constraction troubleshooting

7/29/2019 constraction troubleshooting

1/20

ConcreteConstructionTroubleshootingTips

Problems

AirLossDuringConcretePumping

Blistering

Bugholes(SurfaceAirVoids)

Crazing

CrustingSurfaces(WavySurfaces)

Curling

Discolouration

Dusting Honeycombing

LowConcreteStrengthResults

PlasticShrinkageCracking

Scaling

UncontrolledShrinkageCracking

MortarFlaking

Popouts

Aids

ConversionTable

ConcreteQuickSpecications

www.rmcao.org


2/20


3/20

Problem:

Defnition:

Changesintheaircontentoftheconcreteduetoconcretepumping

operations.

Concreteairentrainmentrequirementsaretypicallybaseduponconcretesampledandtestedfromconcretesuppliedattheendofthechuteof

theconcretetruck.Whenconcreteisplacedviaaconcretepumpand

theacceptancesamplesareobtainedattheendofthepumpthereare

anumberofadditionalfactorsthatthecontractormustconsidersince

pumpingoperationscanreducetheaircontentoftheconcrete.

Air Loss During Concrete Pumping is

more likely to occur when:

n Theconcreteundergoessignicantverticaldrops

n Theconcretehasahighinitialslump

n Thepumpingpressureisincreasedandthereisasuddenpressuredrop

astheconcreteexitsthepumphose

How to avoid problems with Air Loss

During Concrete Pumping:

n Operatetheconcretepumpingboominanupwardorhorizontalposition

asmuchaspossible

n Reduceverticalconcretedropstotheshortestpossiblelength

n Insertmultiple90elbowsintothelinetocreatearesidualamountof

concreteinthelineandtominimizethelongstraightdropoutofthe

pumpingline

n Utilizeagateorowrestrictingdeviceattheendofthepumplineto

provideresistancetoow

n Runthelast35metresofthepumpinghosehorizontallyalongthe

subgradeorformworktoavoidverticaldrops

n Usingcable,looptheendsectionoftherubberhoseintoacircleto

preventdirectfreefalloutofthehose

n Elevatetheplasticaircontentabovethespecicationlimitsattheconcretetrucklocationtoaccountfortheactualairloss(Caution

Inspectionoftheaircontentatboththetruckandthepumpinglocation

becomesextremelycriticalwheneverthereisachangeintheboom

congurationhigheraircontentsinthenalconcretehaveanegative

impactoncompressivestrength)

Concretepumpingonacommercialprojectusingaowrestrictiondevicetoprovideresistancetoowandtopreventdirectfreefall

Photos courtesy of RMC

Concretepumpingonaresidentialradiantoorheatingproject

References:1. ConcreteinPractice#21LossofAirContentinPumpedConcreteNationalReady

MixedConcreteAssociation

2. ACI116CementandConcreteTerminologyAmericanConcreteInstitute3. DesignandControlofConcreteMixtures7thEditionCementAssociationofCanada

Air Loss During Concrete PumpingAir Loss During Concrete Pumping


4/20

Problem:

4

Defnition:

Theirregularraisingofathinlayeratthesurfaceofplacedmortaror

concreteduringorsoonaftercompletionofthenishingoperation.

Blistersformjustunderthesurfaceoftheconcretewheneitherbleedwaterorentrappedairispreventedfromescapingtheconcrete.Thistypically

occurswhenthetopsurfaceoftheconcretehasbeensealedprematurely

duringthenishingoperations.

Blisters are more likely to orm when:

n Thesubgradeiscoolerthantheconcreteresultinginnon-uniformsetting

oftheconcrete

n Insufcientorexcessivevibrationisemployed

n Theconcretesurfaceisprematurelysealedduetoimpropernishing

proceduresortools

n Siteconditionsareresultinginrapidsurfaceevaporationcausingthe

nishertomistakenlyassumethebleedingperiodiscomplete

n Entrainedairisaddedtononair-entrainedconcreteorwhentheair

entrainmentisabnormallyhigh

n Theconcreteelementisextremelythickresultinginlongertimesfor

bleedwaterandentrappedairtorisetothesurface

n Adryshakeisprematurelyappliedtotheconcretesurface

n Theconcreteisplacedoveravapourbarrier

How to avoid problems with Blistering:

n Utilizeproperconcreteconsolidationpractices

n Utilizethepropernishingtoolsandkeepthetrowelingbladesasataspossibletoavoidsealingthesurface

n Placeconcreteduringperiodsoflowersurfaceevaporation

n Avoidplacingconcreteoncoldsub-gradeswheneverpossible

n Avoidtheuseofchemicalretarderssincetheywillonlyintensifytheproblem

n Keeptrowelbladesataslongaspossibletoavoidsealingthesurfaceprematurely

n Considertheuseofchemicalacceleratorstoreducethesettime

n Properlyheatthebuildingand/orsubgradepriortoconcreteplacement

n Avoidplacingconcreteontopofvapourbarrierswheneverpossible

References:1. ConcreteinPractice#13ConcreteBlistersNationalReadyMixedConcreteAssociation2. ConcreteConstructionTroubleshootingTipsTheAberdeenGroup


BlisteringBlistering

Cross-sectionthroughaconcreteblister

Blisteringconcretesurface

Photos courtesy of CAC and CTL


5/20

Problem:

Photos courtesy of CAC and RMC

Defnition:

Smallregularorirregularcavities,usuallynotexceeding15mmindiameter,

resultingfromtheentrapmentofairbubblesinthesurfaceofformed

concreteduringplacementandconsolidation.

Bugholesappearassmallvoidontheoutsideofformedconcretesurfaces.

Thesedefectsaretypicallyduetothepresenceofsmallairpocketsthat

werenotremovedduringconcreteconsolidationoperationsorbythe

incompleteapplicationoftheformreleaseagenttoformworkresultingin

concreteadhesionduringtheformremovalprocess.

Bugholes are more likely to orm when:

n Theconcreteisnotadequatelyconsolidatedtoremoveallentrappedair

n Internalconcretevibratorinsertionsarenotsufcientlyoverlappedor

wellspaced

n Formreleaseagentsarenotusedortheformsareremovedbefore

theconcretehasgainedsufcientstrengthtoresisttheformremoval

pressures

n Concretemixturesareverystifforsticky

How to avoid problems with Bugholes:

n Uniformlyconsolidatetheconcreteensuringthatthevibratorinsertionpatternisuniformandwellspaced

n Reducetheheightofeachconcreteplacementlifttomakeairremoval

easer

n Movethevibratorasclosetotheformworkaspossible

n Properlyapplytheformreleaseagentandonlyremovetheformsonce

theconcretehasgainedsufcientstrengthtoresistanysuctionforces

n Considertheuseofspecialtyconcreteproductslikeselfconsolidating

concrete(SCC)

References:1. ConcreteConstructionTroubleshootingTipsTheAberdeenGroup


Bugholes (Surace Air Voids)Bugholes (Surace Air Voids)

Bugholesonaplywoodformedsurface

Bugholesonaconcretesurfacecreatedwithaformliner

SelfConsolidaConcrete(SCCsignicantlyreducesbughoandcanbeusinarchitecturaconcreteapplications


6/20

Problem:

6

Defnition:

Intersectingcracksthatextendbelowthesurfaceofhardenedconcrete;

causedbyshrinkageofthedryingsurfaceconcretethatisrestrainedby

concreteatgreaterdepthswhereeitherlittleornoshrinkageoccurs;varyinwidthfromneandbarelyvisibletoopenandwell-dened.

Crazingcracksarenerandomcracksonthesurfaceoftheconcretethat

donotaffectthestructuralintegrityoftheconcretebutwhicharevery

unsightly.Thesecracksrarelyaffectthedurabilityorwearresistanceofthe

concreteandareparticularlyevidentwhentheconcretecontainscalcium

chlorideasanacceleratingadmixture.

Crazing cracks are more likely to orm when:

n Theconcreteisnotproperlycuredandprotected.Thesecracksformdue

tothetopsurfaceoftheconcretedryingoutandshrinkingfasterthantheremainderoftheconcrete

n Theconcreteisexposedtorapidorprolongedsurfacedrying(low

humidity,hightemperature,directsunlight,dryingwinds,etc.)

n Thereisexcessoatingortheuseofajitterbugtodepressthecoarse

aggregateresultingintoomuchcementpasteatthesurface

n Theconcretesurfaceishandtrowelnishedandwhenitdoesntcontain

asurfacehardener

n Broadcastingcementbackontothesurfaceoftheconcretetodryup

bleedwater

n Utilizingcalciumchlorideinhotdryweather

How to avoid problems with Crazing:

n Startcuringassoonaspossible.Wetcuringproceduresthatensurethe

concretesurfaceremainscontinuouslywetduringthecuringperiodare

mosteffective

n Avoidintermittentcuringprocedures

n Donotapplycementtothesurfaceoftheconcretetoeliminate

excessivebleeding.Ordertherequiredslumpfromyourconcrete

producerandutilizechemicaladmixtureslikewaterreducerstoeliminateexcessivebleeding

n Utilizeinitialprotectionmethodstopreventthedryingoutofthe

concretesurfaceduringthenishingperiod.Thiscanincludetheuseofevaporationretardantchemicalsorfogspraying

References:1. ConcreteinPractice#3CrazingConcreteSurfacesNationalReadyMixed

ConcreteAssociation2. ConcreteConstructionTroubleshootingTipsTheAberdeenGroup


CrazingCrazing

Crazingonaresidentialgarageoorslab

Crazingonexterioratwork

Photos courtesy of CAC and RMCAO


7/20

Problem:

Defnition:Amouldedlayerofplainorreinforcedconcretewithanon-uniformsurfacedueto

differentialconcretesetting.

Wavyconcretesurfacesorconcretecrustingoccurswhenthetopsurfaceoftheconcretebeginstosetwhiletheunderlyingconcreteisstillinaplasticstate.Surfacecrustingiscausedbydifferentialstiffeningorsettingoftheconcrete.Athinportionofthetopsurfaceoftheconcretebeginstosetwhiletheunderlying

concreteisstillplastic.Surfacenishingoperationsmustthenbecompletedovera

jellylikeconcretebaseresultingindifferentialmovementoftheslabsurfaceduring

nishingoperationswhichresultsinwavyand/orcrackedconcretesurfaces.

Crusting Suraces are more likely

to occur when:n Therearesignicanttemperatureand/ormoisturedifferencesbetweenthe

bottomandtopoftheslab

n Concreteisplacedonacoldsubgrade.Thecoldsubgradeactsasaheatsink

whileportableheatersarebeingusedonthetopsurfaceoftheslabtomaintain

thenecessaryplacementandcuringtemperatures

n Environmentalconditionsareresultinginrapidsurfacemoistureloss.Highwinds,

directsunlightandlowrelativehumidityconditionsresultinconcretesurface

stiffeningduringthedryingprocess

n Concretemixdesignswithlowbleedingcharacteristicsaremoreproneto

concretecrusting

n Chemicalretardersareusedintheconcrete

How to avoid problems with Crusting Suraces:n Minimizetemperaturedifferentialsbetweentheconcretesurfaceandthe

subgradeorformwork.Duringwintermonthsthesubgrademustbeproperly

heatedwellbeforetheconcreteplacementandduringsummermonthswork

shouldbescheduledtoavoidplacingconcreteduringperiodswhentheair

temperatureisrisingsignicantly

n Utilizeproperinitialcuringprotectionstrategiessuchasfogsprayingand

evaporationretardantcompoundtominimizemoisturedifferentialsbetween

thebottomandtopoftheslab

n Considertheuseofnishingtoolsthatopenthesurfaceoftheconcreteand

dontresultinsurfacesealing.Delayoatingaslongaspossiblesincethisistheoperationthatcreatesmostofthehumps

n Ensurethatalloatingandtrowelingequipmentisusedinaatpositionto

minimizethechanceofsealingthesurface

n Considertheuseofchemicaladmixturestoacceleratethesettingrateof

theconcrete.Donotusechemicalretarderstodelaythesettingtimeofthe

concretesincethiswillonlyintensifytheconcretecrustingproblem.Minimize

anyvariationsbetweenloadsofconcreteandavoidunloadingdelays

n Delaypowertrowelingaslongaspossibletominimizethewavinessthatwillbecreatedduringthenishingoperations

n Usethepansonpowertrowelstobreakopentheconcretesurfaceimmediately

afterthebleedwaterperiodendstopromoteuniformconcretestiffening

References:1. ConcreteConstructionTroubleshootingTipsTheAberdeenGroup2. ACI116CementandConcreteTerminologyAmericanConcreteInstitute

3. TroubleshootingCrustedConcreteBruceSuprenantConcreteConstruction4. DesignandControlofConcreteMixtures7thEditionCementAssociationofCanada

Crusting Suraces (Wavy Surace)Crusting Suraces (Wavy Surace)

Walkbehindpowertrowel

Rideonpowertrowel


Anexampleofawavyconcretesurface


8/20

Problem:

8

Photos courtesy of CAC and W. R. Grace

Defnition:

Adeviationofaslabfromitsoriginalshape,usuallycausedbyeither

temperatureormoisturedifferentialsorbothwithintheslab.

Curlingisthedistortionofaconcreteslabintoacurvedshapebyeitherupwardsordownwardsbendingoftheedgesofslab.Thisoccurswhenthe

topandbottomoftheslabchangesize(shrink)atdifferingrates.

Curling is more likely to occur when:

n Thereisasignicantdifferenceineithermoisturecontentortemperaturebetweenthetopandbottomoftheslab

n Theconcreteslabisrelativelythin

n Whenthedistancebetweenjointsislarge

n Theslabisunreinforced

How to avoid problems with Curling:

n Utilizethebestpossiblecuringsystemandconsiderextendingthecuringperiod

n Usethelowestpracticalwaterslumpandavoidretemperingwithwater

n Avoidtheuseofvapourbarriersbeneaththeslab

n Implementmixdesignprincipalsthatminimizeconcreteshrinkage(thelargestpossiblecoarseaggregatesize,minimizethecement

content,etc.)

n Useasmallerjointspacingtoreducethesizeoftheresultingconcrete

panels

n Considerincreasingthethicknessoftheconcreteslaband/orutilizeslab

reinforcementtoreducecurling

n Considertheuseofspecialtychemicaladmixturestoreduceconcrete

shrinkage/curling

References:1. ConcreteinPractice#19CurlingofConcreteSlabsNationalReadyMixed



CurlingCurling

Illustrationofcurlingofaconcreteslabongrade

Exampleofdifferentlevelsofconcretecurlingbasedupontwodifferentmixdesigns


9/20

Problem:

Defnition:

Thedepartureorvariationofcolourfromthatwhichisnormalordesired.

Discolourationcantakemanyformsinconcrete.Theseformsinclude:gross

colourchangesoverlargeareasofconcretetypicallycausedbychangestotheconcretemix;lightpatchesofdiscolourationcausedbyeforescence;

darkblemishesoramottledsurfaceappearance.

Discolouration is more likely to occur when:

n Therearesignicantchangestothemixdesignrelatedtotheraw

materials(cementitiousmaterials,aggregates,admixtures,etc.)

n Therearesignicantchangesintherateofhydrationovertheconcrete

slabtypicallyduetoinconsistentcuringperiodsoroperations

n TherearesignicantvariationsintheW/CMratiooftheconcrete

n Chemicaladmixturessuchascalciumchlorideareusedintheconcrete

n Theatworknisherimproperlyestimatesthetimingofthenishing

operationsresultinginahard-troweledsurface

How to avoid problems with Discolouration:

n Eliminatetheuseofcalciumchloride.Concreteisfarmorelikelyto

discolourwhencalciumchlorideisused

n Conductnishingoperationsatthecorrecttime.Earlynishingtends

toelevatethewater/cementingmaterialsratioatthetopsurfaceandlightenthecolour.Latenishingtendstolowerthewater/cementing

materialsratioatthetopsurfaceanddarkenthecolour

n Implementauniformcuringsystemforthenecessarytimeperiod.

Unevencuringdirectlyaffectsthedegreeofhydrationofthecementandthecolouroftheconcrete

n Ensurethatplasticsheeting,whenusedforcuringpurposes,doesnot

comeindirectcontactwiththeconcrete.Plasticsheetingtendstoleave

colourstreaksontheconcretesurfacewhereitisindirectcontactwith

theconcrete

n

Utilizeeffectiveformreleaseagentsthatpreventthenon-uniformloss

ofmoisturefromtheformedsurface

n Ensurethattherawmaterialsourcesarenotvariedduringtheconcrete

placement.Architecturalconcreteprojectsmayrequirethestockpilingof

rawmaterialsattheconcreteplant(ataconsiderablecost)fortheentire

project

References:1. ConcreteinPractice#23DiscolorationNationalReadyMixedConcreteAssociation


DiscolourationDiscolouration

Discolouringofaresidentialdrivewayduetotheuseofcalciumchloride(accelerator)inonlyoneofthetwoloads

Theproperapplicationofacuringcompound

Photos courtesy of C


10/20

Problem:

10

Defnition:

Thedevelopmentofapowderedmaterialatthesurfaceofhardened

concrete.

Dustingistheformationofloosepowdercausedbythedisintegrationofthetopsurfaceoftheconcreteduetoanextremelyweaksurface.

Dusting is more likely to occur when:

n Anynishingoperationisperformedwhilethereisbleedwateronthe

topsurfaceoftheslab

n Theconcreteisnotproperlycuredresultinginanextremelyweaksurface

n Theconcreteisexposedtocarbondioxidewhilestillinitsplasticstate

n Theconcretesurfaceisnotprotectedduringtheinitialconcrete

placement(wind,rain,snow,freezing)

How to avoid problems with Dusting:

n Donotperformanynishingoperationsontheconcretewhilebleed

waterisstillpresentonthesurface.Ifthenishingoperationsworkthe

bleedwaterbackintotheconcretetheyelevatethew/cmratioofthe

surfacelayersignicantlyanddramaticallyreducethesurfacelayers

strength

n Initiatepropercuringpracticesassoonaspossibleandcurethe

concreteforthespeciedperiod

n Avoidplacingconcreteonvapourbarrierssincetheycanextendthe

bleedingperiodintotheinitialset/nishingperiod

n Ensurethatallheatingdevicesandconstructionequipmentisvented

outsidetheworkareatoavoidcarbondioxidebuild-upabovetheslab

whiletheconcreteisstillplastic

n Addingwatertotheconcretesurfacetoaidthenishingoperationswill

signicantlyweakenthesurfaceandincreasetheproblemswithdusting

References:1. ConcreteinPractice#1DustingConcreteSurfacesNationalReadyMixed



DustingDusting

Anexampleofadustingconcretesurface

Properconcretecuringpracticessignicantlyreducedustingproblems



11/20

Problem:


Defnition:

Voidsleftinconcreteduetofailureofthemortartoeffectivelyllthe

spacesamongcoarseaggregateparticles.

Honeycombingofconcretetypicallyoccurswhentheconcreteisallowedtosegregateduetoobstructionsintheowofconcreteduringplacementor

duetoinadequateconsolidationtechniquesaftertheconcreteisplaced.

Dependingontheextentandlocationofthehoneycombing,thisdefectcan

beeitheracosmeticorstructuraldefectinthenalproduct.

Honeycombing is more likely to occur when:

n Theconcreteelementcontainsreinforcingsteelthatlimitstheabilityof

theconcretetoowthroughtheformwork

n Thereislimitedaccessorlocationsforplacingconcreteintheformwork

resultinginlargespacingsbetweenconcreteplacementlocations

n Highconcentrationsofreinforcingsteelpreventtheinsertionofinternal

concretevibratorsinkeystructurallocations

n Largesizecoarseaggregateisusedinthemixdesignandreinforcement

ispresentintheformwork

n Concretemixdesignsarenotproperlyproportionedforthenecessary

owabilityandworkability

How to avoid problems with Honeycombing:

n WorkwiththeEngineerandthereinforcingsteelcontactortominimize

restrictionsduetoreinforcingsteel.Thiscanincludetheresizingofthe

rebarandavoidingrebarlapsplicesinkeystructuralareas

n Ensurethatoptimumconcretevibrationpracticesarefollowed.This

includesdecreasingtheheightofthelifts,reducingthedistance

betweenvibratorinsertions,etc.

n Designingorre-engineeringtheconcreteelementtoallowforacceptable

concreteplacementmethodsandlocations

n Allowingthecontractortoselecttheappropriateconcreteslumpforthe

placementtechniquebeingutilized

n Designingthemixtooptimizeowabilityandtominimizethecoarse

aggregatesize

n Consideringtheuseofspecialtyconcreteproductslikeselfconsolidating

concrete(SCC)

References:1. PlacingandVibratingPouredConcreteWallsConcreteConstruction2. ConcreteConstructionTroubleshootingTipsTheAberdeenGroup


HoneycombingHoneycombing

Honeycombinginaresidentialshearwall

Honeycombinginaconcretecolumn

SelfConsolidatingConcrete(SCC)canbeusedtosuccessfullyaddresschallengingconcreteplace-ments.However,pleasekeepinmindthatthequalitoftheformworkisalsocriticalsincetheformworksurfacewillbeperfectlymirroredintheconcreteelement


12/20

Problem:

12

Defnition:

Whenthetestresultsfromtheconcretecylindersorbeamsusedasthe

basisofmaterialacceptancefailtomeetthestrengthrequirementsofCSAA23.1Clause4.4.6.6.1.

CSAA23.1recognizesthefactthatwhenconcreteisproportionedtomeet

therequirementsofthestandardlowstrengthresultswilloccurabout

onceortwiceperevery100tests.Acceptableconcretecomplieswiththe

requirementsofCSAA23.1Clause4.4.6.6.1when:

n Theaveragesofallsetsofthreeconsecutivestrengthtestsforthatclass

ofconcreteequalorexceedthespeciedstrength

n Noindividualtestresultismorethan3.5MPabelowthespecied

strength

Low Concrete Strength Results are morelikely to occur when:

n Theconcretetestingisperformedbyunqualiedpersons

n CSAA23.1/.2concretetestingrequirementsarenotfollowed

n Whentestspecimensareimproperlyhandled,curedandtested

n Thejobsiteadditionofexcessiveamountofwaterisallowed

n Thewrongconcreteisorderedfortheconcreteplacement

How to avoid problems with Low ConcreteStrength Results:

n EnsurethatallconcreteeldtestingisonlyperformedbyCSAorACI

Certiedconcretetechnicians

n Ensurethatallconcretetestingisperformedinstrictaccordancewith

CSAA23.1/.2

n Verifythattheproperfacilitiesexistforthesitestorageoftestsamples

priortothestartofconcreteplacement.Everyjobsiteshouldincludea

curingboxwhichmaintainsthesamplesatatemperaturebetween15C

and25C

n Reviewtheconcretedeliveryticketforeveryloadofconcreteand

comparethattospecicationrequirementsfortheelementbeing

constructed

n UtilizethePre-PourMeetingFormtoclearlydesignatethepersonwith

authorityforjobsitewateradditionandspecicallydenetheconditions

whenwateradditionwillbeallowed

References:1. CIP#9LowConcreteCylinderStrengthNationalReadyMixedConcreteAssociation2. ConcreteConstructionTroubleshootingTipsTheAberdeenGroup


Low Concrete Strength ResultsLow Concrete Strength Results

Concretecylindersusedforconcreteacceptancepurposesmustbestoredinatemperaturecontrolledenvironment-notlefttobakeinthesun

Anexampleofpropereldcuringmethodsincludestheuseofatemperaturecontrolledcuringbox

Photos courtesy of RMCAO


13/20

Defnition:

Shrinkagecracksthatdevelopbeforethecementpaste,mortar,grout,or

concretesets.

Plasticshrinkagecracksarecausedbytherapidlossofwaterfromthesurfaceoftheconcretebeforetheconcretehashadtimetoset.These

cracksformafterconcreteplacementandconsolidation,whiletheconcrete

isstillplastic.Theyarerelativelyshallowindepthandtendtoformin

paralleltooneanother.Thecracksareunappealingbutrarelycause

signicantdamagetothestrengthordurabilityoftheoorduetotheir

shallowdepth.

Plastic Shrinkage Cracking is more likely

to occur when:

n Thereisarapidlossofmoisturefromthesurfaceoftheconcrete

n Thereislowrelativehumidity

n Thereishighambientairorconcretetemperatures

n Highwindsareblowingacrosstheslabsurface

n Limitedbleedwaterispresentintheconcreteresultinginrapidsurface

moistureloss

How to avoid problems with Plastic

Shrinkage Cracks:

n Considererectingwindscreensorsunshadestoreducethesurface

evaporationrate

n Utilizefogsprayingequipmentontheup-windsideoftheslabto

maintaintherelativehumidityoftheslabat100%

n Considerpre-dampeningthesub-gradeduringhotdryweathertoreduce

themoisturelossfromtheconcreteintothesubgrade

n Considertheuseofsyntheticbrestoresistthetensileforcescreated

duringtheplasticshrinkageperiod

n Considerplacingtheconcreteduringoff-hourstoavoidhigh

temperature,highwind,highsunexposureperiods

n Considertheuseofevaporationretardantchemicalsappliedbetween

thevariousnishingoperationstopreventtherapidlossofmoisture

fromthesurfaceoftheconcrete

References:1. CIP#5PlasticShrinkageCrackingNationalReadyMixedConcreteAssociation2. ConcreteConstructionTroubleshootingTipsTheAberdeenGroup


Plasticshrinkagecracksonexterioratwork

CSAA23.1denesSeveredryingconditionsaswhesurfacemoistureevaporationexceeds1.0kg(m2.hr


Plastic Shrinkage CrackingPlastic Shrinkage CrackingProblem:


14/20

Problem:

14


Defnition:Localakingorpeelingawayofthenear-surfaceportionofhardenedconcreteor

mortar.

Scalingbeginsassmalllocalizedpatchesoftheconcretesurfacethatdebonds

fromtheconcretetypicallyduetofreeze-thawexposure.Withtimetheselocalized

patchescanexpandandmergetogethertoproducelargescaledareas.Thevarious

levelsofscalingaredenedbytheAmericanConcreteInstitute(ACI)as:

n Light ScalingScalingoftheconcretethatdoesnotexposethecoarseaggregate

n Medium ScalingScalingoftheconcretethatinvolveslossofsurfacemortarto5to10mmindepthandexposureofthecoarseaggregate

n Severe ScalingScalingthatinvolveslossofsurfacemortarto5to10mmindepthwithsomelossofmortarsurroundingtheaggregateparticlesof10to

20mmindepth

n Very Severe ScalingScalingthatinvolveslossofcoarseaggregateparticlesaswellasmortargenerallytoadepthgreaterthan20mm

Scaling is more likely to occur when:n Theconcretecontainsinsufcientairentrainmentorisnon-airentrained

n Theconcretehasnotbeenproperlycured

n Theconcreteisexposedtodeicingchemicalsofanytype

n Improperconcretehasbeenutilizedforexteriorapplications.TheOntarioBuildingCodeandCSAA23.1bothspecifyaminimumof32MPa,0.45W/CM,

airentrainedconcreteforexteriorapplicationsexposedtofreeze-thawcyclesanddeicingchemicals

n Whennishingoperationsarecompletedwhilethebleedwaterisstillonthe

concretesurface

n Theconcreteisplacedduringadverseweatherconditions(extremeheat,extremecold,duringtherain,etc.)

How to avoid problems with Scaling:n Orderandplacetheproperconcretefortheapplication(32MPa,0.45W/CM,

airentrainedconcrete)

n Properlycuretheconcrete.Exteriorconcreterequiresaminimumof7dayscuringinordertoensurethattheconcretesurfacedevelopsthenecessarydurabilitypropertiestoresistscaling

n Avoidtheuseofdeicingchemicalsontheconcretesurface.Deicingchemicals

shouldnotbeusedatallduringtherstwinterandonlysparinglyafterthat

n

Avoidtheuseofdeicingchemicalsthatchemicallyattackconcreten Allowatleast30daysofairdryingoftheconcreteslabafterthecuringperiod

beforeexposingtheslabtofreeze-thawcycles.Theelevatedmoisturecontentof

newconcreteinitiallyreducestheeffectivenessoftheairentrainment

n Considertheproperuseofconcretesealerstoreducetheabsorptionofmoisture

andchloridesintotheconcrete

n Utilizewetcuringmethodsduringhotweatherandseveredryingconditionsand

fogspraytheconcretesurfacebetweennishingoperations

References:1. CIP#5PlasticShrinkageCrackingNationalReadyMixedConcreteAssociation2. ConcreteConstructionTroubleshootingTipsTheAberdeenGroup3. ACI116CementandConcreteTerminologyAmericanConcreteInstitute4. DesignandControlofConcreteMixtures7thEditionCementAssociationofCanada

5. OntarioBuildingCode2000,OntarioMinistryofMunicipalAffairsandHousingHousingDevelopmentandBuildingsBranch

Lightscalingofaconcretesidewalk

Mediumscalingofaconcretesidewalk

Properconcretecuringpracticessignicantlyreduceinstancesofconcretescaling

ScalingScaling


15/20

Uncontrolled Shrinkage CrackingUncontrolled Shrinkage CrackingProblem:

Defnition:

Crackingofastructureormemberduetofailureintensioncausedbyexternalor

internalrestraintsasreductioninmoisturecontentdevelops,carbonationoccurs,orboth.

Concretebothexpandsandcontractswithchangesinmoistureandtemperature

anddeectsdependingontheelementsize,reinforcing,loadingforceandsupport

conditions.Allthesefactorscanleadtouncontrolledcrackingiftheproperdesign

andjointdetailsarenotaddressedpriortothetimeofconstruction.Inorderto

preventuncontrolledshrinkagecrackingthedesignerandthecontractorshould

effectivelyutilizethefollowingconcretejointingsystems:

n Isolation Joints Jointsthatpermitbothhorizontalandverticalmovementbetweentheslabandtheadjacentconcrete

n Contraction Joints Jointsthatpermithorizontalmovementoftheslabandinducecontrolledcrackingatpre-selectedlocations

n Construction Joints Jointsthatarestoppingplacesintheprocessofconstruction

Uncontrolled Shrinkage Cracking is more likely

to occur when:n Thedesignerorcontractorhasnotdevelopedaproperjointingsystemandlayout

priortothestartofconcreteplacement

n Thesub-gradeisnotproperlypreparedandcompacted

n Thereisjobsiteadditionofexcessiveamountsofwater

n Impropernishingproceduresareimplementedortheinstallationofcontraction

jointsisnotcompletedinatimelyfashion

n Thereisinadequateconcretecuring

How to avoid problems with Uncontrolled

Shrinkage Cracks:n Ensurethatthesubgradeisadequatelypreparedbasedupontheexposureand

loadingconditionsthattheslabwillbeexposedtoduringitsservicelife.This

includesusingtheappropriatethicknessofgranularsub-basefortheapplication

andproperlycompactingthesub-base

n Ensuringpositivedrainageofboththesub-gradeandtheconcretesurfaceto

avoidthebuild-upofhighmoisturelevels

n Utilizingtheproperconcretefortheapplication(SeeCSAA23.1minimum

durabilityrequirements)

n Thedesignerandthecontractorshouldreviewtheconcretejointingdetails

priortothestartoftheproject.Itemstoconsiderincludeconcretethickness,

maximumjointspacing(4.5mmax.),brereinforcement,structural

reinforcementandearlyinstallationofcontractionjoints

n Implementcuringproceduresassoonaspossibletoensurethatthe

performancepropertiesoftheconcretefullydevelop

References:1. CIP#4CrackingConcreteSurfacesNationalReadyMixedConcreteAssociation2. ConcreteConstructionTroubleshootingTipsTheAberdeenGroup



Designandconstructionofaproperisolationjoint

Designaconstructofpropercontractijoints

Designandconstructionofproperconstructionjoints

Ifyoufaiproperlydesignfoshrinkageuncontrorandomcrackswoccur


16/20

Problem:

16

Defnition:

Thedislodgingofsmallsectionsofconcretemortardirectlyovertopofthe

coarseaggregateparticlesinexteriorconcreteexposedtofreeze/thaw

conditions.

Mortarakingtypicallyoccursinexterioratworkthatwasnotproperly

curedduringtherst7to28days.Mortarakingistypicallyveryshallow

indepthandconsistsofdistinctdelaminations(akes)thatoccurdirectly

overtopofthecoarseaggregateparticlesintheconcrete.Thisistypically

duetothefactthattheconcretemortardirectlyovertopofthecoarse

aggregatewasallowedtodryoutandwasnotproperlycured.Anyexcess

bleedwaterthatispresentintheconcreteisforcedtotravelaroundthe

coarseaggregateparticlesasitrisestothesurfaceandthemortardirectly

abovefailstodevelopthenecessarystrengthrequiredtoachieveproper

durabilityandbond.

Mortar Flaking is more likely to occur when:

n Theconcreteisplacedduringperiodsofrapidsurfacedrying

n Whentheconcreteisnotcuredatall

n Whencuringcompoundisappliedtoolateafterconcreteplacementor

notuntilthefollowingday

How to avoid problems with Mortar Flaking:

n

Ensurethepropercuringproceduresarefollowedatalltimes!Properconcretecuringshouldeliminatethisproblem

n Duringperiodsofrapidsurfacedryingconsiderusinginitialcuring

procedureslikeevaporationretardantsorplacingplasticsheetingover

theconcretesurfacebetweennishingoperations

n Considertheuseofwetcuringmethodsduringseveredryingandhot

weatherconditions

n Considertheuseoffogsprayingsystemstoprotectthesurfaceofthe

concretefromdryingoutuntilwetcuringcanbeinitiated

References:


Mortar FlakingMortar Flaking

MortarakingonaconcretesidewalkNotethattheaggregateissoundandonlythemortarabovetheaggregatehasfailed

Cross-sectionthroughamortarakenotethatonlythemortarabovethecoarseaggregatehasfailed

Photos courtesy of RMCAO and CTL


17/20

Photos courtesy of RMC

Defnition:

Conicalfracturesoftheconcretesurfacecausedbytheexpansionofice

insideporouscoarseaggregateslocatedjustbelowtheconcretesurface.

Popoutsresultwhensoftporousaggregates,foundbothinlimestoneandgravelsources,undergofreeze/thawconditionsinasaturatedstate.While

airentrainmentprovidesprotectionforthecementpastefromtheexpansive

forcesgeneratedduringwinterfreeze/thawcycles,itdoesnotprovideany

protectionforthecoarseaggregateparticles.Ifthelocalaggregatesources

containevenasmallpercentageofsoft,porousparticles(likechert),the

coarseaggregatecanabsorbsignicantquantitiesofmoistureandfractures

duringfreeze/thawcycles.Theresultingexpansionfracturesboththe

aggregateandthesurroundingconcrete.Popoutsaredistinguishedfrom

mortarakingbythepresenceoffracturedaggregateinthepopout(as

showninthesamplephoto).

Popouts are more likely to orm when:

n Thelocalaggregatesourcescontainsoft,porousmaterial

n Theconcreteisinafullysaturatedcondition

n Theconcretehasntachieveditsultimatedurabilitypotentialdueto

inadequatecuring

How to avoid problems with Popouts:

n

Considertheuseofalternativeaggregatesources.Thismayrequiretheimportofaggregatesatasignicantadditionalexpense

n Considerchangestotheaggregateprocessingprocesstofurtherreduce

thequantityofsoftporousmaterial(thecompleteeliminationofallsoft

materialisnotnormallypossible)

n Ensurethattheoveralldesignminimizesthebuild-upofexcessmoisture

intheconcrete.Thiscanbeachievedthroughpropersurfacegrading

anddrainingofthesurroundingsubgrade

n Ensurethatproperconcretecuringandprotectionpracticesarefollowed

toachievethehighestpossibleconcretedurability

n Considertheuseofsealerstolimittheinowmoistureintotheconcrete

References:


Popoutsurfacedamagecasedbythefractureofasoftaggregateparticleduringwinterfreeze/thawcycles

Across-sectionalviewofaconcretecoretakenfromapopoutareanotethelargechertparticleinthislimestoneaggregatesourcethatisresponsiblefortpopout

PopoutsPopoutsProblem:


18/20

To Obtain Multiply By To Obtain Multiply By

millimetres inches 25.40

centimetres inches 2.54

centimetres feet 30.45metres feet 0.3048

metres yards 0.9144

kilometres miles 1.6093

inches millimetres 0.03937

inches centimetres 0.3937

inches metres 39.37

feet metres 3.281

feet kilometres 3280.90

yards metres 1.094

yards kilometres 1094.60

miles kilometres 0.61

grams ounces 28.35

kilograms pounds 0.4536

kilograms shorttons 907.185

kilograms longtons 1016.05

tonnes pounds 0.0004536

tonnes shorttons 0.9072

ounces grams 0.035

pounds kilograms 0.2205

pounds tonnes 2204.59

shorttons kilograms 0.0011

shorttons tonnes 1.1023

longtons kilograms 0.0010

longtons tonnes 0.9842

squareinches centimetres2 0.1550

squarefeet centimetres2 0.00108

squarefeet metres2 10.764

squareyards squarefeet 0.1111

squareyards metres2 0.3987

acres metres2 0.000247

acres hectares 2.471

squaremiles hectares 0.003861

centimetres2 squareinches 6.4529

metres2 squarefeet 0.0929

metres2 squareyards 0.8361

kilometres2 squaremiles 2.59

kilometres2 acres 0.00404

cubicinches cm3 0.06104

cubicinches litres 61.02

cubicfeet m3 35.3143

cubicfeet litres 0.3532

cubicyards m3 1.3079

Imp.gallons cubicfeet 6.236

Imp.gallons litres 0.22

Imp.gallons m3 219.97

cm3 cubicinches 16.387

cm3 cubicfeet 28.32

m3 Imp.gallons 3.154

m3

cubicyards 0.764

C F 5/9(F-32)

F C (9/5C)+32

MPa psi 0.006895

psi MPa 145

LENGTH

AREA

TEMPERATURE

WEIGHT/MASS

VOLUME/CAPACITY

PRESSURE

Conversion TableConversion Table

18


19/20

Concrete ApplicationClass oConcrete

MaximumW/CM

Minimum28d Strength

(MPa)

Chloride IonPermeabilityat 56 days

ReerenceStandard

Agricultural

Reinforcedbeams,slabsandcolumnsovermanurepitsexposedtoseveremanuregases

A1 0.40 35 1500Coulombs CSAA23.1-09

Reinforcedwallsinexteriormanuretanks,silos,

andfeedbunkersexposedtoseveretomoderate

manuregases

A2 0.45 32 N/A CSAA23.1-09

Structurallyreinforcedinteriorwalls,beams,

slabsandcolumnsinacontinuouslysubmerged

conditionexposedtomoderatetoseveremanure

gases

A3 0.50 30 CSAA23.1-09

Non-structurallyreinforcedslabsongradeexposedmoderatemanuregasesorliquidswithoutfreeze-thawexposure

44 0.55 25 CSAA23.1-09

Industrial/Commercial/Institutio

nal

HighPerformanceConcrete CXL 0.40 50within56days 1000Coulombs CSAA23.1-09

Structurallyreinforcedconcreteexposedtochlorides(Bridgedecks,parkingdecks,etc.)

C1 0.40 35 1,500Coulombs CSAA23.1-09

Non-structurallyreinforcedconcreteexposedto

chloridesandfreezingandthawing(Garageoors,

pavements,sidewalks,curbs,etc.)

C2 0.45 32 CSAA23.1-09

Continuouslysubmergedconcreteexposedto

chloridesbutnotfreezingandthawing(Under-waterportionsofmarinestructures)

C3 0.50 30 CSAA23.1-09

Non-structurallyreinforcedconcreteexposedto

chloridesbutnotfreezingandthawing(Under-

groundparkingslabsongrade)

C4 0.55 25 CSAA23.1-09

Concreteexposedtofreezingandthawingina

saturatedconditionbutnottochlorides(Pool

decks,patios,tenniscourts,etc.)

F1 0.50 30 CSAA23.1-09

Concreteinanunsaturatedconditionexposedtofreezingandthawingbutnottochlorides(Exterior

wallsandcolumns)

F2 0.55 25 CSAA23.1-09

Concretenotexposedtochloridesorfreezingand

thawing(Footingsandinteriorslabs,wallsand

columns)

N SpeciedbytheDesigner CSAA23.1-09

Residential

Footingsforwalls,columnsandchimneys R1 0.7015

(36%air)CSAA23.1-09

Foundatio ns,walls,gr adebeams,piers,etc. R2 0.7015

(47%air)CSAA23.1-09

Interiorslabsongroundnotexposedtofreeze-

thawwithoutavapourbarrierbeneaththeslabR3 0.65 20 CSAA23.1-09

Garageoorsandallconcreteexposedtofreezing

andthawinganddeicingchemicals(Driveways,sidewalks,patios,steps,etc.)

C2 0.45 32 CSAA23.1-09

OwnermayorderconcretetoPerormance Specifcations(concretesupplierisresponsibleforconcreteasdelivered)orPrescriptive Specifcations(Ownerisresponsibleforconcreteasdelivered).

DetailedConcreteMixProportionsshallnotbedisclosedbytheconcretesupplier.

CONCRETE PLANT CERTIFICATION SPECIFICATION:The concrete supplier shall submit to the concrete purchaser a currently valid Certifcate o Ready Mixed Concrete Production Facilities or a currently Certifcate o Mobile Mix Concrete Production Facilities as issued by the Ready Mixed Concrete Association o Ontario to the plant being used.

References:

1.OntarioBuildingCode-2006,OntarioMinistryofMunicipalAffairsandHousing-HousingDevelopmentandBuildingsBranch

2.CSAA23.1-09ConcreteMaterialsandMethodsofConcreteConstruction,CanadianStandardsAssociationInternational

WiththepermissionofCanadianStandardsAssociation,materialisreproducedfromCSAStandardA23.1-09/A23.2-09, Concrete Materials and Methods of Concrete Construction/Methods of Test and Standard Practices for ConcretewhichiscopyrightedbyCanadianStandardsAssociation,178RexdaleBlvd.

Toronto,Ontario,M9W1R3.Whileuseofthismaterialhasbeenauthorized,CSAshallnotberesponsibleforthemannerinwhichtheinformationispresented,norforanyinterpretationsthereof.A23.1/23.2-04isintendedtobeusedinitsentirety.Cautionshouldbeexercisedinextractingindividualclausesortab

andusingtheminprojectspecications,sincetakingthemoutofcontextcanchangetheirmeaning.For more information on CSA or to purchase standards, please visit their website at www.shopcsa.ca or call 1-800-463-6727.

Concrete Quick SpecConcrete Quick Spec


20/20

www rmcao org

THISINFORMATIONTOBEUSEDASAGUIDELINEONLY.FORMOREDETAILEDINFORMATIONORSPECIFICATIONS,PLEASECONSULT REFERENCES.

Photoscourtesyof:

CAC-CementAssociationofCanada

CTL-ConstructionTechnologyLaboratories,

Inc.

RMCAO-ReadyMixedConcreteAssociation

ofOntario

Preparedby:

Ready Mixed Concrete

Association of Ontario

365BrunelRoad,Unit#3

Mississauga,OntarioL4Z1Z5

Tel:905.507.1122

Fax:905.890.8122

Email:[email protected]

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