Natural factors related to the differential heating of aggregates exposed to microwaves

Abstract The heating produced by microwaves has been demonstrated to be effective in materials such as aggregates, although notable differences in heating have been observed between different types of aggregates. The geological factors of each material are responsible for these differences in heating due to compositional elements such as the mineralogy and chemistry of the material and physical characteristics such as crystal size and apparent density. The study of each of these characteristics could unravel the factors determining differential heating in aggregates, which would be relevant for different applications in the mining industry (heating, drying, and comminution) and in civil engineering in self-healing (microcrack repair) or winter road maintenance (surface de-icing). This paper investigates the influence of microwave heating on the chemical, mineralogical, and physical properties of aggregates susceptible to be used in asphalt mixtures. For this, aggregates with different characteristics have been selected. Various tests were conducted to determine the factors affecting heating: thin-section studies (mineralogy and crystal size), XRD (mineralogy) and XRF (chemistry) composition studies, and bulk density of the rocks. These results were correlated with dielectric permittivity data (loss tangent) and direct heating data (parameter T70). Both techniques have proven helpful as an indicator of susceptibility to microwaves. Finally, multiple regression models were proposed to apply this knowledge to any rocks suitable as aggregate.