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! I ;Concrete for industrial floors Licensed copy: [email protected], PELL FRISCHMANN CONSULTING ENG LTD, 22/11/2010, Uncontrolled Copy, ®The Concrete Society Ac know I edg e me nt 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 industrial floors - Good Concrete Guide 1 Published by The Concrete Society CS 127 Published September 2007 ISBN 1-904482-38-4 OThe Concrete Society

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te for industrial floors G Utd a nce o i specification and mix design

A joint report from The Concrete Society Industrial Floors Group and the Association of Concrete Industrial Flooring Contractors Licensed copy: [email protected], PELL FRISCHMANN CONSULTING ENG LTD, 22/11/2010, Uncontrolled Copy, ®The Concrete Society to.- reword I Preface

This updated Guide was originally published in 1998; it was then This revised document gives practical guidance on current best and still is the result of collaboration between the contractor practice for the specification, design, production and delivery and members of the Association of Concrete Industrial Flooring of concrete for direct-finished industrial floors constructed by Contractors (ACIFC). The Association’s objective continues to large-area pour methods. Much of the information is also rele- be assisting its members to deliver better, more consistent, vant for any large interior floor construction method. quality concrete ground-floor slab construction. This Guide is intended primarily to establish a working interface This Guide now takes full account of new and updated British between all parties involved in floor construction, including and European Standards for materials and, where appropriate, specifiers, contractors, concrete producers and the materials and Codes of Practice.The advent of the new concrete standards BS equipment supply chain so that it brings together a consensus EN 206 and BS 8500 has changed several aspects of concrete of views and recommendations that have been reached after production, in particular specification methods, descriptions extensive consultation and deliberation. and requirements for determination of conformity. Kevin Sutherland The guidance given in the original version of this document was Tarmac Central Ltd 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. It was the forerunner of other specialist guides on other aspects of this type of construction.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 is 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 reference to lack of full dispersion during the mixing process. It is true to say that admixtures are more widely used now, particularly those materials specifically designed for use in floor construction.The correct choice of admixture type and mixing procedures to ensure a fully consistent concrete in every load remains of paramount importance in the very large pours that characterise fast-track floor construction process.

The ACIFC andThe Concrete Society believe that all 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 it will give support to the ACIFC’s objective of delivering better quality by improving understanding of how to achieve it.

David Harvey Chairman, ACIFC Licensed copy: [email protected], PELL FRISCHMANN CONSULTING ENG LTD, 22/11/2010, Uncontrolled Copy, ®The Concrete Society Concrete for industrial floors Gu dance on specification and mix design

Contents

Acknowledoements Inside Front Cover In-situ concrete properties 14 Foreword ii Thermal movement 14

Preface ii Drving shrinkage ' 14 Standards for future reference iv Abrasion resistance 15 Compaction of concrete 15 Introduction 1 Influence of curina 15

Health, safety and environment 2 Batching and pre-delivery of concrete 16 Introduction 2 -a 16 Health and safety on site 2 Pre-delivery planning 17 Health and safety for concrete production 2 Environment 3 Conformity and identity testinq 18 Conformity 18 Project planninq 4 Identity testing (strength) 18 Identity testing_(consistence) 19 Concrete specification 5 Designation 5 References 20 Strength 6 Cement content 6 -Appendix A: Guidance on the specification and use Waterkement ratio 7 of admixtures in concrete for industrial floors 21 Consistence 7 Introduction 21 Water-reducina admixtures 21 Materials 8 Other admixtures 21 Aagregates 8 Batching admixtures 22 Cements and combinations 8 Site addition of admixtures 22 Admixtures 10 placing and finishing characteristics 22 Mixing water 10 Steel, macro-synthetic and micro-synthetic fibres 11 bpendix B: ldentitv testing criteria 23 Strength criteria 23 Concrete mix desian 12 Consistence criteria 23 Introduction 12 Consistence 12 Fine aggregate content 12 Finishabilitv 13 Licensed copy: [email protected], PELL FRISCHMANN CONSULTING ENG LTD, 22/11/2010, Uncontrolled Copy, ®The Concrete Society Standards for future reference

BS 3892-1 1997 Pulverised-fuel ash. Specification for pulverised fuel ash for use with Portland cement BS 4027: 1996 Specification for sulfate-resisting Portland cement BS 6699: 1992 Specification for ground granulated blastfurnace slag for use with Portland cement BS 7979: 2001 Specification for limestone fines for use with Portland cement BS 8203: 2001 Code of practice for installation of resilient floor coverings BS 8204-2: 2003 Screeds, bases and in-situ flooring. Concrete wearing surfaces - Code of practice BS 8500-1 2006 Concrete - Complementary British Standard to BS EN 206-1. Method of specifying and guidance for the specifier BS 8500-2: 2006 Concrete - Complementary British Standard to BS EN 206-1. Specification for constituent materials and concrete BS EN 197-1: 2000 Cement. Composition, specifications and conformity criteria for common cements BS EN 197-4: 2000 Cement. Composition, specifications and conformity criteria for low early strength blastfurnace cements BS EN 206-1 : 2000 Concrete. Specification, performance, production and conformity. BS EN 450-1 : 2005 Fly ash for concrete. Definitions, specifications and conformity criteria BS EN 933-3: 1997 Tests for geometrical properties of aggregates. Determination of particle shape. Flakiness index BS EN 934-2: 1998 Admixtures for concrete, mortar and grout. Concrete admixtures. Definitions and requirements BS EN 1008: 2002 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 BS EN 2350-1: 2000 Testing fresh concrete. Sampling BS EN 2350-2: 2000 Testing fresh concrete. Slump test BS EN 2350-5: 2000 Testing fresh concrete. Flow table test BS EN 2390-2: 2000 Testing hardened concrete. Making and curing specimens for strength tests BS EN 2390-3: 2002 Testing hardened concrete. Compressive strength of test specimens BS EN 12620: 2002 Aggregates for concrete BS EN 13263: 2005 Silica fume for concrete BS EN 1367-4: 1998 Tests for thermal and weathering properties of aggregates. Determination of drying shrinkage BS EN 14216: 2004 Cement. Composition, specifications and conformity criteria for very low heat special cements BS EN 15 167: 2006 Ground granulated blastfurnace slag for use in concrete, mortar and grout PD 6682-1 : 2003 Aggregates for concrete. Guidance on the use of BS EN 12620 BS EN IS0 14001: 1996 Environmental Management Systems. Specification with guidance for use BS IS0 9000-2: 1997 Quality management and quality assurance standards. Generic guidelines for the application of IS0 9001, IS0 9002 and IS0 9003 Licensed copy: [email protected], PELL FRISCHMANN CONSULTING ENG LTD, 22/11/2010, Uncontrolled Copy, ®The Concrete Society Concrete for industrial floors - Guidance on specification and mix design Chapter 1

I ntrod uct on

Concrete industrial floors must give a high standard of performance and durability. Close attention to the construction materials and working practice is necessary if floors are to be constructed that need minimal maintenance.

The majority of 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 producers practical material specifications 0 mixer trucks with dissimilar mixing efficiency concrete supply rates control of fresh concrete including uniformity of mixing and consistence 0 quality of workmanship, in 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. Licensed copy: [email protected], PELL FRISCHMANN CONSULTING ENG LTD, 22/11/2010, Uncontrolled Copy, ®The Concrete Society Chapter 2 Concrete for industrial floors - Guidance on specification and mix design

Health, safety and e nvi ro n ment

I nt roduct ion safe handling of materials that are potentially hazardous to health; the Control of Substances Hazardous to Health Regu- Without exception, the most important issue for those managing lations (COSHH) apply (particularly with regard to concrete, synthetic and steel fibre, concrete admixtures, dry-shake or engaged in construction activity is the safety of all persons on the site. Currently, as the construction industry accounts for powder and sealants) providing formal health and safety inductions for other sub- a quarter of all deaths at work and for more than 4000 injuries contractors each year, the reduction of these numbers is a government provision of first-aid by suitably trained personnel priority.The Health and Safety Executive (HSE) enforces with establishing a reporting system, including arrangements for vigour the Health and Safety at Work Act and has declared its complying with the Reporting of Injuries, Disease and Dange- intention to seek criminal convictions for any breaches. rous Occurrences Regulations (RIDDOR) training to ClTB Health and Safety Test level and enforcement of CPCS cards Health and safety on site on-site/off-site traffic management and control consideration of other trades There are significant risks on most construction sites and, workplace lighting although not exhaustive, some examples are as follows: mess and toilet facilities demarcation of working and storage areas vehicle and construction plant movements establishment of a suitable audit and assessment process, use of power tools preferably by an independent person manual handling provision of a banksman and safe access for ready-mixed working at height, for example when constructing mezzanines, concrete trucks climbing ladders of mixer trucks, placing of laser levelling if intending to add materials or modify the concrete at site, a equipment contractor must provide risk-assessed procedures, suitable working in confined spaces equipment and adequate supervision. exposure to hazardous materials such as fresh concrete high-voltage power sources. The types of specific risks referred to above can be managed safely by implementing the appropriate systems and procedures. Employers have legal obligations under the Health and Safety at However, the most difficult risk to manage is employee and or Work Act and the main contractor will have a health and safety subcontractor behaviour: over 90% of all injuries, fatalities and management policy and procedures in place, including an near misses arise from unsafe acts, not unsafe conditions.The induction process. The flooring contractor, including his suppliers visible and uncompromising management of health and safety and any subcontractors, should seek to integrate their own is necessary to establish a culture of safety awareness among health and safety procedures into this in advance of flooring the entire site workforce, including subcontractors. Unsafe operations taking place. In particular, the preparation of risk behaviour should always be vigorously challenged and it should assessments and operational method statements should be be made clear to everyone that repeated or deliberate failure to considered essential; these will enable the main contractor to comply with procedures and instructions will invariably lead to issue the necessary Permits to Work to both the main flooring permanent exclusion from site and possibly criminal conviction. contractor and any other subcontractor engaged in the floor construction. Health and safety for concrete Some specific issues that should be addressed are: production ensuring the health and safety policy is appropriate to the type of work carried out by the specialist flooring contractor The concrete producer will have a health and safety policy and supply of appropriate personal protective equipment (PPE) documented safe working procedures in place.This will include and enforcement of its use periodic surveillance and reporting. As part of these operations the truck mixer operators or drivers will have been included in

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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 crush injuries when folding the chutes.

The truck operators or drivers, technicians and other representatives 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.

Environ ment

Most concrete producers are moving towards Environmental Management Systems based upon BS EN IS0 14001, with third- party accreditation from bodies such as the British Standards Institution (BSI). Additionally all static concrete plants are now licensed by the local authority under the Environmental Protec- 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 all emissions, including dust, waste water and waste concrete.

In addition to any contract-specific environmental issues, there are a number of areas common to all 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 concrete prevention 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 the impact of a construction site on the environment and to take steps to minimise the effect wherever possible.

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Project planning

Planning is the key factor in the successful execution of a flooring An important aspect of planning concerns how the work will be contract. Remember:'FaiIing to plan, in reality, is planning to executed and this needs to take into account details of the work fail'. However, a well-thought-out and structured approach will such as the method of construction, for example large-area pour, help to ensure that the job is completed on time, that the floor long bay, and also the method of concrete placement - will it meets the client's and main contractor's expectations and that be pumped or direct discharge, see Figure 1. Added to this are construction costs are kept under control. the finishing process and other post-concretingwork such as the application of a dry-shake topping, joint formation and/or The primary reasons for planning are to assess whether targets sawing, application of top-surface sealant or curing membrane are attainable, to identify cost, time scale, potential problems etc. Other factors such as placing external slab-work or where and to make decisions at the outset that will prevent future the floor is suspended may need additional resources and there- surprises. It is important that the flooring subcontractor's plans fore need to be an integral part of the plan. Figure 2 shows a are linked to the main contractor's plans and consistent with partially completed large-area warehouse floor. local supply chain output capacity and availability.

Every contract must have a project manager based at site or at the contractor's office who will be responsible for the delivery of E ?l the floor to time, quality and budget. A site meeting to define and agree goals and objectives and how they will be achieved should precede the contract start date.This meeting should include representatives from the following, irrespective of the size of the contract:

0 floor-laying subcontractor main contractor concrete supplier and concrete pumping contractor suppliers of other products, such as toppings, steel fibre.

Where the floor is to be designed and constructed to meet a specialised need it is essential to invite the engineer and building owner, or the end-user of the floor, to the pre-contract meeting; this will ensure that all parties understand fully what is agreed Figure 1 - Placing concrete and can reasonably be delivered.

It is recommended that the initial outline planning should include a task sequence and programme analysis; conformance to this working document should be regularly monitored throughout the 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 technical requirements and the project finances are kept within budget. Continuous monitoring of the key activities sometimes leads to minor adjustment of the work logistics.This is acceptable provided that the changes are controlled; timely recognition of the need for change will reduce the risk of failure to deliver to the overall plan. Additionally, regular progress review meetings should be held and must include the main contractor.These will assist in providing clear communication thus avoiding disputes over work progress and quality. Figure 2 - A partially completed large-areawarehouse floor.

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Concrete specification

Designation The concrete is ordered by its required performance in terms of its strength class subject to any restrictions on materials, mini- The majority of concrete is likely to be purchased through a mum or maximum cement content, maximum water cement ready-mixed concrete supplier. In order to purchase concrete (w/c) ratio and any other properties required. The purchaser this way, the requirements of the concrete need to be specified. must supply all the relevant information on use to enable the producer to design the concrete accordingly. A ready-mixed concrete plant is set up to produce many types of concrete, the concretes having been designed to meet the potential specifications of clients. As the constituent materials are batched by weight and not volume, this means that batched Proprietary concretes concrete should meet the original mix design specification and comply with the rigorous quality control systems implemented. The proprietary concrete approach is appropriate where the concrete is to achieve a particular performance, using defined Concrete, whether site-mixed, ready-mixed or produced in a test methods.The proprietary concrete is selected in consulta- precast plant, should be specified in the UK in accordance with tion with the concrete producer and the project specification is BS 8500, the complementary British Standard to BS EN 206-1. appropriately drafted. Part 1 of BS 8500 - Methodofspecifjhg andguidance for the specifier - is intended for the person or body establishing the specification for fresh and hardened concrete or who passes the specification to the producer, i.e. the purchaser of the ready- Prescribed concretes mixed concrete. Part 2 - Specification for constituent materials andconcrete - is for the producer and contains specification Prescribed concrete is a concrete where the purchaser prescribes requirements for the producer’s production control. the exact composition and constituents of the concrete and is responsible for ensuring that these proportions produce a con- BS 8500 allows concrete to be specified via a suite of concrete crete with the required performance. Essentially, the purchaser designations, namely designated, designed, proprietary, pre- selects the materials and proportions to satisfy the required scribed, or standardized prescribed concrete. For the majority strength and durability needs but does not specify these para- of industrial floor applications the designed concrete route is the most appropriate. meters. The concrete is ordered by its constituent materials and the properties or quantities of those constituents to produce a concrete with the required performance.The assessment of the Designated concretes mix proportions will form an essential part of the conformity requirements if the purchaser so requires. 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 Standardized prescribed concretes on the site conditions and the application for which it is to be used.The concrete is produced in accordance with BS 8500 and Standardized prescribed concretes (ST1 to ST5) are selected from requires the producer to hold a current accredited production a restricted list in BS 8500 and made with a restricted range of control certification based on product testing and surveillance, materials as detailed in the Standard.The assessment of the coupled with approval of the producer’s quality system to BS EN concrete proportions will form an essential part of the conformity IS0 9000. requirements.These concretes are appropriate where concrete is site-batched on a small scale or obtained from a ready-mixed supplier who does not have third-party accreditation. Designed concretes BS EN 206-1 Section 6 and BS 8500-1 Section 4 require that the For flexibility in specifying and purchasing, designed concretes specifier of the concrete shall ensure that all the relevant are appropriate as they cover the application and constituent requirements for the concrete properties are included in the materials. It is a mix design for which the purchaser is responsible specification given to the supplier/producer.These are covered for specifying the required performance and the producer is res- as Basic requirements and Additional requirements. For flooring ponsible for selecting the concrete proportions to produce the concrete the basic requirements will be similar to conventional specified performance. Effectively,the producer has responsibility concrete, e.g. strength class, exposure class, consistence. for the mix design to meet the purchaser’s needs, for example Additional requirements may be included for other technical exposure environment, working life, strength, consistence. requirements requested by the specifier, e.g. shrinkage.

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The typical characteristic strength specified for direct finished floors is UW35 or C32/40. This dual compressiveStrength class refers to cylinder/cube strength, the lower value being the cylinder strength. Also see the section #brasion resistance,' page 15.

Lower strengths may be specified 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 quality of finishing is enhanced or dry- shake topping is to be applied.

Assessment of strength ofsite-cast specimens, known as identity testing, is covered in BS EN 206- 1 Annex B, with clarifi- cation in BS 8500- 1 Annex A. 10 and Annex B.5.73is will give an Figure 3 - Large-area warehouse floor indication of whether a defined volume of concrete belongs to the same population as that verified as conforming to the The specifier is also required to inform the supplier of the concrete characteristic strength via conformity assessment by the properties needed for transportation, delivery, placing, compac- producer. This gives a reasonable guide to the quality and tion, curing and further treatment.This could also include special consistency of the concrete supply. requirements, e.g. for finish. This is covered under Exchange of information in BS EN 206-1 Section 7.1 and BS 8500-1 Section 5.1. Cement content Strength For industrial floors with power-trowelling, a minimum cement The required concrete compressive strength class is selected content of 325kg/m3 is considered suitable to achieve satisfac- from Table 8 of BS EN 206-1. Additional classes to those given tory abrasion resistance. are provided in BS 8500-2 Table 9. Commentmy Commentmy To achieve a satisfactory abrasion resistance the surface Specific guidance on concrete specification, related to design, must be capable of being power-trowelled and so sufficient expected use and trafficking conditions of a floor is given in finer fines must be available. When a 2Omm nominal maxi- two key documents, The Concrete Society Technical Report mum size coarse aggregate is used, a minimum cement 34"' and BS 8204-2: 2003. content of 325kg/m3is normally specified for direct-finish industrial floors and reflects current national construction The concrete compressive strength class relates to its charac- practice. 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 Experience has shown that lower cement contents may not and tested in accordance with BS EN 12390-2 and BS EN provide abrasion-resistant concrete with low dusting charac- 12390-3. The statistical approach to production control teristics. However, current research indicates that w/c ratio means that the average strength of the concrete supplied has more effect on abrasion resistance than the cement will usually exceed the specified characteristic strength by a content. In practice, where power-trowel finishes are specified design margin, the magnitude of which is dependent on a minimum cement content of325kg/m3ensures that there the quality control of the production of the supplying plant. is sufhcient volume of cement in the concrete to achieve a dense and uniform wearing surface. Cement contents above It must be recognised that the compressivestrength of con- 360kg/m3are unlikely to improve abrasion. crete has little relevance to the engineering design ofa concrete floor, as the flexural strength is more critical to its perfor- Cemen t contents above 400kg/m3can lead to finishing mance underload.However, the test for flexural strength has problems since the time available for floating and trowelling poor precision. The flexural strength of a concrete generally reduces with increasing cement content (see the section falls in the range 8- 15% of the compressive strength, the 'Finishability,' page 13). aggregate type having a significant influence on this factor.

I 1

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For direct-finishedfloors, BS 8204-2 recommends increasing Commentury cement content and strength class to achieve improved The selected consistence should reflect the level ofcompaction abrasion. It is recognised that specialist flooring contractors that will be applied to the concrete. As the slump or flow can achieve high levels ofabrasion resistance at cement increases, the effort required to achieve full compaction will contents lower than those specified in BS 8204-2:2003 and reduce. For strip construction methods a concrete with a this is noted in clause 6.2 of that Standard. It is therefore lower consistence value can be used. The consistence needs recommended that this issue should be agreed between only to be high enough to achieve full cornpaction with the the floor designer and the specialist flooring contractor. compaction equipment available, whether the concrete is placed by direct tipping, pumping or by dumper.

Most specialist flooring contractors prefer to use higher I Wat erkement ratio consistence classes for both strip construction and large- area pour methods. Specify a maximum w/c ratio of 0.55, or a lower value if appro- The producer should ensure that the proposed concrete is priate. sufficiently cohesive to avoid segregation of the constituent materials. This is particularly relevant if the flooring contractor will be adding super-plasticisers to the concrete on site. Commentary Fibres, particularly steel and macro-synthetic fibres, are This maximum value of w/c ratio reflects current practice in increasingly used in floor construction. The producer and the UK and is consistent with guidance given in The Concrete contractor should note that a small reduction ofabout Society Technical Report No. 34'').It is desirable to keep the lOmm slump may occur when micro-synthetic fibres (poly- free water content as low as possible to minimise drying propylene) are added to a concrete. Steel fibres and macro- shrinkage and excessive bleed etc. but the concrete must be synthetic have a greater effect on consistence than micro- capable of being placed and finished with the equipment fibres and the slump may be reduced by more than 25rnm, available. The producer can adjust the concrete design by depending on the fibre shape, length and quantity. Conse- increasing the cement content while maintaining the origi- quently, minor constituent adjustments may be necessary nal water content, or by using admixtures ora combination to maintain the w/c ratio and to maintain plastic properties. of both. Using an admixture to decrease the overall water The specified consistence should take account of this, par- content will help to control and/or reduce drying shrinkage. ticularly if the contractor intends to add fibres to the concrete at site.

Consistence

Select a consistence class that is appropriate to the method of construction.The contractor should inform the producer if admixtures or fibres are to be added to the concrete at site.

Consistence classes 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 with BS EN 12350-1.The concrete producer will normally target consistence at the mid-range value. Slump and flow tests are carried out in accordance with BS EN 12350-1 and EN 12350-5 respectively. See the section 'Identity testing (strength): page 18 and Appendix B, page 23.Table 1 provides typical consistence classes for floor construction.

I I Directpour I Pumped I I Long strip 1 52 or 53 I 53 I Laser screed 53 53 Large area F5 F5 Table I - Suggested consistenceclasses for floor construction

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Materia Is

Aggregates 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 A wide variety of aggregate types are in use in the UK, depending entirely and a procedure for rectifying surface defects should on local geology and the economic boundaries of particular be agreed prior to letting of the contract. 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 structural concrete. Commentary The following materials may cause particular problems if Most floors are constructed with concrete containing 2Omm present in significant quantities. maximum size coarse aggregate.Theremay be logistical and Lignite. This black or brown coal-like material ranges from practical reasons for not using larger sizes but the potential very soft to hard, Particle sizes of 1 mm and above have technical benefits of using them are that total water and cement historically led to surface defects. Lignite occurs in many content can be reduced for a given strength and consistence inland and marine aggregate deposits. Suppliers generally class. have systems to reduce or remove unacceptablelevels. Some lignites are soluble and may lead to localised retardation or discoloration of the concrete. Surface pop-outs and cavities Commentary may also OCCUI: BS EN 12620 Annex G4 gives limits for the Aggregates that do not conform to BS EN 12620 in respect of lignite content ofaggregates which should not be exceeded. particle size distribution are frequently used in structural con- “Where appearance is an essential feature of the concrete, crete and so should not be precluded if concrete made with aggregates should not contain materials in proportions that them can be satisfactorily placed and finished. Fine aggre- may adversely affect surface quality or durability.” gates that are gap graded may result in concrete that bleeds unacceptably and is difficult to finish. If the suitability ofa Pyrites. These iron compounds can cause surface staining proposed aggregate is not established, advice should be but in general are less problematic in floors than lignite as sought from the concrete producer, For example, evidence they do not tend to float to the surface. ofa satisfactory history of use in direct-finish flooring applications may be available which will allow confident use of Clay agglomerates. These can cause surface pop-outs in the proposed material. finished floors when the clay dries out. Close inspection of aggregates by the supplier should minimise this problem.

The following criteria are of particular relevance. BS EN 12620 Annex G4 states: “Where appearance is an essential feature of the concrete, aggregates should not The coarse aggregate should meet the requirement of a maxi- contain materials in proportions that may adversely affect mum Los Angeles coefficient of 40 (LA,,) or have established surface quality or durability.“Similar guidance is given in BS suitability through history of use. 8500AnnexA7.1 and BS 8204-2 clause5.3.I. The flakiness index should not exceed FI,, when tested in accordance with BS EN 933-3: 1997 Determination ofparticle If there are concerns about impurities in an aggregate shape - Flakiness index. source, the concrete producer should seek assurances from Aggregate drying shrinkage value should not exceed 0.075% the supplier about procedures to control the problem. when tested in accordance with BS EN 1367-4: 1998 Determi- lnformation on the history of use should also be sought. nation of drying shrinkage.

Commen tary Cements and combinations This maximum shrinkage value excludes aggregates prone to high drying shrinkage and is the limit recognised by most con- Cement may be Portland cement or Portland cement with an tractors and clients. The water content ofconcrete has a far addition e.g. ggbs or fly ash greater influence on moisture-related movements, i.e. drying shrinkage, than differences between normal aggregates, see The following cement types have established suitability for floor The Concrete Society Technical Report No. 34? Section 10.3. construction provided that the finished concrete is adequately

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cured (see the section’lnfluence of curing: page 15). All factory- sawing.This is also dependent on the proportion of ggbs used, produced cements conforming to BS EN 197-1 have a CEM prefix and the most practical approach, if problems are envisaged, is to e.g. CEM I, CEM II/B.The equivalent combinations manufactured reduce the proportion of ggbs. Conversely, the slower setting in the concrete mixer are prefixed with C, for example CII/B, and characteristics can be used to advantage at higher temperatures to conform to BS 8500-2 Annex A. A list of the general-purpose lengthen the finishing window and improve the quality of finish. cements and combinations is given in BS 8500-2Table 1.

Portland-fly ash Portland cement This cement type is widely available in the UK. Factory-produced This cement is suitable for most applications and is the least Portland-fly ash cements are available in some areas but more sensitive to the lower placing temperatures that are likely to often combination cements are produced by batching Portland occur in winter. During warmer weather, the shorter setting cement and fly ash in the mixer.The term fly ash conforming to times may cause difficulty with power floating and trowelling BS EN 450 encompasses pulverised-fuelash (pfa) covered by BS since the’finishing window’can be shortened significantly. 3892: Part 1, which is expected to be withdrawn in 2007.The Under these circumstances the contractor should consider proportion of fly ash is typically in the range 21-35%, the resul- having additional manpower and plant available for finishing, ting combination having been used extensively in flooring or reconsider the cement type. construction.

Portland cement has a relatively high rate of strength gain, The partial replacement of the Portland cement content with typically achieving around 80% of final strength within seven fly ash has a marked effect on the properties of the concrete. days. Setting times are normally shorter than for other cements. The water demand will typically be reduced by some 6%, for It may be necessary to commence the sawing of joints less than the same slump value, Alternatively, the consistence can be 24 hours after casting to prevent the formation of random early increased while maintaining the same w/c ratio,The cohesive- thermal contraction cracks. This form of cracking is influenced by ness of the concrete is also improved.Theseeffects are due to the ambient site conditions (particularly extremes of tempera- the spherical particle shape of the material and the increase in ture), the heat of hydration of the cement and by the curing the cement-paste volume that results from the lower particle that is applied. density of the fly ash.These characteristics can be used to improve the concrete, particularly where, for example, the locally available aggregates are angular or poorly graded.

Sulfate resisting Portland cement The seven-day strengths are lower than the equivalent-strength Portland cement concrete. As with concrete containing ggbs, This form of cement is not widely available in bulk form in the UK. the setting time can be extended at low temperatures and this Where sulfate resistance is required, it is achieved through the may cause finishing difficulties. Conversely, the longer finishing appropriate cement combination in accordance with BS 8500-1 window at high temperatures can be beneficial. to suit the ground conditions.

Port la nd-li mestone cement Port la nd-slag cement These cements are available in some areas and have been used Combinations of Portland cement with ground granulated in a wide range of applications. In terms of setting time and blastfurnace slag (ggbs) conforming to BS EN 15167 (replacing strength development these cements are very similar to Port- BS 6699) are widely available in the UK. In some areas, factory- land cement. produced Portland-slag cements are also available. Although the characteristics of these cements vary widely, depending on the proportions of the two components, many high-quality floors have been successfully constructed with them.The pro- Portland cement with additions of silica portion of ggbs is usually in the range 30-50Yo.The rate of setting and hardening is dependent on this proportion but, in general, fume or metakaolin setting is slower than Portland cement. At seven days, strengths are lower than the equivalent-strength Portland cement con- These are special combinations and properties depend on the crete.The addition of ggbs affects the properties of the fresh proportion of silica fume (EN 13263) or metakaolin, the degree concrete, particularly its consistence and mobility: it is consi- of dispersion achieved and the formulation of the concrete. dered easier to compact and finish than concrete containing The rate of strength gain and final strength are also determined Portland cement only. by the formulation. Silica fume concrete can be produced with high flexural strengths and this may allow slab thickness to be At low ambient temperatures, the use of ggbs may increase the reduced. Additionally, very high surface abrasion resistance and potential for bleeding of the concrete and extend setting times, chemical resistance can be achieved. Specialist advice should which may cause difficulty with the timing of finishing and be obtained from the concrete producer.

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Commentury Cornmentary High proportions of ggbs or fly ash are not usually within A prime requirement of mix designs for flooring concrete is the scope of current practice so these are not discussed here. to keep the water content as low as possible (see Chapter 4 Where the proposed cement contains higher proportions of ‘Concrete specification,‘ page 5). This frequently necessitates ggbs or fly ash, the contractor should seek confirmation the use of admixtures to modih the properties of fresh con- that the concrete will satisfy performance requirements for crete and to avoid large increases in the cement content and, abrasion resistance. consequently,the cost of the concrete.

lfjoints are to be sawn in the floor after placing, the choice Where concrete with a slump class 52 or 53 is to be used, the of cement may affect the timing of the sawing operation. cement content may be significantly reduced by using admixture types (a), (b) or (c). Conversely, where flow class For all cement and combination types given above it cannot F5 is required, i.e. 560-620 mm flow diameter,admixtures be overemphasised that to achieve satisfactory abrasion (a), fb) or (c) can be used to increase consistence without resistance the effectiveness of curing is paramount. ChapIinf2j increasing either the total water content or cement content. reports that concretes based on cements with additions have significantly lower abrasion resistance than those containing In certain conditions, some admixtures retard the hydration only Portland cement, if concrete is air-cured only. When of the cement. This extends the setting time of the concrete concrete was effectively cured, the abrasion resistance was and can significantly delay finishing operations. These effects satisfactory. can increase at low temperatures, and when combination cements are used - see the section ’Cements and combina- Contractors, when selecting the cement to be used in the tions,’page 8. flooring concrete, should, in consultation with the concrete producer, consider the ambient temperature, relative humi- Admixtures are now available that are specifically formula- dity and site exposure conditions that are anticipated at the ted for flooring applications, and have a minimal effect on time of construction. setting rimes.

The range of cements currently available has a spectrum of In warm weather, or at high ambient temperatures, admix- performance in terms of temperature sensitivity, setting time tures that delay setting times may be used to extend the time and strength gain. These characteristics are discussed below. for placing, levelling and finishing. However, strict control on dosage and mixing is needed to ensure that concrete sets in The rates ofstrength gain described in the following commen- the same order as it was placed, thus avoiding differential tary are typical for test cubes manufactured and cured in setting. accordance to BS EN 12390-2.However, in-situ strength development in floor slabs is influenced by a number of The choice of admixture should be made with due conside- factors, including effectiveness of curing, temperature, slab ration of site conditions and the contractor‘srequirements. thickness, cement type and content. It must be accepted that variations in weather conditions may force changes to be made to the concrete or construction operations at short notice.

Admixtures

Admixtures for flooring concrete should conform to BS EN 934-2, Mixing water Concrete admixtures - Definitions and requirements. The following types can be beneficial in flooring concrete: Mixing water should conform to BS EN 1008 Mixing water for concrete.This Standard includes potable water and establishes (a) water reducers the suitability of water that is recovered or reclaimed from (b) mid-range water reducers processes in the concrete industry or where water from non- (c) superplasticisers. 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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Steel, macro-synthetic and micro- synthetic fibres

The use of steel and macro-synthetic fibres in flooring concrete has 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 document Steel Fibre Reinforced Concrete lndusrrial Ground For a more detailed assessment of the use of steel and macro-synthetic fibres, Concrete Society Technical Reports TR63(41and TR6F respectively, should be consulted. Manufacturers and suppliers will also give specific advice and additionally some suppliers will provide a bespoke design service.

Figure 4 - Warehousefloor in operation

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Concrete mix design

Introduction that a 1 Omm 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- The majority of concrete will be ordered through a ready-mixed gate content will vary. supplier as a designated or designed concrete and hence the mix design is the supplier's responsibility based on information Concretes should be designed to have sufficient mortar to obtain given by the specifier. However, it is useful to outline which fac- a satisfactory finish. High fine aggregate contents may result in tors need careful consideration when designing a concrete that too thick a surface layer of mortar and this will increase the risk is easy to place and finish, as well as meeting the specification. 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. Co nsi ste nce

The concrete should be sufficiently cohesive to avoid segrega- Commentary tion of the coarse and fine constituents at the specified consis- Optimising concrete design is necessary because the majority tence, particularly at the upper consistence limit. Additionally of specialist flooring contractors place concrete at slumps the free water content should be as low as possible, although in excess of 100mm.Higher consistence classes or targets not less than 160 litres/m3.Thew/c ratio should not exceed 0.55. necessitate some adjustment to the concrete design to ensure that the concrete remains suficiently cohesive to avoid A higher slump or flow for a given strength or maximum free segregation of the solid constituents and to compensate for w/c ratio can be achieved by increasing the cement and water the higher water content. This is usually achieved by adding content of the concrete.The use of admixtures to reduce water sand, cement and water. However, increasing the mortar content will reduce drying shrinkage but contractors are some- fraction also increases drying shrinkage and can affect the times reluctant to choose this method due to historical problems finishing characteristics. of achieving effective mixing and dispersion of admixtures. How- ever, it should be recognised that the frequency of admixture- The total quantity of mortar in the concrete has a significant related problems has reduced significantly due to improvement effect on the quality of the finished floor surface. Too little in the control and dispensing of admixtures together with mortar may result in a dimpled surface or loose coarse advances in admixture technology. aggregate particles or both, while too much may cause crazing, 'blisters,' delamination and increased risk of drying shrinkage cracking.

Fine aggregate content The following rnix design options can be considered but other factors such as drying shrinkage, thermal movements and The fine aggregate and cement content should be such that the abrasion resistance requirements must be considered. (Refer concrete remains homogeneous after placing and compaction. to The Concrete Society Technical Report TR34'),Sections It must also allow a sufficient, but not excessive, surface mortar 10.3 to 10.5.) layer to form, which can be levelled and finished to the required standard. However, the mortar content should be kept as low Increase the cement and water content in proportion to as possible to minimise shrinkage. maintain the w/c ratio at the required consistence and fine aggregate content. The fine aggregate content that is selected depends on the Incorporate fly ash in the rnix design. physical characteristics of the aggregates and the required Use an admixture to increase the consistence or to reduce consistence of the concrete.The combination of coarse and the total water content. fine aggregate should be such that a continuous particle size Use a balanced Combination of the above. grading is achieved. Gap-graded aggregates may cause concrete to lack cohesion and be prone to bleeding. When any type of fibre is to be included, there may also be scope for a small reduction in fines content, typically 1 -2%, Concrete batched using coarse aggregates with a maximum size since fibres increase cohesion. of 2Omm that has an excess of lOmm size particles will necessitate higher fine aggregate contents. It is preferable therefore to By ensuring that the concrete remains consistently homoge- reduce the lOmm fraction of the coarse aggregate towards the neous at the point ofplacing and at the specified consistence, lower end of BS EN 12620 conformity limits. Experience shows a dense closed-surface finish is usually achieved.

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Finishability

To achieve a dense closed finish, a minimum free water content m3is likely to be necessary; lower water oses of admixtures may result in a concrete of the required consistence but prevent the formation of a mortar layer at the surface, due to the increased viscosity of the concrete. It should be stressed that this is a minimum amount of water; the particular physical characteristics of the aggregate higher water content.This may not apply to proprietary concrete formulations that have low water contents. In this case specialist advice on handling is normally given to the or by the concrete producer. Figure 5 shows a typical compacring and levelling operation using a laser screed.

L Figure 5 - Compacting and levelling concrete using a laser screed

The quality of the finish will also depend on the’bleed’characteristics of the concrete. Ex ve bleeding may result in a weak surface and increased risk of crazing and drying shrinkage. Con- versely, if little OF no bleeding takes place, the surface of the aturely, before trowelling and floating are ed bleeding, particularly at 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 delamination.

The rate at which bleeding occurs is determined by many factors: for instance, the use of g r fly ash (particularly at low temperatures),the grading of the aggregates, the cement type and its setting time, the use of retarding admixtures, admixtures that entrain air, and low ambient temperatures.

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In-situ concrete properties

Therma move me nt Comrnentury The hydratia..of cement is an exothermic c. .emical reaction and Drying shrinkage should be considered at the mix design and the temperature of concrete can rise significantly after setting. planning stage. Many drying shrinkage problems are directly The temperature peaks 18-36 hours after placing, depending attributable to high water contents. The use ofadmixtures on the cement type used. After the peak temperature has been can enable the requirements for high consistence to be met reached, the temperature of the floor slab may fall rapidly due to while avoiding problems associated with drying shrinkage. the high ratio of surface area tavolume.This causes the concrete to contract rapidly and the risk of the formation of cracks is Keeping a constant w/c ratio will increase consistence. The increased since its tensile strength has not fully developed. consequence of adding water to increase consistence is to reduce strength and abrasion resistance unless cement is It is therefore of paramount importance that any movement also added. It is the increase in water that causes the shrink- joints are sawn as soon as practicable after slab laying and age, not the cement as such. At constant slump or flow, finishing to release stress build-up. In severe conditions, the cement can be added (sand reduced) without increasing outer cuts should be sawn first, working in towards the middle water. If this is done, shrinkage will in fact reduce. Increasing of the slab. the cement content while maintaining a constant free w/c ratio will lead to increased drying shrinkage. The cement type and content will influence the timing of the sawing operation.The peak temperature in the concrete slab Sawingjoints will not stop drying shrinkage movement, but will increase as the total cement content increases, so it is bene- will concentrate this shrinkage movement at acceptable ficial, particularly when the ambient temperature is high, to keep locations. the cement content close to the specified minimum. Generally, concrete made using only Portland cement (CEM I) needs to be The use of fibres or fabric reinforcement can also control, as sawn earlier than concrete containing combinations with ggbs opposed to prevent, the effects of moisture-related move- or fly ash since the combinations generally result in a lower and ments'3 5J. For further information regarding thermal move- later temperature peak than €EM I only.Thus during summer it ment and drymg shrinkage refer to Technical Report TR34Y may be beneficial to use combinations as the window for sawing Figure 6 shows a finished floor being surveyed for regularity, will be longer; conversely, during winter, the shorter window the methodology is covered in TR 34. with CEM I may be more practical.

Drying shrinkage

Drying shrinkage can be reduced to an acceptable level but not eliminated completely. In order to minimise drying shrinkage:

keep the free water content as low as possible, but see the section'Finishability:page 13 select aggregates in accordance with the section 'Aggregates: Page 8 minimise restraints to slab movement and provide effective movement joints where applicable.

Figure 6 - Floor level surveying

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rasion res isIan Influence of cu

For direct-finish concrete, the quality and abrasion resistance of The necessity for curing has been discussed in the sections the surface depends on a sufficient cement content minimum ’Cements and combinations: page 8 and ‘Abrasion resistance: of 325kg /m3,a free w/c ratio not greater than 0.55, the quantity page 15. Most floors are cured with high-efficiency spray-on and quality of the finishing work, and, equally important, the membranes, and these have a significant beneficial effect on efficiency of the curing. the durability of the floor surface, improving abrasion resistance and reducing crazing. In flooring construction, early curing is Proprietary toppings and dry-shake materials are available, some not normally required to reduce or control plastic shrinkage or of which have Agrement Certificates. These are specifically plastic settlement since trowelling operations usually mean designed to give high abrasion resistance.The quality of work- that these phenomena do not occur. manship and curing are of paramount importance to achieve the best possible performance with these materials. Where thermoplastic sheet or tile floor coverings are to be installed, it should be noted that floors which have been treated Secondary factors that influence surface durability are the overall with spray-on membranes will take a considerable time to reach quality of the concrete and, to a lesser extent, the properties of the relative humidity level of 75% specified in BS 8203: 2001 the aggregate. Historically, problems have occurred where joint Code ofpractice for installation of resilient floor coverings.This arrises have been damaged by forklift truck wheels, particularly period will probably be greater than six months and may exceed where concrete below compressive strength class C32/40 has one year. Therefore, rather than using spray-on membranes been specified. This problem with construction joints can be -see Figure 7-, an alternative method of curing may be more avoided by the use of proprietary steel armoured joint systems. appropriate, such as covering with plastic sheeting. Effective curing is best achieved by using spray-on curing systems such as The fine aggregate for direct-finish concrete floors should not 90% efficiency resin-based compounds or acrylic sealers. Good contain soft or friable particles. curing can be effected using polythene sheeting, but the pace of construction is such that undisturbed curing for sufficient Refer to BS 8204-2 and Technical Report TR34(’]for further time is unlikely to be a practical option. guidance on abrasion resistance.

Commentary Concrete that is prone to excessive bleeding may have poor abrasion resistance as a result of very fine material migrating 7’ ‘1 with the bleed water to the slab surface. This fine material -r-. -. can form a weak laitance at the top surface, which will break .. down when normal traffic commences.

Impurities, such as soft lignite and shells, which are directly below the wearing surface, may result in damage to the wearing surface when in service. When damage occurs, as 1:. the resulr ofsuch surface defects, normal use of the floor I may cause the damaged area to increase in size.

Figure 7 - Spray application of curing compound

Compaction of concrete Further information on moisture in concrete floors is now available; refer to The Concrete Society Project Report No. 4‘61 It is essential for short- and long-term durability that concrete is Moisture in concrete and the performance of impermeable floor adequately compacted during construction. In large-area con- coverings. struction methods where high slump or flowing concretes are used, this is rarely a problem; however, due attention should be given to compaction around joints, box-out details and adjacent to walls and columns.The latter areas normally need to be compacted using a poker vibrator.

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Batching and pre- delivery of concrete

Batchi ng Failure to disperse the admixture completely may lead to pockets in a concrete batch containing excessive concentrations of the The concrete producer should have accreditation by a third- admixture.This may cause localised areas of concrete to be party quality assurance body e.g. QSRMC or BSI. The batching retarded and have excessive percentage of entrained air. It is should ensure that the materials are fully mixed to recommended that cement should come into contact with a produce homogeneous concrete. Detailed batching procedures proportion of the mixing water before it is added to prevent the should be used to ensure consistency from batch to batch.The admixture affecting the initial formation of cement hydrates mixing time, whether the process is wet or dry batch, should be and the possibility of excessively rapid hydration. consistent. For central mixing plants, the mixer manufacturer's recommendations should be followed. For truck mixers, this is The batching and mixing sequence should be consistent to usually 6-1 0 minutes, but this depends on the design of the minimise variation between batches. mixer drum and its mixing speed (typically 1&14rev/min). if it is intended to add further materials to the truck mixer at site, the additional mixing time is best established by trials and then agreed between parties as the standard.

Commentary The majority of ready-mixed concrete plants in the UK employ the dry batch process, using truck mixers, which have been designed to mix emcienr/y The main difference between central mixer plants and dry batch plants is the higher out-

a puts that can be achieved with central mixing. Well main- tained truck mixers will produce high-quality and consistently 116 rl " homogeneous concrete.

It must be emphasised that the mixing times referred to in the section 'Batching,' page 16 are minimum recommended times.

Figure 8 - Trucks queuing to deliver concrete Historically, inadequate dispersion of admixtures has been a key problem for flooring contractors and has resulted in All batches should be visually checked for consistence and many contractors being deflected from using these poten- appearance prior to despatch from the concrete plant. It is also tially beneficial materials. Admixture manufacturers advise advisable to agree with the producer that concrete will be that the cement be wetted prior to the addition ofadmixrures mixed at full mixing speed for a minimum period of 2 minutes in order to avoid the problems discussed above. Appendix A, at site, before sampling or discharging. Figure 8 shows mixer page 22 gives informationon batching and mixing ofadmix- trucks queuing before discharge. tures including site addition. When the concrete includes admixtures it is essential that full Concrete producers accredited by third-party quality assu- and even dispersion is achieved during mixing. Normally the rance schemes are required to have work instructions for addition of the admixture is made at the same time as the batching and mixing. These will have been assessed for addition of water to ensure complete dispersion. effectiveness.

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Pre-delivery pla n n i ng

It is of prime importance that, before concrete is 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 construction establish'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 nt s) agree procedures for sampling and testing of concrete agree 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 supply make provision for weather changes identify how to contact key personnel, both contractors and producers agree arrangements for washing down truck-mixer discharge chutes on site.

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Conformity and identity testing

Conform ity Commentary The approach to concrete conformity and testing has been The user or specifier should be aware that the producer is fundamentally changed with the introduction of BS EN 206-1 required to veri@that the description of the concrete given and the complementary British Standard BS 8500. Conformity on the delivery ticket is correct. BS fN206- I states: "Conformity testing and evaluation are processes that are carried out either control is an integral part ofproduction control'! For a by the concrete producer or by a third party on his behalf.The producer to declare conformity to BS 8500-2, he is required producer is responsible for the concrete design process that to establish systems for production control that include establishes the required properties and is also obliged to operate selection of materials, concrete design, concrete production, production control systems and procedures. inspection and tests, the use of data arising from testing and calibration, and conformity control. The properties that the concrete producer is required to control for designed concrete, in accordance with the BS 8500, that are Whereas the producer is required to inform the specified relevant to concrete for use in industrial floors are: user of any non-conformity that was not obvious at the time ofdelivery, non-conformities obvious at the time of compressive strength delivery are either accepted or rejected there and then. waterkement ratio Examples ofself-apparent non-conformity at the time of cement content delivery are consistence, colour and aggregate size. consistence class or target value for either slump or flow chloride content of the concrete.

Where a prescribed concrete is specified, the following are Identity testing (strength) subject to conformity control: Where a contractor or a third party instructed by the contractor, cement type and class client, engineer or architect carries out sampling and testing of consistence class or target value for either slump or flow the concrete, it is called identity testing.The procedure and types of aggregate conformance criteria for determining whether a defined volume type of admixture or addition if required of concrete comes from a conforming concrete of the specified sources of concrete constituents, where specified strength class are outlined in BS EN 206-1 Annex E, with clarifi- constituent proportions. cation in BS 8500-1 Annex A.10 and Annex B.5.

In the event of non-conformity,the producer is obliged to take The contractor must be aware that the measured strengths of the following actions: test cubes are intended to exceed the specified characteristic strength by a design margin - see the Section'Strength: page 6. Check test results and, if invalid, take action to eliminate errors. This margin is necessary to allow for plant and material variations If non-conformity is confirmed, take corrective actions inclu- and to ensure an acceptably low probability of strength confor- ding a management review of relevant production control mity failures. procedures. Where there is a confirmed non-conformity with the specifi- However, the need to meet the specified requirements for cation that was not obvious at delivery, give notice to the maximum w/c ratio and minimum cement content may result specifier and user in order to avoid any consequential damage. in a concrete with a higher strength than is needed to satisfy Record all actions on the above items. strength conformity criteria.Therefore, high average strengths should not be regarded as a sign of poor control, but an indication that the producer is conforming to all aspects of the specification.The converse is also applicable where cubes are attaining the 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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Commentary A practical way of dealing with this is for the producer and If the high average concrete strength results in dificulties for contractor to agree a method that enables the consistence the contractor, the cause and the options should be discussed to be adjusted at site. Rules must be agreed on the quantity with the producer. It would not normally be prudent to relax of water required to increase the consistence from the mea- the specified maximum w/c ratio, but a change of cement sured initial value to that specified. A suitably experienced type could reduce the strength while still satisfying specifica- person should supervise this procedure. This should ensure tion requirements.If the cement content is the main factor, that the maximum specified w/c ratio or the w/c ratio then once again, a change in cement type may help. required for 28-day strength, whichever is the controlling value, is not exceeded. After water is added, the concrete The responsibility for demonstrating conformity of concrete should be remixed for at least 2 minutes at full speed to supplied in accordance with the Standard for concrete, BS ensure dispersion. EN 206- I, is placed upon the concrete supplier. BS 8500- I strongly recommends that the producer holds third-party certification, 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 i n g (con si s t e 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 18 of 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 the truck mixer and therefore wider limits apply. BS 8500 Annex B provides the identity testing criteria, depending on the method of sampling (spot or composite). It should also be noted that measured slump test value is reported to the nearest 10mm. The allowable limits are given in Appendix B, page 23.

Commentary Contractors frequently stipulate a narrower slump or flow range than that given in the Standard. This may cause some dificulty 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 ofwater by aggregates. Traffk delays will exacerbate this.

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References

1. The Concrete Society. Concrete lndustrial Ground Floors -A Guide to Design and Construction.The Concrete Society, Camberley, 2003, Technical Report 34 (Third Edition). 2. Chaplin R. G. The Influence ofggbs andpfa Additions and Other Factors on the Abrasion Resistance oflndustrial Concrete Floors. British Cement Association, Camberley, 1990. 3. Association of Concrete lndustrial Flooring Contractors. Steel Fibre Reinforced Concrete lndustrial Ground Floors. The Concrete Society, Camberley, 1999. 4. The Concrete Society. Guidance on the Use of Macro-synthetic-fibre-reinforced Concrete. The Concrete Society, Camberley, 2007,Technical Report 63. 5. The Concrete Society. Guidance for the Design ofsteel-frbre-reinforced Concrete. The Concrete Centre, Camberley, 2007, Technical Report 65. 6. 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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Guidance on the specification and Ise of admixtures in concrete for industrial floors

I nt roduction Admixtures based on, or modified with, the following are likely to enhance retardation and should be avoided in flooring Admixtures, and particularly water-reducing admixtures, can offer concrete, especially under cold conditions and where fly ash or substantial benefits in flooring concrete by reducing the free ggbs are being used: water content while maintaining appropriate consistence for rapid placement and compaction.This reduces drying shrinkage 0 hydroxyca rboxyl ic acids sa Its 0 carbohydrate-based polymers (hydroxylated polymers, corn in the concrete and hence cracking and curling of the slab. syrups and malto-dextrins) 0 molasses. Other types of admixture can further reduce shrinkage, speed the setting to allow earlier finishing or can aid the finishing of flooring concrete. Other admixtures As with all admixture applications, careful selection of admixture type and grade is essential to obtaining a satisfactory result. Other admixtures that may have special applications in concrete Correct addition and mixing are also key to obtaining a uniform floors include: concrete.These guidelines are intended to assist the supplier

and user of flooring concrete to optimise the advantages from 0 set-accelerating admixtures that can bring about quicker the use of admixtures. stiffening and allow earlier finishing, especially in cold conditions 0 shrinkage-reducingadmixtures that can reduce cracking Water-red ucing admixtures due to drying shrinkage and cut down on the number of joints. 0 finishing aids that can be incorporated into dispersing Admixtures whose major active ingredient is based on the following materials have been found most suitable for use in admixtures of the types indicated above. concrete floors.They disperse easily through the concrete and maximise the water reduction. In hot weather some additional Other admixtures that may cause problems with concrete retardation may be necessary with these admixtures.These floors are noted below. materials are: 0 Air-entraining agents should be avoided in floors that will be power finished as the entrained air can be one of the 0 sulphonated naphthalene formaldehyde condensates causes of surface delamination after hardening. 0 sulphonated melamine formaldehyde condensates 0 Some admixtures may cause an increase in the level of air in 0 polycarboxylated ethers. the concrete and should, therefore, be used with caution - check with manufacture. 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 additional care is 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.

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Batc hi ng admixtures the effect on set time of ambient temperature when the concrete is delivered. checking for uniformity of consistence before and after the When batching admixtures, the following comments should addition of admixtures, fibres, water or other materials be noted. calibration of dosing equipment, uniformity of dosing, It is desirable that all the components of the concrete, inclu- dosage rate, batching sequence and mixing time recording any materials, including admixtures and water, ding admixtures, are mixed at the batching plant. Where this added at site and the time of addition, consistence before procedure is not adopted, site addition must be under the direct supervision of a concrete technologist or engineer, and after addition, quantity added and additional fast should be restricted to the admixtures detailed in the section mixing time consideration of the effect on setting time due to batch- 'Admixtures', page 10 and to the guidelines for site addition covered in Chapter 8'Batching and pre-delivery of concrete', to-batch variation in admixture dosage and time of admixture addition original mixing. page 16. after 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 Factors affecting placing and finishing procedure. Further guidance on this can be found in the section 'Admixtures', page 10 of this Guide characteristics 0 It is essential that flooring concrete is uniformly and consistently mixed.To achieve this generally requires greater The following factors should be considered before starting a job. attention to the mixing procedure and duration. 0 It is essential that only mixers and mixer trucks with blades 0 Take account of the likely weather and the potential for a and drums in good condition are used and are loaded within significant change from the expected ambient temperature recommended capacity for mixing. on the day of concreting. 0 After batching, sufficient mixing must be given to ensure 0 Ensure specified consistence at the time of placing will be uniform dispersion of admixture and other materials. compatible with the placing method. It is essential that, during addition, the admixture does not 0 Account for consistence loss resulting from the use of fibres, come into contact with dry cement. delays in delivery and placing. The concrete will only have uniformity of consistence and 0 Large batch-to-batch variation in consistence and late set across the slab if there is consistency in the order and additions of water can both affect setting time and should I timing of the concrete batching sequence and this is parti- therefore be avoided. cularly important when admixtures are being used. The compatibility and effect on setting of the concrete must be determined when dry-shake and colour systems are used A CAA Guidance Document of recommended practice for as they may also contain undeclared admixtures. addition of admixture to concrete is available from the Cement Admixture Association at the address shown below. This guidance was produced by a VWAClFCjoint taskgroup which met as a subgroup of the ACK Concrete Mix Design andAdmixtures Working Party. Site addition of admixtures For general information on admixtures contact: If admixtures are being added at site then the following points should be borne in mind. John Dransfield, Secretary Cement Admixtures Association 0 The addition of any concrete component including water at 38Tilehouse Green Lane the site is not recommended unless it is actively supervised Knowle by a qualified concrete technologist or engineer. It should West Midlands also be restricted to the addition of those types of admixture B93 9EY detailed in the section 'Admixtures', page 10. 0 Admixture addition at the plant followed by a further TeVFax: 01 564 776362 addition on site is more likely to cause inconsistency than a Web: www,admixtures,org.uk 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 by all parties.The procedure should include:

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Identity testing criteria

Strength criteria Slump class Slump range: Maximum allowable deviation mm on range limit: mm The test result used in the assessment is the average of the Spot sample Composite sample results of two or more specimens - normally cubes in the UK - 51 10-40 -1 0, +30 -1 0, +20 cast from one sample for testing at the same age. Where the I 52 I 50-90 I -20,+30 1 -10, +20 I range of test values (a result is the average of two cubes from the 53 100-1 50 -20, +30 -1 0, +20 same sample) is more than 15% of the mean, the results shall 54 160-21 0 -20, +30 -1 0, +20 be disregarded unless an investigation reveals an acceptable I 55 I 2220 I -20, - I -10, - I reason to justify disregarding an individual test value. Table 62 - Identity criteria for slump class, BS 8500- 1 Samples should be taken in accordance with the composite method in BS EN 12350-1 and represent a defined volume of concrete. For a floor slab a defined volume could be the concrete Target slump: mm Maximum allowable deviation on target delivered to a site within a fixed period, or a particular slab area, value: mm but not more than 400 m3. I 540 I -30,+40 I -20, +30 I BS 8500-1 Annex B.5 states that each defined volume should preferably be represented by six test results or if a volume I 50-90 I -40,+50 1 -30, +40 I contains more than six test results, they should be split into I 2 100 I -50,+60 I -40, +50 I groups of six for assessment.The results should represent a Table 63 - Identity criteria for target slump, BS 8500- 1 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 Table Flow class Flow range: Maximum allowable deviation on range mm limit: mm B1 below are satisfied. Spot sample Composite sample F1 5340 -1 40, +40 -1 40, +30 Number of test results for Criterion 1 1 Criterion 2 F2 350-41 0 -30, +40 -20, +30 comPressivestrength Mean of results: I Anv individual test result: from defined volume I N/mm2 N/mm2 F3 420-480 -30, +40 -20, +30 F4 490-550 -30, +40 -20, +30

2-4 >f,+l z f<, - 4 F5 560-620 -30, +40 -20, +30 F6 2630 -30, - -20, - I 5-6 I >f<,+2 I z f?,- 4 I Where fckis the concrete characteristic strength i.e. the strength class

Table 61 - ldentity criteria for compressive strength, BS EN 206-1 Annex B

value: mm Consistence criteria

Consistence is either specified as a class or target. Although a supplier will endeavour to provide the required consistence, Table 65 - Identity criteria for target flow, BS 8500- 1 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 concrete truck and a compositesample taken throughout the load.

Licensed copy: [email protected], PELL FRISCHMANN CONSULTING ENG LTD, 22/11/2010, Uncontrolled Copy, ®The Concrete Society 23 Flooring Advisory Service Inadequate floors seriously reduce the efficiency of warehouse operations. Face Consultants have the specialist expertise to optimise floor performance in new-build projects and existing premises. Consultancy services include: e Design e Mechanlcal handilng efflclency

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Concrete for industrial floors Guidance on specification and mix design

This updated guide provides practical guidance on best practice far specification, design, production and delivery of concrete for direct 1cnithed industrial floors constructed by large area pour metWAlso mlewmt Ocn any large interior floor construction method. Covers concrete spacffication, materials, mix design, in-situ concrete behaviour and properties, mixing and 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

CS 127

Good Concrete Guides give concise, "best practice" guidance on materials, design and construction.

For other publications in the Good Concrete series visit the Concrete Bookshop at: www.concretebookr hop.com Licensed copy: [email protected], PELL FRISCHMANN CONSULTING ENG LTD, 22/11/2010, Uncontrolled Copy, ®The Concrete Society