Shotcreting is the process of applying concrete by the use of a nozzle in which compressed air is introduced to the material flow. Shotcreting is usually classified as a wet mix or dry mix and the type of aggregate used, coarse or fine.
Wet mix shotcrete - Shotcrete in which all of the ingredients including water, are mixed before introduction in to the delivery hose (ACI-506R4).
Dry mix shotcrete - The cement-aggregate mixture is fed into a special mechanical feeder or gun called delivery equipment, which is metered by a device such as a feed wheel, rotor or feed bowl. The material is carried by compressed air through the delivery hose to nozzle body. The nozzle body is fitted inside with a water ring, through which water is introduced under pressure and mixed with the other ingredients. (ACI-506R-4) 1.6.1).
Comparison of Dry & Wet Mix:
- Control over mixing water
- Suited for light weight mixes
- Material transported longer distance
- Minimal material waste
- High strengths
- Water accurately measured
- Mixing more consistent
- Less dust and cement loss
- Normally less rebound
- Greater production
Shotcrete - Metamora Waste Water Treatment Plant, Metamora, IN: