Choosing the right water-cement ratio is one of the key technical points in the construction of sprayed concrete, which directly affects the fluidity, adhesion, strength and final construction effect of concrete. The following aspects should be considered to reasonably determine the water-cement ratio:

　　1. Design requirements: First of all, the design documents and relevant specifications of the project should be followed to clarify the expected strength grade and other performance indicators of the concrete, which is the basis for selecting the water-cement ratio.

　　2. Construction conditions:

　　- Type of spraying equipment: Different spraying equipment has different requirements for the rheological properties of concrete. Some equipment may be more suitable for thinner (higher water-cement ratio) concrete, while others are suitable for thicker (lower water-cement ratio).

　　- Spraying height and distance: When spraying over long distances or at high altitudes, a higher water-cement ratio may be more helpful in maintaining the fluidity of concrete and facilitate long-distance transmission.

　　- Spraying area shape: Spraying on complex curved surfaces or narrow spaces may require higher viscosity (i.e., lower water-cement ratio) to help the concrete fit and hang on the wall better.

　　3. Raw material properties:

　　- Aggregate type, particle size and gradation;

　　- Cement type. Different types of cement have different water absorption and different requirements for water-cement ratio;

　　- The influence of admixtures, especially plasticizers and water reducers, can significantly change the workability and strength performance of concrete.

　　4. Experimental verification: In addition to theoretical calculations and design guidance, trial mixing before actual construction is a very necessary step. By making test blocks, their physical and mechanical properties, such as compressive strength and elastic modulus, are measured, and the construction performance of concrete, such as slump, cohesion and water retention, are observed at the same time, which is used as an important basis for adjusting the water-cement ratio.

　　5. Site conditions: Taking into account environmental factors such as temperature and humidity on the day of construction, changes in these natural conditions will affect the initial setting time and hardening speed of concrete, and thus affect the choice of water-cement ratio.

　　6. Safety considerations: Safety is always the primary principle, especially in spraying operations. Although too high a water-cement ratio improves the fluidity of concrete, it may sacrifice long-term structural stability and safety.

　　In summary, choosing the right water-cement ratio requires comprehensive consideration of many factors, and the most suitable ratio is determined through scientific calculations, laboratory tests, and rich practical experience. In addition, continuous on-site monitoring and timely fine-tuning are also indispensable to ensure the quality of shotcrete construction.