Shotcreting refers to a process in which compressed air forces mortar or concrete through a hose and nozzle onto a surface at a high velocity and forms structural or non-structural components of buildings. It is also known as spray concrete as the force of jet impacting on the surface compacts it so as to make itself supporting.
Shotcrete can be applied by two distinct application techniques, the dry-mix process and the wet-mix process.
Wet mix Process
In a wet-mix application cement, aggregate, ad-mixture and water are mixed together before being pumped through a hose and pneumatically projected. Typically, a concrete truck supplies the wet-mix and it is pumped through a shotcrete rig for placement. Generally, wet-mix is used for large volume placements with easy access for construction vehicles.
Dry mix Process
In dry-mix applications cement, aggregate, and ad-mixture are mixed together, conveyed pneumatically through a hose and then, at the nozzle via a water ring, water is injected evenly throughout the mix as it is being projected. Generally, dry-mix is used for small to medium volume placements or for conditions with limited vehicular access.
Applications of shotcrete
- For thin section such as RC walls, shells, folded plates, wall of water tank etc.
- Tunnel lining.
- Repair of RC members ( patch repair of concrete wall damaged by corrosion & water tank damaged by corrosion)
- Stabilizing rock sections.
- Encasing of steel sections.
- Fire proofing of steel.
- Concrete overlays and wearing coats up to 100 mm thickness.
- Shotcrete is more typically referred to as Gunite and is commonly used for application of inground swimming pool installation. Gunite swimming pools are typically more durable and longer lasting than other conventional materials. Additionally, the use of Gunite allows for customization in shape, depth and style not available in traditional pool kits. Gunite pools can also have many different types of finishes from tile or quartz to glass beading.
Types of shortcrete
- Accelerated Shotcrete
- Polymer-Modified Shotcrete
- Silica-Fume Shotcrete
- Fiber-Reinforced Shotcrete
Shotcrete is advantageous in situations when formwork is cost prohibitive or impractical and where forms can be reduced or eliminated, access to the work area is difficult, thin layers or variable thicknesses are required, or normal casting techniques cannot be employed. Main disadvantage of shortcrete is we need skilled labor & equipment’s its ultimately increases the cost. Cement content in shortcrete is more compared to traditional concrete.