With the restoration of major projects across the country, the construction of railways and highways and other transportation projects, coupled with the continuous promotion of the “Belt and Road” strategy, has become the focus of capital construction and investment. With the construction of tunnels around the world, tunnel wet sprayers can be seen everywhere with their high quality and service. So what should you pay attention to during the construction process? Let me take a look at it below.
During the spraying process, the nozzle movement should be adapted to the local conditions. The strips, vertical bars and circles should be used alternately to ensure that the concrete pile leaves to a certain thickness, and then the injection area of the wet shotcrete machine is gradually expanded. After the upper and the first wall are arched, when there is unevenness, the groove should be recessed and filled before the nozzle is spiraled or S-shaped slowly and evenly, and the front half of the ring is pressed to reduce the rebound. The spray length should be controlled at 3-4m in order to smooth and smooth the sprayed concrete surface.
Rebound refers to the mixture falling from the sprayed surface due to the collision between the concrete surface and the rock face, steel bars and aggregate particles. The amount is due to the injection position, air pressure, cement dosage, water cement ratio, aggregate. The particle size, the amount of steel and other factors vary. Generally, the amount of rebound is large at the initial stage of the injection. When the plastic layer is formed, the coarse aggregate is easily embedded and the amount of rebound is reduced. Therefore, the thickness of the primary spray layer is not less than 4 cm. At the same time, since the rebound material contains impurities and the amount of cement is small, it cannot be re-injected and the collected rebound material cannot be used in the next batch.
In the spraying process of wet shotcrete equipment, the nozzle should be perpendicular to the rock face, and the side wall spraying should be about 10° down the nozzle, so that the wet shotcrete machine can be sprayed on the top of the thick concrete during the spraying work. The top should be sprayed in the diameter direction. If the spray surface is covered with a grille or steel bars, the nozzle can be slightly inclined but not less than 70°. The angle should be too small to cause the concrete material to roll on the spray surface. The wave surface is generated while increasing the rebound amount; the injection distance should be determined by the minimum rebound amount and the highest intensity. Generally, the beam concentration and the rebound amount are the minimum, and the jet length of the wet shotcrete equipment should be controlled. In the range of 0.6-1.2 m, the air pressure at the nozzle is controlled at 0.3-0.5 MPa.
