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- 1- -

!

p GoodConcrete

Guide -

;Concrete for industrial f loors

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Acknow edgemen s

The Association of Concrete Industrial Flooring Contractors pay particular tribute to Dr Tom Harrison who chaired

the original Working Party, and Kevin Sutherland ofTarmac, who took on the challenging role of coordinating

author and subsequently of revising editor for this updated Guide.

Acknowledgement is also given to the original collaboration between the contributing members of the ACIFC

and The Concrete Society.

Concrete for indus tr ial f loors - Good Concrete Guide 1

Published by The Concrete Society

CS 127Published September 2007

OThe Concrete Society

ISBN 1-904482-38-4

The Concrete Society

Riverside House,4Meadows Business Park, Station Approach, Blackwater, Camberley, SurreyGU179AB

Tel: +44 (0)1276 6071 40 Fax: +44 (0)12766071 41 www.concrete.org.uk

Other publications in this series are available from the Concrete Bookshop at www.concretebookshop.com

Tel: +44 (0)7004607777

A ll rights reserved. Exceptas 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 toThe Concrete Society.

Although The Concrete Society does its best to ensure that any advice, recommendations or information it may give either in this publication

or elsewhere is accurate, no liability or respons ibility of any kind (including liability for negligence) howsoever and from whatsoever cause

arising, is accepted in this respect by the G roup, its servants or agents.

Readers should note that publications are subject to revision from time to time and should therefore ensure that they are in possession of the

latest version.

Printed by Holbrooks P rinters Ltd, Portsmouth, Hampshire UK.

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COncreteGuideood 1

GUtdanceo ite for ind ustr ial f loors

specification and mix design

A joint report from The Concrete Society Industrial Floors Group

and the Association of Concrete Industrial Flooring Contractors

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.- I

toreword Preface

This updated Guidewas originally published in 1998;itwas then

and still is the result of collaboration between the contractor

and members of the Association of Concrete Industrial Flooring

Contractors (ACIFC).The Association’s objective continues to

be assisting it s members to deliver better, more consistent,

quality concrete ground-floor slab construction.

This Guide now takes full account of new and updated British

and European Standards for materials and, where appropriate,

Codes of Practice.The advent of the new concrete standards BS

EN 206 and BS 8500 has changed several aspects of concrete

production, in particular specification methods, descriptions

and requirements or determination of conformity.

The guidance given in the original version of this document was

the culmination of discussions and recommendations of both

users and suppliers of the essential element of the slab, namely

that of concrete and its constituents. Itwas the forerunner of

other specialist guides on other aspects of this type of construc-

tion.The special interest and the assistance of the Industrial

Floors Group ofThe Concrete Society, ready-mixed concrete

producers and admixture suppliers are acknowledged.

No publication can be definitive.This updated edition of the

Guide gives current best practice, while still recognising that

further investigation and development work is needed. It s in

the interests of contractors and their suppliers to progress

knowledge of the best use of concrete to achieve consistently

good value from such a versatile material.

Comments were made in the previous version of this Guide

regarding the use of admixtures in floors, with particular refe-

rence to lackof full dispersion during the mixing process. It is

true to say that admixtures are more widely used now, particu-

larly those materials specifically designed for use in floor con-

struction.The correct choice of admixture type and mixing

procedures to ensurea fully consistent concrete in every loadremains of paramount importance in the very large pours that

characterise fast-track floor construction process.

The ACIFC andThe Concrete Society believe that al l parties

involved in the design and delivery of high-quality industrial

floor slabs - some 6 million square metres per year in the UK

alone, and absorbing some 1.5 million cubic metres of concrete-will continue to benefit from this straightforward Guide and

that itwill give support to the ACIFC’s objective of delivering

better quality by improving understanding of how to achieve it.

This revised document gives practical guidance on current best

practice for the specification, design, production and delivery

of concrete for direct-finished industrial floors constructed by

large-area pour methods. Much of the information is also rele-

vant for any large interior floor construction method.

This Guide is intended primarily to establish a working interface

betweenal l parties involved in floor construction, including

specifiers, contractors, concrete producers and the materials andequipment supply chain so that itbrings togethera consensus

of views and recommendations that have been reached after

extensive consultation and deliberation.

Kevin Sutherland

Tarmac Cen tral Ltd

David HarveyChai rm an, ACIFC

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Concrete for industrial floorsGu dance on specification and mix design

Contents

Acknowledoements Inside Front CoverForeword iiPreface iiStandards for future reference iv

Introduction 1

Health, safety and environment 2

Introduction 2

2

2

Environment 3

Health and safety on site

Health and safety for concrete production

Project planninq 4

Concrete specification 5

Designation 5

Strength 6

Cement content 6

Waterkement ratio 7

Consistence 7

Materials 8

Aagregates 8

Cements and combinations 8

Admixtures 10

Mixing water 10Steel, macro-synthetic and micro-synthetic ibres 11

Concrete mix desian 12

Introduction 12

Consistence 12

Finishabilitv 13

Fine aggregate content 12

In-situ concrete properties 14Thermal movement 14Drving shrinkage ' 14

Abrasion resistance 15

Compactionof concrete 15

Influence of curina 15

Batching and pre-deliveryofconcrete 16

- 16Pre-delivery planning 17

Conformity and identity testinq 18

Conformity 18Identity testing (strength) 18Identity testing_(consistence) 19

References 20

-ppendixA: Guidance on the specification and use

of admixtures in concrete for industrial floors 21

Introduction 21

Water-reducina admixtures 21

Other admixtures 21

Batching admixtures 22

Site addition of admixtures 22

placing and finishing characteristics 22

bpendixB: ldentitv testing criteria 23

Strengthcriteria 23

Consistence criteria 23

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Standards for future reference

BS 3892-1 1997

BS 4027: 1996

BS 6699: 1992

BS 7979: 2001

BS 8203: 2001

BS 8204-2: 2003

BS 8500-1 2006

BS 8500-2: 2006

BS EN 197-1 2000

BS EN 197-4: 2000BS EN 206-1 :2000

BS EN 450-1 : 2005

BS EN 933-3: 1997

BS EN 934-2: 1998

BS EN 1008: 2002

BS EN

BS EN

BS EN

BS EN

BS EN

2350-1: 2000

2350-2: 2000

2350-5: 2000

2390-2: 2000

2390-3: 2002

BSEN

12620: 2002

BS EN 13263: 2005

BS EN 14216: 2004

BS EN 15 167: 2006

BS EN IS 0 14001 1996

BS EN 1367-4: 1998

PD 6682-1:2003

BS I S 0 9000-2: 1997

Pulverised-fuel ash. Specification for pulverised fuel ash for use with Portland cement

Specification for sulfate-resisting Portland cement

Specification for ground granulated blastfurnace slag for use with P ortland cement

Specification for limestone fines for use with Portland cement

Code of practice for installation of resilient floor coverings

Screeds, bases and in-situ flooring. Concrete wearing surfaces -Code of practice

Concrete -Complementary British Standard to BS EN 206-1. Method of specifying and guidance for the

specifier

Concrete -Complementary British Standard to BS EN 206-1. Specification for constituent materials and

concrete

Cement. Composition, specifications and conformity criteria for common cements

Cement. Composition, specifications and conformity criteria for low early strength blastfurnace cementsConcrete. Specification, performance, production and conformity.

Fly ash for concrete. Definitions, specifications and conformity criteria

Tests for geometrical properties of aggregates. Determination of particle shape. Flakiness index

Admixtures for concrete, mortar and grout. Concrete admixtures. Definitions and requirements

Mixing water for concrete. Specification for sampling, testing and assessing the suitability of water,

including water recovered from processes in the concrete industry,as mixing water for concrete

Testing fresh concrete. Sampling

Testing fresh concrete. Slump test

Testing fresh concrete. Flow table test

Testing hardened concrete. Making and curing specimens for strength tests

Testing hardened concrete. Compressive strength of test specimens

Aggregates for concreteSilica fume for concrete

Tests for thermal and weathering properties of aggregates. Determination of drying shrinkage

Cement. Composition, specifications and conformity criteria for very low heat special cements

Ground granulated blastfurnace slag for use in concrete, mortar and grout

Aggregates for concrete. Guidance on the use of BS EN 12620

Environmental Management Systems. Specification with guidance for use

Quality management and quality assurance standards. Generic guidelines for the application of I S 0 9001,

I S 0 9002 and IS 0 9003

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Concrete for industrial floors - Guidance on specification and mix design Chapter 1

Introduct on

Concrete industrial floors must give a high standard of perfor-

mance and durability. Close attention to the construction

materials and working practice s necessary if floors are to be

constructed that need minimal maintenance.

The majorityof floors are satisfactory; however, construction

and finishing difficulties too often lead to the need for remedial

work due to inadequacies or failings in one or more of the

following important areas:

poor communication and coordination between specifiers,

contractors and concrete producerspractical material specifications

0 mixer trucks with dissimilar mixing efficiency

concrete supply rates

control of fresh concrete including uniformity of mixing and

consistence

0 qualityof workmanship, n particular finishing and curing

variable weather and site conditions.

This publication gives guidance and advice on relevant materials

technology in order to achieve the objectives of all parties

involved in the specification and construction of industrial floors.

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Chapter 2 Concrete for industrialfloors - Guidance on specification and mix design

Health, safety and

enviro

nmen

Introduct on

Without exception, the most important issue for those managing

or engaged in construction activity is the safety of all persons

on the site. Currently,as the construction industry accounts for

a quarter of al l deaths at work and for more than 4000 injuries

each year, the reduction of these numbers is a governmentpriority.The Health and Safety Executive (HSE) enforces with

vigour the Health and Safety atWork Act and has declared it sintention to seek criminal convictions for any breaches.

Health and safety on site

There are significant risks on most construction sites and,

although not exhaustive, some examples are as follows:

vehicle and construction plant movements

use of power tools

manual handlingworkingat height, or example when constructing mezzanines,

climbing ladders of mixer trucks, placing of laser levelling

equipment

working in confined spaces

exposure to hazardous materials such as fresh concrete

high-voltage power sources.

Employers have legal obligations under the Health and Safetyat

Work Act and the main contractor will have a health and safety

management policy and procedures in place, including an

induction process. The flooring contractor, including his suppliers

and any subcontractors, should seek to integrate their ownhealth and safety procedures into this in advance of flooring

operations taking place. In particular, the preparation of risk

assessments and operational method statements should be

considered essential; these will enable the main contractor toissue the necessary Permits to Work to both the main flooring

contractor and any other subcontractor engaged in the floor

construction.

Some specific issues that should be addressed are:

ensuring the health and safety policy s appropriate to the

type of work carried out by the specialist flooring contractorsupply of appropriate personal protective equipment (PPE)

and enforcement of its use

safe handling of materials that are potentially hazardous to

health; the Control of Substances Hazardous to Health Regu-

lations (COSHH) apply (particularly with regard to concrete,

synthetic and steel fibre, concrete admixtures, dry-shake

powder and sealants)providing formal health and safety inductions for other sub-

contractors

provision of first-aid by suitably trained personnel

establishing a reporting system, including arrangements for

complying with the Reporting of Injuries, Disease and Dange-

rous Occurrences Regulations (RIDDOR)training to ClTB Health and Safety Test level and enforcement

of CPCS cardson-site/off-site traffic management and control

consideration of other trades

workplace lighting

mess and toilet facilities

demarcation of working and storage areas

establishment of a suitable audit and assessment process,

preferably by an independent personprovision of a banksman and safe access for ready-mixed

concrete trucksif intending to add materials or modify the concreteat site, a

contractor must provide risk-assessed procedures, suitable

equipment and adequate supervision.

The types of specific risks referred to above can be managed

safely by implementing the appropriate systems and procedures.

However, the most difficult risk to manage is employee and or

subcontractor behaviour: over90% of all injuries, fatalities and

near misses arise from unsafe acts, not unsafe conditions.The

visible and uncompromising management of health and safety

isnecessary to establish

aculture of safety awareness amongthe entire site workforce, including subcontractors. Unsafe

behaviour should always be vigorously challenged and itshould

be made clear to everyone that repeated or deliberate failure to

comply with procedures and instructions will invariably lead to

permanent exclusion from site and possibly criminal conviction.

Health and safety for concrete

production

The concrete producer will have a health and safety policy and

documented safe working procedures in place.This will include

periodic surveillance and reporting.As part of these operations

the truck mixer operators or drivers will have been included in

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Concrete for industrial floors - Guidanceon specification and mix design Chapter 2

these safe working systems and procedures. The concrete and

quarrying industry Standard now includes rotating amber hazard

beacons, reversing alarms and cameras. Additionally, mixer trucks

now have safe access platforms around the loading chute and

modifications to the folding discharge chutes to prevent crushinjuries when folding the chutes.

The truck operators or drivers, technicians and other representa-

tives of the concrete producer will have suitable PPE and will

have received safety induction training to cover safe working

both at the concrete production plant and the construction site.

Many sites have specific safety induction requirements.The

flooring contractor should ensure that the concrete producer is

aware of these requirements and where necessary arrange

inductions.

Environmen

Most concrete producers are moving towards Environmental

Management Systems based upon BS EN I S 0 14001,with third-

party accreditation from bodies such as the British S tandards

Institution (BSI). Additionallyal l static concrete plants are now

licensed by the local authority under the Environmental P rotec-

tion Act as a class B process covering the use and handling of

bulk cement.The concrete production unit will have undergone

an environmental impact assessment covering al l emissions,

including dust, waste water and waste concrete.

In addition to any contract-specific environmental issues, there

are a number of areas common to al l sites where environmental

aspects must be considered and these would include:

0 preventing emissions and pollution (dust,site runoff, provision

of drainage)

0 disposal of excess concreteprevention of mud transfer to public roads

venting of lorry exhaust fumes from working areas

control of noise pollution

concrete supplier and other supply chain responsibilities

concerning delivery or working on site

washdown facilities for concrete mixer trucks following

discharge.

The main contractor would normally address some of these

items but it is incumbent on all contractors to be aware of theimpact of a construction site on the environment and to take

steps to minimise the effect wherever possible.

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Projectplanning

Planning is the keyfactor in the successful execution of a flooringcontract. Remember:'FaiIing to plan, in reality, is planning tofail'. However,a well-thought-out and structured approach willhelp to ensure that the ob is completed on time, that the floormeets the client's and main contractor's expectations and thatconstruction costs are kept under control.

The primary reasons for planningare to assess whether targetsare attainable, to identify cost, time scale, potential problemsand to make decisions at the outset that will prevent futuresurprises. It is important that the flooring subcontractor's plans

are linked to the main contractor's plans and consistent withlocal supply chain output capacity and availability.

Everycontract must havea project manager basedat site or at

the contractor's office who will be responsible for the delivery ofthe floor to time, quality and budget.A site meeting to defineand agree goals and objectives and how they will be achievedshould precede the contractstart date.This meeting shouldinclude representatives from the following, irrespective of thesize of the contract:

0 floor-laying subcontractor

main contractorconcrete supplier and concrete pumping contractorsuppliers of other products, such as toppings, steel fibre.

Where the floor is to be designed and constructed to meeta

specialised need it is essentialto invite the engineer and buildingowner, or the end-user of the floor, to the pre-contract meeting;this will ensure that all parties understand fully what is agreedand can reasonably be delivered.

It s recommended that the initial outline planning should includea tasksequence and programme analysis; conformance to this

working document should be regularly monitored throughoutthe contract period and sections of work should be signed off

when completed.This should ensure that the work progresses as

anticipated, the floor is constructed to the specified technicalrequirements and the project finances are kept within budget.Continuous monitoring of the key activities sometimes leads tominor adjustment of the work logistics.This is acceptable pro-vided that the changes are controlled; timely recognition of theneed for change will reduce the risk of failure to deliver to the

overall plan. Additionally, regular progress review meetingsshould be held and must include the main contractor.Thesewill assist in providing clear communication thus avoiding

disputes over work progress and quality.

An important aspect of planning concerns how the work will be

executed and this needs to take into account details of the worksuch as the method of construction, for example large-area pour,long bay, and also the method of concrete placement-will itbe pumped or direct discharge, see Figure 1. Added to this are

the finishing process and other post-concretingwork such as

the application of a dry-shake topping, oint formation and/orsawing, application of top-surface sealant or curing membraneetc. Other factors such as placing external slab-work or wherethe floor is suspended may need additional resources and there-fore need to be an integral part of the plan. Figure2 shows a

partially completed large-area warehouse floor.

Figure 1 - Placing concrete

E ?l

Figure2 A partially completed large-areawarehouse floo r.

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Concrete for industrialfloors - Guidance on specification and mix design Chapter 4

Concrete specification

Designation

The majority of concrete is likely to be purchased through aready-mixed concrete supplier. In order to purchase concretethis way, the requirements of the concrete need to be specified.

A ready-mixed concrete plant is set up to produce many typesof concrete, the concretes having been designed to meet thepotential specifications of clients.As the constituent materialsare batched by weight and not volume, this means that batchedconcrete should meet the original mix design specification andcomply with the rigorous quality control systems implemented.

Concrete, whether site-mixed, ready-mixed or produced in a

precast plant, should be specified in the UK in accordance withBS 8500, the complementary British Standard to BS EN 206-1.Part 1 of BS 8500-Metho dofspe cifjhg andguidance for thespecifier - s intended for the person or body establishing thespecification for fresh and hardened concrete or who passes thespecification to the producer, i.e. the purchaser of the ready-mixed concrete. Part 2- Specification for constituent materialsandconcrete - s for the producer and contains specificationrequirements for the producer’s production control.

BS 8500 allows concrete to be specified via a suite of concrete

designations, namely designated, designed, proprietary, pre-scribed, or standardized prescribed concrete. For the majorityof industrial floor applications the designed concrete route isthe most appropriate.

Designated concretes

An alpha-numeric reference system is used to’designate’these

concretes for particular purposes.The concrete is chosen from a

list of designated concretes (GEN, FND, PAV, RC etc.) depending

on the site conditions and the application for which it is to be

used.The concrete is produced in accordance with BS 8500 andrequires the producer to hold a current accredited productioncontrol certification based on product testing and surveillance,

coupled with approval of the producer’s quality system to BS EN

I S 09000.

Designed concretes

For flexibility in specifying and purchasing, designed concretes

are appropriate as they cover the application and constituentmaterials. It s a mix design for which the purchaser s responsible

for specifying the required performance and the producer is res-ponsible for selecting the concrete proportions to produce thespecified performance. Effectively, he producer has responsibilityfor the mix design to meet the purchaser’s needs, for exampleexposure environment, working life, strength, consistence.

The concrete is ordered by its required performance in terms of

it s strength class subject to any restrictions on materials, mini-mum or maximum cement content, maximum water cement

(w/c) ratio and any other properties required. The purchasermust supply al l the relevant information on use to enable the

producer to design the concrete accordingly.

Proprietary concretes

The proprietary concrete approach is appropriate where the

concrete is to achieve a particular performance, using definedtest methods.The proprietary concrete is selected in consulta-

tion with the concrete producer and the project specification is

appropriately drafted.

Prescribed concretes

Prescribed concrete is a concrete where the purchaser prescribesthe exact composition and constituents of the concrete and is

responsible for ensuring that these proportions produce a con-

crete with the required performance. Essentially,the purchaserselects the materials and proportions to satisfy the required

strength and durability needs but does not specify these para-meters. The concrete is ordered by it s constituent materials andthe properties or quantities of those constituents to producea

concrete with the required performance.The assessment of themix proportions will form an essential part of the conformity

requirements if the purchaserso requires.

Standardized prescribed concretes

Standardized prescribed concretes (ST1 to ST5) are selected froma restricted list in BS 8500 and made with a restricted range ofmaterials as detailed in the Standard.The assessment of the

concrete proportions will form an essential part of the conformityrequirements.These concretes are appropriate where concreteis site-batchedon a small scale or obtained from a ready-mixedsupplier who does not have third-party accreditation.

BS EN 206-1 Section 6 and BS 8500-1 Section 4 require that thespecifier of the concrete shall ensure that al l the relevant

requirements for the concrete propertiesare included in thespecification given to the supplier/producer.These are covered

as Basic requirements and Additional requirements. For flooringconcrete the basic requirements will be similar to conventional

concrete, e.g. strength class, exposure class, consistence.Additional requirements may be included for other technical

requirements requested by the specifier, e.g. shrinkage.

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Chapter 4 Concretefor industrial floors - Guidance on specification and mix design

Figure3 -Large-area warehousefloor

The specifier isalso required to inform the supplier of the concreteproperties neededfortransportation, delivery, placing, compac-tion, curing and further treatment.This could also include specialrequirements, e.g. for finish. This is covered under Exchange of

information inBS EN206-1 Section7.1 and BS 8500-1 Section5.1.

Strength

The required concrete compressive strength class is selectedfrom Table 8 of BS EN 206-1. Additional classes to those givenare provided in BS 8500-2 Table 9.

CommentmySpecific guidance on concrete specification, related to design,

expected use and trafficking conditions o f a floor is given in

two key documents, The Concrete Society Technical Report

34"' and BS 8204-2: 2003.

The concrete compressive strength class relates to its charac-

teristic strength, as defined in BS EN 206-1 clause 3.1.32. In

the UK it is based on the strength of test cubes made, stored

and tested in accordance with BS EN 12390-2 and BS EN

12390-3. The statistical approach to production contro l

means that the average strength of the concrete supplied

will usually exceed the specified characteristic strength by a

design margin, the magn itude of which is dependent on

the quality control of the production of the supplying plant.

It must be recognised that the compressivestrength of con-

crete has little relevance to the engineering design o fa con-

crete floor, as the flexural strength is more critical to ts perfor-

mance underload.However, the test for flexural strength has

poor precision. The flexural strength o f a concrete generally

falls in the range 8- 15%of the compressivestrength, the

aggregate type having a significant nfluence on this factor.

The typical characteristic strength specified for direct finished

floors is UW35 or C32/40. This dua l compressiveStrength

class refers to cylinder/cube strength, the ower value being

the cylinder strength. Also see the section #brasion resistance,'page 15.

Lower strengths may bespecified on the basis of engineering

judgement, such as on design-and-construct contracts

where the contractor has full control of the construction

process or where the qua lity of finishing is enhanced or dry-

shake topping s to be applied.

Assessment of strength ofsite-cast specimens, known as

identity testing, s covered in BS EN 206- 1Annex B, with clarifi-

cation n BS8500- Annex A.10and Annex B.5.73is w ill give an

indication of whether a defined volume of concrete belongsto the same population as that verified as conforming to the

characteristic strength via conformity assessment by the

producer. This gives a reasonable guide to the qua lity and

consistency of the concrete supply.

Cement content

For industrial floors with power-trowelling,a minimum cement

content of 325kg/m3sconsidered suitable to achieve satisfac-tory abrasion resistance.

CommentmyToachieve a satisfactory abrasion resistance the surface

must be capable of being power-trowelled and sosufficient

finer fines must beavailable. When a 2Omm nominal maxi-

mum size coarse aggregate s used, a minimum cement

content of 325kg/m3s normally specified for direct-finish

industrial floors and reflects current national construction

practice.

Experience has shown tha t lower cement contents may not

provide abrasion-resistant concrete with ow dusting charac-

teristics. However, current research indicates tha t w/c ratio

has more effect on abrasion resistance than the cement

content. n practice, where power-trowel finishes are specified

a m inimum cement content of325kg/m 3ensures that there

is sufhcient volume of cement in the concrete to achieve a

dense and uniform wearing surface. Cement contents above

360kg/m3are unlikely to mprove abrasion.

Cemen contents above 400kg/m3can lead to finishing

problems since the time available for floating and trowellingreduces with increasing cement content (see the section

'Finishability,' page 13).

I 1

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For direct- finished loors, BS 8204-2 recommends increasing

cement conten t and strength class to achieve improved

abrasion. I t is recognised that specialist flooring contractors

can achieve high levels ofabrasion resistance at cementcontents lower than those specified in BS 8204-2:2003 and

this is noted in clause 6.2 of tha t Standard. t is therefore

recommended that this issue should be agreed between

the floor designer and the specialist flooring contractor.

Laser screed

Large area

Concrete for industrial floors -Guidance on specification and mix design Chapter 4

53 53

F5 F5

Waterkement ratio

Specify a maximum w/c ratio of 0.55,or a lower value if appro-

priate.

CommentaryThis maximum value of w/c ratio reflects current practice in

the UKand is consistent with guidance given in The Concrete

Society Technical Report No. 34' '). t is desirable to keep the

free water con tent as low as possible to minimise drying

shrinkage and excessive bleed etc. but the concrete must be

capable of being placed and finished wit h the equipment

available. The producer can ad just the concrete design by

increasing the cement content wh ile maintaining the origi-

nal water content, or by using admixtures o ra com bination

of both. Using an admixture to decrease the overall water

content w ill help to control and/or reduce drying shrinkage.

Consistence

Selecta consistence class that is appropriate to the method ofconstruction.The contractor should inform the producer if

admixtures or fibres are to be added to the concrete at site.

Consistenceclasses are given in BS 8500-1: 2006Tables B.l to 8.4.The maximum allowable deviation is based on a spot sample

taken from the initial discharge of a ready-mixed concrete truck

or as a composite sample, both being taken in accordance withBS EN 12350-1 The concrete producer will normally targetconsistence at the mid-range value. Slump and flow tests are

carried out in accordance with BS EN 12350-1 and EN 12350-5

respectively.Seethe section 'Identity testing (strength): page 18

and Appendix B, page 23.Table 1 provides typical consistenceclasses for floor construction.

I I Direc tpour I Pumped I

I Long strip 1 52 or 53 I 53 I

Table - Suggested consistenceclasses for floor construction

Commen uryThe selected consistence should reflect the level o fcompact ion

tha t will be applied to the concrete.As the slump or flow

increases, the effort required to achieve full compaction w illreduce. For strip construction methods a concrete wi th a

lower consistence value can be used. The consistence needs

only to be high enough to achieve full cornpaction wi th the

compaction equipment available, whether the concrete s

placed by direct tipping, pumping or by dumper.

Most specialist floor ing contractors prefer to use higher

consistence classes for both strip construction and large-

area pour methods.

The producer should ensure that the proposed concrete s

sufficiently cohesive to avoid segregation of the constituentmaterials. This is particularly relevant if th e flooring contrac-

tor wil l be adding super-plasticisers to the concrete on site.

Fibres, particular ly steel and m acro-synthetic ibres, are

increasingly used in floor construction. The producer and

contractor should note that a small reduction ofabo ut

lOmm slump may occur when micro-syn thetic ibres (poly-

propylene) are added to a concrete. Steel fibres and macro-

synthetic have a greater effect on consistence than m icro-

fibres and the slump may be reduced by more than 25rnm,

depending on the fibre shape, length and quantity . Conse-

quently, minor constituent adjustments may be necessary

to maintain the w/c ratio and to maintain plastic properties.The specified consistence should take account of this, par-

ticularly f the contractor intends to add fibres to the concrete

at site.

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Materia s

Aggregates

A wide variety of aggregate types are in use in the UK,depending

on local geology and the economic boundaries of particular

sources. Aggregate should generally conform to BS EN 12620

Aggregates for concrete, or have an acceptable history of use

and should be of a quality suitable for the production of struc-

tural concrete.

Most floors are constructed with concrete containing 2Omm

maximum size coarse aggregate.Theremay be logistical and

practical reasons for not using largersizes but the potentialtechnical benefits of using them are that total water and cement

content can be reduced for a given strength and consistence

class.

CommentaryAggregates that do no t con form to BS EN 12620 in respect of

particle size distribution are frequently used in structura l con-

crete and so should not be precluded if concrete made wi th

them can be satisfactorily placed and finished. Fine aggre-

gates that are gap graded may result in concrete tha t bleeds

unacceptably and is difficult to finish. If the suitability o fa

proposed aggregate s not established, advice should be

sought from the concrete producer, For example, evidence

o f a satisfactory history of use in direct-finish looring appli-

cations may be available which wi ll allow confident use of

the proposed material.

The following criteria are of particular relevance.

The coarse aggregate should meet the requirement of a maxi-

mumLos Angeles coefficient of 40 (LA,,) or have establishedsuitability through history of use.

accordance with BS EN 933-3: 1997Determination ofparticle

shape -Flakiness index.

Aggregate drying shrinkage value should not exceed 0.075%

when tested in accordance with BS EN 1367-4: 1998Determi-

nation of drying shrinkage.

The flakiness index should not exceed FI, when tested in

Commen aryThis maximum shrinkage value excludes aggregates prone to

high drying shrinkage and is the imit recognised by most con-tractors and clients. The water content ofconcrete has a far

greater influence on moisture-related movements, i.e. drying

shrinkage, than differences between normal aggregates,see

The Concrete Society Technical Report No. 34? Section 10.3.

Aggregates should be free of impurities or materials that

may affect the integrity or appearance of the surface of the

finished floor. It is often impossible to eliminate impurities

entirely and a procedure for rectifying surface defects should

be agreed prior to letting of the contract.

CommentaryThe follow ing materials may cause particular problems if

present in significant quantities.

Lignite. This black or brown coal-l ike mate rial ranges fromvery soft to hard, Particle sizes of 1m m and above have

historica lly ed to surface defects. Ligni te occurs in many

inland and mar ine aggregate deposits. Suppliers generally

have systems to reduce or remove unacceptab le evels. Some

lignites are soluble and may lead to localised retardation or

discoloration of the concrete. Surface pop-outs and cavities

may also OCCUI: BS EN 12620 Annex G4 gives limits for the

lignite content ofaggregates which should not be exceeded.

“Where appearance s an essential feature of the concrete,

aggregates should not con tain materials in proportions tha t

may adversely affect surface qual ity or du rability.”

Pyrites. These iron com pounds can cause surface staining

but in general are less prob lematic in floors than lignite as

they do not tend to float to the surface.

Clay agglom erates.These can cause surface pop-outs in

finished floors when the clay dries out. Close inspection of

aggregates by the supplier should minim ise this prob lem.

BS EN 12620 Annex G4 states: “Where appearance s an

essential feature of the concrete, aggregates should no t

contain materials in propor tions th at may adversely affect

surface quality or durability.“Similar guidance s given in BS

8500AnnexA7.1 and BS 8204-2 clause5.3. .

If there are concerns about impurities n an aggregate

source, the concreteproducer should seek assurances from

the supplier abou t procedures to control the problem.

lnformation on the history of use should also be sought.

Cements and combinations

Cement may be Portland cement or Portland cement with anaddition e.g. ggbs or fly ash

The following cement types have established suitability for floor

construction provided that the finished concrete is adequately

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cured (see the section’lnfluence of curing: page 15).All factory-produced cements conforming to BS EN 197-1 have a CEM prefixe.g. CEM I, CEM II/B.The equivalent combinations manufacturedin the concrete mixerare prefixed with C, for example CII/B, and

conform to BS 8500-2 Annex A. A l ist of the general-purposecements and combinations s given in BS 8500-2Table 1.

Portland cement

This cement is suitable for most applications and is the least

sensitive to the lower placing temperatures that are likely tooccur in winter. During warmer weather, the shorter settingtimes may cause difficulty with power floating and trowellingsince the’finishing window’can be shortened significantly.Under these circumstances the contractor should considerhaving additional manpower and plant available for finishing,or reconsider the cement type.

Portland cement has a relatively high rate of strength gain,typically achieving around 80% of final strength within sevendays. Setting times are normally shorter than for other cements.It may be necessary to commence the sawing of joints less than24 hours after casting to prevent the formation of random earlythermal contractioncracks.This form of cracking is influenced bythe ambientsite conditions (particularly extremes of tempera-ture), the heat of hydration of the cement and by the curingthat is applied.

Sulfate resisting Portland cement

This form of cement is not widely available in bulk form in the UK.

Where sulfate resistance is required, it is achieved through the

appropriate cement combination in accordance with BS 8500-1

to suit the ground conditions.

Portand-slag cement

Combinations of Portland cement with ground granulatedblastfurnace slag (ggbs) conforming to BS EN 15167 (replacingBS 6699) are widely available in the UK. In some areas, factory-produced Portland-slag cements are also available. Althoughthe characteristics of these cements vary widely, depending onthe proportions of the two components, many high-qualityfloors have been successfully constructed with them.The pro-portion of ggbs is usually in the range 30-50Yo.The rateof settingand hardening is dependent on this proportion but, in general,setting is slower than P ortland cement.At seven days, strengthsare lower than the equivalent-strength Portland cement con-crete.The addition of ggbs affects the properties of the freshconcrete, particularly ts consistence and mobility: it is consi-dered easier to compact and finish than concrete containing

Portland cement only.

At low ambient temperatures, the useof ggbs may increase the

potential for bleeding of the concrete and extend setting times,

which may cause difficulty with the timing of finishing and

sawing.This is also dependent on the proportion of ggbs used,

and the most practical approach, if problems areenvisaged, is to

reduce the proportion of ggbs. Conversely, the slower setting

characteristics can be used to advantageat higher temperatures to

lengthen the finishing window and improve the quality of finish.

Portland-fly ash

This cement type is widely available in the UK. Factory-producedPortland-fly ash cements are available in some areas but moreoften combination cements are produced by batching Portlandcement and fly ash in the mixer.The term fly ash conforming toBS EN450 encompasses pulverised-fuelash (pfa) covered by BS3892:Part 1, which is expected to be withdrawn in 2007.Theproportion of fly ash is typically in the range 21-35%, the resul-

ting combination having been used extensively in flooringconstruction.

The partial replacement of the Portland cement content withfly ash has a marked effect on the properties of the concrete.The water demand will typically be reduced by some 6%, forthe same slump value, Alternatively, the consistence can beincreased while maintaining the same w/c ratio,The cohesive-ness of the concrete is also improved.Theseeffects are due tothe spherical particle shape of the material and the increase inthe cement-paste volume that results from the lower particledensity of the fly ash.These characteristics can be used to im-prove the concrete, particularly where, for example, the locally

available aggregates are angular or poorly graded.

The seven-day strengths are lower than the equivalent-strengthPortland cement concrete.As with concrete containing ggbs,the setting time can be extended at low temperatures and thismay cause finishing difficulties. Conversely, the longer finishing

window at high temperatures can be beneficial.

Portand-l mestone cement

These cements are available in some areas and have been used

in a wide range of applications. n terms of setting time andstrength development these cements are very similar to P ort-

land cement.

Portland cement with additions of silica

fume or metakaolin

These are special combinations and properties depend on the

proportion of silica fume (EN 13263) or metakaolin, the degree

of dispersion achieved and the formulation of the concrete.

The rate of strength gain and final strengthare also determined

by the formulation.Silica fume concrete can be produced withhigh flexural strengths and this may allow slab thickness to be

reduced. Additionally, very high surface abrasion resistance andchemical resistance can be achieved. Specialist advice should

be obtained from the concrete producer.

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Chapter 5 Concrete for industrial floors - Guidance on specification and mix design

CommenturyHigh proportions of ggbs or fly ash are not usually within

the scope of current practice so these are not discussed here.

Where the proposed cement contains higher proportions ofggbs or fly ash, the contractor should seek con firmation

tha t the concrete will satisfy performance requirements for

abrasion resistance.

lfjoints are to be sawn in the floor after placing, the choice

of cement may affect the timing o f the sawing operation.

For all cement and combination types given above it cannot

be overemphasised that to achieve satisfactory abrasion

resistance the effectiveness of curing is pa ramount. ChapIinf2j

reports that concretes based on cements with additions have

significantly ower abrasion resistance than those contain ingonly Portland cement, f concrete s air-cured only. When

concrete was effectively cured, the abrasion resistance was

satisfactory.

Contractors, when selecting the cement to be used in the

flooring concrete, should, n consu ltation w ith the concrete

producer, consider the ambient temperature, relative humi-

dity and site exposure conditions th at are anticipated at the

time of construction.

The range of cements currently ava ilable has a spectrum of

performance n terms of temperature sensitivity, setting timeand strength ga in. These characteristics are discussed below.

The rates ofstreng th gain described in the following commen-

tary are typical for test cubes manufactured and cured in

accordance to BS EN 12390-2.However, n-situ strength

development n floor slabs is influenced by a number of

factors, nclud ing effectiveness of curing, temperature, slab

thickness, cement type and content.

Admixtures

Admixtures for flooring concrete should conform to BS EN 934-2,

Concrete admixtures-Definitions and requirements.The following

types can be beneficial in flooring concrete:

(a) water reducers

(b) mid-range water reducers

(c) superplasticisers.

Cornmen aryA prime requirement of mix designs for floor ing concrete s

to keep the water content as low as possible (see Chapter 4‘Concrete specification,‘ page 5). This frequently necessitatesthe use of admixtures to m od ih the properties of fresh con-

crete and to avoid large increases in the cement content and,

consequently, he cost of the concrete.

Where concrete with a slump class 52 or 53 is to be used, the

cement content may be significantly reduced by using

admixture types (a), (b) or (c). Conversely, where flow class

F5 is required, i.e.560-620 mm flow diameter,admixtures

(a), b) or (c) can be used to increase consistence wi thou t

increasing either the total water content or cement content.

In certain conditions, some admixtures retard the hydrationof the cement. This extends the setting t ime o f the concrete

and can significantly delay finish ing operations. These effects

can increase at low temperatures, and when combination

cements are used- ee the section ’Cements and combina-

tions,’page 8 .

Admixtures are now available that are specifically formu la-

ted for flooring applications, and haveaminim al effect on

setting rimes.

In warm weather, or at high ambient temperatures, admix -

tures that delay setting times may be used to extend the timefor placing, evelling and finishing. However, strict contro l on

dosage and mixing is needed to ensure that concrete sets in

the same order as it was placed, thus avoiding differentia l

setting.

The choice of admixture should be made wi th due conside-

ration of site conditions and the contractor‘s equirements.

It must be accepted that variations in weather conditions may

force changes to be made to the concrete or construction

operations at short notice.

Mixingwater

Mixing water should conform to BS EN 1008Mixing water for

concrete.This Standard includes potable water and establishes

the suitability of water that is recovered or reclaimed from

processes in the concrete industry or where water from non-

mains sources such as boreholes is in use.

Appendix A‘Guidance on the specification and use of admixtures

in concrete for industrial floors’, page 21, gives comprehensive

information for this application.

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Concrete for industrial floors -Guidance on specification and mix design Chapter 5

Steel, macro-synthetic and micro-

synthetic fibres

The use of steel and macro-synthetic fibres in flooring concretehas increased significantly with the development of fast-track

construction and so-called jointless floors. Micro-fibres are not

normally used on their own, although may be combined by

some suppliers with steel or macro-synthetic fibres.

For further information refer toThe Concrete Society Technical

Report TR34") and the ACIFC documentSteel FibreReinforced

Concrete ndusrrialGround Fora more detailed assess-

ment of the use of steel and macro-synthetic fibres, Concrete

Society Technical Reports TR63(41 nd TR 6F respectively, should

be consulted. Manufacturers and suppliers will also give specific

advice and additionally some suppliers will provide a bespokedesign service.

Figure 4 - Warehouse loor n operation

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Chapter 6 Concrete for industrial floors -Guidance on specification and mix design

Concrete mixdesign

Introduction

The majority of concrete will be ordered through a ready-mixed

supplier as a designated or designed concrete and hence the

mix design is the supplier's responsibility based on information

given by the specifier. However, it is useful to outline which fac-tors need careful consideration when designinga concrete that

is easy to place and finish, as well as meeting the specification.

Con istenceThe concrete should be sufficiently cohesive to avoid segrega-

tion of the coarse and fine constituents at the specified consis-

tence, particularlyat the upper consistence limit. Additionally

the free water content should be as low as possible, although

not less than 160 litres/m3.Thew/c ratio should not exceed 0.55.

A higher slump or flow for a given strength or maximum free

w/c ratio can be achieved by increasing the cement and water

content of the concrete.The use of admixtures to reduce water

content will reduce drying shrinkage but contractorsare some-

times reluctant to choose this method due to historical problemsofachieving effective mixing and dispersion of admixtures. How-

ever, itshould be recognised that the frequency of admixture-

related problems has reduced significantly due to improvement

in the control and dispensing of admixtures together with

advances in admixture technology.

Fine aggregate content

The fine aggregate and cement content should be such that the

concrete remains homogeneous after placing and compaction.

It must also allow a sufficient, but not excessive, surface mortarlayer to form, which can be levelled and finished to the required

standard. However, the mortar content should be keptas lowas possible to minimise shrinkage.

The fine aggregate content that is selected depends on the

physical characteristics of the aggregates and the required

consistence of the concrete.The combination of coarse and

fine aggregate should be such that a continuous particle size

grading is achieved. Gap-graded aggregates may cause concrete

to lackcohesion and be prone to bleeding.

Concrete batched using coarse aggregates with a maximum sizeof 2Omm that has an excess of lOmm size particles will necessi-

tate higher fine aggregate contents. It is preferable therefore to

reduce the lOmm fraction of the coarse aggregate towards the

lower end of BS EN 12620 conformity limits. Experience shows

thata 1Omm fraction of 30-40% is suitable with most aggregates.

The surface and shape characteristics of crushed and rounded

aggregates vary widely and therefore the necessary fine aggre-

gate content will vary.

Concretes should be designed to have sufficient mortar to obtain

a satisfactory finish. High fine aggregate contents may result in

too thick a surface layer of mortar and this will increase the risk

of crazing and surface delamination in service. For pumpable

concrete, the fine content should be sufficient to ensure a

reasonably cohesive concrete that can be finished as required.

CommentaryOptimising concrete design is necessary because the majority

of specialist flooring contractors place concrete at slumps

in excess of 100mm.Higher consistence classes or targets

necessitate some adjustment to the concrete design to ensure

tha t the concrete remains su ficiently cohesive to avo id

segregation of the solid constituents and to compensate for

the higher water content. This is usually achieved by adding

sand, cement and water. However, ncreasing the mortar

fraction also increases dry ing shrinkage and can affect the

finishing characteristics.

The total quantity of mortar in the concrete has a significant

effecton the quality of the finished floor surface. Too little

mortar may result in a dimpled surface or loose coarse

aggregate particles or both, while too much may cause

crazing, blisters,' delamination and increased r isk of drying

shrinkage cracking.

The following rnix design options can be considered but other

factors such as dry ing shrinkage, thermal movements and

abrasion resistance requirements must be considered. (Refer

to The Concrete Society Technical Report TR34'),Sections

10.3 to 10.5.)

Increase the cement and water content n proportion to

maintain the w/c ratio at the required consistence and

fine aggregate content.

Incorporate fly ash in the rnix design.

Use an admix ture to increase the consistence or to reduce

the total water content.

Use a balanced Combination of the above.

When any type of fibre is to be included, there may also be

scope for a small reduction n fines content, typically 1-2%,

since fibres increase cohesion.

By ensuring that the concrete remains consistently homoge-

neous at the point ofplacing and at the specified consistence,

a dense closed-surface finish is usually ach ieved.

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Finishability

To achieve a dense closed finish,a minimum free water content

m3 s likely to be necessary; lower water

oses of admixtures may result in a concreteof the required consistence but prevent the formation of a

mortar layerat the surface, due to the increased viscosity of the

concrete.I tshould be stressed that this is a minimum amount

of water; the particular physical characteristics of the aggregate

proprietary concrete formulations that have low water contents.

In this case specialist advice on handling s normally given to the

or by the concrete producer. Figure5 shows a

typical compacring and levelling operation usinga laser screed.

higher water content.This may not apply to

LFigure 5 - Comp acting and levelling concrete using a aser screed

The quality of the finish will also depend on the’bleed’charac-

teristics of the concrete. Ex ve bleeding may result in a weak

surface and increased riskofcrazing and drying shrinkage. Con-

versely, if little OF no bleeding takes place, the surface of the

aturely, before trowelling and floating are

ed bleeding, particularlyat a

slow rate,which continues after the surface has effectively been closed

by floating and trowelling, may result in sub-surface voids or

hollows.This in turn may increase the risk of localised delami-

nation.

The rate at which bleeding occurs is determined by many

factors: for instance, the use of glow temperatures), he grading of the aggregates, the cement

type and its setting time, the use of retarding admixtures,

admixturesthatentrain air, and low ambient temperatures.

r fly ash (particularlyat

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Chapter 7 Concrete for industrial floors -Guidance on specification and mix design

In-situ concrete

propertiesTherma movement

The hydratia..of cement is an exothermicc. .emical reaction andthe temperature of concrete can rise significantlyafter setting.

The temperature peaks 18-36 hours after placing, depending

on the cement type used.After the peak temperature has beenreached, the temperature of the floor slab may fall rapidly due tothe high ratio of surfacearea tavolume.This causes the concrete

to contract rapidly and the risk of the formationof cracks isincreased since its tensile strength has not fully developed.

It is therefore of paramount mportance that any movementjoints aresawnas soonas practicableafter slab laying andfinishing to releasestress build-up. n severe conditions, the

outer cuts should be sawn first, working in towards the middle

of the slab.

The cement type and content will influence the timing of thesawing operation.The peak temperature in the concrete slab

will increaseas the total cement content increases,so it is bene-

ficial, particularly when the ambient temperature is high, to keepthe cement content close to the specified minimum. Generally,

concrete made using only Portland cement(CEM I) needs to be

sawn earlier than concrete containing combinations with ggbsor fly ash since the combinations generally result ina lower andlater temperature peak than€EM I only.Thus during summer itmay be beneficial to use combinations asthe window for sawingwill be longer; conversely, during winter, the shorter window

with CEM I may be more practical.

DryingshrinkageDrying shrinkage can be reduced to an acceptable level but noteliminated completely. n order to minimise drying shrinkage:

keep the free water contentas lowas possible, butseethe

section'Finishability:page 13

select aggregates in accordance with the section 'Aggregates:

minimise restraints to slab movement and provide effective

movement oints where applicable.

Page8

Comrnen uryDrying shrinkage should be consideredat the mix design and

planning stage. Many drying shrinkage problems are directly

attributab le to h igh water contents. The use ofadmixtures

can enable the requirements for high consistence to be met

while avo iding problems associated with drying shrinkage.

Keepinga

constant w/c ratio wil l increase consistence. Theconsequence of adding water to ncrease consistence s to

reduce strength and abrasion resistance unless cement is

also added. t is the increase in water tha t causes the shrink-

age, not the cement as such. At constant slump or flow,

cement can be added (sand reduced) wit hout increasing

water. f this is done, shrinkage wil l in fact reduce. Increasing

the cement content wh ile maintaining a constant free w/c

ratio wil l lead to increased drying shrinkage.

Sawing oints will no t stop drying shrinkage movement, but

will concentrate his shrinkage movementat acceptable

locations.

Theuse of fibres or fabric reinforcement can also control,as

opposed to prevent, the effects o f mo isture-related move-

ments'3 5J. For further info rmation regarding thermal move-

ment and drymg shrinkage refer to Technical Report TR34Y

Figure 6 shows a finished floor being surveyed for regularity,

the methodology is covered in TR34.

Figure 6 - Floor level surveying

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Concrete for industrial l o o r s - Guidance on specifi cation and mix design Chapter 7

rasion res isIan Influenceof cu

For direct-finish concrete, the quality and abrasion resistance ofthe surface depends on a sufficient cement content minimum

of 325kg /m3,a free w/c ratio not greater than 0.55, the quantityand quality of the finishing work, and, equally important, theefficiency of the curing.

Proprietary toppings and dry-shake materialsareavailable, someof which have Agrement Certificates. These are specificallydesigned to give high abrasion resistance.The quality of work-manship and curing are of paramount importanceto achievethe bestpossible performance with these materials.

Secondary factors that influence surface durability are the overallquality of the concrete and, to a lesser extent, the properties of

the aggregate. Historically, problems have occurred where jointarrises have been damaged by forklift truck wheels, particularlywhere concrete below compressive strength class C32/40 hasbeen specified. This problem with construction oints canbe

avoided by the use of proprietary steel armoured joint systems.

The fine aggregate for direct-finish concrete floors should not

contain soft or friable particles.

Referto BS 8204-2 and Technical Report TR34(’] or furtherguidance on abrasion resistance.

CommentaryConcrete that is prone to excessive bleeding may have poor

abrasion resistanceas a result of very fine material migrating

with the bleed water to the slab surface. This fine mate rial

can form a weak laitance a t the top surface, which w ill break

down when norma l traffic commences.

Impurities, such as soft lignite and shells, which are directly

below the wearing surface, may result in dam age to the

wearing surface when in service. When damage occurs, as

the resulr ofsuch surface defects, normal use of the floor

may cause the damaged area to ncrease n size.

Compactionofconcrete

It is essential for short- and long-term durability that concrete isadequately compacted during construction. In large-area con-struction methods where high slump or flowing concretes are

used, this is rarelya problem; however, due attention should begiven to compaction around oints, box-out details and adjacent

to walls and columns.The latter areas normally need to becompacted usinga poker vibrator.

The necessity for curing has been discussed in the sections’Cements and combinations: page8and ‘Abrasion resistance:

page 15.Most floors arecured with high-efficiency spray-onmembranes, and these have a significant beneficial effect onthe durability of the floor surface, improving abrasion resistanceand reducing crazing. In flooring construction, early curing s

not normally required to reduce or control plastic shrinkage orplastic settlement since trowelling operations usually meanthat these phenomena do not occur.

Where thermoplastic sheet or tile floor coverings are to beinstalled, itshould be noted that floors which have been treatedwith spray-on membranes will take a considerable time to reachthe relative humidity level of 75% specified in BS 8203: 2001Code ofpractice or installation of resilient floor coverings.Thisperiod will probably be greater than six months and may exceedone year. Therefore, rather than using spray-on membranes-see Figure7-, an alternative method of curing maybemore

appropriate, suchascovering with plastic sheeting. Effectivecuring s best achieved by using spray-on curing systems suchas

90% efficiency resin-based compounds or acrylic sealers. Goodcuring can be effected using polythene sheeting, but the paceof construction is such that undisturbed curing for sufficienttime is unlikely to bea practical option.

7’ 1

1:.

-.r-

.

I

Figure 7 -Spray application of curing compound

Further information on moisture n concrete floors is nowavailable; refer to The Concrete Society Project ReportNo.4‘61Moisture n concrete and the performance of impermeable floor

coverings.

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Chapter 8 Concrete for industrial floors- Guidance onspecificationand mix design

Batchingand pre-

delivery of concrete

Batchng

Theconcrete producer should have accreditation bya third-party quality assurance body e.g.QSRMCor BSI.Thebatching

produce homogeneous concrete. Detailed batching proceduresshouldbeused to ensure consistency from batch to batch.Themixing time, whether the process is wet or dry batch, should be

consistent.Forcentral mixing plants, the mixer manufacturer'srecommendations shouldbefollowed. For truck mxers, this isusually6-1 0minutes, but this depends on the design of themixer drum and itsmixing speed (typically 1&14rev/min).

should ensure that the materials are fully mixed to

116 rl "

a

Figure8 - Trucksqueuing to deliver concrete

A ll batches should be visually checked for consistence andappearance prior to despatch from the concrete plant. It salsoadvisable to agree with the producer that concrete will bemixedat full mixing speed fora minimum period of2minutesat site, before sampling or discharging. Figure8 shows mixertrucks queuing before discharge.

When the concrete includes admixtures it s essential that fulland even dispersion is achieved during mixing. Normally theaddition of the admixture s madeat the same time as theaddition of water to ensure complete dispersion.

Failure to dispersetheadmixture completely may lead to pocketsinaconcrete batch containing excessive concentrations of theadmixture.This may cause localised areas of concrete to beretarded and have excessive percentage of entrained air. It s

recommended that cement should come into contact witha

proportionofthe mixing water beforeitis added to prevent theadmixture affecting the initial formation of cement hydratesand the possibility of excessively rapid hydration.

The batching and mixing sequence should be consistenttominimise variation between batches.

ifitis intended to add further materials to the truck mixeratsite, the additional mixing time is best establishedby trials andthen agreed between partiesas the standard.

CommentaryThe majority o f ready-mixed concrete plants in the UKemploy

the dry batch process, using truck mixers, which have been

designed to mix emcienr/y The main difference betweencentral mixer plants and dry batch plants is the higher out-

puts that can be achieved with central mixing. Well main-

tained truck mixers wi ll produce high-quality and consistently

homogeneous concrete.

I t must be emphasised tha t the mixing times referred to in

the section 'Batching,' page 16are minimum recommended

times.

Historically, inadequate dispersion o f admixtures has been

a key problem for flooring contractors and has resulted in

many contractors being deflected from using these poten-tially beneficial materials. Admixture manufacturers advise

that the cementbe wetted prior to the addition ofadmixrures

in order to avoid the problems discussed above. AppendixA,

page22gives informationon batching and mixing ofadmix-

tures including site addition.

Concrete producers accredited by third-party quality assu-

rance schemes are required to have work instructions for

batching and mixing. These will have been assessed for

effectiveness.

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Concrete for industrial floors - Guidance on specification and mix design Chapter8

Pre-del very plann ing

It s of prime importance that, before concrete s first supplied

to a site, the contractor and producer liaise, plan and agree the

general conduct of the project. In particular, they should:

agree the concrete specification and sources of materials

agree the concrete design criteria for the method of placing

and constructionestablish'call off'procedures and access routes to site

determine the maximum concrete volume for each pour

and delivery rate

confirm the location of the ready-mixed concrete plants from

which supply will be made (consider effects of variations in

consistence and setting time between concrete from

different pla n )

agree procedures for sampling and testing of concreteagree conformity criteria (see Chapter 9'Conformity and

identity testing: page 18)

arrange procedures for addition of any admixtures, fibres or

water at site

identify key representatives for each party and establish

communication methods and channels

agree procedures for dealing with breakdowns or interrup-

tions to supplymake provision for weather changes

identify how to contact keypersonnel, both contractors and

producers

agree arrangements for washing down truck-mixer dischargechutes on site.

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Conformityand identity

testing

Con orm y

The approach to concrete conformity and testing has been

fundamentally changed with the introduction of BS EN 206-1

and the complementary British Standard BS 8500.Conformity

testing and evaluation are processes that are carried out either

by the concrete producer or by a third party on his behalf.Theproducer is responsible for the concrete design process that

establishes the required properties and is also obliged to operateproduction control systems and procedures.

The properties that the concrete producer is required to control

for designed concrete, in accordance with the BS 8500, that are

relevant to concrete for use in industrial floors are:

compressive strength

waterkement ratio

cement contentconsistence class or target value for either slump or flow

chloride content of the concrete.

Where a prescribed concrete is specified, the following are

subject to conformity control:

cement type and class

consistence class or target value for either slump or flow

types of aggregate

type of admixture or addition if required

sources of concrete constituents, where specified

constituent proportions.

In the event of non-conformity, he producer is obliged to take

the following actions:

Checktest results and, if invalid,take action to eliminate errors.

If non-conformity s confirmed, take corrective actions inclu-

ding a management review of relevant production control

procedures.Where there is a confirmed non-conformity with the specifi-

cation that was not obvious at delivery, give notice to the

specifier and user in order to avoid any consequential damage.

Recordall actions on the above items.

CommentaryThe user or specifier should be aware that the producer is

required to veri@ hat the description of the concrete given

on the delivery ticket is correct.BS fN206- states: "Conformity

control is an integ ral part ofprod uction control'! For a

producer to declare conformity to BS 8500-2,he is required

to establish systems for production control that include

selection of materials , concrete design, concrete production,

inspection and tests, the use of da ta arising from testing

and calibration, and conformity control.

Whereas the producer is required to nform the specified

user of any non-conform ity tha t was not obvious at the

time ofdelivery , non-conformities obvious at the time of

delivery are either accepted or rejected there and then.

Examples ofself-apparent non-con formity at the time of

delivery are consistence, colour and aggregate size.

Identity testing (strength)

Where a contractor or a third party instructed by the contractor,

client, engineer or architect carries out sampling and testing of

the concrete, it is called identity testing.The procedure and

conformance criteria for determining whether a defined volume

of concrete comes from a conforming concrete of the specified

strengthclass are outlined in BS EN 206-1 Annex E, with clarifi-

cation in BS 8500-1 Annex A.10 and Annex B.5.

The contractor must be aware that the measured strengths of

test cubes are intended to exceed the specified characteristicstrength by a design margin- see the Section'Strength: page 6.

This margin is necessary to allow for plant and material variations

and to ensure an acceptably low probability of strength confor-

mity failures.

However, the need to meet the specified requirements ormaximum w/c ratio and minimum cement content may result

in a concrete with a higher strength than is needed to satisfy

strength conformity criteria.Therefore, high average strengths

should not be regarded as a sign of poor control, but an indica-

tion that the producer is conforming to all aspects of the speci-

fication.The converse is also applicable where cubes are attainingthe required margin but not their true potential.This may indi-

cate poor control.The allowable criteria are given in Appendix B,

page 23.

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Concrete for industrialfloors - Guidance on specification and mix design Chapter 9

CommentaryIf the h igh average concrete strength results in dificu lties for

the contractor, the cause and the options should be discussed

wi th the producer. It would not norm ally be prudent to relaxthe specified maxim um w/c ratio, but a change of cement

type could reduce the strength while still satisfying specifica-

tion requirements. f the cement content is the main factor,

then once again, a change in cement type may help.

The responsibility for demonstrating conform ity o f concrete

supplied in accordance w ith the Standard for concrete, BS

EN206- , is placed upon the concrete supplier .BS 8500-

strongly recommends tha t the producer holds third-party

certif ica tion, e.g. QSRMC or BSI to provide an independent

audit on conformity. Specifiers ofconcrete should therefore

have a high degree of confidence in the material's conformity.

The contractor and the producer must cooperate over

sampling and testing requirements.This will avoid wasting

manpower and also disputes about conformity.

Id entity test ng (con siste n ce)

Identity testing for consistence (slump, flow) is carried out to

the same limits as those applicable to the concrete producer.

Concrete producers normally undertake to supply concrete

with consistence conforming toTable 18of BS EN 206-1.The

permitted slump or flow range can,as a result, be wider than

that consistent with the contractor's placing method and

finishing requirements, particularly since samples for a slump

test are frequently taken from the initial discharge from thetruck mixer and therefore wider limits apply. BS 8500 Annex B

provides the identity testing criteria, depending on the method

of sampling (spot or composite).Itshould also be noted that

measured slump test value is reported to the nearest 10mm.

The allowable limits are given in Appendix B, page 23.

CommentaryContractors frequently stipulate a narrower slump or flow

range than tha t given in the Standard. This may cause

some difi cu lty for producers since reductions in slump

occur between concrete plant and site due firstly to water

loss by evaporation, and secondly as the result of stiffening

and absorption ofw ate r by aggregates. Traffk delays will

exacerbate this.

A practical way of dealing w ith this is for the producer and

contractor to agree a m ethod tha t enables the consistence

to be adjusted at site. Rules must be agreed on the quantity

of water required to increase the consistence from the mea-sured initial value to tha t specified.A suitably experienced

person should supervise this procedure. This should ensure

tha t the max imum specified w/c ratio or the w/c ratio

required for 28-day strength, whichever s the controlling

value, is not exceeded. After water is added, the concrete

should be remixed for a t least 2 minutes a t full speed to

ensure dispersion.

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References Concrete for industrial floors -Guidance on specification andmixdesign

References

1.

2.

3.

4.

5.

6.

The Concrete Society.Concrete lndustrial Ground Floors - A Guide to Design and Construc tion.The C oncrete Society, Camberley,

2003, Technical Report 34 (Third Edition).

Chaplin R. G. The Influence ofggbs and pf a Addit ions and Other Factors on the Abrasion Resistance oflndust ria l Concrete Floors.

British Cement Association, Camberley, 1990.

Association of Concrete lndustrial Flooring Contractors.Steel Fibre Reinforced Concrete lndustrial Ground Floors.The Concrete

Society, Camberley, 1999.

The Concrete Society. Guidance on the Use of Macro-synthetic-fibre-reinforced Concrete. The Concrete Society, Camberley,

2007,Technical Report 63.

The Concrete Society.Guidance for the Design ofsteel-frbre-reinforced Concrete.The Concrete Centre, Camberley, 2007, Technical

Report65.

The Concrete Society.Moisfure in Concrete and the Performance oflmpermeable Floor Coverings.The Concrete Society, Camberley,

2004, Project Report No.4.

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Concrete for industrial floors - Guidance on specification and mix design Appendix A

Guidance on the

specification and Ise of

admixtures in concrete

for industrial floors

Introduction

Admixtures, and particularly water-reducing admixtures, can offer

substantial benefits in flooring concrete by reducing the freewater content while maintaining appropriate consistence for

rapid placement and compaction.This reduces drying shrinkage

in the concrete and hence cracking and curling of the slab.

Other types of admixture can further reduce shrinkage, speed

the setting to allow earlier finishing or can aid the finishing of

flooring concrete.

As with al l admixture applications, careful selection of admixture

type and grade is essential to obtaining a satisfactory result.

Correct addition and mixing are also key to obtaining a uniform

concrete.These guidelines are intended to assist the supplierand user of flooring concrete to optimise the advantages from

the use of admixtures.

Water-reducing admixtures

Admixtures whose major active ingredient s based on the

following materials have been found most suitable for use in

concrete floors.They disperse easily through the concrete and

maximise the water reduction. n hot weather some additional

retardation may be necessary with these admixtures.Thesematerials are:

0 sulphonated naphthalene formaldehyde condensates

0 sulphonated melamine formaldehyde condensates

0 polycarboxylated ethers.

The polycarboxylated ether types have proved particularly

beneficial as they give exceptional uniformity of dispersion and

minimal retardation of set.

Admixtures based on sugar-reduced lignosulphonatescan be

suitable for floors if additionalcareis

exercised over mix design,uniformity of mixing and the possibility of greater retardation.

This is especially the case in cold weather and/or when fly ash

or ggbs is being used.

Admixtures based on, or modified with, the following are likely

to enhance retardation and should be avoided in flooring

concrete, especially under cold conditions and where fly ash or

ggbs are being used:

0 hydroxyca rboxyl c acids sa ts

0 carbohydrate-based polymers (hydroxylated polymers, corn

syrups and malto-dextrins)

0 molasses.

Other admixtures

Other admixtures that may have special applications in concrete

floors include:

0 set-accelerating admixtures that can bring about quicker

stiffening and allow earlier finishing, especially in cold

conditions0 shrinkage-reducingadmixtures that can reduce cracking

due to drying shrinkage and cut down on the number of

joints.0 finishing aids that can be incorporated into dispersing

admixtures of the types indicated above.

Other admixtures that may cause problems with concretefloors are noted below.

0 Air-entraining agents should be avoided in floors that will

be power finished as the entrainedair can be one of the

causes of surface delamination after hardening.0 Some admixtures may cause an increase in the level of air in

the concrete and should, therefore, be used with caution -check with manufacture.

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AppendixA Concrete for industrialfloors -Guidance on specification and mix design

Batchi ng admixtures

When batching admixtures, the following comments should

be noted.

It s desirable that all the components of the concrete, inclu-

ding admixtures, are mixed at the batching plant.Where this

procedure s not adopted,site addition must be under the

direct supervision of a concrete technologist or engineer,

should be restricted to the admixtures detailed in the section

'Admixtures', page 10and to the guidelines for site addition

covered in Chapter 8'Batching and pre-delivery of concrete',

page 16.

0 Prior to supply of concrete, the contractor and the concrete

supplier should agree the admixture type, admixture addition

time and method, concrete mixing and consistence checking

procedure. Further guidance on this can be found in the

section 'Admixtures', page 10of this Guide

0 It s essential that flooring concrete is uniformly and consis-

tently mixed.To achieve this generally requires greater

attention to the mixing procedure and duration.0 It is essential that only mixers and mixer trucks with blades

and drums in good condition are used and are loaded within

recommended capacity for mixing.0 After batching, sufficient mixing must be given to ensure

uniform dispersion of admixture and other materials.

It s essential that, during addition, the admixture does not

come into contact with dry cement.The concrete will only have uniformity of consistence and

set across the slab if there is consistency in the order and

timing of the concrete batching sequence and this is parti-

cularly important when admixtures are being used.

A CAA Guidance Documentof recommended practice for

addition of admixture to concrete is available from the Cement

Admixture Association at the address shown below.

Site addition of admixtures

If admixtures are being added at site then the following points

should be borne in mind.

0 The addition of any concrete component including water at

the site is not recommended unless it is actively supervised

bya qualified concrete technologist or engineer. Itshould

also be restricted to the addition of those types of admixture

detailed in the section 'Admixtures', page 10.

0 Admixture addition at the plant followed by a further

addition on site is more likely to cause inconsistency than a

single addition at one location.0 If circumstances, such as hot weather or differential delays in

delivery, dictate that admixture addition is best made on

site, a written procedure must be agreed and implemented

byall parties.The procedure should include:

the effect on set time of ambient temperature when the

concrete s delivered.checking for uniformity of consistence before and after the

addition of admixtures, fibres, water or other materials

calibration of dosing equipment, uniformity of dosing,dosage rate, batching sequence and mixing time

recording any materials, including admixtures and water,

addedat site and the time of addition, consistence before

and after addition, quantity added and additional fast

mixing time

consideration of the effect on setting time due to batch-

to-batch variation in admixture dosage and time of

admixture addition after original mixing.

Factors affecting placing and finishingcharacteristics

The following factors should be considered before starting a job.

0 Take account of the likely weather and the potential for a

significant change from the expected ambient temperature

on the day of concreting.0 Ensure specified consistence at the time of placing will be

compatible with the placing method.0 Account for consistence loss resulting from the use of fibres,

delays in delivery and placing.0 Large batch-to-batch variation in consistence and late

additionsof water can both affect setting time and should

therefore be avoided.The compatibility and effect on setting of the concrete must

be determined when dry-shake and colour systems are used

as they may also contain undeclared admixtures.

This guidance was produced by a VWAClFCjoint taskgroup which

met as a subgroup of the A C K Concrete Mix Design andAdmixtures

Working Party.

For general information on admixtures contact:

J ohn Dransfield, Secretary

Cement Admixtures Association

38Tilehouse Green LaneKnowle

West Midlands

B93 9EY

TeVFax:01564 776362

Web: www,admixtures,org.uk

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Concr ete for industr ial loors - Guidance on s pecification and mix design AppendixB

Slum p class

51

Identity testing criteria

Slump range: Maximum allowable deviation

m m on range imi t : m m

10-40 -1 0,+30 -1 0, +20

Spot sample Composite sample

Strength criteria

53

54

The test result used in the assessment is the average of the

results of two or more specimens - normally cubes in the UK -cast from one sample for testing at the same age. Where the

range of test values (a result is the average of two cubes from the

same sample) is more than 15% of the mean, the results shall

be disregarded unless an investigation reveals an acceptable

reason to justify disregarding an individualtest value.

100-1 50 -20, +30 -1 0,+20

160-210 -20, +30 -1 0,+20

Samples should be taken in accordance with the composite

method in BS EN 12350-1 and represent a defined volume ofconcrete. For a floor slab a defined volume could be the concrete

delivered to a site within a fixed period, or a particular slab area,

but not more than 400 m3.

Flow class

F1

F2

F3

F4

F5

F6

Flow range: Maximum al lowable deviat ion on range

Spot sample Composite sample

mm l im i t : mm

-1 40, +40 -1 40, +30340

350-41 0 -30, +40 -20, +30

-30, +40 -20, +3020-480

490-550 -30, +40 -20, +30

560-620 -30, +40 -20, +30

2630 -30, - -20, -

I 52 I 50-90 I -20,+30 1 -10, +20 I

Numb er of test results for

comPressive t rength

Criterion 1 1 Criterion 2

Mean of results: IAnv individual est result:

I 55 I 2220 I -20, - I -10, - I

f rom def ined volume I N/mm2

Table62 - Identity c riteria for slum p class, BS 8500- 1

N/mm2

Maximum allowable deviation on target

value: m m

Target slump: m m

BS 8500-1Annex B.5 states that each defined volume should

preferably be represented by six test results or if a volume

contains more than six test results, they should be split into

groups of six for assessment.The results should represent a

short chronological period to minimise the risk of including a

step change in quality. Conformity is thus judged for the whole

of the defined volume of concrete. Concrete is deemed to

come from a conforming population if both the criteria in TableB1 below are satisfied.

2-4 > f , + l z f<- 4

I 5-6 I >f<,+2 I z f?,- 4 IWhere fcks the c onc rete characteristic strength i.e. he st rength class

Table61- ldenti ty crit eria for compressive streng th,BSEN 206-1 Annex B

Consistence criteria

Consistence is either specifiedas a class or target. Although a

supplier will endeavour to provide the required consistence,

deviations in production and sampling apply.Tables 82 to B5

below give the maximum allowable deviation based on a spot

sample taken from the initial discharge of a ready-mixed con-

crete truck and a compositesample taken throughout the load.

I40 I -30,+40 I -20, +30

I 50-90 I -40,+50 1 -30, +40 I

I 2 100 I -50,+60 I -40, +50 ITable63 - Identity criteria for targ et slump, BS 8500- 1

value: m m

Table65 - Identity criteria for targ et flow, BS 8500- 1

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Flooring

AdvisoryServiceInadequ ate floors seriously reduc e theefficiency of w arehouse operations.

Face Cons ultants have the specialistexpertise to optim ise floor p erformance innew-build projects and existing prem ises.

Consultancy services include:

e Design e Mechanlcal handilng efflclency

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Due dlllgence and dilapidatlons

Call us for an initial no-obligation consultation.

FACE CONSULTANTS LTDGlobal F l o o r i n g C o n s u l t a n t s

HUDDERSFIELD AND NEWBURVTel: t 44 (0)1484 600090 Email : nfo@face-consuI tan ts .com

The Total So lu tion ProviderWe offer the fu l l Design and Construct ion Package -

Our expertise and knowledge of the Construction Industry means

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construction fibres or visit our website for further information.

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ADFIL Unil 28 BergenWay Sutlon Fields Industrial E state (West) Hull HU 7 OYO England

T +44 (0) 482 863777 W: www.adfi l .co.uk

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www.concretebookshop.com

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THE CONCRETE

BOOKSHOP

The Concrete Bookshop supplies a wide

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cretebookshop.com

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GoodConcrete

Guide

Concretefor industrial floorsGuidanceon specification and mix design

This updated guide provides practical guidance on b e s t practice farspecification, design, production and delivery of concretefor direct 1cnithed

industrial floors constructed by large area pour m e t W A l so mlewmt Ocn

any large interior floor construction method. Covers concrete spacffication,materials, mix design, in-situ concrete behaviour and properties, mixingand

delivery, and identity testing. Appendices summarise admixture types and

their effects on concrete properties, and the criteria for identity (acceptance)

testing.

ISBN 1-901482-38-4

CS127

Good Concrete Guides give concise,"best practice" guidance on

materials, designand construction.

For other publications in the Good Concreteseries visitthe Concrete Bookshop

at:www.concretebookrhop.com

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guide to industrial floors

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