Precast May 2011 by Concrete Manufacturers Association (CMA)

PRECAST VOLUME FIVE ISSUE 1 • MAY 2011

the cma – QUaLItY caSt IN cONcRete RecouRse

GuaRantee

expeRtise

Value foR money

compliance

consistency

DuRability

time saVinG

• Royal Bafokeng saves R-millions • The 20/40 MiniBlock • Poor detailing in low-level river-crossing design

“This retaining wall provides a strong support, whilst being eco-friendly, versatile and aesthetically pleasing. It’s smart concrete engineering!” – Fatima Naidoo

QUALITY CAST IN CONCRETE

Discover how concrete retaining walls can transform your world call: +27 11 805 6742 e-mail: main.cma@gmail.com

www.cma.org.za Durability Consistency

Expertise Value for money

Time saving Compliance

Guarantee Recourse

PRECAST VOLUME 5 • ISSUE 1 • MAY 2011 1

contents 2

REMACon fiRST To gAin SABS

18 RoYAl BAfokEng SAVES R-MillionS WiTH ConCRETE BloCk PAVing

CERTifiCATion on ConCRETE RETAining BloCkS

20 THE 20/40 MiniBloCk – 4

WHAT’S in iT foR YoU?

AVEng MAnUfACTURing infRASET inTRoDUCES ECo-fRiEnDlY Roof TilE

22 flooDS HigHligHT PooR DETAiling of 6

loW-lEVEl RiVER-CRoSSing DESign

PRECAST ClADDing – foR foRM AnD fUnCTion

27 CMA MEMBERSHiP liST 6

MAPEi SUPPoRTS ElDoCRETE WiTH PURPoSE-SPECifiC ADMixTURES

PRECAST VOLUME FIVE ISSUE 1 • MAY 2011

THE CMA – QUALITY CAST IN CONCRETE

MoBiCAST – MUTli-TASking WiTH

RECOURSE

GUARANTEE

EXPERTISE

VALUE FOR MONEY

COMPLIANCE

CONSISTENCY

DURABILITY

TIME SAVING

The CMA has adopted a fresh approach

its

advertising

strategy. in addition to promoting its members’ products, it has

PRECAST ConCRETE

chosen to go the corporate route as well, with the emphasis on the

BoSUn ADDS TWo nEW ToPPing ColoURS To PAVing RAngE

CMA brand and its associated • Royal Bafokeng saves R-millions • The 20/40 MiniBlock • Poor detailing in low-level river-crossing design

benefits for the consumer.

The first of the new adverts has already appeared in print and is depicted on our front cover. Crafted

MiCRoWAVE MoiSTURE MEASUREMEnT CAn iMPRoVE PRoDUCTiViTY

on the theory that a simple message is the most powerful, the advert is headed ‘Quality Cast in Concrete’ (the registered Trade Mark of the CMA). The bulk of the page is devoted to the CMA logo

10 gRoUnD-BEAM foUnDATion SYSTEM CAn SPEED UP HoUSing DEliVERY

which is displayed as an embossed image stamped in

smooth concrete. like the embossing on the

back of an exclusive watch, the image conveys an immediate sense of quality; both through the

12 DUBAi TRAffiC inTERCHAngES STABiliSED WiTH TERRAfoRCE

fine detailing of the embossing itself, and the permanency of the branding.

RETAining SYSTEMS 12 ARMoRflEx BloCkS PREVEnT MinE flooDing 14 CHRYSo EnHAnCES PolokWAnE ConCRETE SCUlPTURE 14 ECHo MoVES inTo CAPE flooR SlAB MARkET 15 noRTHlAnDS PRojECT PAVED BY BoSUn 16 inlAnD AnD WESTERn CAPE PRojECTS DoMinATE CMA AWARDS

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 Publishers isikhova Publishing & Communications Po Box 651793, Benmore, 2010, South Africa Tel: +27 11 883 4627, Fax: +27 11 883 4627 Website: www.isikhova.co.za Publisher: Andrew Meyer Tel: +27 11 883 4627, Cell 082 456 5175 E-mail: andrewm@isikhova.co.za Editor: David Beer Tel: +27 11 478 0239, fax: +27 11 678 0254 E-mail: bigsky@ibi.co.za Advertising: Rui Chirindja Tel: +27 11 883 4627, Cell: 082 717 2851, E-mail: communications@isikhova.co.za Design, layout and production: Joanne Brook The views and statements expressed in this publication are not necessarily those of the editor or the publishers and neither he/publishers 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.

ReMacon fiRst to gain saBs ceRtification on concrete retaining blocks Concrete retaining blocks (CRB’s) pr oducer ReMaC on Products recently gained SA Bureau of Standards (SABS) cer tification on its main products – the first producer of CRB’s in South Africa to do so. The company, which is due to have the remainder of its products tested and awarded cer tification by the SABS before the end of 2010, views certification on its products as important because it provides independent confirmation of their efficiency and reliability in performing the functions for which they are designed. “it makes absolute sense for us to obtain the SABS certification applicable to CRB’s as we produce CRB’s exclusively, unlike many other concrete block manufacturers, who produce them along with a range of products used in other applications,” commented Silvio ferraris, the company’s Managing Member. The SABS standard for CRB’s, SAnS 508, was introduced in 2007. “As part of the certification we are obliged to have the products tested periodically to ensure that they continue to conform to the standard. it requires that we test a sample of every production run on each of the certified products and maintain records of the tests,” ferraris explained. “To make this practicable we have acquired the necessary equipment to do the testing ourselves. in addition, the SABS conducts six-monthly audits at our site to check that we adhere to the quality management system that also has to be applied as part of the certification requirements.” The SABS certifications already obtained apply to the company’s popular ReMblok 30, ReMRock 220 and Terraforce l18 blocks. The products still to be certified are its Terraforce l11, Scooploc SC30, Scooploc SC50 and WaterScooploc WSC65 blocks. ferraris said that a further important motivation behind gaining SABS certification is that it provides advance proof to the relevant authorities – and to the market – that the company and its products conform to most of the provisions of the Consumer Protection Act (CPA), which is due to be promulgated soon.

ReMaCon Products’ managing member, Silvio Ferraris (left) and a quality technician seen here with the test equipment used to maintain the SABS quality certifications on its products. The test unit is a hydraulic cube press with a capacity of 2000 kN. The SANS 508 standard stipulates that each block tested be able to withstand a pressure of 15MPa per minute.

4 PRECAST VOLUME 5 • ISSUE 1 • MAY 2011

aVeng ManUfactURing infRaset intRoDUces eco-FrienDlY rooF tile Sunrise4.4™, an eco-f riendly r oof ing

tile manufacturing technology at Aveng

Horizon and Sunset tiles in which five tiles

tile, has been launched by Aveng Manu-

Manufacturing infraset’s plant at Rossway,

are strapped together in a single pack. This

facturing infraset.

Midrand. The tile it is greatly favoured by

reduces breakages and makes the stack-

Weighing in at only 4.4kg Sunrise4.4™

Mediterranean countries and is

ing and laying of tiles on roof much

offers several weight-related benefits with-

used extensively in italy, Spain and

easier,” advises Uys.

out compromising on the inherent advan-

Portugal.

tages associated with concrete roof tiles.

“Sunrise4.4™ is primarily

“in the first instance it uses less

aimed at up-market develop-

Aveng Manufacturing infraset has achieved an outstanding reputation for the production of concrete roof

material to manufacture,” comments

ments and we are producing it in

tiles and other concrete products

grant Uys, roofing product manager of

several popular through-colours:

to the highest standards. The same

Aveng Manufacturing infraset. “it also

amber; slate; red; terracotta;

commitment to quality is evident in

requires less energy to load and transport,

brown and a multi-colour ed

the manufacture of Sunrise4.4™,

and is easier to handle and lay. Moreover,

vintage tile. it is being marketed

and according to Uys, the tile will

like most concrete products it is fully

with a full range of complementary fittings,

exceed the standard of the South African

recyclable. These fators mean it will assist

including Aveng Manufacturing infraset’s

Bureau of Standards (SABS) for concrete

in the compliance of SAnS 204 (energy

newly introduced roof insulator, Eco

roof tiles. The tile has also been registered

efficiency in buildings).”

Shield™ and flashing material, infra-flash™.

as a trademark.

A deep-profile tile, Sunrise4.4™ is

“it is packed with the same system

produced using the latest italian roof

used on Aveng Manufacturing infraset’s

The Sunrise4.4™ roof tile recently introduced by Aveng Manufacturing Infraset.

PRECAST VOLUME 5 • ISSUE 1 • MAY 2011 5

011 589 8800

011 662 4600

011 589 8955

6 PRECAST VOLUME 5 • ISSUE 1 • MAY 2011

PRecast cLaDDing Ð For Form anD Function Precast concrete cladding provides the

offers the following:

• In colder climates, the use of concrete

designer with substantial choice in form,

• Exceptional fire resistance;

sandwich panels, incorporating thermal

texture and expression. it is cast off-site

• Superior acoustics that will assist in

insulation, retain warmth.

in a controlled manufacturing environment

keeping traf fic and industrial noise at

where skilled workers can pay full attention

bay; and

Precast cladding offers a wide range of finishes. in off-the-form finishes, the mould

to the demands for accuracy and high-

detail is mirrored in the concrete surface

quality finishes.

as, for example, board-marked finishes,

Architectural concrete cladding

ribbed finishes, or rope-patterned finishes.

generally falls into two categories:

Exposed aggregate finishes, on the other

• Those that serve purely as enclosures,

hand, reflect the natural colour of the

either as self-finished panels or as backing

aggregate. other finishes include polished

components to other façade materials,

reconstructed stone, polished stone or

such as brickwork; or

ceramic tile.

• Those that form an integral part of

Har sh c o as t al en v ir onm en t s m a y

the framework of a building and perform

threaten the lifespan of some cladding

structural as well as cladding functions.

materials but older concrete structures

Cladding panels can be manufactured

(such as the Port Elizabeth Post office

in a variety of shapes and sizes but are

building, north of the CBD and virtually next

mainly applied as storey-height or spandrel

to the corrosive influences of the ocean)

panels. The storey-height units span floor

bear testimony to concrete’s exceptional

to floor; and spandrels form sill walls below

durability. The façade of the main adminis-

fenestration strips.

trative building and Council Chamber wing of

Storey-height panels can be manu-

the johannesburg Civic Centre (a landmark

factured with apertures for windows and

near the top of Rissik Street) still looks at-

doors, the latter being installed on site.

tractive after four decades. large precast

Window frames can also be attached and

concrete panels, 8,7m high and 2,1m wide

painted before the panels are delivered

and weighing 6 800kg, constitute the walls

to site.

of the Council Chamber.

Apart from its major cost benefits, pre-

finally, it is crucial that input from an

cast cladding offers property owners long-

experienced precast specialist is obtained

term durability and minimal maintenance

in the early decision-making stages of any

without the need for frequent cleaning. Moreover, the inherent capabilities of concrete means precast cladding also

cladding project. Precast concrete cladding provides the designer with substantial choice in form, texture and expression.

MaPei sUPPoRts eLDocRete WitH PurPose-sPeciFic aDmiXtures

(information supplied by the Cement & Concrete institute, www.cnci.org.za).

M a p e g r o u t R a p i d o, a s h r i n k a g e compensated rapid-set repair mortar, also makes up part of the comprehensive Mapei admixture solution supplied to Eldocrete. Any damage or detoriation, be

Mapei South Africa Pty (ltd) is assisting

superplasticiser, Dynamon nRg1020, to

it on a vertical or horizontal surface, can

Eldocrete, a Centurion-based precast

speed up production.

be repaired with Mapegrout Rapido. The

c o n c r e t e m a n u f a c t u r e r, t o b o o s t

“Quick setting, it offers substantially

fast-setting mortar is easily trowellable

production and profitability with the latest

improved early strength gains, quicker

with excellent thixotropic properties, and is

in admixture technology. This has helped

m o u l d t u r n a r o u n d s, a n d i n c r e a s e d

suitable for application up to 30mm thick. it

Eldocrete reduce setting times, lower

productivity,” says offenberg.

sets within 30 minutes, when it is already

production costs, and produce consistently superior precast concrete products.

As a result of the superplasticising

strong enough to carry loads.

action, the admixture also reduces the

Mapei also supplies purpose-built dis-

Antony offenberg, Mapei admixtures

amoun t o f cemen t r equir ed w i thou t

pensing systems. These are either weight

product manager, says Mapei supplies

c omp r omising on s tr eng th, th er eb y

or volume based and provide for the accu-

Eldocrete with an accelerating

reducing production costs.

rate and fast dispensing of admixtures.

8 PRECAST VOLUME 5 • ISSUE 1 • MAY 2011

MoBicast Ð multi-tasking WitH Precast concrete CMA producer member, Mobicast, has once again demonstrated its versatility in the production of diverse precast concrete products. The southern Cape producer recently completed two very different fasttrack projects simultaneously. These involved the casting of the 300 concrete weight collars for Mossel Bay’s new desalination plant and supplying 7 000m² of concrete block paving (CBP) for the parking lot of the newly extended knysna Mall.

Precast concrete collars, manufactured by Mobicast and installed at the new desalination plant in Mossel Bay.

Mobicast’s new cobble stone pavers seen here at the new Knysna Mall parking lot.

stone paver with a very smooth “natural

Mobicast managing director, Chris

Van Zyl said steel reinforcing on the col-

van Zyl, says the projects represent two

lars was complex and the real challenge was

contrasting sides of the precast concrete

maintaining concrete cover during casting.

“The development work on the cobble

market, the artistic and architectural

“ T h e f inish e d p r o du c t r e quir e d a

stones took a considerable amount of

versus highly technical civil engineering.

stone” finish.

tolerance of 0 – 3mm on the collars’ inner

lead time; for instance we had to make

“However, the common factor linking

radii. Mobicast used self-compacting

up special moulds and this placed our

the two projects were extremely tight

concrete which was poured very carefully

production facility under tremendous

pr o duc tion sche dules. B o th se ts o f

to achieve the desired quality. Despite this

pressure. To meet our deadlines, we placed

pr oducts wer e manuf actur ed at our

the project was completed well within the

our cobble stone production plant on a

modern production facility at great Brak

required schedule.”

24-7 basis and used steam curing as well.

Approximately half the knysna Mall

This enabled the moulds to be stripped

parking area was paved with Smartstone’s

every six hours. needles to say, the

The concrete weight collars weighed be-

50mm Paduan paver (Mobicast is

project was completed on time at very

tween 1,3 and 2,7 tons each and were pro-

SmartStone’s franchisee in the Southern

high quality standards.”

duced to a strength rating of 40MPa, which

Cape); and the other half was covered with

is suitable for extreme marine conditions.

a new Mobicast 150 x 150 x 73mm cobble

River, situated between george and Mossel Bay,” said van Zyl.

for further enquiries call 044 874 2268 or see www.mobicast.co.za.

BosUn aDDs tWo neW toPPing coLoURs to Paving range

are carefully sourced and graded, and this

one of the most memorable South African

equipment allows us to not only produce

Blended colours, which vary from paver

advertising slogans of all time is: “it’s not

unique colours, but also facilitates some

to paver and create a uniquely random,

inside, it’s onnnnn top”.

of the smoothest dry-cast concrete pav-

organic effect, comprise:

Bosun CEo,David Wertheim Aymes, c oncur s, his c omp any ha v ing

ing finishes available,” explains Wertheim Aymes.

yields products that not only comply with, but in most instances exceed, current SABS specifications.” The Bosun CBP now boasts 10 colours.

• Autumn • Multi

released two new topping

“We consider our CBP

• Sahara

colour s to its ex tensi ve

topping to be a r eal market

• Granite

r a ng e o f c o n c r e t e b l o c k

di f f er entiator. We have spent

pavers (CBP).

• Marble

many years testing and developing

Dubbed granite and Marble, the

our pr oducts in or der to f ind the

Solid colours comprise:

colours were launched after extensive

per f ect topping mi x tur es and will

• Grey

testing. Considerably lighter

continue doing so. Apart from

• Black

than the other blended

the obvious aesthetic benefits,

• Tan

colours in the Bosun r a n g e, t h e y a r e m a d e with imported cement in a state-of-the-art blending facility. “our german block manuf acturing

our toppings also offer superior abrasive resistance.

• Brown • Red or terracotta

“However, this does not mean our uncoloured, rough concrete finish pavers are neglected. our aggregates

Visit www.bosun.co.za for more details or phone 011 310 1176.

MicRoWaVe MoistURe MeasUReMent can imProve ProDuctivitY Hydronix, a world leader in moisture measurement technologies, is working with Birkenmayer as the approved local distributor, to establish moisture measurement as a standard aid to many industrial processes in South Africa. Bir k enm a y er claim s th a t H y dr o ni x digi t al mi cr o w a v e measurement sensors of fer concrete manufacturers and aggregate producers an opportunity for large-scale cost savings and more reliable processing. Hydronix process control instruments help to improve the manufacturing of homogenous and consistent materials. for example, when water is added to a material mix, Hydronix sensors provide real-time and accurate moisture measurement. This assists in reducing the number of wasted or spoilt batches, and helps achieve products of a consistently high standard. Hydronix microwave sensors are said to be more accurate than traditional instruments. They are wear resistant and parts which are subject to wear-and-tear are individually replaceable. As suppliers of Hydronix sensors as well as Eirich mixers, Birkenmayer offers a complete automated mixing package including brick-making machines. When the two are used in combination, profitability can be boosted.

A Hydronix microwave moisture sensor.

A Birkenmayer HB14 brick-making machine.

10 PRECAST VOLUME 5 • ISSUE 1 • MAY 2011

gRoUnD-BeaM foUnDation sYsteM can sPeeD uP Housing DeliverY government-subsidised housing projects

gauteng. it is designed to support single-

in gauteng could be accelerated and

storey structures up to 6.6 x 6.2 m, and

b uil d qu ali t y sub s t an tiall y imp r o v e d

strict quality manufacturing and installa-

through the introduction of a new foun-

tion conditions have been imposed by the

dation system based on Echo hollow-core

Agrément Board.

prestressed concrete floor slabs, tradi-

“like all great ideas, it’s simple,” says

tionally used in multi-storey commercial

Echo Prestress marketing director Melinda

and residential buildings.

louw. “And it is also a much faster way to

long-term tests have shown the groundbeam system outperforms traditional foundation systems when used in the construction of small, single-storey structures.

build sound foundations for governmentsubsidised housing.” Trials using the system were initially carried out in the free State, where for

Echo’s ground-beam foundation which is ideal for government-subsidised housing.

The Agrément-approved method involves

several years, people have been living

made an impressive contribution to some

embedding separate cut-to-measur e

in houses on ground beam foundations

of the country’s most successful social and

prestressed slabs in the ground across

installed by Bloemfontein-based slab-

affordable housing projects.

the width or length of the house. The edges

manufacturer Stabilan.

“This has included multi-storey, high-

which protrude above ground then form a

“The houses are looking good,” says

density apartment blocks. Echo is geared

firm foundation on which floor slabs can

louw. “no cracks have developed – which

to bring its extensive experience and

be installed.

is in strong contrast to surrounding

expertise to bear in support of government

homes built on traditional rafts which are

initiatives which use the foundation system

cracking badly.”

in the construction of single-storey social

officially known as the CMA Building foundation Beam, the Concrete Manufacturers Association being the Agrément

Using its pioneering technology refined

certificate-holder, Echo Prestress holds

during 25 years in the hollow-core concrete

the manuf acturing licence rights f or

slab business, the Echo group has already

housing,” louw says. More information from Echo Prestress on Tel: 011 589 8800.

12 PRECAST VOLUME 5 • ISSUE 1 • MAY 2011

DUBai tRaffic inteRcHanges staBiLiseD WitH terraForce retaining sYstems Two recently built traffic interchanges

The embankments were retained with

in Dubai, both stabilised with Terraforce

Terraforce l16 (split face) composite

r etaining wall block systems, clearly

retaining walls and vertical freyssinet panel

T he se c ond in t er change a t j eb el

demonstrate how the company is

retaining walls at heights ranging between

Ali involved similar challenges and was

competing successfully in the international

0,5m - 4m. T he blocks were used to

completed shortly thereafter using similar

construction arena.

support both sides of four ramps, as well as

Terraforce systems.

T h e f i r s t, c o s t i n g R 5 0 0 m i l l i o n,

the approaches to a cross road. Covering

9 300m², the walling was reinforced with fortrac 35/20 – 20 T geogrid.

Terraforce managing director, Holger

commenced in 2007 and was completed

Rust, says that limited space is a problem

in December 2009.

common to many traffic interchanges.

Situated in the suburb of Mirdiff, it

“This requires creative engineering

entailed enlarging and improving an existing

and designs which rely on cost-effective

interchange which was no longer able to

retaining structures. Moreover, they need

accommodate increasing traffic volumes.

to be built rapidly while offering a safe and

Planned as a single-point system, it was

long lasting solution.

designed to cater for increased traffic

“owing to their versatility, our blocks

volumes for 15 to 20 years. The project

are becoming widely used for this type of

presented the following challenges:

application.

• Limited space necessitated steep

“Being hollow, they can be filled with

embankments to minimise the impact on

crushed stone or concrete, and don’t re-

surrounding land and facilities

quire connectors for anchoring reinforcing

• Utility services had to be diverted and

material between the blocks. laboratory

traffic flow had to be maintained during

tests have shown that the pull-out resist-

construction

ance of our blocks (the force required to

• Planners had to avoid the costly exercise of shifting a large telecommunications tower on the site.

The Jebel Ali Interchange, Dubai, where L16 Terraforce blocks, manufactured by Consent LLC, were used to retain ramp embankments.

separate the reinforcing grid from the block facing) is above the industry standard,” says Rust.

aRMoRfLeX BLocKs Prevent mine FlooDing Technicrete’s concrete Armorflex erosion-

“initially, gabions were proposed, but

future flooding at the workings – it is making

protection blocks have been used to

on closer examination, we decided to

an environmentally conscious contribution

prevent stormwater flooding an opencast

take the Armorflex route. not only has

to the area,” Ruthven says. “Eventually,

platinum mine in northwest Province.

it saved the client more than R2-million

the new channel will be transformed into

in construction costs, but we halved the

an attractive grassy stream in summer.”

The environmentally beneficial Armorflex system, which uses slotted blocks, is also saving R-millions in construction costs over original estimates. The project involved the rerouting of a seasonal stream which flows near the mine and excavating an entirely new channel. The diversion channel was lined with the Armorflex concrete block system, +- 50 000m² blocks having been laid along its 2,5km length.

construction time.” Water draining from the northern slopes of the Pilansberg hills into the stream has been the prime cause of flooding at the mine in recent years. “The project was sufficiently advanced to ensure there was no flooding at the mine this summer,” said van der Merwe. The block-laying was handled by specialist paving company, Pavebuild Civil Contractors

According to Peet van der Merwe, of

and was completed at the end of february.

Midrand-based civil engineering construc-

once laid, the blocks were covered with

tion company, VVB Construction, Tech-

top-soil to encourage the growth of grass.

nicrete’s Armorflex system was chosen

“By rerouting the existing channel, the

because it offered the best solution.

mine is doing a lot more than preventing

Technicrete’s concrete Armorflex erosion-protection blocks are laid in a diversionary channel which was excavated to prevent flooding of an open cast platinum mine in Northwest Province.

14 PRECAST VOLUME 5 • ISSUE 1 • MAY 2011

cHRYso enHances PoLoKWane concrete sculPture Concrete repair products and admixtures

t o a i d in e a r l y m o ul d s t r ip p ing a n d

supplied by Chryso South Africa played an

handling. Chryso xel 650 is a chloride-free

important role in enhancing the concrete

accelerating admixture ideal for reducing

“initial soil reports showed favourable

used for the construction of the Progress

setting time and significantly improving

founding conditions with bearing capacity

Tower at the nelson Mandela Traffic Circle

early compressive strengths in reinforced

ranging between 200kPa to 350kPa on

on the n1 highway in Polokwane.

concrete units.

what seemed a well constructed sub-base

He said some major challenges had to be overcome in completing the project.

Commissioned by the Polokwane Arts

“Chrysofluid optima 206 ‘new genera-

of the road. However, a 450mm diameter

and Heritage Department, the 15m high

tion’ super-plasticiser formed part of the

stormwater pipe was then discovered

structure comprises a steel frame clad

concrete mix for the precast panels. it was

underground. it had been installed to

in precast concrete. it was designed by

used to reduce the water-cement ratio,

discharge water into an existing manhole

local artists under the curatorship of

improve the plastic properties of the con-

in the centre of the traffic circle.

renowned johannesburg designer, Clive

“This pipe ran right through the centre

van den Berg of Trace, whose concrete

o f the nor ther n c oncr e t e b ase. We

creations include the acclaimed Eland

overcame this problem by constructing a

sculpture at the Braamfontein gateway

reinforced concrete culvert around the pipe

site in johannesburg.

and ensuring that the bearing capacity of

keith Mclaren of onsite Tools, Chryso’s

the founding material was not exceeded.

limpopo and Mpumalanga distributor, said

“There were also severe time constraints

two Chryso repair mortars were used by

on Twin Structures, the manufacturers of

Corestruc, the company which erected the

the steel elements, because the steel

structure for the main contractor, Vision

structure had to be used as a template for

Construction.

the fabrication of the concrete formwork.

“Corestruc needed to achieve consist-

“The concrete panels had to be fixed

ent colouring on the precast panels as

to the steel structure with galvanised

well as negate the imperfections caused

The new Polokwane sculpture on the N1 features precast concrete panels fixed to a steel structure.

bolts which were inserted through cast-

We recommended Chryso Rep fR to fill

crete and improve workability at a relatively

f ixing points on the steel structur e

the ferrule holes and for the patchwork.

low slump ratio. optima 206 also helped

proved extremely challenging. However, it

Chryso Rep fC repair mortar was then used

avoid drying shrinkage and anchor point

was achieved with the use of a surveyor

as a fairing coat to give a uniform finish,”

stressing on the panels. The overall objec-

w ho me asur ed the posi tions on the

Mclaren stated.

tive also was to contain costs,” he added.

steel structure and then plotted them

“Coreslab, the manufacturers of the

Clive van den Berg said a water-cement

into the formwork. in addition, a 30mm

sculpture’s concrete precast elements,

ratio of 0,37 yielded concrete strengths of

tolerance was implemented to absorb any

used Chryso xel 650 as an accelerator

up to 50MPa.

inaccuracies,” van den Berg added.

by the repair work on the ferrule holes.

in sleeves. Matching the sleeves to the

ecHo MoVes into caPe Floor-slab market The Echo group, South Africa’s largest

in a d di ti o n t o To p f l o o r’s e x is ting

manufacturer of hollow-core concrete floor

products, entirely new products developed

Topfloor, first established in Belville

slabs, has acquired ownership control of the

by Echo engineers will in future be available

South in 1996, will retain its name, identity

Cape manufacturer Topfloor, giving Echo a

in the region. They will include a new

and top management, headed by managing

national footprint in the highly competitive

ground-beam foundation system designed

director, Renn Holtzhausen.

precast and prestressed floor industry.

expressly for social housing.

Echo already has two manufacturing

lord commented that the takeover will

plants in gauteng and one in kwa-Zulu natal.

enable Topfloor to play a greater role in the

Chairman, Peter lord, said Echo’s 26

Western Cape’s government-funded social

years of expertise in the hollow-core floor

producer of precast flooring,” says lord.

housing programmes.

slab sector would immediately be injected

“The takeover will enable the group to

into the Cape operation, widening its

spread some of its fixed-costs across four

product range and market penetration over

manufacturing plants, thereby securing

the entire Western Cape region.

its position as the country’s lowest-cost

Topfloor’s manufacturing plant, situated in Cape Town.

PRECAST VOLUME 5 • ISSUE 1 • MAY 2011 15

noRtHLanDs PRoject PaveD bY bosun An area of over 200 000m² has been

offers safe parking and easy access and

adverse weather conditions. The coloured

p a v e d w i th B o sun’s S A B S - ap p r o v e d

Bosun Brick has been reliable supplier,

(white, yellow or red) reflective surface

concrete kerbs concrete block pavers

developing considerably along the way – as

is an integral part of the manufactured

at northlands, a business park property

we have.”

paving units, and apart from occasional

development in northriding, johannesburg.

Bosun Brick, CEo, David Wertheim

The project comprises eight separate

Aymes, says the company is proud to

business parks covering a total area of 1

be associated with the nor thlands

100 00 m², of which 750 000m² have been

de velopment. “our r elationship with

already completed.

northlands Projects has developed to

northlands is a mixed business-use

be much deeper than merely a supplier

development accommodating retail, show-

of products. northlands is one of our

rooms, factories, mini factories and offices.

prestigious installations and includes

Construction work began in 1999, and

unique and innovative products such as

from the outset, Bosun Brick supplied

cleaning, is maintenance-free.

reflective pavers.”

paving, kerbs and other infrastructural

Bosun Brick’s reflective pavers and

concrete products to various projects

kerbs offer a permanent, cost-effective

within the development.

alternative to traditional painted road

“Concrete pavers fulfill an essential role

markings. Their primary function is to

in this development,” says Darin D’oliveira,

promote the safety of motorists and

director of nor thlands Projects, the

pedestrians alike, by providing clearly

developer of the project. “The development

visible markings, especially at night and in

The paved entrance at Northlands.

16 PRECAST VOLUME 5 • ISSUE 1 • MAY 2011

inLanD anD WesteRn caPe PRojects Dominate cma aWarDs

johannesbur g; T he islands E sta te a Re t aining Walls E lemen ts >3m high project at Hartebeespoort Dam, north West Province; and a gautrain noise mitigation project which won a premier

o f the 35 awar ds pr esented by the

w i th floor Slabs and the inno v a ti v e

award in the innovative Concrete Products

Concrete Manufacturers Association

Concrete Products categories. As the

category.

(CMA) for its 2010 Awards for Excellence

number of CRB entrants has increased

The Cape-based Premier Award went to

compe ti tion almost all wer e won by

substantially over the previous 10 years

Quality Public Spaces, a Commercial and

projects based either inland or in the

it was decided that this division warranted

Community Concrete Block Paving project,

Western Cape. inland projects took 18

a trophy of its own.

in Phillipi, Cape Peninsula.

awards and the Western Cape 15, while

As was the case in 2006 & 2008,

Although Premier Award certificates

the Eastern Province and kwaZulu-natal

C a t h a y in du s t r i e s w e r e t h e a n c h o r

were presented to each member of the

only managed one apiece this year.

sponsors of the event. The company is

project team, the actual trophy will reside

Regional Cape-based awards were

one of the world’s leading manufacturers

with the entrant.

presented at a ceremony at the University

of high quality oxide and a global player in

Besides taking four Premier Awards

of Stellenbosch Business School in Belville

the manufacture, blending and marketing

last year, inland projects also took six

on october 26th and the Premier, national

of ferrotint pigments.

national Awards, six Regional Awards,

and Regional inland awards were presented

in addition to the five Premier Awards,

and two Special Commendation Awards.

at a gala dinner at the Theatre on the Track

14 national Awards, 12 Regional Awards

in addition to its Premier Award, the

in kyalami, Midrand, on november 6th.

and four Special Commendations were

Western Cape was also awar ded six

The event was the culmination of all the

presented last year. national Awards are

national Awards and six Regional Awards.

activity surrounding last year’s Awards

only made if the entries meet standards

it also took a Special Commendation

for E xcellence competition, including:

which the judges f eel ar e wor thy of

Award. Special Commendation Awards are

the pr ep ar a tion o f the en tr ies; the

national Award status and this year 18 of

made in instances where the judges rate

appointment of the judges and the judging

the 21 award categories made the grade.

two entries in the same category almost

process; extensive media coverage; and

of the five projects awarded Premier

equally and both are worthy of an award.

the ceremonies.

Awards, four were inland projects and one

T he breakdown of the 14 national

The awards were made in the following

was Cape-based. The four inland projects

Awards is as follows: Concrete Block Paving

categories: Concrete Block Paving (nine);

comprised: a Community Housing Concrete

(4); Concrete Roof Tiles (4); Concrete Ma-

Concrete Roof T iles (nine); Concrete

Roof Tile project, Hlanganani gardens,

sonry (2); Concrete Retaining Block Walls

Masonry (four); Concrete Retaining Block

in C o sm o C i t y, g a u t e ng; R e si d e n c e

(2); Suspended Concrete floor Slabs (2).

(CRB) Walls (seven); Suspended Concrete

kok an individual Housing project in the

floor Slabs (four); and innovative Concrete

Concrete Masonry category in Saxonwold,

The following projects won national Awards:

Products (two). The competition is held biennially, last year’s being the 13th since the event was first staged in 1986. CMA director, Hamish l aing, says the aim of the competition is to promote excellence and innovation in the use of precast concrete. “it also serves to highlight the significant role that CMA member companies are playing in the provision of community housing, educational buildings, access to fresh water, improved sanitation, roads, innovative infrastructural products and eco-friendly construction practice.” last year’s competition was notable in that a fifth premier award was introduced. The award was created for the Concrete Retaining Block category and was sponsored by CMA member, Terraforce. in the past this category shared a trophy

Five CMA Cathay Industries Premier Award trophies were presented at a gala dinner on November 6th, 2010, in Midrand. Pictured here are representatives of all the trophy winners: Jorrie Jordaan (left), Trade Sales Manager, Marley Roofing; Paul Phipps, General Manager, Southern Pipeline Contractors (SPC); Gerhard de la Ray and Sam Malemela of SPC; Steve Delport, SPC Sales Manager; Barry Kok, B2 Architects; Hans Barnard, Watson Concrete; JJ Coetsee, Watson Concrete; Claude Gorgulho, Managing Member of C.E.L. Paving Products; Tony da Silva, Cathay Industries; Anca Szalavicz, ASA Architects; Mark Irving, Marley Roofing MD; Samantha du Plessis, a Marley Roofing Sales Executive; Silvio Ferraris, CMA President and CEO of ReMaCon Products; Rene Coetzer, ReMaCon Products; and Jaques Roosendaal, MC Civils.

PRECAST VOLUME 5 • ISSUE 1 • MAY 2011 17

Concrete Block Paving

and Community category; and Parsonage,

The judging of last year’s competition

The Curzon in Constantia Cape Town in

Colleen glen, Eastern Cape in the Vin-

took place in july when some 150 entries

the Residential category; and Market

tage category.

were critically assessed by two teams of

Square, Hermanus in the Roads category.

judges at the CMA’s Midrand premises. All

Tw o n a ti o n al Aw ar ds w e r e m a d e in

Concrete Retaining Block Walls

experts in their respective fields, they com-

the Vintage Paving category and they

Public Transport Shared Service Centre,

prised architects, landscape architects,

comprised: the Palazzo Hotel, Monte

Cape Town, in the Retaining Walls <

civil engineers and a quantity surveyor.

Casino, johannesburg; and Walter Sisulu

3m high category; and the inanda Club

national Botanical gardens, Roodepoort.

johannesburg, in the Vintage category.

Concrete Roof Tiles

Suspended Concrete Floor Slabs

on their selection of winning entries. That

Val du lac, franschhoek, in the individual

Steenberg Social Housing Project, Cape

they were most impressed with the entries

luxury Housing category; Mahlathini Pri-

Peninsula, in the Residential Houses,

is borne out by the fact that 18 out of a

vate game Reserve in Phalaborwa in the

flats and Townhouses category; and novo

possible 21 national awards were won. This

luxury Complex Housing category; River

Packhouse, Paarl in the Commercial and

is indicative of CMA members’ and other

falls office Park, Pretoria in the Commer-

industrial category.

manufacturers’ commitment to maintain

The judges scrutinised and debated the merits of the entries with great deliberation and carefully considered comment was given

cial and Community category; and Rosebank Union Church in the Vintage category.

The awards presentation was a black tie event attended by manufacturers,

and improve standards in the production and application of precast concrete.

professionals, the judges and the media.

laing observes that the competition

Concrete Masonry

T he awards were presented by Silvio

would carry very little value without the

international Car Rental facility, Cape Town

ferraris, president of the CMA, and Tony

expertise and unbiased input of the profes-

international Airport, in the Commercial

da Silva of Cathay industries SA.

sionals who assume the judges’ mantel.

18 PRECAST VOLUME 5 • ISSUE 1 • MAY 2011

RoYaL BafoKeng saVes R-MiLLions WitH concrete block Paving In 1996 the Royal Bafokeng Administration (RBA) took a brave decision. It chose to use what was then the largely unproven system of concrete block paving (CBP) rather than the widely-used asphalt system to surface the roads of its 28 villages situated in Northwest Province. Although the initial capital outlay for CBP

the fact that the RBA had invested in a

is marginally higher than the asphalt al-

CBP manufacturing business, Bafokeng

projects. They have performed extremely well and have required minimal mainte-

ternative, the decision to use it is now

Concor Technicrete in 1996, and opting for

nance. We do, however, run a preventative

paying handsome dividends, saving the RBA

CBP road surfaces as opposed to asphalt

maintenance programme through local con-

millions in ongoing maintenance, creating

ensured that the business had at least

tractors, which essentially involves clean-

jobs and providing skills training for locals.

one reliable sales outlet. Since then the

ing and the painting of road signage. on

“Since we began the project some

company has supplied over 1 800 000m² of

the rare occasion when there is a problem

300km of six metre wide village roads have

concrete block pavers for the village roads

such as subsidence, it is generally caused

been covered with concrete block paving,

project alone.

by a leaking pipe or weed growth.

making the RBA the country’s largest user

“We opted for 60mm grey 35MPa zigzag

“Several local contractors have achieved

of the product,” says lucain Paulik, capital

interlocking pavers for all our village road

high competency levels in CBP laying and

project manager of the Royal Bafokeng

we employ them on all our projects. They

Administration.

in turn employ local residents from the

“little did we realise when we began the

villages and train them to a high level of

project how significant our decision would

proficiency. Health and safety factors are,

be. not only have we been saving approxi-

of course, also included in the training.”

mately R13 million (R42 000 per kilometre)

Besides the benefits listed above, Paulik

in maintenance costs annually, but we have

says there has been a substantial green

created road surfaces which are safe, du-

aspect to the project.

rable and aesthetically pleasing.” Paulik confesses that the initial decision to take the CBP route was aided by

One of the Royal Bafokeng village roads paved with concrete block paving (CBP). Note the open drain next to the road surface.

“This lies in the fact that our base material is comprised of waste rock sourced locally from the platinum mines. Apart from transport costs, the material was supplied to us at no charge. “Because it is waste material, the rock has a low-embodied energy content. it is an extremely stable sub-base material which will provide a solid road foundation for many years to come. Moreover, we have also assisted the mines by clearing unsightly dumps.” over the past 15 years all Royal Bafokeng roads surfaced with CBP have been designed by Vela VkE, SMV and Phatwe Consulting Engineering. Although several contractors have been used, recent projects have been handled by the Bayvi/Dimakotso joint venture with Bayvi Construction & Mining as the lead partner. Pha t we C onsulting Engineer ing’s dir ec tor, P e ter Mashaba, say s tha t

A road being surfaced with concrete block paving (CBP) in Lefaragatlhe, one of the 28 Royal Bafokeng villages which has benefitted from the system.

the only real problem encountered with the roads has not been with the paved

PRECAST VOLUME 5 • ISSUE 1 • MAY 2011 19

surfaces, but the silting of the stormwater drainage under the roads. “We found that blockages were occurring in the stormwater infrastructure under the village roads. it was for this reason that we used surface rather than subterranean drainage on our last four projects. These were situated in the villages of lefaragatlhe, luka, Chaneng and Rafredi,” said Mashaba. The open drain concept was the brainchild of Riaan Bredenkamp a civil engineer of SMV Engineers, who worked in close collaboration with lucain Paulik on the surface drainage idea. Measuring 1 500mm across and 200mm deep, the open channels link into convention-

A close-up of an open-channel drain paved with concrete block paving in Lefaragatlhe, one of the 28 Royal Bafokeng villages in Northwest Province.

al stormwater drainage systems. As they

RBA’s village roads. in addition to the

are laid with the same 60mm pavers used

benefits of being clog-free, open drains

“The paving of our villages is an ongoing

on the roads, the channels form an integral

can also be used as bicycle and pedestrian

project and roads are surfaced as and when

and visually harmonious part of the roads.

paths,” says Paulik.

budgets are available. To date +- 10% of

sidewalks and several other places.

“This system has proven very success-

The Royal Bafokeng Administration

our 28 village roads have been paved and

ful, so much so, that the RBA has adopted

has used CBP for other projects such as

the intention is to eventually pave them all,”

open drainage as its standard model for

parking lots, schools, community centres,

concludes Paulik.

20 PRECAST VOLUME 5 • ISSUE 1 • MAY 2011

tHe 20/40 MiniBLocK Ð WHatÕ s in it For You? Rising costs in both materials and labour continue to put the brake on South Africa’s housing delivery targets. This is why any product which offers the means of boosting productivity and reducing costs should be taken full advantage of.

its usage has, until now, been confined to

as much as 50%, and also reduces wastage.

that province. So what makes the 20/40

The system is particularly suitable for the

MiniBlock special? Size, in a word.

affordable end of the housing spectrum.”

larger than standard imperial units but

The 20/40 MiniBlock was designed as a

smaller than conventional blocks, 20/40

cavity walling system in the Western Cape

MiniBlocks offer significant economy-of-

because of the region’s persistent rainfall.

scale benefits. only 20 blocks are required

However, it is equally suitable for solid wall

to fill a square metre as against the 52

construction, typically found inland.

units of a standard brick when used in

laing says another huge plus is the fact

single-skin applications, and only 40 units

that the system presents an ideal match

According to Concrete Manufacturers

are required for double-skin walls - hence

for modular masonry.

Association (CMA) director, Hamish laing,

the name 20/40 MiniBlocks.

“full modular masonry is akin to lego

the 20/40 MiniBlock is just such a product

laing says that the system is far

and offers several advantages over its

and deserves the full attention of specifiers

more productive than the standard brick

conventional counterpart. These include:

and housing providers.

alternative.

first introduced in the Western Cape as

“it cuts labour costs by roughly one

the SuperMaxi block some 10 years ago,

third, reduces mortar and water costs by

Some of the units at the Steenberg Social Housing Project where the 20/40 MiniBlock was used with considerable success.

PRECAST VOLUME 5 • ISSUE 1 • MAY 2011 21

increased productivity; minimal wastage

MiniBlocks have an excellent finish and don’t

apartment block, Aquarius, was completed

owing to little or no chopping of blocks;

necessarily require plastering.

shortly before the World Cup.

and a good fair-face finished wall with

“ideally speaking all double-skin walls

“We use the 20/40 MiniBlock for double-

excellent durability. The 20/40MiniBlock

should be cavity-based because recent

skin cavity outer walls and single skin inner

modular masonry system is available with

tests conducted by the Clay Brick

walls and don’t use any other product.

a full suite of complementary units com-

Association confirmed that the thermal

Besides costing less than standard bricks

prising a full block, cavity closure units for

properties of these walls are greatly

we found the product is also quicker to

window and door openings, corner blocks

superior to collar-bonded solid walls and

lay. Because it only requires 20 20/40

and half blocks.

the cavities allow for extra insulation to

MiniBlocks to fill a square metre it takes

be added if desired,” says laing.

about half the time to build a wall with

“Unfortunately full modular masonry is rarely applied in South Africa. This scenario

20/40 MiniBlocks have been used with

the system. The bricks form an excellent

would be quite different if specifiers and ar-

great success by two Cape Town-based

plastering surface and our mixture of two

chitects were aware of and insisted on the

construction companies Rémey Construc-

bags of cement, four bags of lime and eight

use of complementary units,” says laing.

tion Pty (ltd) and Anton Mulder Construc-

wheelbarrows of sand works extremely

The 20/40 MiniBlock is more than twice

tion, the former on the Steenberg Social

well. no shrinkage or cracking has occurred

the size of a standard brick. However,

Housing Project and the latter on several

on any of our projects.”

because it is hollow, it weighs in at 6kg

high-rise buildings in Bloubergstrand.

in comparison to the 3.6kg of a standard

one of Rémey’s directors, contracts

laing says that the 20/40 MiniBlock modular system could make a substantial

brick. This means it can be still be handled

manager Dawid Addendorf f,

says the

contribution to alleviating the housing

with one hand and laid like a standard brick,

low cost of the 20/40 Mini-Block system

shor t age gi v en i t s ob v ious b ene f i ts

which why it is dubbed MiniBlock.

enabled Rémey to not only make substantial

described above.

Measuring 290mm, the 20/40 MiniBlock

savings for SoCHo Amalinda Housing on

is 33% longer than the standard 222mm

the Steenberg project, but to meet all its

brick and when designed into buildings con-

requirements as well.

sisting of 300mm modules it incorporates

“We used over a million blocks for building

standard doors and windows perfectly. its

double-skin cavity walls, some of which

width of 90mm is slightly narrower than

were bag-washed and others plastered. We

a standard brick and matches the metric

also requested the manufacturer to close

brick standard. However, its height of

off the top of each unit to prevent mortar

157mm is where the difference is really

falling into the hollows,” said Addendorf.

significant, a course of 20/40 MiniBlocks

Project manager, juriaan linde, of

being precisely equivalent to two courses

Anton Mulder Construction, says his

of standard bricks.

company has used the 20/40 MiniBlock on

“T his f eatur e of f ers substantial

six high-rise buildings in Bloubergstrand

productivity gains,” comments laing.

ranging from seven to seventeen stories.

“in the first instance it saves a course

The most recent project, a 14 storey

for further information contact the CMA on (011) 805 6742.

A partially-built wall demonstrating the use of the 20/40 MiniBlock at last year’s housing conference in Cape Town.

of mortar and the block’s extra length means that additional mortar is saved through fewer perpend-joints. And being substantially larger than a standard brick, it is also quicker to lay. “in fact the system really comes into its own when deployed as cavity walling for external walls as 20/40 MiniBlock modular masonry and cavity-walling go hand-inglove. for example, corner units are used on doors and windows as cavity closures. “A n o t h e r a d v a n t a g e i s t h a t t h e blocks are length and height compatible with imperial bricks and can be used in combination with standard face bricks. for example, 20/40 MiniBlock masonry can be used for the inner walls, and the standard face system on the outer.

However, it

should be noted that fair-face 20/40

The living area of one of the units at the Steenberg Social Housing Project. The 20/40 MiniBlocks can be seen through the bag-wash finish which is both durable and aesthetically pleasing.

22 PRECAST VOLUME 5 • ISSUE 1 • MAY 2011

Figure 2: Downstream of an LLRC shown in Figure 1 once the flooding has started to subside.

PRECAST VOLUME 5 • ISSUE 1 • MAY 2011 23

fLooDs HigHLigHt PooR DetaiLing of loW-level river-crossing Design By Alaster goyns, owner Pipeline installation and Professional Engineering Services CC

The January of 2011 was, for much of the country, the wettest in 50 years. Widespread flooding in eight of nine provinces resulted in excess of 100 lives being lost and damage totalling R-Billions. Low-level river crossings (LLRCs) which are designed to over-top were particularly flood prone, exposing those who ignored the danger to life-threatening consequences. in the wake of january’s calamitous events some serious

high-recurrence-interval floods, they are inadequate

questions on the performance of llRCs during heavy

for low-recurrence intervals, ie severe flooding, and

flooding must now be posed. it appears that in some

designers should make allowances for this.

instances their designs and detailing exacerbated the

Under certain circumstances the flow of water

flooding and aggravated the ensuing damage to property,

over llRCs becomes super-critical and the danger of

river bank erosion and the threat to motor vehicles and human life. Most of these problems occurred in small rivers and streams where low-level crossings using multiple culvert cells were installed. Costing considerably less than bridges and much simpler to build, llRCs are deployed on the basis that they are likely to be flooded for short periods during their lifespans. it is therefore essential that road users understand the limitations of these crossings and don’t attempt to ford them when they are over-topped beyond a certain depth (1,p65) Provided they are correctly designed and detailed, ther e ar e other ad vantages to l l RCs, such as minimal earthworks in the approaches. it is, however, essential that they are designed so that very little or no environmental damage takes place when they are

Figure 1: Over-topping of a low level crossing over the Hennops River in Centurion.

over-topped. in addition to their flow-handling capacity other major considerations in their designs are: • Upstream flooding • Blockages at the upstream end • Roadway over-topping • Downstream erosion • Siltation under the LLRC. Apart from siltation, these events all occur during periods of flooding, and to minimise their impact, the size of the waterway under the llRC should not be less than that of the natural channel itself. Moreover, any impediments to the flow, not only of water but of driftwood and other debris, should be minimised. As culvert dimensions and configurations are selected for

Figure 3: Upstream blockage after flooding.

24 PRECAST VOLUME 5 • ISSUE 1 • MAY 2011

driving over them under these conditions

only 200m deep would be sufficient to lift a

during january’s floods there are certainly

is not widely appreciated. However, what

vehicle and carry it off a low-level crossing.

some lessons to be learned from its

does grab the public’s attentions is when

performance.

cars are washed off llRCs. Drivers are

A TYPICAL CASE STUDY

either not aware of or ignore the warning

f i g u r e 1 sh o w s a l l R C c o m p l e t e l y

each providing an opening of 1.8m across

signage and the guide blocks which indi-

submerged by a flooded Hennops River in

and 1.2m high. The channel itself is about

cate flow depths. SAnRAl’s (The South

Centurion. in this instance the upstream

16m wide and 2m deep. The Hennops flows

A f r ican na tional Roads Agency l td)

water level is almost 500mm above the

fairly strongly throughout the year, and as a

drainage manual recommends that vehicles

road surface, indicated by the fact that

result, trees and dense bush flourish on its

should not attempt to cross llRCs when

the guide blocks are not visible. The flow

banks. During floods, broken branches, logs

super-critical flow-depths exceed 100 mm

over the crossing is super-critical and the

and other debris are swept downstream.

and sub-critical depths exceed 150 mm.

downstream guide-blocks are submerged

Much of this material is obstructed by

(1, p6 10).

by a hydraulic jump, which they caused.

llRCs, becoming wedged against the walls

When a car or any other object

The car on the far side of the crossing

between the culvert cells. This occurs

obstr uc ts a super -cr itical f low, the

attempted to ford the river but fortunately

because the width of the individual cells is

water jumps up to its corresponding

was washed off the road before it reached

inadequate to allow for the free passage of

sub-critical flow level. if the wheels of a

the super-critical flow section in the middle

debris through them. The water level then

vehicle moving through a super-critical

of the river. (This was not the only vehicle

rises behind this obstruction forming a

flow initiate a hydraulic jump, there may

that got into trouble trying to negotiate

“weir” when it is over-topped. Downstream

insufficient clearance under the vehicle

this crossing during january.) The flooding

of this weir the smooth surface of the road

for the jump to develop fully. This can

was aggravated by logs and other debris

over the llRC facilitates a super-critical

result in a conversion from velocity-head

that were jammed against the culvert

flow with an energy level which equals the

to pressure-head which can then actually

upright sections under the road. This

flow upstream of the obstruction.

lift the vehicle and deposit it downstream.

caused damming upstream of the llRC.

When the flood waters subside the de-

The average car weighs just over a ton, or

Some of these logs can be seen in figure 1.

bris continues to restrict the flow through

the equivalent of 12kn, and covers a plain

Although the over-topping of this llRC

the culverts and extends the period of

area of about 6m². This means that water

clearly could not have been prevented

over-topping. This can be seen in figure 2,

This crossing consists of seven culverts

PRECAST VOLUME 5 • ISSUE 1 • MAY 2011 25

where another car is trapped. The picture also shows the water flowing over the side of the channel, causing potential erosion. figures 3 and 4 show the upstream and downstream condition of the same crossing after the flow has returned to normal. Debris has reduced the capacity of the inlet by nearly 50% and erosion has occurred downstream. if this llRC had had culverts with 3.6 m openings, the flow area would have been greater and inlet obstructions significantly less. it would have been more costly to have constructed concrete wing walls downstream of this llRC, but the need for subsequent and frequent remedial measures would have been eliminated. A CHANGE IN APPROACH Tr adi tionall y l l RC s wer e located at the most suitable point, both from the hydraulic and engineering perspectives, and roads were routed to these points, even if it meant them covering greater

Figure 4: Downstream erosion after flooding.

distances. However, today llRCs are frequently built to fit the road alignment,

high velocities due to the softer material

handle the average annual storm without

irrespective of the actual hydraulic and

composition of their banks and beds. it is

over-topping their banks and may flow full

engineering conditions at the crossings.

therefore essential that all such outlet

a few times every year. over the long-term

As a result, the conditions are often not

transitions are designed to dissipate

the cross-sectional dimensions of these

ideally suited to minimising the impact of

energy and reduce the velocity to a level

channels will remain fairly constant. Dense

flooding. Moreover, some designers do

which will not erode natural channels.

vegetation and wooded corridors grow

not consider the frequency of storms in

along perennial watercourses, so it is to

the catchment area and the anticipated

WHAT CAN BE DONE

be expected that logs and dead trees will

run-off. They also don’t consider extremes

one of the major mistakes designers make

be carried downstream during flooding.

in precipitation which can lead to extreme

with llRC designs is not visiting the actual

The case study described above is a

flooding. Another consideration of ten

site and inspecting the natural channel

good example of what can happen and, one

ignored is that during periods of low-flow

before designing the structure. factors

hopes, provides the motivation for paying

velocities may be insufficient to prevent

r equiring obser vation include er oded

closer attention to such crossings during

siltation. This results in a reduction of

channel cr oss-sections which should

the design and detailing stages.

the flow area under the llRCs, thereby

indicate stream levels during flooding, the

There are various organisations, such as

further compromising their performance

typical size and types of debris found in the

the Pretoria and Stellenbosch Universities,

when extreme events occur.

stream during flooding, and the condition of

the South African Road federation (SARf)

T here are some basic rules which

the river banks immediately upstream and

and the P.i.P.E.S. Division of the Concrete

should be followed when designing urban

downstream of any existing crossings. The

Manufacturers Association (CMA) which

stormwater systems which comprise

detailing of llRCs and the methods used to

offer CPD validated courses for qualified

various types of inlets and a piping network.

cope with the prevailing conditions can have

designers on river hydraulics and storm

for instance, minimum and maximum

a significant impact on how llRCs perform

wa ter dr ainage. B y a t tending these

velocities should be prescribed and the

under extreme events. They should be

courses designers will gain an insight into

transitions should be carefully detailed.

designed to minimise the impact on water

the design of llRCs and other hydraulic

The discharge from man-made systems

flows at all times.

storm water structures.

which may flow at high velocities into

Many of the streams and rivers in

natural water courses is where the serious

gauteng are perennial and have a well-

problems frequently occur. The natural

defined central channels that are, say, 15m

channels are unable to tolerate these

to 20m wide and 2m to 3m deep. They can

REfEREnCES 1. SAnRAl Drainage Manual, 5th Edition, Published by The South African national Roads Agency ltd, Pretoria, 2006

PRECAST VOLUME 5 • ISSUE 1 • MAY 2011 27

Producer members M = Masonry COMPANY NAME

P = Paving

Pi = Pipes

TELEPHONE

R = Retaining Blocks

PRODUCT

S = floor Slabs

COMPANY NAME

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

Baybrick

(035) 792 5218

Boland Concrete

(021) 875 5365

T = Roof Tiles TELEPHONE

PRODUCT

(032) 944 4155

082 324 7277

Mobicast Mossel Bay

(044) 874 2268

MVA

(012) 386 0050

Monier Roofing South Africa (H.o.)

(011) 222 7300

Monier Roofing South Africa

Bosun Brick Brits

(012) 250 1711

(016) 430 8000

Bosun Brick Midrand

(011) 310 1176

MPR

Monier Roofing South Africa (free State)

(051) 432 5089

Monier Roofing South Africa (north West)

(012) 250 2218

Monier South Africa (Cape Town)

(021) 534 1441

Brick and Concrete industries

(00264) 61 321 3000

Brickcast industries

(031) 507 5525

MPR

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

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

ReMaCon Products

(011) 393 5504

Concrete Units

(021) 386 1923

Rocla

(011) 670 7600

Conframat

0861 33 5599

Salberg Concrete Products

(011) 357 7600

Corobrik

(031) 560 3111

Southern Pipeline Contractors

(011) 914 8500

Deranco Blocks

(041) 463 3338

Stabilan

(051) 434 2218

Deranco Paving

(041) 933 2755

Shukuma flooring System

(041) 372 1933

Deranco Precast

(041) 463 3338

Stanger Brick & Tile

(032) 457 0237

Eagle Roof Tiles

(044) 874 0290

Stone Age Concepts

(012) 802 1496

Echo floors

(011) 662 4600

Technicrete

(011) 674 6900

MPRT

Echo Prestress

(011) 589 8800

Technicrete (Mpumalanga)

(013) 758 1203

MPRT

Echo Prestress Durban

(031) 569 6950

Technicrete (Mpumalanga)

(017) 689 2100

MPR

(00263) 448 6620

Technicrete (Mpumalanga)

(013) 696 1153

MPR

fort Concrete inca Concrete Products

(021) 904 1620

Technicrete (free State)

(057) 391 4200

MPR

inca Masonry Products

(043) 745 1215

MPRT

Technicrete (north West)

(018) 790 4380

MPR

infraset

(011) 876 5500

Technicrete (limpopo)

(015) 293 8083

MPRT

infraset

(012) 652 0000

MPR

Technicrete (gauteng)

(011) 203 7700

MPR

infraset

(031) 569 6900

Technicrete (north West)

(018) 484 6234

MPR

kwena Concrete Products

(00267) 392 2850

Technicrete (E.Cape)

(041) 372 2230

klapmuts Concrete & Cape Retaining

(021) 875 5151

Topfloor

(021) 951 7700

kopano/Altocrete

(016) 363 0340

Vanstone Precast

(012) 541 2056

kwena Rocla

(00267) 393 2850

Vibro Bricks

(012) 374 0208

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 1098

28 PRECAST VOLUME 5 • ISSUE 1 • MAY 2011

AssociAte members COMPANY NAME

TELEPHONE

ARQ Consulting Engineers

(012) 348 6668

ilifA Africa Engineers

(016) 981 0591

j C Paving Consultant

(011) 431 0727

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 2400

C&Ci

(011) 315 0300

Chryso Southern Africa

(011) 395 9700

Dick king lab Supplies

(011) 499 9400

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

Soillab

(021) 988 7410

Smartstone

(011) 310 1161

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