PRECAST VOLUME ONE • JUNE 2007
• First permeable paving contract • New plant expansion • Professor Shackel visits South Africa
contents 2
Message from the president
4
New plants will meet rising demand for precast concrete products
8
Echo Prestress opts for Sika ViscoCrete-20HE
8
Civil contractor growing its fleet of Manitous
9
World expert to present at CMA paving seminar
10
3 Concrete organisations what they do and who they serve
34
Concrete pipelines boost capacity in Tshwane’s Pienaars River outfall sewer system
36
Inadequate specifications on CRB walling lead to failures
38
South Africa’s first permeable paving contract completed
40
Member details
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 11 315 4683
12 20
Why concrete paving blocks discolour Litigation on failed pipelines looms North American expert
24
Concete roof tiles - the most economical and best looking roofing material
27
Precast concrete delivers on social upliftment
32
Hollow-core slabs offer versatility across numerous applications
e-mail: main.cma@gmail.com
website: www.cma.org.za
Editor: David Beer Tel: +27 11 478 0239, Fax: +27 11 678 0254 email: 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 email: andrewm@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 VOL 1 JUNE 2007
Message from the president Welcome to Precast, the official journal of
modern world of fast track and modular
the Concrete Manufacturers Association
construction, in many instances leading
(CMA). You may well ask if there is a need
the way with innovative technologies
for yet another construction related
and applications. It has certainly been
journal. A resounding yes. Precast is
at the forefront of introducing quality
the only journal which caters exclusively
products to the affordable housing market
to the precsast concrete industry –
in South Africa.
our industry.
Through this medium we intend reaching
the widespread confusion as to how the
all our members throughout southern
roles and functions of the three concrete-
Africa as well as the key role players in
related bodies, the CMA, the Cement and
our industry: civil engineers; architects;
Concrete Institute (C&CI) and the Concrete
specifiers; and government authorities,
Society of Southern Africa (CSSA) differ.
A recent survey brought to our attention
among others. We want the construction
Precast will assist in promoting an
industry to not only know the CMA brand
understanding that the CMA is devoted
but to have a clear understanding of what
solely to growing the precast concrete
we do and stand for.
industry to the benefit of its members and
• Precast Suspended Floor Slabs
the public at large.
• P.I.P.E.S (Pipes, Infrastructural Products
we promote and market new and innovative
and Engineering Solutions)
products and ideas, as well as introduce
brand, a brand which above all, stands
new methods and technologies in both
for the consistent maintenance of high
focusing on expanded roof tile production
the inst alla tion and manu f ac tur e o f
standards, and Precast will provide us
and the construction of a major paving
those products.
with a platform to further promote the
plant we cover the introduction of new floor
Through our current divisional structure
The CMA stands for excellence. We
The CMA has developed into a powerful
The CMA has developed into a powerful brand
develop and write the national standards that govern the quality of products within our industry and we develop best practice methods, in printed and electronic format. We are also engaged in long-term research
For instance, in this issue, in addition to
slab plants which have either been recently completed or are still under construction. We also take a look at alternative uses of concrete floor slabs; include a cost comparison of different roofing materials; examine the benefits of permeable paving;
in a number of areas in order to improve
brand. In an era when shoddy building
warn the industry about inadequate tender
our products and their application.
practice is no longer the exception, the
specifications for concrete retaining block
The precast concrete industry has
CMA and its members of fer peace of
wall applications; focus on some of the
grown explosively since the Second World
mind to prof essionals f or whom high
achievements of our members in providing
War, both globally and in South Africa.
standards coupled with steady and reliable
the affordable end of the housing market
It plays a major role in our economy
service underscore their approach to
with cost-ef fective products made to
generating revenues in the R billions. This
doing business.
globally acceptable standards. And, as
growth has spurred investment in virtually
We will endeavour to provide editorial
has already been mentioned we explain
all our divisions. Several new factories are
that serves to enlighten our readers,
the differing roles of the CMA, the C&CI
close to completion or are currently being
exposing them to material, which will be
and CSSA.
commissioned which bodes well for the
of professional benefit to them and their
consumer and professional alike.
organisations. We also aim to provide an
your feedback and input. The CMA believes
This is your magazine. We would welcome
editorial mix representative of our six
that Precast will become an ideal medium
of cement and has contributed significantly
divisions, namely:
in which to promote your own products and
to the required new investment in capacity
• Concrete Masonry
brands and to grow your business in our
and construction of new factories.
• Concrete Block Paving
dynamic industry.
• Concrete Roof Tiles
Our industry is the single largest user
Precast concrete is a building material
which slots very comfortably into the
• Concrete Retaining Block Walls
Garth Gregory, CMA President
P
4 PRECAST VOL 1 JUNE 2007
New plants will meet rising demand for precast concrete products Consistently high levels of growth in the construction industry since 2001 has witnessed a concomitant surge in demand for precast concrete products. No let up seems likely as the build up to the 2010 World Cup gathers pace, and several precast concrete manufacturers are increasing production capacity, either through the expansion of existing plant or through the addition of completely new factories. Production of precast hollow-core concrete slabs, concrete roof tiles, concrete paving and concrete retaining blocks (CRB), has been or is in the throes of being increased significantly. Three new hollow-core slab factories were built during the course of 2006, increasing the number of CMA affiliated production facilities from four to seven and widening the technology’s geographic footprint. HOLLOW-CORE SLABS The new factories were built by Echo Prestress in Effingham, Durban, Shukuma in the Eastern Cape and by Top Floor in Cape Town. This development introduces fast-track building technology to KwaZulu-Natal and the Eastern Cape for the first time, while capacity in the Western Cape has been doubled. Managing Director of South Africa’s largest hollow-core slab manufacturer and past vice president of the CMA’s Floor Slab Division, Monique Eggebeen, says that hollow-core slabs are finding increasing favour with developers, engineers and contractors because of time saving factors and the huge lack of skills in the construction industry.
Marley Roofing’s concrete roof tile factory at Ekandustria, where a new production line has been installed.
“One of the advantages of precast concrete slabs is that they are manufactured in a controlled environment which ensures structural integrity and quality. This is a big plus for an industry where a lack of site supervision is endemic,” comments Eggebeen. Although approximately 90% of all precast slabs produced in SA are used for flooring in multi-storey buildings, other applications such as security walling, retaining walls, foundations and reservoir roofing are taking hold. For example, the technology is suitable for seating platforms in sports stadiums such as those due to be built for the 2010 World Cup soccer competition. Another application is the pedestrian bridge and it is anticipated that many of the bridges on the Gautrain rail network will use the technology. A further factor pushing up demand is that as land required for building residential, commercial and retail accommodation in and around major centres becomes increasingly scarce, affordable and low-cost housing is being forced to go the multi-storey route. Eggebeen notes that hollow-core slab technology enjoys a much higher profile in the EU, Russia and Dubai than it does in South Africa. “We are still very conservative in our approach to construction and many engineers are not familiar with the technology. But this is changing, which is why the market for hollow-core slabs is growing and will continue to do so,” says Eggebeen.
PRECAST VOL 1 JUNE 2007 5
NEW PAVING PLANTS A new paving plant in Midrand, Gauteng, has been commissioned by Cast Industries. The paving machinery, manufactured by Germany’s MASA, is the world’s largest and embodies the latest technology and systems. It will ensure very fast cycle times and high production volumes and its massive size and power will enable Cast Industries to produce very dense high-quality concrete, ensuring an end-product of the highest quality, well in excess of the national standard. This increased capacity will enable Cast Industries to introduce new paving products to the South African market, and to broaden its existing range in a wide array of colours and textures. Garth Gregory, managing director of Cast Industries and current president of the CMA, says the paving market is buoyant and demand good. However, he says there is significant additional capacity coming into production and this may affect the long-term prospects of the sector. Infraset’s Landscaping Division has also invested in new paving plant, replacing its Columbia C50 machine with a new Columbia CPM50 at its Rossway factory in November 2006. It has also installed an automated strapping plant. Incorporating the latest state-of-the-art technology, the CPM50 includes a computer-based command system, low vibration and maintenance properties, and a modem link to Vancouver, Washington State, USA, for support. At one tenth the cost of a new factory, the new plant will produce Masonique and Cottage Stone pavers, as well as stadium seating and retaining wall units for the next 25 years. CONCRETE ROOF TILE PLANT Production of concrete roof tiles is also increasing significantly and Marley Roofing has installed a new production line at its Ekandustria factory. Completed at a cost of R45 million, Marley’s new plant has been in full production since January. The plant will more than double Marley’s installed capacity at Ekandustria and will provide adequate supplies of tiles in the traditional and affordable housing market well into the future. Mark Irving, managing director of Marley Roofing, says the new tile line is only the second of its kind worldwide and incorporates the latest state-of-the-art roof tile technology. Manufactured in Europe to Marley’s specifications, special attention was paid to high-level efficiencies and low maintenance requirements. “High-speed and fully-automated, the line is all-inclusive, and, in addition to tile production and curing, incorporates raw material preparation and the packing of finished product. It also includes a fully automated curing system that comes with automatic temperature and humidity control – a crucial factor in maintaining high quality standards. Once cured, the tiles are automatically packed and transferred into the stacking yard,” says Irving. The line has enabled Marley to introduce Double Roman Plus a new Victorian-styled tile. Unique to South Africa, it features a deep roll with a symmetric profile; a design which yields exceptional strength and cost-effectiveness. The tile is available in five standard colours, terra-cotta, slate, brown, red and amber, and is aimed at large housing developments where costs are a major consideration. In addition to the new tile line, the plant boasts a new, fully automated fitting line for the production of ridge and rake tiles. This will ensure that there is an adequate supply of high quality fittings at all times.
A new strapping machine, recently installed at Infraset’s Rossway factory where various precast products such as concrete paving blocks and stadium seating are manufactured.
This example of the world’s largest paving block machine, manufactured by MASA in Germany, was recently installed in a new paving plant in Midrand, by paving block manufacturer, Cast Industries.
Irving says that during the first half of 2007 Marley’s existing plant at Ekandustria is being upgraded at a cost of R12 million to improve efficiencies and increase capacity by 20%. Commenting on the state of the concrete roof tile market he said that Marley anticipates demand shifting from more traditional markets to the affordable housing sector and that he expects only marginal growth overall. Marley Roo f ing has been awar ded ISO 14 001 : 2004 certification for its three roof tile factories, which are based in Gauteng and KwaZulu-Natal. Besides demonstrating its commitment to environmental sustainability, the benefits of operating under ISO 14001 : 2004 Environmental Management System (EMS) have assisted Marley Roof ing in r educing environmental risk, conserving input materials and energy, and helping it create a healthy working environment.
6 PRECAST VOL 1 JUNE 2007
CRB PLANT In anticipation of rising demand, Remacon Products commissioned a low-tech, labour intensive concrete retaining block CRB factory in 2005. The product line manufactures specialist concrete retaining wall blocks and erosion control systems. CRB walling is typically found in areas with sloping terrain, and besides retaining walls, often includes attenuation ponds and controlled storm water run-off. ReMaCon chief executive and vice president of the CMA’s CRB Division, Silvio Ferraris, said the CRB industry has grown in tandem with the overall demand for precast concrete products and by way of example he said that ReMaCon had increased production by 125% during the fourth quarter of 2006. “The new factory has created jobs for over 60 workers, all of whom are now multi-skilled. This is to everyone’s benefit; our workers have acquired several skills, making them more versatile and alleviating the monotony of doing the same job day-in-dayout. And from management’s perspective multi-skilling gives us far greater planning flexibility, enhancing our productivity and cost-effectiveness considerably.” Ferraris says ReMaCon is undertaking further expansion during 2007, specifically aimed at improving product handling efficiency. “The industry is demanding better quality as well as a more professional approach to retaining wall block structures. To this end, ReMaCon offers engineer design services which guarantee structural integrity. The quality of CRB mix designs and mould
modifications is improving dramatically as is the use of additives which yield improved early strengths f or better handling properties,” concludes Ferraris. P
Prestressed hollow-core concrete slabs, manufactured at Echo Prestress’ new factory in Durban, are offloaded and lowered into position at a 360m² office development in Mount Edgecombe, KZN. The slabs were installed in January shortly after the launch of Echo’s new factory.
Quality CONCRETE
PAVING PRODUCTS
Postal Address: P.O. Box 418, Halfway House, Midrand, 1685, South Africa Physical Address: 38 Spanner Road, Clayville, Ext. 11, Midrand Tel: +27 11 316 2375 | Fax: +27 11 316 2394 E-mail: castind@mweb.co.za
8 PRECAST VOL 1 JUNE 2007
Echo Prestress opts for Sika ViscoCrete-20HE Echo Prestress has introduced Sika ViscoCrete-20HE, a third generation concrete admixture for the production of prestressed slabs at its production plant in Chloorkop, Midrand. The strengths required by Echo Prestress were far exceeded during testing and allowed a reduction in cement usage. Echo Prestress required high early-release strengths without compromising on quality and this was easily achieved with the addition of the admixture. Sika ViscoCrete-20HE offers good flow rates as well as a homogeneous and stable concrete matrix. It achieves high densities, fewer voids and high strength due to a low water content. High durability is another benefit of a low water/cement ratio. It also of fers excellent waterproofing performance. Further advantages include reduced carbonation and chloride ingress - a direct result of reduced porosity. T he technology f acilitates economical stripping times for precast and in-situ concrete, ensuring that fast track, durable concrete with high density, high strength and reduced permeability is achieved. This faster turnaround of formwork results in higher output, improved surfaces and appearance, an d e ar l y r el e ase s tr eng ths f a cili t a t e quicker h an dling and transportation. Since its introduction, Sika ViscoCrete technology has been used globally for high early strength and self-compacting
A slip former machine in the process of casting Echo Prestress’ 200mm hollowcore prestressed floor slab.
concrete. The technology was developed in the mid 1990s and perfected in the early 2000s using polycarboxylates. For further information visit www.sika.co.za
P
Civil contractor growing its fleet of Manitous Durability was the main reason for the procurement of several Manitou rough terrain forklifts by Poort Beton, a company involved in civil works throughout Northern Cape Province. Poort Beton originally purchased a Manitou MC30 to load and unload bricks and other building materials on site. Within only a few months, the company decided to add a second MC30 to its range, citing quiet operation, ease of use and reliability as its main benefits. The MC range is designed to handle heavy, large and awkward loads in outdoor yards and on slippery or rutted surfaces. The MC30 masted forklift has a standard lifting height of 3.7m, and is capable of lifting up to 3t loads. Its four cylinder Perkins diesel engine, combined with a smooth transmission, makes for one of the quietest, most powerful and flexible machines in its field. Various standard attachments, such as tilting carriages for single or multi-forks and double sideshift carriages, mean these workhorses can cope with a very wide range of applications. Manitou’s success stems from the building industry, where its first machines quickly built a reputation as versatile, economic workhorses. The French company has since developed a full range of forklift trucks and access platforms suited to the needs of every branch of the building trade. P
Poort Beton director, Riaan Strauss, takes delivery of a new Manitou MC30.
PRECAST VOL 1 JUNE 2007 9
World expert to present at CMA paving seminar Professor Brian Shackel, of the University of New South Wales, Australia, will be lecturing on permeable paving during a seminar on concrete block paving (CBP) hosted by the CMA on 8th June in Midrand. The seminar is aimed at consulting engineers, landscape architects, local government officials, paving contractors and property developers. A world leader on all aspects of CBP, Shackel will focus on design elements and various applications of permeable paving, and will also elaborate on his computerised paving design programme, LOCKPAVE. South Africa was one of the first countries to adopt the programme which can be used for domestic and industrial applications, as well as airport aprons and runways. Professor Shackel is no newcomer to this country, having spent a two-year sabbatical on full-scale pavement research with the CSIR’s National Institute of Transportation and Road Research, and having visited on several subsequent occasions. Local paving experts, Professor Alex Visser and John Cairns will also be making contributions to the seminar which is free of charge. For further details and bookings contact Pam Zukor on (011) 805 6742 or via email at main.cma@gmail.com. P
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10 PRECAST VOL 1 JUNE 2007
concrete organisations – what they do and who they serve
The roles of three concrete industry organisations, the CMA, C&CI and CSSA, are not always clearly understood by the construction industry. What they do, who they serve and what their objectives are, remains mysterious to some, hence this article.
Concrete Manufacturers Association (CMA) The Concrete Manufacturers Association is the primary representative of the precast concrete industry. It initiates and applies standards in close cooperation with StanSA, and in close collaboration with its members, develops new products and services. The CMA is focused on growing the market purely for precast concrete. It promotes the cost-ef fective and correct application of precast concrete products, ensuring they are manufactured and installed to either StanSA or CMA standards. Its promotional activities target architects, engineers, developers, contractors and property owners through its six di v isions: Concr ete Masonr y; Concrete Block Paving; Concrete Roof Tiles; Concrete Retaining Block Walls; Precast Suspended Floor Slabs; and P.I.P.E.S. (Pipes, Inf rastructural Products and Engineering Solutions) Although the maintenance of minimum product standards is an important CMA function, its prime focus is on ensuring that its members’ products are applied correctly. A CMA mark ser ves as a guarantee of quality and the CMA takes responsibility should a problem arise. Member s ar e encour aged to hold the SABS mark or to manufacture to specifications laid down by the CMA. Should a problem arise the CMA will
carry out an investigation, and, if the product does not conform to the required standard, the member company is obliged to rectify the situation. Research is another important CMA function. Several new products have been introduced to the local market over the past four years, many of them aimed at previously disadvantaged communities, and all manufactured to standards offering durability and aesthetic appeal. The CMA also runs refresher courses and holds seminars to introduce new technology and methodology. These often feature overseas experts. A G a u t e ng - b a s e d r e p r e s e n t a t i v e is marketing CBP as a road sur face, especially in f ormer township ar eas. Roads built with CBP are labour intensive, generate employment and involve skills training that can be applied to other construction fields.
Cement and Concrete Institute (C&CI) T he C emen t and C oncr e t e Insti tu t e is a technical marketing organisation committed to growing the market for all forms of concrete by offering a range o f ser v ices to the southern A f rican b uil ding a n d c o n s t r u c t i o n in d u s t r y. These include marketing, information, t e c h n i c a l, e d u c a t i o n, r e s e a r c h a n d regulatory services. Members fall into three categories: P r o duc er s, A sso cia t e s, and Buil t Env ir onmental Pr of essionals. As the central marketing organisation for the South African concrete industry, C&CI aims to assist anyone involved in design and constr uc tion to r ealise the f ull potential of concrete. C&CI’s information centre houses an
extremely comprehensive collection of books, journals and technical reports. Access is free through personal visits, or by telephone, fax, e-mail or Internet enquiry. Most of the 40 C&CI publications are free of charge and a list is available online. A quarterly journal, Concrete Trends is also free on request. In dep en den tl y au di t e d s t a tis ti c s on national cementitious demand are published monthly. The annual Cement and Concrete Review summarises cementitious usage for the previous year, looks ahead at the coming year and provides a historical summary of demand. C&CI’s School of Concrete Technology offers courses in concrete technology ranging from introductory courses to the internationally recognised Advanced Concrete Technology course. City & Guilds International correspondence courses are also available, as are custom-made courses and continuing professional development programmes for civil engineers. Tr aining is o f f er e d in C ap e To w n, Durban, and Port Elizabeth and Midrand and can be arranged at suitable venues anywhere in southern Africa. The School has full NQF accreditation. The Institute’s members also sponsor c our se s f or s tuden t s s tud y ing ci v il engineering, architecture, building science and quantity surveying at universities and technikons throughout South Africa. Independent, professional technical services are provided for private and public sector clients. Consulting can take the form of advice, verification or investigation and Institute engineers are available for consultation by telephone, at C&CI’s offices or on construction sites any where in southern Africa. General technical advice is available through the free advisory service. C&CI undertakes industry research and development as well as coordinating
PRECAST VOL 1 JUNE 2007 11
all concrete research activities through its Research Advisory Committee. It oversees the review of existing concrete related standards and the introduction of new standards, ensuring the effective implementation of StanSA standards. More information is available from John Sheath on 011 315 0300 or the website on www.cnci.org.za
Concrete Society of Southern Africa (CSSA) The Concrete Society of Southern Africa is an independent, non-profit organisation that promotes excellence and innovation in the use of concrete and related products and services. Membership is open to anyone with an interest in concrete and CSSA provides a forum for networking and technology transfer between its members. The Society is affiliated to the American
Concrete Institute and the Concrete Society UK and, as a result, CSSA members qualify for special benefits from these organisations. T h e C S S A h o s t s th e p r e s tigi o u s ‘Fulton Awards’, staged every second year to honour excellence in concrete construction. Over the past 25 years, these awards have recognised Southern Africa’s major concrete projects and this event is well known and well supported by the entire Industry. Each of the Society’s four branches countrywide run their own annual calendar of events. These include technical meetings and seminars where inf ormation is disseminated among the members. The topics vary and depend on the availability of speakers. Where projects of interest are in progress, site visits are usually arranged. T hese ar e well a t tended and enable members to see concrete in action. On a branch level there are also the ‘Concrete Achiever Award’ and ‘Concrete Man of the Year Award’ which are presented to the individual or team of a particular
project worthy of recognition. During 2006 the Concrete Society was registered as a Voluntary Association of ECSA (Engineering Council of South Africa). As a result of this the Society is able to review and accredit technical talks and symposia and issue CPD certificates for members who attend these events. This is a great benefit for all our professional members. While CSSA provides a forum for sharing knowledge, a wide variety of social events are also arranged. The concrete boat race, golf days and year-end functions provide ample time for social interaction and networking. Apart from the concrete boat races, the concrete cube competition and egg protection device events are also very competitive, and involve many students. As such, these events encourage valuable interaction between Industry and new entrants to the market. More information from Irma Dyssel Tel: 012-809-1824 or the website on www.concretesociety.co.za P (CSSA text supplied as above)
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Why concrete paving blocks discolour By Nick Doulgeris Although relatively rare, under the right conditions, staining can and does occur on the surface of concrete paving blocks. This article examines research as to the possible causes of discolouration and postulates the prolonged presence of moisture, ef florescence and alkali-aggregate r eacti v ity ar e the main contributing factors. Fortunately, discolouration is only an aesthetic aberration which, over time, may disappear through normal attrition and weathering.
Photo 1 THE PROBLEM For more than two decades sporadic inciden ts o f c oncr e t e p a v ing blo ck s
discolouring have been reported; mostly black, it was observed countrywide. In some cases the causes were easily determinable, for example, when red clay was deposited into the surface cavities of paving blocks, but in others they were illusive. Although several possible causes were cited, including the use of fly-ash waste, variable manufacture, and the contamination of aggregates, it appeared that in all cases the process was heavily dependent on the presence of moisture. The following observations on discolouring were made: • It could occur with a certain degree of consistency in small or large patches, or randomly on individual pavers surrounded by perfectly sound blocks, and in other instances, only on portions of individual blocks. • E n t ir e sur f a c e s w e r e n o t a l w a y s discoloured, in some cases the staining took on a mottled appearance and in many cases only the tips of protruding surface aggregate were affected (see Photo-2 and Photo-3). • Staining was noticeable usually within six months after laying and occurred in trafficked as well as non-trafficked areas. • T he st aining consist ed o f a har d, glossy coating which was attached to par ticles of aggr egate and was ver y difficult to remove, either chemically or physically. Some investigations reported that it could be scratched off using a steel needle. One solution, which proved aesthetically acceptable, was the relaying of blackened pavers randomly among unaffected blocks. INVESTIGATIVE WORK Following a request from a contractor who laid domestic driveways in an area close to an industr ial bel t sou th o f Johannesburg, a detailed investigation was initiated in 1990. The work involved the PPC and PCI laboratories as well as the universities of Durban-Westville, Witwatersrand, and Pretoria. Possible
causes were investigated, many of which were eliminated. The more significant of these are listed below. Rubber In many instances, black staining occurred on the top of protruding aggregates, and because these surfaces are abrasive, it was initially concluded that black staining was caused by deposits of tyre rubber. However, this did not explain why nontrafficked areas, including isolated pavers situated in drains or immediately adjacent to buildings etc, were also discoloured. Furthermore, a wide variety of rubber solvents could not remove the staining. ATMOSPHERIC POLLUTION Air and rainfall pollution should have affected all pavers equally i.e. entire surfaces. COAL AND BIOTITE MICA Some aggr ega t es used in the “ Vaal Triangle” area were contaminated with small particles of coal and biotite mica. A few manufacturers were also reportedly using dump ash. It was suggested that as the surface wore down, coal and mica particles would smear and darken the surface. This should have af fected all pavers under similar traffic conditions, but it was not the case. A microscope revealed that the particles remained equally intact within and adjacent to the stained areas as well as in un-stained pavers. Although the presence of the particles may have contributed in a small way to the blackening of some pavers, their presence is believed to be irrelevant to the mechanism of staining. This conclusion is backed by the fact that staining has occurred in other geographical areas where these minerals were not present. ALGAE Professor Baecker of University of Durban West ville-in K ZN pr oved conclusively that there were no organic substances present.
14 PRECAST VOL 1 JUNE 2007
PIGMENT Research by the PPC Laboratory showed that pigments used remained inert. NATURAL WEATHERING Some researchers believed that with time, normal weathering exposed darker underlying aggregate particles thus making the surface appear darker. Again, this should then have occurred similarly on all paving blocks. From the above, two main theories were proposed. 1. UNIVERSITY OF PRETORIA Mrs SMC Verryn (Department of Geology) conducted a number of tests on the staining and reported it was more concentrated in areas which appeared to be more porous than the rest of the block. This observation is believed to be very pertinent to the problem. The dark stain on the tops of the surface aggregates were subjected to X-Ray and qualitative electron microprobe analysis. The following main elements were detected – Ca, Si, Al, Fe, Mg, K and Ti. It was reported that the most abundant material present was calcite (calcium carbonate) which is not unexpected as Lime Bloom (carbonation of the free lime or CaOH2) is commonplace and had been observed to have taken place in most staining incidents. The presence of certain minerals as well as minute dirt particles (such as those held electro-statically on a T V screen) reportedly accounted for the dark colour. As mica was known to be present, it was assumed, perhaps erroneously, that this was the origin of the silica. If the dark particles were encapsulated in what was predominantly calcite, then it should have been relatively easy to clean the staining using dilute acid, but this wasn’t the case. 2. BAYER PIGMENTS Other research conducted by Dr Puttbach of Bayer AG in Germany [3], indicated that the staining was a consequence of what he termed silica efflorescence, better known as alkali-silica reactivity or alkaliaggregate reactivity. This interpretation w as c on f ir me d b y P r o f e ssor R oland Merkle of the University of Pretoria. The resultant silicates produce a hard, glossy insoluble gel which coats all particles (including calcite) in the reaction zone. This would explain the difficulty in stain removal (sodium silicate is sometimes used as a floor hardener). This report
again mentioned that the hard, perhaps brittle, layer could be scratched off using a steel needle. However, for such a chemical reaction to occur, the following conditions had to be met: • The presence of a reactive type of aggregate, usually strained quartz. • A high alkali presence, usually derived from the cement. • The prolonged presence of moisture. At that time it was considered unlikely that all these conditions would be found within concrete paving blocks. DISCUSSION It is rar e f or the semi-dr y concr ete mixture used in the manufacture of South African paving blocks to contain more than about 350kg/cu m of cement as only 25MPa and 35MPa paving blocks are specified (overseas 60MPa and 70MPa is the common standard) and the alkali content of all South Af rican cement types is generally held below a 6.0% Na2O equivalent. Concrete block paving is segmented and normally facilitates good drainage, particularly in earlier stages of its life cycle. From the above, initial expectation w o uld b e f or A SR r e a c ti v i t y n o t t o occur. However, the following should be considered: • Some contractors use plastic sheeting under block paving and, depending on gradient and the quality of the bedding sand, this can act as a water reservoir for considerable periods of time. • Concrete paving blocks produced in South Africa are generally porous and therefore, under the right circumstances, are more prone to efflorescence. This me ans tha t soluble c ons ti tuen t s, particularly the highly soluble alkaline products of hydration, are brought to the surface by capillary action. • A semi-dry concrete mixture is used in the manufacture of concrete block pavers. As it is not practical to allow the pavers to cure, the potential exists for limited initial hydration to take place. If the paving blocks are hydrated after laying, say by rain, more of the alkaline material will be brought to the surface through efflorescence. • Photographic evidence shows that in almost every case staining is accompanied by efflorescence. The occurrence and/ or ex tent of ef florescence is largely dependent on the internal structure of the concrete (void and capillary systems). One of the most difficult tasks in paving
block manufacture is to obtain uniform compaction throughout. By observation and from detailed laboratory investigations, it has been shown that very significant variations in density can exist, not only between individual paving blocks, but also within an individual block. This factor explains how only part of an individual paving block can be stained and how mottled staining can occur (see Photo-2). In the latter case one such paving block was studied in more detail. The mottled stain areas were outlined in pencil and then subjected to an initial absorption test in which the block’s bottom surface was submerged in water. Surprisingly only the stained areas absorbed moisture, and within a very short time. The internal structure below these areas must have been perfect for this to occur. • Photo-4 shows calcite at the top of the surface particles, evidence that soluble salts have been drawn into the surface particles by surface tension and remain on the surface after water evaporation has taken place. With continuing efflorescence, the concentration of alkalis on the top of surface particles becomes greater and more prolonged. • If alkali reactive silica or argillaceous dolomitic limestone material/aggregate is present, alkali-silica or alkali-carbonate reactivity is possible under the conditions mentioned above. Further, Messieurs H Wang and JE Gillot [2] report that this reactivity is enhanced by the presence of free lime (calcium hydroxide). Calcium hydroxide acts as a buffer maintaining a high concentration of hydroxyl ions in pore solutions (high pH). The calcium ions gradually replace the more soluble K and Na ions (derived from the cement) in the silicate salts thus liberating these more soluble ions and allowing further reaction to take place with reactive silica. As the top surface of reactive aggregate is (increasingly) the most alkaline, it is not surprising that most staining occurs here. • The question remains whether the prolonged presence of moisture is possible. The absorbed moisture content within paving blocks will depend on their internal structure, the size of the inter-connecting pores and channels together with ambient weather and other local conditions. These same properties also affect the rate of moisture gain as well as the rate of moisture loss. It has already been stated that the practice of using plastic sheeting beneath
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16 PRECAST VOL 1 JUNE 2007
Photo 2
Photo 3
paving blocks inhibits rapid drainage. During manufacture moulds are not filled with a level of consistency that prevents: variable degrees of compaction; variable voids; variable capacity for absorbing and holding water; and variable capacity for efflorescence. This is clearly evident by observing a paved area after a rain-storm (see photo -5). Here it will be noticed that the voids can vary within individual paving blocks. Some paving blocks have been observed to retain moisture for more than 48 hours, especially in shaded areas. • Photo-6 and Photo-7 show a flagstone and a concrete slab both of which retain moistur e suf f iciently long enough to permit organic growth during the rainy season. There are many such examples available. In Photo-6 the flagstone on the right is sub-standard and porous and remained damp for up to three days after a rain storm. In Photo-7 the sloping roof deflects the slightest rain water and even night dew to a central area (see insert). Photo-5 shows that even with exposure to the sun and wind, some paving blocks are still very wet after a period of 48 hours. Some manufacturers use a weathered granite aggregate which contains a high proportion of unsound particles and which can absorb over two or three percent of water. During the rainy season these areas could remain damp for months even if it rained only every two or three days. Also if a reactive strain of quartz aggregate were present, alkali-reactivity would certainly be possible. Therefore there appears to be a strong correlation between staining, the severity of successive rainy seasons, and/or the dampness of site conditions. • The paving blocks depicted in Photo-5 were laid during the dry winter of 2005 and photographed towards the end of the 2005/2006 summer rains. Photo-8
shows the same paving blocks at the start of the 2006/2007 summer rains. It can be seen that those blocks which retained moisture for longer periods are the ones that have discoloured. Careful examination of Photo-5 and Photo-8 shows that staining had already started during the first rains after laying. In conclusion, there are a few points worthy of mention. • Based on past per f ormance, it is desirable that a better quality of paving
block is specified. Whilst 25MPa and 35MPa paving blocks may be acceptable from the point of view of traffic loading requirements, their long-term durability is not assured, especially in terms of wear resistance. Durability is greatly enh an c e d b y imp r o v ing c omp a c ti o n . Although full compaction is not essential and is comparatively difficult to achieve, manufacturers should strive to produce the densest possible paving blocks with the available materials and equipment, at least to the degree that internal voids and capillaries are not interlinked. This will enhance durability and reduce the potential for discolouration. Suitably dir e c t e d r e se ar ch w ill b en e f i t b o th supplier and user. • Vaal River sand is extensively used t h r o u g h o u t t h e “ Va a l Tr i a n g l e” a n d beyond. More testing for alkali-aggregate reactivity of such siliceous material is indicated. Perhaps this should also include specific dolomitic aggregate as several investigators reported that a dark brittle coating ex isted on dolomite sur f ace particles. They attributed the staining to the presence of these dark particles.
Photo 4
Photo 5
Photo 6
Photo 7
PRECAST VOL 1 JUNE 2007 17
This might suggest that alkali-carbonate reactivity might have taken place even though Oberholtzer [1] reports that until 1986 there were no reported incidents of such reactivity taking place in South Africa. Further research is essential to confirm the fact that alkali-aggregate reactivity has indeed taken place and it is suggested that the best starting
Photo 8
point will be to analyse the glossy stain coating itself. • In the mid-1980s a decision was taken by the majority of manufacturers in favour of producing smoother concrete paver finishes, especially as this would enhance the appearance of coloured paving blocks. To achieve this it became necessary to use more finely graded aggregate. This in turn made it more difficult to adequately fill the moulds and resulted in lower densities, higher voids and a tendency for efflorescence to take place. • Verryn [7] reports that certain minerals and impurities will cause calcite to turn black. Note that the waste dump ash from Lethaba Power Station is highly mineralised. • The problem sites in the “Vaal Triangle” area were re-visited in March 2006 after a period of 16 years. Although there was still evidence of slight staining at some sites, at others, which were previously stained, no staining could be detected.
Early laboratory tests had shown that the staining could only be removed if the surface was physically damaged. This seems to be precisely what has happened naturally over time by normal trafficking and weathering. As staining was confined to the tops of the protruding aggregate, it only remained for the top layer particles to be removed for the staining to be removed. This may not necessarily apply to other sites which were not re-visited. P R eferences - [1] Oberholster R E Alkaliaggregate reaction – Fultons Concrete Technology 1986. [2] Wang H and Gillot J E Mechanism of Alkali-silica reaction and the signif icance of calcium hydr oxide. Cement a n d C o n c r e t e R e s e a r c h . Vo l 21. C a l g a r y, C anada 1991. [3 ] Technical Repor t B ay er AG “Discolouration of pavers” 28/02/94.[4] Technical Reports Portland Cement Institute. [5] Technical Report Pretoria Portland Cement. [6] Technical Report Grinaker Precast (Pty) Ltd. [7] Technical Report Department of Geology University of Pretoria.
20 PRECAST VOL 1 JUNE 2007
Litigation on failed pipelines looms - North American expert Gerrard F. Mulhern, Vice President of the North American company, Hanson Pipe
the ACPA Marketing Committee and is
and Precast, was in South Africa during
an associate member of the Technical
October last year at the invitation of the
Committee for Non-Pressure Plastic Pipe
Concrete Manufacturers Association
of the Canadian Standards Association.
(CMA). He participated in three seminars
He is also a former member of the board
on inf rastructural piping which were
of directors of the Corrugated Steel Pipe
attended by civil and municipal engineers
Institute of Canada.
and contractors. A leading authority
on gravity pipe products, he has wide-
Galway, Ireland, in 1979 with a Bachelor
ranging expertise on several dif ferent
of Engineering in Civil Engineering.
types of infrastructural piping including
Following P.Eng graduation in Ontario he
corrugated metal, HDPE, and concrete.
worked as a municipal engineer in Ireland
He graduated from University College
before moving to Canada in 1981.
The seminars were held to provide
South African engineers with information
Mulhern is responsible for all aspects
on the attributes of both rigid concrete
of Hanson’s technical marketing and
Ltd, later known as Armtec Ltd, and
In 1982 he joined Armco Canada
and flexible plastic piping and were based
promotion in the north-eastern United
progressed to vice president of Sales
on the theme “Protecting Yourself as a
States and in Ontario, Canada. The
and Marketing. Armtec is the largest
Gravity Pipe Designer”. Mulhern spoke
company is a world leader in building
pr oducer of corrugated steel pipe
about the technical and per formance
materials and is one of the world’s
products in Canada and is also that
related dif ferences between rigid
largest producers of concrete gravity
country’s largest producer of profile
c o n c r e t e p ip ing an d f l e x ib l e p l a s ti c
and pressure pipes. He is a member of
HDPE products.
piping and how South Africa was likely to follow the North American example of suing contractors and engineers for pipe systems that fail.
During his stay here he also delivered
a paper “Protecting Yourself as a Gravity Pipe Municipal Engineer” at the IMESA conf erence. T he paper was very well received and earned an award as the best non-member paper.
Not all pipes are created equally says
Mulhern and treating them as such leads to product failure, huge expense and possible litigation.
“Most engineers and contractors in
North America and probably South Africa as well, don’t understand the difference between a rigid concrete pipe, which is both a structure and a conduit, and a flexible plastic pipe, which is only a conduit Interlocking concrete pipes, 1 650mm in diameter, are offloaded for installation in a main storm water pipeline in Pretoria.
and for which the structure has to be built on site,” he says.
PRECAST VOL 1 JUNE 2007 21
“The whole purpose of my visit was to
bring a global perspective on infrastructural piping so that local specifiers would be better able to make informed decisions on pipe selection. It should also help protect them against possible future litigation. The USA and Canada are very litigious societies and professionals are getting sued for pipe failures. The same is likely to happen here, especially within the framework of the Occupational Safety Health Act (OSH Act).
“I get the impression that the legislation
is in place in South Africa but in many instances is not being adhered to.
“One of the ways of saf eguar ding
against failure and subsequent litigation is the simple deflection test. Municipal engineers who don’t specify some form of deflection testing are operating on a wing and a prayer, hoping the contractor is going to do the job properly. Almost all the delegates who attended the seminars said that deflection testing did not form part of pipe trenching specifications.
Gerry Mulhern (left), vice president of the North American company, Hanson Pipe and Precast, and Danie Greeff, vice president of the CMA P.I.P.E.S Division, demonstrate a point at a pipes seminar held in Midrand last year.
“Both Mandrel and infra-red testing
force the contractor to lay pipes properly.
diameter of 1 800mm then the differential
“A flexible manhole coupling is required
Mandrels are very simple to use and are
is 36mm. This will let a lot of water escape
to take up that deflection. The problem
deployed widely across North America.
unless the joint has the capacity to take
with grouting flexible piping into manholes
Laser technology is newer and is available
up that kind of differential.
is that when deflection occurs the grout
in South Africa.
“I am surprised that there are no
cracks and breaks up. This represents a
“D e f l e c t i o n t e s t i n g i s e s p e c i a l l y
flexible water-tight couplings for joining
potentially huge area for future pipe failure
im p o r t a n t f o r P V C, H D P E a n d G R P
flexible piping to manholes in this country.
in South Africa,” observes Mulhern.
(f lex ible) piping because 95% o f the
In the USA they have existed for many
strength of a flexible pipe comes from the
years and there is certainly a need and
grow th in the use of HDPE piping on
soil. If a pipe deflects more that 5% it has
a commercial opportunity for them here.
Nor th American inf rastructural pipe
not been installed properly. Obviously, the
Grouting is the correct procedure for
installations.
higher the deflection rate the shorter the
connecting concrete piping to manholes,
service life.”
wher eas gr outing f lex ible pipes into
for agriculture, and, with small loads it
The past 10 years have seen significant
“HDPE piping was first used as tubing
Mulhern also cautioned that engineers
concrete manholes, as is done over here,
works very well. Then the manufacturers
should be very careful about the types of
sooner or later results in failure through
started to increase diameters and this
joints that are available on different piping
deflection.
introduced an entirely different set of
materials in South Africa, because this is where failure is most likely to occur.
“Engineers need to educate themselves
on PVC, HDPE and GRP joints because all flexible pipes are designed to deflect. “Take an example where two flexible pipes are joined. If the one pipe deflects 3% and the other 5%, it creates a 2% differential. Assuming that the piping has a
They tend to fall into the trap of thinking that because flexible piping is lighter it is easier to install
laying parameters. What works well with pipe diameters up to 150mm does not necessarily apply to larger sizes. “Flexible and corrugated metal piping have their place, but specifiers need to understand what the appropriate applications are. They tend to fall into the trap of thinking that because flexible piping is lighter it is easier to install.
22 PRECAST VOL 1 JUNE 2007
substandard and has a higher risk of
Society for Testing and Materials.
install incorrectly, but it’s very difficult to
ultimate failure and collapse.
install correctly. Part of my presentations
“Ohio’s D ep ar tmen t o f Tr ansp or t
what one does, but what one fails to do, and
in South Africa included information on
provided 13 pipe installation sites for
I suspect the same applies in South Africa.
correct installation procedures for plastic
examination. Of these, 12 were found to
The main point here is that one must make
piping. T his includes trenching which
have deflections greater than 5%. There
the right decision with the host pipe. If not,
is one of the most hazardous construction
was also evidence of buckling, cracking and
the consequences both in terms of expense
practices.
disjointing. Looking to the USA as a whole,
and ruined reputations can be punitive.
“O n e o f t h e m aj o r d i f f i c u l t i e s i n
some 39 installations were inspected in
installing flexible pipes is adhering to
2000. Twenty six had deflections greater
un d e r s t an d c o n c r e t e, b u t v e r y f e w
safety standards and regulations while
than 5%.
understand plastics.
following installation specifications. One
or the other is generally compromised.
Departments of Transportation in the
Africa we asked the audience a series of
“C o n c r e t e p i p i n g i s a r e i n f o r c e d
United States are subject to a lot of lobbying
questions:
structure with built-in strength. It is much
pressure from different industry sectors.
• How many people have ever taken a
less dependent on embedment material
However, when we make presentations to
course on cement?
than a flexible pipe. Because of its rigid
consulting engineers and municipalities in
• How many people have ever taken a
“That’s simply not true. It’s easy to
“One must recognise that the State
One of the major difficulties in installing flexible pipes is adhering to safety standards and regulations while following installation specifications
“Litigation in the US involves not only
“We have found that most engineers
“During each of the seminars in South
course on concrete mix design? • How many people have ever taken a course on reinforced concrete design?
“Significantly more than 50% of those
in attendance answered positively to all three questions.
“We then posed further questions:
nature, contractors don’t incur the same
the US they take notice immediately, in
• How many people have ever taken a
sort of difficulties with concrete pipes
large part because American society is
course on plastic raw materials?
as they do with the proper installation of
litigious and because of issues pertaining
• How many people have ever taken a course
flexible pipe products. These difficulties
to professional liability.”
on structural design of plastic pipe?
become even mor e pr onounced when
working in trenches.”
recent case of plastic pipe failure on a
who attended these seminars answered
By way of example Mulhern cited a
“Only two of the over 200 people
storm drainage system.
the first question positively and nobody
that plastic piping is supposed to have a
responded positively to the second.”
lifespan of up to 50 years, problems and
West Virginia, an engineering company,
pipe failure were already apparent after
an HDPE plastic pipe supplier, and an
are presented with a glossy piece of
comparatively short lifespans.
installation contractor. Six years after
literature in which, in most instances,
“The whole 50 year assumption is based
the installation of the drainage system the
the relevant information they require is
on piping being installed properly. During
pipe was found to be collapsing. Expensive
not included; certainly not in the brochure
the seminars I quoted some figures from a
remedial work was required. The developer
material that I have studied in South Africa.
study conducted by a forensic engineering
sued the pipe manufacturer who in turn
It’s very impressive at first glance, but
company on the performance of plastic
sued the engineering company and the
crucial aspects are missing. So part of
piping over the past 10 years in the US.
contractor.
my task here was to advise local engineers
The figures, which were published by the
“The developer brought in an expert on
about the type of information they need to
American Concrete Pipe Association,
plastic piping, Dr Ernest Selig, a professor
seek. Once they understand the structure
relate to the state of Ohio and the country
from the University of Massachusetts.
versus the conduit aspect they tend to be
as a whole.
He said the combination of the pipe
a lot more comfortable with concrete,”
“As mentioned earlier one of the criteria
profile design and the pipe material was
comments Mulhern.
f or the installation of thermoplastic
the cause of the failure. The HDPE pipe
piping, such as HDPE or PVC, is that
manufacturer maintained that the failure
peace of mind, concrete is the route to go.
deflection should be no greater than 5%
was the r esult of poor construction
We can’t afford to have reworks in South
after installation; any deflection greater
practices and a f ailure to adhere to
Africa. Whatever we do must be done right
than this is regarded as deficient or
requirements laid down by the American
the first time.”
Mulhern said that despite the fact
“It involved a developer from Charleston,
“What often happens is that engineers
“If you want value for your money and
P
24 PRECAST VOL 1 JUNE 2007
Concete roof tiles the most economical and best looking roofing material Concrete roof tiles are still the most
cost-effective roofing material for roofs
pitch and truss spacing, among others,
built with trusses - a conclusion based on
as well as cost factors such as truss and
an updated survey coordinated on behalf
timber sundries, roof erection, roofing
of the CMA by roofing specialist, Victor
material and f i x ing, wer e taken into
Booth Pr Eng. – an independent consulting
account. Prices were based on complete
engineer.
roof structures, however, fascia boards
The timber framework of a typical example of The CMA Roof System is subjected to stringent load testing prior to receiving an Agrément certificate 2003/302.
Factors such as floor area, roof area,
First conducted in 2003, the latest
and gutters were omitted from the survey
survey used data gathered in February
because these are optional items which
this year from many sources. It focused
make no difference to the costing. Likewise
• Labour costs for the erection of the
on three building models, a 57m² (floor
no pr ov ision was made f or underlay,
timber structures and the fixing of the
a r e a ) h o u s e, a 13 4 m ² h o u s e a n d a
membrane or ceiling construction.
roof covering material are included in the
1 158m² commercial building. The results
cost comparison.
of each has been published by the CMA in
simplify the cost models. For instance,
• General sundries exclude fascia boards
three leaflets, one for each model.
while some housing developments comprise
and barge boards.
CMA director, John Cairns, said the
many units and developers/contractors
• The cost of gable masonry has been
survey assessed complete roofs built with
can negotiate special project discounts,
excluded as it is constant for all roofs.
trusses which allow for the inclusion of
the majority of builders construct one-off
• The rates exclude VAT.
ceilings and underlays, and in each case
houses and are therefore obliged to source
• Waste is included in all calculations.
concrete tiled roofs proved the most cost-
roofing materials from their local suppliers
effective material.
at less advantageous prices.
models f or concr ete tiled r oo f ing in
the 57m² house category, one using a
“An increasing number of low-cost
Certain assumptions were made to
The survey takes the following into
Concrete roof tiles are laid using The CMA Roofing System.
The updated survey focuses on two
housing developments are using roofs
account:
conventional concrete tiled roof, and the
built with trusses as they have better
• Roof truss prices are based on standard
other deploying a roof using The CMA
insulation and aesthetic properties and
industry pricing practice.
Roofing System. The latter, which has been
ultimately, make for much sounder long-
• All costs are based on Februar y
awarded an Agrément certificate, was
term investments,” observes Cairns.
2007 figures.
introduced two years after the first survey
PRECAST VOL 1 JUNE 2007 25
to make concrete tiled roofing even more affordable, and the results of the current
The Golf Course Ext Development, an affordable housing initiative adjacent to the King Williams Town Golf Course, in the Eastern Cape, the first housing project in which the recently introduced CMA Roofing System was used.
survey confirm this.
Alumaz natural slate at a cost of R514.
would be an architectural design feature
of the building.
The R/m² costs for a concrete tiled
Certain assumptions were made to
roof on the first model at R187 are 11%
simplify the costing model for the office
lower than the next most cost-effective
building. For instance the floor area of
demonstrates is that property developers
material, corrugated iron sheeting at
1 158m² was chosen arbitrarily and has no
can have the best of both worlds on roofs
R209, whereas, the R/m² costs for the
special significance other than being fairly
built with trusses–attractive roofs which
model using The CMA Roofing System are
representative of architectural practice.
enhance the value of r esidential and
17% lower at R179. The first model was
The roofs were all pitched at 26º as it
commercial property at the most cost-
also compared with other materials such as
was felt that in most circumstances this
effective prices.
corrugated fibre cement, pre-painted IBR metal sheeting, and pressed metal tiles.
The survey revealed that a conventional
concrete tiled roof at R187 costs 20% less than the R232 of corrugated fibre cement, 21% less than pre-painted IBR metal sheeting at R235, and 35% less than pressed metal tiles at R287. Pre-painted metal sheeting, pressed metal tiles, fibre cement slate and Alumaz natural slate were the materials selected for comparison with through-colour concrete roof tiles on the 134m² house and the 1 158m² office building.
The R/m² costs on concrete roof tiling
for the house at R228 was eight percent lower than that of pre-painted IBR sheeting at R248. They were 27% lower than the R311 of pressed metal tiles, 46% lower than fibre cement slate at R355, and 50% lower than Alumaz natural slate at a cost of R448.
The R/m² costs on concrete roof tiling for
the office building at R288 were 13% lower than that of pre-painted IBR sheeting at R329. They were 21% lower than the R362 of pressed metal tiles, 32% lower than fibre cement slate at R421, and 44% lower than
Cost comparison on a 57m2 house.
Cairns says what the survey clearly
P
26 PRECAST VOL 1 JUNE 2007
PRECAST VOL 1 JUNE 2007 27
Precast concrete
delivers on social upliftment A broader range of products and systems designed to
low-income housing units, was introduced.
serve all sectors of South Africa’s diverse communities
has been the prime focus of the CMA and its members
mono-pitch configurations, was developed by the CMA
during the past six years.
with engineering input from Victor Booth, a well known
The Association has met with considerable success
independent roofing consultant. Its development has
in improving quality of life, especially for historically
culminated in the awarding of the prestigious Agrément
disadvantaged communities (HDCs), be this through
certificate by Agrément South Africa.
economic housing development, the paving of gravel
roads in townships, improved sanitation and running
concrete tiling generally makes for the best form of
water, or through the construction of community
roofing, it is still perceived as a more expensive option.
centres such as schools and clinics.
The system, which is available in either dual-pitch or
Cairns says although it is widely accepted that
“When deployed in The CMA Roofing System,
Precast concrete is a multi-billion rand industry
however, roofs covered with concrete tiles are not
employing hundreds of thousands. It is the country’s
only the most attractive and durable solution, but the
single largest user of cement and is contributing
most cost-effective as well. Furthermore, houses built
significantly to new capacity in skills and plant.
with concrete roof tiles have higher market values than
CMA director, John Cairns, says while the CMA
those roofed with low-cost materials such as steel
strives to ensure that the South African consumer
sheeting. They also make a greater impact on pride of
has access to an exceptional choice of high-quality
ownership and self-worth, very important factors in
precast concrete products, systems and services,
the transformation process,” notes Cairns.
the curr ent f ocus is on addr essing the needs
of HDCs.
Roofing System are some specially designed timber roof
The secret behind the development of The CMA
“The HDC strategy and that of our members entails
trusses, which have been thoroughly tested to meet all
the introduction of affordable systems based on
the technical requirements of Agrément South Africa.
precast concrete products, and, wherever possible,
Sample roofs were subjected to stringent tests, one of
the stimulation of job creation.
which entailed trusses being loaded with more than twice
“Several innovative products and systems have
their total design capacity and nearly four times their
been introduced as a result of precast concrete
working load capacity, far in excess of what would normally
manufacturers’ initiatives. All aimed at the mass
be applied. No measurable movement was detected.
market, the products retain the inherent qualities of
manufactured concrete at prices which are affordable
System is of course the concrete roof tile. These are
at market entry levels.
supplied by CMA members and the standards which
The other major component of the CMA Roofing
T hese include a new r oof ing system, a new
foundation and flooring system, precast toilets, and concrete masonry,” says Cairns. QUALITY ROOFING MADE AFFORDABLE Until two years ago concrete roof tiles were used exclusively on middle and upper-income housing, the prevailing perception being they were too expensive for economic housing units. Then in 2005, after two years of research and product development, The CMA Roofing System, a high quality roofing system using concrete roof tiles aimed specifically at affordable and
This low-cost housing development is considerably enhanced with the installation of concrete-tiled roofs and concrete masonry.
28 PRECAST VOL 1 JUNE 2007
apply in the manufacture of these tiles are on a par with the world’s highest. T iles produced by CMA members are subjected to stringent quality standards based on a new South African standard specification which was approved by the
Engineers must ensure that the trusses are manufactured and roofs erected in accordance with these standards Agrément certificate.
of building af f ordable houses in poor soil conditions.
national committee StanSA TC 5120.61
“Both the video and the booklet can
Construction Standards in accordance
be used to train semi-skilled and unskilled
with procedures laid down by Standards
labour and we anticipate that the training
State, where to date 50 houses have been
South Africa in 2004.
material will be used mainly on turnkey
constructed. These have been monitored
The system is being tested in the Free
E ngin e e r s m u s t e n su r e t h a t t h e
projects in which communities become
for the past three years and have
trusses are manufactured and the
involved in building their own houses,”
compared very favourably with adjacent
roofs erected in accordance with these
explains Cairns.
houses built with conventional strip
standar ds and ever y completed r oof
footings and in situ concrete slabs.
carries an engineering certificate.
exclusively marketed as a complete roofing
“The results are impressive and we
Cairns notes further that the idea
package by CMA roof tile manufacturers
are confident that the requirement for
behind The CMA Roofing System is to not
and the training material forms part of
a stable and cost-effective alternative
only provide a high quality concrete tiled
this exercise.
to building in these conditions has been
T he CMA Roofing System is being
realised. The system offers the additional
roof for low-cost housing developments but also the transfer of skills for the
NEW FOUNDATION SYSTEM FOR LOW-
a d v a n t a g e o f q u i c k e r c o n s t r u c t i o n,
creation of employment opportunities. It
COST AND AFFORDABLE HOUSING
consistent quality and a guaranteed
was with this in mind that the Association
One area in which the precast concrete
product,” observes Cairns.
produced a training film (on CD) and a
industry has been particularly successful
booklet to be used as ‘how to’ guides
in creating more affordable manufactured
SANITATION
for the erection of roofs using the CMA
concrete products, is in the prestressed
CMA member companies have been involved
Roofing System.
hollow-core concrete slab.
with providing concrete toilets for both
Available from the CMA at no charge,
One of many applications is a new
rural and squatter communities. These
the CD demonstrates how to construct
foundation and flooring system which
are contributing to a healthier environment
a roof correctly with a span of 6.6m,
will provide an innovative and economical
and are assisting with the Government’s
the maximum allowable in terms of an
approach to overcoming the hazards
drive to bring water and sanitation to all South Africans.
“Other forms of toilet structures such
as brick, corrugated iron and modular concrete do not offer the performance of the one-piece precast concrete structure, and require higher levels of management during construction, not to mention ongoing maintenance.
“One o f the major ad v an t age s o f
precast concrete toilets is that they are six times quicker to install than toilets erected onsite with panels and the rate of manufacture at the factory is also quicker,” says Cairns. CONCRETE MASONRY Two CMA members, Western Cape-based False Bay Bricks and Columbia DBL, have CMA representatives Queen Zondo and Solomon Nkosi examine a recently completed road in the Free State surfaced with concrete block paving.
30 PRECAST VOL 1 JUNE 2007
achieved a major breakthrough in the use of concrete blocks for economic housing. Both have gained NHBRC approval for the thermally-efficient single-leaf hollow-core 140mm concrete block which can be used
South Africa is one of the world leaders in the deployment of concrete block paving (CBP)
without plastering.
characteristics of concrete blocks in order
popularity of the 140mm block. The unit is
Cairns says rigorous testing by the
to ensure consistent thermal resistance
very economical to manufacture and gives
South African Bureau of Standards (SABS)
values and comply with the NHBRC’s
the best labour and layout efficiency.
on blocks submitted by the manufacturers
monitoring requirements.
has demonstrated conclusively that they
Cairns notes that although the 140mm
has similar performance attributes and
comfortably exceed the NHBRC’s thermal
hollow concrete block is the most widely used
certain advantages over its larger sibling
performance requirements for concrete
masonry unit for low-cost and affordable
indicates that demand for the block is likely
masonry in single-leaf walls and don’t
housing in the country, prior to the SABS
to strengthen, especially in the wake of
require plastering for additional thermal
tests very little work had been done to
these tests,” notes Cairns.
insulation.
establish a thermal properties standard.
However, Cairns observes that a suitable
It was mainly a concern about
STIMULATING EMPLOYMENT
waterproof coating is a requirement to
condensation, especially in the Western
The CMA and its members have had some
meet the NHBRC standard for building with
Cape, which prompted the NHBRC to call
notable successes in job creation, having
these thermally efficient blocks. To this
for the tests. Condensation causes mould
been particularly successful with concrete
“The fact that a less expensive block
paving, although concrete masonry (see above), concrete piping and concrete rail sleepers have also played a significant role in this regard. Concrete paving South Africa is one of the world leaders in the deployment of concrete block paving (CBP). Over 10 million square meters are laid annually, nearly all by hand. Unskilled people can be trained to lay concrete blocks with a high degree of workmanship and the CMA is actively promoting its wider application. Two hollow-core concrete block panels shortly before undergoing a thermal performance test.
“Besides its labour intensive and job
creation attributes, CBP has proved to be
end CMA member, Techfin, has developed
growth which is unhealthy and the thermal
very durable and aesthetically appealing.
a suitable waterproof skin which has been
properties of walling material is a factor
We are promoting its use in areas where
granted Agrément certification and meets
which affects condensation. Based on the
traffic density is high, for example at traffic
the NHBRC’s requirements.
thermal model of a clay brick ‘standard
interchanges, or where it enhances visual
“This is a landmark decision for it not only
house’ the NHBRC recommended certain
appeal, such as in townships, shopping
provides housing developers with a thermal
minimum thermal properties for hollow
centres, office car parks and residential
benchmark but it opens the door for other
concrete blocks.
driveways,” says Cairns.
concrete block manufacturers to submit
their hollow-core blocks for testing and
of the 140mm block is almost equal to
Concrete piping
approval. Once a test proves successful,
the 190mm block it presents several
C o n c r e t e p i p i n g ’s c o n t r i b u t i o n t o
brick producers must then satisfy the
advantages. It is about 2kg lighter and
employment is also notewor thy. T his
NHBRC that they have a monitoring system
production output is approximately 50%
was borne out in an independent survey
in place to ensure consistent quality of
greater, which obviously results in cost
conducted in 2005 on behalf of the CMA by
manufacture,” says Cairns.
savings. It is also easier to lay and it
LHA Management Consultants. Concrete
provides more floor space.
piping was found to generate significantly
more employment oppor tunities than
CMA manufacturers are currently
in the process of analysing the physical
“Although the thermal performance
“It is these factors which account for the
PRECAST VOL 1 JUNE 2007 31
other piping materials.
two-and-a-half times higher than for
CMA member, Infraset, Spoornet can now
HDPE piping and five and half times higher
source its turnout sleepers locally.
diameter classes of 300mm, 600mm
than was the case for GRP piping.
and 1 200mm and examined total labour
The survey also covered total laying
breakthrough, and there are many, is that
content on three storm water and sewer
cost. All three piping systems were found
new jobs have been created for South
piping materials, concrete, high density
to be comparable in instances where local
Africans, not only in the manufacture of
pol y e thy lene (HDPE ) and glass f ibr e
materials can be sourced for bedding
the sleepers themselves, but across the
reinforced plastic (GRP).
and fill. However, when bedding and fill
entire value chain, stimulating employment
Concrete piping was found to be up to
material is imported, concrete piping was
opportunities in the steel and cement
six times more labour intensive when the
found to offer a total laying cost which
industries as well.
labour content on 100 metres of pipe was
was substantially the lowest, in some
calculated across the total value chain of
instances by as much as 50%.
T he sur v ey was conduc ted in the
One of the spin-offs of this technological
IN CONCLUSION There is no doubt that precast concrete’s
raw material supply, pipe manufacture and installation.
Concrete rail sleepers
contribution to the social upliftment of
T h e di f f e r e n c e in l a b o u r c o n t e n t
Until quite recently Spoornet was obliged
historically disadvantaged South Africans
was especially pronounced in the larger
to import expensive and scarce hardwood
is both substantial and meaningful. It is
diameters, mainly in manufacture and
sleepers for the maintenance and upkeep
a contribution that is likely to accelerate
deli ver y. For instance the ‘mandays’
of some 15 000 turnout sets. No longer.
as the clear advantages of this versatile
r e q u i r e d t o m a n u f a c t u r e 10 0 m o f
Thanks to the introduction of innovative
constr uc tion medium impac t on the
1 200mm concrete piping was up to
and world-first concrete technology by
professional classes that use it.
P
32 PRECAST ISSUE 1 JUNE 2007
Hollow-core slabs By John Cairns, CMA director Sever al alternati ve uses f or hollowcore slabs have been developed by local manufacturers. In each case the result is
offer versatility across numerous applications
the same, superior functionality, quicker erection times and maintenance-free
in the strip footing. Regular-sized slabs
a certain degree of foundation movement
properties. Some of the applications are
are then lowered onto the beams to form
without causing the super str uctur e
described briefly below.
the floor of the house.
to crack.
The system can be used in stiff soils,
• Beams and slabs are manufactured in
FOUNDATION AND SLAB SYSTEM FOR
pr ov ided their pr oper ties have been
factories where strict quality controls
ECONOMIC HOUSING
determined and the performance of the
guarantee concrete strength and quality.
A complete precast hollow-core foundation
beams approved by a qualified engineer
• Meets mass-housing production require-
and ground slab system for the economic
to ensure they meet the essential design
ments - up to 50 slabs can be placed in a day
housing market has been developed and
requirements.
which allows masonry work to begin much
tested by the CMA and an Agrément
earlier than with in situ systems.
certificate for the system is pending.
and classified as C or H in accordance
• P l a c em e n t o f sl a b s i s e a s y, o n l y
2
Potential sites must be assessed
Designed for a standard 40m masonry-
with the Code of Practice Foundations
requiring a forklif t. Where necessary,
built house, with a floor area of 6,6m x
and Superstructures for single storey
training is given to contractors.
6,2m, the system is competitive in soil
residential buildings - a code of practice
conditions which require foundations
laid down by the joint structural divisions
that the ground must be fairly level and
that provide more than a simple and
of SAICE and IStructE and adopted by
waste water must be kept away from
conventional strip footing.
the NHBRC.
the foundation.
The foundations are laid using two split
slabs 600mm wide which are placed on end
The benefits of the system are:
• Provides a floating raft, which allows
Two pre-requisites of the system are
A reservoir is enclosed using hollow-core concrete slabs.
PRECAST VOL 1 JUNE 2007 33
• Electric wire or security fencing can
in situ concrete.
structed. These have been monitored for
easily be fitted on top of the wall.
the past three years and have compared
storage sheds where potatoes were
very favourably with adjacent houses built
in Bloemfontein, serve to illustrate this
with conventional strip footings and in situ
application. Two walls were constructed to
concrete slabs.
safeguard military equipment, one at a SA
Reservoir Roofs
To date 50 houses have been con-
Three outstanding examples, all of them
Excellent examples are two potato
stored up to a height of six metres.
Air Force base, the other at a SA Defence
Precast hollow-core slabs are ideal for
SECURITY WALLING
Force equipment depot. A third wall was
covering reservoirs. The slabs can be
Prestressed hollow-core slabs are ideal
built for the Post Office in the industrial
delivered to site and lowered directly
f o r b uil ding se cur i t y w alling ar o un d
area of Hamilton.
onto the reservoir wall, greatly reducing the time o f constr uc tion as well as
prisons, military bases, airpor ts and storage facilities. Tests have proven that
RETAINING WALLS
guaranteeing quality.
it is almost impossible to break through
Prestressed hollow-core slabs, placed
this type of wall.
either ver ticall y or hor izontall y, ar e
structure can also be precast and any
The columns and beams of the sub-
being successfully used as retaining wall
access holes can be cut on site.
system, which comprises 4,0m long panels
structures.
being placed vertically into 1m foundations
• Guaranteed quality of slabs
of soilcrete, a mixture of compacted soil
framework in which slabs are slotted into
• Speed of erection
and cement.
the webs of the steel columns. With the
• No on-site wet cast operations including
vertical system the slabs are attached to
shuttering, propping, curing etc.
panels are not connected.
beams or slabs at the top and bottom of
the wall.
was the construction of a 3 500m 2
• High-strength, high-quality solid concrete
(30 000m 3 ) reservoir for the supply of
panels, which cannot be penetrated.
• High-strength high-quality concrete
fresh water to industrial and residential
• Speed of erection – up to 100 linear
panels, reinforced to meet very high
areas in the south-western district of
metres per day/per team.
horizontal loading requirements.
Maseru, Lesotho’s capital.
• N o r e q u i r e m e n t f o r s h u t t e r i n g ,
• Speed of erection – 300 – 400m² per day.
propping, on-site curing or formwork.
• Building operations can continue prior
to use hollow-core slabs for the walls of
• Drainage outlets can be accommodated
to the erection of the retaining wall.
a reservoir but as yet has not been tried
in the slabs as required.
• No formwork, propping, steel fixing and
and tested.
To date several facilities have used the
Although placed next to each other, the The benefits of the system are:
The horizontal system uses a steel
The benefits of the system are:
The benefits of the system are:
One recent southern African project
Currently a system is being developed
P
An example of security walling using hollow-core slabs at an SA Defence Force equipment depot in Bloemfontein.
A potato warehouse which was built using hollowcore concrete slabs.
One of 50 houses in Excelsior, Free State, in which hollow-core concrete slabs were used as an alternative foundation system.
34 PRECAST VOL 1 JUNE 2007
Concrete pipelines boost capacity in Tshwane’s Pienaars River outfall sewer system In a R74 million upgrading project, the
such as Waltloo, Nelmapius, Wilgers,
for a substantial number of years. Both
Pienaars River Sewer-Section Mamelodi in
Mamelodi and Silver Lakes.
the old and new line will drain into the
north-eastern Tshwane (Pretoria) is being
“The new project consists of two pipeline
B a v iaansp o or t S e w er Wor k s on the
boosted with the construction of a sewer
sections covering a combined distance of
northern side of the Magaliesberg range,
tunnel and an additional pipeline, all of it
some 3.4km, a 770m long tunnel and two
but unlike the old line, which follows the
concrete. The main contractor consortium,
bridges with a combined length of over
Pienaars River through the Baviaanspoort
Cerimele - Phenduka Joint Venture began
100m spanning the Pienaars River. Initially
Kloof, the new line takes a more direct
working on the project in June 2005 and
the new pipeline sections will be linked
route to the works via a tunnel through
will have it completed by the end of August
through an existing line in Moretele Park.
the mountain,” says Wessels.
this year.
However, this line has also been earmarked
Both phases form part of Tshwane’s
Johann Wessels, Deputy Manager:
for an upgrade in a second phase operation
master plan as compiled by GLS consultants
Replacement and Upgrading of the Tshwane
later this year and will entail the laying of
and are expected to serve the area for the
Metropolitan Council’s Water and Sanitation
1.7km of HDPE lined concrete piping with
next 30 years on a demographic basis of
Division, says the system will relieve the old
an internal diameter of 1 800mm.
pipeline which drains the rapidly developing
Kungwini-west area and residential areas
used as an emergency bypass system
“The old pipeline will continue to be
A section of HDPE-lined piping is installed on the R74 million Pienaars River Sewer-Section Mamelodi upgrading project in north-eastern Tshwane (Pretoria).
PRECAST VOL 1 JUNE 2007 35
25 units per hectare.
Gerrie van Heerden, a director of GVM,
bends ensure good flow rates without the
Situated in Mamelodi, the upper section
the consulting engineers responsible for
sudden hydraulic losses typically found in
of Phase 1 covers a distance of 2.9km and
designing Phase 1, says that in contrast
manhole bends. They are also less prone
comprises HDPE-lined concrete pipe, with
to the concrete pipes which are being
to the settlement of material which can
an internal diameter of 1 500mm. The lower
protected with an HDPE lining, the tunnel
cause maintenance problems,” concludes
section which links into the tunnel section
wall will be lined with dolomitic aggregate
van Heerden.
on the south side of the Magaliesberg,
concrete to control corrosion.
comprises 550m HDPE-lined concrete pipe
“This type of lining allows water seepage
P henduk a J V, said tha t some o f the
with an internal diameter of 1 800mm. The
to occur. Had the tunnel itsel f been
challenges on this project have included
piping for both sections was supplied by
protected with HDPE lining, it could have
drilling through large quantities of hard rock
Southern Pipeline Contractors.
resulted in the build up of water pressure
and then dealing with sections of unstable
behind the lining.
crumbling shale.
and 770m long, was constructed in a drill
“T he new sewer has been designed
“The crumbling shale meant we had to
and blast operation through rock with
with an optimum slope of 1:400 and it
excavate trenches with battered sides
compression strengths of up to 200MPa.
includes two drop structures to eliminate
seven to eight metres deep. This was one
The tunnel will initially accommodate the
excessive velocities. We were fortunate in
of the main reasons why concrete piping
flow from only 1 800mm section of concrete
that there was sufficient space to build the
was chosen for this project. With wall
sewer. However, it has treble that capacity,
line with long radius bends which allowed
thicknesses designed at 10% of internal
having been designed to serve the total
a 45º bend over a distance of 14m. These
diameters, concrete pipes are able to
Pienaars River catchment area - which by any
sections will comprise 10 pipes 1.4m long
withstand much greater loads than other
standards is huge - for the next 100 years.
with 4.5º deflected sockets. Long radius
materials,” observes Cerimele.
The tunnel section which is arch-shaped
Eduardo Cerimele, who heads Cerimele-
P
36 PRECAST VOL 1 JUNE 2007
Inadequate specifications on CRB walling lead to failures South African concrete retaining block
site to view and a poorly described bill item.
“There is no excuse for the submission
(CRB) wall contractors are being handed
“Contractors generally react in one
of inadequate CRB wall specifications, nor
job specifications which lack essential
of two ways to this type of specification.
for the omissions of drawings. All CRB wall
information, and in many instances, are
They can either make certain assumptions
specifications should be accompanied by a
brazenly inadequate, particularly as they
in their favour, such as a low wall, which
set of drawings showing heights, etc. And
appear in tender bill of quantity briefs.
will enable them to submit the lowest
for those not sure what a comprehensive
Silvio Ferraris, vice president of the
possible quote, or, if the site is ready
specification entails, the CMA’s CRB
CMA’s CRB Wall Division, says that a
for viewing, they can visit it, make more
wall installation manual includes a typical
typical specification reads as follows:
accurate assumptions, and quote more
bill o f quan ti ties and co v er s all the
“Construct a 116m² wall with retaining
appropriately. Although the higher quote
requirements for constructing a CRB wall.
blocks on a straight and curved section at
reflects the contract requirements far
The Association has also produced a film
an angle of 60º and fill in retaining blocks
more accurately, the client is more likely
(available on CD) which provides step-by-
with selected material”.
to opt for the lowest quote.
step construction guidelines.
“Then, when the winning contractor
“CRB wall specifiers should also refer
accurately on such a brief especially if it
arrives on site he generally finds that
to two SA BS standar ds, SA NS 207
is not accompanied by a set of drawings,
the project involves a higher wall as well
for geofabric material used to stabilise
which is often the case.
as other elements not dealt with in his
CRB walls, and SANS 508 : 2007, a
Ferraris notes it is impossible to price
“Does the brief indicate that the wall
quote, such as poor access, more backfill,
specification for retaining blocks. The
is 116m long and one metre high, or is it
fabric reinforcement, drains and stronger
latter is in its final draft form and will
38m long and an average height of three
foundations. He then either cuts corners,
be available for comment during 2007,”
metres? Is it against ‘cut’ or ‘fill’? Are
building a wall in which the risk of failure
concludes Ferraris.
there loads above the wall and how close
is high, or he revises his quotation, and
are those loads to the top of the wall?”
the project goes hopelessly over budget.
Either way it eventually ends up costing
Ferraris says it is virtually impossible to
make valid assumptions with no drawings, no
considerably more.
P
An example of a well constructed CRB wall at a new Pick ‘n Pay warehouse in Modderfontein, Gauteng. The wall reached a maximum height of 10 metres and used four skins up to a height of 7.5m in certain sections. The blocks were supplied by Anchor Retaining Walls.
38 PRECAST VOL 1 JUNE 2007
South Africa’s first permeable paving contract completed T he dr i veway s and yar d ar eas o f an af f or dable housing development, T he Reeds, in Fairland, Johannesburg, are South Africa’s first to have been paved with a permeable paving system using solid paving blocks. Permeable paving functions in one of two ways, either soaking the surface stormwater back into the ground-water table, or storing and then channeling the water into storage sumps or tanks as “grey” water to be used when required for the watering of gardens, cleaning purposes and flushing toilets. In this instance the former option was selected. Permeable rather than conventional run-off paving was specified for The Reeds because the storm-water drainage system in this part of Fairland was built some 35 years ago and lacks the capacity to handle any additional run-off. T he permeable paving blocks were custom made for the project by CMA m emb er, C on c o r Te chni cr e t e . S om e 89 000 square units and 94 000 rectangular units were supplied to cover an area of 4 320m². John Cairns, CMA director, says he believes that permeable paving is set to take off in a big way in South Africa. “Until now local engineers have resisted the system mainly because they mistakenly believe that water and sub-base material
don’t mix. However, the system has been used successfully for the past 20 years in Europe and for the past 10 in Australia, and we do have engineers who are prepared to try it. In addition, local councils are likely to begin approving new building projects with the proviso that some or all the paving is permeable,” observes Cairns. T he Reeds system was laid in the following manner: 500mm of top soil was removed and the exposed surface was then covered with an SABS approved BIDIM A5 geotextile membrane manufactured by Kaytech Engineered Fabrics. Rock f ill compr ising 160mm stone 50 0mm deep f or med the nex t lay er followed by a second layer of geotextile membrane. The stone was non-friable so as to avoid breaking up too much when being graded by a 10 ton roller. Once compacted, the rockfill was covered with 80mm of coarse washed river sand and this in turn was compacted. To this was added another 20mm of washed river sand for bedding purposes. The same sand was used for jointing. Rated at a compressive strength of 30MPa, the paving blocks were laid in a pattern specified by Concor Technicrete. Based on an overseas design, the pavers include vertical slots (three millimetres deep) at either end through which the water will flow into the sub-base. When
newly laid, the absorption rate will be approximately 9 000l per square metre per hour. Over the long-term this rate will reduce to roughly 1 000l per square metre per hour which means a cubic metre of water will still be absorbed in an hour. Cairns says that besides water conservation permeable paving has other benefits. “Developers will see the economic benefits when they realise they no longer have to build storm water drainage and can add extra accommodation units to their developments. Roads can also be built with permeable paving which once again saves on storm-water drainage. Roads will remain dry even if they are completely level,” concludes Cairns. The main contractor on The Reeds project was ASH Plant-Hire & Civils. Other members of the project team included Lidwala Consulting Engineers and Special Perfect Paving, the paving contractors. P
A 10 ton roller compacts rockfill comprising 160mm stone some 500mm deep during construction of the permeable paving surface at The Reeds, an affordable housing development in Fairland, Johannesburg. South Africa’s first permeable paving project using solid paving blocks nears completion at The Reeds. Rockfill is carefully graded during the construction of South Africa’s first permeable paving surface using solid paving blocks.
40 PRECAST VOL 1 JUNE 2007
Membership May 2007
Company Name
Phone No
Fax
Product
ARW Concrete Holdings
011 460 0921
011 460 0924
R
A Fick Cement Works
022 913 1921
022 913 2370
M
Bafokeng Concor Technicrete
014 538 0818
014 538 0806
MPRT
Baybrick
035 791 1238
035 791 1253
P
Boland Concrete
021 875 5365
021 875 5021
M
Bosun Brick Midrand
011 310 1176
011 310 1178
P
Brick & Concrete Industries
00264 61 321 3009
00264 61 321 3041
MP
Brickcast Industries
031 507 5525
031 507 7094
P
Brikor
011 316 1200
011 316 1380
T
Cape Brick
021 511 2006
021 510 2172
MPR
C.E.L. Paving Products
021 905 5998
021 905 5998
P
Cast Industries
011 316 2375
011 316 2394
P
Columbia DBL
021 905 1665
021 905 4049
MPR
Concor Technicrete
011 495 2200
011 495 2489
MPRT
Concrete Units
021 386 1923
021 386 2514
Pi
Consteen
011 701 3875
011 701 3395
P
Corobrik
031 560 3911
031 560 3180
PR
Deranco Blocks
041 463 3338
041 463 2602
MR
Deranco Paving
041 933 2755
041 933 5910
P
Deranco Precast
041 463 3338
041 463 2602
S
Eagle Roof Tiles
044 874 0290
044 874 0282
T
Echo Floors
011 957 2033
011 957 2037
S
Echo Prestress
011 393 4655
011 393 4651
S
Echo Prestress KZN
031 569 6950
031 569 6974
S
False Bay Bricks
021 904 1620
021 904 6115
MP
Inca Masonry Products
043 745 1215
043 745 1501
MPRT
Infraset
011 876 5500
011 872 1713
Pi
Infraset
012 652 0000
012 652 0132
MPRT
Infraset KZN
031 569 6900
031 569 6903
PR
Kopano
016 363 0340
016 363 0714
P
KuluCrete South Coast
039 685 4165
039 685 5166
MPR
Lafarge Roofing South Africa
016 430 8000
016 430 8068
T
Lategan’s Cement Works
021 873 1154
021 873 4910
M
Marley Roofing
011 316 2121
011 316 1498
T
PRECAST VOL 1 JUNE 2007 41
Mimosa
016 362 0507
016 362 1451
P
Mobicast Mossel Bay
044 874 2268
044 873 3114
P
MVA
012 386 0050
012 386 0073
P
Neat Contech
046 624 3377
046 624 1359
MPRS
Panda
00267 244 2106
00267 244 2110
MP
PRO Brick & Block
021 905 3362
021 905 4889
M
ReMaCon Products
011 393 5504
011 393 5502
R
Rocla
011 670 7600
011 472 2141
Pi
Salberg Concrete Products
011 316 3410
011 316 3402
Pi
Southern Pipeline Contractors
011 914 8500
011 914 4524
Pi
Stabilan
051 434 2218
051 435 3925
S
Stanger Brick & Tile
032 457 0237
032 457 0237
MP
Topfloor
021 552 3147
021 552 6892
S
Van Dyk Steengroewe
022 713 1244
022 713 1500
M
Vanstone Precast
012 541 2056
012 541 1808
PR
Vibro Bricks Pretoria
012 374 9300
012 374 9301
P
Watson Concrete
011 740 0910
011 744 4472
MP
White River Cement
013 750 2710
013 750 0822
MPR
P=Paving
M=Masonry
R=Retaining Blocks
T=Roof Tiles
S=Floor Slabs
Pi=Pipes