Assessing the Influence of Material Selection and Mixture Design Parameters on Fuel-Resistant Airfield Asphalt Mixtures

Abstract

Fuel-resistant asphalt (FRA) mixtures have emerged as a viable solution for resisting premature degradation from fuel exposure on airfields. Fuel resistance is generally achieved by combining a highly modified asphalt binder (namely, performance grade [PG] 88-22 or PG 82-28) with lower design air voids (i.e., 2.5% V_{a, des}) than conventional airfield mixtures to promote lower permeability and higher effective binder volume. Both the Federal Aviation Administration and Department of Defense have adopted FRA airfield specifications, which feature multiple unique specification requirements compared to conventional airfield mixtures, relating to the asphalt binder grades, design method, V_{a, des} level, nominal maximum aggregate size (NMAS), natural sand use, and in-place density requirements. The objective of this research was to systematically assess the influence of these FRA material selection and mixture design parameters to better inform specifications moving forward. Twenty-eight different mixture variants based on four primary airfield asphalt mixtures were designed and produced in the laboratory and characterized using fuel mass loss (FML), fuel-conditioned indirect tensile strength (S_t), and asphalt pavement analyzer wheel tracking. Ultimately, it was recommended that (1) no changes be made at this time to binder selection, (2) FML criteria be adjusted based on specimen size, (3) Gradations 2 and 3 (effectively 12.5 and 9.5 mm NMAS, respectively) be allowed, (4) up to 15% natural sand be permitted, and (5) future adjustments to V_{a, des} and in-place target densities be further explored using field data.