Cements in Nebraska: NDOR Research Into FlyAsh Alternatives

Cements in NebraskaMick Syslo, P.E.Materials & Research Engineer, NDOR

Cements In Nebraska• A quick review• What’s changed• Where we are headed

A QUICK REVIEWCement

• Crushed Rock Limestone* Shale Iron Ore Sand

• Heated to 2700 oF

QUICK FACTSMost consumed substances in the world?

#1 - Water

#2 - Concrete

#3 -

Back to CementCement

• Crushed Rock Limestone* Shale Iron Ore Sand

• Heated to 2700 oF

CO2 Emissions• 50% Limestone Burn

off CaO3 = CaO + CO2

• 50% burning of fuel to heat

What’s Changed?

Late 70’s – 80’s• Emission Requirements began to

change• Resulting in changes in the

alkali / alkalinity of Cement–Sodium Oxide (Na2O)–Potassium Oxide (K2O)–Calcium Oxide (CaO)

The Effects?Concrete

• Rock Ledge Rock Gravel Sand

• Water

• Cement

Since Cement changed Concrete Changed

•ASR

Not new, but MUCH MUCH more prevalent!

ASR = Alkali-Silica Reaction• Alkali – Cements (CaO)• Silica – Aggregate

(SiO2)• Water (H2O) ASR

Gel

CaO

H2OSiO

START EXPERIMENT

The Effects?Concrete produced after 1985 began showing early distresses

The Effects?By late 1990’s and early 2000’s Nebraska….well the nation had major issues!

The Effects?Some pavements build during the same era did not have the distresses

NDOR Reviewed the PCC Mix designs & began a research project.

• All projects with IPF or IPN Cement had performed well while the others had not

– As a result in 2004 moving forward only IPF could be used

– 25% F-ash blended with Type I/II cement

Chemical Testing of Cement

• How do we verify that we are getting 25% F-ash

– NDOR established a chemical ratio

– No major changes in cement specification for next 10 yrs

CaO SiO2

Changes go on elsewhere

• Other states become aware of the their ASR issues and soon several states began requiring IPF. (TxDOT)– Results in lower F-ash supply availability

• Emission requirements for changed for Coal Ash production(Remove more Nox gases-Ammonia, Carbon-Mercury, & Sulfur – Sodium)

– Results in lower F-ash supply availability• 2 major flyash incidents in Tennessee & North

Carolina(Rivers contaminated from ash slides)– Results in risk of flyash being labeled Hazardous

Where are we headed?

• Chemistry

Where are we headed?

• We can get the right chemical balance through blending or other materials.

– NDOR established a chemical ratioCaO SiO2

How it worksMaterial SiO2 CaO Ratio

CaO/SiO2 Mitigate ASR

Cement I/II 22 63 2.8 NO

How it worksMaterial SiO2 CaO Ratio

CaO/SiO2 Mitigate ASR

Cement I/II 22 63 2.8 NOCement + 25% F-ash 29 48 1.65 YES

How it worksMaterial SiO2 CaO Ratio

CaO/SiO2 Mitigate ASR

Cement I/II 22 63 2.8 NOCement + 25% F-ash 29 48 1.65 YES

Cement +25% C-ash 25 52 2.08 NO

How it worksMaterial SiO2 CaO Ratio

CaO/SiO2 Mitigate ASR

Cement I/II 22 63 2.8 NOCement + 25% F-ash 29 48 1.65 YES

Cement +25% C-ash 25 52 2.08 NO

Cement + 25% Slag 25 57 2.28 NO

How it worksMaterial SiO2 CaO Ratio

CaO/SiO2 Mitigate ASR

Cement I/II 22 63 2.8 NOCement + 25% F-ash 29 48 1.65 YES

Cement +25% C-ash 25 52 2.08 NO

Cement + 25% Slag 25 57 2.28 NO

Cement +40% Slag 27 53 1.96 YES

How it worksMaterial SiO2 CaO Ratio

CaO/SiO2 Mitigate ASR

Cement I/II 22 63 2.8 NOCement + 25% F-ash 29 48 1.65 YES

Cement +25% C-ash 25 52 2.08 NO

Cement + 25% Slag 25 57 2.28 NO

Cement +40% Slag 27 53 1.96 YES

Cement +25% Cal. Clay

26 50 1.68 YES

Our Current Specification• Allows the following cements:– IP, 20% or 25% F-ash or Calcined Clay

– IS, 30%-40% Slag

– IT, Blends of SCM’s up to 40% F-ash, C-ash,

Calcined Clay, Slag, Lime Dust, Zeolites…….

Material SiO2 CaO Ratio CaO/SiO2

Mitigate ASR

Cement I/II 22 63 2.8 NO

Cement + 25% F-ash 29 48 1.65 YES

Cement +25% C-ash 25 52 2.08 NO

Cement + 25% Slag 25 57 2.28 NO

Cement +40% Slag 27 53 1.96 YES

Cement +25% Cal. Clay

26 50 1.68 YES

Know your cement• Each cement is different– Workability

– Set Times (saw cutting)

– Strength Gains (opening strength)

– Water Demand

EXPERIMENT RESULTS

Questions?