Intro to Sprayed Concrete

1

Foreword................................................................ 2

Acknowledgements ................................................ 2

The Association ..................................................... 3

History .................................................................. 4

Properties and Advantages .................................... 6

Typical Applications and Uses ................................ 8

The Dry Process .................................................. 10

The Wet Process .................................................. 12

Surface Finishes .................................................. 14

Constituent Materials........................................... 15

Health and Safety ................................................ 18

Quality Control and Testing .................................. 20

Training and Certification..................................... 24

Design and Specification – Wet and Dry Process .. 25

Relevant Publications and Bibliography ................ 29

CONTENTS

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This Introduction to Sprayed Concrete is issued by the Sprayed ConcreteAssociation based in the United Kingdom.

It is intended to be used by industry professionals who may require practical knowledgeof the techniques of sprayed concrete for the first time. It is not intended to be acomprehensive Specification or Standard. (Those documents are available and listedon pages 29-31.)

This publication covers the broad range of processes that are commonly used togetherwith descriptions of the more commonly used materials available in the marketplace.It will refer the user to the best ways of carrying out these processes safely and withthe expectation of a high quality end product.

It will encourage the use of a member of the Association for advice, design, supplyand application of the sprayed concrete.

ACKNOWLEDGEMENT

The Sprayed Concrete Association would like to thank the following memberorganisations and their representatives for their contribution and assistance inthe production of this document:

Aliva Ltd - Paul WellsBalvac Whitley Moran Ltd - Roger Bridge

Concrete Repairs Ltd - Tony RimoldiFEB MBT Ltd - Ross Dimmock

Lightcem Ltd - Nick VarleyQuickseal Specialist Contractors - Pat Quarton

Sika Ltd - Richard Barton

FOREWORD

3

In 1976 a small group of the UnitedKingdom’s leading sprayed concretecontractors came together to form the

Association of Gunite Contractors. Thisgroup of skilled and like minded expertswere all committed to a common set ofaims:

! to encourage and promote the use ofsprayed concrete

! to develop and maintain codes ofpractice and specifications

! to develop, encourage and maintainlinks with other interested bodiesboth nationally and internationally

! to encourage and promote, throughregular meetings, publications,conferences and exchange of viewsadvances in the technology ofsprayed concrete.

In 1986 the Association changed itsname to the Sprayed ConcreteAssociation.

Since 1976 the Association has workedhard to achieve its aims. It has fostereda much better understanding of thebenefits of sprayed concrete. Initiallycontractor led, the Association nowincludes a comprehensive list ofAssociate Members including majorindustrial companies involved in themanufacture of materials and the supplyof specialist plant.

The Association also includes a numberof Consultant Members, many of whomhave spent much of their working careersinvolved in the specification, design andexecution of sprayed concrete.

Links are closely maintained withoverseas contracting members therebyenabling the Association to call upon afull range of expertise and experience.

The full list of members is published asa directory and updated every two years.This book details each Members’ area ofexpertise and their areas of operation.

Working within a very busy industry withever tighter deadlines demands a highdegree of professionalism andcommitment from contractors. Commonsense requires, and legislation demands,that works are carried out safely and tothe highest quality.

The Sprayed Concrete Associationsupports and promotes trainingespecially for safety and the use of newproducts. It recognises that theprocesses it promotes are some of themost operator sensitive in theconstruction industry. It thereforeencourages all its members to establishand maintain the highest standards ofworkmanship.

THE ASSOCIATION

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Concrete is probably the mostversatile material used in theconstruction industry. In

compression it is strong enough to formthe basic material for the most massivestructures. Before it has set its fluidityallows it to assume the most complexshapes. Indeed, and with addition ofsteel reinforcement, there are virtuallyno elements of a structure that cannotbe formed from concrete.

If there is a drawback to the use ofconcrete it is the need for formwork orshutters necessary to create a mould forthe concrete whilst in its fluid state.

Dr Akeley needed to develop a device toenable the mortar mixture to be sprayed.After experimentation he developed asingle chamber pressure vessel whichcontained a mixture of cement and sand.When pressurised with compressed airthe mixture was forced through anopening and along a delivery hose. Atthe end of the hose was a nozzle whichwas fitted with a water spray. Whenpassing through this spray the mixturewas hydrated.

This equipment was known as the“Cement Gun” and the sprayed materialnamed “Gunite”. The methods werepatented in 1911 and taken over by theCement Gun Company. After movingfrom the USA to Germany in 1921 iteventually became a British ownedcompany in 1953.

HISTORY

In 1895 at the Field Museum of NaturalScience in Chicago USA, the curator, DrCarlton Akeley was searching for a wayto create models of prehistoric animals.A skeleton frame had been manufacturedbut the body shapes could not be formedby the application of conventionaltrowelled mortars.

5

The early machines placed the dry mixof sand and cement into the pressurisedchamber from where it was projected toa nozzle where water was added. Thissystem was therefore termed the “dryprocess”.

As the dry process was being developedthe “True Gun” method was also beingdeveloped. This required the sand andcement mixture to be fully mixed withwater before being pumped through afundamentally different machine.Because of its different mixing thesystem became known as the “wetprocess”. The wet process was not fullydeveloped commercially until well intothe 1970’s, much of its experimentationbeing carried out in the USA.

It is at this point that a few momentsshould be spent considering terminology.

The original name for the sprayed mixtureof sand and cement was “Gunite”. Otherterms have been, and are still usedincluding “Sprayed Concrete” “ShotConcrete” and “Shotcrete”. The term“Shotcrete” is often used when describinga mix whose maximum aggregate size ismore than 10mm.

However, the currentacceptance is that“Shotcrete” is used inthe USA and “SprayedConcrete” is the morewidely used term inEurope.

The acceptance anduse of sprayedconcrete is now world-wide. The processes

allow complex shapes and structures tobe formed without the high costsassociated with formwork.

Early applications of sprayed concretewere for reinforced concrete repair work.Soon its advantages were adopted fornew construction.

During the Second World War freestanding hangers for Spitfire fighterswere constructed, some of which stillexist today. The Mersey Tunnel inLiverpool is another example of a majorengineering structure lined with sprayedconcrete.

Today it is a common procedure to usesprayed concrete for structural repair,for fire protection to steel framedstructures, for tunnel and refractorylinings and for other structures such asswimming pools, river walls, domes andshell structures.

Installed properly by experiencedapplicators, sprayed concrete providesdesigners with a cost effective andadaptable method to create and repairconcrete structures.

HISTORY

6

Sprayed concrete exhibits certainproperties that in some respectsmakes it superior to poured

concrete. However, it must beremembered that these properties arelargely as a result of the differentmethods of mixing, transporting andplacing rather than fundamentaldifferences in component materials.

Low Water/Cement Ratio

Sprayed concretes generally have a lowerwater/cement ratio than pouredconcrete. This is particularly true in thedry process where a low slump mixcapable of supporting itself withoutsagging is quite normal. Wet processmixes achieve a similar result using aplasticiser.

High Strengths with RapidStrength Gain

Sprayed concretes can be expected toattain high compressive strengthsparticularly with a low water/cementratio and the dense compaction achievedby the high velocity of application. Rapidstrength gain is also achieved, especiallywhen using factory batched materials.Compressive strengths 30% higher thanconventionally placed concretes can beexpected.

High Density/Low Permeability

The high velocity of placement ensuresgood compaction and high densitycoupled with low permeability and waterabsorption. This results in a durablehomogeneous material with excellentfreeze/thaw resistance, low surfacecracking and a high degree of abrasionresistance. These properties may befurther enhanced by the use of fibrereinforcement in the mix.

Enhanced Adhesion and BondStrength

As with so many operations inconstruction, good surface preparationis vital. Assuming that the substrate isproperly prepared then the bond strengthwith sprayed concrete is generallyexcellent. Furthermore, the use ofbonding agents and coatings is usuallyunnecessary and, under cer tainconditions, damaging to the bond.

High Speed High Output

Sprayed concrete can deliver highvolumes quickly and economically. Freeformed tunnel linings or retaining wallscan be sprayed immediately afterexcavation. Walls up to 1m thick havebeen constructed in the USA using thewet process even with very highreinforcement densities. Multiple layerapplication can reduce the generation ofthermal stresses in construction.

PROPERTIES AND ADVANTAGES

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Reduction in FormworkCosts

In comparison withconventionally pouredconcrete, sprayed concreterequires far less formwork.This is especially so if curvedor organic shapes arefavoured by the designerwhich may be impossible toachieve using conventionalformwork. Vir tually anyshape can be formedespecially thin shells andlinings.

Ease of Access

The ease of application of sprayedconcrete means that material canbe applied in restricted areas, oftenconsiderable distances from thepoint of access. Without the needto transport and erect bulkyformwork only the operator anddelivery hoses need to be able tovisit the workface. The cement andsand mixture can be transportedover long distances from theproduction plant.

PROPERTIES AND ADVANTAGES

8

The following examples demonstratethe unique adaptability of sprayedconcrete.

New Construction

! Shell roofs and domes

! Retaining walls

! Piled wall facings

! Silo structures

! Barrel vaulting

! Diaphragm walls

! Caissons

! Blast proof structures

! Bank vaults

Underground Construction

! Tunnel linings

! New Austrian tunnelling method

! Storage reservoirs

Water Retaining Structures

! Sea and river walls

! Reservoirs and dams

! Aqueducts

! Swimming pools

! Water towers

! Canal linings

! Irrigation and drainage channels

TYPICAL APPLICATIONS AND USES

9

Protective Coatings

! Fire protection to structural steelwork

! Refractory linings

! Pipeline encasement

! Rock and soil stabilisation

TYPICAL APPLICATIONS AND USES

Strengthening and Repair

! Concrete damaged byreinforcement corrosion

! Fire damaged structures

! Housing

! Cooling towers

! Bridges

! Jetties andwharves

! Brick arches andtunnels

! Tunnel linings

! CathodicProtectionoverlays

Free FormedStructures

! Swimming pools

! Landscaping

! Climbing walls

! Theme parks

! Sculpture

! Water sportsslalom courses

! Bobsleigh runs

! Zoologicalstructures

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General Information

In dry process sprayed concrete apredetermined ratio of cement andaggregate is batched and mixed

without added water. The mixture is fedinto a purpose-designed machine,pressurised and introduced into a highvelocity air stream and conveyed throughflexible hoses to the spraying nozzle. Atthis nozzle a finely atomised spray ofclean water is added to the stream ofmaterials to hydrate the cement andprovide the right mix consistency so thatthe uninterrupted stream of materialscan be projected at high velocity intoplace, where the impact compacts thematerial. Because water or admixturesare not necessarily required to giveworkability during transportation or toachieve compaction, dry process sprayedconcrete with suitable aggregates andaggregate/cement ratios can be placedat low water/cement ratios, with noslump characteristics. This enables itto be placed without admixtures tolimited thicknesses on vertical andoverhead surfaces.

Admixtures can be introduced in powderform into the dry pre-mix, in liquid formwith the added water at the sprayingnozzle or as a separate injection at thenozzle. Steel or other fibres can beincorporated in the pre-mix.

Equipment offering a wide range ofthroughputs is available, allowingaccurately controlled low rates ofapplication for thin layers or on awkwardor intricate structures. High rates ofapplication for tunnel construction slopestabilisation and larger areas are alsopossible.

The application nozzle is generally handheld and the stream of materials isdirected by the nozzleman, who alsoadjusts the amount of water added. Thewater can only be varied within a limitedrange, as too little water will prevent themixture compacting into a homogenousmass, while an excess will make it tooworkable, causing slumping. Remotelycontrolled robotic spraying arms areoften used in tunnelling work where theyenable the sprayed concrete to be placedin situations that could be hazardous fora nozzleman. They also avoid the needfor temporary access in order to placethe material at high level.

The technique is very flexible, capableof wide variation in throughput, able tohandle virtually all types of cement anda wide range of conventional andlightweight aggregates. Aggregate sizesup to 20mm can be used but there isnormally no advantage in using materialover 10mm.

The range of aggregate/cement ratiomixes that can be sprayed is limited andthe range used is typically 3.5/1 to 4.0/1 by weight. Because the rebound ismainly aggregate, the placed mix will bericher in cement than the batched pre-mix. The performance characteristics ofdry process sprayed concrete are gooddensity, high strength (typically 40 to 50N/mm2) and very good bond to a suitablesubstrate. The intrinsic properties tendto be more variable than conventionalconcrete or wet process sprayedconcrete.

THE DRY PROCESS

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Dry Process Equipment

Sprayed concreting has been carried outusing the dry process for many years,traditionally using twin chambermachines such as the Boulder Gun andmany copies. This type of machine wasvery good using refractory materials orvery dry sand/cement mixes. Problemsarose however when the material to besprayed had a moisture content of morethan about 3%, causing the machine toblock up with material.

Other versions of the Boulder type gunhave also been made, still using thesealed chamber principle but allowing aconstant feed by using a rotary valve tofeed material into the chamber.

Most dry mix machines today are therotor type, a design whereby the dry mixis fed into an open hopper, dropping bygravity into a revolving barrel and isblown by compressed air into thespraying hose and to the water injectionnozzle where the water is applied by thenozzleman’s judgement. The nozzle canbe a great distance from the machine (upto 600 metres).

The newer machines available from many

manufacturers today are capable ofhandling moisture contents of up to 10%with outputs up to 10m3/h. This isachieved by the use of liners in the rotorand air chamber, normally the placesassociated with blockages in rotor typemachines.

Machines are also manufacturedspecifically for the application of pre-bagged dry materials. By the use oflubricated sealing plates and oversizemotors, the rotor can be clamped to amuch greater tension than previously,stopping dust escaping from the rotor/sealing plates to a great degree. All typesof dry spray machine are only a methodof feeding an amount of sand/cement/aggregate mixture into an air stream ata steady rate. If the feed rate is notconstant the nozzleman will experiencegreat difficulty in maintaining the correctwater/cement ratio.

Dry spray machines have been used forapplications ranging from structuralrepairs due to fire damage, cooling towerand bridge strengthening to newconstruction in housing, tunnelling,mining, swimming pools and zooenclosures.

THE DRY PROCESS

the “dry spray”processs(typical)

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General Information

Wet process sprayed concreteconsists of a mixture of cementand aggregate, weight or volume

batched and mixed with water prior tobeing pumped through a hose or pipe to adischarge nozzle. High velocity air is usedto propel the mix into position and thissupply of high pressure air is introducedat the nozzle and the resultant velocitypropels the concrete into position where itis compacted by its own momentum.

Wet mix sprayed concrete can be suppliedby ready mix or site batching facilities, ormay be supplied as a dry, pre-blendedmaterial in bags. Bagged material isfavoured for small operations of lowvolume, such as repairs, where site accessmay prohibit large wet-mix concretedeliveries.

With the wet process the water cementratio can be accurately controlled and withwater reducing plasticisers, water cementratios below 0.45 can be easily achieved.

Concrete strength requirements can bespecified in a similar manner toconventional concrete although in the wetprocess high strengths are usually achieveddue to the cement rich characteristic. Itis usual for wet mix designs to use cementcontents in the range of 350kg to 450kgper cubic metre. The resulting cubestrengths will normally be between 30N/mm2 and 60N/mm2 at 28 days.

With the use of hydration controladmixtures, the working life of wet mixconcrete can be extended up to 72hoursallowing the system great flexibility, andpreventing the need to clean out the systemafter each application.

The Specialist Contractor should be freeto design the mix to achieve the requiredstrength and durability, and to take intoconsideration the balance of fine andcoarse aggregates to ensure optimumpumping performance and reduction ofrebound.

Where the Specifier considers that a waterbar or joint sealing system is necessary,the Contractor’s advice should be soughtprior to the commencement of work toestablish the appropriate design detail andsequence of work.

The designer should consider buildabilityof the structure, reflecting the constructionprocesses employed in spraying concrete.Particular care is required for joints andreinforcement details. The emphasisshould be to reduce the quantity of steelreinforcement wherever possible. Theoption of fibre reinforcement should beconsidered where appropriate.

Spraying techniques are varied accordingto the nature of the work but usuallyconcrete is built up in layers of up to150mm thick. Further layers may beapplied to achieve greater thicknesses oncethe underlying layer has achieved a finalset. Care should be taken that the surfaceto receive the new sprayed concrete layershould be free from deleterious substancesby jet washing with air-water, starting atthe top of the structure and workingdownwards. This is normally achieved withthe sprayed concrete nozzle.

Whereas tolerances of ± 10 millimetresover a 3 metre length are attainable onplain flat surfaces, special provisions willbe required in respect of more complicatedshapes or difficult locations.

THE WET PROCESS

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Wet mix sprayed concrete can be astructural material and provide adecorative finish depending on theselection of the appropriate system. Sharpreturns and fine details are not advisablebut where they are specifically required theyshould be clearly defined by the Engineerin the specification as they will requirecareful attention during placing.

Wet mix sprayed concrete can bepigmented for architectural purposes.

Wet Process EquipmentWet process sprayed concrete pumpsinclude machines with piston and wormpumps where the concrete is delivered tothe nozzle as a dense stream. At the nozzle,air and accelerator (if required) are addedto project and compact the material to thesubstrate.

Worm pump machines can deliver concretewith maximum aggregate sizes of 4mm,and are typically used for repair and surfacefinishing projects. The output is typicallyup to 4m3/h.

Double piston pump based machines alsosupply a dense stream of concrete to thenozzle, and should be virtually pulse freewhen spraying. This type of machine canproduce high outputs from 4m3/h to25m3/h, lending itself to tunnelconstruction or where large structural

volumes are required. Accelerator dosingunits are usually fitted to these pumpsallowing synchronised dosing with theconcrete output. These wet processsprayed concrete pumps may take mixeswith up to 20mm aggregate.

Rotor chamber pumps normally used forthe dry process have been adapted to spraywet mix concrete. These pumps can deliverbetween 4 and15m3/h with up to 20mmaggregate. The material is conveyed bycompressed air to the nozzle in a thinstream, where accelerator (if required) isadded.

Spraying equipment should be capable ofdelivering concrete to the substrate at aregular rate and be free from pulsationeffects that can cause mix segragation andover dosing with additives.

All concrete deliverylines should be sealedand lubricated priorto pumping concreteusing a grout mix.

Transport linesconsisting of flexiblehoses and steel pipesshould be laid asstraight as possible or

in gentle curves. The transport pipesshould have a uniform diameterappropriate to the mix and fibrecharacteristics determined by site trials,and be free from any lips, dents and kinksbetween the spraying machine and nozzle.

All equipment should be cleaned andmaintained at regular intervals to preventthe build-up of concrete in the hopperand delivery system.

THE WET PROCESS

the “wet spray” process (typical)

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In both the wet or dry processes

It is usual for the concrete to be placedslightly proud of the required alignmentand screeded to the required profile with

a timber or steel derby.

On thin coatings (less then 25mm)trowelling is undesirable as it can disturbthe impaction bond, unless a specificallydesigned mix (eg including polymers) isused.

Generally, it is preferable that the finishedsurface should also be left as sprayed as

SURFACE FINISHES

any finishing of the surface other thanvery light trowelling, can cause plasticcracking which may be detrimental to theend product.

If required this surface can be finished,preferably with a wooden trowel or, ifabsolutely necessary, a steel float. Noadditional water should be used to aidfinishing. A very thin flash coat ispreferable. Typically, the finer theaggregate, the easier it will be to floatand the better the end product.

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Pre-Bagged Materials

Material for both dry and wet processescan be supplied ready mixed and factorypre-proportioned. These qualitycontrolled products are available fromthe Association’s Manufacturer Members.They are suitable for both small and largevolume work and may be batched tocomply with the specification.

Site Batching

Should site-batching be required the mixshall be carefully designed using anumber of constituents and additives.

CementsTraditional Portland cements are usedfor most sprayed concrete applicationsand should comply with the requirementsof BS12 and EN 197. In general, Class42.5N or Class 52.5R cements arerecommended for sprayed concrete.Other cements shall comply with thenational standards or regulations validin the place of use.

Alternative cements, include such assulphate resisting cements (to resistsulphate attack), calcium aluminatecements (for high temperature andspecial requirements) and naturalcements (for low heat, fast settingrequirements). Reference should be

made to the supplier prior to using theseproducts.

As a general rule the higher the C3Acontent and the higher the specificsurface (Blaine) and the class, the higherthe reactivity in terms of setting time andearly strength gain, particularly incombination with set accelerators.

AdditionsPulverised fuel ash (PFA) is a finelydivided inorganic pozzolanic materialwhich can be added to concrete duringwet or dry batching to improve or achievecertain properties in the plastic and/orhardened state. Fly ash used in sprayedconcrete should comply with EN 450 andBS 4328.

Ground Granulated Blastfurnace Slag(GGBS) is a fine granular latent hydraulicbinding material which can be added toconcrete in order to improve or achievecertain properties in the plastic and/orhardened state. GGBS should meet therequirements of BS6699:1992.

Condensed Silica Fume is an extremelyfinely divided, highly active inorganicpozzolanic material which can be addedto concrete during wet or dry batchingto improve pumpability, cohesiveness andadhesion. Improvements in some

CONSTITUENT MATERIALS

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16

hardening properties are also achieved.

Pigments should be used in accordancewith the requirements of EN 206 and thesupplier’s recommendations.

Cement additions may also be specifiedas a cement replacement, but should notexceed the relative proportions given inTable 1.

AggregatesAggregates in general should comply withthe requirements of BS 882, and shouldbe checked for their susceptibility toalkali-silica reaction.

The aggregate gradation curve for the wetand dry mix processes should normally

lie in the respective envelopes defined inFigure 1.

It is the responsibility of the contractorto choose the most suitable grading forthe process and materials available.

For dry mixes the natural moisture contentin the aggregate should be as constant aspossible and a maximum of 6%.

Proprietary lightweight aggregates maybe used but should not be specifiedwithout reference to a specialist supplier/contractor.

Mixing waterPotable water is suitable for sprayedconcrete. Other sources should be


Figure 1: Aggregate grading curves for the wet and dry-mix sprayed concrete process

3

8

1 2

2 1

3 5

6 0

10 0

1 8

3 4

4 9

6 2

7 3

10 0

1 1

2 2

3 7

5 5

7 3

10 0

2 6

5 0

7 2

9 0

10 0 10 0 10 0

1

8 8

8

4

9 0

1 2

0

10

20

30

40

50

60

70

80

90

100

0.1 1 10 100

Particle size (mm)

Pe

rce

nta

ge

pa

ss

ing

Wet-mix process gradingenv elope

Dry-mix process gradingenv elope

0.12

5

0.2

5

0.5

1 2 4 8 16 ISO

Sie

vesi

ze (

mm

)

0.1

5

0.3

0.6

1.1

8 2

3.3

5 5 14

BS

Sie

vesi

ze (

mm

)

0.21

2

0.42

5

6.3

Fine Medium Coarse Fine Medium Coarse

S A N D G R A V E L

17

checked in accordance with BS 3148 forsuitability. It should be noted that themixing water temperature influences thefinal mix temperature.

AdmixturesA sprayed concrete mix may includeadmixtures to improve the properties ofthe fresh mix and the hardened concrete.

The following list of admixtures arecommonly included in sprayed concretesystems:

Accelerators increase the stiffening rate,to produce a fast set and provide earlystrength development. A fast settingconcrete may be necessary to build upthe required thickness and to ensureoverhead stability. The dosage should beoptimised to ensure good cohesionbetween individual passes thusproducing a single layer and minimisingany adverse effects on long term strength.

Different accelerator types are availablefor different applications. Guidanceshould be sought from the manufacturer.

Superplasticisers and Plasticisers areused in sprayed concrete to minimise theamount of water in the mix, therebyimproving the final quality.Superplasticisers offer greater waterreduction than plasticisers, withoutretardation of the mix.

Hydration control admixtures are addedto sprayed concrete in order to maintainworkability and extend the open timeduring transportation and applicationwithout reducing concrete quality.

Retarders are added to retard the settingof the concrete. With the use ofretarders, preconstruction tests on site

with the actual materials and mix designshould be conducted prior tocommencement of the work, in order toverify the dosage rate of the product.

FibresFibres are added to sprayed concrete toimpart one or all of the following materialproperties:

! Control of plastic shrinkage cracking! Control of thermal cracking! Improved abrasion and impact

resistance! Improved fire resistance! Improved ductility and toughness! Enhanced tensile and f lexural

strengthFurther technical information is providedby the Sprayed Concrete Association’sTechnical Data Sheet No.1.

Steel reinforcementSteel reinforcement increases the flexuralstrength and controls cracks. Steelreinforcement is normally in the form offabric and is recommended for thicklayers (≥ 50 mm). For most uses,reinforcing steel fabric with a mesh of50 to 150 mm and a wire diameter of nomore than 10 mm is widely accepted.

Curing agentsLiquid curing agents should be specifiedto maximise hydration of the cement byreducing water evaporation.

There are two types of curing agent:Externally spray applied curing agents andinternal curing admixtures added to theconcrete. Both types should be used inaccordance with the manufacturer’stechnical instructions.


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Whilst inherently safe, like allactivities in construction,spraying concrete needs to be

planned and executed with due regardto Health and Safety.

It is advisable only to employ the servicesof competent designers, suppliers andcontractors (members of the SprayedConcrete Association) to carry out theseworks. Since the Health and Safety atWork Act of 1974 and subsequentlegislation such as COSHH (Control ofSubstances Hazardous to Health) andCDM (Construction Design Management)it is vital that due consideration is givento safety issues.

Construction Design andManagement RegulationsFrom the design stage onwards all partiesto the contract are expected to have dueregard of the Health and Safetyimplications of their proposals. Via thesite safety plan and the Risk Assessmentall parties are now expected to plan andcreate a safe working environment whererisk is, at best, eliminated or certainlyreduced.

A safe work site must be maintained.This will include security to preventunauthorised visitors, especiallychildren, a safe means of access to theworks (scaffolding etc) and theelimination of risk to passers-by.

After due consideration at the designstage the construction team will worktogether to maintain this safeenvironment.

The site safety plan will accompany the

works and form an “as built” record forthe future. This is especially relevantwhere services or structures may behidden by the spraying operation.

Control of Substances Hazardousto Health – COSHHThe material components of sprayedconcrete contain cementitious productsand possibly other additives andchemicals.

Material manufacturers and contractorsare duty bound to issue a COSHHassessment for the handling and use ofthe materials. This assessment willhighlight the hazards that may exist andthe measures required to eliminate riskto the user.

Particular consideration should be givento special circumstances e.g. highbuildings, confined spaces etc. Allmaterials should be used in accordancewith the manufacturers’ instructions.

Personal Protective Equipment(PPE)The risk assessment and COSHHassessments will inform the user thatspraying concrete is going to be a noisyand dirty process.

The nozzleman, mixing gang and thoseadjacent to them must be issued withappropriate PPE. This will includeoveralls, gloves and safety helmet withfull face visor or specialised helmet withbreathing apparatus and safety boots.This equipment must be maintained andreplaced when damaged or worn out.

HEALTH AND SAFETY

19

PlantSprayed concrete plant is essentiallyfairly simple. A large air compressorfeeds the wet or dry spray plant via aseries of valves and hoses. A mixer mayalso be used for the dry process.

Plant must be maintained and servicedproperly and used in accordance with themanufacturers’ instructions. Protectiveguards should be checked and used.Unsafe or improperly maintained plantshould never be used until it is repairedand checked by competent persons.

Plant should never be used incircumstances that exceed themanufacturers’ specification.

WC facilities, and a separate clean areafor taking breaks and eating.

Disposal of WasteSprayed concrete operations usuallygenerate significant quantities of wastematerial. This will include overspray andrebound material together with packagingfrom the delivered materials andadditives.

This waste must be properly disposed ofto licensed tips by licensed contractors.Wherever possible the material selectionshould minimise the disposal of wasteand the impact on the environment.

HEALTH AND SAFETY

Working EnvironmentA safe workingenvironment should becreated and maintained.This will include levelledground and proper accessto the work area.

Proper lighting should beprovided and, if necessary,ventilation, especially fordust extraction or whenworking in a confinedspace. Protection againstoverspray and airbornedust should be providedwhere necessary.

The workforce must enjoyproper welfare facilities.These will includeaccommodation wherethey can change and dryclothes, washing facilities,

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General

Tests should be carried out on aroutine basis on cores or othersamples taken from sprayed

concrete applied in the Works. Only forcertain specific tests as indicated in thefollowing clauses should panels or beamsbe prepared for test purposes.

The Site Trials should be repeated if thesource or quality of any of the materialsor the mix proportions are required tobe changed during the course of theWorks.

An agreed testing regime should becarried out on a routine basis.

Specimens should be tested inaccordance with the EFNARCSpecification: 10.

Preconstruction testsThe frequency of carrying out each testfor mix control should be in accordancewith the EFNARC Specification: 11.2

Composition of the sprayed concrete isdetermined in the course ofpreconstruction tests in which therequired proper ties are checked.Examples of properties to be checkedare:

Fresh concrete:! water demand, workability,

pumpability,

! sprayability/rebound! slump, density! accelerator dosage and compatibility

with cement type

Hardened concrete:! compressive strength and density at

7 and 28 days! flexural strength! residual strength! fibre content! bond! permeabilityThe need for such tests is dependent onthe type of project and the utilisation ofthe sprayed concrete, but should alwaysbe done in control class 3.

Quality controlThe production of sprayed concrete shallbe subject to quality control procedures.Different levels of control can beexercised dependent upon the complexityof the project.

There are 3 classes of control:

1. Minor control2. Normal control3. Extended controlThe choice of control class is the decisionof the designer, based on type of projectand consequence of failure.

There are no special requirements for theorganisation of the work in controlclasses 1 and 2. In control class 3 thereshould be an organogram for each projectwith a quality assurance engineer,dedicated to quality control.

The frequency of the tests is decided bythe designer, bearing in mind the functionof the sprayed concrete (includingstructural integrity), its design life, thedifficulty of installation, theenvironmental classification and theconsequences of a failure. The values

QUALITY CONTROL AND TESTING

21

given in Table 2 may be used as a guide.

Location of test specimens

The location of specimens to be takenfrom the Works should be proposed bythe Contractor and approved by theEngineer. For repair works it isrecommended to only measure thecompressive strength on cores taken fromrepresentative test panels. In the eventof a failure the Engineer may requireverification from cores taken from thepermanent works.

Marking of test specimens

Each core or beam should be marked withan appropriate reference mark and thedate and time of spraying.

Test MethodsThe tests should be carried out using themethods listed in Table 3.

Test panels and samples

Moulds should be made of steel or othernon-water-absorbing rigid material. Theminimum plan dimensions are 600 x 600

mm for hand spraying and 1000 x 1000mm for robot spraying. The thicknessshould be appropriate to the size of testspecimens to be cut from the panel, butshould not be less than 100 mm.Appropriate measures should be takento avoid entrapment of rebound in themould (such as using chamfered orslotted sides).

The moulds are positioned vertically andsprayed with the same operator,equipment, technique, layer thicknessper pass, spraying distance, etc. as theactual work. The panel should beprotected immediately against moistureloss using the same method to be usedin construction. The samples are markedfor later identification (Mix, location,date, operator).

The panel should not be moved within18 hrs of being sprayed. Curing shouldcontinue thereafter for 7 days or untilsamples are to be extracted.

The test samples should be cored inaccordance with EN 7034 or sawn from


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22

the panel, but should not includematerial within 125 mm of the edge (withthe exception of the ends of beams forflexural/toughness testing).

During transportation to the testinglaboratory the panel or sawn samples arepacked to protect against mechanicaldamage and moisture loss.


Compressive strength and density

The required minimum compressivestrength should in accordance with theEFNARC Guideline to the Specification:9.1, tables 9.1.1 and 9.1.2 as shown inthe example below:

40 MPa x 0.8 x 0.85 = 27 MPa

where:

40 = Characteristic cast cube requirement0.8 = conversion for cube/cylinder specimen0.85 = conversion factor for in situ sampling

Compressive strengthtests should beperformed inaccordance with EN4012 on drilled corestaken from the sprayedconcrete structure orfrom sprayed testpanels. Theirminimum diametershall be 50mm and theheight/diameter ratioshall be in the range1.0 to 2.0. Test resultsfrom cores with height/diameter ratio different

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23

from 2.0 shall be converted to equivalentcylinder strengths using the values givenin Table 3.

Alternatively the compressive strengthcan be determined from cubes cut fromsprayed test panels. The minimumdimensions are 60 x 60 x 60mm and thesamples tested in accordance with EN4012.

The density is determined by weighingthe sample in water and air in accordancewith EN 6275 (water displacementmethod).

Normal testing ages are 7 and 28 days.

The test report shall contain:

! test specimen identification! moisture condition of the test

specimen! test specimen dimensions! curing conditions and age at test! maximum load and compressive

strength (to nearest 0.5MPa)


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00.2 51.1 00.1

57.1 21.1 79.0

05.1 01.1 59.0

52.1 70.1 39.0

01.1 30.1 98.0

00.1 00.1 78.0

57.0 88.0 67.0

CRANFEecruoS

24

Spraying concrete is without doubt oneof the most demanding activities inconstruction. Its success relies very

heavily on the skills of the nozzleman andhis team. It is vitally important thereforethat specifiers and designers insist upon andverify the background and training methodsadopted by their prospective contractors.

The Sprayed Concrete Association has formany years recommended a formal recordkeeping, training and certification scheme.

The nozzleman’s actions on site are crucialin maintaining the quality and consistencyof the final product. With the dry processthey control water content and hence themix design. With both dry and wet processestheir skills determine the density andcompaction of the sprayed material and theprevention of voids and “shadows” behindreinforcement. They will be able to placematerial overhead in multiple layers whilstminimising rebound and overspray, and willalso be able to achieve the required surfacefinish to the sprayed material.

His support team will often hand batchmaterials and certainly be responsible forproviding the nozzleman with a constantsupply of controlled materials without riskof inconsistency or blockage.

Many of these skills will be learnt on sitethrough experience. On site apprenticeshipand training provides a firm grounding totrainees. Their progress should be recordedin a recognised log book such as that issuedby the Sprayed Concrete Association.

Experienced operators have in the past beenable to record their skills by the issue of“Grandfather Rights”. This is a certificatesigned by their employer confirming theholder’s past experience and success.

As this route to certification is graduallyphased out more formal approvals are nowavailable. The Construction Skills CertificateScheme (CSCS) now provides a simplemethod of extending certification to acommon standard across the industry byaccreditation.

The more recently introduced NationalVocational Qualification (NVQ) is the goal tobe aimed at by all competent employees.Both schemes are linked and supported bythe Sprayed Concrete Association, theConstruction Industry Training Board (CITB)and many employers.

Formal training schemes are offered by theCITB. These courses are usually residentialand quite intensive. The desired result is afully trained nozzleman who is not onlycapable of spraying concrete but also ableto create test pieces for checking. He mustalso be able to understand the technicalitiesof the process.

TRAINING AND CERTIFICATION

It is vital therefore that training andcertification within the industry is bothsupported and maintained. Any reluctanceto provide that commitment could result insubstandard work or potentially dangerousstructures and the resultant Health andSafety risks.

25

The following information applies toboth the wet and dry processes.

Overall DesignWith sprayed concrete the Designer canhave the freedom to achieve almost anyshape. The Specifier should ensure thatadequate plans with detailed dimensionsare provided. This will enable theContractor to accurately assess theSpecifier’s requirements.

StrengthThe strength of sprayed concrete shouldbe specified as follows:

Grade Characteristic strength at 28 days30 30N/mm²40 40N/mm²50 50N/mm²

The Contractor should be free to designthe mix to achieve the specifiedcharacteristic strength. He should ensurethat the gradation of fine and coarseaggregates is such that the mix can bepumped (wet or dry) without problems(such as “bleeding” within pumping linesin the case of a wet mix).

ReinforcementThe Designer may require the sprayedconcrete to be reinforced. Mesh, bar orfibres could be specified. Thereinforcement should be specified as forconventional concrete but with a limit onlarger bar sizes. Reinforcing bars greaterthan 25mm should be avoided.

Clear spacing between parallel main bars,including laps, should be at least fourtimes the bar diameter or 50mmwhichever is the greater. Where concreteis sprayed against an existing structurethe back cover to reinforcement shouldbe between 25mm and 40mm dependingon the concrete mix in use. Overlays inexcess of 25mm thick shall be reinforced.

Where two layers of reinforcement areincorporated, the bars on the front faceshould be in line with those on the rearface. In constricted areas it may bepreferable to spray the rear layer ofreinforcement to ensure goodencapsulation of the steel prior to fixingthe front layer.

The Engineer should specify the type andspacing of fixings to ensure that thereinforcement can be adequately securedto prevent vibration or displacementduring spraying, Cover shall be as forconventional concrete.

Glass, steel or other approved fibres maybe used in appropriate quantities tomodify the characteristic of the sprayedconcrete. Certain lightweight reinforcingfabrics, which do not comply with therequirements of BS4483, may bespecified.

CementExcept where otherwise specified thecement should be Portland Cementcomplying with the requirements ofEN197.

All cement should be fresh and afterdelivery should be stored in a dry areaor in a purpose made bulk silo.

DESIGN AND SPECIFICATION

26

AggregateAggregate should consist of sharpwashed sand graded in accordance withBS882 (1984). Medium Grade ispreferable. Where this grade is notreadily available other fine aggregatesmay be employed if the Contractor candemonstrate that the specification canbe achieved.

Coarse aggregate should comply withBS882 and in general should not exceed16mm, although a maximum size of10mm is preferable.

Some aggregates, such as proprietarylightweight aggregates that can only bepumped in a high slump condition,should not be specified without referenceto a Specialist Contractor.

WaterWater should be clean and free fromharmful matter. Where tests are requiredthey should be in accordance with therequirements of BS3148.

AdmixturesPlasticisers and water reducing agentsmay be used with the approval of theEngineer. Admixtures, such asaccelerators, may also be used with theapproval of the Engineer but the methodof introduction and concentration shouldbe proposed by the Specialist Contractor.

Where admixtures are employed a typicaldosage shall be specified. The effects ofincorrect dosing should also be madeclear, particularly with regard to strengthand long term durability.

PlantIf site-batched concrete is to be usedthen the required proportions of cementto aggregate should be determined byweigh batching.

Alternatively, if the size of the contractdoes not warrant the provision of weigh-batching equipment, volume batchingmay be permitted.

The mixing equipment must be capableof thoroughly mixing the materials andof discharging the whole of each batch.It should be inspected and cleaned atleast once each day. Hand mixing maybe allowed on small contracts but ineither case care should be taken thatmixed materials are placed before theoccurrence of initial set of the cement.

Pumping and delivery equipment shouldbe specifically designed for sprayedconcrete work and be capable ofdelivering a continuous, even flow ofmaterial to the nozzle. The equipmentshould be inspected and cleaned daily.

An uninterrupted supply of compressed


27

air to the nozzle should be maintainedat a pressure sufficient to ensure evendistribution of material.

Delivery pipes and hoses should beinspected before laying out to ensure theyare clean and that coupling end rings arenot damaged. Couplings and sealsshould be in good condition. Deliveryhoses should be laid out prior to thecommencement of work and during thecourse of the work should be maintainedwithout kinks or sharp bends.

As required, the air or water line shouldbe inspected for soundness and laid outalongside the concrete delivery line. Inthe area of work it should be attached tothe delivery line at regular intervals.

WorkmanshipThe Contractor should be a member ofthe Sprayed Concrete Association orprovide satisfactory written proof ofexpertise in sprayed concrete.

The Contractor should employ a full-timeworking Foreman on the project who hasat least five years specialist spraying

experience, including two years as anozzleman. Also, he should haveexperience in concrete mix design andbe fully conversant with the relevantcodes of practice and specification.

The quality of sprayed concrete is largelydependent on the skill of the nozzleman.The nozzleman must be competent andexperienced in such work and have aworking knowledge of concrete practice.Pump operators should have a goodworking knowledge of the machinery theyare using to ensure optimumperformance.

The control of alignment and thicknessof sprayed concrete is the responsibilityof the Contractor. Where sharp edges oraccurate lines are required, these shouldbe set out by screed boards, guide wiresand/or depth spacers. The contractorshould ensure that these are suitablysecured to prevent movement duringapplication of the sprayed concrete.

After any specified interface preparationhas been carried out, and immediatelyprior to the spraying operation, thesurface must be thoroughly cleaned anddampened with a strong blast of air andwater.

Sprayed concrete must not be placed onto a frozen substrate, nor placed whenthe air temperature falls below 5°C. Itshould be maintained at not less thanthis temperature until the final set isachieved.


28

Application should commence at thebottom of vertical or near verticalsurfaces and each layer of sprayedconcrete built up by making severalpasses of the nozzle over the work area.

For reinforced concrete the distance ofthe nozzle from the work should bebetween 600mm and 1500mm and heldperpendicular to the application surfaceexcept when spraying around areinforcing bar when the nozzle may beheld closer and at a slight angle in orderto facilitate full and total encasement.If the work is of a non-structural nature,the nozzle may be held at a greaterdistance provided the specification canbe achieved.

The sprayed concrete should emergefrom the nozzle in a steady flow, free frompulsation. Excessive cement “paste” orsegregation caused by poor mix designshould not be incorporated in the work.Should the flow become intermittent itshould be directed away from the work.

A proportion of sprayed concrete willrebound and measures should be takento prevent it from being incorporated inthe finished work. The amount ofrebound will vary according to a numberof factors including the parent surface,location, the applied material’s mix andthe type/quantity of reinforcing.

Maximum layer thickness is governed bythe requirement that the material shouldnot slump or sag in such a manner thatit can cause a break in bond. TheContractor shall duly consider factorssuch as position of reinforcement; planeof application; mix design andconstituents including admixtures thatmay contribute to slump and sag.

Where thick layers are applied thehorizontal leading edge should bemaintained at a slope. Where necessaryto achieve greater overall thickness,subsequent layers must not be applieduntil the preceding layer has attainedadequate strength. Prior to sprayingsubsequent layers, loose materialsshould be removed using a strong blastof air.

Construction joints should be tapered atapproximately 30o and cut back squareto the outer layer of reinforcement,unless otherwise specified by theEngineer. The entire joint should bethoroughly cleaned and dampened priorto the placement of adjacent sprayedconcrete.

When applying additional layers thereinforcement should be cleaned of anypreviously deposited hardened materialwhich might prevent a proper bond orencasement.

In general the sprayed concrete shouldbe cured in accordance with therecommendation set out in EN 206.Where the ambient temperature exceeds25°C or in exposed conditions where airmovement may cause a rapid drying ofthe concrete surface, as the sprayingproceeds the work should be immediatelyprotected by wet hessian or a fog spraysystem. In these conditions no surfaceshould be exposed for longer than onehour.


29

In addition to the publications listedbelow, the Sprayed ConcreteAssociation produces a number of

documents related to Sprayed Concrete,a list of these publications may beobtained from Association House.Members of the Sprayed ConcreteAssociation are happy to answer anyquestions regarding sprayed concreteapplication. The membership variesacross the spectrum of contractors,material and plant supplier’s andconsultants.

ICE - design and practice guides- Sprayed concrete linings(NATM) for tunnels in softground.In 1994, the collapse of two tunnels, oneunder construction beneath a street inMunich and the other under constructionin the centre of London’s HeathrowAirport, caused major concern in theinternational tunnelling community andto the public. These incidents broughtinto question the use of sprayedconcrete, a system more commonlyreferred to the New Austrian Tunnellingmethod (NATM), for the initial supportof tunnels in soft ground. As a result ofthis world-wide concern, the Institutionof Civil Engineers has issued this guideto consider the implications of the useof sprayed concrete support methods insoft ground in urban areas and provideguidance on how the associated risks ofthis method can be minimized. The guidehas been specifically complied to:

! respond to public concerns over theuse of NATM in soft ground in urbanareas;

! examine NATM design andconstruction principles and theirapplicability to soft ground in urbanareas; and

! provide guidance on the proper useof sprayed concrete linings in softground in urban areas, with specificreference to London Clay.

Contents: Introduction - What is NATM -General experiences of SCL - Procurementof SCL Tunnels - Design - Guidelines onConstruction - A comparison withsegmentally lined tunnels - Conclusions -References.

Published by Thomas TelfordISBN No. 0-7277-2512-2

EFNARC - European SpecificationFor Sprayed ConcreteEFNARC was founded in March 1989 byfive national trade associationsrepresenting producers and applicatorsof specialist building products. TheSprayed Concrete Technical Committeewas formed in early 1991, whicheventually led to the publication of a finalversion of this document in 1996.

This specification treats sprayed concreteas an entity and makes no reference tofields of application such as tunnellingwhich is the case of many otherpublications. The subjects covered arethorough and contain information tosatisfy the requirements of specifiers,contractors and suppliers alike on allaspects of sprayed concrete. Thespecification has been specificallycompiled to:

! provide guidance to meet the

BIBLIOGRAPHY AND USEFUL PUBLICATIONS

30

requirements of all stages of sprayedconcrete from selection of materialsand design mix through toapplication, requirements, safety andquality control.

! provide a consistent level ofinformation and guidance to all usersof sprayed concrete throughout theEuropean community.

Contents: Scope - Reference Standards -Definitions - Constituent Materials -Requirements For Concrete Composition -Requirements For Durability - MixComposition - Execution Of Spraying -Requirements For Final Product - Testmethods - Quality Control - Health & Safety.

Available from the Sprayed ConcreteAssociation - ISBN No. 0-9522483-1-X

EFNARC – Specification ForSprayed Concrete – GuidelinesFor Specifiers & ContractorsThis 1999 publication is to be read inconjunction with the EFNARCSpecification for Sprayed Concrete. Theseguidelines refer to the Specificationsregularly and all references relate to theclause numbers in the specification. Theguidelines also contain a number ofupdates that supersede items in theSpecification, particularly a list of thelatest CEN test methods relevant tosprayed concrete and a revised sectionon the execution of spraying.

These guidelines have been produced to:

! provide a reference document aimedat use during the application ofsprayed concrete and present thecontractors and clients alike with

guidance as to best practice methods

! work in conjunction with the EFNARCSprayed Concrete Specification.

Contents: Foreword - References - ConstituentMaterials - Requirements For ConcreteComposition - Requirements For Durability -Mix Composition - Execution Of Spraying -Requirements For Final Product - TestMethods - Quality Control - Environment,Health & Safety.

Available from the SCA

Simon Austin & Peter Robins -Sprayed Concrete PropertiesDesign and ApplicationThis book provides a comprehensivecoverage of all aspects of sprayedconcrete. Materials technology, design,installation and application are all dealtwith. It forms an essential reference workfor all who seek guidelines on the subject.

Contents: Sprayed Concrete as aConstruction Material - Design andInstallation - Applications.

Published by Whittles PublishingISBN 1 870325 01 X

Austrian Concrete Society –Guideline ShotcreteThis publication produced by theAustrian Concrete Society is acomprehensive document that has takenseveral years to produce. It applies to theproduction of structural componentsmade of plain and reinforced concreteas well as the close-textured reinforcedconcrete placed by the method ofspraying.


31

The document predominantly covers thetesting and design of sprayed concretemixes but does so by investigating therequirements placed on the finishedmaterial. There is some informationcovering the placement methods but thisis limited. The one failing of thisdocument is that currently all charts andgraphs are still German which makesthem awkward to use. Other than thispoint the document is technically goodand covers all aspects of sprayedconcrete.

Contents: Scope - Definitions - EnvironmentalCompatibility of Shotcrete - Mix - ShotcretingProcedures - Requirements to be met byShotcrete - Structural Requirements - SpecialProcedures - Testing - Quality Management -Testing Procedures - Standards, Guidelines.

This document is not generally availablein this country but the Sprayed ConcreteAssociation may be able to obtain copies.

HSE – Safety of New AustrianTunnelling Method (NATM)TunnelsOn 21st October 1994 three paralleltunnels under construction beneathHeathrow Airport started to collapse.These tunnels were being constructedusing a system referred to as NATM forthe primary lining. This system failed.The HSE were requested to considerwhether there were any broader healthand safety implications concerning boththe construction of NATM tunnels in theUK, and the safety of the finished tunnelin comparison with traditional methods.This report covers these subjects.

The report predominantly reviews safety


of the NATM process throughout theworld, it also relates this to current UKSafety Legislation. The repor t isinteresting reading, in particular thesections which cover Safety Managementof Sprayed Concrete operations, usefulinformation to managers of sprayedconcrete activities.

Contents: Introduction, scope & purpose ofreview - Summary of findings - Principal HSEconclusions - The NATM Process - World WideReview of NATM Safety - UK. Health & SafetyLegislation - NATM Safety Principles -Designing for Safety - ManagementArrangements - Appendices - Glossary ofTerms - References & Reading List

Published by HSE Books - ISBN No. 0-7176-1068-3

HSE – Post Construction Audit ofSprayed Concrete Tunnel LiningsThis report researches the presentpractice in the auditing of the finished,sprayed concrete tunnel lining structure.As with many of the publications relatingto sprayed concrete this focus’s on tunnellinings specifically. A number of theprocedures described could be appliedto any type of sprayed concrete work ofa structural nature. The systems areaimed at large sections of work and maynot be suitable for small projects.

Contents: Summary - Introduction - SprayedConcrete - Design of Sprayed ConcreteTunnel Linings - testing of Sprayed ConcreteTunnel Linings - Performance Requirements- Appropriate Testing Methods for SprayedConcrete Tunnel Linings - Recommendationsfor Post Construction Audit - References

Published by HSE Books - ISBN No. 0-7176-1026-8

32

PHOTOGRAPHS

The SCA gratefully acknowledges the following for providing photographs andillustrations for use in this publication:

Aliva Ltd

CMS Pozament Ltd

The Construction Industry Training Board

Gunform International Ltd

Graham Daws Associates Ltd

National Power plc

Polycrete

Sika Ltd

© Sprayed Concrete Association 1999

£10

ISBN: 1 870980 08 5

Sprayed Concrete Association offices are at:

Association House, 235 Ash RoadAldershot, Hampshire GU12 4DD

Tel: +44(0)1252 321302

Fax: +44(0)1252 333901

Visit SCA on the web at:

www.sca.org.uk

where you can see a complete list of SCA members,news of events and other information

Also available from the SCA:

Picture of theDirectory

Picture of theEFNARC Spec

Intro to Sprayed Concrete

Documents

speci fi cati

proprietary lightweight aggregates

austrian tunnelling method

sprayed test panels

sprayed concrete linings

sprayed concrete association

site safety plan

hydration control admixtures