Explain about Shotcrete, its type and choice between dry mix or wet mix.

Shotcrete: Shotcrete is defined as the concrete or mortar conveyed through a hose and pneumatically projected at high velocity onto a surface to be freshly constructed or repaired. In simple words, it is a way of applying concrete that's like using a paint spray. Imagine if we were painting a wall with a paint spray gun, but instead of paint, we are using concrete mix.

The different type of shotcrete process is:

1. Dry mix process
2. Wet mix process

Dry mix process: The process consists of:

• Thoroughly mix the dry material such as cement, sand, and aggregates. This means there is no water added to the mixture.
• Feeding of this material into a mechanical feeder or shotcrete gun. It's a big hose that sprays the concrete mix onto a surface.
• Carrying the material by compressing air through a hose to nozzle.
• Introduce water at the nozzle and immediately mix it with other ingredients at the nozzle.
• Jetting the mixture from the nozzle at high velocity onto the surface to receive the shotcrete.

Advantage: Dry mix Shotcrete has advantages over conventional concrete in that it allows for better control of the water-cement ratio as well as lower rebound (the amount of material sprayed that doesn't stick to the surface and falls back). Due to the dry mix's tendency to attach to surfaces more effectively, it is also appropriate for overhead or vertical applications.

Wet mix process: The process consists of:

• Thoroughly mixing the whole ingredient except the accelerating admixture, if used.
• Feeding or placing the mixture into the delivering equipment or machine such as a shotcrete gun spray nozzle.
• Delivering the mixture by compressed air through a hose to nozzle.
• Jetting the mixture from the nozzle at high velocity on the surface to receive the shotcrete.

Advantage: Wet mix shotcrete has benefits in terms of mixing simplicity, simplicity, and application speed. It's especially helpful for large-scale areas or projects where efficiency is important.

To modify the structural properties of mortar/concrete being placed. polypropylene, the fibre of steel, or other materials as may be specified could also be used together with the admixture.

Deciding Between Dry Mix and Wet Mix Shotcrete:

The choice between dry mix and wet mix shotcrete depends on several variables, such as the requirements of the particular project, the surface's conditions, the desired finish, and the availability of equipment. Both approaches have advantages and uses. while regulating the water-cement ratio is important or while working on vertical surfaces, dry mix shotcrete is frequently recommended. Wet mix shotcrete is preferred for large-scale applications because of its efficiency and ease.