Tunnel shotcreting is generally divided into dry shotcrete, damp shotcrete, wet shotcrete and mixed shotcrete according to the process flow. The main difference is the different feeding schedules for each process, especially the timing of adding water and accelerator.
Dry shotcrete is to mix the aggregate, cement and quick-setting admixture in a certain proportion, and then into the jet machine. The compressed aggregate is used to make the dry aggregate in the hose in a suspended state and then sent to the spray gun, and then in the nozzle. It is mixed with high-pressure water and sprayed onto the rock at a higher speed.
The aggregate is pre-applied with a small amount of water to make it moist, and then cement is added to reduce the dust during feeding, mixing and spraying. A large amount of water is still added and sprayed at the nozzle, and the spraying process is the same as the dry spraying process. At present, the construction site often uses a tidal spray process.
The aggregate, cement and water are mixed evenly according to the design ratio, and are sent to the nozzle by a wet jet machine, and then the quick-setting agent is added to the nozzle and then sprayed out.
It’s also known as cement wrap sand shell injection method. It is to add a part of sand to the first water to mix wet, and then put all the cement to force the agitated shell; then add a second water and water reducer to form SCE mortar; Force another part of the sand and stone and quick-setting agent to stir evenly. Then, they are separately sent to the mixing tube by a mortar pump and a dry jet to be sprayed.