Impact of Aggregate Gradation on Airfield (P-401) Asphalt Mixture
The Federal Aviation Administrations' (FAA) current asphalt mixture gradation specification limits are finer, and the allowable ranges are more restrictive than control points for similar nominal maximum aggregate size mixtures within the Superpave mix design methodology. Ensuring the gradation specification limits requirements are allowing asphalt mix designers to produce the best performing, most economical, and lowest carbon footprint mixtures will safeguard airfield pavements into the future and were goals of this research.This research utilized three material sources, one each from Arizona, Nevada and Washington to develop mix designs using the Baily Method inside the P-401 gradation specification limits requirements (in spec) and outside the P-401 gradation specification limits requirements (out spec). In and out of spec mix designs within each source were developed with the same asphalt cement (AC) and volume of effective binder. The rutting, moisture susceptibility, top-down cracking, low temperature cracking, durability (Cantabro mass loss) and permeability performance of each mixture was evaluated. However, broadening the FAA P-401 gradation specification limits did not compromise mixture volumetric requirements or affect the rutting performance, moisture susceptibility, durability or the permeability of the mixtures from the three states. This work was part of a national effort by three laboratories including the Western Regional Superpave lab at UNR, the National Center for Asphalt Technology at Auburn University and the Heritage Research Group in Indiana. The final proposed adjustments to the gradation specification limits are anticipated to take place in the near future with the goal of providing the least restrictive gradation specification limits possible while maintaining the mixture performance expected of FAA P-401 mixtures.
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