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IMPACT OF AIRPORT PAVEMENT DEICING PRODUCTS ON AIRCRAFT AND AIRFIELD INFRASTRUCTURE SUMMARY Airfield pavement deicing and anti-icing are essential activities to maintain safe winter oper- ations of the aviation industry. Airfield pavement deicing products (PDPs) traditionally con- sisting of urea or glycols have become less popular owing to their adverse environmental impacts. New PDPs have emerged as alternatives that often contain potassium acetate (KAc), sodium acetate (NaAc), sodium formate (NaF), or potassium formate (KF) as the freezing point depressant. When it comes to airfield pavement deicing and anti-icing there are no sim- ple solutions to the competing, and sometimes conflicting, objectives of aircraft safety, envi- ronmental regulatory compliance, materials compatibility, and operational implementation viability. The objectives of this synthesis are to report how airports chemically treat their airfield pavements to mitigate snow and ice, and the chemicals used; review damage reported to air- craft components and airfield infrastructure in association with the use of traditional or mod- ern PDPs; and identify critical knowledge gaps on these subjects. Information was acquired through a comprehensive literature search and from a survey. In addition, responses representing approximately 100 airports were gathered from a 2006 EPA questionnaire, which indicated that KAc and sand are most widely used at U.S. airports for snow and ice control of airfield pavements, followed by airside urea, NaAc, NaF, propylene glycol-based fluids, ethylene glycol-based fluids, and others. Catalytic oxidation of aircraft carboncarbon composite brakes resulting from airfield PDPs has become a growing concern to be monitored in the ever-changing operation envi- ronment. As nontraditional chemical contaminants, modern PDPs may be responsible in recent years for the more rapid structural failure of carboncarbon composite brakes. To avoid potential safety implications, this concern has to be mitigated through more frequent proactive maintenance and inspection activities incurring high direct and indirect costs. Although the fundamental mechanisms of catalytic oxidation by PDPs are well under- stood in well-controlled laboratory settings, and advances in technologies for its prevention and mitigation have been made in the last decade or so, the problem seems far from solved. There is still a need to establish a comprehensive PDP catalytic oxidation test protocol. Furthermore, research is needed to better understand relationships between brake design, anti-oxidant treatment, and PDP contamination as factors in catalytic oxidation. Field reports increasingly suggest that contact with modern PDPs promotes damage to air- craft components, especially cadmium (Cd)-plated components. Until recently, the principal evidence connecting alkali-metal-salt PDPs with Cd-plating corrosion has been that a trend of increased reports of the latter occurred concurrently to the introduction of the former. Although the fundamental mechanisms of Cd corrosion in water are relatively well studied, the link between alkali-metal-salt-based PDPs and Cd-plating corrosion has yet to be experi- mentally validated and thoroughly investigated. There is still a need to establish a comprehen-

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2 sive metallic corrosion test protocol for PDPs. More research is needed to better understand the interactions among the aircraft component design, the corrosion-inhibiting compounds used, and the contamination of PDPs in the processes of metallic corrosion. Finally, there is still a lack of academic research data from controlled field investigation regarding the aircraft metal- lic corrosion by PDPs. Alkali-metal-salt-based PDPs accelerate the precipitation and buildup of thickener residues from modern aircraft deicing/anti-icing fluids (ADAFs). The contamination effects of ADAFs have been well-observed, but not yet thoroughly quantified. Acquisition of hard data will assist in the generation of inspection schedules and may spur development of improved thickener formulae for ADAFs. Research will be needed to better understand the interactions between ADAFs and PDPs, as new ADAFs and PDPs are continually introduced to the market. The last decade has seen an increase in alkalisilica reaction (ASR) occurrence with the use of alkali-metal-salt-based deicers applied on airfield portland cement concrete pave- ments. Limited laboratory studies indicated that these modern PDPs could cause or acceler- ate ASR distress in the surface of portland cement concrete pavement by increasing the pH of concrete pore solution. Therefore, there is a need for research data from controlled field investigations regarding the effects of alkali-metal-salt-based PDPs on concrete pavement. Furthermore, it is essential to unravel the specific mechanism by which alkali-metal-salts cause or promote ASR. Concurrent with the use of acetate and formate-based deicers in the 1990s, asphalt pave- ment in Europe saw an increase in pavement durability problems. The damaging mechanism of asphalt pavement by modern PDPs appeared to be a combination of chemical reactions, emulsification, and distillation, as well as the generation of additional stress inside the asphalt mix. There is a need for research data from controlled field investigations regarding the effects of alkali-metal-salt-based PDPs on asphalt pavement. Furthermore, there is a need to unravel the specific mechanisms by which alkali-metal-salts and other PDPs (e.g., bio-based deicers) deteriorate asphalt pavement. Other airfield infrastructure that comes into contact with PDPs includes ground support equipment, signage, lighting, and other electrical systems. Empirical evidence exists indicat- ing that PDPs are responsible for damaging such infrastructure. However, no academic peer- reviewed scientific information could be found to corroborate these empirical observations.