The Shotcrete 

In simply, this is a type of concrete mixture of cement, aggregates, and water. This mix or mortar spraying to surface at high velocity from nozzle of shotcrete machine. The shotcrete machine used compressor for spraying the concrete through hose pipes. It is also know as Gunite, Sprayed concrete or Gunned concrete.

The shotcrete firstly used in 1907 by Carl Akeley. The shotcrete has same time of placement and compaction and thickness of shotcrete depends upon site condition.

In shotcrete mixing, we can add additives likes Retardar, Accelerator, Plasticizer, Superplasticizer, Curing agents for improving  results.

Placing of Shotcrete

Before placing shotcrete shall be carefully cleaned of all loose material, The optimum distance between nozzle and surface 1.0 to 1.5 meter at right angles to the surface with may be 5.5 - 6.0 bar pressure.

Placing of shotcrete

Type of shotcrete 

Mainly two types 

1) Dry shotcrete 

2) Wet shotcrete 

1 ) Dry Shotcrete :In this method applying the concrete on the surface by pneumatically, the nozzle man control the additional water mixing at the nozzle.

2) Wet Shotcrete: In this method all aggregates and other admixture are mixed with water and convey through hose line with high velocity to surface.

Material for Shotcrete

• Cement
• Water
• Aggregates
• Fibers
• Accelerators
• Micro silica/silica fume 
• Hydration control agents
• Super plasticizers
• Curing Agent

Capacity of fiber reinforced shotcrete 

Capacity of Shotcrete = 2*Shear strength of shotcrete * thickness of shotcrete/ size of opening * maximum shear stress

Shotcrete's benefits

1.  Good bonding ability
2.  High strength
3. Corrosion resistance
4.  Support pressures reduced
5. Good resistance to weathering, fire, or some chemical attack.
6. Economical than conventional concrete
7. Low permeability
8. Resistance to freezing and thawing
9. Easy to place on irregular surface

Quality control and testing

We can test shotcrete in three distinct situation :

• Before placing the shotcrete (Preconstruction) 

• At the time of placement (During construction)

 • After hardening and different - different time aged