# Study on Microwave Deicing of Carbon-Fiber-Modified Concrete under Multi-Factor Coupling Effect
## 3 Results  
### Effects of Carbon Fiber Content and Length on Heating Temperature  
Five groups of ice-free concrete specimens (PC, 0.1 CFC3, 0.3 CFC3, 0.6 CFC2 and 0.6 CFC3) were subjected to a wave absorption heating test. The temperature-time curve and the temperature-change-rate-time curve of the five groups of specimens are shown in the Figures 5 and 6, from which the following conclusions can be drawn:  
1. In the same group of specimens, with increased height (straight-line distance between microwave receiving surface and bell-mouth component), the temperature rises gradually and then decreases. When the vertical height is 20 mm, the absorbing heat efficiency is the highest. The increase in temperature amplitude of the PC group was higher than 40 mm when the microwave source height was 60 mm, and that of 0.6 CFC2 was 20 mm when the microwave source height was 40 mm. This indicates that the optimal heating height of concrete varies depending on the length and content of carbon fibers used for modification, and there is no optimal height suitable for all concrete materials. At the same height, the temperature of the specimen increases in a process of dynamic stability; the optimal carbon fiber length and content of the modified concrete are not affected by heating height, but these parameters affect the heating efficiency.
2. When the height was 20 mm, the rate of temperature increase of 0.6 CFC2 and 0.6 CFC3 varied considerably, and the temperature increase rates of the two test groups fluctuated to a certain extent. The other test groups, such as PC, 0.1 CFC3 and 0.3 CFC3, all reached a plateau, and the temperature rose steadily from 20 s to 40 s. Therefore, with increased height, the temperature increase rate of 0.6 CFC2 and 0.6 CFC3 specimens emerged as stable, showing that carbon fiber modification of concrete in the process of microwave heating increase the temperature rate fluctuation to stable value relative to carbon fiber content and fiber length. Regardless of the height, the shape of the temperature increase rate curve first increases rapidly and then tends toward a stable value.
3. When the height is 20 mm, the temperature increase at the central point (T\({}_{0}\)) of the PC specimen is 32.3 \({}^{\circ}\)C, that of the 0.6 CFC2 specimen is 61.4 \({}^{\circ}\)C, and the absorption and heating efficiency are increased by 1.90 times. When the height of the microwave source trumpet is 40 mm, the temperature increase of the PC specimen is 20.4 \({}^{\circ}\)C, and that of 0.6 CFC2 is 53.0 \({}^{\circ}\)C, representing an increase of about 2.60 times. This indicates that carbon fiber has a more obvious improvement effect on the ice-free wave absorption heat performance of concrete at a height of 40 mm for the 0.6 CFC2 specimen, which is the best performance in the test group.
4. Overall, height has a considerable influence on the absorption and heating performance of CFRP. For the same specimen, the temperature increase at a height of 20 mm is about 1.5 to 2 times higher than that at a height of 60 mm. Our results are consistent with those reported in a study by [PERSON] [24] on the wave-absorbing and heat-generating properties of concrete with different carbon fiber lengths, confirming that longer carbon fiber length results in improved wave-absorbing and heat-generating properties of modified concrete.