Types of Shotcrete: Comparison Between Wet and Dry Systems
Types of Shotcrete: Comparison Between Wet and Dry Systems
Shotcrete technology is divided into two main categories based on the application method and how the material is fed into the machine. While both systems have their unique advantages, the project's speed, cost, and application area directly determine which system is selected.
In the dry system, the mixture of cement and aggregate (sand/gravel) is fed into the machine dry or slightly damp. The material is conveyed into the hose with the help of a rotor plate inside the rotor machine and air pressure. The water required for the mixture is added at the nozzle (spray gun) located at the very end of the hose.
Mechanism: The material is conveyed using high-pressure air.
Application Area: Generally ideal for smaller-scale jobs, repairs, and situations where the machine is distant from the application area.
In the wet system, the concrete is prepared in advance with all its components, including water, using a mixer and fed into the machine in a fluid state. The wet mix concrete pump conveys this ready-mix through the hose to the nozzle. At the nozzle, only accelerating admixtures are added to ensure the concrete adheres when it strikes the surface.
Mechanism: The concrete is conveyed by mechanical pumping power (usually a piston or peristaltic system).
Application Area: Large tunnel projects and professional construction sites requiring high-capacity production.
The differences between the two systems directly affect on-site efficiency:
Rebound: In the dry system, the rate of material rebounding off the surface is higher. In the wet system, waste is lower because the concrete is more cohesive.
Dust Formation: While the dry system generates intense dust during application, the wet system offers a much cleaner and operator-friendly working environment.
Hose Distance: Since conveyance is done with air in the dry system, concrete can be easily transported over much longer distances and heights.
Equipment Maintenance: Dry system machines (gunite) are much easier and faster to clean after the job. In the wet system, the cleaning process is more critical to prevent the concrete from hardening inside the hose.
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