Shotcrete is a construction technology that involves using mechanical equipment to spray concrete at high speed onto a structural surface to form a tightly bonded layer. Based on the state of the concrete and the construction method used during the process, shotcrete construction techniques can be categorized into three types: dry-mix shotcrete, semi-wet mix shotcrete, and wet-mix shotcrete. Each method has its unique features and applications.

　　1. Dry-Mix Shotcrete

　　Dry-mix shotcrete involves conveying dry concrete materials to the nozzle, where they are mixed with high-pressure water before being sprayed onto the structural surface. The main characteristics of this method include:

　　- Flexible Material Control: The water-cement ratio can be adjusted on-site, allowing for better adaptation to varying construction conditions.

　　- High Rebound Rate: Due to incomplete mixing during spraying, some materials tend to rebound, leading to increased waste.

　　- High Dust Production: The dry process generates significant dust, impacting the construction environment and workers' health.

　　2. Semi-Wet Mix Shotcrete

　　Semi-wet mix shotcrete is a method that falls between dry-mix and wet-mix shotcrete. It involves adding a portion of water to the concrete materials before feeding them into the shotcrete machine, which then uses high-pressure air to spray the mix onto the structural surface. Features of this method include:

　　- Moderate Material Consistency: Partial water addition reduces dust generation while maintaining a certain level of rebound.

　　- Simplified Construction: Compared to dry-mix shotcrete, the semi-wet mix method is easier to operate and offers better controllability during construction.

　　- Wide Applicability: Suitable for various construction environments, especially those with high dust control requirements.

　　3. Wet-Mix Shotcrete

　　Wet-mix shotcrete involves spraying already fully mixed wet concrete directly onto the structural surface through delivery pipes. Its main characteristics include:

　　- Low Rebound Rate: Fully mixed concrete before spraying significantly reduces material rebound, minimizing waste.

　　- Minimal Dust Production: The wet process generates almost no dust, making it more environmentally friendly and healthier for workers.

　　- High Construction Quality: The wet-mix method allows for better control of concrete uniformity and adhesion, enhancing construction quality.

　　The choice of shotcrete construction technique should be determined based on specific construction requirements and site conditions. Dry-mix shotcrete is suitable for sites where material control is crucial but dust impact is not a major concern. The semi-wet mix method offers a balanced approach between dust control and material management. Wet-mix shotcrete, with its high quality, low dust, and low rebound characteristics, is often the preferred choice for high-standard construction projects. Reasonable selection and application of different shotcrete construction techniques can significantly improve construction efficiency and project quality.