Microwave heating improvement of asphalt mixtures through optimizing layer thickness of magnetite and limestone aggregates

Abstract

The key to the development of microwave deicing technology in asphalt pavement engineering is to improve the heating efficiency using less magnetite aggregate with regards to the aggregate resource shortage. In this work, four asphalt mixtures with different magnetite layer thickness (MALT) by volume of the limestone aggregate were prepared. The microwave heating capacity test of magnetite aggregate was carried out firstly. Surface temperature, heat distribution, radiation depth, deicing time, and thermal diffusion for asphalt mixtures were also investigated. Results show that 4.75mm–9.5 mm is considered as the most suitable sieve size according to its higher microwave heating efficiency (MHE) and the highest proportion in aggregate gradation. The reduction of MALT in asphalt mixture can significantly improve the MHE ascribed to higher thermal conversion and utilization, related to the lower microwave reflectivity and shorter propagation path of internal heat to the surface obtained through adjusting MALT. The heat distribution of asphalt mixture with thinner MALT was more unevenly, which can be mainly attributed to the higher heat generating rate. Besides, the heat generated by the upper layer can be quickly transferred to limestone aggregate layer and thus the heat depth can not be used to represent the depth of radiation. In addition, both MALT and initial temperature have effect on the heat diffusion. The reason behind the higher deicing efficiency for asphalt mixture with thinner MALT was owing to both higher MHE and higher heat transfer efficiency.