Limitations and potential improvement of the aircraft pavement strength rating system to protect airport asphalt surfaces

Abstract

A pavement strength rating system is internationally adopted in order to protect aircraft pavements from inadvertent overload. The system has two elements. The primary element is designed to protect the pavement against subgrade rutting and the second is intended to protect asphalt pavement surfaces. The surface-protection element is arbitrary and empirical, placing category-based limits on aircraft tyre pressures. In 2008, increases in the tyre pressure limits were proposed by aircraft manufacturers and these were approved in 2013. The research reported in this paper assesses the impact of tyre pressure and individual wheel load increases on calculated flexible pavement stress indicators, as well as identifying an improved surface layer protection element. Stresses were calculated near the surface, at the surface layer interface and at the subgrade. Tyre pressure and wheel load combinations included current (18 t and 1.35 MPa), imminent (33 t and 1.75 MPa) and future (40 t and 2.15 MPa) aircraft. Surface layer stress increased significantly (20–30%) with increases in both tyre pressure and wheel load. The subgrade stress increased near-equally (97%) with wheel load but was insensitive (<1%) to tyre pressure changes. The ability of the current aircraft pavement strength rating system to protect pavements from the increasing demands of aircraft was demonstrated to be limited to the subgrade. It is recommended that the tyre pressure rating be amended to reflect the combined impact of both tyre pressure rating and individual wheel load. It is also recommended that ongoing efforts to incorporate additional asphalt surface failure modes into routine pavement design be given high priority. The importance of these issues is reinforced by the limited availability of remedies to counter any negative impacts of increased surface layer stresses, especially in hot climates.

Keywords:

• Asphalt shear stress
• airport surface stress
• ACN–PCN

Acknowledgements

Historical information regarding the development of the ACN–PCN system and the incremental increase in tyre pressures and wheel loads was provided by Bruce Rodway.