## 2 Material and Methods  
When a liquid droplet exists on a solid surface, the angle formed between the liquid-gas interface and the liquid-solid interface is a measure of how well the solid surface can be wetted by the liquid. When a liquid droplet is present on a solid surface, the balance of two forces determines the shape of the liquid droplet. One force is cohesion, which refers to the attractive forces between the molecules within the liquid itself, and this force tends to make the liquid droplet spherical. The other force is adhesion, which refers to the attractive forces between the liquid and the solid, and this force tends to spread the liquid droplet widely on the solid surface. Therefore, the shape of the liquid droplet is determined by which of these two forces is dominant [15]. Figure 3 below illustrates this concept. The contact angle, as shown in Figure 3, is the angle measured on the inside of the liquid between the liquid-gas interface and the liquid-solid interface. Therefore, when cohesion is dominant, the contact angle increases (close to a sphere), and when adhesion is dominant, the contact angle decreases (spreads widely). When a liquid exhibits a small contact angle and spreads completely on the solid surface, it is referred to as hydrophilic, and significant wetting occurs. The solid surface is said to be hydrophilic. On the other hand, when the liquid exhibits a large contact angle, with minimal wetting occurring on the solid surface, and water droplets roll on the surface, it is referred to as super-hydrophobic. In this case, the liquid exists as separate nearly spherical liquid droplets on the solid surface [15]. Based on these principles, for adhesive strength measurement, it is important to clearly outline the key parameters to develop a quantitative measurement method with minimal influence from the fewest variables possible. For this, reference to existing adhesion strength measurement methods and outlining the key principles of these methods is required. Types of Adhesion Strength Measurement Methods for Self-Adhesive Waterproofing Sheets (Laboratory Testing Methods)  
For adhesion peel testing, various methods exist, including the roller drum peel method and 90\({}^{\circ}\) and 180\({}^{\circ}\) peel adhesion testing. These methods, as shown in Figure 4, are employed to measure the adhesion strength. While there may be slight variations in certain test conditions, such as the sample size and testing speed, the testing methods remain consistent across both domestic and international standards [16; 17]. However, all existing adhesion strength testing methods, including those shown in Figure 4, require the use of an UTM or specialized peel testing equipment, where the force is applied vertically. Currently, there are no specific testing standards available to measure the adhesion strength of waterproofing sheets adhered to vertical concrete surfaces. The only relevant adhesion strength testing standard for waterproofing sheets is the peel-out test specified in KS F 4934, which does not allow for testing on vertical surfaces. The roller drum peel method shown in Figure 4a, the American Society for Testing and Materials (ASTM D 3167) [18], is the most similar to the peel-out test method in KS F 4934 and can be considered a Korean adaptation of that method. In this method, when the waterproofing sheet is pulled by the crosshead, the substrate moves in proportion to the distance the sheet is peeled. Figure 3: Contact angle due to surface tension. The 180\({}^{\circ}\) peel method shown in Figure 4b [19] requires the sample to be peeled off the concrete surface while maintaining a 180\({}^{\circ}\) angle. This makes it difficult to secure the sample to the testing equipment. Even if the sample is attached, when measuring in the vertical or horizontal directions, the uneven concrete surface can affect the applied load on the measurement area due to the movement of the crosshead.