Shotcrete in underground works such as tunnels can be applied with different methods and equipment: wet-mix spraying or dry-mix spraying, manual or mechanized equipment with robot arm.
The wet-mix already includes all ingredients before pumping, including water, whereas it is added to the dry-mix in the nozzle just before spraying.
Wet-mix concrete spray system with robot arm offers substantial advantages, although manual dry-mix shotcreting is often used in environments with extreme temperatures, in small tunnels and galleries or for logistic reasons.
1. Higher quality and homogeneous support
The water / cement relation is controlled automatically when using mechanized wet-mix spraying, whereas it depends on the operator when manual dry-mix spraying is applied. The water / cement relation is directly related to the strength of the shotcrete support.
2. Healthier and safer working conditions
Dry-mix spraying generates a lot of dust, which compromises operators´ health in the long run. Besides, manual spraying is an exhausting job, so the operator cannot fully concentrate on spraying finish quality. In general, spray with robot arm is more healthier and safer.
3. Energy savings
One robot arm concrete spraying equipment achieves the same performance as three machines for manual dry-mix spraying, working all with the same power and air requirements. It saves energy and money.
4. Less manpower required
A mechanized shotcrete equipment can be operated by two workers, while manual spraying requires more manpower.
5. Less rebound
The amount of water in the shotcrete mix, among other factors, influences rebound quantity. The wet-mix method can reduce rebound in comparison to the dry-mix method.
6. Higher spraying output
Robot arm concrete spraying equipment offers higher spraying outputs than manual spraying, the max. concrete flow can be 30 m3/h.
7. Time savings
Higher spraying outputs and faster preparation of the shotcrete mix allow total time savings of up to 30% with robot arm wet-mix spraying.
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