Pumping Air

Entrained Concrete

Marllon “Dan” Cook, Ph. D

Research Associate

Civil & Environmental Engineering

Oklahoma State University

Research Team

Principle Investigator:

Tyler Ley, PE, PhD

Graduate Students:

Justin Becker, Nick Seader, Chad

Staffileno

Acknowledgements• Oklahoma DOT

• FHWA

• Kansas DOT

• Nebraska DOT

• Iowa DOT

• Minnesota DOT

• Idaho DOT

• N. Dakota DOT

• Penn. DOT

• Connecticut DOT

• Illinois DOT

• Indiana DOT

• Michigan DOT

• Wisconsin DOT

• New Jersey DOT

• RMC Foundation

• American Concrete

Pumping Association

Why Air Entrain Concrete?

Cracking

Scaling

Entraining Air in Concrete is Easy,

Right?

Question:

Mixture Batched Over Time

Air

Do

sag

e (

oz./

cw

t)

Dosage Required for

6% Air volume

Air Dosage Over Time

How Long Do You Spend Chasing Air?

Parameters Effecting Air Dosage

• Weather & temperature

• Sand gradation

• Fly ash production changes

• Water temperature

• Inadequate mixing

• Admixture/cement incompatibility

• Alkali content of binder

• Material source change

• Pumping concrete…………….list goes on and on

1. Air volume will go down

2. Air volume will go up

3. Air volume will stay the same

- Ken Hover

When Pumping Air-Entrained Concrete 1 of 3 Things Happen:

Pumping Changes The Concrete

Before the Pump After the Pump

3.5% Air6.1% Air

Why Does Pumping Impact Air?

1. Pressure

Mechanism

2. Vacuum

3. Impact

Where Should We Measure Air?

Before the Pump After the Pump

OR

What Does the Engineer Say?

• Test at point of placement

• Engineering logic says:

“This will represent

hardened properties”.

What Does the Producer Say?

• Test at point of discharge

• Supplier logic says:

“Concrete met specs

before the pump. That’s

what I can control”.

Before the Pump After the Pump

OR

Where Should We Measure Air?

www.youtube.com/tylerley

Experimental Investigation

• Investigate the following before and after pumping

• Both field and laboratory testing

Testing Methods:

• Air volume with SAM (AASHTO TP 118)

• Air void spacing with SAM (AASHTO TP 118)

• Spacing factor (ASTM C 457)

• Freeze-thaw performance (ASTM C 666)

Before the Pump After the Pump Hardened

We Measured The Air

Before the Pump After the Pump Hardened

We Measured The Air

And Then Freeze-Thaw Testing

Super Air Meter (SAM)

• AASHTO TP 118

• Measures vol. & bubble distribution

• Modified pressure meter with larger

pressure steps

• The test takes 8 - 10 minutes

• Uses SAM number to indicate bubble

distribution.

www.superairmeter.com

digital

gauge

six

clamps!

different

bleeder

valve

Comparing Meters

• AASHTO TP 118

• Measures vol. & distribution

• Multiple pressure steps

Type B Meter SAM

• AASHTO T152

• Measures volume

• 1 pressure step

Which is a Quality Air Void System?

Large Bubbles Small Bubbles

OR

• Small bubbles contribute to freeze-thaw resistance and improve overall durability

• Large bubbles form inconsistently, don’t contribute to f-t, decrease strength, and create inconsistencies for dosage rates.

Large & Small Air Bubbles

• Mixing process: “entrapped” air (0.5% to 2.5%)

• Inadequate mixing

• Admixture and/or cement incompatibilities

• Cement grinding aids

• Alkalis in cementitious mat.

• Sand gradation

• Changes in temperature

• Pumping

Large Air Bubbles Created By

Large Bubbles

• Provides air volume and air distribution of hardened concrete.

• Takes roughly 6 weeks for lab.

• Usually completed if there's a problem.

Harden Air Void Analysis

Take Core

Cut Core

Harden Air Void Analysis

Polish Sample

Color

Harden Air Void Analysis

• Measures cored length and SSA.

• Calculate the spacing factor from cored length

Scan Path

on Sample

Freeze-Thaw Testing

• Measure f/t performance

• ASTM C666/AASHTO T161

• 0.45 w/cm

• 20% Class C fly ash

• 6.5 sacks (611 lbs.)

• Limestone & natural sand

• 6% air content

• 20 laboratory mixtures

Mixture Design in Laboratory

Concrete Pump Network

• 4” diameter pipe

• 60’ of steel pipe

• 10’ Rubber hose

• pumping pressures from 55 to 110 psi

Recirculation Procedure

Testing Performed1. Before pump2. After 1 cycle 3. Every 6 cycles after

This side is very

important!!!!

When You See Pistol Pete…

Air Volume & Pumping Cycles

Approximately 20% air loss after one circulation through the concrete pump.

Air Volume & Pumping Cycles

Recommended Threshold

SAM Number & Pumping Cycles

Recommended Threshold

SAM Number & Pumping Cycles

What does Higher SAM # Mean?

Large Bubbles Small Bubbles

OR

Discussion of Fresh Concrete

• After one cycle:

➢Air content decreased

➢SAM Number shows loss of small bubbles when you pump.

• Air void system in the fresh concrete changed due to pumping with these materials and equipment.

Where does the air change within

the pump network?

Question:

Test Locations

Air within Pump & Pipe Network

Data Shows Pressure Mechanism

1. Pressure

Mechanism

2. Vacuum

3. Impact

What About Hardened Concrete?

Durability Factor & Air Vol.

Durability Factor & Air Vol.

Durability Factor & SAM

Durability Factor & SAM

Similar Spacing Factors

Air Comes Back!!!

Air Comes Back!!!

Discussion

• After pumping the hardened air content was on average 1.15x higher in the fresh air content.

• For example – After pumping 6% fresh and about 7% in hardened concrete

• The fresh measurements after pumping do not seem to represent the performance or properties of the hardened concrete.

Discussion

• Since the air volume is going down and SAM Numbers are going up this means that we are losing small bubbles in the fresh concrete during pumping.

• BUT! ➢Concrete not pumped: fresh air = hardened air➢Concrete pumped: fresh air < hardened air

• Satisfactory freeze thaw performance of pumped concrete was observed even though there were low air contents and high SAM Numbers after pumping.

Why is the air lost right as the

concrete leaves the pump?

Sample Preparation

Investigating Paste Pressure

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

Discussion

• The pressures during pumping causes the bubbles to dissolve and so they are not present in the fresh concrete when it discharges from the pump.

• This is why the air volume decreases and the SAM Number increases.

Mechanism: What is Happening???

• The pressures from pumping causes the small bubbles to temporarily dissolve.

• Good performance in the petrographic analysis, freeze-thaw testing, and reducing SAM Number over time suggests that the dissolved air comes back before the concrete hardens.

• When the air comes back it seems to be well dispersed and provides a similar spacing factor to what went into the pump.

Mechanism: What is Happening???

Mechanism: What is Happening???

What does this Mean for Concrete?

• Air Content and SAM testing after pumping may not be representative of the hardened concrete.

• If this is true then concrete should not be rejected for low air or high SAM Number after pumping.

• It appears that sampling the concrete prior to pumping is a good indicator of the air void system in the hardened concrete.

How to Avoid Air Loss?

Air loss occurs more in the following:•Higher pumping pressures•Smaller diameter lines•Mixtures with poor aggregate gradations

•Lower slump mixtures•A-frame and arch configurations

Air loss doesn’t matter

because the important air

comes back!!!

But Remember!

What do I think needs to happen?

• Testing air at the point of discharge from a pump is dangerous and it is not representative of the properties of the hardened concrete.

• We need to test concrete with the SAM before pumping and not require testing at the point of placement.

• We need to have local discussions about how we can change our specifications and construction practices.

Before the Pump After the Pump Hardened

Where Should We Measure Air?

www.youtube.com/tylerley

Questions?

Marllon.cook@okstate.edu

Tyler.ley@okstate.edu

www.tylerley.com

www.superairmeter.com

Is this true for other equipment, pipe

configurations, and mixtures?

Question:

Field Pumping Information

• 62 different mixtures tested

• Bridge decks, walls, sidewalk, parking lot, drilled shaft

• 18 Different Types of Pumps

• Boom lengths ranged from 100’ to 180’

• Pipes from 4” to 6” in diameter

• Used three different boom configurations

• Oklahoma, Kansas, Missouri

• 4% to 8% air content

• With & without WR

• Aggregate sources varied

Mixture Designs in Field

Pipe Configurations

Flat Arch A-frame

Pipe Configurations

Flat

Arch

A-frame

Air Vol. Before & After Pumping

Discussion of Field Data

*Most flat configurations in the lab showed a change in SAM

Configuration

% of mixtures

that lost > 1%

air

A-frame 39%

Arch 37%

Flat* 0%

SAM Before & After Pumping

Discussion of Field Data

Configuration

% of mixtures

that SAM

changed > .05

A-frame 45%

Arch 60%

Flat* 40%

*Most flat configurations in the lab showed a change in SAM

Both Arch and A-Frame…

Discussion

• We are seeing similar things in the lab and the field!

• For A frame or Arch we are losing > 1% air ~ 40% of the time

• For all configurations we are losing SAM > 0.05 > 40% of the time.

Spacing Factor B & A

We need to complete more

hardened air void analysis!!!

Stay tuned!!!!

Spacing Factor B & A

Measuring field concrete

To convince our industry that this is real then we need more data.

We need SAM measurements and hardened air void analysis before and after pumping.

97

SAM + cylinder

Here is what I need

98

Discussion

• The hardened and fresh measurements closely matched prior to pumping.

• After pumping the hardened air content was on average 1.15x higher than the fresh air content.

• For example – After pumping 6% fresh and about 7% in hardened concrete

Discussion

• These are the same findings from the lab but from 62 different mixtures and 18 different types of pumps using a variety of pump configurations!!!!

• The fresh measurements after pumping do not seem to represent the performance or properties of the hardened concrete.

Pumping Changes The Concrete

• 60% of ready-mix concrete is pump.

• Pumping effects:• Slump

• Segregation

• Air

Pumping Changes The Concrete

5” Slump

Before the Pump After the Pump

2” Slump

Pumping Changes The Concrete

SegregationNo Segregation

Before the Pump After the Pump

Air Volume & Distribution Over Time

• In order to learn more we decided to do a

pump mixture in the lab and then measure the

change in the SAM Number over time.

• While discharging from the pump concrete was

placed in separate containers.

• These containers were sampled over time.

Air Volume Over Time

SAM Volume Over Time

Variation of test method

Line of agreement

Remember!!!!