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71 8.1 Summary There are many benefits to using permeable pavements for stormwater management, but there are also risks. Based on the literature review and aviation industry survey responses, experience with permeable pavement at airports (airside and landside) is limited. There are relatively few airport permeable pavement projects, particularly in areas where aircraft operate. Airside appli- cations of permeable pavements have included runway and taxiway shoulders, general aviation aprons, and service roads, while landside applications have been primarily parking lots. Permeable pavements are selected to fulfill specific stormwater management requirements. While the traditional design is for full infiltration, the permeable pavement designs investigated in the case studies were not full-infiltration systems. Rather, the systems were designed for other stormwater management needs, such as delaying the time of peak discharge or providing a paved surface that did not increase the impermeable area on the airport. Where used in areas of aircraft operations, permeable pavements have been designed for infrequent, heavy aircraft (e.g., for shoulders) and more frequent, light aircraft (e.g., general avia- tion). Thickness design has been performed with the FAAâs design methodology and FAARFIELD program (and LEDFAA, previously), as well as the AASHTO thickness design methodology. However, neither methodology is specifically calibrated to permeable pavement performance but rather is based on conventional pavement performance models. Materials selection plays a significant role in the performance of the pavement. For example, abrasion or raveling observed in some pavements appears to be attributed to mixtures that were different from current recommended industry guidance. Current guidance from industry groups (ACI, NAPA, and ICPI) needs to be considered in selecting materials for any project. Projects have primarily used state standards for materials specifications. The identified projects did not pursue an MOS to use FAA-approved specifications, nor where they constructed with funding through the FAA. Permeability of the pavement can be maintained over time with routine maintenance (such as vacuum sweeping). User awareness of what permeable pavement is, and establishing maintenance procedures, can provide for a long-term pavement alternative. However, the operations and maintenance for permeable pavements are different from those for conventional pavements. 8.2 Future Research Needs While research about and implementation of permeable pavements for vehicular applications are readily available, few projects have been identified that have aircraft loadings. The low number of projects can be attributed, in part, to the lack of long-term performance data in an airport C h a p t e r 8 Summary and Future Research Needs
72 Guidance for Usage of permeable pavement at airports environment and no design and construction guidance in the FAAâs policies. Some research topics that could be beneficial to the use of permeable pavements at airports are: â¢ Development of FAA pavement specifications for permeable pavement layer types that take into account the difference in loadings and environmental effects on an airport. â¢ Development and validation of thickness design methods for aircraft loadings. â¢ A pilot project site using FAA-based design methods and specifications to obtain long-term performance data and design validation. This could be constructed at the FAA National Airport Pavement Test Facility to accelerate results. â¢ Continued development of maintenance, repair, and rehabilitation guidelines in relation to permeable pavements. â¢ Laboratory testing assessment to determine if there is a method to predict surface abrasion under aircraft tire loadings and use the testing method to develop durable mixtures.