## 3 Test Methods and Result for Analysis of Swelling Property of Water-Expandable Polyurethane
### Swelling and Leakage Test Methods and Results  
#### 3.1.1 Swelling Rate Test Methods and Result  
(1) Swelling Rate Test Methods  
(1) Specim Preparation  
To identify the volume expansion ratio of the polyurethane with water expansion properties according to the superabsorbent polymer content, polyurethanes were prepared by adjusting the content of the superabsorbent polymer to be constant. In order to clearly confirm the change of water expansion properties according to the content, the adjustment of the superabsorbent polymer content was planned to increase by 1% of the weight of the curing agent (B-side), as shown in Table 3. A total of 20 test specimens were fabricated by increasing the superabsorbent polymer content by up to 20%.  
Figure 5: The schematic diagram of the waterproofing principle and the sealing status of the damaged area due to water expansion in the event of actual damage: (**a**) Water ingress through damaged areas; (**b**) Reaction with water and waterproofing due to expansion; (**c**) Damaged area (width 1 mm)—plane; (**d**) After reaction with water and expansion—plane; (**e**) Damaged area (width 1 mm)—section; (**f**) After reaction with water and expansion—section.  
The test specimen was fabricated by stirring the base resin (A-side) and the curing agent (B-side) for 5 min with the use of a mechanical stirrer, applying the coating material with a thickness of 2 mm, and curing it in a constant temperature chamber at 20 \(\pm\) 2 \({}^{\circ}\)C for 168 h. Table 4 and Figure 6 show the specimen fabrication conditions and status.  
2 Calculation of Swelling Rate  
The swelling rate test on the prepared specimen was conducted in accordance with the test method specified in a KS M 3736 Waterproofing sheet with expandable bentonite. The test was done by taking about 2 g of the sample, putting it in a graduated cylinder (100 mL), and filling 50 mL of distilled water up to the 50 mL scale mark of the graduated cylinder containing the sample by means of a burette. Then, the volume of the water remaining in the burette is set as the initial volume (mL). After that, enough distilled water is added to the graduated cylinder to expand it for 120 h, and the distilled water is then removed to measure the volume after expansion in the same way as the initial volume measurement. The swelling rate is calculated using Equation (1), and the status is shown in Figure 7[16].  
\[\mathrm{V}_{e}=\frac{V_{1}-V_{2}}{V_{1}}\times 100 \tag{1}\]  
where: \(\mathrm{V}_{e}\)--swelling rate (%); \(V_{1}\)--initial volume (mL); \(V_{2}\)--volume after expansion (mL).  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Division** & **Condition** \\ \hline Mixing ratio & 1:4.25 \\ (A-side:B-side) & \\ Mixing method & Mechanical stirrer, 5 min stirring \\ Coating thickness & 2 mm \\ Curing & (20 \(\pm\) 2) \({}^{\circ}\)C, 168 h \\ \hline \end{tabular}
\end{table}
Table 4: The specimen fabrication conditions.  
Figure 6: The specimen fabrication process: (**a**) stirring; (**b**) coating; (**c**) curing.  
The evaluation results showed that the swelling rate of the water-expandable polyurethane increased with an increase in the superabsorbent polymer content.