A Practical Look at Concrete

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A

a t concrete

John

G.

Richardson



A

pract ical l ook

at co nc rete

John

G.

Richardson

FlCT

The Concrete Society



A pract ical look at concrete

John G. Richardson

ISBN 0 946691 83

5

Ref: CS 132

John

G.

Richardson

Design and Production: Jon Webb

Published by The Concrete Society, 2002

Further copies and information about The Concrete Society, including membership, may be

obtained from:

The Concrete Society,

Century House, Telford Avenue,

Crowthorne, Berkshire RG45 6YS,

UK

Tel: +44 (0)1344 466007, Fox: +44(0)1344 466008

Email: enquir [email protected], www.concrete.org.uk

All rights reserved. Except as permitted under current legislation no part of this work may be

photocopied, stored in a retrieval system, published, performed in public, adapted,

broadcast, transmitted, recorded or reproduced in any form or by any means, without the

prior permission of the copyright owner. Enquiries should be addressed to The Concrete

Society.

Although The Concrete Society (limited by guarantee) does its best to ensure that any advice,

recommendations or information it may give either in this publication or elsewhere

is

accurate, no liabil ity or responsibility of any k ind (including liability for negligence)

howsoever and from whatsoever cause arising,

is

accepted in this respect by the Society, its

servants or agents.

..

I I



Contents

The issue of

Concrete

in which the page first appeared is shown

in

italics

A few words abou t Cubco man

few words abo ut the author

Publishers Note

vi

vii

viii

EXCELLENCE

Excellence

1

Excellence

2

Standards

Quality assurance

Efficient co nstruction

Testing

M ore testing

Th e Conc rete Society

Awards

Jub/Atgust

1991

Sep

teniberl October 1996

Stpteniber 1982

Azgust

1981

Jub/August 200

Jatzuary/ February 1993

Jub/At/gr/st 1996

January 2000

October 2002

1

2

3

4

5

6

7

8

9

10

C O MMUN CAT10

N

S A ND

D

ETA1L

Drawings November I981

Geomet ry 1

Janiiary 1982

Geometry

2 February 1982

Detail: the need for comm unication

October 1983

Detail: people’s inpu t April

1981

Detail: concrete

March 1981

Methods and com municat ion Jub

1979

Panel joints

June 1980

Computers in construction

March 1999

11

12

13

14

15

16

17

18

19

20

Computers

Com puters and design

Jub/Aigi ~st 993 21

June

1997 22

FORMWO RK AN D FALSEWORK

Setting-out points January 1979

Detail: form work June

1984

Kickers

1 Septenzber 1977

Kickers 2 October 1977

Nibs an d corbels November 1977

Cores and formers

December 1977

Ramps and intersections

February 1978

Staircases

June 1983

Circular work August 1979

Props and propping

December 1980

Striking formwork

August 1982

Aluminium forms

November 1980

Trough and waffle floors

October 1980

GRC formwork

March 1983

Formwork failure

January 1981

Formwork March/Apri l l992

Formwork systems

Falsework

1

Falsework 2

Falsework

3

Form work and falsework

1

Formwork and falsework 2

Formwork and falsework

3

March/Aprill996

October 1982

November 1982

Deceniber

1982

March 1998

May

2001

June 2002

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

---

- -

40

41

42

43

44

45

46

...

111



REINFORCEMENT

Reinforcement 1

Reinforcement

2

Reinforcement

3

Reinforcement

4

Reinforcement, fittings and accessories

Reinforcement and accessories

Cast-in fixings

Locating inclusions

Ties

Reinforcement accessories

Fibres

Jatiuay I999

JanuaryylFebruary 1994

October 1978

M q 1979

M q 2002

March 2001

Janualy 1978

September 1983

J u b 1984

M q 2000

September 2002

47

48

49

50

51

52

53

54

55

56

57

58

PRODUCTION A ND PLACING

Preparing

to

concrete

Th e pre-concrete check

1

Th e pre-concrete check 2

Production, plant and equipment

Con struction joints

Production and handling

Placing concrete 1

Placing concrete

2

Batching

Conc rete mixing and batching plant

Ready-mixed con crete

1

Ready-mixed concre te 2



Slab construction

Flatwork

Hot- and cold-weather concreting

Winter workmg

Concrete in adverse conditions

Placing, compa cting and caring

Self-compacting concrete

February 1979

March 1979

April 1979

Februay 2001

November 1978

Jub/August 1994

Ju b 1978

January 1983

Jub/August 1998

September 1997

February 1997

September/ October 1992

February 200

1

June 1999

M q 1981

September 2000

Juh/Aigust 1999

September 198

1

Mq/June 199s

April 2000

March 2002

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

SURFACE FINISH

Surface finishes

1

Surface finishes

2

Surface finishes

3

Surface finishes 4

Surface finishes 5

Surface finishes 6

Fixing

to

concrete

Surface retarders

Architectural conc rete

Con crete surfaces

Maintaining conc rete finishes

Protecting concrete

Cleaning concrete

Weathering

Repairs and remedial work

M q 1977

June 1977

Mq/June 1993

AuguJt 1977


ANgtlst 1980

September 1980

September 1979

November/December 1998


February 1999

January/Febmay 199s

Januay 1998

June 1981

December 1978

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

i v



HA NDL ING AN D SAFETY

Lifting

Lifting equipment

Safety

Sitesafe

'83

Moving loads

Supervision

Cranes

Cranes - ommunications

Getting things moving

Ergonomics

Safe working with small dum pers

December 198

June 1982

October 1979

Februay 1983

Jub

1980

October 1981

August

1983

December 1979

J M ~983

Murch 1984

December I983

Precast concrete: samples and prototy pes

Precast concrete 1

Precast concrete 2

Precast concrete 3

Prestressed concrete 1



Prestressed concrete

4

Con crete moulds for precasting

Mould design

Polymer moulds and liners

Flexible mould s

Conc rete ingredients

Concrete as a mould material

Precast erection

1

- general

Precast erection 2

-

site factors

Conc rete sculpture

Decorative concrete and finishes

Lightweight and foamed concrete

glass fibre-reinforced concrete

Tilt-up construction

Slipform an d tilt-up constructio n

Bridge construction

Bridges

PRECAST A N D PRESTRESSED CONCRETE

October 2001

October 1999

Nolieniber/ Deceniber 1991

Februay 1984

M y 1978

March 1980

M q 1997

Mq 1982

June 1978

April 1980

March 1982

A p d 1982

Mq 1998

March 1978

Noveniber 1979

Januuy 1980

Noiieniber/ December 200 0

Jtily/August2002

Noven iberl December 1996

97

98

99

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

April 1984 129

April 1983 130

March 2000 131

Noveniber/ December 2001 132

Noveniberl Deceniber 2002 133

INDEX

134

V



A few

words

about Cubco

man

Cubco man was employed by Cube Company

Limited (trade name Cubco). Cubco originated in

the Leonard Trotter* series of articles published

in the Journal

Precast

concrete (now

Quality

concrete)

in

1972. The firm was

a

small (imaginary) manu-

facturing concern whose entrepreneurial spirits

foresaw a market for concrete specimens of such

a

standard tha t they would have a

99.9%

chance of

meeting any given specification. Rumour has

it

that, long before fibres of any kind were used

elsewhere in any concrete application, Cubco

introd uced micro-fine and virtually invisible fibres

into the specimens they produced, thereby

ensuring the required pass rate for the product.

Jack Barfoot, then editor of

Concrete,

saw these

illustrations

as a

means of conveying practical information to his readers and the page was

bor n. Since May 1977, in the pages entitled Ilooking atitpractka/&, we have attempted to convey

the practicalities of the use of conc rete in constru ction . We have detailed meth ods fo r forming ,

casting, handling and finishing concrete, and touched o n planning and organisation as well as

critical details of safety. Early pages consisted

of

simple details, with few - f any

-

people

to

be seen in the illustrations. In 1978, the need arose to intro duc e the human element and C ubc o

man was pressed into service.

Cub co man has developed with age. It could be said that his character has become rounded over

the years. Initially he was con cerned with t he intimate details of construc tion, kickers, starter bars,

stripping fillets, noggings and suchlike. Thes e days, while still maintaining his interest in the finer

d et d s, h e is involved with greater things, industry-wide. Cubc o man today appreciates such things

as

the advantages to be ob tained from new materials and m ethods, the benefits to be gained by

applying techniques such as networking and value analysis and even the use of computers in

design. Although his ability to appreciate the marvels of new technology and the seemingly

infinite range of products designed to speed construction and improve quality has advanced over

the years, he sull retains an essentially practical attitude to such developments:

a

‘feet upon the

ground’ approach, as he would p ut it.

Th e page Looking atitpractica4 has been used as a training aid by major contractors. Th e author

used it as such for many years in the course of nearly 20 years working

a s

a lecturer in

construction topics at the Cement & Concrete Association (now BCA) Training C entre at

Fulmer Gra nge . near Slough, Berkshire. As well as these applications, Cu bco m an has variously:

advertised the Advisory Service of T h e C onc rete Society, appeared in exh ibitions, illustrated

research reports and information bulletins, popped-up in

a

series of C D Roms for Continuing

Professional Education of Engineers, and instructed site personnel on the installation of

precast elements.

Since 1978, he has go ne from s treng th to strength to th e point wh ere his image is

to

be found

on

notice boards on construction sites, within works, offices and laboratories. The pages are

often annotated with names of persons with whom , in the mind o f the viewer, he has been

associated by deed o r action.

Ov er th e years, several people have suggested that

a

compilation of the pages would make

a

useful book , recording t he practicalities and intro ducin g possibilities of emerging techniques to

the reader. T h e suggestion was taken up w ith enthusiasm by Nick Clarke, Publications Manager

and Managing Edito r of

Concrete.

So

here

it

is

John

G .

Richardson

FICT High Wycombe, Buckinghamshire Nov emb er 2002

*

Pen name of Philip L. Owens

HNC,

MPhil, FICT,

MCIWM, and

n o connection with Del

Boy

or any of his

family



A few words abou t the author

O n

leaving school, and before joining the Royal Engineers, John worked briefly as a n

architectural drau ghtsm an, meanwhile studying architecture which in th ose days involved tuition

in mechanical and still life drawing Following an introd uction to army life with the Infantry, and

the Mons Officer Training School, the FE16 RE OCTU at Newark provided an education in

construction, erection and demolition.

After the army, employment as a

draughtsman and study at the renowned

Brixton School of Building served to feed

John’s interest in concrete work and

prompted a specialisation in formwork.

During this time, further education was

received from contact with his all-time

hero, Cyril Parry,

a

formwork consultant

whose works included the floating jetties

used in the Norman dy landings of World

War I1 and the notorious Sellafield

chimneys.

Formwork des ign and detai l ing with

Holland, Hannen and Cubitt , a major

contractor of the time, embraced mould

design for precast and prestressed

concrete leading to a move in to precasting

as

a

mould shop supervisor. What seemed

a natural progression led through site

supervision of formwork with Scaffoldmg

(G rea t Britain) 1,td to fo rm wo rk man u-

facture and then employment

as a

production engineer with Trent Concrete

Limited, at Colwick and Hoveringham

Works, Notting ham .

A

move to the lectur-

ing staff o f the Cement & Concrete

Association followed som e years

as

works

manager for Concrete Limited at Iver,

Bucks. Th ese latter employments a fforde d

the opportunity to study works manage-

ment at evening classes and as

a

day-

release studen t.

Con curren t with the service at the C&CA

and during the following ten years as a

self-employed consultant and lecturer,

John worked as Technical Assessor fo r the

British Standards Institution in their

Firms of Assessed Capability Scheme. A

varied (somewhat chequered) career has

provided a wealth of conta ct with all

manner of people in construction, from

the man on the job to top management,

from steelfixer to des igner and f rom

consultant to concretor, both

on

site and

in works. Indee d, much of these worthies’

knowledge has been incorporated in the

pages Looking

at itpractical4

in Concrete

John

at

work

on

Cubco

man

...

... and Ctlbco man returns the compliment

v i i



Publisher's note

John R~chardson'sLooking at itpractica& pages published in Conmete magazine

since 1977 cover a wide range of topics and present a wealth of advice on safe,

practical concrete construction. Some of the pages were prepared to draw

attention to

a

new code of practice or guidance document, and new editions of

some of these documents have since been published. Some of the site practices,

materials and systems shown in these pages may

also

have been replaced or

improved by more efficient approaches. Mmor amendments to the captions

have been incorporated to highlight these but as far as possible the pages have

been retained essentially in their original format, reproduced from the printed

pages

of Conmete

magazine.

Readers should make sure that any standards, codes

or

guides they refer to are

current and relevant to their situation.

...

V l l l



EXCELLENCE

he general acceptance of quality assurance in construction processes and products

has focussed Cubco man’s attention on standards of performance, Unlike the past

T

here h s only measure of accomplishment was comment - or, even worse, lack

of comment

-

on his product or outputs, there are now published procedures he observes.

His work is carried out using these and incorporating h s suggestions.

No

longer are thngs

done the way that ‘our Mr Smith or our Mr Jones always did’.

In his home life, he has become accustomed to awards and award ceremonies for

everything from television soaps to good housekeeping, so that the existence of accolades

for ‘Excellence in concrete’ comes

as

no great surprise. Cubco man has always felt pride in

his work.

He

is aware that, as well as earning his living using concrete to build a bridge,

hospital, or somethmg as down to earth as a road or drainage scheme, he is contributing

to

the welfare

of

the community as a whole. Thus an award for ‘Excellence in concrete’

seems wholly appropriate and more meaningful than many other awards.



Excellence 1

111

/i,& of n i e Coi ic re te Society Awards, our bnejivas

t o

cons ider EXCELLENCE

inputs necessary t o achieve

the

standards exliibited b y

the

i u i u n i t ~ ~ qrqerts

We

pondered t l i r

. .

ENCI h ‘ EERI iVG

sk i l l s

and

a b i l i t y

E X T E N S I V E

plaizirin~q

videnced

b y

die outcome

of die operations . .

t r \

2



Excellence 2

3



Standards

\

No,

don

get

excited

-

we know the word

‘sturidard

is

e.rtrenielv eniolive

We are

using the word in the uppearunce

corite.rt..

._. nd,

while a

lot is

said

ut nieeriiigs arid

lectures..

.._we clre well

uwre

that

people

are

somet imes disuppoirited wheii

they see

the

real thing

_..about

the

dangers o sniul l

samples

-

products o the sample-maker i skills ..

The

Formwork Report*

has some good

advice to off..

Where there are speciul detui ls , feattires,

day joints, tie holes. kickers. strrrters.

retirrris

ctnd

so on

...

U

niodel shotrld he mude

to

emitre

that

i

E.speciully rvheri they have taken coru ideruhle

cure over

desigii

mid detail.

. . it reconinieiid.y that. using site riiuterials

ctnd

t h e intended equipn~ent..

Of cotme. not every job cuii

,qet

(111

rnvard

-

.

._.

specially

the skills

on

site. .

stundurds are established

f o r

cletuil,Jeuture

und iriish.

ucceptahle staiiclurds are.

but at

least

evetyoiie knows what

t he

*

Concrete Society

Technical

Report

No. 13. Since revised as ‘Forinwork

-

U guide

o

good practice

’,

The Concrete Sociery, 1995.

4



Qu ali ty assurance

F i r m wisliing to become regi.stererlJrin.s of

assessed cupubiliijv within /lie BSI scheiiie

first

tlrrash out

[heir quulity

po1icie.s and

nominute resporuihle people.

Theri

an ussessnient

of

the conrpuny

s

people.

proc/uct.s

r i n d

systeiiis

wi l l

be

nifide

to

ensure

thut.

... clruwing office

uric1

orguriizution of qiiulity

procednres [ire

in orcler:

4 7

... loucling proceciiires,mid the ..

The qiirrlity niuiiiiul produced by /lie

hi

Iias to he

~sirbini t ted..

eyuipnrent

is

up

to

scrcrtcli.

Tliut

routine

testing

... rrnd

upproved

by BSI Qirol i t )~

Asslrrunce

Depurtrnent.

... /he qirulity

coritrol

system

of

checks

is

ripercited

us

it

shoirld

he

..

.slrlckirlg. stocks.

.

. segreplion

und disposul

of.suhstondurd

units w e ull curried out in the upproved

IJlrInnel:

The resir// s

Certificutiori -

und

N

continuing

surveillarice

to

ensiire [lie niuintenunce of

u

reudy supply of Q u r r l i ~ ~ ~ssirrecl

prooclrrcts

f o r

speedy

und

economic constr~rctiori

5



Eff ic ient cons truct ion

Wi th developments

in

informatio n technology and coinpiiter

applications proceeding apace, never has our mail beenso aiuare

o f t h e

POW

of in formation i n the desigii and planning stages of

a Contract...

...

nor has

h e

enjoyed SiiCh high levels of comnniriication oii site.

Indeed, the term ‘informatio n overload’ may yet appear in

his

le.xic01i of comtriictioii terms

Rationalised details are ensuring speedy reitiforcement installation

and eco nomic reiise of expensive for mw ork iuith II rediiced

learning cycle for.

..

Materials obtained fr om ap proved,

quality-assit red

srippliers

contribute to th e maintenance of qiiality standards

...

All these fentitres make for sotind and efficient comtriiction.

ensiiring that gainful wor k f or all disciplines is available throrighoiit

the uarioiis stages of the constrrictiori process.

... the skilled workforce, ma ny of

whom

are certificated, and

operating sophisticated eq iiipnient at previoiisly tinimagined

olitpllts.

... con1bining at

site

ivith ‘state o ft h e art’ technology iuhere, for

example, magnetic impulse arid iiltrasonicpiilse readings provide

immediate rneasiires of performance.

As a resiilt o f t h e rediiced incidence of ‘snags’

on

completion, and

with

less

cutting and re-remaking during construction, the

use

o f

electric h am mers and ciittirig tools has become something of a

lost

art to oiir niflti

6



Testing

TTiere appears

to be

tio end to t h e tests

w e

are

required 10 apply to

corrcrete

i n irs various states.. .

break

it, in

a variety ofititeresrirg ways

, i

11 $,

We

may have

to 'slump i r ' .

.

.

'Juiii

test'

i r ,

Orr

site u x

may be called

upotr to buzz

th i rgs

Jigq' i t . .

through

i t . .

Botrtice thirgs o j i t , and getrerally mistreat

it

It's

a

salutary thought, however, that although we

put

a

l o t

ofstore by the results

...

atid whatever

the

boy$rrs come up wi th next,

as u d l as the samp lirg procedures, uh at we mostly

test is..

.

the specimen producer/selector,

the

tester

and the test equipment

7



More test ing

8



The Concrete Society

Although his firm had not yet won an award for excellence in

concrete.. .

our man was prompted to find orrt more about The Concrete

Society.

I n

the magazine CONCRETE, he found descriptions

of

the varied activities ...

such as site visits to prestigious contracts around the coimtr y

(safe. bitt not always fo r the faint-hearted ) along with ...

He noted that seminars and meetings were held both locally and

nationally, often in cooperation with other profcssional bodies, and

that th e Society participated in, and coordinated, research and

development programmes.

and that the chap who had come onto site the day he had a

probleni had been an engineer from

The

Society's Advisory

Service

exhibitions and deminars providing a forum for demonstrations

of

methods and eqiiipment.

He realised, to o, that ma ny of the reports and current practice

sheets tha t had proved so helpful with his knowledge of concrete

testing and interpretation of results were Concrete Society

piiblicatioris

...

Wi th all these benefits in mind, our m an decided

to

join and, not

being inclined t o hang abo ut, filled in his memb ership application

fo rm and posted it straight away



Awards

Learniiig of the factors

assessed

by the judges while considering

submissions for Concrete Society Certificates of Excellertce, our m an

visualised..

.

On

sire, it is unlikely that the ground worker, impressive

i n

action,

...

. . ...

the difficulties rbey would experience in comparing the (excellent)

achievemeitts

of

one

t e a m

of architects, erigitieers

and

coiistructors, with

those o f similnr teams

or the crane driver. workiiig with

his

bauksmnn and slinger to

meet t h e

d em an ds of th e ~ ~ ~ i ~ t r i i c t i o ~ ieam,

...

or the team members busy ‘assistrng’ the rendy-nti.ued truck driver to

deliver the right

mix

to the right place at the right time

..

or the fnlseworkrrs

arid

formuiorkers, together providing safe support,

the completed structure,

...

access arid working co?lditlonS atid determirlhg the Shflpe and fiplish

O f

or even the concretors, responsible for sound compaction, would

have

had much

time

during construction to consider the importance of their

contr ibution to the

excellence

o f the s tructure.

But, of course, whatever their task, everyone involved

in

a Concrete

Society award-whining project will he proud to

have

shared in the

achievement

mid will

enjoy the

reflected

glory

70



COMM UNICA TIONS A N D DETAIL

uring

h s

working life, our man has seen great changes in the way contracts are

organised and the skills of the individual are developed. He worked on site for

D

ome time before he was told how to judge good compaction, and longer before

he was instructed on the importance

of

weighng the constituents of the concrete mix

rather than batching by volume. Much of the learning process and acquisition of skills,

apart from trades such

as

those of the carpenter, depended on observing the work of

others, not always the best s u e d examples

The tide has turned and these days many employers carry out training on site as well as

encouraging training by sending staff on courses. Certification is now an essential

requirement of many facets of construction, particularly where the safety of others

depends upon satisfactory performance.

Our man is aware that knowledge is strength and is always keen to learn of new materials

and techniques. Technical representatives of the firms servicing the construction industry

make a major contribution here by demonst rating their wares, instructing on their use, and

providing a follow-up to their supplies.

Computers have become an essential tool in the construction process and are used by

workers at all levels. Th e batcherman, the designer and the production engineer all use

computers in the course of their day. Cubco man still has his reservations but has to admit

that drawings and schedules are more legible than in his youth, that goods are delivered

when required and machme maintenance is better organised than ever before.

It

seems that

even his wages are dispensed more accurately than when they were calculated by a

timekeeper with a calculator in his hand and

a

pencil behind

h s

ear

c



Drawings

17t 1

‘W

cbt bs,k

?\ dmA T

‘b ML.4

We trust

you w i l l excuse our presrmiption

in

warning against such things as redundant

dimensions.. .

.._uti- informative n otation and revisioi i - ut

this stage ui iarchy sets in

Handing was always a

problem.

And the iiote which said ‘al l us

MK13 RH

but

...

’

It ivas often /ielpJirl o

t r y

to sketch the item we

had u s t drawn to eiisure enough information

had beeii given.

Riiririirig

dimensions were usefirl whe re l inear

work was concerned.

Try to remember that the draughtsnian (or

draughtsperson) ca i i r iot possibly foresee a l l the

site

problems.

Aj ier al l . of ten the only t ime they get

to

site

is when there are diJfic‘cUlties.

12

Our e ight yews 11the drawing board

warned of

the

dangers of over-riotatioii

- he c r i t i cu l bit might be missed

We were sometimes ca ught out

by

the thickness

o a h e

..

oii a 1.1 scale things ( ire a l i tt le

differeii t .

We learned that the check in

the

oJke ~ v u sa r

eusier than the

o i i e

made

11

site. Often thefirst

time a drawing

is

checked

is

rvheri the carpenter

constructs his orni

Such

as

when some unintended geometry

creeps into

the

system.



Geometry 1

T

zzIzI=_

As

we

were

saying ...

i t k

sonietiines rlifficuli

to

visualise the inzplicaiionsof

a

line

on

the

drawing.

Change / h e section ( /he engineer will be niirch

happier with this thickening

at

tlze rooi

of

tlie

cuniilever).

Well, w e could either construci spiral

cohrniris. set

them on

an

a.ri.7 ind epen dent of

/he tower geometry

- or

make iheni circulur:

Well,

le/

s

remind hin i to look b r t rue lines and

dimensions: these und sonie carejirl thought

allow develop nient of&zce.s.

Crrreful

sectioning

reveuls we ’ve

ained

two more

firces than were originully uppureni -plus sonie

fbrniwork problems.

although tlze resirlis in

the

Reading Centre are excelleni.

Take

a balcony

- quure

in p h i wiih

upsiand

wall - niodify the

plan (tlie

urcliiiect j.prerogative )

The result - fnot ccrrejiilly p lu m ed

-

s problems in

consirlrciion.

Le:

:s

wuich

our

circulur work. However;setting

constnrction fab ric

nornzal

o

/he uxis avoids iricln,

form munilfaciitre, such

as

development

of

ellipses

c z n d

bevelled members.

Now

j u s t

f o r f i rn ,

design somefiwniwork

for

this

-

cas/ in

two

1iJi.s. Eusy with our nice ~last ic’ , , f ieslz

concrete. We ‘ve o niuke

euch

ac e icleniicul in

uppearance.

Let :s go

back

to

an old bogey ... raking

colirnins on

U

‘cooler’

._

liere:s a /rap

here

We ‘re

rlealing wiih well knowii

(to us)

principles

... how

/hough

can we

he lp

the

form worker?

OK, so now i f

s

puzzle time - how do we

produce /he suine appearance wiih hvo

separuie precust

elenienis

A

&

BY

(Possible

but highly iniprobable ) Answer

on nexi page.

3



Geometry

2

I \

Continuing from the previous pag e ...

yo u

could precast them this way. Possible but

improbable

-

he trick is the diagonal double

dovetail We could improve the oin t by

tapering the dovetails.

Moisture curing silicone rubber sealant

applied by gun can be used

to

seal between

mould sides and concrete, and so on. Carefirl

about waste

-

t’s expensive

st~@‘

There’s no right answer, but an essential

feature is a stable base which ifcom bined with

a side or sides governs geometty.

Steel m u s t be accurately locaterl- ockets

bolted to sides and ends can position lacer

bars

-

ailing that, there are always plastic

spacers

-

hoose the right shape and niuterial.

Seriously though -previous precasting

of

the

critical bits

ofien

resolves tricky problems.

The cured rubber strip can b e peeled froni

the concrete. When the casting is completed,

the concrete will be unmarked.

7-

Stopends deterniine the section and length.

Seals are iniportant, particularly in moulds

fortning visual concrete.

Precasting today implies mechanisulion in

some orm or other - watch the geonietty -

hinged cornponents niu.st c l e w US in door

geometty.

The precast pieces are assenibled into the base

of the main mould, Here we are casting the

bottom block upside down.

Now

let’s consider the nuts and bolts. You see,

when precasting we con (structural clesign

permitting) cust elements in U variety of ways.

to overconieproblenis ofj inish , cornpaction. etc.

Lijiing eqtiipinent is a separute topic

-

precasting is a mechanical hoiidlirig-iritensive

operation.

A good casting t e r m coupled with a rigid QC

arrungement and our main worty will be

where

to

stuck the product

* ‘The manager :s responsibility f or safety

’,

The Industrial Society, London, 1979.

14



Detail: the need

for

communication

Whui

toe

board?

Whai v ihe extension?

The salesniun said it was hixotropic

When s the nexi

sire

nieeiing?

4

d

d Q Y 0

d o

o

Are you sure ihe dosage

wus

5000ml?

1

The nianual said 7 tonnes

These high-frequ ency vibraiors niake

all ihe diference io ihe produci

Who checked ihe drawings?

There n n i s t he

ano iher type

Hard whai?

Where

b

the nieihod staietneni?

Perhaps ii k ihe plunib bob ihai

b

' ou r ' .

15



Detail: people’s input

Of

course there has ulways beeri the problem

of

ideiitrjcation with

the

product

Of

coiirse formwork is an urtfonii in its own

right..

We do get a bit

“blosi”

however. The passing

comnieiit was

-

“l f lwas pimping 25m3/hour

1

d

want to know where the other end is. I

16

Although such sitiratioris

do

provide un

exercise in coriiniunications

It

must

be

renternbered however

tliut

trrilike

other

iridiistries

where =+0.05 nim

will

“do”,w e

ave to be spot

on

. .

_

.-

And the

s l~upes

hat the dedicated steel man

can achieve have to be seeii to

be

believed

and compact

it, huve a vital impact on he

finished product

The comment

here was -

“ I

said all along

it said

ntmiher

5 1 ”

i -.

Regarding concrete .. the way we

mix it ..

Otrr service iridirstry is

second to

n o m ;

this

despatcher

was

calculuting

the

lady :s

reqrrirernerits o r

her

j s l y ~ o r i d

When

all is said

and

done, how eve^

we

huve

a great spirit of cooperation.



Detail: concrete

1

n

Badly-located drips can cause a loi of

problenis - et iswe adequate space or

aggregate and sufficient substarice

to

avoid damage during striking.

Slightly undersize kickers allow insertion

of

oam

gaskei to ensure groui-tighi joini

wheri casting column.

The 'joiriersfiietid' , ihe quirk, is

a

usefir1

device to help in curtailing exposed

aggregaie - watch coricreie cove<

however:

Recessed kickers can look well

and

solv e diJficirliies of colutnri/kicker oint.

Norniul variabiliv can

upset the most

nieticulous of details. remember forms

arid

mould

spread

arid

growili

'

d o w n

alwuys

occur outwards.

Filled iie boli holes look well whenjill is

kept j u s i below sur juce -plast ic filler plugs

get pinched'

and

are noi reconinierided

Surface reiurder 011 face offeutures which

ure

Iaier to

be iooled ea.ses stripping

and

frrcilitates tooling.

,

J

Forrners casting deep ji.aiures such

us

light

recesses, cable entries and

so

on, strip eus ier

with returder applied by brush or roller:

A layer

ofresiri-itipregiiatedglass niat on

ply nioulcl aces assisis in reducing crazing,

otherwise occurring on sniooih

faces.

The implication o f ines on drawings spring to

light on site

-

we

don

r u i e

the

chances of

survival of

t h i s

deiuil very highly

Talking ubo ir t pinching

-

watch out f o r

grooves

und features which trap fornis

-

xpensive

damage

rnay

result.

to

o r m

f ace

and concrete.

An

odd

one rom ihe deseri Plastic downpipe

proiects

plirnib

line froin wind

-

what about

danipirig bob in ja r o fwatec then

17



Methods and communication

The

most

inipressive chart is

useless

i it

cannot readily be interpreted by the

siniplest per.son to be infornied.

Cliarts are conipletely useless i

out

of

date

or not

niaintuined

Out-of date

drawings are dangerous,

inark tlieni careful1,v

-

keep one set

fo r reference.

Histograms identify peaks and are easy 10

understand.

To check a drawing or

full

information

tvy to draw the elenient or detailfroni

inforniution given.

\

.

I

,

, , ,

. , , ,

.

. .

. , , .

.

. . . , _ ,

Don 'r leave stairs behind, however

-

h e

aniount of deck r apidly diniinishes.

Siniplicity improves cornni~rnicatiori

nuniber

1 i j i . s

and

operations

an

master

sheet, rind use numbers us reference

in

conversation.

Overlaps ensuring continuity of work

are essential

Keep those 'dim books and site diaries

too

-

they w e vuluable

sources

of basic

d i m .

Work at sever ul levels u t one time ensures

continuity or all trades.

A method statenierit or hundbook

avuilable to all provides the knowledge

essential to safe working.

Even U blackboard on the wall in

the

site

office is a start towards more coniplete

conimunication

18



Pane1 jo in ts

Rugged

treatinerit

of

c o r ne r s will

resrilt in

rugged uppearunce of jo in t s -

some

urchitects like this.

The use of

chunfers r ind

margins 'tidies

lip

joints ' und

makes

for N

better production.

I

Regurdirig jo ints - we shotild renieniher t h a t

inaccuracy i n any one panel

may

afect t he

perforniunce of

any of t he 24

other

panels

o r

elenients.

Where

seulurits

[ire

used,

defects

cuused

by t l~e

moulds uhsorbing conipactive efort

arid

cuusing

eritrapnierit

of

air arid writer:

niust be

f i l led and a siiituhle

pr imer

applied.

Drflerentiul

citririg resultingfroni

orientation

in

tlte

stuck

can res i i l t

in

iricicciiracies.

Movenienrs

are mother considerution.

We

huve

been aniozed how IJiohik concrete

cun be in e.rtrenies of

teriiperatiire.

how it

cifects o the r eleiiierits.

Joints which are nurrow do not necessurily

work well - he sealants cuii onlv ucconiodate

niovenients of about

25%

of their owii width.

Norniul vuriubility of production can also

be

a

prohleni.

Look

u t t he

nianufiicturing

dates

-

pre-groding

of panels is possible

-

and

"visucil

adjtistnient

will avoid

local

exceptionul

joints (if it was

OKfor London

Bridge it niiist he acceptable elsewhere )

The iritrodiictiori ofcliunlfers

c i n d

bitllnozing also a v o i h ragged edge.s -

allowing aggregute to i l l t h e nioiild

-

he

corners are ulso

susceptible

to duniage.

A n d

how it

bows when

restruined...

these

moverrieiits

must he considered

i n

design

ofjoints.

Where possible.

serilunt

set into the

structure thus, works well.

Use the

snnie

.sealant

teain

throughout

the

constrnction. Their pride in their work is S O I J ~ ~

guaruritee

of

sulisfactoni

work

79



Computers in construction

--_--------

Our man is impressed by computer-aided design techniques,

but hopes that the people in the office fu l ly understand the

implications of their outp ut.

1 . 1 I t , / .

He is aware'that databases ease the work of the estimato

...

while realising the economics achieved b y computerised stock

control of the product of repetitious processes, such as flooring and

block manufacture, as well as in warehousing and similar tasks ...

and element checking in precasting - can be computer controlled,

our man is at a loss to know w hy ..

He appreciates the ease with which d etails can be produced (and

modified) and wishes that revisions could be made

on

site with just

a click of a mouse

and has always done his utmost to work within the rates they set,

as well as meeting the production demanded by the network

experts. However...

and noting that many demanding operations - such as comparing

process data in the course

of

slipforming operations

...

as they are in industry, com puters aren't able

to

predict the lottery

numhers that wo uld transform his role fro m that of producer to

client

20



Computers

The

irripact

that niicroprocessors ivoiild have ori oi ir

indiistry becariie opparerrt with t h e f i r s t

aritorrratic

batclziry arid iiiuirlg p lnr i t

I

I L,,k

Sirice

tlieri a i i to r i ia ied

cirttirg arid beridir q

riiachirres..

arid

die

sk i l l s of the rriari s p r a y i y y - t r p GRC b e i n g

riiiirirriised b y

r o h t i c s , a r e arrrorg app/ icat ior is that

have cor rriied t h e i r poteritid.

Nor

or i l y

lras CAD revoliiiioriised

the

d r a i v i r y

l ce.. .

At

tlreforrnworkfabricators,

the CAD

systerii

trot

orily prodrices

desigrr

and

derail..

.

.~.

6irl also cor i tro ls triadiirres i r i

t h e

works ,

re-orders

riiaterials arid

plaris t h e

i ise o f ~ ~ c i i t s

- "

.

. * I ,

c o r r r p i i t e r cor?mil/ed arid recorded checks or1

precasr

elerrieirts..

With all this,

it ioori/dri'~

e siirprisirtq

tofirid

oiir

clrap o r i site 6 q y i t i r i i r g

to

ivoi ider iiil~erihe is

to

be

replaced b y

a

'chip'

21



Computers

and design

Our

man

k

briefJlirtatio,i with his home PC

had come

to

an end an d, although they were

-

to

his way of thinking -par t of 'hew

t echnolog '.

...

when engineers used the

techriolog of

the

day

-

lide-rules arid calcula tors in many

sliapes and

sizes

-

al l claiming

to

get the best

approximatioii

to

a result

.., he

had

to

admit to a srieaking admiration

fo r the CAD operators he met i n his work

On efir m had seveii C AD statioris operated

on shifis

His thoughts went back to the days when

most design arid detail work was done lorig-

hand

...

He only hoped the present-day CAD man

could recognise

an

approxiniatiori when he

eiicoimtered on e.

The last approximutiori our

man

had met was

while coririectirig up a p i p e behveeri silos

Mainl,v, however: he recognised the

benefits

o

computer output such as handy-sized

drawings (many including the bending

schedule)..

.._ uch

a

pleasant chungefroni the

drawings

of

yesterday, especially in had

weather or exposed conditions.

He thought to himself

' I

should Jirid out

more

about

tablets. layer s, overlrrys cud

so

on . The way things are going, a little bit of

extra know-how will

s tand

me

iri

good stead

for theJirttrre '.

22



FORMWORK AND FALSEWORK

ur man has seen reports produced by experts on all manner of formwork and

falsework matters such

as

safe loads on props, the development of concrete

ressures, achievement

of

surface finish, wind and friction loadmg and

so

on.

These and many other topics previously comprised the ‘folk lore’ of formwork. H e believes

that the publication of the collective knowledge of such committees must have made the

site

a

safer place to work.

As well

as

seeing permissible lift heights change from a few feet

to

many metres, he has

witnessed the emergence of sophisticated equipment and methods. He estimates that, as

a

result of the adoption of equipment such as table forms, jump forms and slipforms,

outputs per man-hour have increased more than tenfold. Safety, particularly at heights, has

similarly improved.

Much of his work has been simplified -by kickerless construction, for example, and by the

adoption of expanded metal stopends in even the largest lifts of slab and wall. In the

simplest of construction tasks, he is aided by the huge range of accessories such

as

small

panel systems including ties and spacers as well as disposable forms for use in the ground.

23



Sett ing-ou t po ints

Perhaps we may he excused or

metitioning the

3,

4, 5 tria ngle iri

estuhlishing right-angles

_.. he batten to plot arcs

o f

large

radius kriowirig the chord

lengtli

and

rise.

When usirig builder k level and a

board to traii.fer datum s. rotate

hoard to average out any

discrepa ncy in either.

C

Cones

mid caps are easily developed

usirig

radii ah

and ac -

visualise

unrolling slieathirtg until length of top

liiie equals circunference.

And the use ofun equi-marked batten

to divide spaces into equal purls.

These are well known techniqu es arld

very practical. too.

f

We have seeii checks o r square made hy

measuring diagonals The small figur e has

equal diagonals, check side lengths as well

Perhaps less well known is the

p l y

square used to descr ibe semi-circles

0 1 1

a given radius and ..

The lewing surface is widely misunderstood,

where

one

coriter is out ofplurle of the other

tliree theii we have aflewing surface. Watch out

-fo rm s and coristructioii are expensive.

When setting up datunts. initial

and

date your level and record meaning

A record ofirzaccuracies may save

time in months to come.

With hoppe rs and mitshrooms rememher

to

deal

with tr ue lerigths

-

he splay

cut

at

X i s determined by 90' cut set out a j k r

top

arid

bottom bev els have beert struck.

Ellipses caii he plotted by intersections

of

horizontals and verticals run i -om points where

comnioii radii cross circunferences of circles bused

on

major and miiior axis - therwise

use

a tratnmel

with

ama

and am i marked and travel these points

a long vertical and horizontal axes.

Tlie mortar dot

11

concrete improves line

accuracy and the cost of

a

permuiient opticul

base will

ofreri

he amply repuid hy

ease

of

setting out. Provide lockable cover to keep

intruders away

24



Detail : fo rmwork

There's not a lot to say,for the results of I

planted chamfer fillet

Precasters

find

the extruded plastic or

allo,v

sections ideal f o r orming

small

chamfers.

Built-in featu res. wliile more

costly

originally,

cast crisper detail and provid e grout-tight

joints. than paste.

Bull-nosed

corners can

he

neatlyforiiied

and

the orrises illed with aggregate rather

Featurefillet jus t

b lan ted ' onto

tlieforni,face

becomes

displaced arid trapped by infiltration

ofpas te but

.._

... a secondaiy layer

o

thin ply

or hoard

avoids the problem and provides butt joints

to

resist grout. The )>encil'rounds

help

in

striking operations.

Where illet must remain in the

coiicretefi)r

sonie tinie, saw kerfing aids eventual

renioval.

I f

square sides clre speciJied to recesses,

a

two-piece ornie

E . .

LU

Larger oriners,Jirhricated and bolted

to

t h e

forni face using tapped plates or plates with

welded nuts at the concrete/form interface ..

...

eau

he ieer l afler inairiform renioval by

reinserting bolts. The acking action against

the concrete Juce gently ye t j rm ly s t rips

,former: Renieniber end

splay

or draw

... aid.s striking. Half the eature reniairis

f i xed to the orni

and the

reniaiiider is

stripped out

as a

secondaty operation.

Detai1er.s can assist in uchieving excellence

b,v m asking horizon tal joi nts in

striated

work in the shadow

o a

recess but they

ninst

he

alert

to

maintenance o cover

25



Kickers

1

Kicker forination

is

an ersentral part

of

the

"

constriictioii process. Whenever possible

kickers should be cast monolithic with slabs

Shallow kickers of what would

be

scrap

concrete

form

possible points offuiliire.

15Onini

+ depth of kicker allows correct

coinpaction. Ruled join ts should be

included i a fe n i ire of general

construction.

Kickers brought to iiniforni level help to

simply$ succeeding lijis.

Kickers are essential in circular and

geometric work -providing a check 011

accitracy of setting

out

arid governin g line of

fornis above.

Where coniplicated columns are set

on

rake,

kickers provide acciirate location and simplify

fornis above.

. .

. .

Siinple cast criiciform concrete bloc ks..

Kickers provid e restraint. ensure grout-tight

1

of

orni and assist in locating openings.

Kicker blocks set in blinding can

he

used

Depth o kicker provides scope

for

levelling

forni.

... o provide bearing for props and pages

Space forms arid govern

loor

zone as

well

as...

Providing Jixing or urigle steel kicker

fornier.s.

26



Kicker foriiis coil be

siiiiply secured

bv V-slottedply

cleots

driveii

onto

reinforceiiieiit.

4

9

A soc~iidly onstrircted re-usohle kicker foriii

puys oflwlieii

iiioii,v

kickers liuve to be

foriiied.

Kickers

2

A

plute

bolted iiito tie udjoceiit

to

kicker eusesjbriii

locutioii.

steel

reiiiuiii

us periiiuiieiit

foriiiwork.

27



Ni bs

and

corbels

Nibs are

to

walls

as

kickers are to slabs -

they provide grout-tight purchase or return

bay formwork

..

Nibs C U I I be simply formed within irst layer

of for m carcass.

Corbels in precast

elements

present

d f jcu l t i es in i l l .

_..at cross-wall locations

Corbels

ofren

determine

the

horizontul

cons/riictionjoint position. Corbels at top of

lift

ullow good compuction

and

control

of

sleel location.

Rotate the unit to bring corbel

to

top: mould

must

be ree

to

drop away

u s urrowed.

.__nd

where

spandre1.s

spari

between

columns.

I n precast arid i n - s i t ~ i onstruction, it is oJen

permissible

to

insert previously cust corbels

into

the

main casting.

JScastface down,

mould must allow unit

to

slide

when

f o r m

is

rota/edfor

stripping.

Striking pieces allow the in-situ o r m

to

be

struck largely by own weight ..

,..

s o

slow clownfill arid inspect fo r

compaction frequently in locality of corbel

and don

'I

orget strippingJllet

Bolted

pcids within main for m allow corbel

casting without damage

to

main form.

Thiri

p1,v for m s templa te to locate projecting steel.

28



Cores and formers

Tiniberjilleis

ciiid p l y diuphrugiiis forii i

economic cores: pins ihrough hoiisecl

buiieii preveiii tiplift. *

Coiicreie

blocks

loccrie siressed wires:

U

wruppiiig

o

polythene or crujk puper

conipleies

core. *

Sieel iuhes u n d ubricuied c0re.s renioved

hv o

hours cfter cusiirig

orni

cuvities ecoiioniicully fithe is

hvisied to strike. Boih c m be pulled itsirig ‘rutchei

bourd’

mid lever:

Tiinber,fornier depend.7 on wedgiiig actiori

witliiii

orrii

uperture to inuiriiuin shup e.

Eusy

to strike.

Fouiii-plusiic-filled

po[viheiie iuhe

restruined by

siressiiig wires. *

Coricreie

blocks w e ridestriictihle. The wruppirig

o

ihiri

e.vpuiided polysiyrerie

simplifies

release.

niper

erisiires

ihui

block

does iioi

full ihroirgli

sluh

ut time ofstriking.

*

Puier i ied

Meiul

pluies

locuied ( I ) by ritbber inotrldirigs

mid

(2)

by irljlaied

iubes,

ure eusily collupsed

for

recovety

*

Throitgli holes

cuii

he oriiied usiiig iiniber

bohhiris, dowel

reduces

size of hole in orm

Spiral woirrirl curd iiibe

peels

from wuriii

greeii

coiicreie.

Expuiidelecl

polysiyrer ie

wrupped with plusiic

bourd resists inipuci of pokers. Adequuie

resirairit is esseritiul.

Oiiejor

the iiiriovuior

Root

veg shririks

oiri

US

ciiririg proceeds. Sirgur retards fuce of cuviiy



Ramps and intersections

Forms for

spiral

ramp so f i ts are di f icu l t , especially

when splayed sofJt

is

involved.

i

Simple standard tr usses of timber uiid plv cull he

prefabricated on site

or in yard.

Where special unit or table type orms are required,

constnrctiori is eased by assemb1,v o ver Jiill-size

set-out

on

slab

or plv deck.

Set radialb, the

trusses

resolve the geometry

and

simplify

shealhirig operation s.

Tumiel inlersection s with shujis cari present problems of ormwork

geometty.

Here

an

oflset

intersectiori is

set

out

uwuy from the

actual

job.

ProJles spot

tuririel

hi e s relative

to

section

of

shaJ

lirling.

*

Tumiel orme rs built over projles al low sheuthii ig-sh(~t

lining iiiter.section to he plotted urid shearhing

developed.

Chocks generate otherwise difficult-to-generute airing.

Fairing is sheathed usiiig multi-layers ofthiii p l y

or

hardhourd.

* The uuthor is indebted

for

this to E Consdale of Edmimd Nuttall

Lid.



Staircases

/ ‘

On a riuniher ofsite.s, stuir construction

governs overall progress in constructioii

so a capuhle sraircuse hand is riecessary

highlighring the

need

for eurly provisiori

oft he drawings

/

He has experience on his side and niuny

tricks

up

his

sleeve.

Keep an eye

on

the

wuy

he achieves support, however

To avoid rhe prohlenis resuliingf,.oni the

use offornis

as

a ‘right of ~q~’ , . ,

and the use of reiiforceinent as,footholds

Alternative

nieuiis

of

uccess

should

he

indicated

Precasting offers econoniy in speed as well as

simpifying th e inclusion of special finis hes,

riles, Iread~s, arborunduni fo r n on-slip

purposes

Edge casting eiisures two a ces and one

striiig of ex-niould finis h, as well as allowing

gang casting about af ixed centre fo rm

Doli

forget rheflrr t-lij points by th e wa,v

4

15 4

Geonietry aiid varying thickness of head

finish are traps or the U I I M J U ~ ~ffecting

concrete profile

...

Machiiied or pressed sections

can

save tinie

aiid iniprove coricrete profile where it is

critical

Our friend is hest used as a specialisr. moved

fioni job to o b os he is needed

Site precasting is best carried

out

where it

provides ‘hospital’work and where concrete con

he siniply placedfro ni the truck, or example.

31



Circular

work

Although we understand thot the Romans

used

greut

heaps of eurth ..

__.imber arid ply or camhers, concrete

fo r skewed camhers.

Ply

or

liardboard. a double diugorial hoard

over radial ribs gives double curvature -

spun steel skeet provides

mould

liners.

Thin sheet glass-reinforced plast ic and

glass-reinforced cement, either used

as

standalone materials or backed with

concre te, provide excellent

moulds

o r

shuped elements and products.

._. oday, even with all our urniouty of

materiuls and techniques, i rst sight of the

drurvirigs is oJen startling

The carpenter has many ways of deuling

with

corners

arid curves.

Modern materials, extruded

hollow

sectioris

arid polyurethane

can

he

used

to cast detail

work. The casting poly allows

us

to eature

sphericul sheathing.

For barrels and arches, the proprietary

supplier provides an econom ical solutioii ...

However, we have managed fo r years using

traditional lined rib arid lag girigforms...

Recently we even smv ‘Iiorsed concrete

nioiilds

fo r special elenients.

At the other end of th e scale, lightweight

expanded plastic coated or sheatlied witli derise

plastic is great fo r large voids, trans itions, etc.

hiit watch out fo r Jloration and displace ment.

,.. and when it gets real1,v repetitious or

complicated we mustri forget the speciul

formw ork sup plier with his electronics arid

hydraulics

32



Props and propping

Huving seen this x i - l i p recently we thought a

look at props could be helpj i i l

And this

-

riuils und re-bar just

won

? do

System props provide a b i d

in

assiiratice -

spucing,

lacing

arid bracing are provided fo r

Good oundutions are

criiical

-plenty of

spikes arid w henever possible siipport fro m

mature

concrete.

Huvirig

tuken u

close look - we

withdrew

to

iliink ihe

iopic

over

Oiri-ofplumb and

eccentricul ly

loaded

props lose about 50% of their

cupacity

Common props

niiisi

be laced and hruced -

large diuriieter

couplers

are

needed

on ouier

tubes.

Pltonb-in

one

or two props in euch

direciion and eye-in

the rest.

The wel l

calibraied eyeball is remarkably acciirate

This

convinced us ofih e

wisdom

of our

flclions

-

c

The ilted pins o f special

steel niust

be used to

enstire that liublished S W L call he swiained.

Always constilt the makers inutiuul. Soinetitnes

the

height

io

which

U

prop

can

be closed

is

as

irnportani

as thai

to

which it

can he extended.

Firidly -

ake advice on striking and easing

props iri tnulii-storey work. You build so quickly

these duy.s tha t problenis lend io

get

huili

in *

*

See

‘Forniwork- u guide to good pructice ’,

The

Concreie Sociey, 1995

33



striking formwork

OK. So the

concrete

is

OK -

what about

the orniwork

Ideallyfornis should he free to drop on

release of ties.

Moirld treatments are best applied as

mist sprays.

Avoid the

use ofcranes

in striking ruther

than handling

-

he man who swings the

block is a danger

to

hiniselfarid to

others- nd the concrete element.

A great deal of lieart-searching goes on over

types of release agents and so on.

The thin 'dog ? tail' wedge, whilst being

irridesirahle

in

other operations, helps b,v allowing

air in to break the

vaciiiini at

the orni/concrete

interface.

Precasters frequently m op off after ap plication

to

leave the

n i e r e s t j i l n i

at the suflace.

d

Openings afford

ciccess

or wedging

reluctant forms - avoid the pinch

bar though.

Tight oints mid nice points of o rm

construction [ire ul.so most important to resist

grout infiltration.

Earlv striking (conihined with

an

approved

curing reginie) avoids hang-ups caused by

shrinkage and swelling.

Rollers provide

e.rcellerit

applicators o r release

agents and returders.

Hydraulics

to

the rescue - everalJirms

market sniull potent jack s which used

strutegica lly ease the striking imniensely.

34



Aluminium forms

Bit/ there k little doiiht

t h a t

lightnes.s can p a y

off- 2 orms can

he

handled at (I time f o r

e,r.rcIniple ..

A lot of the odvertising

niutericil

is

reminiscent

oj

a n advertfor a well known Irish

)ick-nie-iip

'.

Available systems can be

used

for both walls

arid

floor forms. t h e .stiff.sections

rillow

siihstantial support

and

tie spcicings.

They iise

chemical release

agents to

avoid

'gassing',

ind

piit

011

a

coat

o

lacquer

every

10-12 uses in case of

di,fjicult,v

We 've

looked close1,v

at sites where

altnniniinii

systems

have been

iisedfor months

(in one case

more than a yeor) arid have yet to spot N

dcimaged

section.

The niaferial is clerin to work

wi th

too.

There s

been

the

pro

:s and con

:s

of ~ilaininiani.

lot o

disciissiori regrirdirig

Some

of the system cornporient.s

are

compatible

with

timber: Sections

include

timherJ7llet.s

f o r p(v or

shecithirtgJ7.rinring.

A hit dfferent

to

timber where we've seen

men

clciniber over

piles o short ends tojind

a

long lengtli

-

o clit down to

size

And t he size of tribles in oli irnii i i i ini have

1

he seen to he believed

And of coiirse /lie Aiiiericans mid Canada

huve

been iising

'ulli f . r years.

Circiilrr

work

can

he

curried

out using the

Jrriiig

pieces

rind

.substrintiril

plates

bolted

10

webs.

P

They '11hove (i

job

with this olwninitins

-

hope

the

suw i s a borrowed one.

35



Trough and w aff le f loo rs

A Concrete Society working party worked

hard to produce a guide ...

Formers are extremely robu st although

sometimes almost transparent.

. . .

Uneveri application of striking fo rce cun

jamb ormers and cuuse hang-ups.

The air vent is not a gimmick, air has

to

percolate into interface or for me r sta,vs put.

Don

t

forget to tape the vents prior to illing.

A s to sections and sizes m i d the code

requirements - here is however plenty of

scope o r specials.

They can

be

phy.sically designed

hut

deflections ure critical

rrnd cc117

affect

striking. The specialists have this 'weigh ed-

up ' of course.

We've seen

superb results, from varied

depths

of

w@'e f o r e.raniple.

Care is required regarding choice of

rnateria1.s irt

those

countries which see the

sun.

Excessive local application o f release agetit

has

been

known to cause retcrrdation

t h u s

negating lead allowed 011 former: Control

the application which

must

be by

mist

spray.

111 case of sticking very thin wedges allow air

/o irifiltrcrte arid fre e or me r -g iv e it time

however:

Quickstrip is eased in 'traditional ' supports

by providing 1mm+ clearance overjoist

dimension. System supports of course ullow

normal quickstrip action with support at

intersections of ribs.

0

Rentember

to

irljorm this chap crboirt care or

equipment, / S l l , O O O of u s readers

cl0

it the

message must get through



GRC

fo rmwork

Glass-reinJorced

cement permanent orm s allow the

designer coitsiderable freedorn

as

regurd.s te.xture arid

features.

The use of

GRC

form punels allows

the provision

of

special finish es - white cement arid exotic aggregutes

without resorting to through-mixes in horizontal,

vertical m i d sloping

faces.

PuneIs can be clesignerl to reduce or eliminate

support requirements.

Pre-inspection offornl puriels ensures

satisfactory ii1islie.s

to

concrete structures

bejbre ariy concrete is placed.

In conjunction with polymer

form

liner.s,

interesting testure.s can be provided: no rieecl

f o r lead

and

draw

here

Eliminution of

striking

operatiori free.s men jor

more

productive

work.

Location

of

distribution steel

is

governed

by

h0.u st f leners on form

panels.

,

\-=-----

The GRC punels can

be

munually

hundled with euse: impact re.sistance is

good.

Munr~acttrre s relatively

straigliqonvard using simple moulds

to

generate many o rm units , , .

... mid QC nieusures using 'bag m i d bucket for

exumple maintoin adequate control.

As

well

usformwork, moulr1.s

for

precast (and

GRC) are

i d e d

products.

A

soon-to-be

published design manualfrom t h e

GRCA * will prove invuluable

to

specifying

uuthorities,designers

and

producers.

*

Guide to

GRC perincriieiitformw~~rk.ew

edition in prepurution

(2002). See

also Permanent

forinwork

in construction. CIRIA Publication

C558.

37



Formwork fai lure

. .

. .

.

Not

all fo rm ailures are drarnatic -

although this is how the author k interest in

formwork came about

Failures of the less dramatic kind happen

quite a lot - specially in other people

:s

concrete

oh)

u A L L

Once we recognise the symptonis (such as

local sheathing deflectiori at ove rlaps) we

cui1 take steps

to

correct them.

Another old chestnut is the nib criused by

second deflection where

we

stop-offa pour

part way up

N

o r m

-

an anchor

or

pigtail in

t h e j r s t part of the lifi secures form.

Stopends rarely get the attention

necessuy

to achieve good results. A s much as 60% of

labour can

be

in stopends and day joints -

care in design can make substantial savings

and a void unsightly defects.

Similar deflections cause

nibs

under day

joirits and construction oint s in slabs.

It 5

amazing

how

heat (h ydration ), pressure and

ntoisture cause quiltirig, but then

that

5 how

w e

make bent-wood

chairs

Reduce

spacing of

backing members.

A t

the risk of being boring we must mention

high incidence offiles caused byflutter

induced by vibration und darkening at corners

cruised

by

leakage.

Quite apart fro m th e initiul urge to do

something about

them ...

We can overcome the

problem

by inserting an

a t r a backing member at the oint with

previously cast concrete.

Fewform s are seldom quite "correct to line

and level", it

k

the second layer of carcassirig

which

controls

line.

A little time in stacking

or

rucking orms

between uses

can provide r ed econornies

in

terms of enhanced reuse.



Formwork

CL--- ---\-

Time to get down to

some

detail CONCRETE

presents

a

commentary on the skills em ployed,

for

ever Nfter

Have no ear Help is available in The

lnstitiition of Strirctitral Engineers an d The

Concrete Society publication 'Formwo rk

-

a

guide to good practice' ... It's

a

"good read" for

wet

days in the office

Special form wo rk manufacturer.s have some

neat details fo r sealing joints

(A).

I n traditional

workfoani strip can be effective (b)

...__

ut

beware displacement. For critical work one-

part, moisture-curing sealants are effective (C).

Sheathing deflections con occur

at s t o p e d s

located within contirnrous fo rm s, and in slab

construction against previously cast bays. 111

both

instances

it is unlikely that join ts co incide

with backing members. Avoid "curtains" by

inserting extra "noggings I.

-.__

_.

Stopends. seldom

designed

or

detailed,

must sustain the same pressures

as

the rest

of the

form. Deflections here will be

evident

on

the inished face.

I ~ f o r m a t i o nr o m

the

"Guid e with input

from the practical man

on

site ensure

attention

to

critical detuil such as ..

I n Just tracking ond less critical work.

forms may be located employing kicker-

less techniques

...

using proprietaryfittings

(A), />recastblocks in slab (B), spacer.s

(C&D ). external plates (E) o r plastic

channel spiked to slab (F).

Sheathing

must

be soiindlyfixed

to

bearers, flutt er causes upset to vibration,

the resultant line

of

which can be

rerid on

the&rce

and may prove

to

be

up to

50mm

deep

when the

ace is

tooled.

O~~eriirigormer.s are another

key

area ..

pressrrres fro m

placement

build

up,

causing

surprising orces,

... importance of kickers in geometrical arid

visirul work, providing locution arid a seal

against grout

loss ..

provided the support is

applied correctly.

Stopends

should be ixed through into

backing m emb ers, e.yternal ties support

wide stopends r om form carcass. Joint

rule

fillets are as effective here

as

they

are at

horizontal joints.

Of coiirse concrete placenient

and

vibratory

techniques inlist be m atched

to

the orm

design and method

....

we will look

at

this

another time

39



Form

w o

r

k systems

L e a v i t g

his

collea~rres o nraintain the wntc/r./or ‘ b r i g s ’

i n the cotnlniter, oiir man th r r tn l~ed h r o i g h a brochrrre

dcscribiii,y

proprieetaryforriru4,rk~irk ys tems

He rccaalled the ‘rrenr mortal co rir l~ t’ ndrrred in

nsirg

w h a t was a h v a y s k n o r v n as t rad i t iona l urmrvork

H e ~ r o t ~ dhat srcppliers ivould provide proditct

siipport based rrpon experience

p i n e d

in the course

~Jpr estigio irs contracts

aboir t

t h e world

Propr ietary equ ipment* he learned ,

corrld

s i g n f i c a d y

redttce

the

n u m b e r o f t h ro i r q h ties reqirired. 771is

pleased

h i m os

h e

h a d

experienced

some

prob lems i n

the

past,

particrrlarly hen extracting toper ties t h i n

e n d j r s t )

Althorrglr the d a z z l i n g ormoirry o f

components

ava i lable f r om the ca ta logne

umuld

obvioirsly present

h i m toith plenty o f o p t io n s o n s i t e . ..

The cost o f m a k i i ; y f o r m i o a r k ivoirld also be rediiced.

For example, i n circrtlar

and

tapered

i va / / i i g

steel

edyin ‘gs , so ld ier m en ibe rs , fork arms arid tribes arc’

iised

in c o i ~ i i n c t i o nwith t u r n biickles so that p l y f a c i n y s c a n

be radinssed

to match a

template - n o m o r e e x p e n s i v e

shaped r i b s or rolled sections

1t1brochrrre illrrstratiotrs, he noted

that

t h e f a b r i c o f

m n c / r propr ie tary formumrk permi ts srrbstontial

sections

to

be h a n d l e d

without dismantliirg ber iveer r

uses,

thus

reducirg work

content

a n d

speedirg

th e construction

cycle. The i v o r k i i g p la l fo rms travel too

the

technical

i i? for ina t ion , drawiqs arid method

statements

pt tb l i shed by

the

supp l ier

m ( f h t well

preven t

some

p r o b l e m i n

the

c oi rr se o f s t r i k i r g f o r m s . . .

j o m a c a n r il e v er , fo r i n s ta n ce

Readen

will

appreciate that our man finds

it

difficult

to

identify any specific supplier’s equipment

unless, that is,

he can

see the colour

of

the paint

Bearing in m i n d

his

concrete techtiology, o i ir m a n

reckoned

t h a t ,

by cap i tal i s ing

on

the

b e n e j t s

o f

proprietary

f o r m w o r k i n combina t ion u i th sound crrr ing

practice and es tab l i shment o f striking times r r s i r ~ y

reinperature- inatclled specimens, considerable savings in

t im e and @rt ivoir/d be achieved onfrctrtre contracts

40



Falsework

1

A greui deal ofhord committee work ..

T-

It

rnukes

gripping reading - udvising

umong

other things...

._.

nd

emerge

some

time

laier

with

a

sertsible form work design

I

-

...

and some considerable public comment

preceded.. .

._. he ~JUh~iCaliOnfthe new

Code BS

5975: 1982

Falsework.

.-

.

...

the uppointineitt

of

a

falsework

eo-ordinuior directly responsible

io

the site ntunuger:

The Code

seems

to be devised

so

that

a

suitable yiraliJed persoit could

disappeur into

a

site

office..

The

Code

points

out

ihai

every detuil

of

the sclieme must be considered ..

... and decisions made on method.

The muterials are usually second-hand and so

need partictilar1,v carefiil inspection.

We are told tkui falsework failures ure ofren

sideways und that we should identify the load

patterns and take steps

io

contain them.

Oh, and that's usi the beginning.

41



Falsework 2

Reverting to the Code, Falsework

BS

5975:

1982, we are reminded ofsafe

working loads or adjustable props ..

.._are warned against drilling milituty trestles

..

.._are given useful guidance on wind

forces..

_..

and on ensuring the stability (and

qualiry) of individual members.

Puzzle corner? Figure 25 dealing with

concrete pressures gives plenty of oo d

fo r thought.

I--

? TL .\J

Table 31 raises some iniportant points on

uristiffened webs acting as columns.

\ r

No, not an advert fo r 'Juw s 11' but a source

o

information on wave forces for the advanced

falsework designer:

Figure

10

is representative of a lot ofjob s

we've seen - even as a r as the 'Kam ikaze

dumper driver:

This rings a

bell

somewhere

-

a w arning bell

perhaps.

We

are also warned of th e dungers of

impact ron i floating objects and the

need to avoid a build-up of debris.

Regarding impact loading, we are advised that

the larger the loa d, the more carefully it is likely

to b e placed.

There is also a warning about the eflects

of vibration

42



Falsework 3

The code

BS

5975:

1982

reminds

us to

check extensions

at the

foo t o f

standards..

...

may pronipt

LIS to

seek a glass of the

well known cider advertised in Figure

28A (Oh no, it is

a conin ient on

rotational

and positiorial restraint).

It

wus nice to

see

our old friend Figure 13:

the

code would be incomplete without it ..

and

a t the

head

The comment on spilluge adding I.Skg/ni

o

the

niass

of

tube mqv

provide a solution

to the

age-old

problem

of where

the

estiniator

.s

5%

w s t e went

so much

nicer

thuii

this

uttenipt

Expeviencing

the

accumulation of debris from

frrie

cleaning/boilerscalirtg wliicli inay

have

a

clensit,v of 1600k g/m' (and thus impose

substantial loading on platforms).

A-

We

tliougkt

'Bailey

Bridge Fatigue ' was ail

army complaint warrunting

M + D

until we

read pag e 59

v

The code stresses the iniportance of details -

otnissiori o f a bolt o r wedge ..

.._or failure to tighten N bolt could l e d to

local instability that might endanger the

structure

We

have

found

the

prototype

for

the map

the

~veathermuri

hows

us on TV (noticehow

eveiything revolves around London).

A l l irreverence aside. however; there can he

no doubt

that

the code provides a sound basis

f i r those designing,

constructing

and

checkingJiilsework.

43



Formwork and fa lsework

1

Wi th safety In mi nd, our ntan reflected upo n

the nature

of

the work of the steeplejack

“Nothing.” he thotrght “ Could induce me

to go u p there ” But, remembering some

of the hazards encountered at site and

highlighted in Th e Concrete Society?

best-selling guide ‘-

such as formwork detail that had escaped

the eagle eyes of th e foreman carpenter.

..

out -of- plum b props and sirbstandard pins,

the despair of the site engineer.

..

rrnbraced and unlaced supports, not in

accordance with the proprietary suppliers

manual...

support taken from po or foundations,

to be discovered, we h ope, in the

pre-concreting check ...

changes in placing m ethod. made with out

reference to the planning engineer and the

formwork designer...

and striking procedures other than those

set down in the method statement -

he thought that, all things considered, he

might be safer up a chimney...

Formwork

-

a guide to good practice. 2nd Edition. The Concrete Society. 1995

44

then he thought again



Formwork and falsework

2

Wheir

forniruork a i d falseruork corisrstcd i m r r i l y

of

ncres

of

p/ywood aird

stmidnrds

of

tiriiber sripported by

n seii of

props,

riiitch of

t h e iiiaterriil

ruas

rirorrhoirdled hetiueeii uses.

W i t h

fa lsework,

the

cnpncity

of

props

ruas

siidly overestiriiated.

Apart frotit forriiiirg air nccident bazrrrd, props tbnt ruere

~ ~ r t t - o f - p l i t ~ r r l ~ ,cce,itrically loaded or

wer-c.uteridcd

caitsed

prohleiirs

of

displacemerit

nird

loss

of

litre

and

level.

A/thorrgb mo st coristrrictioirs iiiere robitst a i d strrtctrtrally sort id.

r i inriy

left

irtirch

to

be desired. The iiioir on th e 106 d rew

O I I

I i is

csperie iice h i t o f tei i

ium

rtriniurrre of t h e prcssrrres

mid

forces

dClW/ l Jped l U / J C I l COlICl’efe lWS / ) / i lced.

Fai/rtrrs ocused

the

ntto t t io i i

of

reports, stniidnrds mid codes,

mid

csseritid cl~eckirig

vd

ccrtificntioir tuere ititrodrtcetl. As n resitlt,

tue

1iotii haiic skilled sofc

ciird

efficieirt use

( J / O

vast rouge of materinls mid

techriiqiies. Spoce perittits

orily

o fciv e.uniirples

h t t

it is cielrr thn t ...

... iiieclJniiicnl

haiidlitig

110s iiicrensed oritpiits.

as IJns

slipforiiiiiig

-

particrt lnrly j i in ip fo r~ni~ig .ulieru iritegral platforms improve access

arid

rvorkiiig coitditioris.

T l ~ coriiiruorkeri bogey - crtrveti oiid s h ~ p e t iuork,

oirce

a iiiiijor

item

of

cost - call

I I O I U

Be prodiiced ecorrorrrically rtsitiy oire of

several

systems

that permit geometry to b e

achieved

wi th a titrir

of

tr screiu.

Speciol f i i r islJes. oiice

so

costly to produce. call he foriiied

simply

mid efficieiitly froiir

II

iiariety

of

h e r s .

s(iirre

h e sp o ke

to

meet

a

desigrier’s reqiirreiireirts. Brit th cy

coil

b e I J ~ L W ~ o Iroiidlr11g

teckriiqircs require stirdy

L o ~ ~ k i t r gt illrtstrntiorrs of iiiajor comtrrtctioirs. oitr r m v i gets t /J C

fee / iirg that form uor k mid falseivork desigil

often

preseirt grenter

prob/eiiis

thrr

thos e ericoiiirtercd

1 1 1

desigriiitg the stritctitre itself

45



Formwork and falsework 3

Originallx forntinork iiias the province o f die cwite ri~r ii,itb

liriiited to a l iamnier, saw md rinilhi~r.L a t o t h c iimrk rleiioli~e~lpon

the cnr/)enter,perrnitted to

iise

nll the tools o f b i s trirdc.

toolkit

The forrnruorker

arid

the

ino i i l rh i i ike r r r i rn

lit

~ ~ c - i r r m y

d inisl1. T h e

la tter works to an a cc ri ra sy 6 et tc r t h i

n i n i in

tlic prodnCtion of

many elements,

sirch

as tirnnel segrnerrt prodric-tiori.

W e n a

articiilarly coniplicatctl picre of forrriicwk

is

reiliiircd"

(occasionally

t h e

geometry

c m i

6e

akin to that

of

hoot

o r ship/riii/ifin,y)

the s k i h of a// re tested.

/nnoiialiorrs

can

sinip/i/) t b c

mristriiction tiisk.

_._roprietary systems can droniiitically rcdirce r-ysle times. /.i7rgc.-

panel

systerns

and j i i inpforn is rcdirce the

need

fo r fi7lseiuork

imi

otlJer

siipport, mid incorporate access plrrtforrrrs.

Alt /mi gli qirill ity

arid

acrriracy of finished

concrete

reflect the

~-oni/1iri~7ti~wif s k i l l s ar id teclinology employed, it has to b e

renzenz/~ercd

lmt the concrcter

has

a major impact o n the f inished

prodlict .

Ue/n i i>

groi in i l .

systenis /or forming groirnd

beiinis

irsing expanded

plastic-s are light t o

handle,

easy

t o install and thern ~ally f f icient.

A h i e growid. .

A uki t to the Conrrete ~ooks /Jopt

iuiuii~.concretebookshop.cor?ioI/ l

relied ti rueiilth of pirblzcatioiis proiiidiiig iriforniation o i i d giridance

/or tbc forin arid falsework designer, sirpplier and constriictor.



REINFORCEMENT

n his travels, our man has seen historic examples of decaying, spalled concrete

and rusted, exposed steel resulting from poor concrete, poor compaction, poor

ocation of steel, or where spacers have been omitted. They made him feel

uncomfortable He is more aware than ever that he is responsible for ensuring that cages

are properly secured and supported to avoid displacement during concreting.

Much of the steel he now uses is fabricated into cages before deliver): couplers are a boon

in making longer bars easier to handle and. the fabricated sets of starter bars and shear

assemblies speed the whole construction process.

He

sees

greater use of fabrics and has used stainless steel reinforcement in critical locations:

he has even taken delivery of fibre-reinforced concrete and knows that fibres are used in

cladding production and in many of the drainage wares he installs.

Schedules and details have improved considerably during

h s

time on site.

Ths,

coupled

with the availabhty of an immense range of well designed accessories such as chairs,

spacers, couplers and tie systems, has simplified the whole process of ensuring the correct

cover and maintaining reinforcement position.

47



Reinforcement 1

/ ir

passiirg, rue shorrld i i w i r t i o i r that our iirair npplarrds t h e detailer

iuho /)rodrtces scliedrrles

that are legible a i d

‘riser

frieirdly’

iii srte

COfIdltl(JflS



Reinforcement

2

I t rrrny he

CAR E S approved .ctcr/, r i t t

or id hcvrt

irr

qrrali ty nssirrcd r~ ir~d i~i~ irrs . .oirr rrrcrr

rn i i

soo r r

i i p s ~ t

liot

Iroivcvcr..

.

ivntclr~fiir

l rn t

lntc

lood . ..

properly i r isrol lrd with rlrr corrcrt spncrrs

**

ri locnrc

rlirrrr, nrrd

rrioirrtnirr

h a t iriiportnrrt rover.

I r r

case

c$rxposirrr, iwd cover

cm r

bejrrsr ns Irir/iortnrrt

elsiwlrerc.

*

Scc t h e

Coiicrcte Society Iccport

Tl<.OlKi

'Stand:ird reinforcrd

concrete

dctnil<'

**

S c c

t l i r C o n c r r t c Society R e p o r t CS. 1 0 1 'Spccrs for re inforced C O I I C T C ~ C '

49



Reinforcement

3

Watch that appropriute spacers

are used -

tools

o r vertical

location, rings fo r horizontal.

Home-m ade spacers often

inadvertently break rules of

cove,: before making good . assem bly

Ferrules are usejirl

to

ensure

location. Visual check can b e made

Cage labels left projecting

confirm

use

of correct

Ember or bar lacers avoid

formation offtinnels in top

surface of Ift.

Ply tentplute governs

projecting bar location in

oversize

hole

through orm.

Fillets ease location of bars

cranked back

to

o r m s o r

subsequent use as sturters.

Early erection of o rmwo rk with

formers in position provides template

f o r

steel

fixers.

Staggered joint s iii vertical bars ensure flo w

of work and avoid peak steel-fixing demand

in any one liji.

A brush with grout avoids

rust

and the

staining of cancrete by runs of rusty

water

A bar at the threshold of precast panel will

avoid cra cks in leg. Small prestress applied

to

wires in head helps.

C ou nt ba rs ~ ~ t i i a l l y

reinstated: they can

be

easily missed.

Dummy stopends ensure projecting bars

are accurately located.

Plastic cups or rag ' Jag s' may avoid

serious injury where steel projects in

access ways.

50



Reinforcement

4

Poor tyirig arid lack of spacers arid chuirs can result

iti defects, sonie of which onl,v appear years after

Etid

cover is ofleli overlooked 0s is the rll.st

transferred viu mould oil.

We

have

eveii

seen

casting.

where the tying wire has rusted

... the rei really nothing quite like the i nan

with t he nips in his hutid

. .

Caged stee l should alwa,vs be handled by spreader

heam

oti

bur: especially if the steelfirer foremari is a

big chap

We rorely see the ties illustrated, so here goes ... A, the

'slash tie/ (reversed

at

A,) suitable or itiJill: B, the

'hairpin

excelleiit

for key

bars;

C,

'crowti

' f o r se tt ing

up

arid

springy bars

Beware the late loud of

steel

which

is

burred

o f i static1urd.salso are

boutid to fal l .

SpiruI ties atid clips, w hile siniple to use,

c m slip

on

niild steel atid

after

all ..

...D. he 'ring slash ' ond E, 'ring hairpin

',

prevent sideways displucenient of bar utid

F :

the

splice tie.

at

least

t w o

per splice.

Avoid the *.specialist who uses U tube to correct

diverted steel. The otily sutisjic ton, way is to use a

dog.

:.

..

Tarturi mesh simply cropped and olded yields

excelletit

cages, ideal fo r export work.

Control

that

butidled

steel:

they always say

it is or the tiext bay _..hut

Perhaps the cheapm t piece ofplatit, yet one

of the most useful - he steel rack. Tube and

concrete

are usually reecv available. Failing

thut, use sleepers atid but:

51



Reinforcement, fittings and accessories

O u r ma n rcmeinbers wh en most reinforcing

steel

wa s crrt m d h i t on

site, ofien

in

ncdiineiitury shelters. \Vithorrt progrurnineti

cti t t i irg

there

was

a

degree ofroostage

...

Some designs appeared

to

be based on the ‘Birdcageprinciple’: i f a

bird rnight

escape

froin the ‘cage’, hen inore reinforrrrnent I UOS

needed

Today, spiral ties. clips and tuelding of suitable

steel

are freqnetitly

einployed

in cage

prodrrction.

Traditionally. on contracts large or id

small, steel fixers

have tied

criges

nsing...

A

The ‘ring slash’ tie D and ‘ring hairpin’ E prevent 6ar displacetnent.

Splices require ‘ i t least t w o ‘splice

ties’ E

olthorrgh t o d a y i splices are

ofteii

swaged connections or wiesltanic-a/ couplers.

... and 11cold winter inornirigs. ends

of steel

- possibly bent round

trrandre/s of the tvrong nidius or, dare

w e say,

siibstontiard

steel

-

t U O t l / d f l y OCI’OSS f/Jebar ShCIp

Basic skills /taue clionged little, th ough today’s operatives are more

likely

to

have rrndergone fortrial training

-

essential

as

reinforcernent

hecor nes i nor e ~oph i s t i c~~ ted ,n hylirid, construction for instance.

... t he

‘h‘iirpin’ ie

A (escc l lent for key 60rs), the ‘crown tie’B (for

setting-tip and

tying

springy liars),

and

the ‘ s l ~ ~ l i ’ie C ( for infill ties).

Wi th reuiscd

shape

codes and rationalised

steel

dctailf,

few

problems

wise with shapc and locarioit. Fortrmotely. our

inan

rarely

has

to

reqrrest

altcrations

to prepared cages

* See nlso I.ooking a t

i t

practically,

COX‘CRETE,

January

1999 , M ay

2000 ,ind &larch

1001.

t

i imar ds

ratinrwlising r r i t r f n r re ,no r t

fnr

cnnc’refc

s f n i r l i mx

Rrpurr

of

n Cnncre tc Society \Vwking Party. Technical Report 53.The

Concrrtc

Society. Crowrhonie, 1999. 40pp.

52



Reinforcement and accessories

T~~rinibirrg

hroiigh h i s past copies of CONCRETE. our moir iroted

th e m n u y iiiformatiue articles oir reirrforcemerit. Some p i p i id

C U C l l fCatlIrCd his t/Jfllf&'/ttS 11 tbe SltbieCt.

Of c ou rs e, t h e g re at es t i ~ i n o ~ a t i ~ ~ i r

ris

t o he

the

rritrodiictrorr of

BS 8666: 2000, eucii thorigh our mmi

feels

h e

m a y

miss some of

th e I Preferred Shapes that

have

been removed,

along

rvrth

s o i i t ~

of the Other

Shapes h e

had

m e t

in

the past.

Reading descrip t iom of

irouel

eqiripment em ployed iir the precast

industry to lay-rip composites, he iuas remiirded of the vast range

of materials, iir additioir to steel, auailnble for coricrete

reinforcement.

iV/Jile

o b u ~ o r t s / y

xtremel y effective, th e retro-reiirforcemerit

of

slabs atid beams rising fibre reiiiforced poly mer c ompos ites

reniiitded

him of

a t temp ts a t domestic

D I Y

decoratioii.

Mariy irinouatioits had been described. srrch

as

the desigil economics,

sltorteiied cycle time aitd rediiced f or m reqtciremeirts resrtlting fro m

the cotitrolled applicatiori

of

prestress t o floor slabs.

From

b i ~

o in t of

uieiu,

some of the best imiouatioris resrrlted fr om

site stiidies mtd irrprrt fr om

acadenrin,

siich

as

stiid rail systems that

s i m p l i f y

coliimn/slab connectioirs while beiirg quickly

atid

easily

installed

*.

As

he read

on,

h e

came

across illustratioirs of accessories he

was

already using ... nd so me th a t Ite

wort ld

uery mtrch like to m e

T ~ J C

rticles generally coirfirmed that methods

atid

materials that

provide .advantages arid economies are eirthiisiastically accepted by

the concrete industry.

53



Cast -in f ix ing s

Plated holts in conical holes allow or variation in

setiing-out holding down bolis. Expanded nieial

tubes

provid e excellent ho le former:

Avoid "wriggled in" sockeis. Centering from

forms ensures good qiruliiy concrete

surrounding socket.

For accurate locaiion

of

cast-in fixin gs locate

from dairim marked on all forms.

When custing-in column guards, siair nosings

etc. brighily painted wing nuis and washers

ensure removal prior to striking.

Steel bars support plasiic conduit againsi

displacement during casting process. Draw strings

'p ro ve " conduit and corks prevent grout infiltration

during jointing processes.

Projecting plates orfittings can be protected

againsi vibration in or out o ffo rm by positive

holting to sribstantial bracket.

O

b

Although dovetuil ba tten is easily fixed by

nuiling to forni.face. nails form extreme

hozard afier stripping.

A seasonal

note -

emember that lifting ho

are more brittle in cold weuther; take greui

in slinging io avoid "working" the bars.

Poorly located sockets cause bending in bolts

and possible ailure.

Cast-in holt.s,for lifting should be linked to

main sieel

to

avoid tearing action when units

are placed.

Sticky rape or p o~vsi yrerie voids grorri

infillrution when casting-in tnusofivydots

oks

,

care

,

sockets, holes, checkouis arid pock ets

Also in cold weather it is advisable

to

i l l

rviih

'koly"

to avoid frost damage.



Locating inclusions

Misalignment arid inaccuracy can be very

frustrating .._

se rv ice iristallatio,i [email protected].

d

a

a

I t may help $(with perniission) groups of

former s ure combined into U larger opening.

Cast-in Jixings do have their problems

Cliannel inserts give free dom in

one

direction

and, when conibined with surjk e-fi xed slotted

back section, complete reedom ipi the plane of

the surface. movenient thereajier:

Counter-slotted brackets allow ,some

adjustment.

Cast

serrated brackets allow

adjustrnerit on assembly and restrained

D U ~ U I I I Snforms help with correct location.

.-

a

.. although traditional kchniques overcome

normal variations (now called the

'characteristicaccuracy of concrete*.

Through Jixirigs niade to hardened concrete

solve some problem s of location

..

.. and in lighter applications good accuracy is

achieved by powder-actuated Jixings.

accurately positioned through attachment.

The accuracy of the mechanical engineer can

be matched b y mo trntingfixings onto a cast-

in light sacrificial jig.

The patent foani embedded techniques do

much the same for starter bars: check the

number of bars ajier reinstatenient

*BS

5606:

1978 Code ofpractice fo r accuracy in building

55



Ties

'

. ..:a:

There are those anioiig us who can remeniber

'shutte ring' that was tied with windlassed wire

- and very effective it was too

There's still a lot to be said fo r ordiiiary tie

rods, perha ps using a barrel spacer or set in a

spiral wo und tube or concrete spacer.

U

The coil tie is of course a positive tie arid

spacer and the bolt is simple

to

clean. Large

washers are desirable.

Anchors are invaluable in single-sided

work and ..

Substantial ties with fa st threads can be

thrust through the o rm ..

Coils allow us

to

clinib the ormw ork, one side

at a time, giviiig steel fixers easy access. I t is

advisable to keep the 'clip'

to

a serisihle

minimum , ensuring a tight join t yet avoiding

upset to plumb.

Snap ties used with a proprietary systeni

provid e speed and effficiericy. The 'official'

tool does a niirch betterjob than the claw

hammer

by

the way

Coils permit u s to go back and re-use

strategically plac ed arichorages when

infilling, etc.

... avoid 'curtain s' where we must cast a part

lifr

to

accommodate a beam or other intersecting

nieniber:

Taper ties are good in water-retaining

situations, correctly oriented to the water side

(watch the maii who withdraws them,

however )

v

._.

s can the 'she-bolt assembly that combines a

spacing and tying action. The nice big plat e

washers reduce bearing problems and the angle

plates allow ease of battered wall construction.

A neat fil l is iniportant and systernatic

spacing of ties improves the overall

appearance of a jo b well dune.



Reinfo rcement accessories

Use

o f

loop

type

t i e s

has imp roved our ma n's site-tied cages

beyond belie f

Joi nt formers incorporating co ntinuity steel avoid forests of

projecting steel, any o f which can ta ke a sleeve out of a jacket

(or possib ly an eye out o f a socket ) .

Experience has taught our matt to use the correct type of spacer

fo r a specific applications

-

chairs for vertical support and ring

o r

wheel type for horizontal location

-

and that...

H e understands that proprietary chairs ensure correct location

(and spacing) o f abric in slabs and that 'lattice girders', which are

similar but of heauier construction, combine top spacer and

transverse reinforcement economically.

Steel kickers have improved cycle times, arid allow final adj~rstment

of form position.

Bar couplers resolve 0 lot O f prohler?is, nlthorfgh their

use

with

cranked bars calls for care

111

select~on

he midst ensure stainless steel wire

IS

used iti site-produced

concrete spacers

to

avoid annealed t ying wire in th e all-iinportant

covercrete.

H e appreciates th e excellent support that proprietary strip spacers

provid e /or fabric, partrcrrlarly in narr ow or a wk wa rd areas, but

expects practice will be needed in bending the m to th e m o r e

complicated shapes

57



Fibres

.-‘

C K C rnanirfactirrcrs provide a ruide raiige

of

prodircts - srrcli os

nrchitectrrral feirtrrres, service drrcts. nnd field driirniige elcriiciits

-

hnl

coriipare fnvorrriibly

I ~ I os t orid

/ierforrmrrcc

wi th

iilteririrtirie r~r~ite rinls,

...

I P

hr7d

errcurrritered

f i l m arid

cloth

tuheir Zenrdrairr coirtrolled

perrrtea lility forrriirrrer (CPFJ

ruas

rued. The

/iiiis/i

tuns dcirse

arrrl

rvrtrtdl y Olciiiish-free.

/ - / e

u m reriiirrtl(~i f

other

rrioteriiils

irrcorporirtirrg

c l o t h

irid fihrcs.. .

A t the

triirc.

he thorfght ltere r r ~ i r s tbe N better w a y H e was right

7iiilay

rrrec/iarrisntIi irr aiid nrrtormtrorr

are

eiirployed in

the production

of

elepirrt

iirorrlds

of coirsistort qirnlity /or irrrtltiple re-rise

CK C cvrrrpositcs d s o allirw

dcsigrtcrs arid rrrairtifactitrcrs to

detail

oiid

proilircc thiri-sectiori

iirchitcctrrral

elcnreirts

wi th highly articirlated

srrrfaces.

their

light

rucight prooidrrig

srrBstantial ceoiroriries i?i

trailsport arui

handlirig

O u r

iirair

hod

see?i

ibre-reinforced polyiriers (FRI’)

fiibric used i n the

retro-reirrfi)rL.ciiieiit rid

protectiorz

of

strrrctriral clenierrts and

as plates

t o

protect iirrd strcngtheii circitlar ctrlii117rrs,w i t h groiil iiijectcd into

the

irrrrrtrlrrs. IVhnt next. IJ roondercd

58



PRODUCTION AND PLACING

he ready supply

of

quality assured concrete from the local ready-mixed concrete

depot has made starthng differences to our man’s work. Enquiries about delivery

T

tatus no longer elicit the reply ‘The truck just left the depot ’ Instead, he can have

a hard copy of the intimate details of the batch printed by the computer that has controlled

the whole process. He is also aware that, in the event of breakdown, the plant operator can

get a ‘fix’ online from the manufacturer.

Cubco man can just remember when compaction was controlled by the ganger who

regulated the pouring of concrete from prams brought to the point of placement by a

hoist. On critical work, these prams were fitted with egg-timers and any concrete not placed

by the specified expiry time was scrapped

(He

is amazed that these days concrete can be

chemically ‘sent

to

sleep’ until i t can be placed during the next shift )

More general use of cranes, particularly the tower crane, revitalised the whole handling

process and the next development was the concrete pump. The first pump our man met

was a monstrous wheel, set up

on

land adjacent to the site and squirting concrete through

a massive static six-inch pipeline. These days, his pump arrives

on

site in the morning and

by the afternoon can have left, having placed

200

cubic metres or so of concrete.

From pump

or skip,

placing concrete - whether ‘ordinary’ concrete, flowing, fibre rein-

forced, foamed or what have you

-

demands skill. And whatever the means of handhng, our

man knows he is the final link in the chain for acheving acceptable well-compacted concrete.

59



Preparing to concrete

First

of

all

let k

eiisure

that those involved

unders tand the problenis and the likely

result of oniissions. legible?)

Take a look

at

the drmvirigs

mid

schedules

- are they the latest? (and are they

Be warried, there

is a

traditioiiul ganie of “Snakes

und Ladders ” which goes oti

at

the

bottom

cartier

of

niatiy drawings -

doli t

be caught out.

What has the orm work designer got

in

mind,

rtiuybe

we

cati help with

ideas

arid local detail.

The concrete techiiologist has a contributiori

too - he

cati advise on

tlie

eflects

of

admixtures atid their likely impact

oti

tlie

rlieology

oft l ie mix

Planning techniques

(atid

unplanned

changes in method) can vitally ulter

rate

of

.fill A N D THUS FORM REQUIREMENTS.

No doubt the weuther will have

sonie

iriJlirence on aperutions too

The concrete pum p is

a

poterit

tool and demarids

good uccess o r distribirtion. Full heod

conditions can otherwise develop in minutes.

Good accessfi>rplant and concrete supply is

criticul

to

the concreting operation.

lf

we C N I I

get these trucks

sorted

out by next month we

will tuke a look at the pre-concretitig check

6



The p re-co nc rete check

1

A re f o r m " co rr ec t io line and level"? Does

the carcass maintain line? Watch or distoriion

due to overtightened ties

Is

the sheathing of siritable standurd free

from

holes a n d

burns?

Have gaskets

or

tapes been installed at

sheathing oints?

Has the steel been correctly locaied and

ure

forms ree

of

debris, clippings,

etc?

What nhoi r t those props? Straight, plunib,

hruced, taken to suituhle oundation?

Is

the approved oil or pariing agent

applied

trni$ornily?

Have proprieiaty clips, etc. been used

correctl,v? Has top offorni

been

stgened with walers?

a t

Are ties at correct centres horizontally

and veriically? Are the,v complete?

Were those

tentporaty

works

conipleted?

61



The pre-concrete check

2

O coiirse the check i m s t continire during

the concreting operation.

This is

when

niovenients arid displacentents

tuke

place. wedges slip. screws and bolts

unwind etc.

We

watch fo r signs of distress

Particularly where local deflections cause

difjiculty in itting doors, at kickers. and

where second dejlections o c c u ~

We go hack and check on the placing

techniques.

And watch fo r

spofs

where

oiir

bracing w u s

iiot

too ne11

thought out

I n

case ofproblents. slow dowri or stop

theJill..

Insert butteit at top offill

to

form straight

line,,.

If

it :r bad send fo r

the

i r e hrigude

And theri prepare or the quality discussions

which must ensue

62



Product ion, plan t and equ ipm ent

There is nothing so frustrating as

a

breakdorun, tohatever the

equipment and ruherever it occurs

..

Apart from frayed relationships, breakdowns can be

a

potenri~11

source of accidents when haste over-rules common sense. Safety

engineers beware

... eqir i/me nt is no w m ost easily cleaued b y hrgl~-pressure pray or

by treating surfaces with chemical release paints or coatings.

Usually there is access to

a

sensible stock

of

wearing parts, or

s tandby equipment ‘on tap’. In marry breakdowns, ]IT (just it7

time ) techniqrres wo uld be

I N S

(just not srtfficielrt)

...

particularly where concrete supplies on site are concerned - and

especially in mid-pou r

Fortrrnatel): attitudes

to

marntenance,

so

essential i n a u o l d ~ t ~ g

lmakdoruns ,

have

changed. Instead of using ’elboru grease’, the

‘lttmp’ hamm er, or the trtnibled half-brrckso beloved of old...

Preventive m aintettance is generally emp loye d, and the experienced

plant fitter with his prognostic abilities is always alert to sounds or

vibrations that m ay signal problems.

Today, breakdoiuns are

ofteti

resolved b y fitters or electricians,

prompted via

a

laptop on line to the m anufacturer a t home or

abroad. Indeed, rather than tuinditrg nuts and bol ts , they are more

likely

to

replace

a

card in the control system

63



Construct ion jo in ts

Scabbling is a tedious and

sometimes destructive

process.

J

Fornis to rrrther lifk an

cause

damage adjocent to jogg le.

Modern lacquer-type retarders

provide an excellent surface to

cast against.

3:

The traditionalist k ‘bucketo f

grout ’ can weaken the

construction.

Joggles congest mouth ofjorni

rendering cornpaction df jc ul t.

Joggleforniers entrap air arid water

leaving unsound concrete at critical

point

\

Early age washing and brushing

is sintple and positive.

Grit-blasting provid es un

e.wellent joint sirrjace

- ake

core

over safely aspects.

The ideal joint surface is ree

of

laitance

and presents clean aggregate face s fo r

bonding purposes. Sound joints have

been achieved up

to 100

days.

This ‘rope trick’ ensures a good

key. Rope is jx ed with

lost

head

nails to stopends and is

transferred at striking.

Poor conipaction in first cast causes

loss

of workability adjacent to oint and thus

substandard com paction in fresh lift or

bay. Supplement surface effort by using

poker ’

locally.

Thoughtful oint location

siniplifies construction.

Expanded metal is simple and

cheap to use

-

leaving it in place

observe rides

of

cover

Ear1,v removal offornis eases

joint preparation

-

recaslers

do it all the time.

Provision ofjxings adjacent to

construction joint eases form

j x i n g

-

use ties or additional

inserts - watch cover

Sound detailing puts joint s in

the shade

64



Production and handling

C - - .

eiisirrc n corrtirricoiis sup pl y ofrorirre te c?fcorisisteii/

qrioliry

nrrd

~r~orknbili ty1

t h e

roristrrrctiori s i t e . , ,



Placing conc rete

1

Check the orms, propping, bracing, etc

Beware the ‘teniporaty prop used in

erection.

Ensure that vibrators penetrat e previous

layer:

few

people realise limited radius

of

activity

o

poker:

A similar technique will ensuref i l l under

large voids. Watch or displacement offornier:

Systernaticfilling ofba tterie s, fro m

one

end

only w ill avoid production

of

‘thick and thin ’

units

reduces clean-up time and reduces orm

weight

emember ac cess, withou/ which placem ent

and conipaction will be skimped.

Air bubbles cease. surface glazes, and

sonietinies

sound

changes when good

compaction is achieved.

e A b c

4

~1 M

1

YA

i ‘ r

..

. ~ . .

T T

Retarder (subject

to

approval) will avoid

possibility of dt y oints between layers in

deep fi1I.v.

Removal of workability fin es

on

completion

offill,

and replacement with good fresh

concrete vibrated in, ensures a sound

su

f o c e

ready or brushing or washing.

Fill at one Tide ofwrridoiv openings ( I ) until

concrete surges at A , only then begirifill at

(2).

Retarder (subject to approval) avoids

differential deflections with deep fills.

Surplus concrete ’$titled’ with lifring hook

can be removed and speedily and cheaply

‘the morning after the night before ’

66



Placing con crete 2

Cureful joini preparaiion is aii essential puri

o ihe

process

- achieved by wash

arid brush,

grit blasi or reiardeK

External vibrators niust be curefully

locuied

io ensure

energv

is delivered where ii is

required - n ihe concrete.

.. .

.~

..

.___

A

planned f i l l

ei isures ihe

absence o

voids

and

bridging

...

The use o

f ivo

skips ‘uncouples

replacement froni supply - but watch rate

o f j i l ands iudy the efleci o admixtures on

f o r m pressirres.

Wuier

bur

($specified) niiist be secured

agciinsi displaceinerit - he

strrfiice

ix ing

types have a loi io off;?.

Secureyet easily ,nude Ji.ririgs ure

esseniial

-

vibraioty action niay be

tuned

by angling the

axis o ihe irnii.

/ ‘

...

the

latter

is a

hazard

in congested sections.

I n

precasting we

used

io

‘doctor

the shovels

to avoid choking the

rnou1d.s.

Mortiior the

orins

ihroirghout ihe placing

operation: ihey seldom fai l w iihoui

warning

.

Wiih permission, ii is worih iakirig

out

a ihird o

ihe coarse

uggregaie

front

the

irsi baich. The

posie ihen coats skips arid equipnierii as well as

proviriirigfiries to imp rove

ihe

joint - .~cess

s

broiighi up the orin during

conipciction.

We ure siill likely io need ihe ver.saiile poke r,

poriicularly ivhere ihe forin is ininiobilised by

bolting to previously cast concreie - at the

sides and the kicker

O

course,skip

design

is critical: a n ice chuie.

a ivheel

to

uid conirol

o

discharge

and

a

vibrator

or low

slunip inaierial.

-

...

und, ihoirgh we don

t

like depriving ihe

lads o iheir exercise, a quick wash

down

on

completion is nitrcli kinder to

ihe

plan,

67



Batching

Consideriiig the

tuay in

iuhich concrete

was

mixed historically, euen

oii

major

coiitracts.. .

and how

it

is still sometimes mixed today

(thankfitlly

only

on miiior contracts)...

oitr man is altuays impressed by the scale

of mode rn hatching plants .

Gone

are the traditional

tools

of

the

‘mix er driver’:

iioiuarlays,airthorised m ix prescrrptions

prouided by the qiralrty eiigiiieer.

..

are

eittered itito calibrated contr ol

eqiripment that woirld challeiige eueii

nit airline pilot.

A s iuell

as accirrafely measitring

quantities

of

aggregates. cement , water arid

admixture dosage, the eqi t ipment provides

priiited records

of

the actital amoutits

of

materials in each batch.

1ii the euerit of p r o / ~ l e m s ,o m e eqrripmeitt

can

be remotely monitored from

r he

marirrfacturer’s wo rk s, prouidiiig oii-line

analysis and resolution of system and

equipment

f(l1tlts.

Wi th all this technology

a t

his fingertips,

the Datchermait is regarded by oirr men

as one of the most important members

of the team.



Concrete m ixing and batching p lant

‘Relaxing’ on holiday, promp ted ~ J Y I

surcharge

of

local aggregate,

and

noting the

excellent cohesive properties obtained using

optintitin water con ten t, tho rou gh ntr.urng

and sound compaction, our

inan

houghts

turned to batcl~irtg nd mixin g.

HL’

hCJllg/Jf

Of

tbC pClSt. l l l < 7 l l l f ‘ 7 / / ) ~

/ll/tltlg

tons ( y rs , t h e y i i w e t o n s i n those days) of

aggregates

...

w i t h t h e

odd

bag

of

cement

t h r o w n

i n .

‘Hardl y surprising, ’ he tborrgbt,

’Tlmt

results occasionally

left

something

t o

Oe desired ’

He went on

to

consider ho w everything

is i n faavoitr of qualify results nowadays. H e

had been show n around

a

modern p lan t

producing quality assured concrete, with

operations controlled by efficient

equ ipment

suck

as...

...

L

coinputer

conruining

t b e

inix recipes

cind providing a record

of

the actual

quantities in each hatch, rnicrowaue

ineasureinent

of

water content and

nnntic

diagram indicating the state

of

each piece

of equipinent.

/-le

had heard that,

in

special circumstances,

concrete was being supplied from a fully

self-contained tn ol~ile mtching plant

dedicated to a specific mix

..

...

a n d h e k n e w t h a t ,

in

precast works ,

mixes fro m a programmed autoniated plant

coitld

he

called up front a console at the

placing station

...

high-quality concrete

being deliuered speedily to the spo t by

bullet skip

...

...

a n d ,

on his

site. quality assured produ ct

was being delivered direct to the po in t of

placing.

N o won der tha t the resident engineer, and

even th e general foretnun, seemed happier

wit h his wo rk. ‘Th e results of developinents

in

concrete prod uction technology are

qui te

nragical, ’ he th ought , ‘especially when

1 supply the finishing touch ’

69



Ready-mixed concrete 1

Oitr innit tiiriied his t hough t s to ready-

niixed coiicrete.... H e tuns aware that t h e

foiiiidatioris for

t h e frarne

ouer t he road

had

beeii

poirred

iii a da y iisirig FIND

3

( f o r Class 3 Sitlfate coitditroris)

...

... i i d the floor /ayers 11 he srte next

to

his

ruere pitt t i i ig away ‘acres’ (we l l

hrct(ires) of RC 40 iuearirig sitrftice

coiicrete each iueek. arid Iiardly

gettirig

dirty i i i the process

....

... hat the

brick

c laddi~ lg o

t h e

brrildrrig

rfoiiirr the road w as proceediug apace

iisiiig

ready-riiixed riiortnr.

... he

coilsistericy

Desigiiotioii 111) retarded NS specified,

fiiidirig fauoiir w i t h t h e bricklayers....

Of Sli[JfJ/)f O f l l l f l t e r i ~ /CqttOtillg to

... hat

the iimteriol for backfilliirg a// bose

treiicbes nroiiiid the toroir cirriued

by

tritck, arid that i d t e l l the ’egg’ ons

iritroriiiced

to

t h e soitd/ceiiieiit m i x

aiid

agitutioii coiitiriiteri, oitt canie

iriiniaciilate

foamed coiicrete to deiisity/strerigth

specificatioii..

.

... iid was delivered oil

tinle

by helpfil l

drivers.. .

...

he products

beiizg

inoiiitored, at plarlt

orid site, by srtita6/?~

ualified

techrriciiliis

And ~ l t h o i i g h

Graiid

National’ m i x

(1 2 :2 ) had been OK historically, how

long iri the light o f a l l the auai lable tecb-

iiology,

he

asked

hiinself, was be

destined

to striiggle oii operating

m i d

maiiitaining

Ciibco’s iiiaior piece

of

plaiit?

7



Ready-mixed concrete 2

71



Ready-mixed concrete

3

Oirr nian has bee11 impre ssed

by the

ready-mixed concrete inditstry j

intpact

on the

scale

atid pace

of concrete

placernet~t.

Qitality-assrired

concrete and nrortars are readily available for portrs ruhether for large

contracts, involving /trrndreds of cirl~icnctres of nrateri~7l"

..

or sim i l l jobs arl l i i ig for the odd inetre or

trvo. ( A

consideral~le

anroirrrt

is

tieliuered to the DIY nrm4et.

nirtclt

of iubich

is

Itandled

i n

uery s n r d l l~arrorus )

Sitppl ies

of ready-rnixed concrete are esseittial where, particiilarly in

oitr cities, site space

is

liniited.

Personiiel are trained in testing and techniqires to aid

the

niaintenairce

o f q i r d I t y . Field operotiues a re instrricted in concrete practice and some

sirpport pcrsonnel t o advanced concrete tecltnology level,

and

...

Receipt of instrrrctions for despatch are well-controlled processes

carried out in close cooperation with t he

si te .

Enquiries nborrt

deliveries no longer bring forth tha t fatal message of

old

'It's jirst

leauing the depot , Giiu'.

Indeed,

...

I - lai tding

eqiiilvirent assists i n

i i recti i ig constrrrction cltallenges ...

p i i r np s and conveyors as iuell as suine rentarkable

cotnbinatio~is

f

eqitipnrent

'/%iso n c

i s

(1

printp, I crane

and

a work platform '

optinirtwi resrrlts are acltiwed iultere contractors inclrrdc the reod y-

rni.reti concrete srrpplier's coircrete technolog ist as ivell as the location

i namger

iulten pliinriing

a contract.

oiir inan has great respect for the despatchers

and

triickers who, night

and d a y a n d in all weathers, ensnre that the 'grey stuff ' arrives O I Z

schedrrle

helpiirg them to

meet

prodrrctioii targe ts.

See: TWIGG, C.

More c n n c r ~ ' t e or M o r e I.ondon.

C O N C K E T E . Val.35.

N0.2

, Febru:iry 2001, pp.12-14.

t'lh:inks ro

Ellior

Equipmcnr

Cwnpany,

USA



Ready mixed concrete 4

Having

read the

recent RCB publication

*, our mun

is

impressed by the h uge pours achievable

with

pump-placed

readv-niixed concrete

and

..

Ever innovative, Ciibco has capitalised on ihe u vailabiliiy o

discrere qiiuntities

o the

qualify-ussured niaierial to improve

its

product

...

/ius rioied

ihat,

at the other

end of

ihe scale, U number of

precusiers have rediiced overheads and plant maintenance costs

by using ready-mi.rerl concrete.

On site.

our

man Ieanied

ihai.

alilioiigh man y

of

his colleagires

were

prepured

to

direci a driver io a hardstmiding. _._

...

they

were

likely

to

disappear

i n

the eveni of[Jrob/ems. He

is

ulwuys

concerned about whether ihe people pumping

concreie

u t

40m3/li

know

where ihe other end

is

While admiring the ready-mixer k grusp

of

teclinology. he wonders

how

resident engineers greet

the

tecliniqrre

of

de-aciivating

and

then re-aciivaiing a loudfor use Iaier

* Ready Mixed Concreie Bureau. The benefits

of ready-mixed

concrete

1998.

Finally. lie

lias

concluded that

the

yarn about a driverfilling

a

competitor

:s

car with concrete

is

entirely apo ctyphal.

...

ilte essential ingredient. Crowthorne, Briiish Cenient Association,

73



Slab

construct ion

There

s a lot

of discussion about the casting

of concrete slabs ...

Concrete sliotild he place d, not dumped,

and tramping over the resh concrete is

itof coridricive to uniform compaction.

Steel is placed (when used) on top of the

lower layer of concrete.

So

we

onsulted ou r resident specialist

regarding key points in successfirl

operatioris.

U

The surcharge should be uniform

in

thickness, a surcharge batten

will

help here.

For trowelling, the concrete should bear the

j i t l l

body weight applied via the ingertips

without leaving an impression ... and

When theflat of the hand comes

away clean from the contact with

the surface.

Dowel bars

must

he located parallel

to

the

concrete fac e and steel. where required,

acciirate1,v positioned within substuntia l fo rm s

Hand floating may b e carried

out

with either U

skip

float

or hand J l o ~ t. ower f loat treatment

m i s t

he carefiil1,v tinted ifit is not to develop

into art e.rcavatiot1

..

In achieving the Jinish. the use of “ driers ”

(centenl) nttist be eschew ed.

And wetting down (using water ),

particularly some hours on , avoided like

the plague

A

curing ntentbrane will be ben eficial-

it

is

upplied as soon as the surface moisture has

evaporated. old gracefully.

Failing

all

else

a

plastic sheet will give the

concrete a chance

to

ntature in confo rt and grow

74



Flatwork

Aware

o f t h e u a /~re f

lasers iti the /irocess

and

beorirrg i n niind the

reduced

denionci

for screen rnils, stopeiids

aiid

jobit formers, / J C

th inks

it

ntay

6 e

t i m e to disciirti

his

hitherto trirsty leucL

thu s far he hris only 6een trusted

with

a

6 ~ 1 1/oat. H E

prefers this

to

the

old sleeue

f loat

but has

control pro6lenis from

time

to

time

...

oirr

i n r i n is

irnprcsscd

by todriy's

lizrgc-area

porrrs

i i i

concrete

slab

~ o i t ~ t r ~ r c t i o n ,uith ruIJrit

seem

t o h i m

like

acres

of

sirperflat slob,

cast in one

f i s t

operatioiz.

. .

Thinking

of controls, he I J O S secrtt com rct e paucrs i n applications

srrclt

as c i i rpor t ~o~r~tr irc t ion ,state roads. paueinerits

nitd

even

g a r q e

forecorrrts, ofteii

6eitig

/ ~ a t i d / e d

~recha i i i cn l l...

... arid can

uisiralise

the time ruheit remote-controlled

iiiachrlies rurll

take

on

fzrlly

arrtoniated pauer placenierit.

* see p a g e 21. Contprcters.

75



Hot- and co ld-weather concret ing

Aware

of the rrasty

ways

iir which

omissioir

of

crrre driririg

extrerires of heat aiid drying, as iuell ns freezirrg, cnrr rlffect the

coticrete that

helps

earri

his

lioiitg

(arid his

holidays)

..

In the

past, essetitinl rrroistrire hns

beerr

contairied by

entployirig

a

covering

of

sand

...

l rr

h o t

weather,

provisioii

of

a steady slipply

of

nroistrire

had

ninintaiired the desired

hiinrid

coriditions

...

...

which,

in

critical situations, meded ntowitoriiig

and

control.

...

orir

r i i a i r

forriid

h i i i r se l f ,

fro m the cciiiifort

of is

deckchoir.

rorrrprrririg proced rircs

for

cnririg for coiicrcte ioith those

of

caring

for the h~ iiiinii rrirm

... i r d c ~ i i d i t i ( i ~ ~ s

egitlntcd t h e

rise

of toitirrg, ccirefrilly

auoidiiry

throLcg/i-drrrrcg/~ts.

...

as

had

rrdrrrirristratiorr of ice to coritrol temperatitre

...

T h e

ireed to

wrap r i p

to

preserve residual

herrt as

tenipcratirres fe l l

inrpressed oir our ~rzarr hat ,

conte t h e

tointer,

h e wortld

take care

to

wrap his fresh coricrete eqiially carefiilly

76



Winter work ing

It may

seem

a little uriseusoriable

to

bring

u p

the

topic

at this t ime ofye ar

...

...

but now

is the time

to

plan these days when

the car

won

r sturt ...

... arid eveii the mixer refuses to perform.

Not

to

mention those technical discussions

regarding striking l imes, f o r

example.

However, before we

unip

into the deep end and

start steaming everything in sight ._.

...

let

i ook at

the code recommendation

mid.

f o r

e.rample,

the maturity concept* _..

...

establishing

a

goad correlation

between maturi/y and strength

Make

sure tliere is heat ut

die

mixer

I

’ I

Wrap

u p

the orms, avoiding draughts arid

chilling winds.

Invest in

sonic

‘Quickstrip equipment

and

formalise your system o sturiding supports.

Things should proceed

as

normal.

* CPllO: Part : 1972. p.117. Neville,

A.M.

Properties

of

concrete. 1995, p.304.

Keep

the

warmtli in the concrete, however

we

trunsport it.

Even the odd electric blanket might not

go

amiss - for the benefit o fth e concrete, of

course

77



Concrete in adverse con di t ions

Our man sat arid ponder ed the iopic o

concrete iri extreme cond itions of locatio n,

exposure and tem peratur e arid whai had

been

learned in practice.

...

insulate ihefo rnis, arid

ifmcessauy

heat

them, rioting ihat air siruciures have been used

io advantage as shelters

or

corisiruciion,

concreting and curing’* (wiih ihe tower crane

padded to avoid punctures ).

‘Nexi

winter,

’

he decided,

‘I

will take inore

care of ihe concreie. be more carefiil uboui

ihe choice of adiiii.riiires mid

use

iiiore air-

entrained concrete

..

_..

use

sieani or hot water in ilie mix, as well

as heating

the

aggregaies, order hoi coiicreie

fioii i the

suppliec nioniior

ihe temperatures

mid control

the

curiiig cycle accordingly .

In

ihe

changeable weaiher we class

as

Spring,

he wisrfiilly reflecied ihui in

the

deseris of ihis

world if is good practice to shade

the sieel

and

the concrete

as

well

as

ihe workers , and in hot

climaies to employ ice or chilled wuier io cool

ihe

n i r .

Our man

also

remembered that, whatever the

conditions,

care

must be iuken over test

specimens,

iesier

and test equipment to ensure

reproducabiliiy arid repeatabiliiy arid

’respectable’ esults and

ihui ..

...

when construction or repair works (ire

needed in extreme locuiions, ihe method

siaiemeiit and published procedures o r

access should clearLv describe safe riieiliod.s

wiih siiiiuble protection f i r all irivolved.

He had read** iliey

also

have

to

avoid dust

(a).

mixing

arid

curing waier

(b).

and

groundwuier (e)

that

carry salts, uri)~

which otherwise

cause

subsiaridard

coiistruciiori.

On reflection.

our

nian decided ihat the UK

climate generally, and

the

liiile cloud

thai

seems to

accoriipany hini wherever he works.

are really

quite kind

to

his concreie

* Moor, K . , Woodhead, R. and

Tuiile

H. American conc rete lnsiitute. SBM-2

(91).

pp.109-Ill .

**Fookes. PG. Concre te in the Middle East. Concrete. 1993. p p . 1 4 - 20.

78



Placing, com pacting and caring

It dawned upoti our inati tha t achieueinerit of soirrid con~piictiort

begiris no t

on site hi t

dirririg the design, specificatioii

arid

coritract

planning..

,

...

aboiit

sensible

reiriforcermnt selection,

desigiz and

detailing".

Such aw

agreeinetit

is iieeded

t o

al low

positive fi.riiig

arid

locatioii

as

tuell

as access for uihratory gear arid to resist displacement ditriiig

eirsuing operations.

Provided w ith the essential, steady supply of concrete, desigried

for the con iponen t under construction and deliuered to the point

ofplaci11g

...

...

atid a

to

recognise

when good

compactioit

is

being

achieved

(such as cessation of air bubbles, glazing of t he surface, a line of

paste

a t

the coticretelform interface and

possildy a

change in the

sound

of

the equipnient)

..

...

os agreenieiit is reached oborct permissible

lift

heights,

coiistrirction joint location

and

format ion ,

arid

also...

H e

realised th at the forniwor k

has

to be robttst, grout-tight aiid

resistant

to

the pressures developiiig

as

concrete

is

placed.

...

a crew trairied

iii

the safe iise of approp riate eqciipmeizt and

systeinatic placirig techriiques, with

good

access

to all

parts of

the form

...

...

and asssiining

care

and

atteiztiori

in

stripping the form s

and

the

curing process, the result will be concrete exhibiting all the signs

of good coinpaction.

I n

other words, a

j ob to

be proud

of

79



Self-com pacting c on crete

On

hearing that in Scandinavia one man had placed 900m’ of

self-compacting concrete in a day‘, our man was prompted t o

consider his own experience with new materials.

Encounters with fibre-reinforced concrete had provided some

excitement until fibre-dispensing systems were improved: now,

blown fibres prevent agglomeration.

...

he realised that its adoptio n could reduce stints

on

the poker

and that in the factory there would be fewer external vibrators

to

lug about.

...

form and m ould displacement, poker burns and other defects

caused by vibratory effort would be things of the past. T he material

woiild eliminate such problems and prove popular with designers

and steel-fixers ...

Flowing concrete was a great innov ation, althorrgh he remembere d his

first encounter with the material.

I t

certainly flowed on that occasion

- n at one end of the forms, ou t at the other

He had been impressed on learning the benefits o f high-strength

concrete, such as extra ‘rentable’ pace and less concrete t o handle.

Thinking about further benefits offered by self-compacting concrete, ...

He knew precasters had taken the material

on

board, as it was

excellent in linear production, flowed well through congested

reinforcement and reduced production times. He could foresee that

...

...

who could rely

on

reinforcement remaining correctly located,

undisturbed by compactive effort. He is convinced that, with

experience, self-compacting concrete will prove to be as great an

asset in construction as have the other types



SURFACE FINISH

ur man is delighted that, thanks to work by organisations such as The Concrete

Society in cooperation with major contractors, he is no longer plagued by

mprecise specification. He is aware that specifiers can now see and quote

established samples, thus avoiding the ambiguity

of

historic specifications such as those

that called for fair-faced concrete.

He has noted that most designers have an improved understandmg of the need to detail

concrete finishes with their weathering characteristics in mind, and that they appreciate the

need for large samples and even full-size mock-ups of particularly demanding finishes for

prestigious contracts.

Many new finishes have been devised in our man’s time. He has seen aggregate exposed

by tooling, by abrasive blasting and water jetting. The retarders he now uses are safe, drying

on application, being activated by contact with concrete. The latest development he has

encountered is

a

means of transferring larger-than-life photographs to the concrete

surface as in photogravure.

Cubco man is well aware of the underlying truth concerning all concrete work, namely that

the operative or operator leaves on surfaces, tooled, featured, produced either chemically

or

manually, a stark commentary on his abilities for years to come.



Surface finishes

1

Sirccessful jiriishes demand uniformity of exposure, tooling and texture.

Random tooling should he avoided. Con trolled tooling avoids

Shading'.

~

I

Poor application of retarder will show on surface - use roller-spray or

correct brush.

Tooling taken

to

arrises results in uneven work and damage

-

margins

assist with uniformity.

Sheathing and pa nel joints will reproduce on concrete fa ce - minimise

defects by sound, tight Jxin gs.

Access problems will be revealed by inconsistency of work

-

always

provide adequate work plalforms.



Surface

f inishes

2

Provide and con stantly refer to sizeabl e pre-production samples to

avoid disappointment.

Small defects are inevitable Sp ec fy repair techniques which have

been proven over the years.

Avoid quilting. check fo r design, for m condition, and rate of

J21,

Board onto board won 'r g o - ndented feature allows close

form/concrete oint - essential in heavily grained work.

The scale offe atur es arid details is critic al- larger detail is cheaper

and easier to produce satisfactorily

Consistency offill and control of tie location improve plane surfaces.

Pre-coating or pre-conditioning will avoid shading due to differential

absorption.

A mild acid wash appliedfroni the top downwards over thoroughly

wetted aggregate surface will add lustre to the inish.

83



Surface finishes 3

Visual

concrete provid es a lasting comnientary

o n

the

ability

a f a l l

those concerned in d e s i g n ,

p r o d u c -

tion

arid

construction..

.

Success depend s

on

the

skills of:.

.

- . .

- - - .<-

th e spec$er arid mix d e s i g n e r . . .

w i p / o y i i ~ q pecified

inatevials udiicli have

beeii

proprrly soriipled arid

stored.

-

Surh deta i l s as choice arid application drelease

a p i t

require

carefir1

attention,

as d o a l l aspects I f : .

formwork

des ign ,

construction and erection. Mainte-

nance of accuracy and cover

call

f o r the best ofpracti-

col arid superv i sory skills.

Handling

techniques

have

to

he st irdied

too, i\Jigel

Mansell h a s a lot

to aristrvrfor

Of come, placement and compaction presentjeui

problems to the well trained team . .

hut curing techniques may leave something

to

be

desired.

Th an k goodnessfor the humi d British

cli-

nrate

Concrete characteristics are critiral throughout,

as

well as appropriate uiorkability i n the placing a n d

compaction stages, developrnerit of strength to resist

freezing and nierhariical

darnage

is

iinportarit at

striking time

A

capable

trainer

could

pu t our chaps

wise

to

m a n y

other very practical aspects., , more next time

8 4



Surface f inishes 4

Fornis leaned against fresh ly cast concrete

muy

cause

pernianent mark.\

because of dflerentiul curing.

Keep

.satnples of approved aggregates

to

avoid seasonal cllunges in

shupe

and colour:

Opening

forniers must

be sealed

to avoid

grout leakage criusing staining

-

watch

fo r ornier rotation aboutfiwings.

also

lifr

due

to

concreie

pressure.

Siniilar defkcts can result from stacking precust units on wider

tiniber battens -

use least possible

contact

-

lastic or concrete

blocks

That brown rriark rnay he s teel, p)~rite.s, dniixture.

rust.

rom

pictlog.~, tc. Investigate cureful1,v before reniediu l work .

When exposing concrete

to

considerable (Iepth, increase concrete

cover

accordingly.

Rust inay

not be actual reinforcing steel

hut

s iniply

scale

and dust

transferred

vici

oil

onto

orin.

Joint rules

at

stopends ensure straight-line joints. Additional studding

ensures positive s/ieathing/concrete contact

und

av0id.s

curtain.^

'.

For tricks o the iormv ork trucle,see

the

section onforinwork arid

falsework. p p . 23-46.



Surface finishes

5

W

Fillets

n ) ~ f o m r i i ~ q

rrntgiris

iriill

preserve nrrises.

Qu ir ks ur ritsricntior? strips

1))

assist a t clrnrFrs of

testirre. Alloiimce r i r i r s r

be

r?rnde-fiir lre.fnct tlrnt

vnlirnble

‘cuvercrete’

is

reitroved

r r the

touliiig pru-

cess.

riot the

lenst

are

eryurrorriic

corrsiderntiorls. Our

i r rnr r

linsri’tjrll

currrrul over

the

tool

ivlietr reacliiqq or

stoopiirg.,

best

#or[ is flyplied

b r t i u e e ~ ~/ioirlder

orid krree level.. ,

good

access is critical.

I

.-

a

ibfntry uJtl ie-fnerors cnrr b e deterrriirred, n i i d colt-

trolled, i jn ll pnrties

agrre u t i

stnrrdnrds b y

itreoris

<$

n t i rodel

or

trinl

porrel

os

r e c i i i r i r r i e r r d d i r r

‘Fimi-

wurk

-

grridr 10 good practice’+

Tlrnr

ojerr-speciJlird

‘irrri&rrriity

oJfirrislr’

is

djfficrrlt

f u

nchieve: irie

k r i u i i i of

tirore tlinrr

40

nctors iuh ich

nf l icr

rlre resrrlrs -

erripernrrrre, rriis clrnrocteristics,

tiiiiirrg ofoperntiuris,

etc..

.

Tlierr, wirlr o sorrrrd supply qfcoricrete, placed to

the vibrator it? sirbstaiirial, tightforiris

at n

p o d

rote

q f f i l l , we’re

ivell O H

r l ie way

to success

*

‘Forinwork - n gui de to

good

practice’.Joint Comi i i i t t c c

of The

Collcrctc Soc i r t y

. l i d

The In\titutlon

of

Structural Eiigineerr

86



Surface finishes

6

Used a lot in Amer ica, especially

on

tilt-up

construction, polythene sheet o ver stones

on U

base c asts an interesting feature finish.

‘Face-up precasting allows expression

of

feutirres of aggregate

-

depth of wash

accentuates stones.

Stones settle againsi mould base and present

‘value or money’ -gr ade of retarder governs

exposure in face-do wn casting.

c

(1)

A carved or routered hoardforms a

mould fo r casting polyurethan e liners. (2)

The liner with pierced pl y backing can

then be screw-fixed to o rm (3).

\

1

Erne taken in removingfins ront Douglas Fir

pays off in providing niuny boardmarked

castings. A good mou ld sealer is essential.

\

\

An advantage offace-lip casting is instant

repairahility.

Reinember to avoid details that prevertr

chosen aggregate from filling corners.

Chamfers and rounds help here

-

also

choose aggregate size carefully

Expect sparsity of aggregate at mould sides

and against in-situ form s. External vibrators

are particularly liable to cause this.

Fix feature forme rs fo r striaiions betweeri

ply fillets to present grout-tight fac e to

concrete.

A recent problem

-

ast in brick-facings are

too good

-

he bricklayer ‘humours’ h e top

of th e brick, precusters place fac e down and

equalise inequalities. Mask infill in shadow.

Poorlyfix ed sheathing niay cause lines of

high intensity off ines . Introduce backing

member at joint and double upfixings.

Do, d o, do provide physical key, either integral

or in -built, resined, stainless pins.

87



Fixing t o concrete

\

There is afi sin g o r evevythirig these

days. although high strength concrete

can cause some problems.

a

\

When ixing

to

pre-tensioned concrete

elements

a

look

at

the end of the unit will

help to establish fixin g location.

To

get

a souridfixing using drilled

holes, the hole must be o fth e correct

dianieter arid depth as recommended

by the nianirficturer ....

i’

Ideally the Jixing should be between and

below

steel,

spaced

to

avoid upset

between adjacent fixings.

Ear defenders and goggles should be

used fo r directfixing work.

Also

work in

badly ventilated spaces should be

N

voided.

Penetration depth in concrete will govern

strength offixing

-

istance fro m edges is

critical.

Lines offixings can cause problems

p i

+

...and at right

angles to

the surface.

----------

Concrete provides

a

lot of surprises - his is not

a

most pernianent arrangenient.

Check fo r reinforcing positions to avoid

damage to the tip of the drill and possibility of

interference with anchor expansion.

Follow the maker

k

reconimendations

regarding torque

-

we’ve met the ello w

before.

Trialfixings are essential when important

Jsin gs are concerned. The niunufacturer k

representative has

a

much simpler device fo r

pro0 testing



Surface retard ers

Surface retardem simplifi

the

achievement o

exposed

uggregate

concrete

o acceptable

visual standard.s. Consistent workability and

care with adnii.rtirres is, how ever : e.s.seritial.

Avoid leavin g the container uncovered.

Solvents cari evaporate away

-

onie are

f lammable

too.

Make sure

that

the corituiner is thoroirghly

stirred

- a

mechanical niixer would

help,

Apply

evenly with CLEAN

ro l l e r o r

brush

to

previously seuled surfaces.

Protect coated surfaces

J?om

weather

-

we

are

prortiised a waterproof

returder sooii.

Take care that t he concrete gang are

instructed iri placing techniques arid realise

the

need

f o r carejirl work.

Avoid the "belt-it-in echniqu e which scufls

the retarder

coat

and watch for

those

big

feet

Use

the same people

to brush away retarded

paste

and fines

-

high

pressure

water or air

and water is ideal.

____.__

Don Pfiiiish up reading the instruc tions as a

last resort when all

else

has failed

89



Architectural concrete

Ou r man is impressed by the range

of

concrete finishes available to t he designer.

.

such as the polished finish, the result of

filling, grinding, filling and polishing by

the precaster...

... s rue11 as em erging in-situ floorin g

techniques

171

Scandinavia where pigmented

concretes are placed successively into

previously hardened concrete laid in

predetermined patterns before a final

grinding whe n all is hard

...

...

and, at th e other end

of

the spectrum,

expos ed aggregate partels used i n American

til t-up construction, emp loying 200 mm

Stone cast using the traditional sand-bed

technique - spectacular

He noted the recent developments i n

abrasive and water jetting, particttlarly th e

possibilities these offer designers for

emphasising form arid texture.

He had beeri impressed by t he use of

precast ferro-cement elements in

prestigious buildings

...

He kn ows , of course, that the current

generation of colour-coded snrface

retarders provide accurate control of depth

of

exposure and can be used

on

a n y f o r m

surface, and that ...

'\

'

/

...

wher e the stark structctral integrity

of

concrete is to be expressed, permeable

formzuork ensures a dense durable face.

... nd had seen 'magical' uses of

glass-reinforced concrete, particttlarly in

the M iddle East in building enclosrrres, sun

screens and similar applications.

Abov e all , he is well aware that none

of

these finishes could be achieved without

appropriate skills and training and proper

investment in equipment.



Concrete su rfaces

A s soon

as o u r

men read the specrficatioii,

they

soirglit

out

a copy o ‘Forinwork

-

a

guide to

good

practice ’*,

where

they ound

commentaty

..

Follo~virigJirr/hertir& of the

recommeridations

iii t he

guide, however;

there is

lit/le

doubt

that

our team will in

Jitture use trial pariels

und

establish

saniple

,

standards at site early in each

coritract,

arid

match them in subseqrrent work.

Abrasive blasting. particularly tlie ’hrush-

blast finish , is IieIpJirl in avoidirig crazing

brit

there are

a whole lot

o

regulations to

he

observed

and care to

he

taken

ifour

men

are

to live

to

a ripe old age

111

the ield,

high-pressure water etting arid

wuterboriie

abrasive techniques are proving

p o p ~ l a r :

...

on the economics ofJorniwork,

noting

that

inuppropriate sirrface inishes feature heavily

among

detuils

sucl i as corbe ls. variatioris in

slab soffits.

wal l

heights and column centres,

box-outs arid

inserts, in

ortversely

cffecting

ecorioni,v o

production.

The guide also contaiiis irlforniatiori orifiriishes

iriclirdirig ‘Specialfiiiislies ... Cubco

s

specialities Uifortunaiely, n the past . they

have experienced di f jc r r l t j~n interpreting some

specrficatioris iri this

category.

O w

nieii

were

reminded ofthe need for

carejr l

selection o release ageiits in the pur~suitf

good surface

Jiiiish,

as

well

US

care iii applying

.sprLiys on site. Havirig t l i i r s consulted the

‘Oracle’,o u r men j. thoirgghts turned

to

alternative surJuce inishes that they might off e~ :

Toolirig.. producing a liigli-qualityfiiiishi then

knocking

off’crll

sorts o

spots -

eeins

N

destructiveprocess Althotrgh it is oJen seen

as

a

wr r y

of ‘improving ‘p oo rsurfaces,

oJen

more

blemishes w i l l he exposed as tooling proceeds.

l i i /his case, p l r i n margins w ould have protected

tlie urrises rom our nian

s

at/ack

Striated conc refe and exposed

aggregu/e.s

using

nrr f i ice retarders continire to provide simple,

economic arid practical nieuiis ofprodircing

interesting

strflaces

that

werrther

well. Liners

are very

popirlur

and ‘controlled

permeability’

niatericrls ure making a huge impact on

indirstty, especiully as they improve

‘covercrete qiruliy.

O coiirse,

where really .specialJiiislies such as

stone

mid brick faces are required, oirr

man

realised that the precaster: with his mot10

precasters

d o

it lying down ’. can siniply

produce eridle.s.s varieties offinish.

* Formwork - guide to good practice. 2nd Edition. The Concrete Society.

1995.

91



Main tain in g concrete finishes

Ou r man has kn ow n for a whi le that , a l though he sometimes has

problems bonding things to concrete, his colleagues have little

difficulty in the matter

Many stains respond to dilute acid applied

to

a wetted surface.

f rom the top down ... for w hich he d ons th e correct protective

clothing, goggles an d

-

mportantly - an effective mnsk.

brit really difficult, local blemishes may require poitlticing nnd/or

steam cleaning

...

reminiscent of early medical treatments.

Mud or clay stains are most frequently encountered and he hoses

these off at tbe earliest possible mo men t.

Some stains respond

to

abmsiues , a ir-a dab rasiv e sprays, or

water jetting

._.

Stitbborti stains m ay call for specialist attention. O ur m an n ever

experiences

a

shortage of recommended remedies

Of

course, the best ways

to

reduce maintenance p roblems are

to

protect the surfaces dirritig constrirction and ...

incorporate textured concrete surfaces

to

deter vandals.

92



Protect ing c on crete

\

93



Cleaning concrete

First/) ,

It

1s CSSeIftifll o eSfflb/iS/J

U h i l t

t h e

pro6lem is. Is it rust, pyrites, bitnnien

...

oil? I s it f rom ofi tside or f rom

w i t h i n

t h e

concrete? On ly tuheri the cause is

estahlished

can

the remedial work begin...

perhaps it is time to call in an

expert

There are

plen ty

of cl~ettricals or use in

cleaning concrete. Som e present safety

prob lems or may upset later treatments ....

Best t o stick to proven materials.

Unlia sed advice is available from

trade associations.'zJ

Manrrfactrrrers w orn thii t uapours fro m

some

chernicif/

cleririing agents inay

attack

neorby surfaces, o n d s rns ib l y

aduise tes/ing

a small sample a r e a

Abrasiue blasting, although extremely

effective for cleaning fine textu res

is

operator-sensitive,

and

...

... tooling, used to remove heavy

contaminat ion,

is

bot h operator-sensitive

and concrete-sen sitive arid m ay reveal

further prohlems

_..

1

fiiiled coping oint. gasket or flashing,

the geometry of a feature sloruing the

prrssrlge of tuutcr cau sing deposi ts of dirt.("

Delects shoitki

6 e

rectified 6efore airy

remedial ruork.

Sometimes the oldest remedies d o the trick ...

dilute acid

applied

to w e t concrete, ruasked

o/f with copious amounts of water.

Correct protective wear

is

essential - a

ful l

face

niask with the correct cartridges

installed Lightweight masks d o no t

protect against fumes.

Water jetting or a comhiiration

of water

arid ahra sive seems

to

be the

ki t rdest

treatment /or niost 'ailments' nd

usual ly produces the desired result.

O n comple t ion , it is time to consider

coating or sea ling, parricrrlarly ruhere

cover has been reduced.

( 1 ) Precast concrete cladding. Ed H.P.J.Taylor. Lon don , Edwa rd Arnold.

2) Removal of s tains and grow ths f rom concrete. Crow thorne,

British Cem ent Association. Appea rance M atte rs Series, No.5

94



weather ing

When w e consider the variety of conditions 10

which a structure is subjected it is not

surprising that different weathering patterns

emerge.

,/

This may occu r on a non-modular basis as

d o v e or where windows or curtain walling

cause concentrated movement of dirty water

- hen the marks may be modular:

Reeded or striated , concrete directs the

water in the way

the

designer intends.

Horizontal surfaces allow dust to collect and

upset consistency ofJnish.

Skilled design ofJilce andjcu ture can

eiisnre that weathering or ugeing enhances

the appearance of

U

building.

Reeded surfaces and modular details

prov ide preferential paths crnd loc alise

marking.

The effects of “min i environnients ” are

offen

upparent

at

returns in elevations and

corners of the slructure.

We all have something to contribute from

previous experience

‘ 0 ’

Joints in flashing or other building details

may cuiise discoloration of concrete “hand”

courses, panels or beams by directing water

jlow

Rate of water movement and point

of

discharge are critical to consistency

of

weathering.

I

7

-

. J

a

‘

3 *

:G

Some details forma lize the weathering

process and add

to

the visual effect.

Exposed aggregate and lightly ground or

etched concrete. have a pretty good track

record and it

k

advisable to make the selection

on

the hasis o fjn ish es which have proved

sutisfactory in the local environment.



Repairs and rem edial w o rk

OK,

so

we have

all

ltad troub le with bad contpaction Ultd

duinaged carrier.s. How

can

we repuir these effectively?

\

Clean

the

concrete surfaces, provide

sound

forniwork suitably strutted into position, saturate

the concrete and allow the surface

to d t y

Sieve

the

f ine material

atsd

use muter ial pa.ssing

he

600

nticron sieve - coarser muterial tnay be

used if limeslone.

Use a

I:2X cementtsand mix.

Tlte

marble is ront 'wash-stan d' or the loat is

cast

on

a

sheet of glass.

Where

the duniage

s structural, cortstrlt the engineer as to hest nietliod of repair:

Cut buck concrete to uvoid feather edges and supplement

the

steel with

nte.sh

or

dowel bars. Chentical fixirigs ure

i rse j i i l .

ntechnr~ical aininer or cau lking tool.

Most

important - nsure correct

curin g irsirtg water, hessian o r curin g

unch in structural concrete nt i,~ sing

-~

contpound. Now we are ready fo r the

finishing operation.

Having stippled i n an approved

bondrrtg agent, apply the m ortar tnrx

We have thus avoided the repair made with

Fnishing m aterial '

so

hazardous in

precasting and the special contpound that

leaves 'repairs' suspended on threads afier

a

fe w months.

Dress in

to

a tightfinish using a piece of

ntarble or U centeritfloat.

(Acknowledgements to

H.J.

White. C&CA.)

Our repairs will withstand a.ssault with a

blunt instrument (an offcut of 25mm bar)

and will ring like

a

bell when struck



HA NDL ING A ND SAFETY

uch production and construction includes potentially hazardous operations.

Many thousands of tonnes of steel and concrete are placed and poured daily

M

nvolving the strihng and erection of huge quantities of formwork and

falsework. In the past

25

years, there has been

a

massive change in attitude

to

safety in the

workplace. In his early days in the industry, safety appeared to our man to

be

the last item

on any agenda, almost an afterthought

He knows that safety is now a paramount consideration right from the planning stage.

Training at all levels has instilled in managers, supervisors and operatives awareness that

care and consideration for workforce safety promotes higher quality of product and

improved outputs. Designers and estimators build safety into their calculations and

employers provide equipment, clothing and fachties

to

promote a safety culture on site and

in works. Safety considerations are now an essential aspect of construction and production

operations.

97



Li f t ing

n

We once knew a man in the b lock industry who

lifted I 1 tons ofpa llets every day. .

Chin in, but loo king one’s height (the chin

tucked in elevates head, straightens neck,

relieves back and shoulder m uscles and

helps breathing). Try it

These hand positions d istribute work among

several muscles. Straight arms are impo rtant.

Pushing is difficult to carry out well.

., until someone told hini what he lifted in a

day He demanded his cards and money and

left

Foot position is very important.

( I )

Too

close

-

ack of balance,

(2)

One oot

pointed - good balance, (3) Too ar apart

Balance is everything

-

ifting out of and

over things causes endless damage.

Again chin in, use body weight -possibly

shoulder as well -fro nt fo ot is ready to check

action.

A lot of lifting dep ends on stance.

*

\

Fold fing ers conEfortubly around weight to

apply utmost pressure easily.

A balanced one-handed lift aided by or ce

applied using other hand and arm could be

better i f applicable.

\

Having lifted it. then what? 63% of reportable

accidents result fro m people falling or being

fallen upon

*

The

manager’s responsibility for safety. London, The Industrial Sociev,

1979.

93



Lifting equipment

m

Probably

the most economic ~ttach men t s

by

using throirgli-holes

- p i n s niti.st

be

good

fit and

well secured.

The rnostfreyuent source ofproblein

is

the

eye bolt

-

best avoided.

Spreader bars

are

essential fo r long

members,

avoiding ihe tendency fo r the

ends

to

wunt

io

meet.

Articirlated

spreader bars allow U

vuriety of

sluhs to

be

handled.

Special

brackets rnuy be

required

to

ensure

cladding elements hang in a manner that

allows

insertion of

gaskets.

arid so on.

in

erection.

Ii

seenis like

.sciencefiction

but

lijiing of

plunks in multiples offive or si.x has speeded

irp

erection

on

a

riirniher

of sites.

Beware the ‘7

onne syndrome ’. No

niatter what

it says o n thefitting, the lifting capacity of

any

aitachrnertt

is a

function of

concrete

strength at

the time of l f t ing .

The ungle between slings dererntines /lie

tensile

orce in those

slirig.s:

inset - lie

ntukings

of disaster

Adjirstable

spreader

bars

ensure

correct

upplication of for ce

to

cast-in lifting fittin gs

rind

cater

f o r units with

difserently

located

centres

of gruvity.

A simple rocking

beam caters for elenients

where

lifting hooks

w e

other

ikun

concyclic.

Really heavy elen~e nts enland trunnions or

cast-in plute connections.

The

National Federation

of

Birilding

Trades

Entployers Manual

‘Con.struction Safe ty ’

published by

BAS Mu nugemerit Services

provides

U weullh

oJuseJirl inforination.

99



Safety

Comm on law has established the rights of

the worker, i.e. safe fel low workers ..

Safe place of w ork

And o course we have all attended

lectures on

the

subject.

...

and, safe method

of

working.

However,

some

points come

home more

forcibly than others. personal accidents..

Or accidents

to

rie1id.Y

Accidents are never planned,

The outconie certainly not intended.

Often quite innocent people

are

involved...

Conscientious people working where they

have been told to work using the approved

method.

Some also cotitrihute to their own disaster.

A l l

of which makes it more imperative to keep

.+ty

at

the top of t he list



Sitesafe ’83

Whether architect or

de.sigrier.

truinee itinnager,chuin

boy.

coticreter:.

. .

conirrrct manager, peripuiefic supervisor:

.._

ngineet;

drcrrrghtsnian o r detrri ler:

subcontrucior: form worker, ulseworker:

_.

Clerk o Works.

Resideni

Engirieer..

... or one oftlie coimtless ~houscriidswhich include

the rest

of

i r s

...

cstirnutor or

prodircrioti

p lu l i l ~~ l : . .

curpenter:

...

gerierul oreniaii

S i k w ~ f e83

deniand.s

our supporr.

101





Supervision

Muiritairiing a cheerfit1 and frieridly approach

helps to get the

best out

ofpeople ..

At all costs resist

the

temptation

to

’wrap’ hings

round iiecks.

It

is worth remembering some men work best

if

left

alone.

As is help with other problems where

the

goals

are

much

the same.

After all ‘they’are

riot

responsible fo r

r i l l

your

trou bless.

These driys it seems it ..

u s t not

enough to say

what you want.

Others need rather more attention.

I t

goes without saying the admonition shou

a priva te matteK

contributors

7

Although they might sometimes

he

You

‘vegot

to

show, ho+o,where

r ind

sometimes

often

I when -

A useful point o f contact f o r all is that

of

safety where a commori goal is shared.

And that a little public praise is a good

motivator:

1 3



Cranes

As

he is above our l ine ofs ight , we m ight

forge t the considerable contribution made by

the crane driver

...

. ._and the competent banksman

/

/

The driver b ey e v iew is good for spot t ing

bottlenecks.

In passing

-

tacking beams, piles, bar and

linear stock normal to the travel provides a

bonus in terms of swept area.

On the smaller scale. air hoists make fo r

speedy handling

...

Problems of overlap can be eased by

strategically placed rail and bogeys.

_..and a simple monorail improves

throughputs.

Areas

of

intensive activity can have

supplementary gantry coverage - or he

supplied by ast skip or bullet.

Good comm unications are, of course,

essential.

Watch how the y are .stacked, however. Check

location and number o f battens.

Pendant controls ree a man

to

o in the

production team.

Remember that, until air percolates the

mouW concrete interface, stripping an element

from afixed base is akin to testing the

equipment

to

destruction



Crane communications

Best mid safest results

come

rom using

recommended signals*

...

“Hoist”

(clench

ist for

take slrain)

R

“Lower”

“Sl ew IeJ A ”

-

Slew right B”

-

“Jibup” (hand

on

head)

“Stop.

load”

(clench and uricleiicii) “inch h e

"Jib down” (hand oii head)

“Emergency s top”

“Travel

to

me“ (indicate

with both hands)

“Travel

ront

nie”

(indicate with both hands)

“Ifirid

it

iinpoxsihle

to

signal dire

to

iolforeseen circunistances ”

* Series of c r u i i e signals recommended (with

one

exception ) by the Nationa l Federation of Building Trades Emp loyers arid Federrition of Civil Engineering

Contractors.

05



Gett ing things m oving

R i

b

We

realised long ugo that, setting aside the

expense of the rollers, gravity conies ree. The

problem is stopping ihings rather than siorting

theni

~ - -

_

-

- .

-

-3=----.-

And top ma rks for inriovaiion go to thefitter

supervisor whose roller devices open

up

ihe

works for the crane to

out-load.

Bogeys divorce stack arid load from produciion

- Cuhco man cuii move several tonnes

(downhill ).

We

have lollg advocated the wheel as (1

means

of

controlled discharge ..

In the Midd le

East

you find everything

OH

wheels

-

he

i t t e r ’ s

shop goes everywhere.

The heavy ro l le r has its place

in

concrete

production as well

as

cricket. (Fill

tube

with

rebar

or

concrete.)

Method

study

nien

put

set ters -out

on wheels

to

good eflect in one oinery works.

Storie-age

technology

it

may

be,

hut

ro l lers

allow the easy niovement

of

the most

uwhuard

elements

- or f inishing.

The humble

m o t o r hub

makes

a great

tiirntable

or gritting products.

._. r as a

basis

of a

wire dispenser in

prestressing.

We’ve heard that in the

US

supervisors

have beeri pur on wheels - oller skates,

perhaps.

We would

riot

be

surpr ised

W h a ~

ill

be

the next

use

our inventive ladsfind

for

the

wheel, we wonder?

7 0 6



Ergonomics

-

In /he library, we rook a look at t he

ropic

of

ergonomics. pliysicril charucterist ic.s

We learn/

a

lo/ more about ' ou r ~ n u n

and

his

And, oltliorrgk mos/

of / he work

on

/ l i e /opic

has been based

on

orlter indiistries, / he book

empliusised how

position und conditions

aflec/ / l i e

qirali/y of

/ l i e

prodrrct.

4

. .

Kneeling,

for

instance..

/

-

... r e ~ l i i n g..

' , , . I ) . I I

and overhand work .

. . /he changed

posifion

rind al/ered interface

wi /h

/he

workpiece, . .

...drus/iccilly ajfect results

v

>

;a

Also

how: when

jii/igiie

sets

in....

-

===------ ~

Er~on otnically periking, every

part of

/ l i e

task

varies

- as do t he

re

ul / s . . .

... to / l ie e.r/en/ /liar /lie

workpiece presen/.s

u

perniunent cornrnentury on

the niethod,

skills

und conditions.

We piit / he book back, resolving

/o smdy /lie

ma/terjir/her

1 7



Safe w ork ing w ith sm all dumpers

A most helpful publication appeured

on

our

desk the other day* ..

A

Little points of self-preservation such as ‘the

grip ’.

Ensuring the vehicle (and the driver k vision)

are in efficient working order and good repuir:

\

And, although you will have noticed our man

is aware of the need for head protection ..

. _ . oncern ing small diimnpers and the antics of

some of those who drive them.

c

_

Guards to prevent

people

getting wound into

the works.

Providing effective stop-logs or blocks to

prevent / he niachine running

or$illing

over the

edge of

an

e.rcavation ...

... which may save his life. it won ’t protect his

limbs.

Many of us hcrve seen

the

results arid

it

k

interesting tof ocii s on the details o r a

while.

Prohibiting passengers

iiriless

a piirpose-

built sea/ is provide d (iisuully only oirrid

o n /raining vehicles).

n

... which apparently huppens airly

frequently

The publication is very coniplete arid

includes reJbreiice to the Motor khi cle s

(Cons /riiction and Use) Regulations 1978.

offering assistance over enquiries.

* Safe working with dumpers. Health and SuJdy Executive. HMSO.

708



PRECAST AND PRESTRESSED

CONCRETE

ork in precast concrete production presented our man with

an

insight into the

ways of the precaster. He was impressed by the possibilities presented by the

W

ange of processes available to those worlung in the enclosed environment of

the precast works, and even in works set up

on

site. The outputs resulting from

mechanisation and automation compared favourably with those he was familiar with on

site, offsetting the additional costs of transport and erection.

The hgh rates of production achieved in works stem from the use of equipment such as

gang moulds, battery moulds, static casting machines and mobile extrusion m a ches . These

combine with carefully controlled mix characteristics and, where appropriate, prestressing

techniques

to

ensure economic use

of

expensive facilities. The rapid turnround

of

frame

units and cladding elements displaying exotic aggregates and reconstructed stone finishes

underlines the

SUS

mployed in mould manufacture.

In works and at site, he witnessed the production of both linear beams and segmental

elements for bridges and was impressed by the technique o f incremental, segmental bridge

launching, each freshly cast element being post-tensioned to the previously cast element

as

the bridge took shape over the piers.

Latterly, he encountered tilt-up construction and noted the speed of the operations, use of

traditional skills and the possibhties for incorporating special finishes while maintaining

the simplicity of the site casting processes.

109



Precast concrete: samples and prototypes

In establishing standards of appearance and accuracy, whether f or

cladding

*

or structrrral/visrral elements, large samples are essential.

While indicating possible textur e and colour, small samples often

provide a commentary on the skills of th e sample ntaker

Models that replicate the details included in the prod uction element

provide a niore realistic sample, particularly if produced in the same way

and by the same workers to

be

employed in the production.

Given the fun ds, frill-size pre-production sanzples can be assentbled, in

the factory or on site, to determine standards of finish and validate

connection details ahead of prodtiction.

Althou gh the precaster has the opportunity

to

cast elements in the

ntanner best suited to the achievement of correct cover

to

reinforcement

and good compaction, essential to quality of finish ...

For the designer to have a realistic view of his intentions, product

suspended on a crane can be rotated, and viewed at the distance and

wit h the orientation it will have in t h e structure.

Cast in

stone.

Architectural Cladding Association, 60 Charles Street, Leicester, L E l l F R

Models also have value in comm unicating complicated detail,

as

in

‘hybrid’ structures with high-quality finishes. O therwise, heavy-d uty

bolted and strbsequently welded connections between true comp osites

of structural

steel

and concrete‘ take some understand ing

...

large size santples should be available in the ioorkplace to provide

ongoing reference for the workers. Standards established earlier may

otherwise decline during weeks or m onths of production.

The precaster’s stocks o f elements of specified and approved qualiry are a

critical factor in continuity of supply, erection and progress at site.

‘Interface. Newsletter of Trent Concrete

Lirnlted.

Colwlck, Nottingham, NG4 2BC

110



Precast conc rete 1

1 1 1



Precast con crete

2

Precasters have

been

“Fasr-tracking”for many

years..

.

precasting being carried

on

in time other

than that critical to the overall duration.

To

get

t h e

best

rcsults.fiont precast concrete., , Estab-

l i s h

detail u s i q arge srale samples andjull size

mark-ups.. .

which must

be

produced with manufacture and erec-

(ion in min d. Sim ply “chopping-up” an insitu de-

sien iw ul d vresent difficulties.

Take a

close look

at the.jacilities that the precaster C

f i rs. . . many have

some

particular specialisation.

precasters take pride in the qua lity of their reinforce-

meitt cages, carejully tied and labelled with extreme

care over maintainin<q he cowect cover.. .

an d where prestressittg is ram’ed

out . .

Moulds and steel are caref//y checked

in,?.

.

c a t -

allfinishes are produced itn‘th references to substantial

samples. Inspertion prior

to

despatch ensures..

.

Visit rompleted work to assess acruracy of elements,

quali t y cferection and suitabi l i ty o details..

.

Tl ie ratio ofsupervisors to operatives is imp ort ant

in

terms

o fqua l i ty Check the skills available

too

exotic agqr qat e and stone or brickfaced elements,

each material suitably bonded into the backincc

concrete.

qu al it y produ ct, providin‘f early enclosure, speeding

ii istal lation of services and redun’ng expensive on-sit e

time.

12



Precast co nc rete

3

Trends in techniques f o r designing and

detailing precast concrete (including

perhaps the use of computers

)...

/

7

. .

. .

. . .

- .

...

produced using considerable

mechanisation while ..

... have resulted in greater

use

ofelements

suited to m anufacture...

and erection.

..

...

incorporating the wide range offinishes

available.

... and quality assurance.

..

... such as that applied in theflooring ..

In production there is considerable emphasis

on quality control

..

... and fram e schemes of

BSI,

FCS and CFA

The advantages taken fro m these and

parallel developments in plant and

equipment.. investment.

... when coupled with the skills of 'the lads' ..

._ .

roduce attractive energy-efficient

structures providing early revenue on

113



Prestressed co ncrete 1

Ducts require restraint against downwards movement,

flotation and lateral displacement. Make fixin gs at

‘stationpoints

’ on

catenary o r ease of installation and

checking.

Simple roller hung by angle

steel

fram e assists in

the entering of tendons at a nchorage position.

Wt

Duct location can be determined by

o f f u t s

o

steel welded to mild steel

stirrups or b y wiring to sleeved

dowels.

‘Shrink’ lastic sleeves ensure grout-tight and

strong joi nts in d ucts. Insertion

o

tendons before

concreting helps avoid duct wobble.

Remember that at transfer the units on a long-line bed will move towards the dead-end

abutment

-

bearing plates and projections must be free to slide. When the prestress is

transferred or a pos t- ensioned beam is stressed, the loading

on

base (or alsework) changes

from one which is unifornily distributed

to one

which is imposed at reactions. Check fo r corne r

damage on skew beums.

Failure to indicate clearly the state of beams which

are partially prestressed fo r handling purposes may

result in failu re. M ark with pain t afrer partial

prestress is applied.

Stacking battens should be at or ne ar ends o

most prestressed units and directly abov e

each other:

Bad ground or bad stacking can result in

sideways deflection and creep.

The prestressed manufacturer will generally be

pleased

to

grade units and deliver in such a way

that camber is evened out over bay of

construction.

Most prestressed plank and flooring requires

propping until topping is inished and achieves

specified strength: avoid local ‘dumping’

of

concrete.

114




Equipment should be tested and calibrated arid

the reqirireriierits of the specificutiort observed

re:

provi r ig r ings.

etc.

Grips

(mid couplers)

should be curejirl1,v

examined

for weal: a

tube ‘ do l l y ’

will

ensure

even locatioii of wedges.

Proprietary sleeves form

excelleut

o in t , s t rong and

grout

tight. Observe

[email protected] i ns t ruc t i ons re:

pocket

arid

anchor detui l .

This

w i l l

ensure iiose

o r

j a c k

caii be introduced correct1,v.

Let

:s choose our

brightest

people for

the

work, they n iust be alert atid nius t keep

cureful records.

Avoid

-

sharp

corners 011

stopeiid.s

arid

distr ibut ior t

plutes,

electric (weldiiig) current mid speller from

burning operutioiis, iristunt failure

cuii result.

Provide

space or cast-in

bear ing

plates to

accornrnodute inoventent

at

time of

truiisfer

or

stressing.

Distribution

of

loud on base

chaiiges

at

stressing

too.

Eiisirre

teaiii

rinderstand relatioiiship

hehveei i

gauge reading and

exteiision.

Lack

of

extension

Dolt exceed giveri gauge re ading i n

aii

attenipt to achieve

extension

-stop

-

-

indicates

blockage

offriction in duct.

corisirlt engineer

Ksual uud audio warn ings , bar r ie rs ,

gloves and goggles are

needed for

safety

Erke

over duct loccrtioris. eurly

i rtsertion

of

teridorts

assists

w i th

line. Beware,

uplifr

CUII

displace cage

as

we//

Watch or

correct

skew -

eoms have

been

cast wrong harid. Corners

ure liable

to

duiiiuge

due to camber -

chunifers

will

help avoid spalliiig,

Alwrr.vs observe

recoiiiiiiended

seyirerice

of

stressing

to

avoid traps

uiid

ALWAYS

keep

accurate records.

15



Prestressed con crete

3

Less drmrrotic,

b r i t

eqrt~7lly scititrg. were

post-teiisiorred

iri-sitrr

f l o o rs wher e

sirriply

irrstcrlled teiidorrs arid airclmr‘rgrs, plus

sonre ndditiorrnl

reiriforcerneirt.

rnnke

early str ik ing 111

foriris

possible, speed ing

t h e complete constrrtction cycle.f

*

Techiircal

Report N o 47.

T/Je

Chtcrr fe Society.

t K

CABri t r sh Cenient

Assuciofion

Pirblrcation

I’

Post - tens ioned cirircrele

//orirs i n ntrtlti-storey l m i / d i n p

.

116




When you draw out a section firll-size you realise

the challenge

to

the producer presented b y the

combinatiori ofstee l and ducts.

While we are

at

it we should check those

transverse holes ...

the produc t was perniunent forni work it7 / he

shape of T arid

L

beanis o r an airport

concour.~e.The transverse stressing cleured it up .

Differeritiul camber can result fro m p oor

conipaction - and a nuniber of other lhings.

Works checks against a tuut wire

cat7

assist by

grading elements fo r sequential placement.

rigerits get cross when they realise

thut the

crane n iust be brought back to site to clear a

blockage

Talking of camber

we

had some problems with

sideways camber once ...

The

prestressed Jormwork elements provided

aii

economic answer to spunriing U major

road

-

educing the alsework reqirirements

under the 4-lane span.

\

How ubout this fo r a novelty

-

n 1951 we made

sonie roof units using

30m ?i

p h k s a /t er ii at el y

linked and dehonded ...

when turned on edge they could be opened

out

to form an

elegant

w a g e .

Prestressed plank .sinipliJe.s the ackw ork

below decks

-

55,000were used by the

contractor in the elevated section

of

the M4.

\ \

U*’&

Jun Bobrowskik ‘bendy’cladding

panels

still

take a bit

of

beating, however

117



Concrete m ou lds fo r precasting

A considerable anioiint ofprecastirig can be carried out

on

aya t slab

using paper or polythene

as

a

parting agent. Side nienibers

-

oadfornis

or timber - un be supported by pins

or

plates.

cast

J?om con cre te niorild arid

j u s t

one reniovable side

member:

Where slender units or slabs are precast, a suitable reinforced slab can

be used as U ‘tilting a ble’. Concrete pallets are useJiil in product

manuJacture.

Duct covers, wall units and suitably reitforced

slabs c m

be cost using

concrete sleeper walls and concrete cell dividers.

Artist j.

or

designer i original works c m

readily be translated via concrete muster

nioiilds into ‘ar tfo r eternity

’

Of cours e the iiltiniate mould materiul is

GRC -

ts strength, resistance and

moulclability are the an swer to the mould

designer

k

pruyer

Products and

tiirinel

segntents can

be

battery

cast using gang casting methods - all mould

nieinbers generated from accurate m asters.

18



Mould design

I t S

no

use - he books only give you part

of ilie story To design moulds ...

you musi gei a feeling for ihe skills oJihe

crajismen who build moulds ...

to develop an undersianding of th e impact of

numbe rs, mass.

scale

and geomeity - good mould

n i u n

can piciure eve ry variety.

n

Models will help wiih visualising complex

shapes and understanding geome tty

Muke

a

careful siudy of

all

the details

-

never accepi ihat the per~son roducing

then1 understood i he iniplicutions oJih e

lines

on

the drawing

Take care over details

....

Grout tightness.

lead, draw and siripability

Gei in there yourself and try to improve

your detail and method.

Tighi

oints

carefully locaied

...

andJ.red

nienibers. govern accuracy

and

quality.

Keep u n open mind on materials - ot dijjfjcult or

a

Cubco man Look

closely

ui other peop lek

iechnology.

Make sure your intentions are ihoroughly

understood b y ihose who must use the moulds.

Conirol those concreters - hey have iargets to

meei -you r moulds must allow speed oJJI1 and

the achievement of good compaction.

Maintain the conirol and beware the 'do-it-yourself'

mould demolition kiis provided in loo many works

119



Polymer moulds and liners

A

loi

ofpeople are busy with casting resins

and rubber lately

which may even result in board marks

around

the

column one day

-. .

.

.

-

. . .

_ . . . . . . .

.

. . .

---.- ;

;.

, . .

,

w-

. . . . . .

Reinforcing rod, tube or m esh strengthens

heavy liners, undercuts and iniricate derail

can be reproduced.

The maierial is self-releasing, provided

concrete siregth is such as

to

resist

mechanical damage.

They can be

used

to prov ide both fornl Jircing

and product mould liners.

I .

Whether formula ting or rigid or flexible

liners the proportioning is critical

..

Fixing to orms can be achieved by

embedding pierced ply or subsequent bolting

atiachment.

So your m an can dispense wiih mould orfo rm

oil.

You can buy them ready-m ade, by the roll, as it

were..

as is ihe mixing technique

-

mechanicul stirring

is essential.

A little gentle heat aids ihe curing process

Next, products and reproduction in the

renovation proce ss

..

oh, and some sculpiure

120



Flexib le m oulds

. .

Where some sculpture is io he reinstated or

where intricute undercut details is to he

reproduced..

.

or what is called a “masier”model

--

ohiuin copyright clearance and permission to

work (take

oui

subsiantiul irisurunce )

Coat

the

niaster wiih plasiicene

’*

to produce n

nicely rounded shape - his coa iirig governs

he

thickness of

the

eveniualflexible mould.

Place concrete. plaster or grc niix into he orm

and

allow

to hurden (remember io incorporaie

joint to allow stripping)

We now have ari ouier container into which the

master c m

he

reassembled (withoui its coating).

This can

be

poured into the space beiweeri

master and outer coriiaine,:

Afrer removal of he support

h e

plastic or

rubber mould can be siripped froni the master -

sonic judicious cuiting niay he required at the

tricky parrs.

Take

the

original

stone ....

Assemble the cod ed master in a form

-

or f i x

a form around the master:

Now

we

prepare the polythene, polynier or

nielt the casting rubber (niechanical niixing

is esseniial).

Se aside the niaster and model, assenible the

flexible niould into its supporting container

and evetyihing is ready or he iechnical bit -

casting heproduci

* Registered trademark

121



Concrete ingredients

In

considering the range

of

competing

materials. particularly admixtu res..

.

our man remembered the importance

of

conforming wit h specification

..

although he had kno wn authorities t o

accept appropria tely tested and certified

alternatives.

Wha tever the produ ct. storage in secure

conditio ns is essential, some suppliers

providing bulk containers. A vigilant

storeman is worth his weight in goods

Formal training is essential with so me

products

...

although all are accompanied by

instructions' often read after the event ,

such as when something fails to harden

or set

Certain doors have been know n t o exhibit

precise (sometim es ahstruse) bonus

calculations...although proportioning

has often presented our man with

problems

so...

pre-packed, pie-measured constituents are

favourite.

Also,

as poor mixing practice is

responsible for som e failures, 'h ands-on '

instruction is important, preferably in the

use

of

mechanical means.

Fortunately, established standards and

current materials technology in

combination generally ensure that

specified quality is maintained.

122



Concrete as

a

mould material

Concrete is an excellent mould material. It

is stable, has a dense surface and provides

many uses economically

The muster is set up in a simple box. oiled,

and concrete is cast around it adding steel in

large moulds.

The irst essential in concrete mould niaking is

a good q uality muster

of

timber; concrete. or

plaster incorporating lead and draw.

The resulting mould can be used to prepare

more masters, the master more moulds

q

. . . . . .

.. .

.

. . . .

The concrete must be cured, the surface stoned

and then coated with a sealer:

Handles can be added or large moulds

set on

to a level bed.

For special finishes or accurucy, a GR C or

GRP surface can firs t be laid over the

master and the mould then cast.

Concrete moulds will be usejid when long

units are to be c ast, pil e casting , or panel

casting. Other uses include structural

elements, A -frames, etc.

. _ .

. .

. A .

Concrete moulds can be bred like rabbits

and a fterwards make excellent hardcore

123



Precast erec t io n 1

-

general

First of all. let S sit dowri and mug up the

manual or tlie method statentent.

Insist that every unit is clearly marked with

contract number, mark nitniber and dute of

casting. Colours help.

We

all know hearings are critical yet we do

get

a

motley selection of shims sometimes

/

nother sensible step is

to

get rid

of

makeshiji ladders, so beloved of the

‘cowboys.

Light allo>j with a per~n rrrietit~vttacked

lashing cm7 b e set up quickly an d safely.

Expect difserences

i r r

camber: A laut wire

check in yurd and graded locatiori 017 site

reduce slep.s arid facilitute jn isAiiig.

Watch that handing: it

cuti

present problenis.

Commrrnications on site sometimes go U W ~

Ensure the precaster knows how you intend

handling the

irriits

- erlirtps then he will

leave the lijiing hooks intact

Radio or telephone ensures good control.

.

... especially i f th er ei a

set

in the agent i

o f j ce

To avoid this sort

of

thing, turn

to

the NFBTE

and FCEC recommended visual code of

s i gna~ s

11

page 105.

124



Precast erect ion

2

- si te factors

3

Now for the gear, spreader bars and

long brothers (tested) roller bars and

recently, torque wrenches.

A mock-up in works clears up points o

detail early in course of contract.

A

check in the works (beware of ‘Subbies’ apes)....

Check lists ensure that vital statistics are

available to all.

Ensure that delivery instructions are precise. It takes

a brave man to tell the driver with

a 100

tonne unit

to back up 5 mile.

will save problems on site later:

The connections must be simple, ideally

one

man should be able to make them.

Instant erection frees the crane o r other

logistical detail.

Watch out

-

hose men started when the structure

was one storey high

-

hey haven

‘t

noticed it has

grown.

Not all danger is at heights either

Keep a constant check

on

units made, vs

units cast

-

discrepancy means delays.

For a look at prestressed concrete see pages

114-11 7.

125



Concrete sculpture

Having seen the remarkable products o f artists working with

concrete, our man decided to try his hand. H e had alw ays fancied

himself as a bit of an artist

N o w he had tw o options. Either treat the master with a parting

agent and build a flexible mould onto it using melted silicone

rubber.

Or

coat the master with clay before casting a flexible

polyurethane tnoirld.

Wi th the second meth od, the clay would have to be removed and

the space filled by pouririg in carefully proportioned casting

polyurethane.

After the mould was stripped

-

helped by some judicious slitting

-

high-humid ity curing promoted durability . Our m an fou nd that, a5

well as rrsirig the ‘m aster’, he could use freshly cast prod uct to

generate further moulds.

He produced a ‘master’, taking care not

to

think abo ut garden

gnomes. This was made from wood, although it could have been

carved from plaster or an existing artefact could have been used.

The next operation would be to lay a grp supporting container on

the rubber or clay.

Wi th the mould complete. the whole was assembled and fi l led wit h

a carefully designed concrete mix. Superplasticiser and thorough

vibration ensured all entrapped air and water was removed.

In

inspecting our man’s stock, any similarity with any other

collection * has t o be regarded as totally coincidental

‘Such as that unearthed a t Xi’an, People’s Republic of China . Guard ing the tomb of Qin Shiahuang, perhaps?

126



Decorative concrete and finishes

It is quite likel y that some of 11s have mad e im pro mp tu contribirtions

to concrete finishes at some time in our youth A f e w

of

us may euen

have been caught ... with dire resiilts

On vacation in Hollyiuoo d, our m an found that so-called ‘stars and

celehrities’ are apparently still nt it More sirbtlc for ms of i mprintin g

aiid dry shake treatment kaue charlged the facc ofconcrete ._.

establishing it as a desirable material fo r

he

garden, the park ... and

the the me park tuhere he saw imprint ed finishes, reconstrrtcted stone

arid fibre-reinforced concrete and mortars that made his mind /JOggk

Returni ng hom e am i seeing a coiicrete featrtre ioith hundreds of lights

sparkling fro m a colour concrete backgroirnd, our m an thought it just

as

w e l l

the sparkle tuas provided by fibre optics

Conside ring decorative sur face finrshes in general, our mail has

concluded that unrealistic, and often misleading, small samples of

special finrshes should be relected in favour of

...

inspection and selection from full-size mock-ups of available finishes

such as text ures, exoti c aggregates. or panels faced w ith sto ne, slate

or tiles.

Also,

where applicable, specification reference to acknowle dged

high-qrrality plain or decorative concrete in existing structures can

enstire visual standards are established and maintained, so that ..

designers awd architects can co nfidently detail attractive finishes

to

the

elegant shapes and forms made possible by concrete

-

whether simply

reinforced or rising fi6res o f steel, glass or plastics.

127



Lightw eight and foam ed concrete

D

128



Glassfibre-reinforced concrete

I i

is umazing whai our man can

do

with

a

mixiure of

sand,

cement, glassfibres and a

modicum

o water

=----

The resuliing material c ui ~ e spa ye d, laid-up

and conipacied at ihe mould.

Simple methods,

ihe

so-called 'bag and

buckei

'

techniques to establish maierials

content.

..

... and

tesis

on coupons io establish liniii

o

proportionaliiy and modulus of rupture ensure

qualify muintenance.

...

rejitrbishment

.-

... io

shelter - blocks are laid, coursed,

dty..

...

arid replacemeiii

-

omeiimes beiier

ihan

the

original.

...

and

a

coat ofp rem ix material is trowelled

onto boih stirfaces. The result is

a

siable.

energy-economic struciural wall.

--

e -

The

premixed material can be pump ed into

proditci rnoulds.

' . I1

'

The resriliant strong yet lightweighi products

are e>

rlleni fo r ormwo rk.

Oilier upplications range rom sun screens,

improving

ihe

quality

o Iije

in hot countries

...

I .

.

There is ulso an increasing

use

of ihe material

in

DIY ihe

bagged materiul being ideal fo r

home

use.

129



Tilt up construction

\.-

/

Everything in the

USA

is larger than life as

w e now it

-

even tilt-up operations

__.

o really itius t a sniall step

to

cast the

concrete '011 site

'

at site and pop it into the

vertical location

- -

- .U_

- , . -

-

Insulation installation, use of esotic stone

veneers and airy of the simple finis hin g

techniques - retarder: broadcast wash and

brush or etting - an be used.

Upstands and features can be incorporated by

normal means.

We have even seen paver.7

used

to place the

tilt-up slabs.

On site, you dispense with t he intermediate

slab and tie arrangements mid simply use the

normal skills of the concretec

Full join t detail ca n be incorporated in

timber or steel edge orm s

mid

by eatures

f ixed

to the slab.

Bracing arrangements and handling

techniques are clearly documented.*

\ \ /

When all is considered, precasters have

cast from concre tefor a century or more...

Careful choice of

(I

bond-breaker ensures

an acceptable fac e and a clean slab (#er

lifting.

Slender sections can be suppleinented by

local strong-back niembers - but keep that

mail

out

from under

Expensive plant is required only during

lifting phase (the stack casting overconies

the space problem a t returns).

*Series of articles in Concrete International. April 1980.

130



Slipform and tilt up construction

Scandinauiart forming

sk i l l s ,

conr l i ined wi th carefu l niix design.

p lacen ient , comp act ion and cur ing, have provided

an

impressive

dentonstra t ion

of

inc l ined and taper ing s l ip fo nn constr t rc t ion .

T h e

slipfomi

techniqtre

is

largely

enrployed in

constr t rc t i r tg towers,

silos and ch imneys. (The re are apocryp ha l ta les ( I / resident engineers

resor t ing to b i r toctt la rs for

sonic of

their

inspections )

H <J~U C IW.i t r

ntan

realised ...

tha t

In

rcpetIt iorts hr idge pier cortstrttction, o r a strccession o fsLn i /a r

sta i r towers

o n a

r na jo r p ro je ct . s l i / ~ f i ~ r n t i n ~an p r ~ ~ wo he

eC(1nonlic.

It

occr r r red to

hint

tha t

r i h i

~ ( n t s t r t r c t i n gvry tol l str ttcttrres a

‘storey co rott’ nrrrst

Oc

essent id dur ing the s l ip forming stage... o

auoid

a later denridit ion stage

Silicon VaIIey. USA had impressed o n oi r r n tan the e n i ~ t o n t i e s f

t i l t - r ip cor tst rr tc t ir~r r .

.

u i t

j t ts t

si r tgk-st i i rey co i rstr r tc t ion wi th

plain

srtrface finishes Ini t also...

ntttl t i -storey and e i~cw exposed hortldcr ’ yp e elentcrtts.. . coi?rpletr

tuit h architecttrrol fcatrrres. cornices etc. The aduantagcs

of

the

ntethod are th at concreting an d assocrated actiui t ies can he carr ied

ou t a t g ro r rnd

l e i d

w i t h

..

simplicity

of

fo rm and re i n fo r cen to t t

fixing.

toigether iu i th

ease

of

access

/o r t rucks. pimrping

eqrtip~nent

n d cranes*.

In

the case of

less

exo tic f inishes.

floiuing

concrete

can

be placed di rect ly f ront

the t r t tck.

Wi th concre te to

panels, panel fi.vings

a n d p ro p a n c h i~ r s d y

nrattrred, the strttctr tral elentents are sintplc tri erect

in a

matter of

days.

as

t h e crane

is ruorked orrt

r ~ / t h e

itcp.

131



Bridge construction

Ar my service provided our

man,

and

no

doubt

ntany

reciders o f

CONCRETE,

with opportunities for ‘bands-on bridge-huilding

experience

Tbe

inanhandled componen ts were great for devrloping

inuscles

Each bridge...

Bailey bridges are s t i l l

in use

in various forms.

often ~ J Z

cnrporary

works. Reco/lectioris

O f

the laitnchiny procedure

enrp/oyed tend to

fociis our

man’s

ttention

...

With temporary

nose

attached , the prestressed concrete

element

i s

launched

n iecha i i i ca l l y lhydra~ ~ l i ca l l y

ver slender slipforvied or

junrp-

fornred p iers, even

on

curved a/ignnrents

- n

tbis

esainpk?

i:ornp/ete

with harriers

but

rninrrs

road markings

As

well as

easing prohleriis

of

geoinetry, the rise

of

precast

Beams,

segments and permanent form s for

decks

and piers can ensure tkat the

specified

accuracy

and finish

are

achieved in the

f inal

structure.

...

~ * a suilt on rollers

and l ,~ r incker i

rrariiially across the

gcrp.

occasionalls

wi th

t h e

/usury

of

nrecbanical

assistance

from a

passing

huIldoZer brit generally solely by ‘sapper power’.

...

on

tbr

ionsideriihlc enginecring s k i l l s and production ability applied

to all types of bridge c ons tru ~tio n, articrilarly

srte-cast ,

pris/~-launched

bridges.

~’lis/J-/flr41lC/Ji~~

f

br fdscp

l l l d

the cUrefltl/y Cfl/cli/flk? d,dicattp

bolonciiig

acts in

carttileuer construction

sceni

to hint

to

haue

a

lot in

common

with his early,

in r id1

simpler, bridging activities

Thanks to Kobert Day, Sales

,Manager,

Mabey and Johnsoo Ltd.

f o r input

011 bridge eqiiipinent

32

T od ay ’s ~ ~ i r c r e t eridges are elegant. W it b firrther developmen ts in

construction techniques and

riraterials on

the

horizon,

our

inan

l o o k s

forrcwrri t o

great

advances in the

future



Bridges

Ou r man k interest in bridges was re-awakened by the C onstruction of the

Millennium Bridge across the Tham es. Although aware that few

illustrations could do it justice, the remarkable design reminded him a/. ..

Back to remarkable bridges. He was impressed by an illustration

showing construction of Robert Stephenson’s Britannia Bridge in 18 49.

Method s were similar to those used by civil engineers today, also...

many simple bridges encountered across the world. H e wondered if he

concept o/the Millennium Bridge design was to be found there.

the ‘magical’ Zron Bridge in Coalbrookdale, whic h, at the time, applied

an exciting ne w material... cast iron. There is still considerable

specn htior~ egarding the corrstructiorr me thod.

O ur m an recalled an illustration in CONCRETE showing the Swiss

Sunniberg bridge, where sculpted piers support a n elegant tracery of

cables and deck 60 m above the Landquart riuer”. There have been

awards /or aesthetic and technical merit.

Our man considered that, regardless of the construction m aterial and

engineering problem s overco me, concrete and mortars usually contribute

to the foundations and...

,

ruhilst bridge s, across

t h e

world”“ , illustrate the aesthetic and

engineering potential

of

concrete in every form

...

‘ ee

C O N C R E T E

May

2001,

Vol.

35,No. 5 , p.6.

“ ‘see

C O N C R E T E

October 1999,

Vol.

33 , No. 9, p.12

(sketch

after

photograph

of h e

Flintshire Bridge

(Pont Sir

Y Fflim)

by Roger

Brown

ARPS)

the Norwegian designers wh o achieved an ‘environmentally friendly’

solution t o historic bridge preservation by constrricting a n ew concrete

bridge above it on the same alignm ent, deserved a prize

33



Index

A

abrasive blasting 90, 91, 92, 94

access 60, 66, 72, 79, 82

accidents 100

acid cleaning 83, 92, 95

admixtures 60, 67, 70, 78, 122

advisory services

9

aesthetics 133

aggregates 17, 85

air conte nt testing 8

air hoists 104

air-entrainment 78

aluminium formwork 35

appearance 81-96

architectural concrete 90

assessment 5

automation 21, 68, 69, 71, 75

awards 2, 3, 9, 10

B

balance beams 102

batching 65, 68, 69, 7?

batching plant 21

battery casting 118

battery moulds 66

bearings 124

board marked finishes 87

bond-breaker 130

bonding agents 96

brackets, lifting

99

breakdowns 63

brick-facings, precast 87, 91, 112

bricklaying 70

bridge piers 131, 132

bridges 1 16, 132, 133

C

calibration 68

camber

precast concrete 124

prestressed concrete 117

cantilever construction 132

cantilevers 40, 49

Cast in stone 11 0

castable mou ld material 126

cast-in fixings 54, 55

casting resins 120, 121

certification 5,49

chairs 51, 57

chamfers. formwork 25

134

char ts 18

check lists, erection 125

checking 60-62

chemicals, cleaning 94

chilled water 78

circular work 13, 32, 35, 40

cleaning 63, 94

coatings 94

Code

of practicef0r

accnraq

in

bnildiqs

55

Code of

practice

ortfalsei~~ork

1, 42

coil tics 56

cold-weather concreting 76, 77, 78, 93

columns, raking 1 3

communicat ions 11-22,15, 18,7 1,10 4,10 5, 119,

compact ion 66,7 9, 96

composi te st ructures 110

compression testing 8

computer-aided design 20, 21, 22

compu ters 6 , 20, 21, 113

concrete ingredients 122

concrete moulds 118, 123

Concrete

O I I site 8

concrete pressure 42

concrete production 65

Concrete Society Awards 2, 3, 9, 1 0

concrete supply 63, 65, 79

concrcting, checks 62

connections


124

lifting 99


consistency, finishes 83

constitucnts, materials 122

construction cycle 40

construction joints 64, 67, 79

continuity bar systems 55, 57

controlled permeability form liners 58, 90, 91

conveyors 72

cooling 82, 86, 91, 94

corbels 28

cores, formwork 29, 32

corners, formwork 25

couplers, reinforcement 57

cover

to

concrete 25, 48, 49,

51

C1’110 77

cranes 102, 104, 105, 128, 131

curing 74, 76, 78, 84, 93

differential 19

polymer moulds 120

repairs 96

cutting and bending machines 21

D

da tum on f o r m s 5 4 , 5 5

decorative concrete 127

defects, finishes 83, 86

defects, precast concrete 85

deflections 62

delivery 72

design, com pute rs 21

detail 11-22

f o r mwor k 25 , 44

peoples’ input 16

formwork 83.89

joints 64

prestressed concrete 114, 115

detailing, precast concrete 113

details

concrete 17

communicat ions 15

falsework 43

fixings 54, 55

moulds 119

weathering 95

double-tee beams 116

dowel bars 74

drawings 12, 13, 18, 22, 60

moulds I19

staircases 31

drilling 88

drips 17

driveways 70

dry shake finishes 127

ducts, prestressed concrete 114, 115

dumpcr s 108

lliiralile

bonded post-tensioned

comrete

b r i d p

1 I6

E

early striking 34, 116

economics, formwork 91

edge casting, staircases 21

efficient construction 6

elcment checking 20, 21

equipment


safety 108


crcction 131

ergonomics 107

excellence 1-10

expanded metal 64

exposed aggregate finishes 17.8 9, 90.9 1.95 , 112

extcrnal vibrators 80. 87

F

‘face-up’ precasting 87

failure mode, test cubes 8

failure, form work 38

falsework 41, 42, 43, 44, 45, 46

fast-track construction 111, 112, 128

features: weathe ring 95

fer rocement 90

fibre composircs 53

fibres 58, 70, 80, 129

fillets

formwork 25

reinforcement 50

finishes 58, 92, 127


repairs 96

finishing, slabs 75

fixing reinforcement 51

fixings 88, 96

cast-in 54, 55

details 54, 55

flexible

moulds

121

floating of slabs 74

floors

prestressing 53

trough and waffle 36

flow test 7

flowing concrete 71, 80

foamed concrete 70, 128

form liners 87, 91

form removal 64

form ties 5 6

formers 17

concreting 66

cores 29, 32

floors 36

Forn,iork - a x d e ogoodpractice 4, 33, 44, 86, 91

formwork 23-46

aluminium 35

batteries 66

checking 61



circular 32, 35, 40

corbels 28

detail 25, 44

economics 91

finishes 84, 85

failure 38

features 83, 85, 85

formers 29, 32

G R C 3 7 , 1 2 9

kickers 17, 26, 27

liners 45

pcrmancnt 27

pressures 67

ribs 28

setting-out 24, 26

staircases 31

storage 38

striking 34, 36, 40, 44

systems 32 35, 40, 46

vibration 38

full-scale mock-up s 127

full-size samples 110 , I1 2

G

geometry 13, 14, 24, 94, 119

G R C 9 0 , 1 2 9

formwork 37, 129

moulds 118,123

permanent formwork 58

spray up 21

grinding 90

grit-blasting 64

ground beams 4 6

grout-tight joints 1 7

G R P 5 8

Guide

to

G’ CpermanentfontlitIor~

37

moulds 123, 126

hand trowelling 75

handling 16, 97-108


heated concrete 78

high strength concrete 80, 88

hot-weather concreting 76

ice 78

impact loading 4 2

imprinting concrete 127

inaccuracies in joints

19

inclusions 55

information sources 9,4 6

information technology 6

inspection, precast concrete 112, 113

intersections, forming 30

J

jacks 102

joggles 64

joints

checking 61

construction 64, 67, 79

details, tilt-up 130

finishes 86

grout- t ight 17

moulds 119

panels 19

preparation 64, 67

tapered dovetail 13, 14

jumpformlng 45

K

kickers 17, 26, 27, 57

L

large area pour s 75

laser screeds 75

lift heights 79

lifting 98, 99, 102

lighhveight concre te 128, 129

liners, formw ork 45

loads, movi ng 102, 106

loop ties 5 8

maintaining finishes 92

maintenance 63, 67, 108

markings, precast concre te 124

master moulds 121, 123, 126

materials, finishes 84, 85

maturity 77, 93

mechanisation 11 1, 1 13

niix records 69

mobile batching plant 69

mock-up, precast concrete 125

models 4, 119

modifications to geometry 13

moisture control 76

monorail 104

moulds 110, 11

concrete 118, 123

design 119

flexible 121

GRC 129

G R P 5 8

materials 32

polymer 120

re-use 58

trough and waffle floors

movement, prestressed concrete 114

moving loads 102, 106

non-destructive testing 6, 7, 93

0

openings 55, 66, 67, 85

panel joints 19, 82

pavers 75

permanent formwork 27,3 7, 117

i’ernlanent for nfw ork

in

const~ct ion

37

pigmented concrete 90

placing 59-80

slabs 74, 75

planning 60, 71, 72

compaction 79

plant 63, 10 8

plumb lines 17

polymer liners 120

polymer moulds 120

post-tensioned bridges 1 16

Post-tensioned concrete loors in mii lti- story

bnildings 116

poultices 92

power floating 74, 75

I’recast concretecladding

94

precast concre te 109-1 33

batching 69

detailing 11

3

erection 124, 125

finishes 113

inspection 112, 113

prototypes

110

samples 110, 112

advantages 14

brick-facings 87, 91, 112

concrete moulds 118, 123

corbels 28

‘face-up’ 87

self-compacting concrete 80

staircases 31

use

o f

ready-mixctl concrete 73

precasting,

pre-concrete checks 60-62

prefabricated cages 48, 49, 51

preparing to concrete 60-62

pre-production samples 83

prestressed concrete 109-1 33

checking

detail 115

ducts 114, 115

equipment, 115

erection 116

lightweight concrete 128

long line 114, 116

movement 114

safety 115

tendons 115, 116

prestressing 112

floor slabs 53

planks 117

pre-tensioned concrete 88

production 59-80

production control 72

production systems 104

Properties

.f

concrete,

Neville 77

propping, cold weather 77

props 33, 42, 44, 45, 61, 66, 130

protection 78

protection during construction 92, 93

prototypes, precast concrete 110

pum ping 16, 60, 65, 71, 72, 73, 128

Q

quality assurance 48, 49, 65, 69, 70, 71, 72, 113

quilting 38, 83

railway works 65

raking columns 13

ramps, formwork 30

rationalisation 6, 111

Rafiotiafisationo flat slab reitfircement 53

ready-mixed co ncrete 70, 71, 72, 73, 7?

ready-mixed mortar 70

reclamation of materials 111

reconstructed stone 127

recording 68

records 115, 116

recycling 11 1

reinforcement 47-58, 112

cages 48 ,49 , 51

couplers 57

cutting and bending 21

fixing 51

rationalisation 79

safety 50

tics 51

release agents 34, 35, 36, 61, 84, 91

Kemoua/ .f

stains andgrmtbs

rom

concrete

94

rendering 129

repairs 96

responsibilities 71

retarders 34, 64, 66, 73, 82, 130

135



ribs 28

rollers 106

roofing units 117

rope, joints 64

S

S u j iuorkiig

iuith h n , e r s 108

safety 15,63,97-108

equipment 88,92,94

prestressed concrete 114, 116

props 33,44,45

reinforcement 50

aggregates 85

finishes 83

precast concrete 110, 11 2

samples 4

sampling 8

scabbing 64

scale, drawings 12

sculpture 121, 126

sealants 94

for

moulds 14

panels 19

self-compacting concrete

80

setting-out points 24, 26

shape codes

53

sheathing 24, 30, 38, 61, 82, 87

signals 105

site precasting 31

Sitesafe '83, 101

sketches 12

skills 3, 6, 10, 101, 103, 107, 111, 112,113

skips 67, 128

slab construc tion 74, 75

slipforming 45, 128, 131

slump test 7,

8

snap ties 56

sockets

cast-in 54

steel location 14

spacers 14 ,48, SO, 51, 57

Spucers o r reirlforced concrete

49

special finishes 45, 91, 127, 131

specifications 122

spillage 43

spiral ramps 30

spreader bars 99 02

stability 42

stacking 104

stain removal 92

stainless stecl 57

staircases 31

stairs 18

Standard reiiijrcenient coircrete detuils

standards 4

starter bars 55

steam curing 77, 78

steel kickers 57

stock areas 104

stock control 20

stopends 38,50

stop-logs 108

storage

formwork

38

materials 122

strength testing

8

strengthening structures

58

striking

formwork 34, 36, 40, 44

props 33,44

times 77,93

stripping 104

stud rail systems 53

superplasticizers 126

supervision 103, 112

surface finish 81-96

surface retarders 82, 87, 89

T

tables, formwork 35

taper ties 56

tapered dovetail joints 13, 14

teams 3, 10, 101, 111

temperature monitoring 78, 93

temporary bridges 132

tenung 7,

8,

76, 78

equipment

8

GRC 129


finishes 87

surfaces 92

texture 82

The ben+ o j rea&zixed concrefe 73

The Concrete Society 9

thermal insulation 76, 77, 78, 93

tie bolt holes 17

49 ties 56, 57

formwork 61,83

rcinforcement 51

tilt-up construction 87, 90, 130, 131

tolerances 16

training 72, 79, 84, 89, 90, 103, 122

trench filling 70

trial panels 86, 91

trouble-shooting 15

troughs and waffle floors 36

turntables 106

U

uplift, formers 85

v

vibration, formwork 38, 54

vibrators

66,

67, 79,

80,

86

W

walls, formwork 28

water bars 67

water flow, weathering 95

water jetting 90, 91, 92, 94

waterway construction 65

weather 60, 76, 77, 78, 89

weathering 95

wheel devices 106

wind 42

workability 65, 84

working position 107

136



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A practical look at concrete

John C. Richardson

Since 1977, the page 'Looking at it practically'

in

CONCRETE maga-

zine has covered the skills and techniques of concrete construction

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A Practical Look at Concrete