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This article is intended to investigate the microwave heating performance of asphalt mixtures containing magnetite powders (MPAM). For this purpose, the surface temperatures of asphalt mixtures containing different dosages of magnetite powders were measured during microwave heating. The low-temperature bending test and water sensitivity test were also conducted to evaluate the performance of MPAM. Heating rate and reflection loss of different thicknesses of MPAM were determined using a microwave heating test and arch reflectivity test, respectively. The results showed that because its main components are triiron tetroxide and iron oxide, which have excellent microwave-absorbing properties, magnetite powders can be used as microwave absorbers to improve the ability of microwave absorption and increase the heating rate of asphalt mixtures. The heating rate of the asphalt mixtures increased with the increase of the amount of magnetite powder. The addition of magnetite powder improved the low-temperature properties of the asphalt mixture, but it reduced the water stability of the asphalt mixture. Considering that the microwave-absorbing asphalt mixture used for melting snow and ice should have good water stability, the recommended dosage of magnetite powders was 60%. The microwave-absorbing properties of MPAM were related to its thickness in the pavement structure and frequency of microwaves. In order to greatly enhance the absorbing efficiency, future work should be focused on matching thickness and matching frequency.

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In view of the high cost and poor accuracy in monitoring the internal layered settlement of foundation soil mass, this study has introduced an ultrasonic ranging technique into the layered settlement monitoring of civil engineering foundations. It has also developed a special ultrasonic monitor capable of generating different frequencies (e.g., 200kHz, 400kHz). It has also selected two oscilloscopes that can match the frequencies, the pipe fitting materials, reflecting materials, and propagation mediums that are related to the burying of the ultrasonic monitoring system into a soil mass. After that, it has calibrated the propagation velocity of ultrasonic waves under different water temperatures, tested the ranging technique, and obtained an effective range of at least 45 m. Then, it has carried out actual measurement comparison and error analysis, which show that the accuracy of the ultrasonic monitoring system is in the order of millimeters. Finally, an indoor ultrasonic-monitored settlement simulation test has been carried out. The ultrasonic-monitored burying system has been buried into the soil mass, and the ultrasonic monitoring system has been used to measure the layered settlement of the soil mass after rolling compaction and compression. The comparison with the actual measurements shows that the measurements by the ultrasonic monitoring system are highly accurate. The ultrasonic monitoring system can therefore be used to monitor the settlement of foundation soil mass.