A tool to design rutting resistant asphalt mixes through aggregate gradation selection

•Aggregate skeleton interlocking can be indirectly characterized by simple parameters.•A design parameter for indicating HMA rutting resistance was proposed and validated.•It is possible to estimate rutting resistance of an asphalt mix before lab testing.•Binder and aggregate gradation characteristics affect resistance to rutting. This work focuses on the proposition of a simple tool to evaluate the quality of the grain size distribution and its potential to produce rutting resistant asphalt mixes. The tool is based on the hypothesis of the existence of a main aggregate structure responsible for absorbing and transmitting stresses without developing plastic deformation. Two parameters were proposed in this paper to characterize such a structure: α and C ratios. The first characterizes the degree of interlocking of this structure, called the Dominant Aggregate Size Range (DASR), while the latter is related to the amount of relatively bigger particles within this structure. The Flow Number (FN) was adopted as an indicator of the rutting resistance of 27 investigated asphalt mixes, varying in grain size distribution, aggregate origin, binder type, and binder content. The proposed parameters α and C are established as characteristic parameters of the aggregate skeleton of the asphalt mix, and are well correlated with FN, indicating they have the potential for being useful tools. However, they do not capture the importance of the asphalt binder for the rutting resistance. A third index, κ, is then established as a characteristic parameter of the asphalt mix associated with the rutting resistance. It is a combination of the gradation parameters (α and C), binder content and binder viscosity. An excellent correlation was observed between the FN and the κ index. Finally, criteria for the κ index were suggested as a function of traffic level, as it is conventionally done for FN values. Results from this work contribute to the development of rational tools to design resistant and stable aggregate gradation compositions for higher quality pavements.