The wet spraying trolley uses compressed air to transport the concrete mixture to the sprayed surface through the pipeline, and quickly solidifies on its surface to form a concrete support layer. The shotcrete construction technology is simple, the effect is unique, the cost is low, the construction speed is fast, and it has been widely used in construction, railway highway tunnel construction, mine shaft construction, slope reinforcement and so on.‍

According to the construction process, tunnel shotcrete is divided into dry spray, tidal spray, wet spray and mixed spray four. The big difference lies in the different process conditions, especially the difference in the amount of water added and the concentration time.

Dry spraying is to dry and stir the aggregate, cement and accelerator according to a certain proportion, and then load it into the ejector. The dry aggregate is fed into the spray gun by compressed air in a hose with suspension pressure, and mixed with high-pressure water in the nozzle to spray to the rock surface at a faster speed. Dry fuel injection has the advantages of simple structure, easy mechanical cleaning and fault handling. However, it has a lot of dust and a large resilience, and it must be controlled by the valve of the nozzle during water injection. The control of the water-cement ratio is very difficult and is related to the technical level of the operator.

Tidal spray:

First, add a little water to the aggregate to make it wet, and then mix with cement to reduce the dust during feeding, mixing and spraying. However, a large amount of water is still added and sprayed in the nozzle, and its spray process and mechanical dry spray process are used. At present, in the construction site, the tide water jet technology is used.

Wet Spray:

It is to mix the aggregate, cement and water according to the designed mixing ratio, then press it into the nozzle with a wet spraying machine, and then add the accelerator on the nozzle. The quality of wet shotcrete is easy to control, and the amount of dust and rebound generated during spraying is extremely small. It is a spraying technology that needs to be vigorously promoted, but the requirements for spraying machinery are very high, and the mechanical cleaning and fault handling are also relatively complicated. In soft rock mass or seepage hole with thick shotcrete layer, wet shotcrete method should not be adopted.

Mixing injection:

Also known as cement wrapped sand shell eruption process, is to mix a batch of sand particles with primary water, then add all the cement, forced mixing into a shell; Add secondary water and water reducing agent to form SCE cement; Forcibly mix another sand, stone and accelerator evenly. Then the mortar pump and dry injector will be pressed into the mixing pipe for stirring. The core of the organic combination of sub-feeding mixing and injection technology is the technology of cement-wrapped sand (or sand, stone) shell making. The main mechanical equipment used in the mixing spray technology is basically the same as the dry spraying process, but its quality is better than that of dry shotcrete, and it also greatly reduces the dust and rebound rate. However, due to the large number of machines required and the complexity of the process, problems such as mechanical cleaning and troubleshooting have been caused. Therefore, in the construction of large-scale and large-cross-section tunnels, the mixed spray technology is usually only used for construction.

Due to the differences in the spraying process, the strength of the sprayed concrete is also different. The strength of dry and tidal shotcrete is very low, usually only C20, while mixed spraying and wet spraying can reach C30 ~ C35.‍

The development trend of wet spray trolley: At present, China's water spray machinery mainly adopts two forms of dry and wet, and mainly manual, wet spray irrigation instead of dry needs to be further improved. However, in recent years, due to the progress of science and technology, the popularity of wet spray technology, making the rapid popularization and development of wet spray manipulator in our country, its application is also increasingly valued.