1. Preparation before concrete spraying operation (1) The injection surface should be treated before injection. Generally, high-pressure water can be used to flush the dust and debris from the spray surface. When the rock face is easily deliquescent and muddy, it should be blown with high-pressure air. If it is a mud or sand surface, a steel mesh (the mesh should not be larger than 200×200mm) should be hung, and it should be fixed with a hoop steel bar and an anchor or a steel frame so that it is closely attached to the spray surface to improve the adhesion of the shotcrete. Focus on. Before spraying concrete, it is advisable to spray a layer of cement mortar first and then spray the concrete after the final setting.
(2) Set the mark for controlling the thickness of shotcrete. Generally, the mark shall be marked with the embedded steel bar head. It is also possible to insert an iron wire with a length 5cm larger than the designed thickness when spraying, one for each 1~2m, as construction control.
(3) Check the sprayer equipment and wind, water, electricity and other pipe lines, and test run.
1 The selected air compressor should meet the requirements of the working pressure and air consumption of the spraying machine; pressure and air must be separated before entering the spraying machine;
2 The feeding pipe should be able to withstand the pressure above 0.8MPa, and should have good wear resistance;
3 Ensure that the work area has good ventilation and lighting conditions.
4 The ambient temperature of the spraying operation must not be lower than 5°C.
(4) In the event of a gushing, seepage, or damp rock face on the spray surface, it should be treated according to different conditions before spraying.
1 The majority of the surge of water should adopt grouting and water shutoff before spraying concrete.
2 Small strands of water or fissures Leakage of water should be followed by rock grouting or conduit drainage followed by concrete spraying.
The 3 large areas of wet rock face should adopt cement with strong adhesion, such as adding additives and admixtures to improve the performance of concrete.
2. Concrete Spraying Operation Process (1) The shotcrete operation should be carried out in segments, slices, and layers in sequence. The injection sequence should be from bottom to top. The length of the segment should not be greater than 6m. At the time of spraying, the low enthalpy is roughly leveled, and then it is stratified and reciprocally injected from bottom to top.
1 In the construction of shotcrete section, the slope of the last sprayed concrete shall be reserved. The width of the bevel shall be 200-300mm. The inclined surface shall be flushed and wetted with pressure water before spraying the concrete.
The two-slice jets are to be carried out from the bottom up, and first spray the concrete between the steel frame and the wall, and then spray the concrete between the two steel frames. Sidewall shotcrete should be sprayed upward from the foot of the wall so that the springback does not become trapped in the final spray.
3 When stratified injection, the next layer of spray should be performed after the final layer of concrete is finalized. If spraying is completed after 1h of final coagulation, the surface of spray layer should be cleaned with feng shui. The thickness of a shotcrete is such that the shotcrete does not slip and fall without falling. It cannot affect the bond strength and cohesive force of the shotcrete due to too large thickness, nor can it be too thin to increase the rebound amount. The shotcrete thickness of a side wall is controlled at 7 to 10 cm and the arch is controlled at 5 to 6 cm, and the thickness of the sprayed layer is kept uniform. When the concrete is sprayed on the top, in order to avoid the occurrence of slumping, the interval between the two should be 2~4h.
(2) The jet speed should be appropriate to facilitate the compaction of the concrete. The wind pressure is too high, the injection speed increases, and the rebound increases; the wind pressure is too small, the injection speed is too small, and the pressure strength is small, which affects the strength of shotcrete. Therefore, after starting the machine, observe the wind pressure and start the operation after the initial wind pressure reaches 0.5 MPa. Adjust the air pressure according to the discharge conditions of the nozzle. The general working wind pressure: 0.3-0.5 MPa on the side wall and 0.4-0.65 MPa on the arch. In the loess tunnel shotcrete, the jet pressure is generally not greater than 0.2 MPa.
(3) Keep a proper distance between the nozzle and the sprayed surface when spraying, and the spray angle should be as close as possible to 90° so that maximum compaction and minimum rebound can be achieved. The distance between the nozzle and the sprayed surface should be 1.5~2.0m; the nozzle should be continuous and slow to move in a horizontal direction, and the circle should be pressed half a turn. The ring circled by the sprayer should be 40~60cm in the horizontal direction and 15~20cm in height; When the surface is covered by a steel frame or steel mesh, the nozzle may be slightly deflected, but it should not be less than 70°. If the angle between the nozzle and the sprayed surface is large, it will cause the concrete material to roll on the sprayed surface, creating a bumpy wave spray surface, increasing the rebound amount and affecting the quality of the sprayed concrete.
3. After curing the sprayed concrete for 2 hours, it shall be cured. Spray curing. Conservation time is not less than 14d. When the temperature is lower than +5°C, no watering is allowed.
(2) Set the mark for controlling the thickness of shotcrete. Generally, the mark shall be marked with the embedded steel bar head. It is also possible to insert an iron wire with a length 5cm larger than the designed thickness when spraying, one for each 1~2m, as construction control.
(3) Check the sprayer equipment and wind, water, electricity and other pipe lines, and test run.
1 The selected air compressor should meet the requirements of the working pressure and air consumption of the spraying machine; pressure and air must be separated before entering the spraying machine;
2 The feeding pipe should be able to withstand the pressure above 0.8MPa, and should have good wear resistance;
3 Ensure that the work area has good ventilation and lighting conditions.
4 The ambient temperature of the spraying operation must not be lower than 5°C.
(4) In the event of a gushing, seepage, or damp rock face on the spray surface, it should be treated according to different conditions before spraying.
1 The majority of the surge of water should adopt grouting and water shutoff before spraying concrete.
2 Small strands of water or fissures Leakage of water should be followed by rock grouting or conduit drainage followed by concrete spraying.
The 3 large areas of wet rock face should adopt cement with strong adhesion, such as adding additives and admixtures to improve the performance of concrete.
2. Concrete Spraying Operation Process (1) The shotcrete operation should be carried out in segments, slices, and layers in sequence. The injection sequence should be from bottom to top. The length of the segment should not be greater than 6m. At the time of spraying, the low enthalpy is roughly leveled, and then it is stratified and reciprocally injected from bottom to top.
1 In the construction of shotcrete section, the slope of the last sprayed concrete shall be reserved. The width of the bevel shall be 200-300mm. The inclined surface shall be flushed and wetted with pressure water before spraying the concrete.
The two-slice jets are to be carried out from the bottom up, and first spray the concrete between the steel frame and the wall, and then spray the concrete between the two steel frames. Sidewall shotcrete should be sprayed upward from the foot of the wall so that the springback does not become trapped in the final spray.
3 When stratified injection, the next layer of spray should be performed after the final layer of concrete is finalized. If spraying is completed after 1h of final coagulation, the surface of spray layer should be cleaned with feng shui. The thickness of a shotcrete is such that the shotcrete does not slip and fall without falling. It cannot affect the bond strength and cohesive force of the shotcrete due to too large thickness, nor can it be too thin to increase the rebound amount. The shotcrete thickness of a side wall is controlled at 7 to 10 cm and the arch is controlled at 5 to 6 cm, and the thickness of the sprayed layer is kept uniform. When the concrete is sprayed on the top, in order to avoid the occurrence of slumping, the interval between the two should be 2~4h.
(2) The jet speed should be appropriate to facilitate the compaction of the concrete. The wind pressure is too high, the injection speed increases, and the rebound increases; the wind pressure is too small, the injection speed is too small, and the pressure strength is small, which affects the strength of shotcrete. Therefore, after starting the machine, observe the wind pressure and start the operation after the initial wind pressure reaches 0.5 MPa. Adjust the air pressure according to the discharge conditions of the nozzle. The general working wind pressure: 0.3-0.5 MPa on the side wall and 0.4-0.65 MPa on the arch. In the loess tunnel shotcrete, the jet pressure is generally not greater than 0.2 MPa.
(3) Keep a proper distance between the nozzle and the sprayed surface when spraying, and the spray angle should be as close as possible to 90° so that maximum compaction and minimum rebound can be achieved. The distance between the nozzle and the sprayed surface should be 1.5~2.0m; the nozzle should be continuous and slow to move in a horizontal direction, and the circle should be pressed half a turn. The ring circled by the sprayer should be 40~60cm in the horizontal direction and 15~20cm in height; When the surface is covered by a steel frame or steel mesh, the nozzle may be slightly deflected, but it should not be less than 70°. If the angle between the nozzle and the sprayed surface is large, it will cause the concrete material to roll on the sprayed surface, creating a bumpy wave spray surface, increasing the rebound amount and affecting the quality of the sprayed concrete.
3. After curing the sprayed concrete for 2 hours, it shall be cured. Spray curing. Conservation time is not less than 14d. When the temperature is lower than +5°C, no watering is allowed.
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