Wet spraying machine mixes cement, water and aggregates according to the design proportion, and uses a wet spraying machine to press the nozzle to the nozzle. Then, the accelerator is added to the nozzle and merged with the wind to spray.
Mixing ratio of wet sprayer concrete
The concrete proportioning principle is generally 2350kg per cubic meter of concrete (process requirements, the actual site is 1,650kg, of which sand, stone, water 1300kg, and cement 350kg). The ratio of cement, stone and sand in the concrete is 1: 1.5: 2.25 (weight ratio), and the water-cement ratio is 0.44 (the amount of water per cubic meter of concrete is 200kg). When the aggregate is sieved, the maximum diameter must not exceed 8-10mm to prevent the pump from being blocked.
Additives for wet sprayer
In order to ensure the performance of concrete, it is necessary to add hydration control agents, water reducing agents and accelerators to the concrete.
1. Water reducing agent: Its role is to reduce the water-cement ratio (reduce the amount of water) and ensure the fluidity and pumpability of concrete. The added amount is generally 1% of the weight of the cement (5 kg / 1650 kg mixture on site).
2. Hydration control agent: its role is to control the premature hydration of cement (cement hardens), to ensure that concrete is stored for a long time without becoming hard and has sprayability. The added amount is generally 0.3% -0.7% of the weight of cement (3 kg / 1650 kg mixture on site).
3. Accelerator: Its role is to ensure the rapid solidification of the sprayed concrete, thereby ensuring the initial setting time of the concrete and reducing the rebound rate of the concrete. The added amount is generally 4% -6% of the weight of the cement (the volume of the transportation tank is 2m3, which is added at the site according to 26kg, and the amount of the accelerator used when spraying on the top needs to be increased)
4. Adding order of auxiliary materials: Water reducing agent and hydration control agent are added when mixing the concrete, and quick setting agent is added at the nozzle of the spray gun when spraying the concrete.
Precautions for shotcrete operation
1. The angle between the spray gun head and the rock interface should be kept vertical (90 °) to spray, so that the rebound rate can be minimized;
2. The distance between the spray nozzle and the rock surface must be maintained at 1-1.5 meters, and must not exceed 1.5 meters. The optimal distance is 1 meter to ensure the least rebound rate;
3. The amount of alkali-free accelerator should be controlled within the allowable range of 4-6%. Too much or too little will affect the rebound rate;
4. In order to achieve the least rebound rate, it is necessary to perform high-pressure wind dust removal and water spraying on the rock surface to be sprayed before spraying, in order to achieve effective bonding between the sprayed concrete and the rock surface;
5. For dry roadways, sprayed concrete should be properly sprayed after spraying. If the underground is wet, the concrete can be cured naturally.
