Temperature analyses of porous asphalt mixture using steel slag aggregates heated by microwave through laboratory tests and numerical simulations

The temperature distribution of porous asphalt mixtures with steel slag aggregates (SSA) heated by microwave was analyzed through laboratory tests and numerical simulations in this study. Nine groups of porous asphalt mixture specimens with different SSA replacement ratios and particle sizes were designed to investigate their influences on the microwave heating efficiency. The semi-cylindrical specimen (phi 150 x 50) was placed in the center of microwave oven and heated 120 s. The surface temperature was measured by the thermal imaging camera every 20 s. The photos were imported into Flir tools to obtain the temperature of every pixel. Both the maximum heating temperature and the average heating temperature indicated that when 50% of 4.75-9.5 mm aggregates and 50% of 9.5-13.2 mm aggregates were replaced by SSA, the microwave heating efficiency improvement was optimal. When all the coarse aggregates were replaced by SSA, the average microwave heating efficiency was not as good as other groups. Both the laboratory tests and numerical simulations indicated that the inner heating rate was greater than the surface heating rate. The final inner temperature was higher than the surface temperature. After 120 s heating, there were one or two temperature peaks in the diametric direction of the specimen, and the first peak was at the position of 45-60 mm and the second peak was at the position of 120 mm. The temperature along the height direction firstly increased and then decreased, and the maximum temperature was at the half height of the specimen. The numerical simulation results were well consistent with the results of laboratory tests.