The Super Air Meter: A Test for Plastic Concrete

TheSuperAirMeter:ATestforPlasticConcrete

BradenTabb,RobertFelice,JohnMichaelFreeman,RobertFrazier,DavidWelchel,Morteza Khatibmasjedi,JakeLeFlore

TylerLey,P.E.,Ph.D

Acknowledgements

• OklahomaDOT• FHWA• KansasDOT• NebraskaDOT• IowaDOT• MinnesotaDOT• IdahoDOT• NorthDakotaDOT• ColoradoDOT

• Penn DOT• Connecticut DOT• New Jersey DOT• Illinois DOT• Indiana DOT• Michigan DOT• Wisconsin DOT• RMC Foundation

Outline• IntroductiontoAirentrainedconcrete• WhyistheSAMuseful?

WhyDoWeAddAirtoConcrete?

• Air-entrainedbubblesareakeytothefreeze-thawresistanceofconcrete

Airvolume=freeze-thawperformance

• Smallerbubblesaremoreeffectiveinprovidingfreeze-thawresistanceandhavelessofanimpactonourconcretethanlargerbubbles

TheAir-EntrainmentBlues…

• Themostchallengingaspectofconcretetogetrightistheaircontent.

TheAir-EntrainmentBlues…

• Themostchallengingaspectofconcretetogetrightistheaircontent.

• Largebubblesaretheenemy!

• Volume of air provided is the same for both.

• Case B has a better air void distribution.

A BThis image cannot currently be displayed.

WhatDoYouWantinanAir-VoidSystem?

A B






A B


Large bubbles are more buoyant

Modified C231

Small bubbles

Large bubbles

• Theyleavetheconcreteandchangeyourairvolume

• Theydon’thelpwithfreeze-thawdurability

• Theyreduceyourstrengthmorethansmallerbubbles

Whyarelargebubblesbad?

Whatcauseslargebubbles?• Admixtureincompatibility• Admixture/cementincompatibility• Sandgradation• Inadequatemixing• Alkalicontentofbinder• Cementgrindingaids• Changesintemperature• Pumping

Howdoyoumeasurethem?

Hardened Air Void Analysis

From Hover

0%

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0012

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norm

alize

dAirC

ontentFraction

ChordSize,microns

WROSOnlyPC1+WROS

Freeman et al., 2012

small voids large voids

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norm

alize

dAirC

ontentFraction

ChordSize,microns

WROSOnlyPC1+WROS



Mixture with small bubbles

Mixture with large bubbles

2L

• SpacingFactor– ½oftheaveragedistanceofanaveragesizedvoiduniformlydistributedinthepaste

• DesiredValue<0.008in(ACI201)real concrete idealized concrete

Spacing factorfrom Hover

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ontentFraction

ChordSize,microns

WROSOnlyPC1+WROS



Low spacing factor

High spacing factor

0

0.002

0.004

0.006

0.008

0.01

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0 2 4 6 8 10 12

ASTM

C457Spa

cingFactor,in

Air%

WROS.45

ACI201.2R

Small bubbles

Yes!

No!

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C457Spa

cingFactor,in

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ACI201.2R

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Yes!

No!

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C457Spa

cingFactor,in

Air%

WROS.45

WROS.45+PC1

ACI201.2R

You can’t tell the size of the bubbles by looking at the volume!!!

Small bubbles

Large bubbles

Yes!

No!

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0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00

DurabilityFactor(%)

AirContent(%)

Yes!

No!

0.40 w/cmAdmixtures are not the same

Mix ASmall bubbles

Mix BLarge bubbles

Rapid Freeze Thaw Test

Open symbols failed ASTM C666

0.004

0.006

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2.0% 3.0% 4.0% 5.0% 6.0% 7.0% 8.0% 9.0%

Sp

acin

g F

acto

r (i

n)

Air Content of Concrete (Pressure)

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Sp

acin

g F

acto

r (i

n)


No Polycarboxylate

Polycarboxylate



Mixtures with small bubbles

Yes!

No!

0.004

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Sp

acin

g F

acto

r (i

n)


No Polycarboxylate

Polycarboxylate



Mixtures with large bubbles

Yes!

No!

Summary• Weneedtoknowthesizeofbubbleswithintheconcrete

• Thevolumeofairdoesnottellyouanythingaboutbubblesize

• Althoughahardenedairvoidanalysiscanmeasurethis,itisnotpracticaltorunregularly

SuperAirMeter(SAM)• WehavemodifiedatypicalASTMC231pressuremetersothatitcanholdlargerpressures

• Wehavereplacedthedialgagewithadigitalone

digital gauge

six clamps!

AASHTOTP118

www.superairmeter.com

top chamber

bottom chamber

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50Pr

essu

re (p

si)

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Equilibrium Pressure

Top Chamber

Bottom Chamber

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Air content given here

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release pressure in both chambers

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SAM number

Air content and SAM number given here

Howlongdoesthattake?• WithjusttheSAM• Inexperienceduser– 10min• Experienceduser– 7min

• WiththeCAPE• Inexperienceduser- 7min• Experienceduser– 4.5min

ControlledAirPressureExtenderakaCAPE

Compressed air

Step 1(14.5 psi)Step 2 (30 psi)

Step 3 (45 psi)

Discussion• TheSuperAirMetergivesyoutheairvolumeandtheSAMnumber.

• TheCAPEisaportableairtankandregulatorsthatcanhelpyourunthetestfaster.

WhyistheSAMnumberuseful?

0

0.002

0.004

0.006

0.008

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0.014

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0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

SpacingFactor(in)

SAMNumber(psi)

LabDataOSUFieldDataLABDataFHWA

ACI 201.2R

92% Agreement

Yes!

No

This test takes 7 – 14 days

This test takes 5-10 minutes

83% agreement

PennDOT 50 field mixtures

0

0.005

0.01

0.015

0.02

0.00 0.10 0.20 0.30 0.40 0.50 0.60

SpacingFactor(in)

SAMNumber

Minnesota

CODOT

FHWA

GEIGER

IOWA

MICHIGAN

MIT

NEBRASKA

N.DAKOTA

S.DAKOTA

UDOT

NO

YES! SAM limit 0.20 – 68% agreementSAM limit 0.25 – 79% agreement

10 DOTs over 100 field mixtures

Discussion• TheSAMnumberof0.20correlateswellwiththespacingfactorof0.008”forover350labandfieldmixturescompleted13differentstates.

80% agreement w/ 0.20 limit89% agreement w/ 0.25 limit

No

Yes!

This test takes 3.5 months

This test takes 5 -10 minutes

69% agreement

This test takes 3.5 months

No

Yes!

This test takes 7 - 14 days

Discussion• ASAMnumberof0.20correlatesbettertorapidfreezethawdurabilitythanaspacingfactorof0.008”.

0%

10%

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30%

40%

50%

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100%

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00

DurabilityFactor(%)

AirContent(%)

Yes!

No!

0.40 w/cmAdmixtures are not the same

Mix ASmall bubbles

Mix BLarge bubbles

0%

10%

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30%

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50%

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0 0.2 0.4 0.6 0.8

DurabilityFactor(%)

SAMNumber

Yes!

No!

From Super Air Meter

Mix ASmall Bubbles

Mix BLarge Bubbles

Whyisthisuseful?• TheSAMcantellusaboutthequality(sizeandspacing)ofourairvoidsystembeforetheconcretesets

• Itcantellusaboutthefreezethawdurabilityofourairvoidsystem

• Itcanalsotellusifwewillhaveairvoidstabilityproblemsduringourmixturedesignprocess!!!!

Whyisthisuseful?• Thiscangiveyouimportanttestinginformationthatwasalmostimpossibletogetinthepast

• Thisishelpfulwhen:– mixturesaredesignedinthelab– mixturesareplacedinthefield– trialbatchinginthefield– troubleshootingfieldproblems– measuringvariationinmaterials

HowdoIdothis?

Anexample

• Mix1- SAMnumberof0.22andanaircontentof5%

• Mix2- SAMnumberof0.40andanaircontentof6%

54

Mix 1

Mix 2

This is crazy valuable!!!!!!

PennDOT

Discussion• ByplottingyourdataontheSAMCurveyoucanimmediatelytellifyourairvoidsystemismadeoflargeorsmallbubbles.

• Thisimmediatefeedbackcanbeusedtotroubleshootfieldissuesandgiveyoufeedbackonyourconcretemixturedesign.

ThefollowingstateshaveaSAM

• Michigan(5)• Kansas(16)• Utah• Colorado(2)• Iowa(2)• Illinois(5)• Indiana(2)• Wisconsin(4)• Massachusetts• Idaho(2)• Tennessee(2)

• Pennsylvania• Missouri(2)• California• N.Carolina(3)• N.Dakota• Oklahoma(10)• Nebraska(3)• Ohio(5)• Minnesota(3)• Texas(2)• FHWA(6)

• Georgia• NewJersey• NewMexico• NewYork(5)• S.Dakota• Mississippi• Iowa(2)• Oregon• Manitoba(5)• Ontario(2)• England• Poland(2)

Testmethods Parameter COV

Agreementwithdurabilityfactorof70inASTMC666

Timetocompletethetest

SAMnumber(OSU) 17.1SAMnumber(workshop**) 18.1

ASTMC457 spacingfactor 20.1 69% 7daysASTMC666 durabilityfactor* 22.7 - 3.5months

*assumingadurabilityfactorof75andmethodB**includesallparticipants

80% 10minAASHTOTP118

Discussion• ThevariabilityofSAMissimilartothevariabilityinthehardenedairvoidanalysisandrapidfreezethawtestingandthetestcanberuninthefieldonfreshconcreteinlessthan10min.

Discussion• Idon’tthinkitisacoincidencethatthevariabilityissosimilarbetweenthethreedifferentmethods.

• Eachtestisdesignedtoinvestigatetheairvoiddistribution.Airvoiddistributionmaybemorevariablethanotherconcretepropertiessuchascompressivestrength.

HowdoyouspecifytheSAM?• 1.ReplacetheairmeterwiththeSAMinthefield

• 2.UsetheSAMduringthemixturedesignstageandvalidateinthefield.

SAMreplacesairmeter

• Aircontentmustbeabove4%

SAM

0.17 0.25 0.30Bonus Full Pay Deduct Remove

and Replace

SAMusedduringmixtureacceptance• Duringmixturedesignstageruntrialbatcheswithair<5%andSAMnumbermustbe<0.25.

• Testairaspertypicalpractice.• ValidatethatSAM<0.25andair>4%onceadayorevery1000yds inthefield.

Ineedyourhelp• Takingtheindustryfromahorseandbuggytoaninternalcombustionengineisnoteasy.

• TrytheSAM!• Askquestions!• Givesuggestions

• Sharewhatyoulearnherewithothers• HelpothersbecomeknowledgeableoftheSAM

Ineedyourhelp• HelpextendmyPooledFundStudy.Weneed5morestates.TPF-5(97)

• MyersAssoc.hasaSAMintheexhibitorhall.

• RequestaSAMfromFHWA

• AASHTOWebinarthisThursday(10/20/16)•

Conclusion

• Largebubblesaretheenemy!• Airvolumedoesnottellyoububblesize.• TheSAMcanmeasurethevolumeandsizedistribution ofthebubblesinfreshconcrete

• Thisishelpfulformakingyourairmoreconsistentandensurefreezethawdurability

Conclusion• ASAMnumberof0.20seemstocorrespondtoaspacingfactorof0.008”

• Over90%ofthelabandfielddataiscorrectlyseparatedwiththislimit

• TheSAMnumbercorrelateswithASTMC666testing

• TheSAMhasbeeninvestigatedbyanumberofothersandallhavefoundsimilarcorrelations

[email protected]

www.superairmeter.com

WhatifmySAMnumberistoohigh?• Addmoreair• Changemixtureproportions• Changemixing/batchingoperations

HowdoestheSAMwork?

2”

2”0.75”

0.75”

Air pump

pressure step 0

atmospheric pressuresynthetic AEA

pressure step 1

pressure step 2

pressure step 3

pressure step 4

pressure step 5

pressure step 6

pressure step 7

Atmospheric pressure

pressure step 0

atmospheric pressure

Whatishappening?

• Asyouincreasethepressureyouaredissolvingthesmallbubblesintosolutionandthentheydonotimmediatelycomebackwhenyoudecreasethepressure.

• Noticethatthesebubblesarenotclosetooneanother.

Whyisthishappening?

d

s

PPo

• AccordingtotheLaplace– Youngequationsmallerbubbleshavehigherpressuresinthemthanlargerbubbles

P=Po+4s/d

• Thisiscausedbythedifferencesincurvatureofthebubblewall

Assumes s = 72 dynes/cm

Atmospheric pressure

0

0.05

0.1

0.15

0.2

0 50 100 150 200 250 300

Diameter (microns)

Pres

sure

Abo

ve A

tmos

pher

ic(b

ar)

Whydothebubblesdissolve?

• Henry’sLawstatesthatatacertainpressurethatacertainamountofthegaswouldratherdissolveintheliquidthanremainagas

p=kH cp=pressurec=concentrationkH =Henry’sLawconstant

Morepressureexperiments

• Weranadditionalexperimentswherewetrackedindividualbubblesevery5psifromatmosphericuntil35psi.

• Welookedattwodifferentsituations:1. Highspacingfactor(bubblesfarapart)2. Lowspacingfactor(bubblesclosetogether)

Atmospheric Pressure

35 psi other pressures

not shown

Returned to Atmospheric Pressure

High spacing factor

Low spacing factor

020406080100120140160180200

0psi 5psi 10psi 15psi 20psi 25psi 30psi 35psi 0psi

AirB

ubbleDiam

eter(μ

m)

AppliedPressure(psi)

Low spacing factor

High spacing factor

Bubble dissolves

Results

• Thebubblesinthehighspacingfactorsystem(bubblesfarapart)almostentirelydissolveanddonotcomeback.

• Thebubblesinthelowspacingfactorsystem(bubblesclosetogether)donotdissolveverymuch.

Results

• Ifyouhaveahighspacingfactor(bubblesfarapart)thenthebubblesdissolvefromthefirstsetofpressuresandtheywon’tbearoundtoresistthesecondpressurestep.

• ThiswillcauseahighSAMnumber.• Ifyouhavealowspacingfactor(bubblesclosetogether)thenthebubbleswillonlydissolvealittleandthefirstandsecondpressurestepisaboutthesame.

• ThiswillcausealowSAMnumber.

Results

• Wedidalotoftestingwithalotofdifferentmaterialstofindhowthispressurechangecorrespondedtospacingfactor.

CaseStudiesfromFHWAMobileConcreteLab

These slides are from Jagan Gudimettla

AirVoidSystem- AVA

Air Void Analyzer (AVA)

Slide from Jagan Gudimettla

FHWA Mobile concrete lab

AirVoidSystem– SAMvs.AVA

0

0.1

0.2

0.3

0.4

0.5

0.6

0.000

0.005

0.010

0.015

0.020

0.025

0.030

#1-3 #1-5 #2-4 #2-5 #3-3 #3-4 #4-1 #4-2

SAMNum

ber

SpacingFactor,in

SpacingFactor,in 0.01inLimit(max) SAM

Slide from Jagan Gudimettla

AVA


0.0000

0.0100

0.0200

0.0300

0.0400

0.00 0.20 0.40 0.60

SpacingFactor(A

VA),in

SuperAirMeter(SAM)Number

Idaho

NewMexico

Ohio

NorthDakota

Florida

Michigan


86% agreement

The Super Air Meter: A Test for Plastic Concrete

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Transcript of The Super Air Meter: A Test for Plastic Concrete