Shotcrete is a type of concrete that is placed with a hose. Compressed air is used to spray the concrete onto a surface.
Two spraying techniques have been developed:
Dry spraying: the mixture of cement, aggregate and, possibly, additives, is manufactured dry in a mixer. It is driven by compressed air along pipes to the hose where it is mixed with an adjustable quantity of water.
Wet spraying: The mixture of aggregate, cement and water is mixed in a mixing plant. It is then pumped along pipes to the spraying hose. Compressed air, sometimes mixed with liquid additives, is used for spraying.
The type of cement is selected according to the aggressiveness of the structure’s environment.
Metal fibres can be added to the concrete, in a proportion of about 35 to 50 kg/m³. These improve the cohesion of the concrete and its bonding with the substrate.
Shotcrete can be used to produce thin layers of concrete (a few centimetres thick) which perfectly follow the shape of the substrate.
It is used particularly for undergound works (supporting walls, tunnels, shafts or the faces of tunnels during digging) or for constructing or repairing drainage structures.