## 3 Results and Discussion
### NMR Saturation Test Analysis
Figures 6 and 7 indicate that the amount of water absorption in the concrete and the water diffusion coefficient \(D(\theta\gamma)\) increase. The water diffusion coefficient curves of group J are above the curves of groups K and KS, which indicate that the water diffusion capacity of group J was relatively strong. This implies that the impermeability of cement-based materials is improved by the addition of a waterproofing agent or a combination of a waterproofing agent and nano-SiO\({}_{2}\). Comparing the curves of groups K and KS, the water diffusion coefficient of group KS was significantly lower than that of group K at each section position, which suggested that after nano-SiO\({}_{2}\) is added to the mixture, the cement mortar structure is more uniform and denser than that with only the waterproofing agent. Moreover, there were fewer connected pores, which weakened the water diffusion ability. \(D(\theta\gamma)\), the water diffusion coefficient, is a function that describes the strength of water transport and is positively correlated to porosity. Consequently, the number of pores in the section where the peak surface appears can be assumed to be high. Comparing the curves of group J at 1 and 4 h, as shown in Figure 7, a new peak appeared at 20-30 mm; at 49 h, another new peak appeared near 40 mm. Essentially, as the test time increases, the surface moisture continuously spreads into the material. When it is transmitted to a relatively loose section, it appears as a more obvious peak on the curve. Therefore, by observing the position and time of each peak in the graph, the distribution of the sample density can be evaluated and the approximate depth of water infiltration can be determined. The group K curve also followed a similar law. However, the undulation of the curve was small, which implied that the waterproofing agent effectively improved the compactness of the cement mortar. The group KS curve showed almost no obvious peak during the entire test period, which indicated that nano-SiO\({}_{2}\) further improved the pore distribution of the cement mortar sample and reduced the pore size. The average water diffusion coefficient \(D(\theta\gamma)\) of each group exhibited three curves--high, medium and low--related to the degree of modification of the material, as shown in Figure 8. Although the initial waterproofing effect of the KIM waterproofing agent was not obvious, the test sample had lower saturation during the initial stage of the water absorption test, and the curve differed from the capillary water absorption fitting curve. However, as the test proceeded, the effect of the waterproofing agent was more pronounced and, consequently, the growth rate of the curve was lower than that of group J. The presence of nano-SiO\({}_{2}\) further increased the waterproofing effect in group KS, and the curve increased even more slowly than that of group K. Compared to Figure 2, the slope of the curve began to change after about 49 h of the capillary water absorption test, which indicated that the cumulative water absorption gradually entered a stable state and the water content of the test sample began to saturate. In Figure 8, the three curves have a noticeable transition at about 50 h, indicating that the internal saturation of the test samples changed significantly. This indicates that the water content was at a higher level, which confirms the results of the capillary water absorption test. Figure 8: Relationship between \(D(\theta\gamma)\) and time. Figure 9 shows that the relationship between the water diffusion coefficient of the three test groups. The curves of groups J and K are very close, and the growth rate is significantly larger than that of group KS. This corroborates the curve fitting result of the capillary water absorption test (Figures 2 and 3). Overall, the results of the two tests are in good agreement with each other.