Rebound rate of shotcrete in tunnel What is shotcrete?

1. At present, the rebound of shotcrete in tunnel engineering is generally 30%, which is a big loss. Through technical improvement and strengthening management, the rebound of sprayed concrete can be controlled at about 20%. Shotcrete is a construction method of spraying and pouring fine stone concrete with pressure spray gun. It is usually used for pouring thin-walled structures, such as tunnel lining, walls and ceilings, or the lining of other structures and the protective layer of steel structures.

2. Shotcrete is formed by putting cement, sand, stone, water and a certain amount of additives prepared in advance into a jet machine, feeding them into the nozzle by using high-pressure air and mixing them with accelerator, and then spraying them on the surface of rock or concrete at high speed.

3. Dry mixing method is a method of mixing cement, sand and stone evenly in dry state, sending it and accelerator to the nozzle with compressed air and mixing it with pressure water for sprinkler irrigation. This method must be operated by skilled personnel, the water cement ratio should be small, the stones should be graded continuously, the particle size should not be too large, and the cement dosage should not be too small. Generally, concrete strength of 28 ~ 34 MPa and good cohesive force can be obtained. However, due to the high injection speed, serious dust pollution and rebound, the use is limited.