Modification of the airport pavement strength rating system for improved protection of asphalt surfaces

ABSTRACT

An aircraft pavement strength rating system has been internationally adopted since 1981. Since that time, aircraft tyre pressures and wheel loads have increased significantly and an increase in shear-related surface distress has been reported. The current strength rating system focuses on protection of the subgrade. It also includes a tyre pressure limit intended to protect stress-susceptible surfaces. However, the shear stresses in the surface layer have been shown to be a function of both the tyre pressure and the individual wheel load. A modification to the current aircraft pavement strength rating system is recommended. The proposed modification replaces the current tyre pressure rating with a classification number that reflects the contribution of both tyre pressure and wheel load to surface layer shear stress. Guidance is also provided on the selection of a surface rating and the granting of approval for usage by aircraft with more demanding wheel load and tyre pressure combinations. It is also recommended that efforts to include shear-related surface failure modes into routine pavement design tools be given high priority, as this will allow a more rational approach to surface rating selection.

KEYWORDS:

• Airport pavement
• 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. This assistance was gratefully appreciated.