## 3 Results and Discussion
### NMR Saturation Test Analysis  
Before using NMR technology to visually obtain the internal moisture distribution of the material, calculation and simulation were carried out according to Equation (12) to predict the saturation at a long distance from the water absorption surface. From the root formula, the value of \(\varphi\) can be expressed by Equation (19):  
\[\varphi=\frac{-s+\sqrt{s^{2}+4A\int_{\theta}^{1}\frac{D(a)}{a}da}}{\text{A}} \tag{19}\]  
Then, the relationship between the coordinate \(x\) of a point in the test sample and its relative water content is:  
\[x=\varphi\sqrt{t}=\frac{-s+\sqrt{s^{2}+4A\int_{\theta}^{1}\frac{D(a)}{a}da}}{ \text{A}}\sqrt{t} \tag{20}\]  
In the first half, the saturation of the function gradually decreases with distance, whereas in the second half, it decreases rapidly. The curve of the function is parabolic. The data in [49] also perform well with this function. However, there is a limitation in formula simulation. In the prediction of Equation (20), \(x\) has a maximum value. When the distance exceeds the maximum value, its saturation defaults to 0. The NMR technique uses the MSE sequence to perform spatial encoding by reading the gradient. The acquired data images are shown in Figure 4.  
After the cement mortar samples were saturated with water, the saturation was set to 100%, while that at 0 h was set to 0%. Then, the saturation curve as a function of the spatial position was calculated from the signal value ratio. As shown in Figure 5, the internal moisture distribution of the material obtained by the NMR technique is significantly different from that obtained by the formula calculation simulation. Moreover, the curve does not show a downward trend as the water absorption distance increases. Although the magnitude of the nuclear magnetic signal on the ordinate cannot be directly substituted into the calculation, it can be used to reflect the quality of pure water in the sample. After fitting, the relationship between the semaphore and pure water quality was roughly a function. As the test conditions changed, the scale factor changed as well. Here, the unknown coefficient was defined as \(\gamma\) and was retained, not specifically calculated. From signal value of 0 h and saturated state, the water content \(\Theta_{s}(\gamma)\) in the saturated state of each test group was calculated. The capillary water absorption coefficient \(S\) of each group and the water content \(\Theta_{s}(\gamma)\) in the saturated state of each group were  
Figure 3: Fitting result of early stage. substituted into Equation (13) to obtain \(s\). Subsequently, the \(D_{0}\) of the exponential function and power function were obtained using Equations (15) and (17), respectively (see Table 5). Figure 4: Signal values of the water absorption process obtained by the NMR test. Figure 5: Saturation of water absorption process. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Group**} & **Capillary Water Absorption** & **Saturated Water** & **Exponential \(D_{0}\)** & **Power \(D_{0}\)** \\  & **Coefficient \(S\)** & **Content \(\Theta_{s}(\mathbf{\gamma})\)** & **Exponential \(D_{0}\)** & **Power \(D_{0}\)** \\ \hline J & 1.02454 & 10.22809899 & \(8.15\times 10^{-5}\) & 0.037460 \\ \hline K & 1.02159 & 9.692812897 & \(9.02\times 10^{-5}\) & 0.041472 \\ \hline KS & 0.76777 & 12.742302 & \(2.95\times 10^{-5}\) & 0.013554 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: \(D_{0}\) values of exponential and power functions. Substituting the saturation value calculated from the signal value obtained in the NMR test into Equations (8) and (9), the water diffusion coefficient \(D(\theta\gamma)\) at each depth section at different time intervals was obtained, as shown in Figures 6 and 7. Figure 6: Comparison of the exponential \(D(\theta\gamma)\) at different time intervals. Figure 7: Comparison of the power \(D(\theta\gamma)\) at different time intervals.