Precast April 2010 by Concrete Manufacturers Association (CMA)

PRECAST VOLUME FOUR ISSUE 1 • APRIL 2010

the cma – QUALITY CAST IN CONCRETE

• Sowing the seeds of our own destruction? • Leo Mews sets the pace for gap housing • SA Housing Conference and precast concrete

PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010 1

contents 2

Message from the President

CMA Director retires

32 sewer condition assessment and corrosion prediction 38 cma members make substantial

4 Demand for CRB walls set to grow 5

infraset’s new ridgeblok system

specified for gfip retaining walls

contribution to gfip 40 prestressed hollow-core and

load-bearing masonry - the most

economical solution for medium6

high terraforce crb wall installed

in turkey

rise structures 44 cma membership list

6 pre-sealing makes sense Precast concrete elements were used extensively on Leo Mews, a five star Green Building project situated near Elsies River on the Cape Flats. Coverland roof tiles produced by Monier, concrete bricks manufactured by Columbia DBL, and a rib-and-block flooring system supplied by DBL Decking, all contributed to one of South Africa’s most remarkable eco-friendly gap housing projects to date.

PRECAST VOLUME FOUR ISSUE 1 • APRIL 2010

7 manitou southern africa awarded

THE CMA – QUALITY CAST IN CONCRETE

gehl distributorship

updated permeable paving design

software available from the cma

• Sowing the seeds of our own destruction? • Leo Mews sets the pace for gap housing

• SA Housing Conference and precast concrete

9 cma publishes green paving brochure 10 masonry block-laying training takes off 12 abrasion testing machine for new paving regulations 14 sowing the seeds of our

own destruction?

18 precast concrete provides a key to the housing challenge sa housing conference 21 CMA MEMBERS DONATE BUILDING

MATERIALS TO YOUTH DEVELOPMENT

22 precast concrete dominates in

five-star green building gap

housing project

26 structural and design aspects

of porous and permeable concrete

block pavements in water-sensitive

urban designs

Designed and developed by Cape-based Bitol Technologies, Leo Mews introduces those who will be fortunate enough to move into one of its apartments to a level of comfort, security and environmentally responsible living which sets a standard not only for the Western Cape but for the country as a whole.

Precast is the official journal of the Concrete Manufacturers Association (CMA). Block D, Lone Creek, Waterfall Office Park, Bekker Road, Midrand. PO Box 168 Halfway House 1685 Tel: +27 11 805 6742, Fax: +27 86 524 9216 e-mail: main.cma@gmail.com, website: www.cma.org.za Editor: David Beer Tel: +27 11 478 0239, Fax: +27 11 678 0254 e-mail: bigsky@ibi.co.za Advertising: Cathy Nicolau Tel: +27 11 234 9526, Cell: 082 478 8094, email: classads@mweb.co.za Design, layout and production: Isikhova Publishing & Communications (Pty) Ltd, PO Box 651793, Benmore, 2010 Tel: +27 11 883 4627, e-mail: communications@isikhova.co.za The views and statements expressed in this publication are not necessarily those of the editor and neither he nor the CMA accept responsibility for them. No person connected with the publication of this journal will be liable for any loss or damage sustained as a result of action following any statements or opinions expressed herein.

2 PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010

Message from the President This year promises to be momentous, both

those who either specif y the product

for the country, as the final preparations for

or use it. Architects, civil engineers,

the World Cup unfold, and for the CMA, which

and developers will rely increasingly on

is staging its 13th Awards for Excellence

its distinct benefits as they gear up to

competition. It is also the year in which the

meet this country’s infrastructural and

CMA bids farewell to one of its stalwarts,

accommodation requirements in a context

former director, John Cairns, who officially

of greater urban densities and higher levels

resigned at the end of February. Under

of sustainability.

his steady and inspired leadership, which

A case in point is a technology with

coincidentally also spanned 13 years, the

which I am particularly familiar, namely,

Association flourished, experiencing both

constructing retaining walls using concrete

geographic and membership growth. He

retaining blocks (CRB). Dramatic improve-

also managed the introduction of new or

ments have been achieved over the past 10

revised standards as well as the launching

years, and on some of our mines, walls are

of several new products, most of them

reaching heights of 30 metres and more.

aimed at the affordable end of the precast

Internationally similar elevations have been

concrete market and all of them gaining

achieved on road and bridge abutments.

either SABS or Agrément certification. John has that enviable quality of making difficult and complicated tasks look easy

Heights of 20 to 30 metres are now pos-

For example, the old method of thump-

sible on single-terraced walls and multi-

ing rock into marshy ground to form a

terraced walls are topping 60 metres.

solid base has been superceded by using

and his technical expertise and dedication

Another facet of this advance is that

geofabric and fill material to create a “basal

to the task at hand were perfectly suited

the slopes of CRB walls ar e getting

reinforcement”. It is interesting to note

to the leadership of the Association.

steeper, so much so, that they ar e

that this type of system is being used on

Moreover, his open nature and friendly

being built at angles which would have

the Gautrain line near Centurion, where the

disposition have endeared him to all his

been considered off limits 15 years ago.

possibility of sinkhole formation exists.

colleagues and associates.

Some as high as eight metres and almost

Thanks to these advances, I anticipate

Whatever it took John could always

vertical have been built locally and there

a revolution in CRB wall construction which

be relied upon to deliver, and in many

is no reason why we can’t build them at

will see very high and very steep walls being

instances, this entailed working after hours

87˚ and at even greater heights.

built with good engineering input, fully

and over weekends, often ably assisted by

There are many different CRB materials

compliant with SANS 207. The technology

his wife, Marilyn, who was always there

available to design engineers and one of the

and the materials are in place - all we need

when an additional hand was needed. It

areas where substantial improvements

to do is design and build.

is therefore hardly surprising that having

have been made is in the geosynthetic

In closing I’d like to wish the participants

transferred the reigns to his successor,

materials used to reinforce fills. Put

in this year’s Awar ds f or E xcellence

Hamish Laing, he leaves the Association in

simp l y, t o d a y ’s m a t e r i als ar e mu ch

competition the best of luck with their

excellent shape. We and all those who have

stronger. In the past certain fabrics were

entries. The competition is not limited

worked with him are indebted to him.

prone to stretching and creep and this is

to CM A member s and is open to all

On ma t ter s mor e technical, i t is

why walls were restricted to a maximum

designers, developers, manufacturers or

pleasing to note that precast concrete

incline of 87˚. One of the materials is

users of precast concrete products. I’d

is making huge technological advances

Kevlar which is used in bullet-proof vests

also like to extend a very warm welcome

and its applications are more varied

and is stronger than steel.

to Hamish who, with fresh impetus and

and widespread than ever. One need

Many of the advances in geosynthetics

new ideas, will ensure that the Association

look no further than Gautrain, the GFIP

were covered in GeoAfrica 2009, the

continues to set the pace in the precast

(Greater Freeway Improvement Project)

f ir st A f rican r egional conf er ence on

concr ete industr y. A nd to John and

and the World Cup Soccer stadiums, to

geosynthetics. The conference drove home

Marilyn, your erstwhile colleagues on

find that the technology is indeed playing

the point that geosynthetics are used for

the CMA management committee wish

a significant role in our major construction

just about every application which involves

you both a long, happy and well-deserved

projects. This role is likely to grow in

civil engineering. They are far more cost-

retirement.

the years ahead as its economic, social

effective and more eco-friendly than rocks

and environmental benefits influence

or fill material.

Silvio Ferraris, CMA President

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4 PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010

CMA DIRECTOR RETIRES John Cairns, the CMA’s director for the

on a consultancy basis for a further six

in civil engineering from Leeds University

past 13 years, officially retired at the end

months and will be still very much involved

and has lived and worked in South Africa

of February. His position has been filled by

in this year’s CMA Awards for Excellence

for the past 28 years. Before joining the

newly appointed director, Hamish Laing.

Competition. One of South Africa’s fore-

CMA, he was a technical services manager

most concrete block paving experts, he

with the multi-national Hilti group.

John will continue to work for the CMA

will remain on the committee of the inter-

Hamish brings a wealth of experience in

national paving association, SEPT (Small

concrete technology to the CMA and has

Element Paving Technologists) and will still

held positions with some of South Africa’s

be involved in seminars, lectures and site

leading cement and concr ete suppl y

inspections on behalf of the CMA.

companies. Between 1998 and 2003 he

John has established his own paving

worked for PPC Cement where he developed

consultancy and will be available to assist

and marketed an entire new product range,

with the design, installation and marketing

dry mortar cement. Moreover, he has made

of concrete block paving (CBP) systems.

several other significant contributions to

Hamish was raised and educated in John Cairns

Hamish Laing

Scotland and England. He has a BSc degree

the advancement of this country’s cement and concrete industry.

Demand for CRB walls set to grow The use of concrete retaining blocks (CRBs) in retaining walls has grown steadily since CRBs were first introduced in the 1980s according to Silvio Ferraris, managing member of ReMaCon Products, a Gautengbased manufacturer and supplier of CRBs. This has been particularly evident in commercial and residential applications, as well as in landscaping. Their use in civil projects, such as highway embankments, has also grown, albeit at a slower pace. “CRB’s have gained widespread acceptance in the commercial and residential markets, although sales have fallen off somewhat due to the current recession. However, when the economy recovers I

or near-vertically, closed-face blocks are

foresee demand reviving as increasing

used, acting either as permanent shutters

numbers of people recognise their value

with steel and concrete infill or in multiple

and appeal,” says Ferraris.

layer combinations, allowing for greater

Any doubts engineers and architects

depth and mass.

Retaining walls installed at Orlando Stadium in Soweto, using ReMaCon Products’ open-face ReMblok 30 Split rockface blocks, plus, on the right, where closed-face Terraforce L18 blocks were used for a steep section of the wall.

some have rock-face finishes which can be

had about CRB retaining walls were largely

ReMaCon has developed its own solution,

either moulded or split, the latter using

dispelled in the late 1980s when a retaining

comprising an extension piece that locks

hydraulic machines. This results in a face

wall constructed of Lof felstein blocks

into each of the blocks in the base course.

with surface variations and a more natural

was successfully built against a mine

This provides the necessary ballast to

rough appearance, with no one block being

dump overlooking the Crown Interchange

make a high wall safe and at the same time

identical to any other.

on the M2 freeway in Johannesburg.

costs a good deal less than systems which

The rock-face version of ReMblok 30 was

Unlike traditional retaining walls which

use double and triple skin combinations or

used at the recently completed Orlando

ar e invariably ver tical and built with

deeper blocks.

Stadium in Soweto on a ±600m2 retaining

substantial foundations, most CRB walls

Textured and sand-coloured blocks

wall close to the entrance of the stadium.

slope inwards and have less active earth

came to the market in the mid-1990s

Next to it, a steeper near-vertical retaining

pressure to support.

and today are widely used. Most lines are

wall constructed of Terraforce L18 blocks

offered in both sand and grey colouring and

supplied by ReMaCon, was erected.

When CRB walls are erected vertically,

PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010 5

INFRASET’S NEW RIDGEBLOK SYSTEM SPECIFIED FOR GFIP RETAINING WALLS Infraset Landscape Products has introduced the RidgeBlok, a dry-stacked concrete block system for building retaining walls at angles of between 70˚ and 90˚. The system has already been used extensively to shore up embankments on Gauteng’s A section of a retaining wall which was built using Infraset’s RidgeBlok system at the new entrance to the main campus at UNISA in Pretoria.

Freeway Improvement Project (GFIP) and has also been deployed to build a retaining wall, in some sections 8.5m high, at the new entrance to the main campus at

mean it exerts exceptional clamping force,

UNISA in Pretoria.

especially on the geosynthetic stabilisation

Brennan Small, Infraset Landscape

material usually placed between individual

Products sales manager, comments that

blocks. Therefore any chance of the ma-

the system was chosen for the GFIP

terial being worked loose is extremely

because its smooth finish is best suited

remote. This aspect is seen as a major

freeway embankments.

advantage over conventional concrete

“Should a vehicle stray off course and collide with a wall constructed with the

An 8.5m retaining wall which was built by Thembakele Engineering using Infraset’s RidgeBlok system at the new entrance to the main campus at UNISA in Pretoria.

This retaining wall was erected by Kalode Construction using Infraset’s RidgeBlok system to secure an embankment below the N1 freeway just off the site of the Botha Avenue tollgate in Tshwane.

blocks which rely on friction to prevent geosynthetic creep.

RidgeBlok system, the resultant damage to

“The compressive strength of RidgeBlok

the vehicle would be less than that inflicted

allows for the construction of higher walls

by a wall built with conventional blocks,”

than can be built with hollow blocks. Moreo-

advises Small.

ver, its lip-and-recess system provides a

Small says the RidgeBlok system is suit-

positive interlocking force which effectively

able for tight convex or concave curves, and

dissipates the horizontal forces exerted

is one of the very few which can be erected

on the interfaces between the blocks,”

at a true 90 degrees.

observes Small.

“Factors such as its lip-and-recess

The system can either be used to build a

(tongue and groove) design, its solid con-

solid wall, as in the case of the GFIP - where

crete composition, and its mass of 24kg,

it was used to withstand the pressures of highway traffic loading - or a ‘broken’ wall where the blocks are spaced apart to allow for plant growth. Open spaces between the blocks provide a more open and permeable facing and prevent excessive build-up of pore-water pressure behind the wall. RidgeBloks are cast with grooves on one face and this facilitates their being laid in various visually pleasing patterns. And because they are solid and therefore robust, fewer breakages occur during transportation and construction. Foundation blocks for the RidgeBlok system are available from Infraset in either 75˚ or 85˚ configurations. Further information

Brennan Small, sales manager of Infraset Landscape Products, stands next to a retaining wall built with Infraset’s RidgeBlok system. This section is close to the Botha Ave culvert on the N1 and was built to withstand the pressures of highway traffic loading.

on the system is available from Brennan Small on 012 652 0000, or via bsmall@ infraset.com.

6 PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010

HIGH TERRAFORCE CRB WALL INSTALLED IN TURKEY Geoduvar, a Terraforce licensee in Istanbul,

The road runs for approximately seven

on the land. Thus it was essential for the

Turkey, has designed its highest earth

kilometres of which just over one kilometer

new structure to blend in with the existing

retaining wall to date. The impressive

had to be built on an exceptionally high,

greenery and the surrounding forest.

21,5m high structure involved cut-and-fill

privately owned slope.

slopes for a new road in the Beykoz region of Istanbul.

A preliminary design which entailed an

A major requirement was the appearance

L15 block retaining wall with high strength

of the retaining wall and the landowner did

geotextile reinforcement, and wall angles

The road was specified by the Municipality

not want a fully perpendicular surface

of 70º was approved by the municipality.

of Istanbul to link a hilltop neighborhood,

to support the road, especially as there

An advantage of the Terraforce system

overlooking the Bosphorus, with Istanbul.

were plans to build a residential complex

was that the building of the walls could coincide with construction of the road, which saved time and reduced costs. The height of the wall, which used a light brown L15 Terraforce block produced by Eko Moduler Yapi of Istanbul, ranges from 1m at either end up to 21.5m at the lowest point of the existing grade. The total area of the wall is about 6,500m² and Geoduvar reports that there have been no problems with the structure since the completion of the wall last year.

APOLOGY The Karlitepe Beykozlu Road project in Turkey for which Terraforce licensee, Geoduvar, designed and supplied the concrete retaining wall blocks.

In the previous issue of Precast a story run on the Terraforce hard lawn block carried the wrong Terraforce photo.

PRE-SEALING MAKES SENSE There is now increasing local interest in

products, Pareflo 15 remains an integral

pre-sealing concrete blocks, bricks, tiles

part of the concrete for its entire life,”

and pavers with a silicone water repellant

notes Boardman.

admixture. So says Victor Boardman, Chryso South Africa’s technical services manager, who launched the company’s new pre-sealer, Pareflo 15, on a recent nation-wide tour. “Local concrete component manufacturers and specifiers are generally unaware that pre-sealing can boost concrete’s resistance to water and eliminate unsightly efflorescence. “South African producers and architects – particularly in the coastal areas – have begun to realise that pre-sealing concrete blocks, bricks and pavers sub-

He says some of the other benefits of specifying Pareflo 15 include: • The concrete surfaces resist biological growth because the masonry stays dry • Pr e-sealing concr e te r oo f tiles eliminates the need for periodic washing of the tiles with harsh acid mixtures; • Rising damp is eliminated at the base of concrete walls • Erosion damage due to the effects of salt from sea spray or salt-chlorinated pools is also eliminated • Colours do not weather or deteriorate because of water absorption.

A house built with concrete blocks pre-sealed with Chryso’s Pareflo 15.

such as the Commonwealth Scientific and Research Organisation and the Australian Building Systems Appraisal Council. “Pre-sealing technology is ideal for coloured decorative walls, retaining and basement walls, damp-coursing, load-

stantially reduces maintenance costs.

“Overseas, most block manufacturers

bearing blocks, as well as pavers around

Paying a little more to pre-seal a concrete

have successfully implemented the use of

swimming pools and other wet areas,”

component ultimately works out cheaper

admixtures such as Pareflo 15 in the pro-

Boardman added.

than constantly trying to remove efflores-

duction of concrete blocks, bricks, pavers

For more information about Pareflo 15,

cence, mould or mildew staining.

and tiles. Pareflo 15 has successfully under-

contact Victor Boardman on Tel 011-395-

gone extensive testing by reputable bodies

9700 or visit www.chryso.com.

“When incorporated into concrete

PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010 7

MANITOU SOUTHERN AFRICA AWARDED GEHL DISTRIBUTORSHIP Manitou Southern Africa has signed an

machines offer high performance, ver-

exclusive distribution agreement with Gehl,

satility and are easy to operate. These

the US-based manufacturer of compact

features, in addition to their compact

handling equipment, to supply its range

design, make them ideal for the construc-

of skid loaders to the southern African

tion industry.”

market. This follows the international

Manitou is providing full servicing,

acquisition of Gehl by Manitou BF in

maintenance and parts supply of the skid

October 2008.

loader range.

According to Lindsay Shankland, Mani-

“The partnership between Manitou and

tou Southern Africa managing director,

Gehl is ideal,” notes Shankland. “Manitou

the Gehl products are the ideal comple-

is expanding into the North American

ment to the Manitou range of rough ter-

market, while Gehl is expanding its global

rain handling equipment.

exposure through the well-known Manitou

“The Gehl skid load E-Series features

brand.”

nine models, all of which feature ergonomically designed cabs to ensure operator comfort and maximum productivity. The

The Gehl SL 1640E skid steer loader, which manoeuvres easily in tight places and handles tough construction, agriculture and landscaping challenges with ease.

PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010 9

UPDATED PERMEABLE PAVING DESIGN SOFTWARE AVAILABLE FROM THE CMA Updated versions of PermPave, software

application. Moreover, it allows water

used for designing permeable concrete

requirements and volumes to be speci-

block paving (PCBP) surfaces, and LockPave,

fied, either for storage and re-use or for

software used for designing conventional

replenishing underground water tables,”

concrete block paving (CBP) surfaces,

advises Shackel.

are now available from the Concrete Manufacturers Association (CMA).

A residential street in Sydney, Australia, which has been paved with a permeable concrete block paving (PCBP) system.

Based in Sydney, Australia, Dr Shackel

Professor Beecham is currently Pro-

has worked on many projects worldwide

fessor of Sustainable Water Resources Engineering in the School of Natural and

PermPave Version 2.1 and LockPave

as a consultant for asphalt, block paving

Version 18.1 are available on a single disc

and rigid concrete pavements. He is a

Built Environments (NBE) at the Univer-

at no charge for existing users and at a

recognised authority on CBP and is the

sity of South Australia. He is also Head of

nominal R500 for new users.

author of numerous research papers and

Civil Engineering and Director of the SA

First launched in 2008, PermPave is a

three books on this topic. His work on CBP

Water Centre for Water Management and

software package aimed at assisting civil

surfaces won him an Award for Excellence

Reuse (CWMR).

engineers and landscape architects in the

from the Concrete Institute of Australia.

O ver the last 22 years Professor

design of PCBP systems. LockPave was

He is especially recognised for his work

Beecham has made significant contributions

first launched in the 1990s for the design

on heavy duty pavements including those

to the understanding of urban drainage

of CBP systems. Both packages were

for ports, container handling facilities and

hydraulics and more recently total water

authored by Dr Brian Shackel, and in the

airports. He is also an expert on ecological

cycle management and water sensitive

case of PermPave, he collaborated with

and permeable pavements and has been

urban design (WSUD). Since 1998, he

Professor Beecham of the University of

involved in environmental research in the

has been Australia’s representative on

South Australia.

pavement arena.

the International Water Association’s

The software can be used for various

Shackel has taught pavement engineering

International Group on urban rainfall.

paving products and locations and this pro-

at the University of New South Wales at

During 2005, he was a visiting professor

vides considerable design scope. PermPave

both the undergraduate and post-graduate

at Imperial College London where he worked

is programmed with South African rainfall

level for more than 35 years. He is well

on the impact of climate change on water

data and allows for the further downloading

known to international audiences, having

sensitive urban design.

of local climate and rainfall information.

travelled and lectured extensively in 24

Interested parties should contact Pam

countries including the USA, Canada and

at the CMA on 011 805 6742 or on main.

European countries.

cma@gmail.com.

“It facilitates the selection of paving blocks best suited to a particular

CMA PUBLISHES GREEN PAVING BROCHURE The CMA has published a brochure on

systems to sub-grade (ground) conditions.

permeable concrete block paving (PCBP)

Three systems are covered: full infiltration,

the green alternative to conventional

suitable for ground with good permeability;

concrete block paving (CBP).

partial infiltration for ground not capable of

Its primar y objecti ve is to assist

absorbing all the water; and no infiltration,

landscape designers, property developers,

where the existing sub-grade is poor or

as well as planning, building control and

contains pollutants.

adoption officers to better understand

Other aspects include water quality and

PCBP and the positive impact it is having

the removal of pollutants, service life and

on the environment.

maintenance.

T he brochure highlights the three

The brochure can be downloaded at no

essential pillars of PCBP which are:

charge from the CMA’s website, www.cma.

• Minimising water run-off

org.za . Simply click on ‘Publications’ and

• Improving water quality

follow the prompts. Alternatively, hard copy

• Providing amenity (improving the

versions are available from the CMA, also

environment) and biodiversity

at no charge. Contact Pam Zukor on (011)

Advice is given on how to match PCBP

805-6742 or on main.cma@gmail.com.

The effectiveness of this recent PCBP installation at the Anglican Cathedral in Pietermaritzburg is quite visible here. The non-permeable bitumen surface on the left is still awash with water shortly after a cloud burst whereas the PCBP surface is only slightly damp.

10 PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010

MASONRY BLOCK-LAYING TRAINING TAKES OFF CETA (Construction Education and Training Authority) approved training in masonry block-laying has begun in earnest. Based on course material specifically developed for laying modular masonry blocks as opposed to conventional bricks, the training has been developed by the CMA (Concrete Manufacturers Association) in collaboration with a senior block-laying instructor. “This is a huge step in the right direction

construction as well.

for the construction industry, as it will

“T here is no point in

make a direct and positive impact on the

teaching learners the basic

affordable housing market,” comments

skills in modular construc-

Günter Koch, the CMA’s Western Cape

tion if, when they join the

representative.

real world, they can’t hone

“Over the past 10 years SAQA (South

an d p er f e c t th e se sk ills

African Qualification Authority) and CETA

through further mentorship.

have treated block-laying training as a

As things stand professional

mere adjunct to the brick-laying training

mentorship is woefully in-

material. The net result was twofold. In

adequate if not entirely ab-

the first instance the training of block

sent among the contracting

laying artisans fell short in meeting an

fraternity. It is absolutely

acceptable standard by a considerable

necessary for fledgling skills

margin, and secondly, the quality of houses

to be further entrenched in

built with masonry blocks was inconsistent

the working environment as

at best, and in many instances, well below

learners tend to ‘un-learn’

acceptable performance criteria.

useful skills if they are not

“As most affordable housing develop-

Work in progress at a church in Khayelitsha which was built using genuine modular masonry and thin bed mortar (TBM) construction techniques.

The Gugulethu Child Welfare administration block which was built with genuine modular masonry using concrete blocks.

properly guided.”

ments are built with concrete blocks, it

Although block-laying training began

than they are today. The main reason for

means that for the past 10 years at least,

with the onset of 2009, gaining SAQA

this is that over the years true modular

we have been building sub-standard afford-

approval for certification purposes will still

construction, in which a complete range

able housing. The people who live in these

take some time.

of complementary blocks, such as corner,

houses are having to deal with walls that

“We hope this will happen this year.

half and quarter units, are used, has been

crack and leak, hardly factors designed to

Nevertheless, the fact that we can now

gradually eroded and replaced by sole

encourage pride of ownership. Had block-

use the training material should go a

reliance on concrete blocks – a process

laying been recognised as a distinct trade

long way to re-establishing modular block

which is laborious, wasteful and slow.

from the outset, the R-millions spent on

construction as a discrete masonry skill.

“Our new training programme is designed

erecting affordable houses would have been

This in turn will entrench it as the most

to address this problem and provided we

spent far more wisely and productively,”

cost-effective masonry system, not only

achieve buy-in from contractors, specifiers

says Koch.

for affordable housing, but for high-rise

and building authorities, the re-introduction

Towards the end of 2008 the CMA

buildings, community centres, schools and

of true modular construction will unleash

completed its trainee and facilitator train-

shopping centres, as well as many other

a new and productive era in affordable

ing material for modular concrete block

structures.

housing construction,” concludes Koch.

construction. The course material consists

“Besides a better quality of housing

For further enquires contact Kentse

of 14 outcome-based activities which com-

we should also witness considerable

Mathiba at CETA Guateng on (011) 265

prise the block-laying unit standard.

improvement in the time it takes to

5900 or Peter Cleopha at CETA Western

While expressing optimism on the future

build an affordable house as block-laying

C ape on (021) 94 9 5325. T he T jeka

of block-laying in South Africa, Koch cautions

training takes hold. When modular masonry

organisation provides block-laying training

that it is important for contractors and

was first introduced in the late 1970s

and its regional manager, Gawie Burger,

sub-contractors to embrace full modular

construction speeds were much faster

can be contacted on 021 976 8057.

12 PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010

Abrasion testing machine for new paving regulations

After a specified number of revolutions, the pavers are weighed and the mass loss measured. Former CMA director, John Cairns, says that on a set of eight pavers, the average weight loss must not exceed 12gm. If it does, the pavers will not be considered abrasion resistant. The machine has been built with replaceable liners, as well as safety guarding, which prevents any part of an operator’s body from making contact with, or coming close to moving parts. Furthermore, the machine is backed up by PMSA and is built to last many years. All the components are machined on Pan Mixers’ in-house computer numerically controlled (CNC) machine. Cairns adds that alternate methods of testing – such as wire brushing – are inferior, as there are too many variables that could influence the amount of wear on a paving surface. By using steel ball bearings, these variables are covered, and a comprehensive test result is achieved. Cairns observes that prior to the CMA’s research, it was thought that a paver with a higher compressive strength would offer better abrasion resistance properties.

Pan Mixers South Africa (PMSA), in part-

A new paving block abrasion testing machine manufactured locally by Pan Mixers South Africa in collaboration with the Concrete Manufacturers Association (CMA).

This has, however, proved to be incorrect

a robust abrasion testing machine to

uniform method of testing abrasion to the

charts show that even a block of 59 MPa

assist customers in complying with the

new SABS standard would be to use ball

can have very poor abrasion resistance,

revised South African Bureau of Stand-

bearings. “This technique simulates high-

while a block of only 25 MPa can have excel-

ards (SABS) abrasion requirements for

traffic areas such as loading yards, stock

lent abrasion resistance,” notes Cairns.

concrete pavers.

yards and intersections where abrasion is

nership with the Concrete Manufacturers Association (CMA), has manufactured

The revised standard – SANS 1058

a problem,” adds Ebeling.

- there is no relationship between compressive strength and abrasion resistance. Our

He says that concrete paving blocks which are manufactured according to the

2010 – which was initiated by the CMA, will make way for concrete pavers that are specified - not only in crushing and breaking strength, but in abrasion resistance too. PMSA director, Walter Ebeling, says the abrasion testing machine allows users to carry out their own testing of this portion of the SABS certification, thus eliminating the need to send products to external laboratories and, in turn, minimising downtime.

A set of paving blocks after a run on the abrasion testing machine.

“In the past, paving has sometimes failed

T he abrasion testing machine is a

new standard will provide the consumer

- not because of the paving block strength,

square-shaped drum, onto which four

with the means of being able to compare

but because the abrasion resistance of

pavers can be bolted to each face. A small

the performance of the various pavers on

the pavers was not adequate. The revised

opening allows the surface of the paver to

the market with more accuracy.

standard specifies a measurable standard

be exposed to the ball bearings in the drum.

“The new abrasion standard is good

for abrasion resistance,” notes Ebeling.

When the drum rotates, the ball bear-

news all round, as the industry has been

ings fall onto and rub against the pavers,

pushing for higher standards for many

thereby simulating abrasion.

years,” Ebeling concludes.

After carrying out extensive research, the CM A de termined that the most

14 PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010

SoWING THE SEEDS OF OUR OWN DESTRUCTION? Buildings that collapse and mass housing developments which fail soon after construction are the more visible manifestations of a greater malaise which should be of deep concern to every South African namely, non-compliance with SABS (South African Bureau of Standards) standards in the construction industry and, more specifically, the precast concrete construction industry.

Hamish Laing comments that national standards go to the very heart of how a country views and defines itself. “They frame and measure success in everything we do. Without them we are like rudderless ships, churning the water furiously but making little headway.

In many instances local and national

450 technical committees and sub com-

Winning individuals, winning teams and

government bodies exclude SABS standards

mittees the SABS maintains more than

winning nations don’t achieve their goals

from their tender specifications, while

6 100 standards via its Standards Division.

by ignoring standards. On the contrary,

individual consultants and organisations,

New standards are developed at a rate of

the higher we set the bar, the greater our

whose task is to see that standards

approximately 500 per annum.

chances of competing successfully in the

are applied, appear not to fulfill this

Despite this, and the fact that the

mandate properly. In some instances, the

SABS is state-funded, the days when local

“Since its inception, the CMA has worked

consequences are immediately apparent,

government tender boards specified the

closely with the SABS in the drafting and

as in the failed Mdanzani affordable housing

SABS mark for precast concrete building

preparation of standards for the precast

project in East London. Often, however,

products as a matter of course are long

concrete industry, and these are in line with

the failures take many years to present

past. Or, as Paul Deppe points out, if stand-

best-practice international standards.

themselves, such as in leaking outfall

ards are specified, many suppliers claim to

However, unless they are implemented they

sewers, and are extremely disruptive and

manufacture according to SABS standards,

are of little or no benefit.”

expensive to remedy. What’s to be done?

while not actually holding the mark.

international arena.

Gary Steyn observes that standards in

Precast spoke to some industry players

“This makes a mockery of the whole

the precast concrete industry are actually

about standards relating to the production

s t an dar ds p r o c e ss. A l th o ugh w e’v e

becoming more stringent and in most

and application o f pr ecast concr ete

reported such instances to the SABS, they

instances the private sector insists that

products. Among them were Frank

have never supported us or investigated

they are applied.

Makamo, General Manager (Mechanical

further,” says Deppe.

“It is in the public procurement of

and Materials) of SABS Commercial (Pty)

Why is this? Is it because public and

precast products where the concern lies.

Ltd, and CMA director, Hamish Laing.

o ther pr ocur ement agencies belie v e

Longevity is one of the benefits of precast

Several CMA producer members were also

that by side-stepping SABS standards

products, and by ignoring or just paying lip-

interviewed, including: David Wertheim

they are promoting job creation? Or do

service to the relevant standards, public

Aymes, MD of Bosun Brick; Gary Steyn,

they subscribe to the notion that SABS

procurers are spurning this advantage.

MD of Infraset; Gerhard Rossouw, Technical

standards are superfluous, a ‘nice-to-have’

Director of Rocla; and Paul Deppe, MD of

which can readily be ignored?

Technicrete.

“Many precast concrete products in South Africa are world-class. However, one

One thing is certain; the consumer will

also needs to ensure that the application

T he of f icial SABS website def ines

suffer unless a nationally acceptable set

of these products is equally high. There is

standards as the oil which lubricates

of standards for the precast concrete

no point in producing a world-class product

the machinery of economic growth and

industry, as provided by the SABS, is

if it is incorrectly installed.”

international trade, and also as essential

vigorously pursued on all fronts – and

Gerhard Rossouw adds that the dropping

to ensuring international competitiveness,

soon. Whatever the reasons, ditching

of national standards by local governments

quality and consistency. It states further

national standards can only lead to one

is a huge frustration for those companies

that standards define quality and establish

result, a nation that is less able to feed,

which hold the SABS mark. As he says,

health and safety criteria.

clothe, house and educate its people on a

how does one tell the public that their tax

T he SA BS Standar ds Di v ision has

sustainable basis. And sustainability, the

money is being used for something that may

spent more than 60 years developing na-

mantra of the New Millenium, is certainly

very well let them down in five or 10 years,

tional standards and adapting international

not achievable without the assiduous

rather than lasting for 40 years or more.

standards for local application. Through

application of national standards.

“I believe that the SABS has lost much

PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010 15

of its clout and doesn’t seem interested

role today that people seem to lose track

producers who don’t can drop their prices

in backing its permanent mark holders.

of everything else,” says Rossouw.

by skimping on the quality of materials and

It’s a statutory body that was established

Deppe agrees, saying that consultants

in terms of the Standards Act, 1945

often don’t support products which carry

(Act No. 24 of 1945), and in terms of the

the SABS mark.

production procedures. “If public procurers continue to ignore national standards the time is approaching

latest edition of the Standards Act, 2008

One product currently being specified

when it is simply not worthwhile for major

(Act No. 29 of 2008), it operates as the

by municipalities is the cellulose fibre

players in the precast concrete industry

national institution for the promotion

reinforced pipe (FRC). It doesn’t carry the

to subscribe to national standards. We

and maintenance of standardisation and

SABS mark and doesn’t comply with the

must not allow this to happen as the

quality on commodities and services.

standards set for specific pipe materials.

type of shoddy construction practice we

Surely it is in the public interest for state

Tests conducted by the University of

are currently witnessing in the affordable

funds to be spent on goods and services

Pretoria’s Civil Engineering Department

housing market will spread to the rest

which are subject to these standards and

reveal that the crushing strength of FRC

of the industry, with disastrous conse-

which offer some form of life-expectancy

as a gravity piping material fails to meet

quences for all.”

guarantee? Mark holders spend more

several requirements laid down by SANS

David Wertheim Aymes commented on

money in providing products which carry a

819:2001 (Edition 3.2) for this type of

how it appears as if municipalities have

guarantee and which are produced in ISO

gravity conduit. Despite having several

completely given up on national standards

9001 or ISO 9000 listed factories.”

shortcomings, referred to in an article

for infrastructural precast concrete

“The consulting industry must also

published in this and other construction

products.

share some of the blame. Although it writes

journals, many municipalities still specify

standards into its design specifications, it

the material.

“Without infrastructure, life as we know it is not sustainable. It is absolutely

is often lax when it comes to ensuring that

Laing observes that companies which

critical that when we have money we use it

the specified products are actually supplied

do carr y the SABS mark operate at

soundly. If we don’t get the construction of

by the contractor. Price plays such a big

a competitive disadvantage, as those

the infrastructure right, everything else in

16 PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010

the national economy is adversely affected.

For tunately, pockets of excellence

upcoming entrepreneurial class understand

When one constructs on the basis of price

still exist in South Africa and, as Frank

the importance of national standards to

rather than national standards, quality

Makamo points out, the country can still

both themselves and the country as a whole.

invariably suffers, a situation which is far

boast some of the world’s best concrete

To this end, an urgent priority of the SABS

more expensive to remedy than getting it

technology. This is thanks to bodies such

under the leadership of our new CEO, Dr Boni

right in the first place.

as the SABS, CMA, C&CI (Cement and

Mehlomakulu, will be to organize workshops

“Our company is the only one which car-

Concrete Institute) and CSIR Council for

and breakfast sessions and invite various

ries the SABS 927 mark for concrete kerbs

Scientific and Industrial Research), all of

government departments to them. The

and we manufacture them using the dry-

whom have done much to promote high

SABS intends engaging with them on how

cast method. In fact we won the President’s

standards in precast concrete and in

best to entrench a culture based on high

Award for innovation in kerb manufacture.

construction as a whole.

nationally-based standards, rather than one

Despite this, we are being forced to fight

“One only has to examine the massive

on price to secure orders. Our competitors

construction projects taking place at

“We aim to adopt a strategy which will

use wet-cast moulds which lack consistency

the moment - Gautrain, the World Cup

ensure that the smaller entrepreneur is

in durability, shape and size. Their raw ma-

stadiums, upgraded airports and the GFIP

trained and equipped to produce to SABS

terials are often manually mixed to varying

(Gauteng Freeway Improvement Project) -

standards, while at the same time doing

standards, and their end-products often

to realise that we still have the capacity

everything in our power to ensure that bod-

don’t join up neatly, making for unsightly, and

to construct to world-class standards.

ies such as the Department of Public Works

in some cases hazardous, installations.

However, it would be dangerous to rest on

and local governments specify the SABS

which is price driven.

“We have also encountered several

our laurels. Local companies which are still

mark in their tender documents. There is

instances of fraud and corruption which we

capable of producing to these standards

no reason why SMMEs should not be able

believe are also undermining the application

will either cease to exist or move offshore

to provide quality products which meet

of standards. We estimate that R-billions

if we don’t reverse the current trend.

international best practice standards. I am

ar e being lost in f raudulent tender s annually,” says Wertheim Aymes.

“This poses the question as to how we can ensure that local governments and the

optimistic that we will meet this challenge,” concludes Makamo.

BUILDING A NATION THE CMA - DEVELOPING A BETTER QUALITY OF LIFE The CMA is committed to a better quality of life for all South Africans, especially for its less privileged communities. Education, access to fresh water, improved sanitation, roads and housing, are areas in which our member companies are paying increasing attention. The benefits of innovative concrete technology are wide-spread as witnessed in the building of new houses and schools; the laying of concrete block paved (cbp) roads; and the installation of precast concrete infrastructural products for sewerage, stormwater, lighting, toilets etc.

It doesn’t stop there. A commitment to seeking better and more cost-effective building solutions appropriate to the country’s needs justifies our existance. Watch this space for further developments.

Block D, Lone Creek, Waterfall Office Park, Bekker Road, Midrand PO Box 168 Halfway House 1685 Tel +27 11 805 6742 • Fax +27 86 524 9216 e-mail: main.cma@gmail.com • website: www.cma.org.za

18 PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010

PRECAST CONCRETE PROVIDES A KEY TO THE HOUSING CHALLENGE – SA HOUSING CONFERENCE Precast concrete in various guises, if properly applied, offers technical solutions which can dramatically reduce South Africa’s housing backlog.

a convincing case as to why spending R1 billion on a stadium for the 2010 World Cup benefited the City’s housing policy.

Increased delivery tempos as well as

the conference was attended by 350

Mayor Plato observed that Cape Town’s

considerable improvements in the quality of

delegates including an overseas contingent

housing backlog was exacerbated by migra-

affordable housing using precast concrete

from the United Kingdom, China, Germany,

tion into the city, which was much higher

was the subject of two papers presented

Canada, the Netherlands and Namibia.

than anticipated. The city’s natural popu-

at last year’s SAHF International Housing

Keynote addresses were made by Helen

lation growth rate is 1% of an estimated

Conference and Exhibition. These were

Zille, premier of the Western Cape and the

904 000 households, whereas migration

delivered by former CMA director, John

executive mayor of Cape Town, Dan Plato.

accounts for a further 16 to 18 000 house-

Cairns, and Llewellyn van Wyk, a senior

Both outlined the immense challenges faced

holds a year. Plato said this means that an

researcher at the CSIR.

by the city in providing housing to a growing

Staged in Cape Town during October,

number of squatters and Zille presented

Last year’s SAHF International Housing Conference in session.

PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010 19

additional 20 000 houses are added to the

pleasing finishes were the hallmark of this

affordable housing projects, adding value to

waiting list annually.

development and we believe that if there

individual housing units far in excess of any

High unemployment rates aggravate

were more projects like it going up all over

initial purchase price. In fact independent

the situation. According to the mayor a

the country the housing challenge would be

tests conducted on behalf of the CMA have

startling 77% of all Cape Town households

far less daunting,” he said.

demonstrated that in many instances,

As mayor Plato pointed out, one of the

concrete roof tiles are the most cost-

major problems is the time it takes to

effective roofing option on roofs built with

Premier Zille said that employment and

build a house, a process which must be

trusses, which is most of them.

not housing was the reason why masses

accelerated if the housing backlog is to be

However, both the CMA and the CSIR

of people are streaming into the city. She

meaningfully addressed. A solution offered

contend that concrete blocks will remain

maintains that a sound housing policy must

by Cairns is the precast hollow-core slab

a key component of low income housing

be underpinned by economic growth and job

which, when combined in a foundation and

for some time to come. How their quality

creation. Research initiated by Zille shows

flooring system, can be installed at a rate

and performance can be enhanced was

that many of the migrants exchange solid

of 30 per day by a single team.

live below the poverty datum line and 30% are regarded as being ‘vulnerable’.

the subject of Llewellyn Van Wyk’s paper,

houses in rural areas for plastic covered

“This fast-tracking and Agrément ap-

shacks in the city, so desperate is the need

proved method allows building operations to

Van Wyk based his address around

to generate an income.

begin immediately and speeds up the whole

the central question: “Can we build low-

construction process,” said Cairns.

income housing that performs as well

Growing the local economy is what mo-

“Maximising modular masonry”.

tivated the city to invest R1billion in the

Locally, hollow-core slabs have been

as conventional housing at the same or

Greenpoint Stadium. Zille said it gave Cape

offered for fast-track flooring on double-

a slightly higher cost of a typical poor

Town’s economy a huge boost, realising an

storey housing units since the 1980’s. Ad-

performing low-income house?”

additional R9 billion investment from the

vantages include faster overall construc-

Yes he says, but not just yet. A consid-

state, much of it in infrastructure up-

tion times, better quality controls and a

erable improvement in the application of

grades. She said a further R20-R30 billion

quicker pay-back. The technology has now

modular masonry must first take place.

in private sector construction had taken

been extended to medium-rise buildings;

“Modular masonry offers a fantastic

place in the CBD, all thanks to the city’s

hollow-core slabs have been successfully

opportunity to not only improve housing

initial decision to build a new stadium.

deployed on two medium-rise projects,

delivery, but to build houses with zero

May or P la t o b elie v e s tha t higher

Capital Park, a seven-storey residential

wastage. But before this takes place

densities are essential to sustainable

building in Pretoria, and Bridge-view, a five-

several measures have to be taken,” says

progress in addressing the housing backlog.

storey load-bearing masonry residential

van Wyk.

Three and four storey houses and higher

structure in Johannesburg.

“In the first instance, houses will have

are being investigated. If the city is to meet

Cairns also demonstrated how concrete

to be designed with each and every block

its target of housing everyone within the

roof tiles are increasingly being used on

identified and numbered. If not, the system

next 15 to 20 years current delivery rates will have to be improved considerably and the mayor concluded his address by calling on conference delegates to help Cape Town realize this goal. John Cairns responded by illustrating how precast concrete can be effectively deployed to address the housing backlog in his address “The preferential use of concrete and precast products for the development of township housing and housing infrastructure”. He said precast concrete is already making a positive impact on township housing and cited Pennyville, an attractive affordable housing development south of Johannesburg’s CBD. Most of the building materials used on the project, including the bricks, the roofing, the paving, reticulation poles, and hollow-core precast flooring, were precast concrete based. “Speed of delivery and aesthetically

High-quality affordable housing, most of it built using precast concrete elements, predominate at Pennyville, an affordable housing project in Johannesburg. The picture shows houses built with Sedibeng concrete bricks and roofed with Monier’s Coverland concrete tiles, a path paved with Technicrete’s concrete blocks, and prestressed concrete poles manufactured by Infraset.

20 PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010

won’t work. This places certain constraints

degree of rigidity.

on design flexibility, but at this level the

“Fifthly, full modular masonry will also

importance of building ef ficiencies far

require the standardisation of components

outweigh those of design flexibility.

such as window and door frames. Further-

“Secondly, genuine modular designing will require a full suite of complementary

more, it is also important to choose a roof angle that actually fits the blocks.”

blocks. One can’t treat the 390mm block

Van Wyk says the CSIR’s research is

like a brick. Corner blocks, reveal blocks,

centered on an experimental site at the

sill blocks, and half blocks are required to

Pretoria Campus where several 40m²

make the use of modular blocks effective.

houses have been built to test different

Without a full set of complementary blocks

technologies. Two of them were built using

the advantages of modular construction

modular masonry.

is negated.

“The first was a conventional NHBRC

“Thirdly, modular blocks are far larger

unit built with a 140mm solid concrete

and require a different set of skills. Because

block using a category of contractor who

of this contractors and block layers must

would normally build low income houses. The

be taught how to use modular masonry. It’s

quality of the construction is typical of the

encouraging to note that this process has

quality currently delivered, which is poor.

already begun with CETA-approved modular

We then built exactly the same house but to

training initiated by the CMA.

standards which middle and upper income

“Fourthly, using a full suite of modular

earners would find acceptable.

Western Cape Premier, Helen Zille, delivers one of the keynote addresses at last year’s housing conference.

masonry will solve another very prevalent

“The comparative performance of the

“We are also investigating the construc-

problem, namely, cracked walls. It is

two houses is being measured on the

tion of an advanced construction technol-

one we came across during our work

basis of sub-structure, superstructure,

ogy laboratory for further research work

on behalf of the Department of Science

roof assembly, finishes and services.

and are working on the development of

and Technology in Mdanzani where an

In each instance we recorded the cost

an innovative new suite of modular blocks

af fordable housing project which aims

and quantity of materials used, the time

which will offer performance and quality

to erect 2 500 40m² units, has been

taken to construct each house together

improvements.”

plagued by poor workmanship and shoddy

with the associated labour costs, and the

Van Wyk says that in the future, con-

quality. We solved the problem of cracking

quantity of waste generated. The analysis

crete blocks will have to be designed to

at purlin level at Mdanzani by replacing

is currently under way and forms part of

meet the new regulations for building ef-

the top layer of blocks with a ring beam.

our research into seeking opportunities

ficiency which should be in place by April

Not only does it prevent cracking, but it

for improved performance and innovative

2010. R and U values are going to be re-

provides the houses with an astounding

technologies.

set which means producers will have to make adjustments in the manufacture of masonry blocks to meet these performance criteria. A third concrete technology paper, “The innovative use of cementitious products in social housing”, was delivered by Daniel van der Merwe, an architect who conducts presentations and promotions on behalf of the Cement and Concrete Institute. Van der Merwe demonstrated how creative designs and lateral thinking can transform what would otherwise have been structures of drab uniformity into buildings which are visually stimulating and offer a pleasant living environment. He highlighted the versatility of concrete and how it lends itself to innovative and original designs. His photos of affordable apartment buildings

Llewellyn van Wyk (left) a senior researcher of the CSIR, John Cairns, former director of the CMA, (Concrete Manufacturers Association) Hanlie Turner, marketing manager of C&CI (Cement and Concrete Institute) and John Sheath, strategy and marketing manager of Ash Resources, seen here at last year’s SAHF International Housing Conference and Exhibition in Cape Town.

in Europe, especially in Spain, gave food for thought to those contemplating higher density accommodation in local cities.

PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010 21

CMA DONATES BUILDING MATERIALS TO ORANGE FARM YOUTH DEVELOPMENT CENTRE The Concrete Manufacturers Association (CMA) is donating over R700 000 worth of precast concrete building products for the construction of a youth development centre (YDC) at Orange Farm, a large township with a population of over 1.5 million, located some 45 km south of Johannesburg. The products include concrete masonry blocks, precast floor slabs, concrete block pavers (CBPs) and concrete roof tiles.

MaAfrika Tikkun manages six other community centres countrywide including the Child and Youth Community Centre in Diepsloot, which was built in 2008 with donations of concrete blocks and other precast concrete materials from the CMA. MaAfrika Tikkun will manage the ongoing financial support needed to run

The YDC is being built by MaAfrika Tikkun,

“For example, the masonry work is

Are Kopaneng which is being sourced

an NGO which cares for and nurtures

a case in point, and Watson Concrete

through funds donated by the business

v ulner able childr en in Sou th A f r ic a .

undertook the training of 10 raw recruits

community, various foundations, and the

The Orange Farm YDC will add a much-

on block laying techniques. This was an

national lottery.

needed additional dimension to an existing

extremely successful enterprise as the

community centre, Are Kopaneng (Let Us

picture which accompanies this article

Come Together), which includes an early

testifies. Moreover, these block layers have

childhood development centre for children

acquired a skill which they will now be able

up to the age of six years and a job creation

to sell on the open market.

centre in an adjacent building.

The Are Kopaneng YDC was designed by

The new building will be used to provide

Harold Lipschitz of The Cook Lipschitz Part-

after-school support for 350 children from

nership. The remainder of the professional

seven upwards and teenagers up to the age

team comprises: structural engineer, Erik

of eighteen. On-site services will include

Stern of EJ Stern and Associates; and

a daily meal, homework support, sports

quantity surveyor, Russell Irons of Russell

activities, recreation, life skills, arts and

Irons and Associates. All offered their

culture and counselling. In addition to the

services at discounted rates. The main

new building a running track, paved with

contractors are GT Homebuild and Building

concrete block pavers (CBP) supplied by the

Solutions SA Joint Venture.

Watson Concrete’s 6Flute Biscuit blocks being expertly laid in the construction of the new youth development centre at Are Kopaneng by formerly unemployed Orange Farm residents.

CMA, will be laid around the new building. Construction of the 1 772m² singlestorey YDC began in January and is due for completion in May. The building will comprise a multi-media room where computer skills will be taught, a library, a sports hall, kitchen and pantries, counsellors’ accommodation and administrative offices. CMA members are supplying concrete masonry blocks, floor slabs, concrete block pavers and concrete roof tiles at cost. Approximately 40 000 masonry blocks ar e being supplied by CM A pr oducer member, Watson Concrete, in three styles, a 190mm 6Flute Biscuit block, a Crete (Rock Face) block in 190mm and 90mm, and a grey Fairface block in 190mm and 90mm formats. CMA director, Hamish Laing, says that where possible the project is being used to provide jobs and teach skills to formerly unemployed Orange Farm residents.

A site meeting during which members of the professional team are seen here with former CMA director, John Cairns and Morris Mizrahi, Are Kopaneng’s project manager. They are from left: quantity surveyor, Russell Irons of Russell Irons & Associates; Joe Tshabangu, a BEE partner with the main contractors, GT Homebuild & Building Solutions SA Joint Venture; structural engineer, Erik Stern of Erik Stern & Associates; architect Harold Lipschitz of The Cook Lipschitz Partnership; John Cairns; Morris Mizrahi; Willem Knoetze, Annette van Rensburg and Stoffel van Rensburg, all three of GT Homebuild and Building Solutions SA Joint Venture; and Menzi Kubheka of MaAfrika Tikkun.

22 PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010

Coverland concrete roof tiles provide attractive and durable covering at Leo Mews, a five star Green Building project situated near Elsies River on the Cape Flats which was designed and constructed by Bitol Development.

Double cavity walling, using concrete bricks supplied by Columbia DBL.

PRECAST CONCRETE DOMINATES IN GREEN BUILDING GAP HOUSING P Concrete roof tiles, concrete bricks and a concrete rib-and-block flooring system, are playing a crucial role in the construction of Leo Mews one of South Africa’s most innovative and eco-friendly gap housing projects to date.

unskilled workers, and Bitol is providing

Situated in Leondale, which abuts Elsies

fortunate enough to move into one of its

is being conducted on site in which English

River in the heart of the Cape Flats,

apartments to a level of comfort, security

usage and basic arithmetic skills are being

this 125 twin-bedroom sectional title

and environmentally responsible living

taught. These classes are being run for four

apartment project is in alignment with the

which sets a standard not only for the

hours daily by CETA (Construction Educa-

five-star Green Building* rating system

Cape Flats but for the country as a whole.

tion and Training Authority) in a special

and NHBRC ( Na tional Homebuilder’s

Moreover, the project is being built to a

trailer supplied by Bitol and are principally

Registration Council) specifications.

construction standard which would not

aimed at providing those who wish it with

be found wanting in any of South Africa’s

an opportunity for further study. Classes

affluent urban areas.

begin two hours before the official work

Phase 1 was officially launched by Cape Town’s executive mayor, Dan Plato, in

additional training in various constructionrelated disciplines. In addition, an adult literacy programme

September last year. The project was born

Besides its more visible attributes,

stoppage time and are also held on Sat-

of a ground-breaking partnership between

other less apparent but equally tangible

urdays. Similar programmes run by Bitol

the City of Cape Town, Standard Bank and

benefits are flowing from this project.

on earlier construction projects have led

Bitol Development, the latter fulfilling the

For instance, seventy percent of the

to some of the participants graduating as

design, development, marketing and main

on-site workers were recruited by Bitol

engineers. Andre Swartz, the construc-

contracting roles.

Development from among unemployed

tion manager of Leo Mews, is one of the

Due f or comple tion in May 2010,

local residents. They comprised skilled

beneficiaries of this initiative.

Leo Mews introduces those who will be

(40%) and semi-skilled artisans (40%) and

Aimed at families with a combined

* The South African Green Building Council is yet to provide a residential Green Star rating system. Considering that the South African system is likely to be based on the Australian Green Building rating, Bitol aligned Leo Mews with the latter, thereby ensuring that in the absence of a South African rating system for residential accommodation, the development still incorporated the necessary elements of a reputable Green Star system.

PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010 23

and bathrooms, carpeted bedrooms with

vicinity of the project. This has softened

built in cupboards, and balconies with

what would have been a stark contrast

hidden washing lines.

between Leo Mews and these properties,

Twenty five triple storey apartment

in addition to acting as a catalyst for

blocks are linked together in four self-

uplifting the entire area. As a result a

contained sections. Each block comprises

strong sense of community is developing

five dwelling units, two 45m² units at ground level and three 51m² units situated adjacent to one another on the upper two levels. The top storey units have a tiled kitchen/living area and a bedroom on the downstairs (second) floor, with a master bedroom, separate bathroom and balcony on the upstairs (third) floor. Ground floor units consist of two bedrooms, a separate bathroom and a combined kitchen and living area. Excellent space usage is evident, Phase three of Leo Mews under construction.

Bitol Technologies’ education trailer.

especially in the design of the upper units where the baths extend into what would normally have been wasted space above

IN FIVE-STAR PROJECT

the staircase. The development is being constructed as a four-in-one concept comprising four distinct residential blocks with approximately 30 apartments in each. Instead of one large development in which amenities such as parking and access control are shared, each block has it own access control and secure parking. This reduces

minimum income of R7 200 a month, Leo

the impersonal nature which often typi-

Mews, is an outstanding example of how a

fies large residential developments while

creative approach and sound construction

accentuating exclusivity and upmarket

technique can deliver eco-friendly, hi-

attributes.

quality residential accommodation at

The delivery of sound eco and budget

a budget price. Similar apartments in

friendly accommodation appears to have

C ape Town’s southern suburbs such

been perfected by Bitol Development, a

as Kenilworth are fetching R600 000

multi-faceted Western Cape company,

whereas the units at Leo Mews units

which not only develops and constructs

range between R234 000 and R254 000.

residential properties such as Leo Mews,

This is a remarkable achievement.

but, through its sister company, Bitol

Besides concrete roof tiles, which,

Technologies, also manufactures solar

because of their aesthetic and green

water heating systems and installs plant

attributes, are now being widely deployed

for the petro-chemical industry.

in economic housing projects across the

David Williams, marketing director of

country, the development boasts other

Bitol Technologies, says projects such

green measures such as cavity walling,

as Leo Mews are very demanding, both in

solar heated water and water recycling.

terms of innovative hard skills input such

Moreover, all units have been equipped

as the design and construction work, and

with waste separation bins divided into

creative soft skills intervention, which is

compartments for glass, paper, aluminum,

necessary to ensuring a project’s financial

plastic and non-recyclable goods.

and social viability.

L eo Mews is no t shor t on lu xur y

For instance, before commencing with

fixtures and fittings either; these include

the actual construction of Leo Mews,

wooden window frames, attractive banding

Bitol devoted considerable time and effort

around the windows and doors, tiled floors

in upgrading properties in the immediate

The bathroom in one of the upper level 51m² units where the bath extends over what is normally wasted space above the staircase.

The living and kitchen space in one of the 45m² units showing the high-quality floor tiles and kitchen.

One of the balconies which features: attractive banding around the doors and windows; wooden door and window frames; and a wall behind which washing can be hung without being seen from the street.

24 PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010

between the residents of Leo Mews and

and high-quality concrete roof tiles. All

established Leondale residents.

ex terior masonr y consists of double

(Above from left): Leo Mews nearing completion; a rib-and-block floor system, supplied by DBL Decking, under construction.

“It is far more difficult to develop a

cavity walls which are being built using

high-quality budget property than it is to

Columbia DBL’s 222mm Maxi concrete

advantages include: ease of installation,

build more upmarket dwellings and a high

brick, rated at 14MPa. The balconies are

not only on new roofs but on structural ex-

degree of lateral thinking and innovative

being constructed with 140mm concrete

tensions as well; low maintenance; high UV

planning are required if projects like these

blocks which were also supplied by Columbia

resistance; and suitability to all climates,”

are to succeed. For example, we employ

DBL, and the two upper floors are being

comments Steinbach.

an in-house architect, who in combination

erected with a rib-and-block system

with other cost-saving initiatives, has

supplied by DBL Decking.

enabled us to contain development costs

Bitol estimates that the solar water heating will reduce electricity consumption

One of the reasons why Leo Mews

o n this d e v e l o pm en t b y s om e 6 0 %,

resembles residential housing in more up-

which taken over 125 apartments, is

“Not the least of the challenges on this

market suburbs is its roofing. Coverland

no t insigni f ic an t . B e side s the solar

project is the low-income earning capacity

Double Roman roof tiles supplied by Monier

water-heating panels, which are being

of the potential customer/dweller base.

Roofing, were specified for the project and

manu f ac tur ed by Bitol Technologies,

Many families find it difficult to live within

are being laid on wooden truss systems

additional energy saving is being realised

their means, especially at these income

made by African Trusses. The roof laying

on the hot-water piping, which is insulated

levels, and we are engaging with them on

process is complicated by the fact that

with polyurethane.

how they can budget and thereby improve

five solar panels per five-unit block are be-

Further compliance with the five star

their credit profiles,” said Williams.

ing built and sealed into the roofs and this

Green Building rating system will see Leo

means that instead of a day-and-a-half to

Mews being serviced by three separate

erect the roofs it is taking four days.

water recycling systems. Kitchen and

by a considerable margin.

Unlik e t h e c u s t om a r y singl e - sk in masonry found on most low-cost housing d e v e l o p m e n t s, L e o M e w s i s b e i n g

Monier’s national components manager,

washing water will be chanelled into

constructed with plastered cavity walls

Christopher Steinbach, says concrete roof

collection tanks where it will be filtered

tiles offer exceptional value for money,

and cleaned. It will then be pumped back

long-term durabilit y, good insulation

into individual holding tanks located under

properties and aesthetic appeal.

the roof eaves from where it will be fed as

“As a recent CMA survey has proven,

A close-up view of one of the Coverland roofs.

‘grey’ water into toilet cisterns.

concrete roofs are the most economi-

When the construction phase of Leo

cal form of covering for trussed roofing.

Mews is complete, Bitol has undertaken

Moreover, they enhance the value of

to manage the administration of the

property far in excess of their capital out-

project for five years during which time

lay. It is therefore hardly surprising that

it will train and educate residents on the

concrete roof tiles are making substantial

requirements and intricacies of running a

inroads into affordable and gap housing

successful body corporate. Well done Bitol

developments such as Leo Mews. Other

Development. P

of MAPEI 15 PRODUCT LINES

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PROD PRODUCTS P FOR STRUCTURAL S TRU S TRE STRENGTHENING

PRO PRODUCTS P FOR UNDERGROUND U ND CONSTRUCTIONS C ON

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26 PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010

STRUCTURAL AND DESIGN ASPECTS OF POROUS AND PERMEABLE CONCRETE BLOCK PAVEMENTS IN WATER-SENSITIVE URBAN DESIGNS This article is an edited version of a paper authored by Professor Simon Beecham and Baden Myers of the School of Natural and Built Environments, University of South Australia. It is of particular relevance to architects, civil engineers, property developers and local authorities, or South Africans concerned about preserving and harvesting stormwater for reuse. The original and fuller version of this paper is available from the Concrete Manufacturers Association (CMA).

Pavements (any paved surface) are an intrinsic, seldom-thought-about part of life, particularly in urban areas. However, f or de v eloper s and local au thor i ties addressing stormwater and associated water quality regulations, pavements r em a in v e r y m u c h a t t h e f o r e f r o n t o f p l anning is su e s . T his is b e c a us e impervious surfaces such as pavements have a negative impact on water quality and on the health of natural ecosystems. In response, water-sensitive urban design (WSUD) strategies, such as permeable a n d p o r o u s p a v e m e n t s, h a v e b e e n developed to reduce the environmental footprint of new urban growth and their use as a stormwater management tool is growing. For example, in New South Wales, Australia, the Parramatta City Council is implementing deemed-to-comply development conditions for stormwater management, including the consideration of porous and permeable pavements as a standard WSUD option. ‘Porous’ and ‘permeable’ paving are technologies tha t allow the ingr ess of stormwater. T hey pr ovide f or the infiltration of stormwater on site, and can harvest stormwater for fit-for-purpose re-use using geomembrane sealed subsurface ‘tanks’. Porous pavements allow the ingress of water through the paver itself, whereas permeable pavements are constructed from conventional impervious materials but laid with ‘gaps’ between the pavers to allow for water ingress. Research at the South Australian Water Centre for Water Science and Systems at the University of South Australia is investigating the re-use potential of water harvested using porous and permeable pavements. The design and construction of a car park-sized test model is complete and research is being undertaken on how the storage mechanism affects water quality. This investigation has built on existing research within the centr e, where the infiltration rate, structural properties, lifespan and physical filtration efficiency provided by permeable concrete block paving, have been studied. Another research programme being developed at the University of South

A recent example of a South African permeable concrete block paving (PCBP) installation where a 380m² car park at the Anglican Cathedral in Pietermaritzburg was paved with 80mm Uni-Ecolok pavers manufactured by INFRASET Landscape Products.

Australia will investigate the strength properties of porous concrete pavements.

PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010 27

One of the major inhibiting factors in the

fluid transport properties of the concrete.

only, which is flood prevention. Conventional

use of porous pavement materials is

As recycled aggregates have much higher

systems ‘catch’ or drain overland run-off

the lower strength properties resulting

water absorption ratios, tests were

from the surface of an urban catchment

f r om th e p or o si t y o f th e c on cr e t e .

performed under both soaked and un-

and ‘convey’ it to natural streams and

D u r i n g 2 0 0 6, a s t u d y w a s c a r r i e d

soaked aggregate conditions. In addition,

watercourses. This inevitably leads to

out on the laboratory development of

the microstructure of the testing samples

pollution of receiving waters.

new permeable pavement base course

has been investigated using scanning

Although demonstrably successful in

materials using recycled aggregates.

electron microscopy (SEM), an image

preventing flooding, such an approach

Besides investigating permeable pavement

analysis technique.

to stormwater management has proved

base-course materials, a further objective

to be problematic in the broader sense.

was to develop new cement-tr eated

Problems with urban stormwater run-off

First, simply disposing of stormwater

materials to carry higher traffic loads.

As urban areas develop in a catchment,

run-off into urban streams via engineered

Cement-treated permeable base courses

the area of impervious surfaces, includ-

systems significantly alters the natural

consist of specially formulated mixtures

ing roadways and roof areas, tends to

hydrology of a catchment. Second, urban

of Portland cement, uniform open-graded

increase. One of the many effects of in-

stormwater is known to contain a variety

coarse aggregate and water. The amount

creasing the area of impervious surfaces

of pollutants that are major contributors

of cement required to achieve the balance

is an increased amount of stormwater

to the degradation of streams, wetlands

between high-void space and adequate

runoff. Moreover, urbanisation leads to

and their accompanying habitats. Third,

strength of material was extensively

varying degrees of degradation in the qual-

given Australia’s water shortage, simply

investigated to ensure that only sufficient

ity of stormwater run-off.

disposing of stormwater run-of f is no

c emen t t o c o a t the aggr ega t e w as

Conventional stormwater drainage

used. More than 20 mix designs were

systems, utilise a ‘catch and convey’

examined and some preliminary results

approach. They are designed to achieve the

The need for urban stormwater re-use

were obtained on both the strength and

primary aim of stormwater management

Stormwater, like desalination and new

longer acceptable to the community.

28 PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010

dam constr uc tion, is among se ver al

structural support. In some applications,

latter and arguably more cost-effective

alternative water supply options being

multiple base courses may be applied.

concept is shown in Figure 2.

considered. Both large and small-scale

Depending on the structural demands, this

systems for stormwater re-use are being

layer is usually 300mm thick and consists

pursued to alleviate the Australian ‘water

of 20 – 40mm aggregate. It should be

crisis’. Research being undertaken at

noted that this aggregate differs from

the University of South Australia which

the normal road base material in that it

is investigating the re-use potential of a

contains no fines and drains freely.

small-scale stormwater, is contributing to the growing field of Australian research into water sensitive urban design. Figure 2 - The water re-use concept.

Water-sensitive urban design Australian water-sensitive urban design

Existing examples of permeable pave-

(WSUD) emerged in the early 1990s. It

ment stormwater harvesting include pub-

therefore represents a modern approach

lished data on a system constructed in the

to the management of urban stormwater.

United Kingdom. An Australian case study

Broadly speaking, it seeks to implement

is also available, describing a storage and

the principles of ecologically sustainable

re-use facility in Manly, New South Wales.

development in the context of water

However, performance records of these

resource management. WSUD focuses

systems are not extensively reported.

on the interaction between the urban

Due to the relative infancy of this re-

built form and the natural water cycle

search, it is postulated that stormwater

and can be regarded as an alternative to

harvested, treated and stored in the

the aforementioned ‘catch and convey’

base-course of porous and permeable pave-

approach. It is driven by four broad aims,

ments will be used for outdoor irrigation

each of which should be considered for

purposes only.

the implementation of a stormwater management strategy:

Figure 1 - Typical cross section of a porous or permeable pavement construction.

Research objectives Where a system retains stormwater for

1. The provision of flood conveyance A layer of geotextile is applied on the

re-use as shown in Figure 2 further physi-

base course. Although not essential, it

cal and chemical processes can occur and

3. The removal of contaminants

provides an additional water filtration ele-

these are currently subject to investiga-

4. The promotion of stormwater elements

ment. It also separates the base course

tion at the University of South Australia.

as part of the urban form.

from the bedding course. A bedding course

Storage of water in the base course of the

approximately 30mm thick in most ap-

pavement construction has been shown to

Porous and permeable pavements

plications and 3-7mm aggregate is then

have both positive and negative impacts

– an established WSUD tool

laid on top of the geotextile. Sand is not

on water quality.

The key advantage of porous and permeable

recommended for most applications due to

Using model pavement reservoirs and a

pavements is that they allow for the reten-

a susceptibility to clogging. Pavers may be

control water reservoir exposed to the sur-

tion or detention of stormwater onsite

placed directly on top of this layer.

rounding air, experiments were conducted

2. The protection of downstream aquatic ecosystems

on the water quality effects of storing

without compromising the amenity (environment) of above lying land. They also in-

Water re-use

stormwater within the aggregate base

troduce a variety of potential water-quality

Porous and permeable pavements present

course underneath a porous or permeable

treatment processes which intercept the

a unique opportunity to harvest and store

pavement structure. Stormwater was

contaminants of urban stormwater run-off

urban stormwater. With minimal surface

added to the reservoirs and sampled for

prior to infiltration.

infrastructure, porous and permeable

a period of one week and water samples

The design and construction of porous

pavements provide a serviceable, hard-

were subject to a broad range of water

and permeable pavements has been subject

standing area that f acilitates water

quality analyses.

to significant amounts of research.

harvesting, treatment and re-use.

A typical porous or permeable pavement

Several storage and design options are

construction is depicted in Figure 1.

available. These include submerged tanks,

The results of this experimentation can

After excavating to the desired depth, a

proprietary plastic cell systems, or a

be briefly outlined as follows. On the one

suitable base course is laid. This must be

matrix of base course aggregate contained

hand, the absorption of heavy metal ions

a free-draining material that will provide

within an impermeable membrane. This

leads to an overall improvement of water

Results

PRECAST VOLUME 4 â&#x20AC;˘ ISSUE 1 â&#x20AC;˘ APRIL 2010 29

Figure 3 - Change in alkalinity of stored water (as CaCO3) over a period of one week.

materials available in the Adelaide region.

ing worldwide, they have not been widely

Figure 3 demonstrates the changes

adopted in Australia. This limited use is

occurring in the alkalinity level of an

mainly due to concerns over their reduced

empty control reservoir exposed to the

structural capabilities, their potential to

air, a dolomite filled reservoir underneath

pollute groundwater and their perceived

a pavement model, and a calcite filled

higher costs. The University of South Aus-

reservoir beneath a pavement model.

tralia is currently involved in a research

Figure 4 shows the significant reduction in

and development programme that aims to

total zinc concentration in water samples

address some of these issues through the

drawn from these same reservoirs.

development of enhanced permeable pave-

The extent and longevity of these effects is yet to be quantified, and modified column studies are currently being undertaken to assess them. Following on from research on sand Figure 4 - Change in total zinc content of stored water over a period of one week.

infiltration systems, researchers at the

quality. However, other water quality pa-

to develop a model for the infiltration of

rameters such as pH, alkalinity and total

stormwater through porous and perme-

dissolved solids are also measurably and

able pavements as treatment processes

perhaps negatively affected by storage in

- see Figure 5.

ment construction materials. There are three significant aims in this study: 1. The development of a refined laboratory testing programme to optimise existing mix designs of porous concrete materials

University of South Australia are seeking

an aggregate-filled reservoir owing to the chemical properties of the aggregates. The

Development of new pavement materials

aggregates used in these tests were se-

Despite a growing level of awareness on

lected because they are the typical quarry

the benefits of porous and permeable pav-

Figure 5. Treatment processes in porous and permeable pavements.

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

30 PRECAST VOLUME 4 â&#x20AC;˘ ISSUE 1 â&#x20AC;˘ APRIL 2010

with and without additives. Recycled building

The amount of cement to achieve the

materials will be used as aggregates. Test-

desired balance between high void space

ing will examine the load-bearing capacity,

and adequate strength was of pivotal

fatigue life, hydraulic conductivity and pol-

concern. More than 20 mix designs were

lutant removal processes inherent in these

used to produce the samples as seen in

novel pavement construction materials.

Figure 6 and were subject to standard

2. Development of a numerical model

concrete testing procedures. The results

for the simulation of the microstructure

determined both the strength and trans-

behaviour of the materials. The model

port properties of the permeable concrete

will be calibrated using the laboratory

mix designs.

test specimens analysed with the use of scanning electron microscopy (SEM) and

Research results

3-dimensional x-ray microtomography. This

The strength properties that were evalu-

will provide a detailed understanding of the

ated consisted of compressive strength

complex relationship between structural

(Figure 7) and flexural strength (Figure

strength and porosity. It will further allow

8), and resilient modulus. Tests have also

the determination of optimal mixes for

been performed to measure the porosity

permeable pavement design.

and the coefficient of permeability of the

3. Development of a model to simulate

Figure 8 - Flexural strength testing of porous concrete.

porous concrete products.

the hydrologic behaviour and treatment

Interestingly, two different compaction

processes occurring within the permeable

methods were used during sample

pavement base course material.

preparation. One outcome of this research has already demonstrated that samples

Research methodology

prepared on a vibration table tend to have

During 2006 a laboratory study looking into

much higher structural strengths.

the development of new porous pavement

A f ur ther level of complexit y was

base courses was carried out. The objec-

introduced through the use of recycled

tive was to investigate the options available

aggregates. T hese materials tend to

in developing a new, high-strength perme-

have much higher water absorption ratios

able pavement base course material, par-

and tests were performed under soaked

a quantitative description of geometrical

ticularly one that could carry higher traffic

and un-soaked conditions. The optimum

and topological properties of the porous

loads. Priority was also placed on the use

results from this study will be used as

structure to be determined, thereby

of recycled construction materials.

candidate mixture proportions for further

providing for optimal mix designs.

A variety of cement-tr eated base

Figure 9 - SEM image of porous concrete.

research.

courses were selected for the preliminary

In addition, the microstructure of the

investigation. Cement-treated perme-

testing samples has been investigated

Research is being undertaken into the

able base courses consist of specially

using an image analysis technique known

fit-for-purpose re-use potential of storm-

formulated mixtures of Portland cement,

as scanning electron microscopy (SEM).

water harvested and treated by permeable

uniform open-graded coarse aggregate and

An image acquired using this technique is

pavements and stored in the aggregate

water. More recently, experimental trials

shown in Figure 9. SEM analysis will allow

base course. The research has so far

Conclusion

have involved the use of carpet fibre in the

revealed that significant water quality im-

matrix, however the results of this trial

provements are possible with appropriate

are still pending.

design refinements. Research into improving the overall strength of porous and permeable pavement base course is also being undertaken to address the perception of reduced strength properties. Using recycled aggregate materials, researchers have begun an investigation into the strength properties of a variety of cement-treated recycled base course materials. Further research will seek to optimise these mix

Figure 6 - Porous concrete samples.

Figure 7 - Compressive strength testing of porous concrete.

designs to achieve greater structural integrity and improved water quality.

TJDR40710

SOUTH AFRICA’S FUTURE BUILT ON STRENGTH

Nelson Mandela Bay Stadium

Over the last 118 years we’ve helped build some of South Africa’s most prominent structures, but never before have we been more pleased to see our concrete work in such a monumental structure. The concrete work in Nelson Mandela Bay Stadium will remain a testament to the structural integrity of PPC cement for generations to come. You could say we’ve given South Africans yet another reason to trust our strength. Visuals courtesy of Michael Sheehan

32 PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010

A sewer made using dolomitic aggregate and installed in 1960’s looks like new 40 years later.

SEWER CONDITION ASSESSMENT AND CORROSION PREDICTION By Alaster Goyns, Owner Pipeline Installation and Professional Engineering Services CC Many of the sewers serving South Africa’s major urban centres have reached the end of their planned design lives and some are malfunctioning or on the verge of doing so. There is an urgent need for these sewers to be assessed, and where necessary, replaced or rehabilitated.

or protected concrete.

approach in such instances entails the

By using CCTV and supporting inspection

installation of a completely new system

techniques sewer deterioration can be

along a parallel route. The rehabilitation of

measured. Life expectancy can then be

the old sewer is then much simpler. This

predicted using the Life Factor Method.

approach has the advantage of increasing

Measured and theoretical results can be

overall sewer capacity to meet anticipated

compared and any differences investigated

requirements well into the future.

to provide data for use in the design of new sewers.

Long-term performance of sewers

This article gives some pointers on

In order to perform its prime function of

corrosion and life prediction methods

providing a conduit for wastewater dis-

Recent assessments have shown that

for both new and existing sewers and

posal, a sewer must meet several sec-

sewer life using conventional concrete

also discusses the condition assessment

ondary requirements: it must be water-

materials can var y f r om as little as

techniques used to obtain data from

tight so that there is no infiltration or

20 years, where extremely corrosive

operating sewers.

exfiltration with the associated losses

conditions prevail, to well over 100 years

Many of the sewer systems which

and pollution; it must have the strength

under favourable circumstances. The major

require rehabilitation are situated below

to carry the imposed loads; and it must

contributor to sewer deterioration is

developed urban areas, making open trench

be durable. If there are any problems with

probably the lack of attention paid by sewer

access for repair or replacement extremely

the first two requirements they usually

designers to the factors which contribute

problematic. This work invariably involves

appear soon after the pipeline is commis-

to corrosion. Corrosion can be minimised or

the disruption of essential and other

sioned. However, defective durability may

even eliminated by good design practice and

services situated above them. Often, the

take years to manifest, and when it does,

detailing, and through the use of modified

most cost-effective and least disruptive

the adverse consequences can be com-

PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010 33

pounded if the area above the pipeline has

to the development of cavities around pipe

been developed.

lines, and ultimately, to sinkholes.

Provided adequate attention is paid

Certain defects are common to all pipes

to meeting the secondary requirements

irrespective of the material used, while

during design and construction, accute

others are material specific. The two pipe

problems such as blockages, surcharging

materials that dominate the new sewer

due to stormwater, or hydraulic overload-

market are reinforced concrete (RC) for

Figure 1: Comparison of rigid and flexible pipe installation details.

ing generally don’t present a permanent

diameters larger than 300 mm and PVC for

problem. Once the extreme event has been

smaller diameters. This article addresses

When there are significant variations in

dealt with the pipeline continues to func-

the defects common to all pipe materials

vertical alignment the generally accepted

tion normally.

including those that dominate the new

parameter of ± 0.8 m/s for self-cleansing

sewer market.

does not work. At high velocities large

However, should any of the secondary requirements not be met, even once, the

particles can be transported. However,

functionality and structural integrity of

Defects common to all

when the velocity drops below a certain

the pipeline could be irreversibly compro-

pipe materials

value that may be well in excess of 0.8

mised. This is of particular significance

Installation conditions.

m/s, siltation can occur. Siltation occurs

for outfall sewers that flow partially full,

There is a common misconception that the

frequently when outfall sewers flow at

especially if they are situated below other

trench bottom and pipe bedding are one and

velocities significantly lower than that of

services, because they too could be dis-

the same. This is incorrect. A trench bot-

the catchment area. If super critical flow

rupted or impaired.

tom is merely the foundation for the pipe

occurs and the total energy line is not

As most sewers in South Africa are

bedding. Bedding for rigid pipes consists of

contained within the sewer any disturbance

either non-man entry or are dangerous

two components, the bedding cradle and

to the flow, such as a directional change,

for man entry, even if they are large

the bedding blanket. The material used for

can cause a hydraulic jump within the

enough, the use of sophisticated CCT V

the bedding cradle must have the neces-

sewer. T his can r esult in the sewer

camera systems provides a visual record

sary structural properties to enhance the

suddenly flowing full. The sudden energy

of the conditions in the sewer and the

pipes’ load carrying capacity. In the case of

loss and velocity reduction can result in

invert gradient. Moreover, additional data

flexible piping the complete surround mate-

deposition and manholes surcharging.

gathering equipment can be mounted on the

rial is referred to as embedment. This em-

On the other hand at very low velocities

vehicle which carries the CCTV camera.

bedment material must have the necessary

in partially full sections or where there are

Field data from a whole length of sewer

structural properties to be able to carry

rising mains or siphons, a lack of oxygen can

can be recorded on computer and the

the load transferred from the pipes and

occur and the effluent then turns septic

defect location established. The camera,

ensure that they do not deform excessively.

and anaerobic. When this happens there

however, cannot record the actual severity

Figure 1 gives typical installation details for

is insufficient oxygen in the effluent to

of a problem, the physical dimensions of the

both rigid and flexible pipes.

support the bacteria that live in the slimes

sewer, the conditions below the water line,

The trench bottom must always be level

layer on the sewer walls. These bacteria

the effluent properties, the condition of

irrespective of the type of pipe installed. It

then obtain their oxygen from the sul-

the soil support around the sewer, nor the

should also be to grade as well as levelled,

phates in the effluent by reducing them to

causes of most defects. Recent technical

and compacted to provide a foundation with

sulphides. A proportion of these sulphides

developments have addressed several of

an adequate and uniform bearing capacity.

generate hydrogen sulphide (H2S), for which

these issues, namely the use of laser profil-

This must be done before the placement

there is an equilibrium concentration in the

ing to determine the physical dimensions of

of pipe bedding or embedment. Failure to

effluent and the sewer atmosphere at a

the sewer above the water line, and sonar

meet these requirements can result in

given temperature. As this gas is gener-

profiling to determine the physical dimen-

uneven settlement along a sewer and the

ated in the effluent there will be a tendency

sions below the water level. The concentra-

associated problems of deformed pipes,

for it to be stripped from the effluent to

tions of gases, such as hydrogen sulphide

leaking joints and backfalls. Although these

maintain the equilibrium level.

(H2S) can also be measured.

defects may not initially affect the struc-

Once in the sewer atmosphere the H2S

tural integrity of the pipes, over time they

is absorbed into the moisture layer on the

can lead to further defects that do.

sewer walls where it is used by a second

ASSESSING THE CONDITION OF

group of bacteria as an energy source

EXISTING SEWERS Identifying the buried problems

Vertical alignment

and in the process is oxidized to form

There are many causes of sewer defects

The capacity of a sewer that flows partly

sulphuric acid (H2SO4). The rate at which

but the way they present themselves

full is dictated by the section of the sewer

the H2S is stripped out of the effluent

depends on the pipe materials used, the

with the flattest gradient. However, this

and hence the rate at which the H2SO4 is

pipes and the joints. The surrounding

is not the only problem that arises with

formed is directly proportional to the flow

material is invariably affected and this leads

vertical sewer alignment.

velocity. H2S has a pungent odour and it is

34 PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010

extremely toxic. Its release in residential areas is not tolerated and precautions are needed when working in areas with even low concentrations. It is often possible to adjust a sewer system’s vertical alignment by flattening the steep sections, steepening the flat sections, and if necessary, introducing drop structures, where feasible, to ensure that sudden energy losses and deposits occur at locations designed to accommodate them. Even relatively minor adjustments to invert levels can minimise these problems and improve a sewer’s performance. Defects associated with RC pipes Reinforced concrete pipes have many properties that make them ideal for sewers. However, corrosion can pose a serious problem if H2SO4, formed through biogenic activity, reacts with the alkalinity of the

A severely corroded pipe installed in 1952 that was made using siliceous aggregate. Acknowledgements to Sight Lines Pipeline inspection Services.

concrete. This problem can be minimised or even eliminated provided the necessary

There are three options for preventing

see Figure 2, it is particularly applicable to

measures are specified and implemented

or minimising the corrosion in concrete

sewers of 1 000 mm in diameter or smaller.

before sewer construction begins. These

sewers, namely preventing acid formation,

measures are described later.

modifying concrete, or protecting concrete

There are many sewers in South Africa

as published by the author in 2008.

that were installed before the phenomena

1. Acid formation can be prevented

of biogenic corrosion was understood and

or minimised by adjusting the vertical

hence no preventative or control measures

alignment of the sewer and hence its

were taken. Many of these sewers are

hydraulic performance, as described above.

now malfunctioning and in order to make

However, due to physical constraints this

sound decisions about their replacement

is not always possible and some corrosion

or rehabilitation it is necessary to assess

can be anticipated.

Host pipe

Corrosion control lining

Figure 2: Host pipe corrosion control lining concept.

The thickness of linings such as HDPE, which are mechanically locked into the

their condition so that the solutions chosen

2. In most instances, changing the

concrete pipe with anchors or ribs at

are cost-effective but do not compromise

composition of the concrete components

fixed spacings, is independent of the sewer

their future operation. This topic too, is

and /or pr ov iding additional cover f or

diameter. On the other hand the thickness

covered in a later section.

reinforcement is the most cost-effective

of linings or coatings which are bonded to

option. The concept of using a dolomitic

the concrete surface must be specified

PREDICTING PERFORMANCE OF

aggregate in combination with a sacrificial

according to the external ground water

CONCRETE SEWERS

layer, first introduced in the early 1960s,

pressure that can develop between the

Life Factor Model

is adequate for sewers that have no rising

lining and the host pipe. Providing the pipe

The corrosion potential of a concrete sewer

mains or siphons. It is also suitable for

joints are covered by the lining this type of

can be determined using the Life Factor

sewers where the gradients ensure that

lining also offers improved flow capacity. For

Model (LFM) developed by Pomeroy and

the velocities throughout the system are

sewers in excess of 1 200mm in diameter

Parkhurst (1976) and described in detail by

self-cleansing.

the combination of reduced diameter and

McLaren (1984). This is based on system hy-

3. Protecting concrete pipes by using an

the lower relative cost of lining to concrete,

draulics, effluent composition and concrete

inert lining is effective, but only economi-

means that a lined pipe may actually be the

alkalinity. Until recently its application was

cally viable when very severe corrosion is

most cost-effective solution irrespective

limited to Portland Cement (PC) concretes

predicted. In instances where the pre-

of corrosion potential.

and no distinction was made between sub-

dicted corrosion is severe but an inert

critical and super critical flow conditions.

lining cannot be economically justified,

Establishing the remaining life

Recent research by Alexander et al. (2008)

CAC / dolomitic aggregate concrete can

of existing sewers

in South Africa extends the LFM to Calcium

be used to bridge the gap. Referred to as

From CCT V inspections and supporting

Aluminate Cement (CAC) concretes.

the host- pipe sacrificial-layer concept,

techniques the extent of deterioration can

PRECAST VOLUME 4 â&#x20AC;˘ ISSUE 1 â&#x20AC;˘ APRIL 2010 35

be established and the remaining life then

Before a physical inspection can take

said there is no pipe or lining material that

predicted using the Life Factor Method.

place, one or more locations where severe

will suit all sewers, at least not from an

Measured and theoretical results can be

corrosion is anticipated must be identi-

economic standpoint. The conditions in

compared and differences investigated to

fied. Ideally these locations should offer

each sewer need to be determined and the

provide data for design use.

easy access for cutting a window into the

materials chosen accordingly. They must

The CCT V inspections yield valuable

sewer. A physical inspection can then take

be able to handle any aggressive elements

information which is inexpensive to obtain,

place, actual material losses measured and

in the effluent, in the atmosphere above

however, they donâ&#x20AC;&#x2122;t provide a complete

effluent samples taken. This can take place

the effluent, or in the ground water and

picture. Even when laser profiling is used

at the same time and place as the laser

pipe/soil system* surrounding the pipeline.

it is necessary to conduct periodic physical

inspection and serve as a form of calibra-

Moreover, they must be able to handle the

measurements to check the output.

tion for the remainder of the sewer. Some

abrasive effects of materials in the effluent

of this information could be gathered from

and any temperatur e ex tr emes that

a manhole, but the conditions in a manhole

may occur. Under certain conditions the

are not necessarily representative of those

combined impact of chemical and physical

in the sewer itself.

factors can accelerate the deterioration of the pipe material. The material choice must

PIPE MATERIAL SELECTION

therefore include an analysis of the various

Significance of Material Choice

components in and around the pipeline.

Material choice is the most significant

Figure 3: Details of window cut in a pipe showing the measurements to take.

factor in the life of a pipeline. Yet it probably

New Sewer Design

receives less attention than any other

B ecause sewer s oper a te as gr a v i t y

factor during the design process. That

pipelines they frequently follow natural

* The term pipe/soil system is usually associated with structural aspects of the pipeline, but it is equally applicable to durability considerations.

36 PRECAST VOLUME 4 â&#x20AC;˘ ISSUE 1 â&#x20AC;˘ APRIL 2010

watercourses and, as already mentioned, are placed at a depth below most other services. This means that many large diameter sewers are subject to high external loads and variable soils, as well as founding and installation conditions. Although the inherent strength of reinforced concrete makes it the ideal material f or such sewers, there are certain conditions described above where concrete sewers are subject to acidic a t t a ck . T h e s e c o n di ti o n s sh o ul d b e identified during the planning and design stages of a project so that the concrete can be modified or protected to provide the required design life. If corrosion is predicted in a concrete sewer there are three alternatives which are more ef fective than conventional concrete comprised of PC and an inert aggregate. As described above these are: a host pipe and a sacrificial layer made

Physical inspection of a man-entry sewer before commissioning.

of an alkaline aggregate and PC; lining a PC inert aggregate host pipe with a

usually results in the deterioration and

CAC alkaline aggregate corrosion control

leaking of the joints. If there is a flow of

layer; or lining the host pipe with an inert

water through the joints there is a very

lining. The choice should be based on the

high probability that soil is also flowing

severity of corrosion predicted. In making

through the joints and that cavities have

the optimal choice it is therefore essential

started forming in the surrounding soil.

that the LFM be applied.

This can lead to the formation of sinkholes which can have disastrous consequences.

CHOICE OF

When a sewer is rehabilitated sinkholes

REHABILITATION TECHNIQUE

are not necessarily eliminated as a flow path may have already opened through

General principles Corroded sewer showing corrosion above water line and nothing below water line.

the soil adjacent to the sewer. If there is

t o r e p l a c e t h em f r o m t h e su r f a c e .

water pressure between the liner and

annular space between the liner and the

Therefore trenchless techniques have

the host pipe. The external ground-water

host pipe must be grouted. The possibility

to be used. It is essential to establish

pressure would generally be defined as the

of cavities around the sewer must also be

the conditions and identif y the actual

difference between the ground level above

investigated and if they are present these

problem/s, their extent, severity and

the sewer and the invert level of the sewer.

too must be filled.

cause/s before design and construction

Where the sewer crosses a flood plain this

T he problems that occur with the

work begin. And before rehabilitation work

pressure could be higher than ground level

corrosion of concrete sewers can be

begins the sewer must be adequately

pressure under certain conditions.

ex plaine d and c an b e a v oide d i f the

When sewer s in an urban ar ea have deteriorated it is often almost impossible

any possibility that this has happened, the

Secondly the corroded shape of the

necessary investigation is done during

There are several very important con-

sewer bore must be considered. If a step

the sewer design to ensure that the

siderations when choosing the rehabilita-

has developed at the side of a sewer the

pipe material specified has been selected

tion techniques for a particular project.

close or tight fitting techniques that con-

to deal with the anticipated operating

Firstly all the techniques use inert

form to the sewer bore are inappropriate

conditions.

materials that are watertight, which

as they will be subject to unacceptably high

When sewers have to be rehabilitated

means that these liners must be designed

stress concentrations over the step. Un-

it is essential that their condition is as-

to resist the water pressure that can

der these circumstances a solution where

sessed so that the appropriate rehabili-

develop between host pipe and liner. Under

the liner keeps its circular shape should

tation technique is used and attention is

almost all circumstances the critical

be used even if it is more costly.

given to the pipes, joints and surrounding

cleaned and prepared.

loading condition comprises the ground

Thirdly the deterioration of a sewer

material.

38 PRECAST VOLUME 3 • ISSUE 1 • JUNE 2009

CMA MEMBERS MAKE SUBSTANTIAL CONTRIBUTION TO GFIP Concrete Manufacturers Association (CMA) members are making a substantial contribution to the GFIP (Gauteng Freeway Improvement Project). Thus far producer members of the CMA’s PIPES (Concrete Pipe, Infrastructural Pr oducts and Engineering Solutions) Division, have supplied over 24 000 tons

Storm water concrete piping, 1 350mm in diameter, is installed under a section of the N12 west-bound freeway in Gauteng.

of precast concrete infrastructural and construction material to the project. The material includes: storm water pipes; sewer and irrigation pipes; box culverts; façade panels; barriers; sewer and irrigation pipes; manholes; and sundry vibrated products. The R15 billion project comprises 15 A box culvert, partially obscured by loose rock, seen here at the Reading interchange on the N12 freeway.

work sections or work packages as they are referred to by SANRAL (South African National Roads Agency Limited) and cover a total distance of 185km. The upgrade

Concrete façade panels 800mm to 4 900mm long and 1 980mm wide are being used for the protection and aesthetic enhancement of several embankments and cuttings on the N1 freeway between Atterbury Road and the R21 interchange.

entails work on the whole N1 from Soweto

ments such as beams on bridges has been

to the N4 just north of Pretoria and the

indispensable to the upgrading process.

whole N3 from Voslorus to the N1 at

“Existing storm water pipes and box

Buccleuch. It also involves improvements to

culverts have had to be extended under

the N12 from Tom Jones Street in Benoni

the freeways, and in instances where new

to where it joins the N1 at Soweto, as well

interchanges are being built, new culvert

as the R21 from Pretoria to Boksburg.

and storm water systems ar e being

The project entails widening existing

installed,” comments Kotze.

stretches of freeway from three to four

Different types of precast concrete

lanes in certain sections and up to six

barriers are being used on GFIP, some of

lanes in others, for instance between

them as temporary barriers for traffic

Buccleugh and Allandale. It also includes

control. Precast concrete panelling is also

capacity upgrades at the interchanges

being used for embankment reinforcing

as well as additional turning lanes, new

and facades.

bridges and the doubling up and widening of existing bridges.

The Atterbury Road on the N1 freeway interchange where concrete facade panels are being used for the protection and aesthetic enhancement of this embankment.

A 1 500mm diameter manhole near the switch ramp on the N3 north near Alberton.

For instance, panels 800mm to 4 900mm long and 1 980mm wide are being used for

Some interchanges are being completely

the protection and aesthetic enhancement

revamped and are being converted from

of several embankments and cuttings on

diamond layout systems to single point

the N1 freeway between Atterbury Road

systems, while others involve the widening

and the R21 interchange. Precast concrete

of bridges and wider on-and-off ramps.

barriers, 1m high, abut the panels at ground

Acceleration and deceleration lanes,

level, securing them firmly in position, and as

300m to 500m long, are also being built

a finishing touch, precast concrete coping

to facilitate safer entry and exiting of the

panels have been installed at the upper end

freeway system.

of the structure.

SANRAL project manager, Hennie Ko-

Precast concrete beams are being used

tze, says given that the space for staging

on some of the bridges and these vary from

and shuttering support is often extremely

smallish I-beams to huge U beams weighing

limited, the use of precast concrete ele-

up to 70 tons.

Going the extra mile “At AfriSam we always go the extra mile to meet our clients’ specific requirements. Being responsible for major construction clients means dealing hands on with experienced buyers who know what they want and demand the best at all times in terms of quality and integrity, service and backup and, of course, a competitive offer. I enjoy working on unique projects like the freeway networks, overcoming new challenges and ultimately gaining the trust of our customers by proving that we go above and beyond their expectations.”

ARM 29069

Margaret Lawrence – Multi Products Key Accounts (Construction)

www.afrisam.com

0860 141 141

Build with Confidence

40 PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010

Some of the prestressed hollow-core concrete slabs, manufactured by Echo Prestress, which were used in the construction Bridgeview, a medium-rise apartment block built in Braamfontein, Johannesburg.

Bridgeview, a five storey load-bearing masonry structure under construction in Braamfontein, Johannesburg.

PRESTRESSED HOLLOW-CORE AND LOA - THE MOST ECONOMICAL SOLUTION The application of prestressed hollow-core slabs as a flooring and load-bearing masonry material in South Africa has been marked by a high degree of caution and engineering conservatism. Notwithstanding the fact that in other parts of the world the technology has been used for the construction of medium-rise buildings for decades, its local application has been restricted to buildings no higher than three storeys. Until recently that is. During 2009 pre-

verification was handled by Don Theron

stressed slabs were successfully deployed

of DG Consulting Engineers (Capital Park)

on two medium-rise projects, Capital

and Simon Knutton of Knutton Consulting

Park, a seven-storey residential building

(Bridgeview).

• Standard weight concrete was used on both structures • Bearing limits for the hollow-core units are taken as defined in SABS 0100:1992,

in Pretoria, and Bridgeview, a five-storey

section 6.5.4.4, with appropriate allowances

load-bearing masonry residential structure

being made for reduced levels of prestress

in Johannesburg.

(and hence shear resistance) within the

Both projects realised substantial

transmission length of prestress units

savings, 30.76% in the case of Capital Park

• Continuity – 9.53mm strands 1 200mm

and 23.79% on the Bridgeview project over

long were introduced over supports

what the buildings would have cost had in

• Fire resistance properties for hollow-

situ flooring been used. These savings have

core slabs on residential buildings above Precast hollow-core concrete slabs being offloaded at Bridgeview.

two storeys were taken as 25mm minimum

behalf of the CMA by Mark Raubenheimer

Design parameters and assumptions

This provides a one-hour fire rating

of Bathuleng, Wallace, Raubenheimer,

There were several features common to

• Durability – the use of high strength

registered quantity sur veyors. What

the structural design of both buildings.

(up to 60MPa and more), high quality

follows are the details of the studies.

These were:

concrete achieves a guaranteed durable

been authenticated and compared in two independent case studies conducted on

Each building was treated as a separate case study in which precast hollow-core

• Specified imposed load of 1.5KN/m2 plus 1.5KN/m2 for finishes

thickness under cores in hollow-core slabs.

product which complies with the requirements of SABS 0100:1

floors on load bearing masonry and in-

• Deflection limits were taken as defined

• Accidental damage and progressive col-

situ concrete framed structures with

in SABS 0100:1992 to a maximum of

lapse – SABS 0164 Part 1 (4) gives guidance

infill masonry were examined. Design

span/300

on design aspects relating to accidental

PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010 41

Capital Park, a Pretoria-based seven-storey residential building, in which the floors of the five upper storeys were built using prestressed hollow-core slabs.

A view of Bridgeview on completion.

LOAD BEARING MASONRY TION FOR MEDIUM-RISE STRUCTURES damage for category 2 (all buildings of five

Case Study A –

with prestressed hollow-core floor slabs.

storeys and more), to limit the extent of

Capital Park Pretoria

Bricks rated at 14MPa were specified

accidental damage to the immediate vicinity,

The first level was cast in situ and the

for levels two and three and 10MPa units

while maintaining the structural integrity of

six floors above them were constructed

were specified for the upper levels. Class

the remainder of the building.

in load-bearing masonry, five of them

1 mortar was used throughout.

Elemental construction cost per m2 gross floor area for structural options.

July 2009

Trade

Cast in-situ slab method of construction cost

Rate / m2

P.C. Hollow core slab method of construction cost

Rate / m2

Variance

Percentage variance

Rate / m2 variance

1. Concrete, formwork and reinforcement

1,124,625.20

564.44

851,119.86

427.17

(273,505.34)

-24.32%

(132.27)

0.00

0.00%

0.00

2. Masonry

Same for both studies

3. Metal work

0.00

125,615.72

63.05

125,615.72

0.00%

63.05

4. Plastering

365,155.10

178.75

192,298.66

96.51

(163,856.35)

-46.01%

(82.24)

5. Painting

69,735.89

35.00

82,666.92

41.49

12,931.03

18.54%

6.49

1,550,516.10

778.19

1,251,701.16

628.22

(298,814.94)

-19.27%

(149.97)

Sub Total cost [in R] Construction period (weeks) Est. savings in preliminary related costs for portion of construction under review Total cost [in R]

257,142.86

129.06

0.00

(257,957.80)

0.00

(129.06)

1,807,658.95

907.25

1,251,701.16

628.22

(555,957.80)

-30.76%

(279.03)

42 PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010

Case Study B – Bridgeview Johannesburg Bricks of 14MPa were specified for ground and first floor and 10MPa units were specified for the upper levels. English bond and Class 1 mortar was used throughout. Elemental construction cost per m2 gross floor area for structural options

July 2009

Trade

Cast in-situ slab method of construction cost

Rate / m2

P.C. Hollow core slab method of construction cost

Rate / m2

Variance

Percentage variance

Rate / m2 variance

1. Concrete, formwork and reinforcement

2,867,774.84

1,049.88

1,123,395.90

411.20

(1,761,193.59)

-60.83%

(638.68)

871,025.71

318.88

1,042,680.62

381.65

171,654.91

19.71%

62.78

3. Metal work

0.00

778,181.12

284.84

778,181.12

0.00%

284.84

4. Plastering

278,881.94

102.10

247,024.00

90.24

(31,857.94)

-11.42%

(11.68)

5. Painting

95,603.42

35.00

175,726.88

64.32

80,123.46

83.81%

29.32

4,113,285.92

1,505.86

3,367,008.52

1,232.43

(746,277.40)

-18.14%

(273.42)

2. Masonry

Sub Total cost [in R] Construction period (weeks) Est. savings in preliminary related costs for portion of construction under review Total cost [in R]

304,761.90

111.57

0.00

(304,761.90)

0.00%

(111.57)

4,418,047.82

1,617.43

3,367,008.52

1,232.43

(1,051,039.30)

-23.79%

(384.99)

AESTHETIC RANGE:

• •

ReMblok 30 Rock Face Terraforce L11 Rock Face

• •

Terraforce L18 Rock Face ReMRock 220 Rock Face

PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010 43

• Elimination of continuous concrete pouring • No propping or back propping required, allowing quicker completion • No rework due to unskilled labour • Early occupation = money in the bank. Minimal disruption • Hollow-core flooring is produced in a controlled factory environment, and installed immediately on delivery • Hollow-core flooring construction can dramatically reduce the impact of building activities on surrounding areas • Minimised noise and dust, and reduced wastage. Flexible solution • Long slab spans reduce the number of

An artist’s impression of the completed Capital Park building.

vertical rising elements and offer flexTime related savings

that the foundations could be lighter due

ibility in internal layouts especially for the

Faster construction times associated

to the lower cumulative weight of the su-

configuration of large open-plan areas.

with hollow-core slab construction yielded

perstructure.

additional savings. These were realised in

Substantial long-term savings through

site management and on-site activities.

better quality control of the concrete and

• Off-site manufacture to SANS Stand-

A saving was also made in the cost of fi-

less maintenance should be realised.

ards improves the quality of the building

nance, as the shorter construction period

Prestressed concrete is mandatory

Built-in quality

frame, since work is carried out under

meant the time during which interest had

for long spans and offers better long-

closely controlled factory conditions

to be paid was reduced. Faster comple-

term shrinkage and creep performance.

not affected by on-site trades or the

tion times also brought earlier returns.

• * H/C Slab Self Weight

weather. Product delivery is done on a

Tenants were able to move in sooner,

• ** H/C Slab Self Weight + 40mm level-

just-in-time, right-the-first-time basis.

offsetting financing costs. As the table

ling screed

below shows six weeks were saved on the

• *** In-situ Slab weight given for depth

Environmental benefits

Pretoria project and eight on the Johannesburg development.

• Hollow-core is the only precast flooring In summary

element that can be recovered from a

These two projects have convincingly

building and re-used.

Additional savings

demonstrated that precast hollow-core

• All the materials used can be recycled.

Prestressed slabs are shallower than their

slabs offer considerable advantages over

• Hollow-core is a clean and efficient

reinforced concrete counterparts for the

traditional in situ concrete flooring.

construction method which reduces

same span and loading conditions - usually

the impact of building activities on the

65 – 80% of the depth of an equilvalent

Rapid construction

environment. The small amount of waste

reinforced slab.

• Reduced construction time

produced is recycled and used in other

• Ready to use working platforms

precast product.

concrete and approximately 20-35% of

• Elimination of temporary structures

• The carbon footprint is less than that

the amount of reinforcement. This meant

including propping

produced using in situ construction.

Prestressed slabs also require less

Elemental construction cost per m2 gross floor area for structural options

July 2009

Time related Savings Structural Form

Case Study A – Pretoria Frame (weeks)

P.C. Hollow Core Flooring & load bearing masonry

In situ frame

18 Case Study A Saving

Overall (weeks)

Case Study B – Johannesburg Frame (weeks)

Overall (weeks)

6 weeks

Case Study B saving

8 weeks

44 PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010

Producer members M = Masonry

Company Name

P = Paving

Pi = Pipes

Telephone

R = Retaining Blocks

Product

S = Floor Slabs

Company Name

T = Roof Tiles Telephone

Product

(032) 944 4155

082 324 7277

ARW Concrete Holdings

(082) 850 3512

Marley Roofing KZN

A Fick Cement Works

(022) 913 1921

Marley Roofing Cape Town

Bafokeng Concor Technicrete

(014) 538 0818

MPRT

Mobicast Mossel Bay

(044) 874 2268

Baybrick

(035) 792 5218

MVA

(012) 386 0050

Boland Concrete

(021) 875 5365

Monier Roofing South Africa (H.O.)

(011) 222 7300

Bosun Brick Brits

(012) 250 1711

Monier Roofing South Africa

(016) 430 8000

Bosun Brick Midrand

(011) 310 1176

MPR

Monier Roofing South Africa (Free State)

(051) 432 5089

(00264) 61 321 3009

Monier Roofing South Africa (North West)

(012) 250 2218

Brickcast Industries

(031) 507 5525

MPR

Monier South Africa (Cape Town)

(021) 534 1441

Brickbuild T/A Panda

(00267) 244 2106

Monier Roofing South Africa (DBN)

(031) 565 1312

Monier Roofing South Africa (ELN)

(043) 743 2191

Monier Roofing South Africa (George)

(044) 878 1325

Brick and Concrete Industries

Brikor

(011) 316 1200

Cape Brick

(021) 511 2006

MPR

C.E.L. Paving Products

(021) 905 5998

Monier Roofing South Africa (PE)

(041) 463 2629

Cast Industries

(011) 316 2375

Neat Contech

(046) 624 3377

MPRS

Columbia DBL

(021) 905 1665

MPR

PRO Brick & Block

(021) 905 3362

Concrete Units

(021) 386 1923

ReMaCon Products

(011) 393 5504

Conframat

(016) 987 3381

Rocla

(011) 670 7600

Corobrik

(031) 560 3111

Salberg Concrete Products

(011) 357 7600

Deranco Blocks

(041) 463 3338

Southern Pipeline Contractors

(011) 914 8500

Deranco Paving

(041) 933 2755

Stabilan

(051) 434 2218

Deranco Precast

(041) 463 3338

Shukuma Flooring System

(041) 372 1933

Eagle Roof Tiles

(044) 874 0290

Stanger Brick & Tile

(032) 457 0237

Echo Floors

(011) 662 4600

Stone Age Concepts

(012) 802 1496

Echo Prestress

(011) 589 8800

Technicrete

(011) 674 6940

MPRT

(031) 569 6950

Technicrete (Mpumalanga)

(013) 758 1203

MPRT

(00263) 448 6620

Technicrete (Mpumalanga)

(017) 689 2100

MPR

Echo Prestress Durban Fort Concrete Inca Concrete Products

(021) 904 1620

Technicrete (Mpumalanga)

(013) 696 1153

MPR

Inca Masonry Products

(043) 745 1215

MPRT

Technicrete (Free State)

(057) 391 4200

MPR

Infraset

(011) 876 5500

Technicrete (North West)

(018) 790 4380

MPR

Infraset

(012) 652 0000

MPR

Technicrete (Limpopo)

(015) 293 8083

MPRT

Infraset

(031) 569 6900

Technicrete (Gauteng)

(011) 203 7700

MPR

(00267) 392 2850

Technicrete (North West)

(018) 484 6234

MPR

Klapmuts Concrete & Cape Retaining

(021) 875 5151

Technicrete (E.Cape)

(041) 372 2230

Kopano/Altocrete

(016) 363 0340

Topfloor

(021) 951 7700

Kwena Concrete Products

(00267) 393 2850

Vanstone Precast

(012) 541 2056

Lategans Cement Works

(021) 873 1154

Watson Concrete

(011) 740 0910

Marley Roofing

(011) 316 2121

Western Granite Bricks

(021) 904 1620

Marley Roofing

(013) 933 3351

West End Cement Bricks

(011) 851 1828

Kwena Rocla

PRECAST VOLUME 4 • ISSUE 1 • APRIL 2010 45

Associate members

Company Name

Telephone

ARQ Consulting Engineers

(012) 348 6668

ILIFA Africa Engineers

(016) 981 0591

Pipes

(012) 644 0043

Sekhukhune and Associates

(012) 993 4776

SNA Civil & Structural Engineers

(012) 842 0000

Terraforce

(021) 465 1907

Young & Satharia Structural Civil Engineers

(031) 207 7252

CONTRACTOR members

Company Name

Telephone

Daron Construction

(034) 955 1333

Decorton Retaining Systems

(021) 875 5155

Friction Retaining Structures

(011) 608 4321

Galaxy Paving

(011) 815 1175

Kalode Construction

(011) 781 3814

Mondo Paving & Retaining Walls

(011) 708 0800

PYW Paving

(031) 763 5771

Roadstone Civil & Paving

(011) 683 7080

SA Paving Gauteng

(011) 483 1350

Sun Paving

(031) 705 5123

The Paving Creations

(031) 765 4083

Vesles Civils

(012) 662 3031

Valcal International

(011) 867 2471

non-producer members

Company Name

Telephone

Ash Resources

(011) 886 6200

Birkenmayer H

(011) 970 3880

BASF Construction Chemicals South Africa

(011) 203 2471

C&CI

(011) 315 0300

Chryso Southern Africa

(011) 395 9700

Inca (Cape)

(021) 904 1620

Kaytech

(031) 717 2300

Manitou SA

(011) 975 7770

Pan Mixers SA

(011) 397 3754

Rampf Formen GmbH

(0049) 7391 5050 148

Rettenmeier Holzindustrie

(0049) 7971 9585810

Sika South Africa

(031) 792 6500

Siliseal Waterproofing System

(011) 464 1409

Soilcon

(012) 333 7817

Soillab

(021) 988 7410

Smartstone

(011) 310 1161

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Magic Carpet

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