super air meter
TRANSCRIPT
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A New Test Method to Measure the Freeze Thaw Durability of
Fresh Concrete
Braden Tabb, Robert Felice, John Michael Freeman, Robert Frazier, David Welchel
Tyler Ley, P.E., Ph. D
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Acknowledgements
• Oklahoma Transportation Center • CP Tech Center • Portland Cement Association
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Summary
• Some basics of air entrained concrete… • The Super Air Meter • The future
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What is…
Concrete
PCA Photo
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What is…
Air-entrained concrete
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Why Do We Add Air to Concrete?
• Air-entrained bubbles are the key to the freeze-thaw resistance of concrete Air volume = Freeze Thaw Performance
• Smaller bubbles are more effective in providing freeze-thaw resistance than larger bubbles
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• Volume of air provided is the same for both circumstances.
• Case B has a lower spacing factor and a higher specific surface.
A B
What Do You Want in an Air-Void System?
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A B
• Volume of air provided is the same for both circumstances.
• Case B has a lower spacing factor and a higher specific surface.
What Do You Want in an Air-Void System?
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Current Measuring Techniques
PCA photo
ASTM C 231 PCA photo
ASTM C 173 ASTM C 138
These only measure volume!!!
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Hardened Air Void Analysis
From Hover
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Hardened Air Void Analysis
From Hover
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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)
No Polycarboxylate
Open symbols failed ASTM C666
Freeman et al., 2012
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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
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norm
alize
d Ai
r Con
tent
Fra
ctio
n
Chord Size, microns
WROS OnlyPC1 + WROS
Freeman et al., 2012
small voids large voids
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8080
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00 -
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0014
00 -
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1600
- 18
0018
00 -
2000
2000
+
norm
alize
d Ai
r Con
tent
Fra
ctio
n
Chord Size, microns
WROS OnlyPC1 + WROS
Look at the difference in the volume of the air voids!!!
Freeman et al., 2012
small voids large voids
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Summary • It is common to require a certain
volume of air in concrete in order to obtain freeze thaw durability
• The volume of air does not equal air void system quality
• Although, a hardened air void analysis (ASTM C 457) can measure the air-void quality it is not practical to run regularly
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What do we need? • We need a test that can quantify air-
void systems quickly in fresh concrete • Investigate a sample of significant size • Economical • Field ready
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Super Air Meter (SAM) • We have modified a typical ASTM C
231 pressure meter so that it can hold larger pressures
• We have replaced the typical gage with a digital one
• The test takes 8 minutes
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digital gauge
Six clamps!
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How does it work? • Use ASTM C 231 procedures to fill the
measurement bowl • Secure the lid • Add water through the petcocks
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top chamber
bottom chamber
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0
15
30
45
60
75
90
0
App
lied
Pres
sure
(psi
)
Time
Top Chamber, Pc1
Bottom Chamber, Pa1
Equilibrium Pressure, P2When both chambers are in contact with one another
Top Chamber
Bottom Chamber
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0
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75
90
0
App
lied
Pres
sure
(psi
)
Time
Top Chamber, Pc1
Bottom Chamber, Pa1
Equilibrium Pressure, P2When both chambers are in contact with one another
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0
15
30
45
60
75
90
0
App
lied
Pres
sure
(psi
)
Time
Top Chamber, Pc1
Bottom Chamber, Pa1
Equilibrium Pressure, P2When both chambers are in contact with one another
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App
lied
Pres
sure
(psi
)
Time
Top Chamber, Pc1
Bottom Chamber, Pa1
Equilibrium Pressure, P2When both chambers are in contact with one another
release pressure in both chambers
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0
15
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45
60
75
90
0
App
lied
Pres
sure
(psi
)
Time
Top Chamber, Pc1
Bottom Chamber, Pa1
Equilibrium Pressure, P2When both chambers are in contact with one another
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0
15
30
45
60
75
90
0
App
lied
Pres
sure
(psi
)
Time
Top Chamber, Pc1
Bottom Chamber, Pa1
Equilibrium Pressure, P2
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How does it work? • We use an algorithm to find a SAM
number. • The SAM number correlates to air
void distribution • The meter also measures air volume
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How can we prove it? • We made 95 concrete mixtures • Different AEAs • Combinations of AEAs and PCs • Different w/cm (0.39 - 0.53) • Slumps from 0.25” to 10” • Air contents from 1.25% to 10% • Hardened air void analysis (ASTM C
457) was completed on each mixture • Values were compared to the SAM
number
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ACI 201
PASS
FAIL
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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Mod
ulus
(%)
SAM NumberSAM Number
PASS
FAIL
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Observations • When the SAM number is below 0.2
then the spacing factor is below 0.008” for 90% of the samples and 98% of the samples had a spacing factor below 0.010”
• The SAM number seems to correlate with the amount of small bubbles in the sample
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How Consistent Is It? • We ran the following on each of the 95
mixtures with two separate SAMs: – Air contents – SAM numbers – ASTM C 457 hardened air void analysis – Unit Weight
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y = 1.015x - 0.0227R² = 0.9932
0
1
2
3
4
5
6
7
8
9
0 1 2 3 4 5 6 7 8 9
SAM
2 A
ir Co
nten
t (%
)
SAM 1 Air Content (%)
Mean Difference -0.005% Standard dev. 0.064%
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Mean Difference 0.006 Standard dev. 0.049
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y = 0.9982x + 0.2504
R² = 0.9668y = 0.9965x + 0.3611
R² = 0.9651
0
1
2
3
4
5
6
7
8
9
10
0 1 2 3 4 5 6 7 8 9 10
Supe
r Air
(%)
Gravimetric Calculated Air (%)
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Conclusions • The SAM test can be completed in
about 10 minutes with fresh concrete • A SAM number of 0.20 seems to
correlate with the ASTM C 457 spacing factor of 0.008” and freeze thaw durability as per ASTM C 666
• Two SAMs have been shown to provide consistent results.
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www.superairmeter.com
SAMs should be available April 2014
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Questions???