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Aggregate gradation is fundamental concerning asphalt pavement response to loading, especially regarding resistance to permanent deformation. This study assess, in an empirical way, the capability of a gradation-based framework to evaluate the susceptibility to permanent deformation of asphalt mixtures with varying aggregate gradation. The laboratory study was planned to isolate the effect of aggregate gradation by keeping the source of both the aggregates and the binder constant. The work consisted of testing six different asphalt mixtures with varying aggregate gradations using two different methods: wheel tracking and cyclic compression test. Results show that the testing method influences the asphalt mixtures response to loading. The combined normalised result shows a non-significant relationship between the gradation-based framework parameters and resistance to permanent deformation. Additionally, it was observed that the total amount of coarse material have an influence on mixture resistance to permanent deformation.

Film thickness describes the coating around aggregate particles on asphalt mixtures. The standard method of calculating film thickness has proven to present several limitations, such as assuming an average thickness independent of particle size, being completely independent to the porosity of the mixture and considering only one mineral type. In this paper, a binder distribution model is developed for aggregates according to size and role in the structure. The aggregates are separated into two different structures: primary structure, the load bearing one, and secondary structure, smaller material that provides stability to the skeleton. A coating thickness for these two structures is calculated from a geometrical consideration that includes the packing arrangement of particles and the effect of overlapping as the film grows. The results were compared with known rutting performance of field mixtures and moisture conditioned laboratory mixtures, showing a good correlation between film thickness and resistance to failure.

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