Functional grading of viscoelastic defined hot mix asphalt layers
In the design of layered flexible pavements with the mechanistic-empirical (M-A) method, the material characterization of layers is critical for the correct calculation of mechanical responses. The surface layers of flexible pavements produced as hot mix asphalt (HMA) behave as a visco-elastic material under real field conditions. In this study, in which the HMA surface layer was defined viscoelastic by creep-compliance method, functional grading was applied to the surface layer at the same time to increase the fatigue strength of the pavement. Functional grading application was performed in the form of 3, 5, 7, and 9 sub-layers with linear and exponential functions. The pavement life values due to the mechanical responses that occurred in the pavement were determined by the Asphalt Institute and Shell methods. The study results show that the fatigue strength of the viscoelastic surface layer increases significantly as a result of functional grading. Especially in sections with exponential grading, an improvement of more than 10% was achieved even when a small number of sub-layers used. These results show that functional grading can also be successfully applied in field studies, and even with three sub-layers, significant improvements can be provided.