# Model Experimental Study on De-Icing Method of Bridge Pylon Beam Based on Electric Heating
## 4 Results and Analysis of De-Icing Tests
### Passive De-Icing Tests  
#### 4.2.1 Passive De-Icing Evaluation  
When the anti-icing fails, the heating system can be turned on again after the storm weather ends for passive de-icing. Coupled with a certain time of traffic control, the purpose of eliminating security risks can be achieved. Six groups of passive de-icing tests were carried out, and the test conditions are shown in Table 5. The test procedures of the passive de-icing tests comprise first freezing the ice and then melting it. Firstly, the heating surface was sprayed for 120 min; then, the spray  
Figure 15: (**a**) Anti-icing effects after rearranging the CFHC; (**b**) temperature rise rule after rearranging the CFHC under the rainfall condition. system or wind delivery system was turned off, and the ambient temperature was kept constant. Finally, the heating system was turned on, and the ice melting situation was observed. Figure 16 shows the ice melting process when the wind velocity was 0, and Figure 17 shows the relationship between the de-icing time period and the wind velocity. The initial time of heating was recorded as time 0. At the time of 39 min, due to the increase in internal temperature, the ice layer in the left part of the heating system surface began to fall off. In the following three minutes, a large area of ice fell off. By the time of 51 min, the ice layer on the wall surface of the heating system was almost completely removed. At the time of 56 min, the extended ice on the top surface of the heating system fell off, and the ice melting process ended. Figure 16: Passive de-icing process without wind. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Group Number**} & **Ambient Temperature** & **Wind Velocity** & **Thickness of the Ice Layer** & **De-Icing Time Period** \\  & _/_(\({}^{\circ}\)C)_ & _/_(m/s)_ & _/_(mm)_ & _/_(min)_ \\ \hline
1 & \(-15\) & 0 & 8 & 56 \\
2 & \(-15\) & 1 & 13 & 55 \\
3 & \(-15\) & 2 & 17 & 57 \\
4 & \(-15\) & 3 & 18 & 55 \\
5 & \(-15\) & 4 & 19 & 58 \\
6 & \(-15\) & 5 & 21 & 58 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The test conditions and the de-icing time period of passive de-icing tests under windy conditions. The de-icing time periods for all six groups of tests were less than 60 min, with an average value of 56.5 min, and the difference between the longest and shortest de-icing time was only 3 min. As can be seen in Figure 17, as the wind velocity increases, the ice thickness on the heating system surface increases significantly. However, the corresponding de-icing time period shows an irregular change. This indicates that the time period of passive de-icing does not depend on the total amount of icing. This is because when the icing completely covers the surface of the heating system, even though the total amount of ice layer increases, the contact area between the ice layer and the heating area is fixed. In addition, the ice layer on the surface of the beam or heating system is in a vertical position, and when the connected part of the ice layer with the heating system surface melts, the ice layer will fall off naturally due to gravity. Therefore, even though severe climatic conditions increase the amount of ice buildup on the beam, the time required for passive de-icing is not affected to a certain extent. In the electrical heating of a snow melting section of road, the time required to achieve passive de-icing/snow melting is typically 120 to 300 min [14]. At least half of the heating time is spent in the warming process of the road surface, and the rest of the time is spent in the heat absorption and melting process of the snow. In comparison, the ice melting time of the heating system is relatively short. Due to the excellent thermal conductivity of metals, the heating rate of the heating system is much higher than that of concrete pavement. Because of the special location of the ice layer on the beam, the ice layer does not need to absorb a large amount of heat to melt into water but can fall off after the connected part when the heated surface melts.