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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
• Volume of air provided is the same for both.
• Case B has a better air void distribution.
WhatDoYouWantinanAir-VoidSystem?
• Volume of air provided is the same for both.
• Case B has a better air void distribution.
A B
WhatDoYouWantinanAir-VoidSystem?
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
Hardened Air Void Analysis
From Hover
0%
1%
2%
3%
4%
5%
6%
7%
8%
9%
10%0-1
010
-20
20-30
30-40
40-50
50-60
60-70
70-80
80-90
90-10
010
0-1
1011
0-1
2012
0-1
3013
0-1
4014
0-1
5015
0-1
6016
0-1
7017
0-1
8018
0-1
9019
0-2
0020
0-2
1021
0-2
2022
0-2
3023
0-2
4024
0-2
5025
0-2
6026
0-2
7027
0-2
8028
0-2
9029
0-3
0030
0-3
1031
0-3
2032
0-3
3033
0-3
4034
0-3
5035
0-3
6036
0-3
7037
0-3
8038
0-3
9039
0-4
0040
0-4
1041
0-4
2042
0-4
3043
0-4
4044
0-4
5045
0-4
6046
0-4
7047
0-4
8048
0-4
9049
0-5
0050
0-5
5055
0-6
0060
0-6
5065
0-7
0070
0-7
5075
0-8
0080
0-8
5085
0-9
0090
0-9
5095
0-1
000
1000
-12
0012
00-14
0014
00-16
0016
00-18
0018
00-20
0020
00+
norm
alize
dAirC
ontentFraction
ChordSize,microns
WROSOnlyPC1+WROS
Freeman et al., 2012
small voids large voids
0%
1%
2%
3%
4%
5%
6%
7%
8%
9%
10%0-1
010
-20
20-30
30-40
40-50
50-60
60-70
70-80
80-90
90-10
010
0-1
1011
0-1
2012
0-1
3013
0-1
4014
0-1
5015
0-1
6016
0-1
7017
0-1
8018
0-1
9019
0-2
0020
0-2
1021
0-2
2022
0-2
3023
0-2
4024
0-2
5025
0-2
6026
0-2
7027
0-2
8028
0-2
9029
0-3
0030
0-3
1031
0-3
2032
0-3
3033
0-3
4034
0-3
5035
0-3
6036
0-3
7037
0-3
8038
0-3
9039
0-4
0040
0-4
1041
0-4
2042
0-4
3043
0-4
4044
0-4
5045
0-4
6046
0-4
7047
0-4
8048
0-4
9049
0-5
0050
0-5
5055
0-6
0060
0-6
5065
0-7
0070
0-7
5075
0-8
0080
0-8
5085
0-9
0090
0-9
5095
0-1
000
1000
-12
0012
00-14
0014
00-16
0016
00-18
0018
00-20
0020
00+
norm
alize
dAirC
ontentFraction
ChordSize,microns
WROSOnlyPC1+WROS
Freeman et al., 2012
small voids large voids
Mixture with small bubbles
Mixture with large bubbles
2L
• SpacingFactor– ½oftheaveragedistanceofanaveragesizedvoiduniformlydistributedinthepaste
• DesiredValue<0.008in(ACI201)real concrete idealized concrete
Spacing factorfrom Hover
0%
1%
2%
3%
4%
5%
6%
7%
8%
9%
10%0-1
010
-20
20-30
30-40
40-50
50-60
60-70
70-80
80-90
90-10
010
0-1
1011
0-1
2012
0-1
3013
0-1
4014
0-1
5015
0-1
6016
0-1
7017
0-1
8018
0-1
9019
0-2
0020
0-2
1021
0-2
2022
0-2
3023
0-2
4024
0-2
5025
0-2
6026
0-2
7027
0-2
8028
0-2
9029
0-3
0030
0-3
1031
0-3
2032
0-3
3033
0-3
4034
0-3
5035
0-3
6036
0-3
7037
0-3
8038
0-3
9039
0-4
0040
0-4
1041
0-4
2042
0-4
3043
0-4
4044
0-4
5045
0-4
6046
0-4
7047
0-4
8048
0-4
9049
0-5
0050
0-5
5055
0-6
0060
0-6
5065
0-7
0070
0-7
5075
0-8
0080
0-8
5085
0-9
0090
0-9
5095
0-1
000
1000
-12
0012
00-14
0014
00-16
0016
00-18
0018
00-20
0020
00+
norm
alize
dAirC
ontentFraction
ChordSize,microns
WROSOnlyPC1+WROS
Freeman et al., 2012
small voids large voids
Low spacing factor
High spacing factor
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0 2 4 6 8 10 12
ASTM
C457Spa
cingFactor,in
Air%
WROS.45
ACI201.2R
Small bubbles
Yes!
No!
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0 2 4 6 8 10 12
ASTM
C457Spa
cingFactor,in
Air%
WROS.45
WROS.45+PC1
ACI201.2R
Small bubbles
Large bubbles
Yes!
No!
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0 2 4 6 8 10 12
ASTM
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!
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
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
Rapid Freeze Thaw Test
Open symbols failed ASTM C666
0.004
0.006
0.008
0.010
0.012
0.014
0.016
0.018
0.020
0.022
0.024
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)
0.004
0.006
0.008
0.010
0.012
0.014
0.016
0.018
0.020
0.022
0.024
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)
No Polycarboxylate
Polycarboxylate
Open symbols failed ASTM C666
Freeman et al., 2012
Mixtures with small bubbles
Yes!
No!
0.004
0.006
0.008
0.010
0.012
0.014
0.016
0.018
0.020
0.022
0.024
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)
No Polycarboxylate
Polycarboxylate
Open symbols failed ASTM C666
Freeman et al., 2012
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
0
10
20
30
40
50Pr
essu
re (p
si)
Time
Top Chamber, Pc
Bottom Chamber, Pa
Equilibrium Pressure
Top Chamber
Bottom Chamber
0
10
20
30
40
50Pr
essu
re (p
si)
Time
Top Chamber, Pc
Bottom Chamber, Pa
Equilibrium Pressure
Air content given here
0
10
20
30
40
50Pr
essu
re (p
si)
Time
Top Chamber, Pc
Bottom Chamber, Pa
Equilibrium Pressure
0
10
20
30
40
50Pr
essu
re (p
si)
Time
Top Chamber, Pc
Bottom Chamber, Pa
Equilibrium Pressure
0
10
20
30
40
50Pr
essu
re (p
si)
Time
Top Chamber, Pc
Bottom Chamber, Pa
Equilibrium Pressure
release pressure in both chambers
0
10
20
30
40
50Pr
essu
re (p
si)
Time
Top Chamber, Pc
Bottom Chamber, Pa
Equilibrium Pressure
0
10
20
30
40
50Pr
essu
re (p
si)
Time
Top Chamber, Pc
Bottom Chamber, Pa
Equilibrium Pressure
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
0.01
0.012
0.014
0.016
0.018
0.02
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%
20%
30%
40%
50%
60%
70%
80%
90%
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%
20%
30%
40%
50%
60%
70%
80%
90%
100%
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
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
FHWA Mobile concrete lab
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
FHWA Mobile concrete lab
86% agreement