ABSTRACT
Most modern aircraft pavement thickness design methods are mechanistic-empirical, with the mechanistic element based on layered-elastic analysis of trial pavement structures, which are refined until they are optimised for the subgrade conditions and project aircraft traffic loadings. An elastic modulus and Poisson’s ratio are assigned to each layer in the pavement. In the past, presumptive or standard values of modulus have been used for the various pavement layers. This includes the granular crushed rock or natural gravel, as well as the asphalt surface and sub-surface asphalt layers. However, in modern times, there is great interest in using a mixture-specific dynamic asphalt modulus. As the traffic speed increases and the temperatures reduces, the asphalt modulus increases significantly. Because the temperature of asphalt changes with the depths of the layer within the pavement and with day-night and summer-winter fluctuations, dynamic modulus is complex and is not readily incorporated in layered-elastic software. This research measured the modulus of a typical dense graded airport asphalt mixture at various temperatures and load speeds and incorporated the resulting dynamic modulus into aircraft pavement thickness design using APSDS via asphalt sub-layering. It was concluded that the difference in modulus associated with summer and winter, or day and night, temperature profiles changed the predicted life of the pavement by orders of magnitude, suggesting that all significant pavement damage occurs on the hottest few days of the pavement’s life. Although dynamic asphalt modulus was relatively efficiently incorporated into APSDS, its use in routine layered elastic design is unlikely to be justifiable and is it expected to introduce more challenges than it is likely to solve.
