## 3 Test Results
### AC Impedance Test Results  
Figures 7-14 show the electronic impact spectroscopy test results for group A and B samples, among which Figures 7a-14a are Nyquist diagrams, and Figures 7b-14b are Bode diagrams. Nyquist and Bode diagrams reflect the changes in the corrosion system process of the steel. Based on the equivalent circuit, the \(R\)c values of asphalt-coated steel and bare steel were calculated, as shown in Figure 15. It can be concluded from Figures 7a-10a that there are two resistance arcs in the figure, namely the resistance arcs with small radii in high- and low-frequency areas. This feature indicates that the reinforcement is rusted. From Figures 11a-14a, one can observe two capacitance reactance arcs, namely the semicircle resistance arc with a small radius in the high-frequency region and the capacitance arc with a large radius in the low-frequency region, and the tail drag phenomenon in the low-frequency area is short. The capacitance information for the interface between the surface of the coating and the pore electrolyte solution of magnesium oxychloride cement in the high-frequency region is the resistance and the barrier capacitance of the coating. The greater arc resistance radius in the high-frequency area indicates a better protective effect of the coating on the reinforcement. The capacitance information for the interface between the bottom reinforcement and the electrolyte solution corresponds to the resistance arc in the low-frequency region. The drag phenomenon [37; 38] is also produced, indicating the appearance of diffusion-related Warburg impedance of the original corrosion system. The reason for the tail dragging in the low-frequency area is that the solution gradually invades the inside of the coating, causing the steel bar to rust, and the corrosion product concentration at the interface is high; thus, it needs to spread to the outside. During the whole immersion period, the arc radius of the high-frequency zone increases and decreases continuously. The main reason for this behaviour is that the formation of a corrosion layer acts as a barrier, and the barrier prevents further corrosion. As the corrosion further invades the inside of the coating, the impedance value increases and decreases, causing the change in the resistance radius in the high-frequency region. In addition, Figures 7b-14b show that the time parameters of group A samples occur in the high-frequency area with a frequency of \(10^{3}\)-\(10^{5}\) Hz, and there is no time parameter generation at other frequencies, indicating that corrosion occurs on the surface of the steel bars and the corrosion substance acts as protection. For group B, the time parameters appear in the low-frequency region (25) with a frequency of \(10^{-2}\)-\(10^{-1}\) Hz; that is, corrosion on the surface of the substrate occurs. For group A, \(R_{\rm C}\) was 1440.21 \(\Omega\) at 0 days and 113.51 \(\Omega\) at 2160 days, exhibiting a trend of decreasing with the increase in soaking time. For group B, \(R_{\rm C}\) was 6.71 \(\times\) 104 \(\Omega\) at 0 days and 842.57 \(\Omega\) at 2160 days, and it decreased with the increase in soaking time.  
Figure 6: Calculation results for corrosion current density.  
Figure 8: Nyquist and Bode diagrams for group A specimens (540–990 days).  
Figure 7: Nyquist and Bode diagrams for group A specimens (0–450 days).  
Figure 9: Nyquist and Bode diagrams for group A specimens (1080–1530 days).  
Figure 11: Nyquist and Bode diagrams for group B specimens (0–450 days).  
Figure 12: Nyquist and Bode diagrams for group B specimens (540–990 days).  
Figure 10: Nyquist and Bode diagrams for group A specimens (1620–2160 days).  
Figure 14: Nyquist and Bode diagrams for group B specimens (1620–2160 days).  
Figure 13: Nyquist and Bode diagrams for group B specimens (1080–1530 days).  
Figure 15: Polarisation impedance for group A and B specimens.