm. This ensures that the maximum
must be adequately addressed in
and care must be taken to ensure that the
difference between the highest and lowest
order to prevent the formation of
lubricating oil does not come into contact
points of the top surfaces of the beams
water ponds adjacent to the beams.
with the strands. Should this occur the
is no greater than 30mm. Compaction of
oil must be removed by wiping the steel
trench bases may also be required if soil
with a cloth.
has been disturbed through excavation,
Concrete should be batched by weight
and in some cases concrete blinding may be
on a calibrated scale and the required mix
required to ensure proper bedding.
proportions should yield a minimum crushing
Once in position, the line and level of the
strength of 50 MPa after 28 days and
beams must be further checked to ensure
35 MPa after 18 hours, when destressing,
they are parallel and that the floor slabs will
i.e. the cutting of the prestressing steel,
rest horizontally. The foundation trenches
takes place.
can then be back-filled and hand-compacted in layers not exceeding 100mm. The exposed ends of the beams must
Curing of the beams is accelerated One of the houses erected on Agrément-approved building beam foundations in Excelsior.
through the use of steam-heated moulds, a process in which the temperature must
be closed off with a stiff 1:3 cement sand
be maintained at between 60ºC and 70ºC.
mortar trowelled flush and, once dry,
And, once poured, the concrete should
waterproofed with a cementitious coating
be covered with poly thene sheets to
at least 23mm thick to prevent corrosion
assist with the curing. each production
of the prestressing steel.
batch must be tested in accordance with
CMA Building Foundation Beams are
SANS 5863.
designed to provide stable support for
The beams should be identified by means
precast floor slabs and this suppor t
of metal tags indicating panel mark, project
should be sufficiently horizontal for the
name, project number, production sequence
construction of walls. Moreover, the precast floor slabs will be designed to be
Another of the houses erected on Agrément-approved building beam foundations in Excelsior.
adequately stiff to avoid deflections that could cause internal walls to crack. Drainage and details of articulated pipe connections must meet Sections 6.3 of the Code of Practice – Foundations and Superstructures for Single Storey residential Buildings of Masonry Construction, issued by SAICe and IStructe in 1995. In summary, the engineer or other competent person is required to ensure the following: • Founding conditions should be either Class C or H and be classified as such by a qualified geotechnician or a professional engineer
number and the date of manufacture. Beams passed by the quality controller should be marked with green spray paint,
The accurate preparation of foundation trenches is another Agrément prerequisite. To ensure this, special attention must be given to the training of workers.
and those rejected with red spray paint. TrANSPOrTATION AND SITe HANDLING CMA approved foundations beams should be transported to site on trucks that are loaded and off-loaded with cranes, and care should be taken to ensure that the beams are safely strapped onto trucks. Building sites should be prepared to allow truck access and for the unimpeded operation of cranes. Furthermore, all aspects of the Occupational Health and Safety Act must be adhered to during transportation and site handling.
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36 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009
Infraset supplies concrete roof tiles for affordable housing project An example of a galvanized steel U-Truss assembly, manufactured by Vela Steel Building Systems, on one of the houses at Chief Albert Luthuli (CAL) Park.
Concrete roof tiles, supplied by CMA producer member, Infraset Building Products, are being used for the roofing of an affordable housing project at Chief Albert Luthuli (CAL) Park on the East Rand. A Gauteng Department of Housing development, it forms part of the Government’s Breaking New Ground policy which involves the creation of integrated communities. In its current phase it involves the building of 1 801 houses in CAL Park extension 2 (206 units), ext 3 (285 units), ext 5 (310 units) and ext 6 (1 000 units). At 42m² each, the houses comprise two bedrooms, a fully installed bathroom and a kitchenette.
An internal view of a galvanized steel U-Truss assembly at CAL Park.
Infraset is supplying its bold roll Sunset range of concrete roof tiles for the development which are being used in a variety of colours, including terracotta, slate, dolomite and a vintage multi-blend. The tiles are being laid on metal trusses in CAL Park extensions 2, 3, and 5 and on timber trusses in extension 6. In line with Government policy, unskilled locals have been trained to do all the construction work, including the erection of the roofs. Infraset was given the responsibility of training the roof construction teams, four in all. Two teams comprising four workers in each are erecting roofs on extensions 2, 3, and 5, while the other two are
Some of the recently completed roofs at CAL Park ext 2 where Infraset’s terracotta bold roll Sunset tile elevates the development several notches, both in terms of value and aesthetic appeal.
working on extension 6. Infraset’s roofing product manager, Grant Uys, says that each team has reached an exceptionally high level of productivity, taking no more than an hour to complete a roof. This means that eight roofs a day can be erected. “Not only does this one hour period include the laying of the tiles and underlay material, but involves the installation of the truss assembly as well. Once this project has been completed, these workers will be able to sell their acquired roof construction skills on the open market, either as independent sub-contractors, or as individual workers. “We have created a special range of Sunset concrete roof tiles for the affordable housing market and besides CAL Park these have been deployed on several other
Some completed roofs at CAL Park ext 2 demonstrate how the use of various roof tile colours breaks what could easily have been a monotonous roofscape.
projects in areas such as Krugersdorp, Mafikeng and rustenburg. Although very competitively priced, these
Reg. No. 200702266507
“Manufacturers of quality concrete paving products”
“Manufacturers of quality kerbing products”
P.O. Box 418 Halfway House Midrand 1685 South Africa
38 Spanner Road Clayville Ext. 11 Olifantsfontein Tel: +27 11 316 2375 Fax: +27 11 316 2394 E-mail: castind@mweb.co.za
38 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009
tiles carry the inherent aesthetic and durability properties which make concrete roof tiles such an attractive roofing solution for the affordable housing market. “One of the reasons why the roof construction teams are so productive at CAL Park is due to the way in which we pack our tiles. We use a modern system in which five tiles are strapped together in a pack. This facilitates the easy stacking of tiles on truss assemblies prior to laying and has also resulted in a marked reduction in tile breakages during transportation,” notes Uys. Thabong Civils is the main contractor on extensions 2, 3, and 5. Thabong site manager, Jakes Buthelezi, observes that roofing affordable houses with concrete
CAL Park Extension 6, where Infraset’s Sunset bold roll tile in a combination of dolomite, vintage and multi-blend colours create a striking roofscape which adds a value to the whole development far in excess of its cost.
tiles makes a considerable difference to
crete tiled roofs. Concrete roof tiles add
by Vela Steel Building Systems.
their ultimate value.
value to affordable housing far in excess of
Petzer, sales and marketing manager of
riaan
“The CAL Park units are being erected
their cost. I’ve always maintained that
Vela SBS, says the U-Truss system was
nex t to a subur b wher e the houses
it’s not the people who bring down the
developed specifically for the low-cost and
are valued at between r300 000 and
value of housing estates but the building
affordable housing sectors.
r450 000, and we have not witnessed
materials used in their construction,”
any drop in value since the onset of the
comments Buthulezi.
“The U-Truss system is manufactured from high tensile galvanized steel and was
CAL Park project, which is on the other
One of the metal truss systems being
engineered to carry concrete roof tiles. It
side of the road. The main reason for this
used at Chief Albert Lethuli Park is Vela U-
employs a bolt-and-nut fastening system
is that the houses at CAL Park boast con-
truss, a system which has been developed
which allows for easy assembly on site. Individual pieces are flat-packed to reduce
Once this project has been completed, these workers will be able to sell their acquired roof construction skills on the open market, either as independent subcontractors, or as individual workers.
transport costs, and purlins and battens can be cut to size which means there is no wastage. Moreover, the system is light which makes for ease of handling and fast construction times,” observes Petzer. Infraset is one of country’s leading producers of precast concrete products and it is worth noting that the concrete poles used for electricity reticulation at CAL Park were also supplied by Infraset. The company entered the concrete roof tile market comparatively recently having begun manufacturing from a state-of-theart factory at rossway in 2007. Besides the Sunset range, Infraset also manufacturers a flat shingle tile, Horizon, in a range of five through-colours. The company has overcome certain weaknesses in the design of traditional flat roof tiles by re-enforcing the transversal ribs for extra strength. This has improved on site handling and reduced breakages.
P
This birds’ eye view of CAL Park Extension’s 2 roofscape highlights how Infraset’s concrete roof tiles are lending aesthetic appeal to this and other affordable housing developments.
Marley Modern Concrete Roof Tiles Manufactured in the Western Cape and Gauteng — Now available nationwide
WILDLIFE PHOTOGRAPHY DENNY ALLEN
Drawn from Africa’s rich tapestry of colours, the Marley Modern Rustic Range is aimed at upmarket projects such as resorts, hotels, park boards, game lodges, residential villages and other theme developments where the roof is an important design element.
RODES INDUSTRIAL 9306
The Rustic Range Available in a variety of colours and colour blends with a textured striated surface finish which recreates the natural beauty and rustic appearance of traditional grass and thatch roofing materials — without the fire risk. Exclusive to Marley, this premium range is manufactured against confirmed order. Contact us for full details.
Marley Roofing Gauteng: KwaZulu-Natal: Western Cape: Mpumalanga:
ISO 14001 CERTIFIED COMPANY
Tel: 011 316 -2121 Tel: 032 944 - 4155 Tel: 021 374 -1018 Tel: 013 755 -2791 -
e-mail: olifants@marley.co.za e-mail: tongaat@marley.co.za e-mail: capetown@marley.co.za e-mail: nelspruit@marley.co.za
CMA National Trophy Winner 1998, 2000, 2002, 2004, 2006, 2008 Website: www.marleyroofing.co.za
Matombu Game Lodge, Mpumalanga
CMA National Trophy Winner 2006
This private game lodge is situated at the mouth of a gorge overlooking the picturesque Loskop valley near Middelburg. Over 10000 Modern Rustic Brown tiles were used to create this masterpiece.
Years ahead in roofing!
40 PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009
ProdUCEr MEMbErS - JUNE 2009 COMPAny nAME ArW Concrete Holdings A. Fick Cement Works Bafokeng Concor Technicrete Bamburi Special Products
TELEPhOnE
PROduCT
COMPAny nAME
TELEPhOnE
PROduCT
r
Infraset
012 652 0000
MPr
022 913 1921
M
Infraset
031 569 6900
Pr
014 538 0818
MPrT
00267 392 2850
P
011 704 2557
Kwena Brickforce
00254 20 2893000
P
Klapmuts Concrete & Cape retaining
021 875 5151
r
Baybrick
035 792 5218
P
Kopano/Altocrete
016 363 0340
P
Boland Concrete
021 875 5365
M
Lategans Cement Works
021 873 1154
M
Bosun Brick Midrand Brick and Concrete Industries Brickcast Industries Brickbuild T/A Panda
011 310 1176
P
Marley roofing
011 316 2121
T
00264 61 321 3009
MP
Marley roofing
013 933 3351
T
031 507 5525
MPr
Marley roofing KZN
032 944 4155
T
Marley roofing Cape Town
082 324 7277
T
Mobicast Mossel Bay
044 874 2268
Pr
00267 244 2106
MPr
Brikor
011 316 1200
T
Cape Brick
021 511 2006
MPr
MVA
012 386 0050
P
C.e.L. Paving Products
021 905 5998
P
Monier roofing South Africa (H.O.)
011 914 4580
T
Cast Industries
011 316 2375
P
Monier roofing South Africa
016 430 8000
T
Columbia DBL
021 905 1665
MPr
Monier roofing South Africa (Free State)
051 432 5089
T
Concor Technicrete
011 495 2200
MPrT
Monier roofing South Africa (North West)
012 250 2218
T
Concor Technicrete (Mpumalanga)
013 758 1203
MPrT
Monier South Africa (Cape Town)
021 534 1441
T
Concor Technicrete (Mpumalanga)
017 689 2100
MPr
Monier roofing South Africa (DBN)
031 565 1312
T
Concor Technicrete (Mpumalanga)
013 696 1153
MPr
Monier roofing South Africa (eLN)
043 743 2191
T
Concor Technicrete (Free State)
057 391 4200
MPr
Monier roofing South Africa (George)
044 878 1325
T
Concor Technicrete (North West)
018 790 4380
MPr
Monier roofing South Africa (Pe)
041 463 2629
T
Concor Technicrete (Limpopo)
015 293 8083
MPrT
Neat Contech
046 624 3377
MPrS
Concor Technicrete (Gauteng)
011 203 7700
MPr
PrO Brick & Block
021 905 3362
M
Concor Technicrete (North West)
018 484 6234
MPr
reMaCon Products
011 393 5504
r
Coastal Concor Technicrete
041 372 2230
MP
rocla
011 670 7600
Pi
Concrete Units
021 386 1923
Pi
Salberg Concrete Products
011 357 7600
Pi
Conframat
016 987 3381
P
Southern Pipeline Contractors
011 914 8500
Pi
Corobrik
031 560 3911
Pr
Stabilan
051 434 2218
S
Deranco Blocks
041 463 3338
Mr
Stanger Brick & Tile
032 457 0237
MP
Deranco Paving
041 933 2755
P
Shukuma Flooring Systems
041 372 1933
S
Deranco Precast
041 463 3338
S
Stone Age Concepts
012 802 1496
P
eagle roof Tiles
044 874 0290
T
Topfloor
021 552 3147
S
echo Floors
011 662 4600
S
Vanstone Precast
012 541 2056
Pr
011 589 8800/8899
S
Watson Concrete
011 740 0910
MP
031 569 6950
S
Western Granite Bricks
021 904 1620
M
West end Cement Bricks
011 851 1828
P
echo Prestress echo Prestress Durban Fastfloor Botswana
011 393 4655
S
Inca Concrete Products
021 904 1620
MP
Inca Masonry Products
043 745 1215
MPrT
Infraset
011 876 5500
Pi
M = Masonry r = retaining Blocks
P = Paving S = Floor Slabs
Pi = Pipes T = roof Tiles
PreCAST VOLUME 3 • ISSUE 1 • JUNE 2009 41
ASSoCIATE MEMbErS - JUNE 2009 COMPAny nAME
TELEPhOnE
Pipes
012 644 0043
Sekhukhune and Associates
012 993 4776
SNA Civil & Structural engineers
012 842 0000
Terraforce
021 465 1907
ILIFA Africa engineers
016 981 0591
Young & Satharia Structural Civil engineers
031 207 7252
CoNTrACTor MEMbErS - JUNE 2009 COMPAny nAME
TELEPhOnE
Daron Construction
034 955 1333
Decorton retaining Systems
021 875 5155
Friction retaining Structures
011 608 4321
Galaxy Paving
011 815 1175
Kalode Construction
011 781 3814
Mondo Paving & retaining Walls
011 467 7111
PYW Paving
031 763 5771
roadstone Civil & Paving
011 683 7080
SA Paving Gauteng
011 483 1350
Sun Paving
031 705 5123
The Paving Creations
031 765 4083
Vesles Civils
012 662 3031
Valcal International
011 867 2471
NoN-ProdUCEr MEMbErS - JUNE 2009 COMPAny nAME
TELEPhOnE
Ash resources
011 886 6200
Bell equipment Co.
011 928 9700
H. Birkenmayer
011 970 3880
BASF Construction Chemicals South Africa
011 452 6557
Cement & Concrete Institute
011 315 0300
Chryso Southern Africa
011 395 9700
Inca (Cape)
021 9041620
Imperial Dedicated Contracts
016 341 5124
Kaytech
031 717 2300
Manitou SA
011 975 7770
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031 700 8456
Pan Mixers SA
011 397 3754
rampf Formen GmbH
0049 7391 5050
rettenmeier Holzindustrie
0049 7971 9585810
Sika South Africa
031 792 6500
Siliseal Waterproofing System
011 464 1409
Soilcon
012 333 7817
Soillab
021 988 6919
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011 310 1161
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021 535 4455