At present, shotcrete machine is divided into two kinds: wet shotcrete machine and dry shotcrete machine. Both of them are commonly used for pouring such thin-walled structures as tunnel lining, walls and ceilings, as well as the covering layer of steel structure.
Dry shotcrete machine mixes cement, sand and gravel in a dry and evenly state, a method to compress the air to deliver materials to the nozzle where they are mixed with pressure water for pouring; it must be operated by skilled personnel, and the particle size shall not be too large, however, as large amounts of cement are required and the jet velocity is large, which lead to severe dust pollution and rebound, its usage is thereby restricted.
Wet shotcrete machine delivers well mixed concrete to the nozzle through conveying and pumping, and compressed air is added at the outlet of delivery pump, which makes materials and air fully integrate with one another in the pipe, so that perfused materials become more even. In addition, accelerator is sprinkled on the nozzle for making materials solidify rapidly and reducing the rebound rate. Besides, its working efficiency is higher than dry shotcrete machine as the mixture of materials can be easily controlled.
Wet shotcrete machine is widely used for concrete spraying operation in places such as mine, tunnel, culvert, railway, hydro-power project, underground engineering and revetment.