Production of Hollow core Slabs

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PROCESSDESCRIPTION

HOLLOWCORESLABPRODUCTIONBYEXTRUDER

HOLLOWCORESLABPRODUCTIONPLANT

HollowcoreslabproductionbyExtruder

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Keywords:Hollowcoreslabproductionplant,prestressedhollowcoreslabs,extruder,precastflooring,flooring


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PROCESSDESCRIPTIONHOLLOWCORESLABPRODUCTIONBYEXTRUDER

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ThisdocumentisownedbyElematic,Finland.Alldatainthisdocumentissubjecttochange.

Content page

1. Introduction ............................................................................................................................ 31.1. Advantages ................................................................................................................... 3

2. Production process ................................................................................................................ 52.1. Cleaning of beds and pulling of strands ........................................................................ 62.2. Tensioning of strands .................................................................................................... 62.3. Concrete transportation ................................................................................................. 62.4. Extruding ....................................................................................................................... 72.5. Draw openings by plotter .............................................................................................. 72.6. Making of openings (if needed), covering the slab ........................................................ 7

2.7.

Cutting on the bed ......................................................................................................... 8

2.8. Lifting of the slab, drilling of drainage holes .................................................................. 82.9. Transportation to storage .............................................................................................. 82.10.Handling of the slabs in storage .................................................................................... 9

3. Production facility requirements .......................................................................................... 104. Technical data ..................................................................................................................... 115. Additional information .......................................................................................................... 12


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1. Introduction

1.1. Advantages

Prestressedhollowcoreslabsareamongthemostadvancedproductsintheprecastconcreteindustry,

especiallywithregardtotheirhighqualityandlowconsumptionofmaterials.

Hollowcoreslabsarethemostwidelyusedtypeofprecastflooring.Thisisduetothehighlyefficient

designandproductionmethods,choiceofunitdepthandcapacity,smoothundersideandstructural

efficiency.

Hollowcoreslabshavelongitudinalcores,whosemainpurposeistoreducetheweightofthefloor.They

aremainlyusedinbuildingswithlargespanssuchasofficebuildings,hospitals,schools,shoppingcenters,

industrialbuildings,etc.Anothercommonapplicationisapartmentbuildingsandhousesbecauseofthe

favorablecostrateandthefasterection.

Generally,prestressedhollowcoreunitshavenoreinforcementotherthanthelongitudinalprestressing

strandsatthebottom.Hollowcoreslabsdonothaveorneedanytransversalreinforcement.Upperstrands

areusedincantileverslabsolutionsoragainstloadscausedbyhandling.

Prestressedhollowcoreslabsarenormally1200mmwideandupto20mlong.Standardslabheightsvary

between150

to

500

mm.


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Prestressedhollowcoreunitsaremanufacturedusingeitherlonglineextrusionorslipformprocesses.The

steelbedsareusually1200mmwideand80to150mlong.

Thedegree

of

prestressing,

strand

pattern

and

depth

of

units

are

the

main

design

parameters.

TheElematicmanufacturingprocessdeploysdrymixconcrete,whichmeanslesscementisneeded

comparedtoconventionalprocesses.

Thevoidssaveroughly50%concretecomparedtomassiveslabwithsamethickness;thatis27.500tonsa

year(whenproductionis100.000m,200mmdeepslabs).

Theprestressingprocessreducestheconsumptionofsteel.Thenspansareover3.5msavingcanbe50%or

evenmore.Thatmeansseveralthousandsoftonsina100.000m/acapacityfactory.Benefitsaremore

substantialwhencomparedwithreinforcedconcreteslabproduction.

WiththeproductionprocessusingmodernstateoftheartElematicmachinesandexperiencedcrews,you

canachievesavingsof2530%inlaborhourscomparedwithconventionalslabproduction.Youcan

manufacture1.5to2.5mhollowcoreslabswithsamematerial,energyandlaborcostsyouneedto

produce1mslabswithequivalentdepth.


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2. Productionprocess

1. Cleaningandoilingofthebed

2. Strandpulling

3. Tensioningofstrands

4. Liftingtheextruderonthebed(not

shown)

5. Concretemixing(notshown)

6. Concretetransportation

7. Concretedosingtoextruder(notshown

8. Extruding

9. Drawopeningsbyplotter(notshown)

10.Makingopenings

11.Coveringof

slab

12.Curingofslab

13.Recoveringofslab

14.Cuttingofslab

15.Liftingofslab

16.Drillingofdrainageholes

17.Transportationtostorage

18.Handlingofslabsinstorage

19.Transportationtosite


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2.1.

Cleaningof

beds

and

pulling

of

strands

Prestressedhollowcoreslabsareproducedoncastingbeds.Before

casting,thebedsarecleanedandoiled.Thenthestrandsarepulled

andspreadbyaspecialdevice,BedMaster,whichsimultaneously

cleansthepalletwitharotatingbrush.WhentheBedMasterreturns

totheactiveend,itliftsthestrandsonthecastingbedandoilsthe

bedwithformoil.

BedMasterEL411

2.2.

Tensioningofstrands

Allofthestrandsforonebedaretensionedsimultaneously(or

singlestrandscanbeindividuallytensioned).Aspecialunithasbeen

developedforthispurpose.Theunitmovestransverselyatoneend

ofthehallsothateachcastingbedcanbehandledbythesame

machine.

Castingbedspecificstressingcylinderscanbeusedasalternative

stressingmethod.

Prestressingdevice

2.3. Concretetransportation

Concreteistransportedfromthebatchingandmixingplantbyan

overheadtransportsystem.Ashuttlebringstheconcretebatch

automaticallytocorrectplaceoveranoverheadbucketgantry,

whichdischargesthebatchintotheextruder.

Shuttleandextruder


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2.4.

Extruding

A

high

performance

extruder

is

the

key

component

in

the

productionprocess.Itextrudestheslabsascontinuousprocess.

ExtruderE9

2.5.

Drawopeningsbyplotter

Allopeningstobemadeinslabsaremarkedwiththeplotter.Also

thepointwheretheslabiscutorsplit,recessesandneededslab

identificationdataaremarkedwiththeplotter.Slabdataneededfor

plottingisloadedintheplotterinadvance.

Plotter

2.6.

Makingofopenings(ifneeded),coveringtheslab

Recessescaneasilybemadeafterthecastingprocesswhilstthe

concreteisstillgreen.Openingscanbemadewithamachineofby

hand.Whentheprocesshasbeencompleted,thecastslablineis

coveredwithtarpaulinstominimizeevaporation.

Openingsinthefreshlycast

slab


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2.7.

Cuttingon

the

bed

Aftercuring,tensionofthestrandsisreleasedandtheslabiscut

accordingtomeasuredmarkings.Cuttingoperationiscarriedout

withdiamondtippedsawthattravelsonthesamerailsasthe

extruder.

SlabsawEL1300A

2.8.

Liftingoftheslab,drillingofdrainageholes

Afterthecutting,slabsareliftedfromthecastingbedbyan

overheadcranewithclamps.Theslabsarethentransferredtoan

automaticdrillingdevicethatdrillsdrainageholesinbothendsof

theslab.

Liftingbeam

2.9.

Transportationtostorage

Slabswhicharesetontransferwagonsnowundergoqualitycontrol,

afterwhichthevoidsarefittedwithsealingplugsandtheslabends

markedwithprojectnumbers,etc.Thenthewagonsproceedtothe

storage.


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2.10.

Handlingof

the

slabs

in

storage

Anoverheadcraneequippedwithliftingclampsisusedforhandling

theslabsinthestorageandloadingtheme.g.ontrucksfordispatch

tothebuildingsites.


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3. Productionfacilityrequirements

Theproduction

hall

is

like

anormal

industrial

hall.

The

hall

has

to

fulfill

the

local

requirements

and

its

structuresneedtocarryverticalloadsandbendingmomentofnormalloadsandloadsfromfactory

equipmentlikecranes,shuttles,tracks,etc.Lengthoftheproductionhallisabout20m+bedlength+30

m.Foroptimalcasting,theambienttemperatureshouldbearound+20C.

Electricity:Normallytheplantgetsitspowerfromthelocalelectriccompany,butsometimesaplantsown

generatorisusedforheatingofconcrete,castingbedsandproductionhallandotherfacilitieslikeusage

water,office,etc.Theneededheatingpowerforaplantwith4castingbedsisapprox.450kWand700kW

foraplantwith8beds.

Watercomesusuallyformalocalwatersupplier.Watercanbedividedtosocalldrinkingwaterand

processwater(notdrinkable).Processwaterisusedformachinerycleaningetc.

Wastewatertreatmentplantisnowquitecommon.Recycledwaterisreusedformachinerycleaning,

washing,etc.

Wasteconcreteandrejectedslabsarenormallystoredinastorageareaandwhenapileishighenough,

thewasteconcreteiscrushedintosmallerpieces.Thiscrushedproductcannotbenormallyusedfor

hollowcoreslabproductionbutitcanbeusedforfillingpurposes.Steelisseparatedduringthecrushing

andsuppliedtosteelmillsforrecycling.

Storageareaisnormallyanopenarealocatedattheendoftheproductionhall.Therearegantrycranes,

overheadbridgeorAframeloadingsystems.Thecranesliftsingleslabsorbundleofslabsonto15mof

slabsrequire

1m

ground

area,

driveways

for

truck

and

outdoor

transportation

wagons

take

also

their

shareofthegroundarea.

Arackforslabtesting,i.e.forcarryingout1:1fullscalestrengthandbendingtests,canbelocatedinthe

storagearea.Alsoanareaforrecuttingtheslabs,whichareusablebutneedsomeadditionalwork(a

shorteningorananglecutetc.)isneeded.


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4.

Technicaldata

Constructionofaproductionplantnormallystartsbymakingthefeasibilitystudytakingintoaccountthe

market,needs,constructioncircumstances,buildingtypes,financingetc.requirements.

Theproductioncapacityofafloorproductionplantiscalculatedbasedonannualcapacity.

Thesmallestproductionplantcontainsjustonesinglecastingbed,butitisnotveryeconomical.Biggest

plantscanhaveseveralproductionhallswhileonehallmayhave812castingbeds.

Designdrawingofahollowcoreslabproductionhall

Annualcapacity(example)

Requiredannualproductioncapacityis200.000mwithonecastingbedperdayandwith250working

days.

Thecalculateddailycapacityis200.000m/250d=800m/d.Thisgives800m/1.2m=666.7linealmeters

ofslab.

6linesofbeds111.1m+6m117m

with6x6mx1.2m=43.2mofwasteor

5linesofbeds133.3m+6m139m

with5x6mx1.2m=36mofwaste.

Wechoose5castinglineseach144long.

Thisgivesanannualcapacityof5x(144 6)x1.2x250=207.000mcastonceaday,andiftwofull8h

shiftsareused,itispossibletocast23bedstwiceadayandincreasethecapacity.

Somecastingbedscanbecasttwiceaday(dependingonthecementquality(hardeningtime),process

cycletimeandworkingtimes).Asaverage,iftheproductioncapacitymustbeincreasedwithexistingbed

capacity,thecapacitycanbecalculatedsothatthedailycastingfactoris1.21.5,butthecycleanddaily


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workingtimemustbechecked.Alsotheplanttypedetermineshowthecastingispossible,i.e.whentwo

castingmachinescancastparallel,itiseasiertocastsomebedstwicecomparedtoonecastingatatime.

Theproduct

type

(thickness

of

the

slab)

also

affects

the

casting

cycle

and

times,

smaller

(i.e.

thinner)

productscanbecastfasterthanthickerones.Alsootherthingslikequantityofopening,recessesetc.will

affectthecastingtime.

Workscheduleforfourbedhallwithonecastingmachinewherecastingisdoneonceaday.

5. Additionalinformation


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Elematicisaleadingsupplierofprecastconcretemachineryandequipmentaswellastheonly

suppliercapableofdeliveringcompleteproductionplantsanywhereintheworld.Elematics

superiortechnologyandindustryexpertiseiscurrentlyinuseinmorethan100countriesacross

fivecontinents.ElematicisheadquarteredinToijala(Akaa),Finland.

www.elematic.com

Production of Hollow core Slabs

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