Do you know what causes the rebound of shotcrete? How to control the rebound of shotcrete?

　　What causes the rebound of shotcrete?

　　The main reasons for the rebound of shotcrete are as follows:

　　1. Improper spraying operation:

　　- The spraying distance is too large: the impact force of concrete during the spraying process is weakened, and it cannot effectively adhere to the sprayed surface, resulting in increased rebound.

　　- The spraying angle deviation: The angle between the spray gun and the sprayed surface is not appropriate, so that the concrete cannot vertically impact the sprayed surface, reducing the bonding force and increasing the rebound.

　　2. Unreasonable wind pressure control: If the wind pressure is too high, the speed of the sprayed concrete will be too fast, and it will rebound after impacting the sprayed surface; if the wind pressure is too low, the concrete spraying will be weak and easy to rebound.

　　3. Mix ratio problem:

　　- Improper water-cement ratio: If the water-cement ratio is too large, the concrete slurry will be too thin, easy to flow and rebound; if the water-cement ratio is too small, the concrete will be too dry and hard, which is not conducive to bonding with the sprayed surface.

　　- Unreasonable sand ratio: Too high or too low sand ratio will affect the workability of concrete and increase rebound.

　　4. Raw material quality:

　　- Poor aggregate grading: Aggregate particle size is too large or too small, and grading is uneven, which will affect the performance of concrete and increase rebound.

　　- Unstable cement quality: Cement strength, setting time and other indicators do not meet the requirements, affecting the strength and bonding properties of concrete.

　　5. Condition of sprayed surface:

　　- Uneven sprayed surface: The surface is uneven, making it difficult for concrete to adhere evenly and easy to rebound.

　　- There are debris or floating dust on the sprayed surface: It affects the bonding between concrete and the sprayed surface, resulting in increased rebound.

　　6. Improper use of accelerator: The type and dosage of accelerator are not appropriate, which affects the setting time and early strength of concrete, thereby increasing rebound.

　　How to control the rebound of shotcrete?

　　Here are some ways to control the rebound of shotcrete:

　　1. Choose the right mix ratio: Determine the optimal ratio of cement, sand, stone, water and admixtures through experiments to improve the workability and cohesion of concrete.

　　2. Optimize the spraying process:

　　- Control the spraying distance: The distance between the nozzle and the sprayed surface should be kept at 0.6-1.2 meters. Too close or too far will increase the rebound.

　　- Master the spraying angle: The spray gun should be perpendicular to the sprayed surface, and the deflection angle should not exceed 10°.

　　- Control the spraying air pressure: According to factors such as the spraying distance and the length of the feed pipe, the air pressure should be reasonably adjusted, generally 0.1-0.15 MPa.

　　3. Improve the skills of operators: Train operators to master the spraying technology.

　　4. Improve the conditions of the sprayed surface: Remove pumice, debris, etc. on the sprayed surface to ensure that the sprayed surface is flat and clean to reduce rebound.

　　5. Segmented and pieced spraying: Spray in a certain order to avoid repeated spraying and missed spraying.

　　6. Use appropriate spraying equipment: choose a sprayer with good performance and uniform discharge.

　　7. Control the spraying speed: spray evenly and continuously to avoid fast and slow.

　　8. Add admixtures: such as using viscosity enhancers, accelerators, etc. to improve the performance of concrete and reduce rebound.