Shotcrete is a commonly used construction technique, widely applied in tunnel construction, slope reinforcement, and underground engineering, among other fields. Depending on the construction method, shotcrete can be divided into three techniques: dry-mix shotcrete, wet-mix shotcrete, and moist-mix shotcrete. Each technique utilizes different equipment, namely dry-mix shotcrete machines, wet-mix shotcrete machines, and moist-mix shotcrete machines. The primary distinction between these techniques lies in the material feeding process, particularly the timing of adding water and accelerators.

　　1. Dry-Mix Shotcrete Technique

　　Dry-mix shotcrete involves conveying dry concrete materials to the nozzle via high-pressure air and then mixing with water at the nozzle before being sprayed onto the construction surface. The main features of dry-mix shotcrete are simple equipment, wide applicability, and fast spraying speed. However, since the material is dry during spraying, it generates a large amount of dust pollution. Additionally, dry-mix shotcrete exhibits high rebound rates and significant material waste, while the dust pollution in the construction environment poses a threat to the health of operators.

　　2. Wet-Mix Shotcrete Technique

　　Wet-mix shotcrete involves pre-mixing concrete materials with a certain amount of water before entering the nozzle, then spraying them onto the construction surface using spraying equipment. Compared to dry-mix shotcrete, wet-mix shotcrete can effectively reduce dust pollution and rebound. However, due to the relatively small amount of pre-mixed water, the flowability and workability of concrete are still not as ideal as the moist-mix shotcrete technique.

　　3. Moist-Mix Shotcrete Technique

　　Moist-mix shotcrete involves thoroughly mixing concrete materials and water in a mixer before pumping the moist concrete to the nozzle, where it is mixed with accelerators and then sprayed onto the construction surface. The advantages of moist-mix shotcrete lie in its good flowability and workability, enabling more uniform coverage of the construction surface and reducing rebound and material waste. Moreover, moist-mix shotcrete generates less dust pollution, contributing to improved construction environment and operator health protection.

　　In practical construction, choosing the appropriate shotcrete technique requires comprehensive consideration of specific project requirements, environmental conditions, and economic factors. Although dry-mix shotcrete has simple equipment and low costs, its limitations due to high dust and rebound rates restrict its applicability. While wet-mix shotcrete partially addresses these issues, it still falls short of the ideal performance of moist-mix shotcrete. Although moist-mix shotcrete involves more complex equipment and higher costs, its construction quality and environmental performance are optimal, making it suitable for projects with high requirements for construction quality and environmental standards.

　　Each shotcrete technique—dry-mix, wet-mix, and moist-mix—has its pros and cons, and the choice of technique should be balanced according to specific project needs. With technological advancements and increasing environmental requirements, the application of moist-mix shotcrete in modern engineering projects is becoming more widespread, and its advantages are becoming increasingly evident.

　　By understanding and applying different shotcrete techniques, engineers can better select suitable construction methods to ensure construction quality and safety.