Research on temperature-dependent complex permittivity for large-size heterogeneous asphalt mixture

In order to assess the temperature-depended complex permittivity for asphalt mixture of microwave hot in-place recycling (HIPR), a free-space method based on the gangway-reflection-line (GRL) was applied to temperature-dependent complex permittivity for large-size heterogeneous asphalt mixture at the 2.45 GHz microwave frequency. The academic model of the measurement method was employed, which was assumed that the microwave distribution was considered by the sum of the incident- and reflected-wave components. In addition, the test system was been set up. The GRL calibration method of measurement system and the time-domain-gating (TDG) technique improving the measurement accuracy were discussed. To measure the asphalt mixture dielectric properties in different temperature and fit the data by using the least square method, the data showed that the permittivity of asphalt mixture was nonlinear from 4 degree centigrade to 62 degree centigrade at the 2.45 GHz. The complex permittivity of asphalt mixture decreased with the temperature increase, however it would decrease significantly less than 20 degree centigrade and decrease slowly in the late of heating temperature. Results produce certain influence for electromagnetic field and temperature field within asphalt mixture when microwave heats recycle asphalt mixture.