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Effect of Deicing and Anti-Icing Chemicals on HMA Airfield Runways

Effect of Deicing and Anti-Icing Chemicals on HMA Airfield Runways. D. Christensen, J. Mallela, D. Hein, E. Kalberer, M. Farrar, and R. Bonaquist FAA Worldwide ATT Conference, April 2010. Introduction.

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Effect of Deicing and Anti-Icing Chemicals on HMA Airfield Runways

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  1. Effect of Deicing and Anti-Icing Chemicals on HMA Airfield Runways D. Christensen, J. Mallela, D. Hein, E. Kalberer, M. Farrar, and R. Bonaquist FAA Worldwide ATT Conference, April 2010

  2. Introduction • Some evidence that deicing/anti-icing chemicals (DIAICs) can cause or contribute to premature failure of HMA runways • Purpose of this presentation is to summarize recent research on effect of DIAICs on HMA airfield runways

  3. Background: Deicing vs. Anti-icing • Deicing is the removal of existing ice and/or snow from the runway • Anti-icing is application of chemicals to prevent buildup of ice and/or snow on the runway • Anti-icing is also performed on airplanes in specific locations, using similar chemicals

  4. Background: Chemicals • For aircraft deicing, ethylene and propylene glycol most commonly used • Potassium acetate most commonly used airfield pavement DIAIC • Other chemicals used include sodium acetate, potassium formate and sodium formate • Recent shift away from glycols and urea

  5. Background: Problems • In the 1990s airfields in Norway and Sweden switched from urea to potassium acetate and potassium formate • Problems later observed in HMA runways: softening, stripping, degradation, disintegration

  6. Summary of Previous Research: Scandinavia, Canada • High temperatures probably needed to cause DIAIC-related damage • Chemical mechanism not clear; DIAICs might attack asphalt-aggregate bond, and/or soften asphalt binder • Damage tends to be more severe for HMA with softer binders, higher air voids

  7. Approach in AAPTP 5-3 • Develop laboratory test and evaluate DIAIC-related damage (if any) in the laboratory • Perform airfield site visits, evaluate possible DIAIC-related damage, take specimens for testing in laboratory • Develop recommendations

  8. Lab Testing: Aggregates • Virginia diabase, 9.5-mm • Virginia Limestone, 9.5-mm • Mississippi chert/gravel, 12.5-mm • Virginia siliceous gravel, 12.5-mm • Pennsylvania greywacke sandstone, 9.5-mm

  9. Lab Testing: Binders • PG 58-28 • Two PG 64-22s • One PG 76-22, polymer modified

  10. Lab Testing: DIAICs • Propylene glycol • Sodium formate • Sodium acetate • Potassium acetate • All as 2 % solutions in water

  11. Similar to AASHTO T 283 Gyratory specimens/cores No vacuum saturation 4 days in 2 % DIAIC solution at 60 C Control: 4 days water at 60 C Tensile strength ratio Immersion/Tension (IT) Test

  12. Four Experiments with IT Test • Aggregate effects • Five aggregates • Single PG 64-22 binder • Binder effects • Three aggregates • Four different binders • Air Voids and hydrated lime effects

  13. Aggregate Effects Experiment The PA sandstone and MS chert/gravel are highly AS reactive

  14. Binder Effects Experiment This confirmed that softer binders are more susceptible to DIAIC-related damage.

  15. Air Voids/Hydrated Lime Expt.: Virginia Gravel/PG 64-22 There is possibly some slight DIAIC damage at 7 % air voids

  16. Air Voids/Hydrated Lime Effects: Mississippi Chert/PG 64-22 Lower air voids reduce DIAIC-related damage

  17. Air Voids/Hydrated Lime Expt.: Mississippi Chert/PG 58-28 In this case, HL also seems to reduce damage

  18. Other Laboratory Testing: Surface Tension and Density • As found by other researchers, DIAICs reduce the surface tension of water • DIAICs can also increase the density of water • Decreased surface tension and increased density could aggravate moisture damage

  19. Site Visits • Four airfields: Boston Logan; Colorado Springs; Boise, Idaho; and Friedman in Hailey, Idaho • Inspection of HMA damage • Photographs • Cores • Laboratory tests on cores

  20. Boston Logan

  21. Friedman Airport

  22. IT Test on Field Cores: Water and2 % Potassium Acetate Solution

  23. Conclusions • The IT test successfully demonstrated DIAIC-related damage in the laboratory for one aggregate (Mississippi chert) • Significant DIAIC-related damage was not observed in mixes made using four other aggregates and in testing of field cores using the IT test

  24. Conclusions • It appears that DIAIC-related damage is not a widespread problem in North America • DIAIC-related damage, when it does occur, appears to be an acceleration of moisture damage, and can be treated in the same way—additives, careful compaction to low/normal air voids

  25. Conclusions • The IT test appears promising, but lack of a large number of susceptible mixes made complete evaluation problematic • Additional research on the IT test would be useful, to confirm its effectiveness in identifying mixes susceptible to DIAIC-related damage

  26. Acknowledgments • Support of the AAPTP program • Monte Symons • Co-authors at ARA and WRI • Laboratory personnel

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