# Study on Corrosion Monitoring of Reinforced Concrete Based on Longitudinal Guided Ultrasonic Waves
## 4 Testing of Corroded Reinforcement
### Test Results for RC
#### 4.3.4 Comparative Analysis with Theoretical Corrosion Model  
Combined with the existing corrosion model of the RC [26], the effectiveness of the DI proposed in the paper is demonstrated by comparing the theoretical corrosion times and measured DI-SAD results at different corrosion stages. Combining Figure 17 and Table 3, it can be found that the error of the internal cracking time is within 7% for the RC specimens with diameters of 75 and 110 mm, and the error of the surface cracking time is within 2% for the 110 mm diameter specimens.  
At the same time, it is also seen that there is a large error between the test value and the theoretical value of the internal cracking time and the surface cracking time of the RC specimen with the 160 mm diameter, and the test results are obviously lagging behind. This is because the theoretical corrosion model assumes that when the cover thickness is greater than 30 mm, the opening necessary to start cracking no longer increases with increasing cover thickness. However, the test results show that for the RC specimens with a diameter of 160 mm (cover thickness of 70 mm), the cracking time lags significantly behind that of the RC specimens with a diameter of 110 mm (cover thickness of 45 mm). This phenomenon suggests that increasing the concrete cover thickness is advantageous in delaying the corrosion cracking of the RC specimens. Although the cover thickness of a typical RC structure does not exceed 40 mm, the cover thickness of pixels and prestressed RC structures on sea-crossing bridges is usually much larger. Therefore, the internal  
Figure 17: Comparison of test and theoretical values for cracking time of RC specimens.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \begin{tabular}{c} **Covered** \\ **Diameter** \(D\) ** \\ **(mm)** \\ \end{tabular} & \begin{tabular}{c} **Test Value for** \\ **Internal** \\ **Cracking Time** \\ **\(T_{internal}^{test}\) (h)** \\ \end{tabular} & \begin{tabular}{c} **Theoretical Value for** \\ **Internal Cracking Time** \\ **\(T_{internal}^{theory}\) (h)** \\ \end{tabular} & \begin{tabular}{c} **Error** \\ **Cracking Time** \\ **\(T_{surface}^{test}\) (h)** \\ \end{tabular} & \begin{tabular}{c} **Test Value for** \\ **Surface Cracking Time** \\ **\(T_{surface}^{theory}\) (h)** \\ \end{tabular} & \
\begin{tabular}{c} **Theoretical Value for** \\ **Surface Cracking Time** \\ **\(T_{surface}^{theory}\) (h)** \\ \end{tabular} &
\begin{tabular}{c} **Error** \\ **Error** \\ **Error** \\ **\(T_{surface}^{theory}\) (h)** \\ \end{tabular} \\ \hline \(75\) & \(72\) & \(67\) & \(-6.94\%\) & \(168\) & \(147\) & \(-12.50\%\) \\ \(110\) & \(96\) & \(101\) & \(5.21\%\) & \(216\) & \(212\) & \(-1.85\%\) \\ \(160\) & \(168\) & \(101\) & \(-39.88\%\) & \(336\) & \(274\) & \(-18.45\%\) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Comparison of test and theoretical values for cracking time of RC specimens.  
reinforcement corrosion of the concrete at larger covered thicknesses should be considered; otherwise, the extent of internal reinforcement corrosion at large covered thicknesses will be underestimated.