Rock permittivity characterization and application of electromagnetic mixing models for density/compactness assessment of HMA by means of step-frequency radar

This work aims to determine the compactness/density of hot mix asphalt by measuring its permittivity by means of step-frequency radar. As hot mix asphalt is mainly made of rocks; their dielectric properties are measured in the frequency range of 0.5 - 4 Ghz with step-frequency radar, using cylindrical cavities. The results show that the rocks can be considered as low-loss dielectric. As electromagnetic mixing models are required to translate measured permittivity to the compactness, power law models and unified mixing rules are needed for laboratory experimental data. The slab permittivity of various compactness is determined with the help of the step-frequency radar system. This study shows that: (i) the selection of the electromagnetic mixing model has a critical impact on the accuracy of the calculated compactness; (ii) the choice of the host matrix for a family of unified mixing rules has huge consequences; and (iii) the best assessment of compactness/density is given by the complex refractive index model and Rayleigh and Bottcher models with an aggregate matrix.