Evaluation of Microwave Heating for Potential Applications in Hot In-Place Recycling of Asphalt Pavement

Hot in-place recycling (HIR) has been adopted in pavement engineering because of its low financial cost and lower consumption of nonrenewable material. At present, infrared heating is the most common heating method in HIR, while microwave heating has been proposed as an alternative to it recently. This study investigated and compared the characteristics of microwave and infrared heating by laboratory experiments and numerical modeling. Laboratory tests were first conducted to determine thermal parameters of asphalt mixture and calibrate electromagnetic parameters based on numerical simulation. Two numerical models of microwave and infrared heating under field conditions were further established for analyzing the heating characteristics, including the temperature distribution, heat transfer rate, and energy consumption. The results show that infrared heating can only heat the pavement at shallow depth, while microwave heating can heat the pavement surface and the materials at greater depths to high temperatures. An increase in power was found to enhance the efficiency of microwave heating but to maybe reduce that of infrared heating. Moreover, under the same power, microwave heating needs much less time and energy than infrared heating to reach the same temperature. Microwave heating shows great potential to be applied for HIR of asphalt pavement with the increased recycling depth.