the super air meter: a test for plastic concrete
TRANSCRIPT
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TheSuperAirMeter:ATestforPlasticConcrete
BradenTabb,RobertFelice,JohnMichaelFreeman,RobertFrazier,DavidWelchel,Morteza Khatibmasjedi,JakeLeFlore
TylerLey,P.E.,Ph.D
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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
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Outline• IntroductiontoAirentrainedconcrete• WhyistheSAMuseful?
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WhyDoWeAddAirtoConcrete?
• Air-entrainedbubblesareakeytothefreeze-thawresistanceofconcrete
Airvolume=freeze-thawperformance
• Smallerbubblesaremoreeffectiveinprovidingfreeze-thawresistanceandhavelessofanimpactonourconcretethanlargerbubbles
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TheAir-EntrainmentBlues…
• Themostchallengingaspectofconcretetogetrightistheaircontent.
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TheAir-EntrainmentBlues…
• Themostchallengingaspectofconcretetogetrightistheaircontent.
• Largebubblesaretheenemy!
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• 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?
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A B
• Volume of air provided is the same for both.
• Case B has a better air void distribution.
WhatDoYouWantinanAir-VoidSystem?
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• 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
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Modified C231
Small bubbles
Large bubbles
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• Theyleavetheconcreteandchangeyourairvolume
• Theydon’thelpwithfreeze-thawdurability
• Theyreduceyourstrengthmorethansmallerbubbles
Whyarelargebubblesbad?
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Whatcauseslargebubbles?• Admixtureincompatibility• Admixture/cementincompatibility• Sandgradation• Inadequatemixing• Alkalicontentofbinder• Cementgrindingaids• Changesintemperature• Pumping
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Howdoyoumeasurethem?
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Hardened Air Void Analysis
From Hover
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Hardened Air Void Analysis
From Hover
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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
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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
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2L
• SpacingFactor– ½oftheaveragedistanceofanaveragesizedvoiduniformlydistributedinthepaste
• DesiredValue<0.008in(ACI201)real concrete idealized concrete
Spacing factorfrom Hover
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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
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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!
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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!
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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!
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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
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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!
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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!
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Summary• Weneedtoknowthesizeofbubbleswithintheconcrete
• Thevolumeofairdoesnottellyouanythingaboutbubblesize
• Althoughahardenedairvoidanalysiscanmeasurethis,itisnotpracticaltorunregularly
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SuperAirMeter(SAM)• WehavemodifiedatypicalASTMC231pressuremetersothatitcanholdlargerpressures
• Wehavereplacedthedialgagewithadigitalone
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digital gauge
six clamps!
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AASHTOTP118
www.superairmeter.com
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top chamber
bottom chamber
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0
10
20
30
40
50Pr
essu
re (p
si)
Time
Top Chamber, Pc
Bottom Chamber, Pa
Equilibrium Pressure
Top Chamber
Bottom Chamber
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0
10
20
30
40
50Pr
essu
re (p
si)
Time
Top Chamber, Pc
Bottom Chamber, Pa
Equilibrium Pressure
Air content given here
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0
10
20
30
40
50Pr
essu
re (p
si)
Time
Top Chamber, Pc
Bottom Chamber, Pa
Equilibrium Pressure
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0
10
20
30
40
50Pr
essu
re (p
si)
Time
Top Chamber, Pc
Bottom Chamber, Pa
Equilibrium Pressure
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0
10
20
30
40
50Pr
essu
re (p
si)
Time
Top Chamber, Pc
Bottom Chamber, Pa
Equilibrium Pressure
release pressure in both chambers
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0
10
20
30
40
50Pr
essu
re (p
si)
Time
Top Chamber, Pc
Bottom Chamber, Pa
Equilibrium Pressure
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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
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Howlongdoesthattake?• WithjusttheSAM• Inexperienceduser– 10min• Experienceduser– 7min
• WiththeCAPE• Inexperienceduser- 7min• Experienceduser– 4.5min
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ControlledAirPressureExtenderakaCAPE
Compressed air
Step 1(14.5 psi)Step 2 (30 psi)
Step 3 (45 psi)
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Discussion• TheSuperAirMetergivesyoutheairvolumeandtheSAMnumber.
• TheCAPEisaportableairtankandregulatorsthatcanhelpyourunthetestfaster.
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WhyistheSAMnumberuseful?
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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
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83% agreement
PennDOT 50 field mixtures
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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
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Discussion• TheSAMnumberof0.20correlateswellwiththespacingfactorof0.008”forover350labandfieldmixturescompleted13differentstates.
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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
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69% agreement
This test takes 3.5 months
No
Yes!
This test takes 7 - 14 days
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Discussion• ASAMnumberof0.20correlatesbettertorapidfreezethawdurabilitythanaspacingfactorof0.008”.
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0%
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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
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0%
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30%
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50%
60%
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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
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Whyisthisuseful?• TheSAMcantellusaboutthequality(sizeandspacing)ofourairvoidsystembeforetheconcretesets
• Itcantellusaboutthefreezethawdurabilityofourairvoidsystem
• Itcanalsotellusifwewillhaveairvoidstabilityproblemsduringourmixturedesignprocess!!!!
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Whyisthisuseful?• Thiscangiveyouimportanttestinginformationthatwasalmostimpossibletogetinthepast
• Thisishelpfulwhen:– mixturesaredesignedinthelab– mixturesareplacedinthefield– trialbatchinginthefield– troubleshootingfieldproblems– measuringvariationinmaterials
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HowdoIdothis?
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Anexample
• Mix1- SAMnumberof0.22andanaircontentof5%
• Mix2- SAMnumberof0.40andanaircontentof6%
54
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Mix 1
Mix 2
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This is crazy valuable!!!!!!
PennDOT
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Discussion• ByplottingyourdataontheSAMCurveyoucanimmediatelytellifyourairvoidsystemismadeoflargeorsmallbubbles.
• Thisimmediatefeedbackcanbeusedtotroubleshootfieldissuesandgiveyoufeedbackonyourconcretemixturedesign.
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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)
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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
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Discussion• ThevariabilityofSAMissimilartothevariabilityinthehardenedairvoidanalysisandrapidfreezethawtestingandthetestcanberuninthefieldonfreshconcreteinlessthan10min.
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Discussion• Idon’tthinkitisacoincidencethatthevariabilityissosimilarbetweenthethreedifferentmethods.
• Eachtestisdesignedtoinvestigatetheairvoiddistribution.Airvoiddistributionmaybemorevariablethanotherconcretepropertiessuchascompressivestrength.
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HowdoyouspecifytheSAM?• 1.ReplacetheairmeterwiththeSAMinthefield
• 2.UsetheSAMduringthemixturedesignstageandvalidateinthefield.
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SAMreplacesairmeter
• Aircontentmustbeabove4%
SAM
0.17 0.25 0.30Bonus Full Pay Deduct Remove
and Replace
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SAMusedduringmixtureacceptance• Duringmixturedesignstageruntrialbatcheswithair<5%andSAMnumbermustbe<0.25.
• Testairaspertypicalpractice.• ValidatethatSAM<0.25andair>4%onceadayorevery1000yds inthefield.
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Ineedyourhelp• Takingtheindustryfromahorseandbuggytoaninternalcombustionengineisnoteasy.
• TrytheSAM!• Askquestions!• Givesuggestions
• Sharewhatyoulearnherewithothers• HelpothersbecomeknowledgeableoftheSAM
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Ineedyourhelp• HelpextendmyPooledFundStudy.Weneed5morestates.TPF-5(97)
• MyersAssoc.hasaSAMintheexhibitorhall.
• RequestaSAMfromFHWA
• AASHTOWebinarthisThursday(10/20/16)•
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Conclusion
• Largebubblesaretheenemy!• Airvolumedoesnottellyoububblesize.• TheSAMcanmeasurethevolumeandsizedistribution ofthebubblesinfreshconcrete
• Thisishelpfulformakingyourairmoreconsistentandensurefreezethawdurability
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Conclusion• ASAMnumberof0.20seemstocorrespondtoaspacingfactorof0.008”
• Over90%ofthelabandfielddataiscorrectlyseparatedwiththislimit
• TheSAMnumbercorrelateswithASTMC666testing
• TheSAMhasbeeninvestigatedbyanumberofothersandallhavefoundsimilarcorrelations
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WhatifmySAMnumberistoohigh?• Addmoreair• Changemixtureproportions• Changemixing/batchingoperations
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HowdoestheSAMwork?
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2”
2”0.75”
0.75”
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Air pump
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pressure step 0
atmospheric pressuresynthetic AEA
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pressure step 1
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pressure step 2
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pressure step 3
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pressure step 4
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pressure step 5
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pressure step 6
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pressure step 7
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Atmospheric pressure
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pressure step 0
atmospheric pressure
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Whatishappening?
• Asyouincreasethepressureyouaredissolvingthesmallbubblesintosolutionandthentheydonotimmediatelycomebackwhenyoudecreasethepressure.
• Noticethatthesebubblesarenotclosetooneanother.
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Whyisthishappening?
d
s
PPo
• AccordingtotheLaplace– Youngequationsmallerbubbleshavehigherpressuresinthemthanlargerbubbles
P=Po+4s/d
• Thisiscausedbythedifferencesincurvatureofthebubblewall
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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)
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Whydothebubblesdissolve?
• Henry’sLawstatesthatatacertainpressurethatacertainamountofthegaswouldratherdissolveintheliquidthanremainagas
p=kH cp=pressurec=concentrationkH =Henry’sLawconstant
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Morepressureexperiments
• Weranadditionalexperimentswherewetrackedindividualbubblesevery5psifromatmosphericuntil35psi.
• Welookedattwodifferentsituations:1. Highspacingfactor(bubblesfarapart)2. Lowspacingfactor(bubblesclosetogether)
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Atmospheric Pressure
35 psi other pressures
not shown
Returned to Atmospheric Pressure
High spacing factor
Low spacing factor
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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
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Results
• Thebubblesinthehighspacingfactorsystem(bubblesfarapart)almostentirelydissolveanddonotcomeback.
• Thebubblesinthelowspacingfactorsystem(bubblesclosetogether)donotdissolveverymuch.
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Results
• Ifyouhaveahighspacingfactor(bubblesfarapart)thenthebubblesdissolvefromthefirstsetofpressuresandtheywon’tbearoundtoresistthesecondpressurestep.
• ThiswillcauseahighSAMnumber.• Ifyouhavealowspacingfactor(bubblesclosetogether)thenthebubbleswillonlydissolvealittleandthefirstandsecondpressurestepisaboutthesame.
• ThiswillcausealowSAMnumber.
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Results
• Wedidalotoftestingwithalotofdifferentmaterialstofindhowthispressurechangecorrespondedtospacingfactor.
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CaseStudiesfromFHWAMobileConcreteLab
These slides are from Jagan Gudimettla
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AirVoidSystem- AVA
Air Void Analyzer (AVA)
Slide from Jagan Gudimettla
FHWA Mobile concrete lab
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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
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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