## 4 Results and Discussion
### Effect of Coarse Aggregate Content
#### 4.2.2 Numerical Results and Comparative Analysis  
The calculated depths of chloride ion diffusion in the concrete with different aggregate volume fractions when the hydrostatic pressure was 0.5 MPa can be seen in Figure 6. Specifically, when the volume fraction of the aggregate was 0%, the chloride ion diffusion depth was 20.9 mm; when the volume fraction of the aggregate was 20%, the chloride ion diffusion depth was 15.3 mm; when the volume fraction of the aggregate was 40%, the chloride ion diffusion depth was 13.5 mm; and when the volume fraction of the aggregate was 60%, the chloride ion diffusion depth was 12.6 mm. In addition, the chloride ion diffusion depths of the concrete with different aggregate volume fractions under different hydrostatic pressure values are shown in Table 9. Obviously, with the increase of the concrete's aggregate volume, the diffusion path of the chloride ions became more and more tortuous, and the diffusion depth of the chloride ions also increased under the same chloride ion concentration and the same erosion time. This is because the aggregate can inhibit chloride ion diffusion in concrete, and it becomes more obvious with the increase in the aggregate content. The inhibition mechanism was due to the tortuous effect of the aggregate, and the increase in the chloride ion diffusion depth required longer time and more energy.  
The deviation value of the data in Table 8 shows that the error of the physical test results and simulation results increased after the introduction of a coarse aggregate into the cementitious materials. The maximum error of the mortar test block comparison results  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Hydrostatic Pressure: 0.5 MPA**} \\ \hline \multirow{3}{*}{**Number**} & \multirow{3}{*}{**First Group**} & **Second** & **Third** & \multirow{3}{*}{**Experimental Value**} & **Simulation Value** & **Error** \\  & & & & & **(\%)** \\ \hline C-0\% & 20.3 & 20.9 & 21.5 & 20.9 & 20.1 & 3.83 \\ C-20\% & 15.8 & 15.6 & 14.5 & 15.3 & 17.3 & 13.1 \\ C-40\% & 12.6 & 12.9 & 15.1 & 13.5 & 15.0 & 10.8 \\ C-60\% & 11.9 & 11.4 & 14.6 & 12.6 & 13.2 & 4.48 \\ \hline \hline \end{tabular}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{3}{*}{**Number**} & \multirow{3}{*}{**First Group**} & **Second** & **Third** & \multirow{3}{*}{**Experimental Value**} & **Simulation Value** & **Error** \\  & & & **Group** & & & **(\%)** \\ \hline \multicolumn{6}{c}{**(mm)**} \\ \hline C-0\% & 31.6 & 31.0 & 32.9 & 31.8 & 32.2 & 1.15 \\ C-20\% & 22.4 & 20.7 & 24.1 & 22.4 & 25.5 & 13.8 \\ C-40\% & 15.3 & 19.5 & 20.1 & 18.3 & 20.5 & 12.0 \\ C-60\% & 13.2 & 18.5 & 20.41 & 17.37 & 15.2 & 12.5 \\ \hline \hline \end{tabular}
\end{table}
Table 9: Chloride ion penetration test and simulation results of the concrete.  
Figure 6: Simulation results of chloride ion diffusion under different volume fractions of the aggregate under a hydrostatic pressure of 0.5 MPa.  
was only 7.8%, while the maximum error of the concrete test block comparison results was 13.8%. This is a sharp increase, and the dispersion of the concrete contrast error was large. At the same time, the average contrast error of the mortar test block was 6.54%, and the average error of the concrete test block was 8.97%. This phenomenon shows that the model in this paper had some deviation in the study of the concrete model, and it needs further improvement. Furthermore, it was proven that the cement would produce a large dispersion of the whole structure after the introduction of a coarse aggregate, and this needs to be paid attention to in future research.