Twenty-FirstAnnualWestfordSymposiumonBuildingScience

Westford,MA

VaporBarriersInCompactRoofAssemblies

Presenter:MattDupuisPhDPESRIMiddleton,WI

August1,2017

Topics

• ProblemStatements• ConcreteBasics• ConcreteandMoisture• FieldExamples• Research• Recommendations• Questions

ProblemStatements

• Theroofingindustryhasseenadramaticincreaseinmoisturerelatedfailuresfromroofingoverconcreteroofdecks,bothnewconstructionandreroofs.• ThecompressedschedulesinnewconstructionhaveseenGeneralContractorsdirect(demand)theinstallationovergreenconcrete,afteronlydays.• MostabsurdreporttoSRIwas3days!• Materialsandtechniquesforinstallingroofshaschangedfocusingonlaborefficiencyandenvironmentalfriendlyfactors

ProblemStatements

• Theroofingindustryhaslittletonoguidanceontheacceptanceoftheconcretesubstrateassuitabletobegininstallingaroofsystem.• TheguidancethatdoesexistforindirecttestingofroofdecksistypicallylegacyspecificationlanguagetracingitsoriginstobeforeIwasborn

BasicsofConcrete

BasicsofConcrete

•PortlandCementisnotconcrete• PortlandCementisthebindingagent• Concreteisthecompositematerial• Aggregates• Coarse40%-50%byvolume• Fine20%- 30%byvolume

• PortlandCement15%-20%byvolume• Water15%-20%byvolume• Additional“adds”typically<1%

BasicsofConcrete• Additionalcomponents

• Fibers• Accelerators• Retarders• Water reducers• Air entrainment• Fly Ash• Silica Fume• Waterproofing• Magic Pixie Dust

BasicsofConcrete

• ProductionofConcrete• Eachbatchplantwillhavehundredsoreventhousandsofrecipes• Basedonlocalaggregatesandconditions• Requirementsoforderdictatewhichonetheyuse• Developedovertime• Scienceandtrial&error

• Formsforroofdecks• Strippableforms• Steelformdeck

CuringofConcrete

• Note wearediscussingcuringnotdrying• Chemicalprocessofhydration• Allaboutcompressivestrengthgain• Lossofmoistureduringthisprocesscanhaveadverseeffects• Moistcure• Protectfromfreezing

CuringofConcrete

• StructuralEngineerspecifiedstrength• Typicallyspecifiedat28-daycompressivestrength• i.e.5000psiat28days

• 28-dayshasnothingtodowithmoisturecontentonlycompressivestrength

MoistureinConcrete

FactorsThatAffectDrying

• Climacticconditions• Concretesurfacecondition• Rewettingofconcrete• Rain,snow,ice,condensate

• Capillaryclosure

MoistureinConcrete

• EffectsofCuringandDryingEnvironmentsonSplittingandTensileStrengthofConcrete• J.AHanson• 1968

MoistureinConcrete

EffectsofCuringandDryingEnvironmentsonSplittingandTensileStrengthofConcrete- Hanson

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MoistureinConcrete

• Howdowemeasuremoisturecontentofplacedconcrete?• Surfaceemission• Electricalresistance• Electricalimpedance• RelativeHumidityatdepth

MoistureinConcrete• ASTMD4263StandardTestMethodforIndicatingMoistureinConcretebythePlasticSheetMethod• Veryqualitative• Environmentalconditionscangreatlyinfluenceresults/signal

• Easyandinexpensive• Cangivefalsenegative

MoistureinConcrete

MoistureinConcrete

• ASTMF-1869MeasuringMoistureVaporEmissionRateofConcreteSubfloorUsingAnhydrousCalciumChloride• DishofCalciumChlorideisweighedbeforeandafter24hrexposureunderaclearlid• Returnspoundsofwateremittedper1000ft²per24hours• Veryoldtest

MoistureinConcrete

• CalciumChloridetest

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MoistureinConcrete

• ASTMF-2420DeterminingRelativeHumidityontheSurfaceofConcreteFloorSlabsUsingRelativeHumidityProbeMeasurementandInsulatedHood• Uncommontest• Usesarelativehumidityprobeplacedontopofslabinsideasmallinsulatedbox• Givesindicationofmoistureatsurfacenotwhatisintheslab• Uncommontest

MoistureinConcrete• HumidityProbeMeasurementandInsulatedHood

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MoistureinConcrete

• Electricalresistancemeasurement• Drilltwoholesinconcrete• “brush”probesinsertedandresistancebetweenprobescorrelatedtomoisturecontent• NotseenintheUScurrently

MoistureinConcrete

• Impedancemeasurementofconcretesurface• Electricfieldispassedthroughconcrete• Instrumentreadsoutmoisturecontentpercentage.• Onlyreadstop1.5inchesofslab

MoistureinConcrete

• Tramex CMEXII

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MoistureinConcrete

• ASTMF-2170DeterminingRelativeHumidityinConcreteFloorSlabsUsinginsituProbes• Drillholeinconcretedeck• 40%ofdepth

• Relativehumidityprobeinsertedintohole• Sealed• Recovered/readafter72hours

• (24hoursworksjustfine)

MoistureinConcrete

• ASTMF-2170(Continued)• FlooringmanufacturersrequireminimumRHreadingdeliveredviaF-2170beforefloorisallowedtobeinstalled• Wideacceptance• LotsofResearch

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MoistureinConcrete

• Flooringindustrystruggledwiththeissueconcretefloorsandfailuresattheturnofthecentury• Flooringmanufacturersspecifyatwhattestvalues(moisturecontent)theirproductscanbeinstalledoverconcrete• Typicalvaluesrangefrom80%to90%RHviaF2170

MoistureinConcrete

• Howeverfloorsandroofsexistindrasticallydifferentenvironments• Floorscanbelefttillneartheendoftheconstructioncycle• Roofneedstogoonveryearly• Floortypicallyhasconditionedair

• Temperatureandhumidity• Roofisexposedtoweather

• Rewetting

BadandWorse

• Sotheflooringcontractorhasiteasyright?• RemembertheHansongraphs?

BadandWorse

EffectsofCuringandDryingEnvironmentsonSplittingandTensileStrengthofConcrete- Hanson

BadandWorse• DifferencesbetweenRegularWeightConcrete(RWC)andLightWeightStructuralConcrete(LWSC)• Mass(approximate)• RWC150lb/ft³• LWSC110lb/ft³

• Startingwatercontent• Regularweightaggregateshave8- 15lb/yd³ofconcrete• Lightweightaggregateshave150– 200lb/yd³ofconcrete

• Bothcanachievethesamecompressivestrengths• LWSCdoesitwithlessweight

BadandWorse

• Lightweightaggregates• Expandedshalesandclays• Alternatelyreferredtoas“pre-wettedaggregates”• Needtobepondedorsoakedfordaystomonthsbeforebeingbatchedintoaconcretemix• Waterfillsporesandpreventslightweightaggregatesfrominterferingwithmixpropertiesandperformance

• Lightweightstructuralconcretehasrepeatedlybeenshowntotakemuchlongerthanregularweightconcretetodry.

RecommendedReading

• EngineeringBulletin119:ConcreteFloorsandMoisture• HowardM.Kanare• 2008,PortlandCementAssociation

Fieldexamples(TrainWrecks)

FieldExample#1

• Plazadeckoncorporatecampus• Lightweightstructuralconcreteoversteeldeck• Toolateindesigntoswitchtoregularweightconcrete

• IRMAdesignwithfluidappliedandself-adhesivewaterproofingsheets• Deckallowedtocure/“dry”insummerheatforjustover3months

FieldExample#2

• Eastcoasthospital• Roofdeckdesignedtobefloorforfutureverticalexpansion• Operatingsuitesbelowroofdeck

• LightWeightStructuralConcreteonmetaldeck• FullyadheredEPDMwithtaperedISO• Lowrisefoamadhesiveinribbons

• Inplacefor3years

FieldExample#3

• HospitalintheupperMidwest• Roofdeckintendedtobeafloorforfutureverticalexpansion• LightWeightStructuralConcreteonmetaldeck• FullyadheredEPDMwithtaperedISO• Lowrisefoamadhesiveribbon

FieldExample#3

• Topfloorunoccupied• Noleaksreported• Firstindicationwasfullyadheredmembranebillowinginwind• Belowdesignwinds• 9monthsafteroccupancy

• Manufacturerdeniedwarrantycoverageduetotrappedmoisture(interiormoisture)• Insurancecompanydeniedclaimasdefectiveconstruction

ResearchPhase1

ResearchSponsors

ResearchGoals

• PrimaryGoal• Determinewhatmoisturelevelinconcretedecksisappropriateforroofingoperations• Newconstructionandreroof

• SecondaryGoals• Studyinstrumentationcapabilitiesforspeedandaccuracyinthedeterminationofmoisturelevelsinconcreteroofdecks• Studyimpactofweatherandthephenomenaof“rewetting”onmoisturelevelsinconcreteroofdecks

ResearchPlan

• 4ModulesofthePhase1• BeganpreparationandplanningSpring2016• ConcretepoursoccurredJuly11,2016• Studyisongoing• Newinformationlearnedreshapeshypothesesanddirectionofresearch• Phase2startingAugust-September2017

ResearchProgress

• Phase1Fullscaleconcreteweatheringfarmandlabsamples• Received20.43inchesofrainduringthe16weekperiod• TramexCMEXII- ConcreteMoistureMeterused

• Nodiscernabledifferencebetweeninside,outside,normalweight,lightweight

• Onlywasanindicatorofrecentrain

ResearchProgress

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A B C D E F G H I J

Readingon

Tramex

Slabs

TramexCMEXII- ConcreteMoistureMeterReadings

9/5/2016

9/8/2016

9/20/2016

10/2/2016

10/15/2016

10/21/2016

3.25.1

SurfaceisDry

Moistureisdownhere!

• Phase1• UseofF-2170probes• WagnerMetersinRogueRiver,Oregonprovidedhundredsofprobesandaccessoriesforthisstudy.• Calibratedbeforeuse• Readingstypicallytaken1,2,3,6,and24hoursafterplacementweekly• Pans• Slabs• Replicates• Exteriorpansbroughtinlabandprobeagain

• Thousandsofreadingswithconfoundingvariables• Promisingdataneedmoretimetostudy

ResearchProgress

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12:00:00AM 3:00:00AM 6:00:00AM 9:00:00AM 12:00:00PM 3:00:00PM 6:00:00PM 9:00:00PM 12:00:00AM

RelativeHu

midity

(%)

Time

F-2170InsertedintoNormalWeightConcrete(15daysafterpour)

ResearchProgress

• Phase2Hygrothermalcharacterizationofconcrete• E96VaporPermeability• C1794WaterAbsorptionCoefficient• C1498HygroscopicIsotherm• C1699MoistureRetention

ResearchProgress

• Module2Hygrothermalcharacterizationofconcrete

ASTME96calculatedPerm·inLightWeightStructural

ConcreteNormalWeight

ConcreteAge WetCup DryCup WetCup DryCup

28Day 1.48 0.78 3.42 1.0560Day 1.45 0.47 2.03 1.13

ResearchProgress

• Module3Hygrothermalmodeling• WUFI5.3ProHygrothermalprogramutilized

• ConsultingwithjustSmartSolutions theU.S.partneroftheGermansoftwarevendor• ThedataoutputfromthemodelinghasbeenvalidatedwithModule1data• Letuslookatsomeofthethingwecanopinefromjustthesimplegraphs!

NormalWeightConcrete– LabDryDown(4Months)

Top1inchofslab

NormalWeightConcrete– OutdoorDryDown(4Months)

Top1inchofslab

TotalWaterContentperFt2 ofslabRegularWeightConcreteChicago,IL(4Mo.)

TotalWaterContentperFt2 ofslabRegularWeightConcretePhoenix,AZ

(4Mo.)

TotalWaterContentperFt2 ofslabRegularWeightConcreteEdmonton,CAN

(4Mo.)

Research

• Usedhygrothermaldataforcurrentgenerationroofingmaterials• Simulatedroofslabsoutdoorsfor28daysthenroofed• Withandwithoutvaporretarders• 100’sofcombinations

Research

• Desertsouthwestgenerallyokwithoutavaporretarder• Canada…justplanonavaporretarder• Southerntierstates…maybe• AtlantaslabgoesdownJuly1=okwithnovaporretarder• AtlantaslabgoesdownDecember1=failwithoutavaporretarder

• So…doIneedavaporretarder…itdepends

Recommendations

• Preliminaryfindingsofconcreteresearchprogrampointtoadistinctissuewithslabsinnorthernandhumidclimates.• Workonhygrothermalsimulationsandtheirvalidationisongoing(Phase2).• Butgiventhecurrentlyavailableresearchdataandobservationsfromit,thisresearcherisrecommendingthat:• UnlesstheDesignerofRecordapprovesinwritingotherwise,avaporretarderoflessthan0.01permisnecessaryovernewconcreteroofdecks.

• Theimpactofrewettingonexistingconcretedecks(reroof)andmoistureladenroofsystemsisbeingdetermined.

ThankYou

ContactInfo:mdupuis@sri-engineering.com