Shotcrete
Concrete pneumatically projected at high velocity onto a surface, where the impact itself consolidates the material. Used for pools, retaining walls, tunnels, and repairs.
What does shotcrete mean?
Shotcrete comes in wet-mix form, where ready-mixed concrete is pumped to the nozzle, and dry-mix form, where dry ingredients meet water at the nozzle. It can be placed on vertical and overhead surfaces without forms on both faces, which is its main economic advantage. Quality depends heavily on nozzle operator skill, since shadowing behind reinforcement and rebound accumulation cause hidden voids.
In practice
Most in-ground gunite and shotcrete pools in the US are built this way, sprayed against an excavated shell and a rebar cage.