Shotcrete has been widely used for tunneling works and slope protection, it is also used for architectural purposes. There are two types of shotcrete application, the wet and dry process. Shotcrete is a concrete transported by means of air under pressure with high velocity. Shotcrete is applied and compacted in the same time against a surface.

Dry-mix process

The dry shotcrete process consists of the following steps:

(1) A cementitious binder and aggregate are thoroughly mixed.
(2) The cement-aggregate mixture is fed into a special mechanical feeder or gun called the delivery equipment.
(3) The mixture is usually introduced into the delivery hose by a metering device such as a feedwheel, rotor, or feed bowl. Some equipment uses air pressure alone (orifice feed) to deliver the material into the hoses.
(4) The material is carried by compressed air through the delivery hose to a nozzle body. The nozzle body is fitted inside with a water ring, through which water is introduced under pressure and intimately mixed with the other ingredients.
(5) The material is jetted from the nozzle at high velocity onto the surface to be shotcreted.
In dry process, accelerator is supplied from the liquid dosing unit to the mixing tube assembly by means of water under pressure (2-3 bars more than the conveying pressure) or if powder accelerator is used the material is included in the dry mix together with cement and aggregates. The mixing tube assembly being located ~2,5 meters behind the nozzle or at the nozzle directly.

Wet-mix process

The wet shotcrete process consists of the following steps:

(1) All of the ingredients, including mixing water, but usually excluding accelerator, are thoroughly mixed.
(2) The mortar or concrete is introduced into the chamber of the delivery equipment.
(3) The mixture is metered into the delivery hose and moved by displacement or conveyed by compressed air to a nozzle.
(4) Accelerator is usually added at the nozzle.
(5) Additional air is injected at the nozzle to increase velocity and improve the gunning pattern.
(6) The mortar or concrete is jetted from the nozzle at high velocity onto the surface to be shotcreted.

In wet process, accelerator is supplied from the liquid dosing unit to the mixing tube assembly by means of air under pressure (2-3 bars more than the conveying pressure). The mixing tube assembly being located ~ 2,5 meters behind the nozzle or at the nozzle directly.

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