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

Acknowledgements

• Oklahoma Transportation Center • CP Tech Center • Portland Cement Association

Summary

• Some basics of air entrained concrete… • The Super Air Meter • The future

What is…

Concrete

PCA Photo

What is…

Air-entrained concrete

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

• 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?

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?

Current Measuring Techniques

PCA photo

ASTM C 231 PCA photo

ASTM C 173 ASTM C 138

These only measure volume!!!

Hardened Air Void Analysis

From Hover

Hardened Air Void Analysis

From Hover

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

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

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Chord Size, microns

WROS OnlyPC1 + WROS

Freeman et al., 2012

small voids large voids

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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

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

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

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

digital gauge

Six clamps!

How does it work? • Use ASTM C 231 procedures to fill the

measurement bowl • Secure the lid • Add water through the petcocks

top chamber

bottom chamber

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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App

lied

Pres

sure

(psi

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Time

Top Chamber, Pc1

Bottom Chamber, Pa1

Equilibrium Pressure, P2When both chambers are in contact with one another

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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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90

0

App

lied

Pres

sure

(psi

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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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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

0

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30

45

60

75

90

0

App

lied

Pres

sure

(psi

)

Time

Top Chamber, Pc1

Bottom Chamber, Pa1

Equilibrium Pressure, P2

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

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

ACI 201

PASS

FAIL

0%

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100%

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Mod

ulus

(%)

SAM NumberSAM Number

PASS

FAIL

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

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

y = 1.015x - 0.0227R² = 0.9932

0

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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%

Mean Difference 0.006 Standard dev. 0.049

y = 0.9982x + 0.2504

R² = 0.9668y = 0.9965x + 0.3611

R² = 0.9651

0

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8

9

10

0 1 2 3 4 5 6 7 8 9 10

Supe

r Air

(%)

Gravimetric Calculated Air (%)

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.

www.superairmeter.com

SAMs should be available April 2014

Questions???