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33 tine laboratory test for evaluating suspicious asphalt mixes based deicers) deteriorate asphalt pavement. Knowing the when exposed to alkali-metal-salt-based deicers. mechanism(s) of damage will provide necessary guidance for preventing or mitigating such damage and for developing the next generation of PDPs and airfield asphalt pavement. Prevention and Mitigation Advances in technologies related to PDPs and asphalt pave- ment will make both understanding their interaction and To prevent or mitigate the effects of PDPs on asphalt pavement, developing an appropriate compatibility test protocol a con- the first and most important countermeasure is to follow best tinued effort. possible practices in asphalt mix design and paving. Responses to the survey for this project point toward adoption of some of these preventive measures: one European airport reduced IMPACT OF PAVEMENT DEICING PRODUCTS asphalt pavement air void to 3.0%; another European airport ON OTHER AIRFIELD INFRASTRUCTURE indicated that polymer-modified binder is used; and one U.S. airport changed the asphalt binder to PG 76-32, citing current Other airfield infrastructure that comes into contact with PDPs FAA specifications. Nonetheless, the JP Project research includes ground support equipment (GSE), signage, lighting, showed that the resistance of asphalt pavement to deicers can and other electrical systems. Empirical evidence exists indi- be improved only partially by mix design. According to the cating that PDPs are responsible for damaging such infra- laboratory results, binders with high viscosity or polymer- structure. However, no academic peer-reviewed scientific modified binders were recommended when formate/acetate- information could be found to corroborate these empirical based deicers were to be used. High-quality (sound) aggre- observations. The survey and other less technical information gates could also improve the durability of asphalt pavements were heavily relied on in examining the case. in the presence of such deicers, and so did the aggregates with higher pH (Pan et al. 2006). It was recommended that the void In July 2004, the United Kingdom Civil Aviation Author- contents of the asphalt mixes be kept low enough to limit ity issued a Notice to Aerodrome License Holders, the deicer solution in pores. Other suggestions to prevent asphalt authority's standardized procedure for disseminating infor- damages are summarized here (Valtonen 2006): mation about licensing of aerodromes, about the corrosion effects on ground lighting. Premature failure of an aeronau- Prefer harder bitumen (penetration max 70/100) or mod- tical ground lighting centerline fixture was partially attrib- ified bitumen. uted to a rubber removal cleaner; the cleaner destroyed the Use alkaline aggregates and avoid limestone filler. passivated corrosion protection layer and cracking formed. Test the compatibility of the materials in advance. The cracking significantly reduced the strength of the fitting. For security, do not use acetates and formates on asphalt However, it was thought that deicers could also produce a structures. similar effect. The recommended action was to inspect fit- When repaving, mill away the wearing course containing tings, repassivate if needed, and prevent fittings from con- residual deicers and do not use the recycled asphalt pave- tacting fluid with a pH outside of the range of 4 to 8.5 (Aero- ment unless confirming that it is not hazardous (Alatypp drome Standards Department 2004). and Valtonen 2007). In 2005, when one European airport switched from urea Knowledge Gaps and ethylene glycol to formate-based products, corrosion of zinc-coated steel occurred on light fixtures, as well as on Although it was observed in some Nordic airfields that exacer- maintenance and ground operation vehicles. The same air- bated asphalt deterioration occurred with applications of alkali- port now uses stainless steel light fixtures instead of zinc- metal-salt-based PDPs, thus far little observation has been coated steel. Another European airport found that washing reported in U.S. or Canadian airports. Significantly accelerated airport vehicles has decreased the corrosion effects, accord- deterioration of asphalt pavements was found in laboratories ing to the responses to the ACRP synthesis survey. when exposed to acetate/formate-based deicers. There is a need for research data from controlled field investigation regarding The ACRP survey results indicated that lighting cable was the effects of alkali-metal-salt-based PDPs on asphalt pave- also reported to deteriorate during or shortly following deic- ment, which would help differentiate the contribution of such ing events at two U.S. airports. One of these airports suspects PDPs to asphalt deterioration from other possible factors in that the aging of cable insulation plays a role in the deterio- the field environment. One challenge is that the durability of ration. The other airport has upgraded to lighting cable with asphalt pavement is often significantly affected by the mix more resistance to deicers and is in the process of installing design, paving, and maintenance practices, the exposure to cli- a system to remotely monitor the lighting electrical system. matic conditions, as well as the exposure to traffic loading. The FAA has approved a test method for airport contain- Furthermore, there is a need to unravel the specific mech- ers designed to serve as airport light bases, transformer hous- anisms by which alkali metal salts and other PDPs (e.g., bio- ings, junction boxes, and accessories in the presence of