## 3 Results and Discussion
### Effect of Elevated Temperatures on Chloride Ion Diffusion Coefficient  
The chloride ion diffusion coefficient can reflect the chloride ion penetration speed in concrete. Additionally, it is generally considered to comply with the analytical solution of [PERSON]'s second law. The equation shows the chloride ion content of concrete under various working conditions. By analyzing the chloride ion content of concrete under various working conditions, the chloride ion diffusion coefficient D is obtained, as shown in Table 2.  
\[\mathbf{C}=C_{s}\left[1-\text{erf}\frac{x}{2\sqrt{D}}\right] \tag{1}\]  
Figure 2: Chloride ion content of concrete with respect to different compressive stress ratios. (**a**) Specim not heated, (**b**) Specim soaked after 200 \({}^{\circ}\)C, (**c**) Specim soaked after 400 \({}^{\circ}\)C, (**d**) Specim soaked after 600 \({}^{\circ}\)C.  
The chloride ion diffusion coefficient of concrete subjected to different elevated temperatures after 28 days of erosion was explored. The changes of the coefficient with different temperatures are shown in Figure 3. The diffusion coefficient of chloride ions increased exponentially with the increase of temperature, and the chloride ions penetrated comparatively faster when the specimen was under stronger compression.  
To describe the influence of high temperatures on the diffusion coefficient of chloride ions, the influence coefficient \(\alpha\) is introduced in this paper in Equation (2).  
\[\alpha=D_{T}/D_{20}\text{\textdegree}\text{\textdegree}\text{\textdegree} \tag{2}\]  
For the conditions without load, the calculation formula of the chloride ion diffusion influence coefficient at high temperatures of concrete is obtained:  
\[\alpha=3.5734e^{0.0017T} \tag{3}\]  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Temperature**} & \multicolumn{3}{c}{**Axial Compression Ratio (\(\times 10^{-11}\))**} & \multirow{2}{*}{**Erosion Time**} \\ \cline{2-3}  & **0** & **0.1** & **0.2** & **0.3** \\ \hline
20 \(\text{\textdegree}\text{\textdegree}\) & 3.51 & 3.27 & 3.54 & 3.16 \\ \hline
200 \(\text{\textdegree}\text{\textdegree}\) & 5.28 & 5.36 & 5.60 & 5.54 \\ \hline
400 \(\text{\textdegree}\text{\textdegree}\) & 7.37 & 6.68 & 7.20 & 8.64 \\ \hline
600 \(\text{\textdegree}\text{\textdegree}\) & 9.42 & 11.1 & 13.3 & 15.6 \\ \hline
20 \(\text{\textdegree}\text{\textdegree}\) & 2.03 & 1.95 & 1.98 & 1.96 \\ \hline
200 \(\text{\textdegree}\text{\textdegree}\) & 3.96 & 3.71 & 3.37 & 3.31 \\ \hline
400 \(\text{\textdegree}\text{\textdegree}\) & 5.81 & 4.61 & 5.41 & 6.66 \\ \hline
600 \(\text{\textdegree}\text{\textdegree}\) & 7.88 & 9.53 & 11.8 & 14.4 \\ \hline
20 \(\text{\textdegree}\text{\textdegree}\) & 1.29 & 1.18 & 1.33 & 1.31 \\ \hline
200 \(\text{\textdegree}\text{\textdegree}\) & 2.66 & 2.30 & 2.70 & 2.52 \\ \hline
400 \(\text{\textdegree}\text{\textdegree}\) & 4.59 & 4.05 & 4.90 & 5.71 \\ \hline
600 \(\text{\textdegree}\text{\textdegree}\) & 7.24 & 8.93 & 11.3 & 13.9 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Chloride ion diffusion coefficient of concrete.  
Figure 3: Chloride ion diffusion coefficients with different temperatures after 28 days of erosion.