Precast • Issue 2 • 2019 by Isikhova Media

ISSUE TWO • 2019

R49,00

THE VOICE OF THE PRECAST CONCRETE INDUSTRY

• The many advantages of precast concrete • Price pressure killing the market • Raising stairs to new levels

COMPANY NEWS

PROJECTS

2 PMSA SUPPORTS LOCAL ROOF TILE INDUSTRY

26 RAPID ERECTION OF WATER RESERVOIRS

INDUSTRY NEWS

29 VITAL FACTORS TO CONSIDER FOR COLD WEATHER CONCRETING

THE MANY ADVANTAGES OF PRECAST CONCRETE

PRICE PRESSURE IS KILLING THE MARKET

10 GOVERNMENT NEEDS TRAINED CONCRETE TECHNOLOGISTS 12 POOR AGGREGATES? NO PROBLEM

CONTENTS

COVER STORY

16 30

18 NEW ROOF TILE MANUFACTURING PLANT IN KZN

13 UCT PICP/BIO-RETENTION POND SEMINARS ATTRACT HUGE INTEREST

GLOBAL VIEW

PRODUCTS

TECHNICAL

14 IMPROVED PLOTTING PERFORMANCE ON SITE

22 ARCHITECTS LOVE CONCRETE – BUT SHOULD KNOW IT BETTER, SAYS TCI

19 PICP LESSONS FROM THE USA

32 MASSIVE PRECAST BEAMS USED IN HYBRID BRIDGE CONSTRUCTION

23 EFFICIENCY PAVES THE WAY TO SUCCESS 24 COMPRESSIVE VS TENSILE SPLITTING STRENGTH

15 CHEMICALS TO THE RESCUE WHEN QUALIT Y SAND BECOMES SCARCE

PRECAST is the mouthpiece for the Concrete Manufacturers’ Association - CMA Concrete Manufacturers’ Association Physical Address: Office 0400, Standard Plaza Building, 440 Hilda St, Hatfield, Pretoria Postal Address: Post Net Suite 334 Private Bag X 15, Menlo Park, 0102 Tel: (+27 11) 805 6742 Fax: (+27) 86 524 9216 E-mail: admin@cma.org.za Website: www.cma.org.za Publishers: Isikhova Publishing & Communications Postal Address: PO Box 651793, Benmore, 2010, South Africa Tel: (+27 11) 883 4627 Fax: (+27 11) 783 2677 Website: www.isikhova.co.za Publisher: Andrew Meyer Tel: (+27 11) 883 4627 E-mail: andrewm@isikhova.co.za Consulting editor: Raymond Campling Tel: 076 297 2775 E-mail: media@mediasavvy.biz

PRECAST | ISSUE TWO | 2019

36 38 SHORING UP EMBANKMENTS WITH CRB WALLING 39 NEW EXPOSED GLASS PAVER TRANSFORMS WINE ESTATE DRIVEWAY

Coastal editorial: David Beer Tel: 082 880 6726 E-mail: david.bigsky@gmail.com ISSUE TWO • 2019

Advertising Tel: (+27 11) 883 4627 E-mail: andrewm@isikhova.co.za

R49.00

THE VOICE OF THE PRECAST CONCRETE INDUSTRY

Subscriptions/Accounts/ Advertising Admin: Thuli Majola Tel: (+27 11) 883 4627 E-mail: subscriptions@isikhova.co.za Design and layout: Joanne Brook E-mail: joanne.studio@isikhova.co.za

• Many advantages of precast • Price pressure killing the market • Raising stairs to new levels

The views and statements expressed in this publication are not necessarily those of the editor or the publishers and neither the 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. The same applies to all advertising. Precast© 2019. All rights reserved. No part of this magazine may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage retrieval system, without prior written permission from the publishers.

Endorsed by:

ON THE COVER Local concrete equipment manufacturer, PMSA, has played an important role in the establishment of roof tile plants which produce high-quality tiles at economical rates. Over the last decade it has contributed to roof tiles being the preferred choice for residential and commercial buildings

COVER STORY 2

PMSA SUPPORTS LOCAL

ROOF TILE INDUSTRY

Over the past decade local concrete equipment manufacturer, PMSA, has played an important role in the establishment of roof tile plants which produce high-quality tiles at economical rates. This has contributed to roof tiles being the preferred choice for residential and commercial buildings

In Africa’s harsh climatic conditions,

high-quality ABECE equipment pays for

the tiles may even be coated with intu-

itself with tighter tolerances, quicker

mescent paints that can help to reflect

speeds and superior reliability. Longevity

heat. In addition to colouring options,

of the equipment also ensures tiles can

tiles can be made in a wide variety of

be manufactured efficiently for years

shapes and sizes, which assists archi-

to come, which may not be true of less

tects and roof designers to construct

well-made machines.

roofs in a bewildering number of styles.

T h e s am e quali t y e th o s app li e s

Apart from good looks, the density

throughout the process, from correct

of concrete roof tiles means they are

batching and mixing of concrete to the

impervious to water, stronger and able

extrusion onto the production pallets,

to dramatically reduce noise through

colouring, curing on PMSA’s Kraft Curing

During this time the company introduced

the roof. In a value-driven market, the

systems and packaging, either manual

Swedish ABECE roof tile plants, offering

many benefits of concrete roof tiles still

or fully automated, ready for transport.

high-efficiency roof tile manufacturing

shine through and make them a sought-

plants in SA with solutions that deliver

after option, especially where reasonable

Complex process

anything from 1 000-60 000 rooftiles

pricing is maintained through the use of

“Firstly, the process requires precise

per shift.

quality equipment and techniques.

batching and mixing of concrete according

The efficiency of the processes em-

to the design mix,” explains Booysen. “As

ployed by the ABECE plants has also

Why concrete?

a rule, this is in the region of 1kg cement,

contributed towards the viability of es-

PMSA marketing manager Quintin Booy-

3,5kg of blended coarse and fine sand,

tablishing start-up roof tile plants in the

sen adds that the business case for the

30g of oxide and the necessary water

country, making it feasible for established

establishment of a roof tile manufactur-

to ensure optimum mixing for a single

precasting factories to install roof tile

ing plant needs to be established upfront.

manufacturing lines as well.

Provided there is sufficient demand for the product in the region and the price-

Growing demand

out-the-door can compete favourably

High-quality roof tiles are the first choice

with other tile suppliers (and roofing

of most consumers, as they offer un-

types), it pays to invest in high-quality

surpassed durability and last a lifetime

equipment from PMSA.

without rusting or decaying. Aestheti-

He explains that the process of mak-

cally, tiles can also be made in a variety

ing a tile is a complex one and needs to

of modern colours, either through the

be carefully controlled within the process

use of through-colour tiles with oxides or

to ensure optimum efficiency, speed

painting tiles in the production process.

and quality of products. This is where

(Above): Roller and aluminium pallet on an extruder.

PRECAST | ISSUE TWO | 2019

of about 95%. Here we supply Kraft Curing systems that help maintain temperature and humidity for optimum curing.

COVER STORY

(Far left, from left): Automated packing with robots; roof tiles ready for transport and the curing chambers with circulation.

“ T hr ough temper a tur e moni tor ing and adding heat or moisture with a specialised circulation system, the curing process can be completed more evenly and quickly. The humidity is usually generated from the mix, although in dry climates, water misting may be required,” says Booysen. Tight controls through-colour roof tile. The water-to-

to as long as 24 hours, with traditional

“We also offer advanced moisture con-

cement ratio is critical, as too wet a mix

curing techniques. The most important

trol systems to maintain moisture per-

will lead to streaking, improper compac-

advantages of short curing are the ability

centages consistently, batch by batch,

tion or difficulty of extrusion, as well as

to put the same pallet back into produc-

by measuring water in aggregates,

an irregular finish if the mix is too dry.

tion in time for the second shift. These

thereby allowing the volume of sand to be

“Ludwig Moisture Control system

pallets can be made from either steel

corrected before entering the mixture

moistur e sensors ar e usually used

or aluminium, each of which has its own

to maintain the right aggregate-to-

throughout the batching and mixing

advantages and disadvantages.

cement ratio.

content. With the correct mix of con-

Careful balance

up a significant part of the cost of each

crete, the roof tiles are manufactured

“While steel has a longer lifespan than

tile, the need for quality oxides and effi-

on moulds – also called pallets – which

aluminium, it takes longer for profile

cient oxide dosing equipment is essential.

form the underside of the roof tile. Here

changing on the machine – up to one

For this reason, PMSA offers Finke Dry

the utmost precision is required to en-

shift – whereas aluminium takes just a

Dosing systems, which make use of bulk

sure the correct alignment of interlocks

couple of hours. Aluminium is also self-

bags and allow colours to be blended in

between roof tiles to prevent leakage.

supporting and, unlike steel, doesn’t need

the plant. PMSA also offers wet oxide

The tile itself is extruded through rollers

carriers. Aluminium does, however, have

systems, where water-blended oxides

and slippers which form the all-important

a shorter lifespan and a relatively high

can be added to the water.

viewing surface. The extruded shape

scrap value, which makes it susceptible

then goes through a continuous process

to theft.

“Considering that colour oxides make

process to ensure consistent moisture

“Packaging automation is another ar ea that pr ovides potential cost-

“Steel pallets, by comparison, are half

savings on large plants where producers

the price of aluminium and – depending on

have the benefit of reducing breakages

“Immediately afterwards, the tile is

the application – PMSA is able to supply

and lowering the labour cost per tile, as

taken into a curing area where strength

both types. After extrusion, cutting and

well as providing securely strapped tiles

gain is critical and, for the sake of

colouring, the tiles need to be properly

and minimising breakages during packing

profitability, needs to take place in the

cured to achieve sufficient early strength

and transport.”

shortest possible time in order to get

for demoulding as quickly as possible. This

the pallet back into the production cycle.

is imperative to gain strength rapidly.

where each is cut from the next with either a bullnose or straight cut.

New project

Curing times can be anything from eight

“This is best done at a temperature of

PMSA is currently involved in a project

hours, with advanced curing solutions

about 40-50˚C, with a relative humidity

upgrading the batching of a 120-tilesper-minute plant in SA. This plant will incorporate the latest technologies available from PMSA to carefully control moisture, weigh-batching, material handling systems and other processes within the plant to achieve optimum efficiency for better and more costeffective roof tiles. The R12 million project represents a considerable investment from an already established roof tile manufacturer and shows the confidence the company has

(Above): ABECE start-up roof tile machine.

PRECAST | ISSUE TWO | 2019

in PMSA equipment.

9 9 5 R PROFESSIONAL QUALITY MADE AFFORDABLE.

www.bosch-pt.com

INDUSTRY NEWS

The many advantages of construction using pr ecast concr ete structural elements are still not fully understood or realised in the building industry, says Henry Cockcroft, general manager of the Concrete Manufacturers’ Association. “Those who perceive structural steel construction to be faster compared with conventional in-situ reinforced concrete construction are unaware of the favourable production lead times precast concrete can offer. Concrete

THE MANY ADVANTAGES OF PRECAST CONCRETE

structures of fer a huge amount of flexibility in the ways and methods in which they can be constructed.” C o ckcr o f t s a y s th e b en e f i t s o f precast concrete include: • Speed of construction by reducing

propping time for in-situ cast concrete.

• Improved quality because of pre

fabrication’s controlled production

conditions. • Enforced co-ordination and teamwork

because constructability, layout and

for sustainable concrete structures,

temporary concrete casting surface

connection details all have to be

including durability, quality, speed of

near the building footprint. After the

planned well in advance.

construction, appropriate finishes and

concr ete has cur ed, the elements

cost-effectiveness.

are tilted from horizontal to vertical with a crane and braced into position

Factory-made “Concrete has an advantage over other

Long-lasting

until the remaining building structural

materials in that the concrete elements

“Concrete is one of the most durable

components (roofs, intermediate floors

– such as walls, columns, beams, trusses

materials on earth. Well-designed, well-

and walls) are secured.

and slabs – can be constructed in-situ on

constructed concrete offers exceptional

By forming the concrete elements

site, or precast on site on the ground

durability and long life in any structure.

on the ground or in a yard, as opposed

and lifted into their final position, as in

The first line of defence against dete-

to the final position, precast concrete

the case of tilt-up and stack casting, or

rioration is good-quality, impermeable

units provide a convenient construction

precast in a yard and transported to site

concrete.

method saving time, man-hours and

“By pr oducing pr ecast concr ete

formwork. Conventional tilt-up panels

“C o n c r e t e f u r t h e r m o r e h a s a n

in a controlled environment (typically

are structural elements within a building

additional benefit in that all of the above

referred to as a precast yard), it’s pos-

that span from base to roof diaphragm,

options can be combined on one project:

sible to monitor all stages of production,

acting as beams and capable of carrying

some elements can be constructed in-

including adequate curing, compaction,

roof and slab loads. They combine the

situ, with others precast on or off site.

quality and depth of cover concrete, and

building envelope (façade), structure and

In addition, individual concrete elements

ensure that products fully comply with

final finish in one operation.

can be designed and built combining in-

strength requirements.

and erected into position.

situ and precast concrete, known as

Panels are set out in accordance with

“P r e c a s t c o n c r e t e a l s o o f f e r s

a predetermined casting layout drawing.

important benefits in tilt-up construction,

Ideally, panels are cast on the surface

P r e c as t c on cr e t e c ons tr u c ti on

which refers to a concrete building and

bed of the project or on final concrete

addresses all the important requirements

constr uc tion technique w her e the

hardstand areas around the building.

elements are cast on site and lifted into

When it comes to precast concrete

their final position, maximising many of

cladding panels, the same benefits of high

the unique and sustainable benefits of

durability, low maintenance, excellent fire-

concrete for a cost-effective building

resistance and energy-efficiency apply.

‘hybrid concrete’.”

“Concrete structures offer a huge amount of flexibility in the ways and methods in which they can be constructed.” PRECAST | ISSUE TWO | 2019

technique and efficient construction method,” explains Cockcroft.

Pretty durable “ T his p o w er f ul c ombina tion make s

Alternative techniques

precast concrete cladding an ideal

Elements that are to be tilted up are

solution, from prestigious high-rise

f ormed on a concrete slab: usually

offices with aesthetic appeal to low-

the building floor, but sometimes a

cost commercial structures, where

INDUSTRY NEWS 6

economy and durability are paramount.

for cladding, not only in terms of its

material, with fantastic anti-bent, anti-pull

The clearest advantage of architectural

use of natural and renewable materials,

and anti-compact properties. Having only

pr ecast cladding is in the vir tually

but also in terms of durability. Fibre

20% of the weight of traditional precast

limitless design potential that can be

cement cladding won’t rot, is capable

concrete makes it easier to handle on site

achieved with its use.

of withstanding damaging ef fects of

and reduce loads on structures when in

salt spray and ultraviolet rays, and

use. GRC is also strong, with a higher

“Custom-made forms are used to create concrete panels in the precise

can’t be penetrated by birds

tensile strength than precast

sizes and shapes speci f ied by the

or insects. Once installed,

concrete, allowing thinner wall

designer. Specific colour effects can

the product stands up to

sections to be produced.

be achieved through varying sands,

bumps and direct impacts,

aggregates and pigments. And textures

unlike some other cladding

Professional solution

can be customised through the use of

m a t e r i als . F ib r e c em e n t

Cockcrof t believes that

differing levels of sandblast treatments.

panels don’t become brittle

due to the poor circulation

“The recent advances made with

in f r eezing condi tions or

of technology information

‘new-generation’ composite concretes

melt in the presence of heat

regarding precast concrete,

have produced ‘ultra-high-performance

sources,” says Cockcroft.

as well as insufficient pro(Above): Henry Cockcroft of the CMA.

concretes’ with unheard-of strengths of

Another more recent

up to 145MPa. This has the potential to

development is in the field of

change our minds completely about pre-

glass fibre-reinforced concrete (GRC)

to structural engineers, architects

cast concrete by allowing super-strong,

precast cladding systems. GRC or glass

and specifiers, these professionals are

ultra-thin precast slabs. The pressure

fibre-reinforced cement (GFRC) is a

unaware of the wealth of information

resistance corresponds with primary

new kind of high-physical performance

within precast concrete producers.

rocks like granite. Tensile strength is

compound material, whose main contents

Such professionals consequently

comparable with polymer concrete.

are cement, alkali-resistant (AR) fibres

miss out on the design opportunities

and water.

offered by precast concrete elements,

motion of the expertise of precast concrete producers

Using flexible AR fibres in an admixture

particularly columns, beams and stairs.

“Fibre cement cladding offers additional

of cement and sand allows for a high-

Ultimately, the client loses out on the

advantages that make it a green choice

performance superior and thinner cladding

best possible solution for the project.

Innovative types

INDUSTRY NEWS 7

PRICE PRESSURE IS KILLING THE MARKET An uncontrollable snowball – market demand for fast and cheap products – is leading to production variances, ultimately affecting product quality.

gregate supplier and see whether a

With the current South African economy

additives and admixtures. Manufactur-

change aggregate suppliers. This prac-

wearing a bleak jacket, and this reflecting

ers tweak the amounts of water, cement

tice isn’t very favourable because natural

particularly on the broader construction

and aggregate (raw materials) to achieve

stone aggregate varies in characteris-

industry, market conditions and the

products which can be handled pre- and

tics from area to area where it’s mined

battle for business have become rife.

post-production, are of high quality and

and therefore also varies from supplier

Everyone is squeezing the lemon to

are often aesthetically appealing.

to supplier. If a producer changes ag-

get the last drop of juice. An over-

percentage or two can be gained. If that doesn’t work, the next option would be to

gregate suppliers, it requires a process

competitive market is leading to a

Quality mixes

of product testing and re-evaluation to

tendency to supply faster and cheaper

“Water, as an ingredient, doesn’t pose

confirm the delivery of quality product.

than anyone else.

many challenges. Precast concrete pro-

“The second option would be to remain

Unfortunately, “clever clients” have

ducers know that it should be potable,

with the current and trusted natural

noticed this tendency and are capitalising

either bought or pumped from a source.

stone aggregate supplier, but find a way

on the frantic search for business.

The same can be said of cement. Each

to ‘stretch’ the use of the aggregate.

Additional pressure is being put on

precast concrete manufacturer knows

This is done by adding an ‘extender’ to

suppliers to supply at quicker turnaround

the importance of using a good-quality

the natural stone aggregate.

times and lower pricing in order to secure

cement, of the correct strength and

a piece of the pie which is available in our

sourced from a reputable supplier.

difficult construction market.

“Materials used for this purpose would include those with cementitious

“One seldom finds that the quality

properties, stabilised building rubble, ash

of CMUs has been affected diversely

and slag. The danger here is that these

Downward spiral

because of an issue with the cement.

materials may affect the relative density

In the precast concrete industry, one of

As with water, cement is very much a

of the aggregate, as well as porosity and

the ways to cut costs would be to relook

constant in the production of precast

absorbance of the final product, and it

input or raw materials required for pre-

concrete. This brings us to aggregate.

could contain free elements which will

cast concrete production. At first glance,

“Aggregate forms the bulk of the

have a detrimental effect on the quality of

this might seem to be inconsequential,

three main ingredients in the produc-

the units being manufactured. These free

but it can have dire consequences.

tion of precast concrete units. Natural

elements could include ferrous elements,

Concrete Manufacturers’ Association

stone aggregate is normally mined and

unslaked lime and unburnt coal.

(CMA) general manager, Henry Cockcroft,

processed to a specific grading, which

sheds light on precast concrete produc-

means it comes at a cost. It’s therefore

Many pitfalls

tion, particularly on the produc-

obvious that if one wants to cut

“A myriad of things could go wrong with

tion of consistent high-quality

on production costs, to be able to

CMUs manufactured out of contaminated

precast concrete units.

supply at a lower price, one should

aggregates. Quality issues could show

look at where the bulk of the cost is

up during the production or the curing

cally or scientifically inclined,

reflecting and adjust that. Where

phase of the units, or weeks, months and

but rather a ‘manufacturing 101’

other than the aggregates?

even years later. Should the product fail

“This approach isn’t techni-

approach,” he says. “The manufacture of precast concrete, and

in production phases and while still in the Adjusting aggregates

confines of the production facility, the

more so concrete masonry

“We can highlight two prominent

units [CMU], requires three

ways of adjusting ag-

“The snowball causes the most dam-

gregate cost. The

age when the units have been supplied to

t er, c emen t and

first would be to

the market and when used in construc-

aggregate. These

negotiate sup-

tion. CMUs containing inert free elements

are the bases of

plied price with

have a ‘genetic flaw’. It’s very important

production, before

the current ag-

to realise that these units could comply

main ingredients: wa-

PRECAST | ISSUE TWO | 2019

problem can be contained.

INDUSTRY NEWS

to standards and specifications when

corrective measures come into play.

is in fact a highly expensive exer-

they reach the market. The fact remains,

Consider the following summary:

cise. The financial implications of

however, that it’s a matter of time until

• The establishment and completion

this can severely impact the devel-

the free elements, contained within the

of a housing development calls for the

oper or contractor, insurance

aggregate out of which these units were

manufacture and delivery of thousands

companies and the producer of the

manufactured, receive a catalyst.

of concrete masonry units.

c on cr e t e m asonr y uni t s. T h e

• Such developments are normally

extent of that impact could even

ity of the unit will really start to show.

funded by financial institutions and the

lead to bankruptcy and the closure

In most cases, with concrete masonry

developer carries the initial investment

units, moistur e triggers the r eac-

risk. This risk transfers to the owner

tion and the result is clearly seen in

of the property once it’s sold.

owner would probably act against

plaster flaking from walls and the unit

• Should the structure fail at any stage,

the developer or contractor, in

itself showing ‘pop-outs’. The effect of

there will be detrimental consequences

which case the expense factor

pop-outs on concrete masonry units

for either party deemed to be the

comes into play again. The snowball,

is detrimental. This will influence the

‘owner’ of the property.

however, can gain momentum and

o In the case of the developer or

result in threatening bond boycotts affecting the financial institutions

“As soon as this happens, the qual-

quality of the unit and the integrity of

of institutions. o Where a property’s been sold, the

the structure in which the units are

contractor, the onus will remain

used. The duration of the quality incident

with that developer or contractor

can’t be specified. It will last as long as

to implement corrective measures

there’s moisture available and as long as

t o g e t th e d e v e l o pm en t t o a

the property. The implication is

unstabilised free elements are present.

standard where it adheres to

a macro-economic crisis influencing

the required structural soundness

financier, insurer, manufacturer,

Macro-economics

a n d sp e c i f i c a t i o n . T h i s i s a n

developer or contractor, property-

“In most cases where concrete masonry

immensely costly exercise and

owner and the construction market

units fail within a structure due to

could amount to millions of rands.

in general.

quality issues related to free elements

The procurement of a cheap pro-

• Lockdown in market confidence kills

in the raw production material, severe

duc t, to make an ex tr a buck,

involved in the funding of such dev elopment projects or the sale of

business opportunities!”

We are there when you learn

Need to conquer concrete? Our School of Concrete Technology offers special on-site and tailor-made courses to suit your requirements. Study concrete with us. www.theconcreteinstitute.org.za +27 11 315 0300

INDUSTRY NEWS

Quality is everyone’s concern It is a sad fact that the depressed state of the economy has given rise to extreme price sensitivity in the market that may prove to be harmful to the whole construction industry,

including producers of building materials and the entire supply chain, as well as the end user. For this reason, a number of measures should be considered by building professionals in order to prevent poor-quality construction and potentially disastrous failures. Cockcroft suggests the following: Safeguards and guarantees for producers: • Consistency in product quality

requires consistency in quality

• Re-establish your quality manage-

policies, or are implementing a

raw materials.

ment system and the implemen-

quality management system.

• Use only aggregate from repu

tation thereof by talking to your

• Insist on product certification. If

table suppliers to produce pre-

industry custodian, the SMA.

this is not an option, insist on

cast concrete units. Consult Ful-

Should you be a precast concrete

proof of quality management,

ton’s Concrete Technology and

producer not implementing a qual-

testing and record-keeping in all

SANS 1083:2014 for guidelines.

ity management system, be sure

aspects of the production of

• Make sure aggregate “extenders”

to discuss this with the CMA and

the units, as well as raw materials

are fit for use with concrete mix

join the organisation as a Producer

being used. Use CMA Certification

designs. If possible, obtain chemi-

Member. This enables us to secure

Services as resources regarding

cal analysis of the material, as well

the supply of consistent-quality

all precast concrete products.

as “fit-for-purpose” certification.

precast concrete to the market

o Remember that product cer-

This should be done on a constant

on a level playing field. That, in

tification is not necessarily

basis. Bear in mind that certifi-

turn, increases market confidence

a g u a r a n t e e . E s t a b l i s h a

cation might have been issued at

in our industry, leading to business

relationship with your sup-

a specific date, but that the con-

opportunities.

sistency o f the material can

change at any stage, without

Safeguards and

production procedures, par-

prior warning.

guarantees for users:

ticularly the raw materials be-

• Producers should constantly and

• Purchase precast concrete units

ing used in production.

for prolonged periods test prod-

from reputable manufacturers

• Do not force your supplier to

ucts according to the South Afri

implementing a quality manage-

supply cheap products by using

can National Standard, even if

ment system. This secures meas-

“horse trading” tactics. Cheaper

these products are not certified.

ures of control and quality with

products are cheaper for a

In terms of CMUs, the applicable

regard to input materials, manu-

reason. Saving a few rand in the

standard is SANS 1215:2008.

facture, product testing and de

short term can result in disaster

• Do not compromise on the pro-

livery to market.

in the longer term. Rather pur-

duction and curing of your prod-

• Consult applicable industry as-

chase quality precast concrete

uct. Reputable precast concrete

sociations for guidance and recom-

units manufactured from quality

producers know the theory behind

mendations regarding the pro-

raw materials and be assured of

precast concrete production and

curement and selection of sup-

the sustainability and future of

are able to produce quality pre-

pliers and product. In the case

your business.

cast concrete units. Communicate

of precast concrete, contact

quality principles to your client and

the CMA . Precast concrete

ensure they understand the risks

producers belonging to the CMA

of purchasing cheap products from

as Producer Members all comply

your competitors.

with the quality statements and

PRECAST | ISSUE TWO | 2019

p l i e r w h i c h a l l o w s y o u t o understand its quality and

INDUSTRY NEWS

Spotting potential problems, facilitating good concrete practice and producing a quality concrete product can only be done with adequate training, warns John Roxburgh, senior lecturer at the School of Concrete Technology at The Concrete Institute.

He feels it is a matter of deep concern that many key institutions – including South African municipalities and state bodies entrusted with infrastructural and building developments – still have limited concrete technology on call from within their own ranks. “In every civil and construction project, concrete is always extensively used. Concrete is relatively affordable – often costing well below R400 per ton, on average – and is durable, versatile and suitable for many applications in different environments. But if the correct concrete practices aren’t followed, concrete works could become a nightmare and costing could soar unnecessarily, adding to our country’s economic woes.” Site control Concrete technology education is essential for any construction project, particularly during building slumps, when the mark-ups on tenders have to be drastically reduced, leaving little or no margin for error, should unexpected mishaps oc-

GOVERNMENT NEEDS TRAINED CONCRETE TECHNOLOGISTS

cur on site. Roxburgh therefore recom-

who’s had proper training. He or she

ing, streaking, discolouration, inadequate

mends that employers identify suitable

could spot potential problems at an early

compaction, strength and curing, high

people on their staff and “champion”

stage, facilitate good concrete practice

permeability, cold joints, loss of cover and

them to become concrete specialists,

and produce a quality concrete product

lack of abrasion-resistance are just some

both at high-tech and supervisory level.

af ter adequate concrete technology

of the potential problems. I see all of these

“Site control is vital to getting con-

training. The School of Concrete Technol-

repeatedly when visiting sites, yet they’re

crete works done correctly – and on time.

ogy is playing a major role in imparting

Sound concrete technology knowledge

such knowledge at supervisory level.

at supervisory level will ensure that

“Unless staff are trained in concrete

concrete works run smoothly. The skills

technology, many things could go wrong

required to transport, place, compact

on site. Plastic shrinkage, settlement

and cure concrete should be taught and

and thermal cracking, blow holes, honey-

controlled by a competent supervisor

combing, drying shrinkage cracking, dust-

(Above): Matthews Magwaza, lecturer at the School of Concrete Technology, in a practical laboratory session during one of the school’s training courses. (Below): Concrete forms part of the infrastructure all over Africa – from low-cost housing to multi-billion-rand dams – so the need for skilled concrete personnel at all levels is rising.

PRECAST | ISSUE TWO | 2019

all easily preventable with basic concrete

concrete technology and construction

technology knowledge,” says Roxburgh.

courses: SCT41 General Principles and SCT42 Practical Applications. A pre-

Concrete durability

requisite for being accepted for the

He adds that in a life-cycle analysis of a

ACT course is a pass in both the SCT41

structure, maintenance and repair are

and SCT42 courses.

major contributors to the overall cost of

“In any event, at both advanced and

the structure. “This is where a detailed

more basic levels, the school’s always ad-

knowledge of concrete technology enables

vocated a stepped approach to concrete

a professional to design a cost-effective,

technology education. All our courses are

durable and low-maintenance building ac-

set at different standards of competency

cording to its location and environment.

and knowledge. A student should start

Neglecting this will lead to

at an appropriate level in

escalating costs later and a

order not to miss out on

structure with huge main-

important key concepts

tenance demands. Prop-

and practices. Then, hav-

erty and infrastructure

ing successfully completed

owners with access to a

a course, a reasonable

professional with exten-

amount of time should be

sive concrete technology

given to acquiring appropri-

knowledge have a distinct

ate practical experience in

advantage when it comes

the industry. In this way,

to lifetime costing.”

the student will obtain a

In recent years, the importance of concrete

holistic concrete technology education, making him

durability has become paramount. Speci-

or her much more valuable to the concrete

fications for durability are now being

industry and national economy.”

written into SA’s National Standards and many state institutions are insisting on

Relevant training

durable concrete structures. The many

Roxburgh believes it is important that

South African municipalities lagging in

the training provider is able to offer an

the implementation of durability require-

up-to-date, relevant concrete technology

ments are probably without suitable

education. “The School of Concrete

concrete expertise in their employ.

Technology has been the major concrete

When it comes to training at advanced

technology education provider in SA for

levels, employers should encourage

well over 60 years and its consulting

suitable professionals on their staff to

division is constantly involved in the

begin preparing now for acceptance as

writing of standards, publications and

students for the School of Concrete

assessment of latest technologies.

Technology’s Advanced Concrete Technol-

The training provider should also issue

ogy (ACT) course in January and February

certificates that are well recognised

2021. The school offers this highly pres-

within the concrete and related

tigious course every two years.

industries. Here the School of Concrete Technology also leads the pack, as a

Courses coming

certificate issued by it is valued due to

“The ACT examinations and diploma are

the institute’s decades-long recognition

presented by the school on behalf of

in industry,” he adds.

the Institute of Concrete Technology in London. It’s a challenging course, with examinations covering over 60 topics in concrete technology, so extensive and intensive preparation is needed simply to start the studies. “The school therefore recommends that in the lead-up to the 2021 ACT course, prospective students should complete three courses of fered by the school: initially, SCT30 Concrete Technology, followed by two important

“Unless staff are trained in concrete technology, many things could go wrong on site.” (Above): John Roxburgh, senior lecturer at the School of Concrete Technology.

INDUSTRY NEWS 12

POOR AGGREGATES? NO PROBLEM

specialised concrete production such

Precasters seeking consistent quality

mainly used by concrete manufacturers

compensated concrete.

concrete in situations where poor- or

to produce fluid concrete,” he says.

variable-quality aggregates are the norm

as E xpancrete, an expanding agent used in the production of shrinkageThen there are form-release compounds from the Mapeform Eco

can dramatically improve results with

Super-plasticising

range and DMA, used to strip formwork

the addition of an innovative product

A further advantage of using Dynamon

from concrete. Contractors would also

from construction chemical manufac-

with less than the best materials is that

find the curing agents from the Mapecure

turer Mapei.

it counteracts minerals which might

range useful to protect concrete from

According to Ser vaas le Roux,

make super-plasticising the admixture

rapid water evaporation. Completing the

product manager: concrete admixtures,

less ef ficient. T his means that a

range are fly-ash, lime-based fillers, blast

the company’s new Dynamon MS 100

lower dosage of super-plasticisers is

furnace slag and pozzolan.

product is an acrylic-based admixture

needed, but it allows longer workability

for concrete where the variations in

retention of the mix. Although it is

Application

aggregates will not affect the concrete

suitable for concrete production of

D y namon MS 10 0 is supplie d in a

characteristics severely.

any type, it is particularly well suited

ready-to-use liquid form and can be

“This technically advanced product

to produce high-consistency concrete,

a d d e d e i th er t o th e mi x ing w a t er

is formulated to deal with aggregates

self-consolidating concrete, pumped

or immedia tel y a f ter all the o ther

in r eady-mix and pr ecast concr ete

concrete and fair face concrete.

components (such as cement,

containing high amounts of fine parts

Map ei has a r ange o f pr o duc t s

aggregates and mineral additives) have

such as clay and mica, which use more

complementing the Dynamon MS 100,

been added. After adding the product,

water than necessary. It lowers the

including super-plasticisers in the same

Mapei SA recommends extended mixing

water demand of such aggregates,

Dynamon range, viscosity-modif ying,

time to ensure an even distribution

allowing manufacturers stable manu-

fume-based powdered and retarding

of it in the mix. It is most effective if

facturing conditions, even though the

admixtures. The company also recom-

applied in fluid concrete with a super-

raw materials aren’t that stable. It’s

mends additional products to improve

plasticiser.

UCT PICP/BIO-RETENTION POND SEMINARS ATTRACT HUGE INTEREST The last two weeks of May saw some 430 delegates, comprised mainly of civil engineers and landscape architects, attending Permeable Interlocking Concrete Pavement (PICP) and bioretention pond seminars in six major centres across the country. They were organised by Professor Neil Armitage, deputy director of the ‘Future Water’ Research Institute at the University Of Cape Town (UCT) and were presented by Prof Ryan Winston, an assistant professor in the Department of Food, Agricultural, and Biological engineering at the Ohio State University in America. Armitage stressed how stormwater management was essential to any country’s water strategy. Winston noted that without stormwater management the risk of flooding, stream erosion and polluted water was substantially increased which is why the hydrological goal is almost always the controlling element in PICP design. He also stressed the importance of ongoing maintenance and gave examples of what happens when maintenance is neglected. He gave various bio-retention design examples, highlighting material (media) and vegetation options as well as construction techniques and maintenance. Encouraged by the number of attendees, Armitage said the seminars should lead to improved drainage and maintenance practices in South Africa.

(Above): The road outside CMA member Bosun Brick in Midrand is a perfect example of the longevity of concrete brick-paved roads versus traditional bitumen road types. Both types are to be found on this road, with the concretepaved slope section (above) being 20 years old with no repairs done, while the bitumen road serving the same area has been repaired many times and does not last. This road is subject to high tonnage daily, yet the concrete brick section stays good with no standing water when it rains.

PRECAST | ISSUE TWO | 2019

PRODUCTS

“Fast and accurate marking of openings, reser vations and other cuts saves money in the hollow core slab production process. Accurate marking also saves time on the construction.” So says Jani Eilola, product director for floor technologies at Elematic, who

adds that the company’s new automatic Plo t ter E 9 makes b o th sp eed and accuracy in plotting possible and is easy to use, thanks to a simple touch-screen designed to meet the needs of the machine operator. Rather than battling with traditional systems, the new plotter marks cutting lines, rectangles and circles for openings and reservations, as well as identification texts and codes on the cast slab surface. It also marks places for dividers and fittings on an empty bed surface. Both longitudinal and cross-wise text printing are possible. Direct transfer A new level of plotting accuracy is

IMPROVED PLOTTING PERFORMANCE ON SITE

achieved through a direct transfer of slab

wireless remote link connection without

• check and edit the data on machine,

design details file from the design soft-

any manual interventions, which removes

ware (such as Tekla Structures BIM) to

the risk of human errors from this stage

• remove faulty slab sections;

the plotter’s FloorMES machine control

in the process.

• define a new starting point; and

system. The transfer takes place via a

“Automation cuts the number of work hours spent on the plotting process.”

Further improving the plotting accu-

if needed;

• remove geometry.

racy is the continuous laser positioning

The screen also shows work status

along the casting bed. The accuracy of

such as start time, slab number, tasks,

the laser is approximately 1mm. Auto-

elapsed time, alerts and remaining bat-

matic plotting saves time at the factory

tery power and ink levels. The touch-

too. When there are several different

screen is easy to use: you can zoom and

spots to mark, the manual marking time

drag and drop items, similar to any other

may amount to as much as two minutes

smart device.

per slab. This, in turn, means that at the

The plotter is designed with safe

casting rate of 10 000 slabs per year,

operation in mind. It features light

the total time spent for marking annually

sensors on both buf fers, as well as

is 333 hours.

ultrasonic sensors. The machine stops

“I’ve calculated that investing in an

automatically if there are any hindrances

automatic plotting machine pays itself

in its way and is equipped with light and

back in less than 20 months. If automa-

sound alarms.

tion prevents only one mistake in every 500 slabs, you’ll save some €26 000

Ease of use

[approximately R400 000] every year.

No cables are needed, as the plotter

Automation also cuts the number of work

is battery-operated. A fully charged

hours spent on the plotting process, with

battery lasts 16 hours, or one to three

savings amounting to some €36 000

days, depending on the beds and machine

[approximately R554 400],” says Eilola.

usage. An automated waterhole driller is available as an option.

Touch-screen

The plotter offers a range of features

Plotter E9 is operated via a simple

for easy maintenance of the machine.

15,6” touch-screen designed to meet

Those include on-screen quick adjustment

the everyday plotting tasks in precast

and calibration and clog-resistant print

concrete plants. The screen shows

head. The machine is ready for remote

the slabs on beds and on-bed quick re-

trouble-shooting and support via a Wi-Fi

planning allows the operator to:

link (network connection required).

PRECAST | ISSUE TWO | 2019

PRODUCTS

ARCHITECT-INSPIRED PAVER LAUNCHED IN THE WESTERN CAPE Plant-holed pavers have been launched on the local market. As it has done on numerous occasions with other pioneer-

ing landscaping product launches, CMA producer member Revelstone led the way, now offering plant-holed paver op-

could produce them. Naturally, we agreed

tions in its entire flagstone range.

because Revelstone’s reputation has

Plant-holed pavers look like normal

always rested on creating innovative

flagstone pavers, except that each

products based on our clients’ individual

paver can carry up to four or more holes.

requirements.

These can be filled with a variety of plant

“It took us four months to develop the

life such as mondo grass, penny royals

holed pavers. Jane was very happy with

and cacti, among others.

the result and we now anticipate that

Revelstone founder Andrew Cypri-

sion to the landscaped environment by

anos says the rationale for launching

allowing the ingress of water into the

“We currently offer one hole size of

the holed paver is twofold.

ground. This function ties in with Cape

75mm, with a new size of 110mm com-

the concept will catch on in a big way.

“In the first instance, they add an

Town’s Urban Stormwater Impacts

ing soon and landscape architects can

aesthetically pleasing landscaping al-

Policy [2009], which aims to minimise

specify the number of holes per paver,

ternative, enabling a closer and more

the impact of rainwater on conventional

as well their placement. This gives them

artistic integration between the paver

stormwater drainage.”

great scope for creativity in the layout

and its immediate surroundings, be they flower beds, loose stones or lawn.

Cyprianos says he first came across holed pavers at a DIY store in London.

and design of garden paths and patios,” says Cyprianos.

“Secondly, besides providing safe and

“Shor tl y a f t er my r e tur n, Jane

Samples of the new holed paving

durable stepping stones, holed pavers

Baldwin of Jane Baldwin & Associates

range can be viewed at Revelstone’s new

have introduced an eco-friendly dimen-

Architectural Design, asked us if we

showroom in Lansdowne, Cape Town.

It is no secret that the quality of sand

clean-washed filler sand from traditional

CHEMICALS TO THE RESCUE WHEN QUALITY SAND BECOMES SCARCE

sources is a growing concern among

for inland sales and marketing at Chryso

meters of sand in these situations,

South African concrete manufacturers.

Southern Africa, explains that because

namely clay content, fines, absorption

The shortage of good-quality sand

of this situation, the real challenge is to

and particle shape,” he says.

has been driving up the price, often

ensure that the concrete produced is

The aptly named Quad range allows

forcing manufacturers to make the best

of a consistently high quality and that

customers to manuf acture cost-

of lower-quality material. By the same

it matches the technical specifications

optimised concrete, which meets all the

token, projects in remote areas often

demanded by the project.

most demanding performance criteria.

significantly affects the performance of concrete and the increased scarcity of

compel contractors to make use of lo-

“We’re in an ideal position to assist

Incorporating Chryso’s breakthrough

cal materials for their concrete, even if

customers who’re faced with this chal-

“clear” polymer technology, the range

these materials are not ideal.

lenge, as our high-technology admixture

meets the challenges presented by

solutions address the four key para-

crushed sand, including a high clay con-

Hannes Engelbrecht, general manager

tent and excessive fines. A good example of how this technology has recently been used is the remote site of a wind farm in the Eastern Cape. Given the onerous logistics and prohibitive cost of transportation, material from local sources had to be used for the precast elements, which were cast on site. (Left): Chryso’s new-technology admixture solutions address the four key parameters of low-quality sand and making sand more suitable for concrete.

PRECAST | ISSUE TWO | 2019

COMPANY NEWS 16

RAISING STAIRS TO NEW LEVELS

One of the country’s first specialist

Game-changer

precast stair companies is also one of

Looking back, Budde says chance played a

its most innovative, with a full range of

big role in the establishment of what has

steps and stairs that have been specially

become a thriving family business. Having

developed to hasten construction, while

left the corporate world, he started

giving consumers a product that will last

subcontracting for a large hollow-core

the lifetime of the structure in which it

slab manufacturer. These precast slabs

is installed.

made construction of stairwells easier

A ptly named, Steps & Stair s in

and his idea of precasting stairs and

Meyerton, Midvaal, is the labour of

stringer beams would add considerably

love of a dedicated precast concrete

to on-site quality, as well as further

practitioner, Joe Budde, who learnt the

speeding up construction.

construction trade in the 1980s. Back

“It changed the market. Suddenly

then, he began noticing the difficulty

contractors had speed, immediacy and

caused with the construction of in-

controlled manufacture, which meant

situ stairs, which delayed construction

tha t the quali t y o f stair wells was

of upper levels until such time as the

near-perfect every time. As a result,

builders could get it right. And, with

we hit the market running and quickly

dwindling skills availability, each year the

became a force to be reckoned with

problem was only getting worse.

in the urban areas of Gauteng. We’ve

Those observations led him to plot

even had special orders for elements

ideas which he put into practice when

exported to as far afield as Zimbabwe

he got the opportunity to start his own

and Mozambique,” says Budde.

business in 2004. He set about develop-

“Despite engineers’ initial scepticism

ing the kind of step and stair systems

about using precast stringers, they

that he knew would provide building pro-

gradually became more acceptable when

fessionals with viable and cost-effective

engineers started realising that the

alternatives to in-situ concrete, steel

precast elements were equal and, in

or wooden stairs. The ideas were a suc-

many instances, better than traditional

cess and since then, the company has

methods using dwindling skills.”

become a large-scale supplier for many showpiece developments in the Midvaal and surrounding areas.

(Above): Joe Budde of Steps & Stairs. (Left and right): Precast steps, stringers, stairs and pre-formed stairways speed up construction.

PRECAST | ISSUE TWO | 2019

Installation teams

by customers. Most steps are bound

He explains that the elements are made

for domestic and commercial markets,

in accordance with the SANS codes of

especially large developments where

practice, although the company has its

units can be mass-produced for the best

own unique elements, such as cast-in-

economy of scale. Standard construction

treads and other design elements that

methods also lend themselves to further

improve strength and durability, as well

production of units which are available

as making them easier to install. Even

o f f-the -shel f f or a w ide v ar ie t y o f

so, Budde insists that all Steps & Stairs

applications.

products are installed by his own teams.

In terms of stairways, steps and

“This is another key differentiator

landings, the company strives to be

which ensur es that the stairs ar e

an all-in-one solution pr ovider. T he

handled, transpor ted and installed

manu f ac tur er’s on-si te labor a tor y

correctly. We had many instances where

ensures products are manufactured

our stairs were either transported or

correctly first time, every time, with an

installed incorrectly by independent

engineering certificate to prove it.

contractors and then needed to be replaced at cost to the developer, as well

Customer-centric

as delaying further constructing work.

Regarding current market conditions,

“For this reason, nowadays most

Budde says Steps & Stairs has grown

developers and contractors want the

and prospered in dif ficult times and

job done right first time and prefer

ascribes much of the success to its

the convenience of having an all-in-one

family orientation, with his wife Norma,

solution from the factory to the site

son Jona than and “like” son Chr is

and installed at minimal extra cost.

Diedericks holding strategic positions

This is especially true where speed

within the company and having its best

of construction is important, as our

interests at heart, as do the long-serving

stringers and separate steps can be

staff members, who are equally nurtured

transported on site, positioned and

Budde believes this culture of caring

installed quickly and easily. In other

e x t en ds t o c us t om e r s, w h o enj o y

instances, space permitting, we also do

the individual attention and can-do

complete custom-made pre-formed stair

attitude of the company. “Our business

flights, which allow immediate access to

is different because we have a policy of

the next level as it is.”

getting it right first time. This applies to everything from service to design ideas,

Sturdy construction

as well as other equally important behind-

Budde adds that stringers and load-

the-scenes technical services that we

bearing components are pre-stressed

perform on behalf of our clients.

in accordance with requirements and

“We also have decades of integral

the steps are reinforced and cast with

experience in making and installing steps

proprietary concrete mixes that allow

and stairs, so it’s easier for us to assist

adequate hardness to ensure strength

our clients with their on-site challenges.

and durability for the duration of their

Even in a price-conscious market, we

useful lifespan.

believe that service and support are key

In addition, the steps can be cast

and that it’s much easier to service our

with treads or galvanised steel-edge

existing clients properly than constantly

strips and other elements, as specified

be looking for new ones.”

PRECAST | ISSUE TWO | 2019

NEW ROOF TILE MANUFACTURING PLANT IN KZN October 2018 saw CMA member Aveng Infraset begin producing concrete roof tiles in Durban. Situated in a new multi-million-rand plant in Effingham, the factory is equipped with state-of-the-art equipment imported from Italy’s Vortex Hydra, a world leader in concrete roof tile plant and equipment. Aveng Infraset sales consultant Samantha Chetty says the plant is producing the Dusk, a Double Roman concrete roof tile in six colours (red, charcoal, brown, amber, terracotta

A STRONG FOUNDATION FOR INFRASTRUCTURE SUCCESS ROCLA is South Africa’s leading manufacturer of pre-cast concrete products.

colour options. “The plant is equipped with an Internet-based remote control facility and includes a state-of-the-art curing chamber. This leaves very little margin for error and means we’re producing tiles with consistent strength and colour, factors which have enabled us to price the tile very competitively,” she says. Renowned for the exceptional quality of its precast

Surpassing 100 years of product excellence. • • • • • • •

and dolomite) and is also able to produce various multi-blend

concrete products, Aveng Infraset has set quality parameters in the manufacture of the Dusk which exceed the SANS standards for concrete roof tiles. The tile is being supplied

Pipes Culverts Manholes Poles Retaining walls Roadside furniture Sanitation

with various types of roof insulation materials to trussing companies and hardware stores, and is delivered on shrinkwrapped pallets to minimise breakage during transportation. “Before the new factory was commissioned, we were supplying the KwaZulu-Natal market with roof tiles manufactured at our Rossway plant in Gauteng. For example, last year we supplied our Sunset tile to entry-level housing projects in Nhla-

Including other related products within infrastructure development and related industries. Visit us on

www.rocla.co.za

for our nationwide branches

zuka and Vulindlela, Pietermaritzburg, as well as to Durban’s Lower and Upper Inanda housing projects. “However, we reached the point where we were running out of stock. This prompted our decision to set up a manufacturing operation in Durban and we now have plenty of stock,” says Chetty. (Above): Aveng Infraset’s new roof tile plant in Durban.

PRECAST | ISSUE TWO | 2019

GLOBAL VIEW

During the last two weeks of May, a series of countrywide seminars was run on PICP and bio-retention cells. It was organised by Prof Neil Armitage of the “Future Water” Research Institute of the University of Cape Town (UCT) and included presentations by Ryan Winston. Precast’s coastal editor, David Beer, talked to

professor Winston for a first-hand account of American PICP practice in the context of sustainable drainage systems (SuDS). He also gleaned some useful pointers for the local PICP industry. American SuDS vary substantially from state to state and from city to city. A rudimentary form of SuDS first entered the statute books in 1972, when the federal government introduced the Clean Water Act. It heralded the treatment of non-point source stormwater, the regulation of industrial point sources and pipe discharge. Initially urban drainage was largely based on the use of large retention and detention ponds, but over the past 20 years, more stringent state and city regulations have come into play. Some of America’s more environmentally c onscious st a t es ha v e in tr o duc e d legislation in the form of water manuals with guidelines which are updated as new research findings come to light. Stormwater legislation

PICP LESSONS

FROM THE USA Insights into permeable interlocking concrete paving (PICP) in the USA – an interview with Ryan Winston, assistant professor: Ohio State University and the EPA has mandated the use of

are seeing opportunities to replace ponds

innovative technologies (including SuDS)

with PICP. Moreover, it offers flexibility

to limit these dangerous discharges.

in that it can be designed for whatever

Other states, such as Washington, have

PICP and bio-retention cells are two of

storm severity one selects. And because

gone further and introduced extremely

several SuDS tools deployed in the USA.

the aggregate in the underlying PICP

stringent stormwater legislation which

PICP first saw the light of day in the mid-

typically has a 30-40% porosity level,

requires all new property developments

1990s. Its introduction was led by the

a sub-base 1m deep will yield one-third

to match the pre-development hydro-

paving industry and it was initially used

of a metre storage, or the equivalent of

graph. This involves cre-

for pedestrian applications,

330mm of rainfall storage before the

ating a pre-development

primarily in coastal regions.

system’s overloaded,” says Winston.

model and then matching

Parking, driveway and light-

There appears to be little, if any,

it exactly, using very ad-

use residential road appli-

difference between American and South

vanced stormwater cal-

cations came later.

African approaches to PICP design. Both

Winston observes that

vary according to individual requirements.

the demand for PICP is

By far the most common American PICP

In addition, the federal

growing in the USA and

design is the infiltration system, in which

government monitors and

making inroads into other

the bulk of the water infiltrates into the

enforces stormwater pro-

forms of SuDS manage-

ground. Sump designs account for 30-

tection programmes via

ment, such as the attenua-

40% of applications and water harvesting

culations – an extremely expensive process.

systems for 20%.

the Environmental Protection Agency

tion pond market. It offers an advantage

(EPA). For example, the EPA monitors

in that stormwater attenuation can oc-

The sump system employs a perma-

stormwater discharge into rivers and

cur in the aggregate beneath the PICP,

nent pool of water at the bottom of the

lakes, especially when wastewater and

eliminating the need for an attenuation

installation and is better at removing

stormwater are commingled in a single

pond. This saves up to 10% of the land

pollutants from the water, particularly

sewer. The problem here is that during

on a development site.

nutrients. However, sump designs often

overwhelmed and untreated sewage can

Design flexibility

discharge into rivers. This happens sev-

“Because it y ields mor e space f or

(Above): A combined sweeper and vacuum truck, termed a regenerative air street sweeper.

eral times a year in Ohio’s urban areas

development, developers and engineers

heav y downpours, sewers are of ten

PRECAST | ISSUE TWO | 2019

(Left): Ryan Winston, assistant professor: Ohio State University.

GLOBAL VIEW

require a deeper sub-base to ensure structural stability and are more costly, especially when the underlying soil is saturated. A typical PICP sub-base for cars and light trucks in the USA would consist of a 30cm bottom layer of 100mm

aggregate, followed by 10cm of 25mm stone and a bedding course of 5cm of 6-7mm stone. When designers need more water storage or structural support, they deepen the sub-base. However, where American and South African PICP industries exhibit substantial divergence is in their approach to maintenance and the quality of sub-base aggregate. Basic maintenance Most American cities have basic maintenance rules which involve testing infiltration rates either twice

left undone, a fine can be imposed. But

or four times annually, whereas in SA,

what usually happens is that the city

maintenance appear s to be ei ther

does the maintenance itself and then

random or simply non-existent. “If a

sends a bill, which is more expensive

system has more than 10% of its surface

than hiring someone to do it privately.

area blocked, in the USA we say it needs

Once a site is cleaned, post-cleaning

modest amount of suction power for

maintenance,” explains Winston. “We’ve

infiltration tests are done to ensure the

preventative maintenance. The brushes

f ound that good housekeeping also

maintenance was successful.

don’t reach below the surface, since the

(Above): A mechanical street sweeper with no suction which is used for routine, preventative maintenance. (Below): The most powerful sweeper – the vacuum truck.

slows clogging. In autumn, we advise the

“We’ve completed extensive research

gaps between the pavers are too small.

removal of leaves with a blower as soon

over the years – much of it into clogging

Once the PICP is fully blocked, we’ve

as they fall. Similarly, when sediment

and its alleviation. We’ve found that

found that we really need the suction of a

accumulates on the pavement, it should

clogging isn’t spatially homogenous and

vacuum truck to remove the dirt between

be blown over the kerbing.

we’ve identified certain hot spots, such

the pavers. One has to be careful not to

“We use cer tified inspectors to

as proximity to trees and landscaped

‘over-suck’ because the aggregate under

measure infiltration rates in the USA

areas. We’ve also researched threshold

the pavers can be drawn up. So we advise

and we certify them through a training

rates that are good enough for a system

making a first pass on a low suction

course given by universities. Inspectors

to keep working. That work isn’t directly

level and then adjusting the suction as

send infiltration data to cities’ stormwa-

translatable in SA because you’ve got

needed. If infiltration hasn’t reached the

ter engineers and when maintenance is

different rainfall patterns. We regard a

desired performance level, we do another

surface infiltration rate of 200mm per

run at the next level and so on, until the

minute as new. If 10% of the pavement’s

desired performance level is reached.

surface area falls below a minimum

Any bedding stone which is removed is

infiltration rate of 4mm per minute when

replaced with fresh stone.”

we return, we initiate maintenance. Vacuum trucks PICP cleaning

Winston explains that American vacuum

“Most PICP cleaning in the USA is done ei-

trucks are not dedicated to PICP cleaning,

ther with regenerative air street sweep-

but are primarily used for catch-pit

ers [combined sweeper and vacuum] or

cleaning. “They’re very powerful and have

powerful vacuum trucks. However, clean-

a big hose on the back which can suck up

ing can be done manually and involves re-

a brick,” he says. As current research at

moving the upper 25mm of bedding stone

UCT shows, clean aggregate is vital to

and accumulated clogging material using

the proper functioning of PICP.

a tool which resembles a spatula. Ninety-

“If aggregate isn’t cleaned, sediment

five percent of the clogging occurs in the

accumulates inside the PICP installation,”

first 25mm and when it’s replaced with

says Winston. “This means that dust will

new bedding stone, best performance

collect at the bottom of the sub-grade

levels are reinstated.

where the aggregate and soil meet and

“We use street sweepers with a

infiltration will be inhibited. Moreover,

PRECAST | ISSUE TWO | 2019

water hose. Another quarter-load is

the country strives to find workable,

pollutants will be dispersed through

then added and washed until one has

sustainable water management solutions

drains into the sewer.

nice, clean stone. This process seems

in the coming years.

“Every time we work with a new

to meet the specification of 0,5% dust,

quarry, we have to teach them how to

which is good enough to construct the

clean the aggregate.

sub-base.”

“Our quarries use a machine with

Ryan Winston, PhD, PE

GLOBAL VIEW

as dust is washed off the aggregate,

Professor Winston is an interna-

layered sieves to measure the amount

Bio-retention

tionally recognised expert on sus-

of dust lef t on the stone af ter it’s

Winston says the big advantage of bio-

tainable solutions for urban water

washed. It provides us with repeatable

retention systems is the fact that they

problems. Besides collaborating

methodology to determine the amount of

are cheaper to build and do not tend to

with Professor Armitage in SA, he

dust on the stone.

block or clog. “This means they require

shares information with colleagues

“T he sieves with the largest

less maintenance than PICP. They have a

in Sweden, France and Australia.

apertures are placed at the top and the

wide variety of applications in residential,

He has researched several cleaning

smallest at the bottom of the device.

commercial and ultra-urban areas and

mechanisms for permeable paving

The sieve with the smallest aperture is

besides attenuating stormwater, they

installations, is widely published in

what we call the ‘200’ sieve, which has

remove pollutants from the water.

technical and academic journals,

extremely small openings of 0,075mm.

“The drawback is that they require

and has lectured at numerous con-

Whatever passes through that sieve is

5-8% of developed land, meaning that real

ferences, workshops and seminars

considered dust. Anything greater than

estate is lost to stormwater control.

in the USA and internationally. He

0,5% by weight in dust is considered too

Situated 30cm below the rest of the

received his MS and PhD degrees

dirty. So once the weight of the dust is

landscape, they are filters comprised

at North Carolina State University

more than half a percent of the total

of 80+% sand with some silt, clay and

studying under Dr Bill Hunt, for

weight of what one puts in, the stone is

organic matter.”

whom he worked as a research

regarded as too dirty and the material

Although bio-retention systems are

engineer overseeing the construc-

must be washed again. Typically, a truck

rare on the South African landscape,

tion of and research into urban

is filled with one-quarter load of stone,

they certainly offer a worthwhile water

stormwater control measures.

then sprayed with a high-pr essur e

conservation alternative, especially as

TECHNICAL 22

ARCHITECTS LOVE CONCRETE –

BUT SHOULD KNOW IT BETTER, SAYS TCI Concrete is the material of choice for

is incorporated into their concrete

transform the structures they visualise

many architects and structural design-

creations. Faced with more frequent

into reality – free of

ers globally because of the vast design

natural disasters such as wildfires,

limitations,” adds Roxburgh.

spectrum it of fers, but not enough

hurricanes ear thquakes and floods,

Concrete also offers benefits such

South African construction professionals

stability and strength are increasingly

as strength, sustainability, economy,

understand all its techno-

design considerations.

post and beam

thermal efficiency and sound attenuation.

logical aspects, says John

“However, architects

Speed of construction and the opportunity

Roxburgh of The Concrete

need no persuading about

concrete offers to use local labour and

Institute (TCI) in Midrand.

the aesthetic qualities

materials are also important advantages.

Roxburgh, senior

of concrete and are

Roxburgh says the School of

lecturer at TCI’s School of

constantly finding new

Concrete Technology’s five-day Concrete

Concrete Technology, says

and exciting ways of

Te chn o l o g y tr aining c o ur se, t o b e

architects who employ

showcasing its beauty.

presented in Midrand, Durban and Cape

concrete in their designs

Concrete offers unlimited

Town this year, is ideal for architects

because of its versatility

potential. It allows for

and civil and structural engineers. “Not

and flexibility should also

design variations such

only does it provide these professionals

be versed in the practical properties

as gently flowing structures, curves or

with essential technological concrete

of concrete at various construction

straight lines to enhance the artistic

knowledge, but it boosts their career

stages and the variety of finishes –

properties of a building. No other modern

advancement,” says Roxburgh.

both off-shutter and architectural – it

construction material offers the designer

offers. This would not only enhance their

such a variety of forms, colours and

knowledge of the huge design potential of

textures. Furthermore, the plasticity

concrete, but also ensure that durability

o f concr e te enables ar chitec ts to

(Left): Designing with concrete offers unlimited creative potential – but architects should know more about concrete technology, says TCI’s John Roxburgh.

ENDING EROSION Technicrete Armorflex erosion control system provides an alternative for a wide variety of erosion control and drainage projects. When your project calls for protection that can withstand severe applications and climatic conditions, with quick installation with no in-situ concrete or even under water, Armorflex from Technicrete is the engineered solution. Suitable for:

Specially designed:

•

• • • •

Rivers, Estuaries, Dams, Reservoirs Areas subject to wave action Access roads Parking areas Stormwater drift crossings

• • •

Compressed concrete blocks (solid or vertical holes

or horizontal cable ducts)

Interlocking system Partial taper of each block Various sizes of blocks available

Tel: 011 674 6900 Maxi call: 0861 266 267

TECHNICAL 23

EFFICIENCY PAVES THE WAY TO SUCCESS Long-standing CMA member Conframat,

bottom of the building industry’s worst

perfectly poised to increase capacity

in Midvaal and Vanderbijlpark, is a study

slump in living memory also doesn’t make

and take up the increased share, which

of efficiency, from the self-assembly of

it easy,” says Heap.

will make it difficult for newcomers to

its brick-making plants to the careful

The cost dynamics of concrete prod-

optimisation of every aspect of those

ucts have drastically changed over the

open plants in the region.

p l an t s, w hi ch e n sur e s

past eight years, with ce-

From scratch

consisten t quali t y and

ment losing its position as

Heap says Conframat was started dur-

best profit margins.

biggest cost component to

ing this high-demand period after several

This is how owner Mark

bulk aggregates, while the

years of preparation, including market

Heap rises above current

average delivery cost of

studies and mix designs. Conframat’s

market conditions to run a

the final product will soon

first plant was a refurbished Birkenmayer

thriving business in tough

challenge aggregates for

VB2 plant which was able to produce

times. His use of historical

the top cost position. Fuel

35 000 bricks per day. Since then, he has

data and his own care-

costs have increased by

added two Birkenmayer VB5 plants and

fully developed software

60% since 2011 and were

a Birkenmayer VB6 for his newest plant,

programs allow him to for-

it not for the over-supply of

which has boosted the company’s daily

transport services, trans-

production to 500 000 brick equivalents

concrete to ensure quality stock bricks

port would already be the biggest cost

per day at approximately 90% of the

and pavers every time. His exacting

component. The cost-mix will, of course,

combined plants’ capacity.

calculations also show how seemingly

depend on the location of one’s plants.

mulate the right mixes of

(Above): Mark Heap of Conframat.

This translates into a 1 400% growth

insignificant inputs can lead to massive

To make matters worse, demand for

since inception, during which time Heap

cost implications and bankrupt less

bricks from the Vaal Triangle has dropped

has kept a tight lid on overheads, plough-

attentive managers.

from 6 million bricks per day at the peak

ing the company’s profits straight back

Machine set-up is also carefully enhanced across the company’s four plants and is carefully monitored to ensure each process runs like clockwork, thus enabling maximum throughput. Through necessity, some of the minor processes have also been automated to prevent waste and breakages, which can have a negative ef fect on production figures if left unchecked. Tough times “Running a successful business nowadays is difficult, specifically in the building in-

“Demand for bricks from the Vaal Triangle has dropped from 6 million bricks per day at the peak of the building cycle in 2008 to fewer than 2,5 million at present.”

into its operation. Conframat currently has 58 different products and delivers throughout the Vaal Triangle, Gauteng, the Free State and as far afield as KwaZulu-Natal. “Our keys to success have undoubtedly been the maintenance of a perfect recipe to make bricks efficiently and reliably, as well as good, honest customer service and supplying our customers with the products they want. We also strive to maintain consistency in everything we do in order to maintain a position well above the average. We never let a sub-

dustry, where there’s generally an over-

of the building cycle in 2008 to fewer

standard product out of our yards. Most

supply of both products and services.

than 2,5 million at present. With many

importantly, to stay profitable, one must

Margins are therefore very tight and small

of the plants still in operation or moth-

clearly understand and tightly control

improvements, or mistakes, can drasti-

balled, even when the turn in the market

all one’s costs, especially overheads,”

cally affect the bottom line. Being at the

takes place, existing manufacturers are

says Heap.

PRECAST | ISSUE TWO | 2019

TECHNICAL 24

COMPRESSIVE VS TENSILE SPLITTING STRENGTH A common mistake made by lay-people

Particle shapes

strength). Seen more often are concrete

is the assumption that compressive

Should the stone content in a concrete

pavers which cracked under pressure

and tensile splitting strengths in terms

paver be increased (reduced sand), the

(tensile splitting strength).

of concrete paving blocks are inter-

tensile splitting strength will increase.

related, as referred to in South African

It is general practice to increase the

National Standard (SANS) 1058:2012.

sand content in concrete pavers because

It is dangerous to specify concrete pavers

O n e w o u l d a l s o im a g i n e t h a t i f

it assists with the aesthetic appearance

only with regard to compressive strength.

compressive strength of the concrete

of the paving block. However, this is a

A concrete paver might have high

increased, then so would the tensile

practice which manufacturers should

compressive strength, but could fail as

sp l i t t i n g s t r e n g t h . H o w e v e r, t h i s

apply with great caution.

soon as a point load is applied to it. This

Take note

not true. According to the Concrete

The specification of concrete paving

Manufacturersâ&#x20AC;&#x2122; Association (CMA) GM

blocks in design, technical documents

Cognisance should also be taken of

Henry Cockcroft, there is no correlation

and t ender s r emains pr oblema tic.

the two classes of concrete pavers

between compressive strength and

One would presume that the SANS

mentioned in the standar d. During

tensile splitting strength.

sh o ul d an d w o ul d b e th e ul tim a t e

testing, class 40/2.6 should perform

It is a well-known fact that if the

specification. What happens is that

above 90% of all testing parameters.

sand con ten t in the concr e te mi x

many architects, engineers, consultants,

Class 30/2.0 is not recommended for

increases, the compressive strength

contractors, buyers and specifiers are

heavy traffic.

of the unit will increase as well. An

not up to date with recent specifications:

T h e C M Aâ&#x20AC;&#x2122;s P r o d u c e r M e m b e r s

increase in the sand content, however,

SANS 1058:2012 supersedes SANS

manufacture precast concrete units

influences the sheer strength of the

1058:2010 (edition 2).

of high quality and consistency because

is clear from the aforementioned.

unit negatively; in other words, the

The current version of the specification

they all adhere to a certain level of quality

tensile splitting strength reduces.

excludes compressive strength testing

management within the organisations.

This can mainly be contributed to the

and onl y calls f or tensile spli t ting

Precast concrete units adhering to the

homogeneous particle shape of sand

str ength. Concr ete paver s seldom

SANS specifications can be identified

and the way it binds with cement.

crumble under pressure (compressive

as such.

A NAME TRULY CAST IN CONCRETE

GAUTENG | KZN | WESTERN CAPE

PRECAST CONSTRUCTION SOLUTIONS HEAD OFFICE: (011) 589 8800 WWW.ECHO.CO.ZA

TECHNICAL 25

BENEFITS OF SLAGMENT GROW WITH RISING CARBON CONCERNS As a leading producer of high-quality

concrete, especially in applications like

industry and the plant mills this to a fine

cementitious material, AfriSam is ideally

wastewater treatment plants, or where

consistency before blending.

positioned to support customers seeking

there is seawater or sulphate-rich soil.

to reduce their carbon footprint while insisting on superior building material.

“As part of AfriSam’s sustainability journey, we’ve implemented various

Technical solution

strategies in response to the energy-

“However, there’s an added consideration

intensity of the cement manufactur-

produced its trade-named

in business today, as com-

ing process,” says Meyer. “Slagment

“slagment” from ground

panies anticipate the im-

remains a vital part of this journey and

granulated blast furnace

pact of the new carbon tax,”

we continue to develop innovative ways

slag (GGBFS), according

sa y s Me y er. “Slagmen t

of extending its benefits to customers.”

to AfriSam cementitious

assume s a signi f ic anc e

executive Hannes Meyer.

here too, as it reduces the

Many benefits

“We’ve used this latent

amount of clinker in con-

Another important capability of slagment

hydraulic binder in an ex-

crete, cutting the energy

is reducing the thermal heat gradient

tensive range of concrete

consumed and carbon emit-

generated when pouring concrete. This

applications, including major

ted in its manufacture. The

reduces the likelihood of micro-cracking,

structures such as dams,

use of slagment therefore

which may weaken the structur e’s

bridges and roads. Indeed,

offers not just a technical

strength. Slagment can also alter the

only very specific and limited applications

solution, but an opportunity to achieve

colour of concrete to near-white by re-

today demand our cement without added

higher environmental standards.”

placing 50-70% of the concrete, improving

For over half a century, AfriSam has

slag,” he says.

AfriSam’s dedicated slagment plant

He highlights the self-cementing

in Vanderbijlpark has the capacity to

properties of slag, which can double

produce over 800 000 tons of slagment

the lifespan of buildings. Among its key

a year, along with over 200 000 tons

benefits, however, is preventing sul-

of blended cementitious products. The

phate attack and alkali-silica reaction in

slag is a by-product of the steel and iron

PRECAST | ISSUE TWO | 2019

its appearance. In addition, it produces a smoother, more defect-free surface. (Left): Hannes Meyer, AfriSam’s cementitious executive. (Top): By focusing on the beneficial use of slagment, AfriSam significantly reduces its CO2 footprint.

PROJECTS 26

C M A m e m b e r C o r e S l a b’s u n i q u e

install the centre portion of the roof

precast concrete reservoir system is

system, comprising precast concrete

assisting South African municipalities

columns, beams and hollow-core slabs.

to significantly accelerate the delivery of drinking water to rapidly expanding rural

Structured approach

and urban areas.

The process starts with the installation

Two 10Ml reservoirs were constructed

of the columns onto the in-situ bases

in only six weeks using the company’s

that have been prepared by the principal

sophisticated precast concrete system.

contractor, while maintaining constant

It would have taken four to six months

interaction with CoreSlab to ensure high

just to construct the reservoir walls

levels of accuracy.

using conventional in-situ techniques,

It took the company only four working

and this is without the risk of having to

days to build the centre portion of

redo the work, considering the technically

the roof structures for the two 10Ml

complex nature of these construction

reservoirs in Mpumalanga. The factory

projects.

then starts dispatching the wall panels

The company is now preparing to

to the construction site on a just-in-

manufacture another two 10Ml precast

time basis, once the ring beam has been

concrete reservoirs and is hoping to be

completed by the main contractor. They

appointed to work on a 25Ml reservoir

are lifted directly from the truck trailers

project by a leading South African civil

and placed on top of the ring beam using a

engineering contractor shortly. The

mobile crane. The first panel is supported

principal contractor will under take

by props which are removed once it has

the earthworks, as well as construct

set and the remaining precast concrete

the reservoir floor, pipeline and inlet

elements are then placed against the

works. CoreSlab, as the specialist sub-

other to complete the reservoir wall.

contractor, will be tasked with the swift manufacture and installation of the wall and roof of the structure.

RAPID ERECTION OF WATE

Simple method Jaco de Bruin, managing director of CoreSlab, notes an increased interest in the company’s reservoir system as more of the country’s municipalities and water authorities start prioritising SA’s growing water infrastructure backlog. “Reser voir s ar e notoriously complicated and time-consuming structures to build. The construction of the wall demands absolute precision to ensure water-tightness. This slow and meticulous process is followed by the construction of the roof, which entails erecting and installing tons of scaffolding and formwork inside the structure. On most of these projects, work can only take place at one or two faces at any given point. Our modular system enables

(Above): Workers first install the centre portion of the roof system, comprising precast concrete columns, beams and hollow-core slabs. (Below): The first panel is supported by props which are removed once it has set. The remaining precast concrete elements are then placed against the other to complete the reservoir wall.

Exacting measurements CoreSlab’s installation team uses Total Station technology to install each panel precisely, maintaining tolerances of about 5mm. The walls of the two 10Ml reservoirs comprise as many as 60

the construction of the floor, walls

panels, each weighing eight tonnes, 9,8m

and roof simultaneously to deliver the

in length and 1,9m in width, as well as the

infrastructure in a fraction of the time

four 11,7-ton buttresses that reinforce

it would take using conventional in-situ

the structure.

methods,” says De Bruin.

The company is able to manufacture

T h e r o o f a n d w a ll s y s t em s a r e

up to 10 reservoir wall panels of various

manufactured at the company’s state-

widths and lengths at a time at its

of-the-art factory, while the principal

factory using specialised forms which

contractor completes the earthworks

were designed and developed by the

and the reservoir floor. Workers first

company’s own engineering department.

PRECAST | ISSUE TWO | 2019

(Left): The factory starts dispatching the wall panels to the construction site on a just-in-time basis once the ring beam has been completed by the main contractor.

a thorough account of the pre- and postinspections. The extensive quality controls in place at the factory were a major selling point for the civil engineers who promoted the system to municipal officials for use on the two 10Ml reservoirs. One of the challenges was the extremely

remote locations of the two construction sites. They are therefore not serviced by ready-mix producers and the on-site batching of concrete for the walls and roof of the structure would have required extensive quality controls and careful co-ordination of the various materials to avoid delays.

De Bruin says meticulous attention was also paid to the design and development of the grouting and post-tensioning process to overcome the many limitations of other precast concrete reservoir wall systems in the country. Perfecting the design of

the system took more than five years from conception.

ER RESERVOIRS

Best-of-breed Tian de Jager, technical director of CoreSlab, undertook extensive research into numerous leading international precast concrete

Many man-hours were spent refining

reservoir wall technologies available on the

the designs of both the wall and buttress

market. This extensive learning and best

panels to ensure the high levels of precision

practice was refined and modified for the

required for their installation. â&#x20AC;&#x153;The holes at

unique African environment.

the bottom of the wall panels have to align

Notably, it uses vertical and horizontal

with the bolts grouted into the ring beam, as

tensioning to resist applied forces, as

well as the steel plates at the top with the

opposed to conventional construction

voids in adjacent slabs. Just as importantly,

methods, where reinf orcing and post-

the holes that traverse the full width of the

tensioning are used to control applied forces.

panels through which the post-tensioning

About 6,6km of post-tensioning ducts and

strands are threaded also need to line up.

cables were installed by hand between

We also underwent an extensive learning

the joints of the wall panels in preparation

curve during the design of the forms used

for the grouting. This was in addition to

to manufacture the buttresses. Theyâ&#x20AC;&#x2122;re

the numerous three-dimensional printed

extremely complex elements that contain

components to secure the rubber cast that

n um e r o u s c a s t- in c o m p o n e n t s w h i c h

acts as the temporary shutter.

were all manufactured by our engineering department,â&#x20AC;? says De Bruin.

The grout has been designed to reach a compressive strength of 100MPa within

Notably, the various concrete elements

four days and to react further when the

making up the entire wall and roof system are

medium comes into contact with water

manufactured in a controlled environment

as the reservoir is being filled. Moreover,

w hi ch is f ar r em o v e d f r om th e m an y

the grout has to be extremely flowable so

variables encountered on conventional

that it can be pumped through all the post-

construction sites.

tensioning ducts from a single position using two pumps. Its working time is extended by

Quality control

cooling it down to 7Â°C. It took up to 40 hours

Every 70-80MPa wall panel has its own

in a continuous process to pump the grout

technical drawing and documentation,

around the entire circumference of the two

which include detailed specifications and

10Ml reservoirs.

PRECAST | ISSUE TWO | 2019

1907 Tel: 021 465

Find a supplier www.terraforce.com

PROJECTS 28

Competitive pricing

has allayed any concerns regarding the

Skills development

The grout underwent extensive testing

deployment of new technology on these

The main contractors also met all the

ahead of its application and CoreSlab even

municipal projects, especially in light of

municipality’s stringent socio-economic

brought its own water from Polokwane

the poor performance of many precast

targets during the construction of the

to ensure that the medium achieved

concrete structures in the past.”

two 10Ml reservoirs.

the desired reaction. While the cost of

This focus included ensuring that am-

the system is comparative with in-situ

ple opportunity for employment, as well

techniques on smaller structures, it

as skills development and training, were

provides a more affordable means of

created for members of local surrounding

constructing larger reservoirs.

communities during the earthworks, in

De Bruin says this is where the real

addition to the construction of the floors,

value of the system will be realised,

inlet and outlet chambers, as well as

considering the gr owing backlog in

pipelines. Piping and construction materi-

water infrastructure and the pressure

als were also procured from local small

municipalities ar e under to better

black-owned businesses in the vicinity.

manage their dwindling budgets. “The need to innovate to improve infrastructure delivery is also reiterated in an inclusion in the latest Municipal Infra-

There was not a single safety incident (Above): An installation team uses Total Station technology to install each panel precisely, maintaining tolerances of about 5mm.

on both sites, considering that only trained CoreSlab teams worked at heights during the installation of the walls and roof

structure Grant guidelines. Importantly,

He adds that public-sector client

it highlights that the country’s munici-

bodies are also increasingly realising

De Bruin says the two pr ojects

palities – especially those in the B and C

that precast concrete technologies

provided an important opportunity to

categories – need to consider innovation

complement their labour-based

refine and prove the system and thanks

in the full spectrum of infrastructure

construction policies. Precast concrete

the client body, consulting engineers

technologies and associated operations

f a c t o r i e s p r o v i d e m a n y l o ng -t e r m

and contractors for the opportunity to

and maintenance solutions. CoreSlab

and secure jobs, as opposed to only

participate in a project which has again

is contractually responsible for the

temporary employment prospects during

demonstrated the many benefits of

performance of all its systems and this

the construction phases.

precast concrete technology.

of the two reservoir structures.

PROJECTS 29

VITAL FACTORS TO CONSIDER FOR

COLD WEATHER CONCRETING Despite SA’s relatively mild winters, concrete producers sometimes have to contend with the challenge of concreting in cold weather, especially in mountainous regions. Bryan Perrie, MD of The Concrete Institute (TCI), identifies important factors to consider during this process.

water, but care must be taken not

to exceed 60-70°C. At higher tem-

peratures, flash-setting of the cement

and reduced workability may occur.

tection must be given to the batch-

Weather in the concrete industry is

Top considerations

ing and mixing plant, as the concrete

regarded as cold when the ambient tem-

Consideration should be given to the

temperature can drop significantly if

perature falls below 5°C. This does not

following when concreting in cold weather:

the equipment is very cold.

generally happen during the day in most

• Cement type: Because of their slower

• Concrete temperature: The minimum

parts of the country, which means expen-

setting and rate of strength gain,

concr ete temperatur e as mi xed

sive preventative measures such as heat-

the use of highly extended cements

should be higher in colder conditions,

ing aggregates are seldom necessary.

or the partial replacement of CEM I

but may be reduced for concrete

cement with significant amounts of

placed in larger sections. For air

Cold setting

either ground-granulated blast fur-

temperatures of -18-0°C, recommend-

The effect of concrete freezing at early

nace slab (GGBS) or

ed concrete temperatures

ages depends on whether it has set and

fly ash (FA) is not rec-

are 7-18°C.

what strength it had attained when

ommended. It may be

• Transporting and plac-

freezing took place. If concrete which

advantageous to use

ing: As significant heat

has not yet set is allowed to freeze,

CEM I 42, 5R or 52,5N

losses occur during these

an increase in the overall volume of the

cement, rather than

processes, they must be

concrete occurs due to the expansion of

42,5N or 32,5 cements.

carried out quickly. Unless

water, especially in the capillary pores.

• Aggregate protection:

the concrete is adequately

When thawing takes place, the concrete

Water in aggregate may

pr otected, methods of

will set with an enlarged volume of pores,

be prevented from

transport such as con-

which will reduce strength and durability.

freezing by covering

veyors and chutes are not

If freezing takes place after the con-

stockpiles with tar-

recommended.

crete has set, but before it has gained

paulins. If aggregates

su f f icient str ength ( appr ox imatel y

are likely to become

3-5MPa), expansion associated with the

frozen or contain ice and snow, they

concreting is to prevent heat loss of the

formation of ice will cause disruption of

may have to be heated with steam

freshly placed concrete, so in no circum-

the microstructure and irreparable loss

injection or hot-air blowers. When

stances should water-curing methods

of strength and durability.

using steam-heating, adequate drain-

be used. Heat may be retained by us-

When the concrete has achieved

ing must be provided. Typically, the

ing insulated forms, covering exposed

a compressive strength of at least

aggregate should be heated to 10-20°C.

surfaces with insulating materials or

3-5MPa, it can resist a freezing cycle

• Lagging of water pipes: All water pipes

erecting covers with internal heating.

without damage because it has a higher

must be adequately lagged to prevent

Combustion-type heating under cov-

resistance to the pressure of ice and be-

supply pipes from freezing, or even

ers should be avoided. Formwork and

cause a large part of the mixing water will

bursting.

props must be left in place longer than

either have combined with the cement or

• Heating the mixing water: The most

for normal weather and pedestrian and

will be located in gel pores and therefore

common and easiest way to heat

vehicular traffic will also have to be kept

unable to freeze.

concrete is by heating the mixing

off slabs for longer than usual.

PRECAST | ISSUE TWO | 2019

• Batching and mixing: Adequate pro-

(Above): Bryan Perrie, MD of TCI.

Finally, the main requirement in cold weather

PROJECTS

(Left): Rail traffic is resumed on the repaired bridge. (Below): One of the plinths after attachment to an abutment.

PRECAST PLAYS VITAL ROLE IN EMERGENCY RAIL BRIDGE REPAIR Two eight-ton precast concrete support

steel girder beams were evident, along

constructed was accepted by the client.

plinths, designed by Mowana Engineers

with buckled and sheared-of f lateral

This approach would ensure the least

and produced by Cape Concrete in hours,

bracing connections. Extensive damage

amount of downtime. Due to contractual

rather than the days it would normally

was also observed on the southern

obligations, any standing time on the line

have taken, were one of the crucial

beam, where the web was torn apart and

involved a penalty clause of roughly R20

elements in the emergency repair of a

ripped off the flanges. The spherical pot

million per day.

bridge on the Sishen/Saldanha railway

bearings were damaged beyond repair,

line in November last year.

with severe horizontal and ver tical

Urgent transport

misalignment of the track.

Mowana Engineers’ involvement included

Severe damage to a steel composite deck occurred when a loaded low-bed

Mowana Engineers’ recommendation

the design and implementation of the

tr uck, w hich exc e e de d the nor mal

that the existing bridge be demolished

temporary works and the monitoring of

allowable vertical clearance permitted

and replaced with a temporary one which

the emergency remedial measures.

on public roads, collided with the bridge.

could withstand the rail traffic loads

Transnet holds modular emergency

The incident occurred on the R362 north-

until a permanent bridge deck could be

steel-beam girders in Gauteng for just

bound between Vredendal and Lutzville, where the road passes under the iron ore rail line. Fortunately, no-one was injured during the accident and all trains on the railway were halted in time. Completed in 1977, the bridge comprised a single-span, simply supported structure. The deck consisted of two steel plate girders compositely connected to a reinforced concrete top slab. Severe bending Transnet appointed Mowana Engineers to conduct an emergency inspection to assess the extent of the damage and determine the bridge’s structural integrity. It revealed that the deck had been transversely displaced off its spherical pot bearings by the force of the collision. Severe transverse bending and buckling of the bottom flanges and webs of both

(Above): A cross-section of the precast plinth installation.

PRECAST | ISSUE TWO | 2019

such an emergency. One of them was transported by road to the rail bridge site, wher e it was deployed in the construction of the temporary bridge. It had a shallow open deck which made no allowance for ballast. Therefore the existing abutments had to be raised

“The main casting challenge was the high degree of accuracy required.”

by installing precast concrete support

in the proprietary nuts and anchor plates

plinths so that the temporary bridge

having to be flown in from Johannesburg.

structure could be vertically aligned with the existing rail line.

Namaqua Engineering, which provided much of the construction equipment and

In collaboration with Cape Concrete,

personnel on site, assisted by flying the

Mowana Engineers designed, assembled

epoxy and bedding grout for the plinths

shutters, fixed reinforcements, cast,

in via helicopter to the construction

cured and transported the plinths to

site. This enabled adherence to the tight

the site some 300km away, all within 48

construction programme.

hours of confirmation of the design loads

The temporary bridge was assembled

and geometric constraints. Central to

next to the bridge crossing and on

this feat was the use of steam-curing,

We dn e s d a y, s e v e n d a y s a f t e r th e

in which elevated temperatures together

collision, it was lifted into position using

with a humid environment were used for

a 440-ton crane.

the early strength gain of the concrete.

The reinstatement of the rail track,

The concrete plinths had to be securely

overhead electrification and signalling

attached to the existing abutment using

infrastructure followed immediately

threaded stress bars for the horizontal

thereafter and the line was re-opened

stressing and dowels secured in a high-

on 7 December, just nine days after the

strength epox y grouting compound

collision and two days earlier than initially

for the vertical stressing. In order to

estimated. A speed restriction of 30km/h

facilitate this function, sacrificial sleeves

will be enforced until the temporary

were cast into the plinths.

bridge is replaced.

Mould preparation

Fastest replacement

Cape Concrete factory manager Johan

T his project underlines Mowana

Nel says the main challenge in casting the

Engineers’ commitment to providing

plinths was maintaining a high degree of

engineer ing solu tions tha t r equir e

dimensional accuracy and achieving the

initiative, creativity and excellence. It

necessary strength within 18 hours.

also highlights Cape Concrete’s capability

“S tar ting on a Monday mor ning

to respond to emergencies such as

with a set of Mowana’s drawings, we

this and the time-saving attributes of

had to prepare the moulds with all the

precast concrete. Moreover, it was

sleeves in specific positions. In addition,

the shared vision of all the stakeholders

all the rebar had to be cut and bent.

which facilitated the delivery of an

Fortunately, we had all the material

emergency solution in record time.

needed to fabricate the moulds in-house.

Transnet’s spokesperson, Molatwane

It took us until 02:00 on Tuesday to

Likhethe, says the fastest emergency

complete the casting. We then applied

rail bridge replacement prior to this

steam to accelerate the curing.

incident took two weeks to complete.

“ T h a t s a m e Tu e s d a y m o r n i n g ,

Kumba Iron Ore CEO, Themba Mkhwanazi,

Mowana’s engineers certified that all the

commended all involved on their swift

sleeves were accurately placed so that

response, ensuring that the railway line

they could begin drilling into the existing

was re-opened earlier than planned.

abutments in preparation for the arrival of the plinths on site,” recalls Nel.

The CEO of Africa Rainbow Minerals

CONSULTING ENGINEERS

Mowana Engineers is a proudly South African, multi-disciplinary engineering and infrastructure solutions company.

Ferrous placed this achievement in an economic context, stating that iron-ore

Complex assembly

exports are vital to generate foreign

Sourcing all the stress bar components

exchange for SA. By reopening the iron-

in such a short time proved to be another

ore line, the South African economy

challenge, due to a temporary shortage of

gained an estimated R900 million in forex

stock in the Western Cape. This resulted

that would otherwise have been lost.

PRECAST | ISSUE TWO | 2019

MULTI-DISCIPLINARY

Our Mission is to undertake and implement designs that reflect best design practice, Safely and Efficiently through the application of Sustainable and Innovative Solutions.

www.mowana-engineers.co.za

PROJETCS 32

MASSIVE PRECAST BEAMS USED IN

HYBRID BRIDGE CONSTRUCTION What is reputedly SA’s largest privately

on its aesthetic attributes. As such, it is

owned bridge was constructed over the

referred to as an “architectural” bridge.

Berg River in 2017 at Val de Vie, a luxurious lifestyle housing estate near Paarl

Permission granted

in the Western Cape. Spanning 70m, the

The original concept was based on a

bridge links the Val de Vie Estate with

stone bridge with multiple spans reminis-

the R45 provincial road and has reduced

cent of medieval bridges over streams.

the travel time to towns such as Stel-

However, the Department of Water

lenbosch and Somerset West.

Affairs & Sanitation (DWS) would at

A working monument to the practical

first not allow any construction activity

and aesthetic attributes of hy brid

within the full width of the riverbed. At

precast and in-situ concrete bridge

this point, there was little choice other

construction, it was designed by Daneel

than a more modern steel-and-concrete

Str ydom of Bigen Af rica with sub-

composite arch bridge.

consultant assistance on the precast

Permission was eventually granted by

beam design by Pieter Louw & Associates.

the DWS to construct a mid-span single

Built by the main contractor Empa

pier in the riverbed with the proviso

Structures, a subsidiary of the Raubex

that formwork or any form of staging

Gr oup, the str uc tur e di f f er s f r om

would not be allowed within the primary

traditional utilitarian bridge construction

river course (under the western span)

in that considerable emphasis was placed

and stringent guidelines regarding spill-

PRECAST | ISSUE TWO | 2019

Numbering 18, the Val de Vie precast

panels, coping and culverts. Permanent

beams are 35,62m long and 2m high. They

shutters were precast on site by Empa

are the Western Cape’s largest precast

Structures.

beams to date and could well have set a

The revised design had a heavy, but

new record for the entire country. Weigh-

shallow arch appearance, with stone

ing 64 tonnes apiece, their manufacture

elements being used where possible.

required the construction of a dedicated

However, the community was not entirely

stress-bed and an 80-tonne gantry crane

happy with this revised proposal once

at Cape Concrete’s production yard.

tenders had been circulated and an alternative design submitted by the estate’s

Uncharted territory

architect, Boogertman & Partners, was

“We entered uncharted territory with

implemented.

this project and were obliged to operate to extremely tight deadlines,” says Cape Concrete managing director Darty Louw.

Generously proportioned In harmony with the architecture in other

“Every thing happened simultane-

parts of the estate, the bridge has a sin-

ously: the construction of the laying

gle shallow arch rising to the central pier

bed, the erection of the gantry crane,

between the abutments and was built

the manufacture of the moulds and the

with a combination of steel and concrete

preparation of the beams’ reinforcing

balustrades to afford visibility of the river

frame assemblies. The latter comprised

and surrounding countryside. One of the

a combination of rebar, as well as 38

“architectural” requirements was the

pre-tensioned 15,7mm diameter strands

use of smooth precast facing panels which were mounted on the sides of the bridge to accentuate the shallow arch. The abutments were generously proportioned and fringed with arched

“The Western Cape’s largest precast beams to date.”

at the bottom of each beam. Six 5m-long Y40 reinforcing bars at both ends of each beam were also required. “ T he pr e-tensioned strands in the bottom of the beams neutralise the

and embellished walling to create a promi-

mid-span bending moment, whereas the

age into the river were imposed. Water

nent entrance to the estate. They also

Y40s restrain the tension forces in the

quality up- and downstream had to be

provide viewing platforms for people on

top due to moments at each beam end. In

monitored weekly to ensure that con-

foot and for the tethering of horses. Ad-

addition, the Y40s protrude asymmetri-

struction activity did not result in any

ditional viewing coves were constructed

cally from one end of each beam. When

contamination.

on cantilevered platforms situated over

laid end-to-end, as the beams were, the

the central pier.

Y40 extension bars overlapped with the

“Given the restricted access, we had no option but to use as much precast

The initial precast design was based

concrete as was feasible,” says Strydom.

on the use of post-tensioned beams

“However, we were permitted to use

that could be cast on site. However,

in-situ construction for the central sup-

the contractor opted for pre-tensioned

port pier, the two abutments and several

beams constructed off-site for com-

other elements, such as the reinforced

mercial reasons.

deck and the concrete balustrades. The area under the eastern span forms part of the floodplain and construction access to the pier was originally only possible from the east.” Precast elements In order to facilitate easy access for workers and supervisory staff from the main site camp to the pier construction area, Empa Structures pre-fabricated and installed a temporary steel pedestrian bridge over the main channel. Supplied by C ape C oncr ete, the precast concrete elements included

PRECAST | ISSUE TWO | 2019

(Top): The completed bridge. (Left, from top): All the beams are in place, in-situ construction is underway and a precast facing panel is lowered into position. (Below): Sixteen of the 18 beams are in place between the abutments and the central pier.

PROJECTS

huge pre-stressed beams, large facing

PROJECTS 34

bars of the facing beams, thus creating a knitting effect. In order for the trouble-free execution of this Y40 link-up, tolerances had to be extremely tight and the Y40s had to be positioned with great accuracy prior to casting,” says Louw. Good surface finish Concrete pouring commenced once all the beam strands were evenly stressed. A combination of external and poker vibration was used to compact the concrete. This provided a very good surface finish with minimal blow holes. As soon as the pouring was completed, a tarpaulin was placed over the mould and steam was injected under the cover to accelerate the hydration process. This meant that a strength of 40MPa could be achieved in 20 hours and enabled Cape Concrete to produce one beam a day. The final strength required was 60MPa, which was achieved within 28 days. The de-tensioning of the pre-stressed strands took place once the concrete had

A 460-tonne behemoth

reached 40MPa using four 250-tonne hy-

A juggernaut was required to deliver the

draulic jacks. Retarder paste was applied

beams to site by road, one at a time. In

at the end of each beam after casting and

addition, a mobile crane company, Tee-

was washed off with water the next day

mane Cranes, was contracted to offload

to create a rough exposed aggregate fin-

and place the beams. Due to the drought

ish. This provided a good bonding surface

conditions being experienced at that

for the assembly of the bridge.

time in the Cape, a dry area suitable for

The facing panels were also steam-

the mounting of two of the three mobile

cured, the largest units measuring 4m

cranes used for off-loading and placing

x 3m. These panels were cast with a

the beams was put to use.

glass-smooth finish and attached with

The Western Cape’s largest mobile

river’s west bank. They were then lifted

cleverly designed fingers that eliminated

crane, a 460-tonne behemoth, was the

from each end by the 460-tonne crane

the use of visual fixing on the front face.

only mobile crane which could lift the

and a 220-tonne crane positioned on the

Some of the panels were curved, such

beams off the delivery vehicle unaided.

other side of the river and placed into

as those used for cladding of the central

The first nine beams were hoisted off

position between the western abutment

viewing cove.

the truck onto the ground close to the

and the central pier. The operation for the positioning of the second nine beams on the eastern side of the bridge was somewhat different and entailed the use of the third mobile crane, also positioned on the eastern side of the river. Once all 18 precast beams were in position, five diaphragm transverse beams were cast in-situ between the precast beams. They comprised a central beam which binds all 18 (Top): A beam is about to be lifted by the 460-tonne mobile crane prior to placement between the western abutment and the central pier. (Above): Concrete pouring of the pavement. (Left): The central diaphragm’s reinforcing prior to the pouring of concrete. The Y40s can be seen protruding from the ends of the beams in a knitting formation. (Right): The completed bridge.

PRECAST | ISSUE TWO | 2019

the fingers of a panel were inserted and tied temporarily to the deck, final lining adjustments were made using jacks before final grouting took place. The paving of the road and pavements was done by Highland Paving using clay pavers laid in a mortar mixture. Time-saving Empa Structures contracts manager Gareth Stander says that time-saving

EST. 1932

was another benefit of using precast concrete. “The beams were cast in parallel with the construction of the sub-structure and were completed more or less at the same time. This saved at least nine weeks in construction time.” He adds that before construction began, a hydraulic assessment of the river course and the floodplain was undertaken. “Top water levels for a 100-year flood was calculated, as well as the approximate scour depths around the pier and abutments during such a flood. The precast beams together, two mid-span

bridge was constructed above the 100-

beams and two beams above each abut-

year floodline and the panels on the side

ment. The central beam was the largest,

of the bridge were all positioned above

being 1,5m wide and 2m high.

it. So even in a worst-case scenario, the bridge should stand clear and proud

Post-tensioned cables

of the water.

Empa’s construction team had to create

“Moreover, the piles on which the

working platforms on either side of the

entire structure is supported were care-

diaphragm sections by fixing anchors into

fully designed to ensure stability of the

the pier and abutments. This gave them

bridge, even during deep scouring. Not

working space to erect the vertical shut-

being a national thoroughfare, the bridge

tering. In addition to normal reinforcing,

is unlikely to bear unusually heavy traffic.

the central diaphragm beam was further

Therefore our design incorporated the

reinforced with the installation of four

standard NA loading and an NB24 load-

post-tensioned cables, two at the bot-

ing, the latter being the lighter loading

tom and two at the top.

for abnormal loads. However, although

Permanent deck shutters were cast

it wasn’t specified, the bridge can actu-

in Empa’s site yard and were used to

ally take the NC loading (described as a

close the remaining gaps between the

super-load in the design code). Because

precast beams. Measuring 1,2m x 300

of the bridge’s span lengths, the NA

x 50mm, they rested on recesses which

loading resulted in the largest design

had been cast into the beams for that

moments,” says Strydom.

MANUFACTURERS AND SUPPLIERS OF: Civil Engineering Pipes – Man Holes – Storm Water Channels Road Kerbs & Channels – Culverts Lighting & Transmission Poles Precasting, Poststressing & Prestressing to specification – Toilet Cubicles & Bus Shelters – Earth Retaining Systems Building Industry Hollowcore Decking Slabs – Beams Columns – Staircases – Walling Panels & Multi Story Precast Elements

purpose. Concrete was then poured onto the shutters to create the deck. It comprised a 250mm-thick road section and a 335mm pavement section. Heavily reinforced, it included a substantial quantity of Y32s. The casting of the pavements was especially challenging because provision had to be made for the attachment of the precast cladding on each side of the bridge. This involved the use of box-outs to create holes into which the panels’ concrete fingers could be inserted. Once

PRECAST | ISSUE TWO | 2019

See YouTube link for construction video - https://www.youtube.com/ watch?v=EJ1Rgl3f9cc .

Cape Concrete Works 021 9051200 info@capeconcrete.com www.capeconcrete.com

PROJECTS 36

PURCHASE GUIDELINES FOR

CONCRETE RETAINING BLOCK WALLS Retaining walls fall into what some would

T he moti ve f or this appr oach is

Equally understandable is the fact

describe as the â&#x20AC;&#x153;necessary nuisanceâ&#x20AC;?

understandable: property developers

that in allocating budgets, property

category. Although they fulfil a vital

need to show a return on investment

developers prefer to channel any spare

function in shoring up embankments and

in a very tough economy. However,

cash into functional or visible enhance-

securing building platforms, concrete

buying on price alone is both misguided

ments on their main structure, be it a

retaining block (CRB) wall purchase

and inexcusable and can result in much

shopping centre, a hotel or a housing

decisions are of ten based on price,

higher remedial costs further down

estate. The trouble is that this is some-

rather than on structural integrity.

the line.

times done at the expense of peripheral items such as CRB walling and can lead to designs and execution which fall short of what is required for durable, maintenance-free lifespans. Quality first In most instances, bad CRB purchase decisions result from ignorance, rather than wilful negligence. In other words, those who make the decisions are not aware of the importance of the conservative design considerations and engineering required for reliable and durable CRB (Above): An example of what can happen if the rules for building CRB walls are not followed. (Left and right): Examples of well-executed walls.

PRECAST | ISSUE TWO | 2019

“Unless backfill has proper drainage, your wall will fail – it is just a matter of time.”

walling. Instead, the attitude appears to

and a CMA member, identifies several

be that “a wall is a wall is a wall”.

other pitfalls in CRB wall construction

Buying on price should only be accept-

exceed those specified in the design.

• Ensur e tha t y our contr ac tor is

experienced in building CRB walls.

Possible pitfalls Holger Rust, owner of Terraforce, a Cape Town-based precast concrete licensor

which need to be avoided:

able when the lowest tender complies with

• Excavating close to wall foundations.

the necessary best-practice principles.

• Additional loading not accounted for

But some do not, which is why the rate

of CRB wall failure in SA is far too high.

• Limited bearing capacity – poor/sat-

in the original design.

Much has been written in this jour-

urated founding conditions or no foun-

nal about why CRB walls fail, based on

dation at all.

technical input from CMA members,

• Poor connectivity between blocks and

including Aveng Infraset, MVA Bricks,

geogrid.

ReMaCon Products and Terraforce, as

• Excessive lateral earth pressure or

well as geotechnical engineer Trevor Green.

poor-quality blocks, which can result

This article is a distillation of the

in them having linear cracking.

advice found in previous articles, the

Rust, who has been in the industry for

aim being to give property developers

40 years, notes that it is sometimes a

and owners essential design pointers to

combination of these factors which can

assist them in making responsible CRB

cause a wall to fail. He believes there are four cardinal

wall purchase decisions.

rules which should be followed in any CRB guidelines

CRB project:

• Any walls higher than 1,5m should be

1. Ensure that the tender document

provides the design engineer with

one who specialises in CRB wall design.

the necessary information to do a

• Before a wall is designed, soil tests

professional design.

should be conducted. The results of

2. Ensure that your design is done by an

the tests should form part of the

tender document, especially if the

3. Ensure that the products used comply

soil is unstable. This will enable those

tendering to propose designs which

4. Insist on experienced CRB installers

provide for any unusual conditions.

with the necessary knowledge to exe-

• Other information, such as ground-

cute the design professionally.

water and loading conditions, should

be provided in the tender document.

• Ensure that your wall is designed

conservatively, so that it can handle

weather extremes.

• Nearly all wall failures are the result of

poor drainage. Unless backfill has

proper drainage, your wall will fail –

it’s just a matter of time.

• Some designers take short-cuts by

reducing the amount of geosynthetic

reinforcing. Ensure that your re-

inforcing extends to the right depth

in the backfill and has the right spacing.

• Fill material (ie the material between

your wall and the cut face) should

be the appropriate quality for the wall

design and during construction, it

should be regularly compacted.

• Wall angles and heights must not

PRECAST | ISSUE TWO | 2019

experienced professional. with minimum statutory standards.

PROJECTS 38

SHORING UP EMBANKMENTS WITH CRB WALLING When Somerset College, a co-educational private school in Somerset West, was faced with levelling a massive slope for the creation of five new sports fields, major earth-moving was unavoidable. This resulted in exposed cut-and-fill

and a pavilion above the AstroTurf field.

below ground level above the concrete

embankments up to 5m high which

“Icos Engineering submitted a great

the main contractor, Poplar Trading,

design that specified the necessary re-

needed to retain cost-effectively and

inforcing to match wall heights, as well

“We inserted 1,5m of geogrid at every

aesthetically.

as soil and surcharge conditions,” says

second layer of blocks and we filled the

SP van Blerk of Decorton.

first six layers of blocks with concrete

“Level platforms were required for

foundation, which measured 800mm x 350mm deep.

two new rugby fields, two cricket ovals

to reinforce the base of the wall. We also

and a hockey field,” says Keon Marais

filled the area immediately behind the wall

of Poplar Trading. “To achieve this, we

with 300mm of drainage sand and we

moved 80 000m² of earth and inserted

inserted a sub-soil drain at the bottom

55 000m² of drainage. Loxton Irrigation

of the sand which ran the full length of

laid over 50 Po000m of irrigation piping

the wall,” adds Van Blerk.

and Vredenburg Lawns and Yokwana

The earth-moving and walls were

Contracting installed 55 000m² of lawn.

completed in February this year, although

In addition, we built some gabions and Ter-

some landscaping is required to show-

raforce 4x4 step block seating adjacent

case the installation to full effect.

to the hockey field.”

Icos Engineering was the engineer for

Decorton Retaining Systems, the

the project, while QS Bureau was the

sub-contractor and an expert installer

quantity surveyor.

of Terraforce concrete retaining block

Built with Terraforce L12 blocks

(CRB) walls, was awarded the contract

manufactured by Klapmuts Concrete

to shore up the embankments with CRB

Products, the main retaining wall was

walling, staircases and wheelchair ramps

built at an angle of 65˚, was 130m long

for student access. The installation in-

and reached 5,4m at its highest point.

cluded additional space for an entry road

The first layer of blocks was placed

(Above): Terraforce 4x4 step block seating adjacent to the new AstroTurf hockey field. Behind it is the main retaining wall, which shores up a 5m embankment situated below a new rugby field. (Left): A wheelchair ramp buttressed with Terraforce L12 blocks and a staircase built with Terraforce 4x4 step block seating.

PRECAST | ISSUE TWO | 2019

NEW EXPOSED GLASS PAVER TRANSFORMS WINE ESTATE DRIVEWAY A 120m driveway at Quoin Rock, a wine estate just outside Stellenbosch, is the site where CMA producer member CEL Paving’s newly-introduced exposed glass paver was installed for the first time. The paver was used in an attractive layout combination with two other CEL pavers: polished interlockers and coarse char coal exposed blocks. A ll thr ee paving blocks were laid on a section of driveway which skirts the main building on the estate. Installed in sections between April and November 2018, the pavers were used to

vehicles turning into the driveway,” says

replace an exposed aggregate concrete

Peter Visser, a CEL sales and technical

surface which had been put down in

representative.

2000. The exposed glass pavers were

The new paving was laid by Rockor.

used as 200mm-wide edging between

Besides removing the exposed aggregate

the kerbs and the new paving for the first

concrete paving, prep work involved

12m of the driveway. They were also laid

reinforcing the old sub-base with an

in a band across its entrance.

additional G4 base course.

“The advantage of the exposed glass paver is that it combines exceptional durability with an attractive appearance. It has the added benefit of safety, as it refracts light beams thrown by vehicles at night, thereby acting as a guide for

PRECAST | ISSUE TWO | 2019

(Above, from top): Exposed glass pavers create an attractive edging to the driveway entrance; exposed glass paver edging situated between the kerbing and polished interlockers; the driveway entrance with a band of exposed glass pavers (foreground) and behind them the CEL polished interlockers.

MEMBER LIST 40

PRODUCER MEMBERS A FICK SEMENT WERKE BK TEL: (022) 913 1921 PROVINCE/COUNTRY: WC PILLAR: PB

ECHO FLOORS (PTY) LTD TEL: (011) 668 1900 PROVINCE/COUNTRY: GAUT

PROVINCE/COUNTRY: GAUT PILLAR: PB/PI

ECHO PRESTRESS DURBAN (PTY) LTD TEL: (032) 947 3067 PROVINCE/COUNTRY: KZN

TECHNICRETE (PTY) LTD TEL: (011) 672 1425/670 7600 PROVINCE/COUNTRY: GAUT PILLAR: PB/PI

HORIZON BRICK & CONCRETE TEL: (012) 943 3701 PROVINCE/COUNTRY: N/W PILLAR: PB

TOPFLOOR CONCRETE (PTY) LTD TEL: (021) 951 7700 PROVINCE/COUNTRY: WC PILLAR: PB

BANZI TRADE 31 (PTY) LTD T/A BRICKIT TEL: (011) 023 6708 PROVINCE/COUNTRY: GAUT PILLAR: PB/PI

LATEGAN CEMENT WORKS (PTY) LTD TEL: (021) 873 1154 PROVINCE/COUNTRY: WC PILLAR: PB/PI

VANSTONE PRECAST (PTY) LTD TEL: (012) 541 2056/1808 PROVINCE/COUNTRY: GAUT PILLAR: PB/PI

BETA TILES (PVT LTD TEL: (263) 4333735 PROVINCE/COUNTRY: ZIM PILLAR: PB

MANHOLES 4 AFRICA (PTY) LTD TEL: (011) 903 7023 PROVINCE/COUNTRY: GAUT PILLAR: PB/PI

VIBRO BRICKS AND PAVING (PTY) LTD TEL: (012) 374 5533 PROVINCE/COUNTRY: GAUT PILLAR: PB/PI

BOSUN BRICK BRITS (PTY) LTD TEL: (012) 250 1711 PROVINCE/COUNTRY: NW

MARLEY ROOFING (PTY) LTD TEL: (011) 316 2121 PROVINCE/COUNTRY: GAUT PILLAR: PB

WEST END CEMENT BRICKS (PTY) LTD TEL: (011) 851 1005 PROVINCE/COUNTRY: GAUT PILLAR: PB/PI

MOBICAST (PTY) LTD TEL: 086 111 2346 PROVINCE/COUNTRY: WC PILLAR: PB/PI

NON-PRODUCER MEMBERS

AVENG INFRASET (PTY) LTD TEL: (011) 876 5500/872 1713 PROVINCE/COUNTRY: GAUT PILLAR: PB/PI

BOSUN BRICK MIDRAND (PTY) LTD TEL: (011) 310 1176 PROVINCE/COUNTRY: GAUT PILLAR: PB/PI BOSUN BRICK PORT ELIZABETH (PTY) LTD TEL: (041) 405 0100 PROVINCE/COUNTRY: EC C.E.L. PAVING PRODUCTS (PTY) LTD TEL: (021) 905 5998 PROVINCE/COUNTRY: WC PILLAR: PI CEMBLOCKS (PTY) LTD TEL: (014) 538 0311 PROVINCE/COUNTRY: NW PILLAR: PB/PI CEM BRICK MANUFACTURERS (PT Y) LTD TEL: (051) 433 4479 PROVINCE/COUNTRY: F/STATE PILLAR: PB/PI CONCRETE UNITS (PTY) LTD TEL: (021) 386 1923/(016) 362 2236 PROVINCE/COUNTRY: WC/GAUT PILLAR: PB/PI CONFRAMAT (PTY) LTD TEL: (0861) 33 5599 PROVINCE/COUNTRY: GAUT PILLAR: PB/PI CORESLAB (PTY) LTD TEL: (087) 232 2462 PROVINCE/COUNTRY: LIMPOPO PILLAR: PB/PI COROBRIK (PTY) LTD TEL: (031) 560 3252 PROVINCE/COUNTRY: KZN PILLAR: PI DERANCO PRECAST (PTY) LTD TEL: (041) 463 3338 PROVINCE/COUNTRY: EC PILLAR: PB/PI EAGLE ROOF TILES (PTY) LTD TEL: (044) 874 0290 PROVINCE/COUNTRY: WC PILLAR: PB ECHO PRESTRESS (PTY) LTD TEL: (011) 589 8800/8899 PROVINCE/COUNTRY: GAUT PILLAR: PB

MONIER COVERLAND (PTY) LTD TEL: (011) 222 7300/7334 PROVINCE/COUNTRY: GAUT PILLAR: PB

ABEL EQUIPMENT CC TEL: (044) 874 1876 PROVINCE/COUNTRY: EC BASF CONSTRUCTION CHEMICALS SOUTH AFRICA (PT Y) LTD TEL: (011) 203 2400 PROVINCE/COUNTRY: GAUT

MVA BRICKS CC TEL: (012) 386 0050 PROVINCE/COUNTRY: GAUT PILLAR: PI

BIRKENMAYER H (PT Y) LTD TEL: (011) 970 3880 PROVINCE/COUNTRY: GAUT

PANDA (PTY) LTD TEL: (00267) 244 2107/8 PROVINCE/COUNTRY: BOTS PILLAR: PB/PI

CHRYSO SOUTHERN AFRICA (PTY) LTD TEL: (011) 395 9700/ (031) 564 0325/(021) 928 1660 PROVINCE/COUNTRY: GAUT/ KZN/ WC

PORTLAND HOLLOWCORE SLABS (PTY) LTD TEL: (021) 972 1111 PROVINCE/COUNTRY: WC PILLAR: PI

DICK KING LAB SUPPLIES (PT Y) LTD TEL: (011) 499 9400/(031) 700 2551 PROVINCE/COUNTRY: GAUT/DBN

ASSOCIATE MEMBERS AF CONSULTING ENGINEERS & ASSOCIATES (PT Y) LTD PROVINCE/COUNTRY: JHB ASPASA TEL: (011) 791 3327 PROVINCE/COUNTRY: JHB BRITISH PRECAST CONCRETE FEDERATION TEL: +(44) 116 232 5170 PROVINCE/COUNTRY: UK CONCRETE SOCIET Y OF SOUTHERN AFRICA TEL: (012) 348 5305 PROVINCE/COUNTRY: PTA CPI CONCRETE PLANT INTERNATIONAL TEL: (02236) 962390 PROVINCE/COUNTRY: GERMANY JC PAVING CONSULTING TEL: (011) 431 0727 PROVINCE/COUNTRY: JHB SARMA TEL: (011) 315 0300 PROVINCE/COUNTRY: JHB SEKHUKHUNE & ASSOCIATES TEL: (012) 346 1945 PROVINCE/COUNTRY: PTA TACO VOOGT CONSULTING ENGINEER TEL: (012) 669 0125 PROVINCE/COUNTRY: PTA YOUNG & SATHARIA CONSULTING CIVIL ENGINEERS TEL: (031) 207 7252 PROVINCE/COUNTRY: KZN CONTRACTOR MEMBERS

REMACON PRODUCTS CC TEL: (011) 393 5504 PROVINCE/COUNTRY: GAUT PILLAR: PI REVELSTONE (CAPE) (PTY) LTD TEL: (0861) 173 835/(021) 761 9737 PROVINCE/COUNTRY WC PILLAR: PI ROCLA (PTY) LTD TEL: (011) 670 7600 PROVINCE/COUNTRY: GAUT PILLAR: PB/PI SHUKUMA BRICKS (PTY) LTD TEL: (041) 372 1013 PROVINCE/COUNTRY: EC PILLAR: PB SHUKUMA FLOORING SYSTEMS T/A ZITTLAU EIENDOMME (PTY) LTD TEL: (041) 372 1933 PROVINCE/COUNTRY: EC PILLAR: PB SILVERTON PRECAST (PTY) LTD TEL: (012) 804 4525 PROVINCE/COUNTRY: GAUT PILLAR: PI SMARTSTONE (PTY) LTD TEL: (011) 310 1161

FIBERTEX SOUTH AFRICA (PT Y) LTD TEL: (031) 736 7100 PROVINCE/COUNTRY: KZN HAWKEYEPEDERSHAAB TEL: 00 459645 4193 PROVINCE/COUNTRY: DENMARK KERNEOS SOUTH AFRICA (PT Y) LTD TEL: (011) 444 3090 PROVINCE/COUNTRY: GAUT KOBRA MOULDS B.V. TEL: 003111 356 2460 PROVINCE/COUNTRY: NETHERLANDS MANITOU SA (PT Y) LTD TEL: (011) 975 7770 PROVINCE/COUNTRY: JHB PAN MIXERS SA (PT Y) LTD TEL: (011) 578 8700/8600 PROVINCE/COUNTRY: JHB QUANGONG MACHINES CO LTD TEL: +865 958 679 9557 PROVINCE/COUNTRY: CHINA SIKA SOUTH AFRICA (PT Y) LTD TEL: (031) 792 6500 PROVINCE/COUNTRY: KZN TERRAFORCE (PT Y) LTD TEL: (021) 465 1907 PROVINCE/COUNTRY: WC

BUFFALO RETAINING WALLS CC TEL: (016) 366 1801 PROVINCE/COUNTRY: GAUT DECORTON RETAINING SYSTEMS (PT Y) LTD TEL: (021) 875 5155 PROVINCE/COUNTRY: WC FRICTION RETAINING STRUCTURES (PT Y) LTD TEL: (011) 608 4321 PROVINCE/COUNTRY: GAUT POWERGATE CONSTRUCTION CC TEL: 071 603 5070 PROVINCE/COUNTRY: GAUT VALCAL INTERNATIONAL EXPORT CC TEL: (011) 867 2471 PROVINCE/COUNTRY: GAUT CEMENT MEMBERS AFRISAM SOUTH AFRICA (PT Y) LTD TEL: (011) 670 5500/5752 PROVINCE/COUNTRY: GAUT SEPHAKU CEMENT (PT Y) LTD TEL: (012) 684 6300 PROVINCE/COUNTRY: GAUT

PI – Precast Infrastructure PB – Precast Building

PLEASE NOTE: The above member list was correct at the time of going to print. If your details have changed, please contact Rita at the CMA offices on tel: (011) 805 6742.

PRECAST | ISSUE TWO | 2019

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AT I O N

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