Influence of microwave energy on temperature field distribution and properties evolution characteristics of cement mortar containing magnetite

To improve the microwave absorption ability of cement mortar, this study focused on the preparation of magnetite cement mortar (MCM) with magnetite as the main absorbing material. The electromagnetic (EM) parameters of MCM were measured and the microwave reflection loss (RL) was calculated to study its microwave absorption efficiency. Meanwhile, the thermal response of MCM was recorded using an infrared thermal imager to analyze its heating and temperature field distribution characteristics. In addition, to study the mechanical properties of MCM at different microwave heating times from macroscopic and microscopic scale, the press machine, SEM, XRD, and MIP were used. The results showed that increasing the magnetite content could effectively improve the microwave absorption efficiency of MCM. After 240 s of microwave heating, the surface temperature of MCM with 25% magnetite content was up to 184.9 °C, compared to the surface temperature of 162.6 °C in the control group. In the same microwave heating time, although adding magnetite significantly increased the surface temperature of MCM, it caused an increase in the variability of the MCM temperature field distribution, which might generate a certain temperature gradient stress. The maximum surface temperature difference of the control group was 59.9 °C, which was 14.3 °C smaller than that of the MCM with 25% magnetite content. The continuous temperature difference generated attenuated the mechanical and physicochemical properties of the MCM. The compressive and flexural strength of MCM with 25% magnetite content was deterioration about 4.1 and 0.9 MPa, respectively. Although the MCM had favorable heating capability for pavement deicing, its engineering properties deterioration degree should be considered during long-term microwave heating. • The changes of magnetite cement mortar thermal response during microwave heating were studied. • The mechanical strength evolution characteristics of MCM after long-term microwave heating was investigated. • The effect of changes in the pore structure of MCM on its mechanical strength was studied.