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Cements in Nebraska: NDOR Research Into FlyAsh Alternatives
- 1. Cements in Nebraska Mick Syslo, P.E. Materials & Research Engineer, NDOR
- 2. Cements In Nebraska • A quick review • What’s changed • Where we are headed
- 3. A QUICK REVIEW Cement • Crushed Rock Limestone* Shale Iron Ore Sand • Heated to 2700 oF
- 4. QUICK FACTS Most consumed substances in the world? #1 - Water #2 - Concrete #3 -
- 5. Back to Cement Cement • 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
- 6. 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)
- 7. The Effects? Concrete • Rock Ledge Rock Gravel Sand • Water • Cement Since Cement changed Concrete Changed •ASR Not new, but MUCH MUCH more prevalent!
- 8. ASR = Alkali-Silica Reaction • Alkali – Cements (CaO) • Silica – Aggregate (SiO2) • Water (H2O) ASR Gel CaO H2OSiO
- 10. The Effects? Concrete produced after 1985 began showing early distresses
- 11. The Effects? By late 1990’s and early 2000’s Nebraska….well the nation had major issues!
- 12. The Effects? Some pavements build during the same era did not have the distresses
- 13. 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
- 14. 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
- 15. 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
- 16. Where are we headed? • Chemistry
- 17. Where are we headed? • We can get the right chemical balance through blending or other materials. – NDOR established a chemical ratio CaO SiO2
- 18. How it works Material SiO2 CaO Ratio CaO/SiO2 Mitigate ASR Cement I/II 22 63 2.8 NO
- 19. How it works 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
- 20. How it works 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
- 21. How it works 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
- 22. How it works 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
- 23. How it works 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
- 24. 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
- 25. Know your cement • Each cement is different – Workability – Set Times (saw cutting) – Strength Gains (opening strength) – Water Demand
- 27. Questions?