Comparative Evaluation of Microwave and Oven Heating on Silicon Carbide Asphalt Mastics: Insights into Rheological Behavior, Thermal Stability, and Aging Resistance

To promote sustainable asphalt pavement maintenance, this study explores the use of silicon carbide (SiC) powder as a microwave-absorbing filler to partially or fully replace traditional mineral powder in asphalt mastic. A series of SiC replacement ratios were investigated to assess their effects on microwave heating performance, penetration, rheological behavior, and chemical composition. To differentiate the long-term thermal impacts, repeated microwave heating was compared with conventional oven heating, which serves as a reference method based on radiative thermal conduction. Results demonstrate that SiC incorporation markedly enhances the microwave absorption capacity and high-temperature stability of asphalt mastic while inducing a moderate reduction in low-temperature cracking resistance. After 20 heating cycles, microwave-heated SiC asphalt mastic exhibited only a 6% increase in rutting factor and minimal penetration loss (<3%), whereas oven-heated specimens showed rutting factor increases exceeding 10% and penetration losses of 13%–15%. Further, the carbonyl index and sulfoxide index of oven-heated samples were three to six times and 1.5 times higher, respectively, than those of microwave-treated ones, indicating significantly more severe thermo-oxidative aging. These findings are attributed to the rapid, selective, and volumetric heating nature of microwave energy, which minimizes thermal gradients, reduces exposure time, and limits the volatilization of light components. The presence of SiC not only improves microwave absorption efficiency due to its favorable dielectric properties but also acts as an internal maintenance agent by adsorbing volatile fractions and delaying aging. This dual function highlights SiC’s promising role in future microwave-assisted asphalt pavement technologies.