Spray Mixes Concrete: Interesting Facts about Shotcrete

 

Renovation work on and with concrete is essential; after all, this is the vital material that holds everything together in almost all structures—cracks and other concrete damage the aesthetics and the statics of the structure. To keep the structure as safe as possible, it should be checked regularly and renovated immediately if necessary.

 

What is shotcrete?

 

Shotcrete is not a special concrete with a unique composition but rather a concrete process.

Mortar or concrete is pneumatically conveyed from the mixing plant through a closed hose line to the installation site and applied at high speed through a spray nozzle. Hence the name shotcrete. The resulting impact energy ensures that the spray mixes concrete compacts immediately.

 

When is shotcrete used?

 

Shotcrete is used for various tasks in structural engineering, including:

 

• Swimming pool or tunnel construction
• Concrete repair
• Waterproofing work
• Restoration of historical buildings
• Construction pit or slope stabilization  

 

The shotcrete method

 

Wet spray mixes concrete process 

          

All components such as concrete and aggregates are mixed with water in advance and conveyed to the spray nozzle using a mortar pump or compressed air. 

 

The compressed air provides additional compression. The shotcrete is then blown through the nozzle as usual. The wet shotcrete method makes sense when high delivery rates are required for shotcrete. A significant advantage of this process is that it guarantees consistent quality in the spray mixes concrete. Also, in contrast to other methods, the compression can be calculated precisely. However, the wet spray method is technically very complex and expensive. Therefore, it is only used when it is indispensable.

 

Dry spray mixes concrete process

 

Earth-moist ready-mixed or construction site concrete or dry concrete is used here. The concrete and its aggregates are fed dry to a mixing nozzle and conveyed to the spray nozzle in a thin stream with compressed air. Only then do the substances combine with the mixing water. With the dry spray process, it is important to pay attention to the so-called rebound. The rebound is part of the concrete mix that does not adhere to the application surface during spraying. This is a comparatively deficient proportion of the mixture.

 

The composition and amount of rebound depend on many influencing factors:

 

• Amount of water
• Air pressure
• Type of application area
• Nozzle type and distance to the application surface
• Posture and direction of spray
• Angle of incidence

 

In the case of shotcrete, the entire initial mass can therefore never be used. The cement content can only be determined, taking into account the rebound. The concrete mix must consequently be precisely adjusted in advance to be able to apply enough concrete despite the rebound.

 

The dry spray process has many advantages and is therefore often used. For example, large distances can be bridged when applying the spray mixes concrete. This enables it to be used in hard-to-reach places, for instance, when securing rocks.

 

The equipment and the maintenance costs are very low. The dry spraying process also means that the equipment needs to be cleaned significantly less.