Shotcrete Equipment and Application Methods
Shotcrete equipment includes batching and mixing plants, pumps (piston, squeeze-tube, or rotor-stator), delivery lines (hoses and pipes), nozzles, and air compressors. Candidates should understand how equipment selection interacts with mixture design: line diameter, length, and bends affect pressure and segregation; air volume and pressure at the nozzle control velocity and spray pattern; and nozzle type (dry-mix versus wet-mix) determines where water and accelerator are introduced. Wet-mix systems typically use a pump plus compressed air at the nozzle, while dry-mix systems use a rotor or gun feeding material into an air stream with water injected at the nozzle.
Traps: questions may ask about nozzle angle and distance. The nozzle should generally be held perpendicular to the surface (about 90 degrees) at a distance of roughly 0.9–1.5 m (3–5 ft), moved in steady circular or sweeping motions. Too great a distance causes segregation and rebound; too close causes excessive build-up and voids. Air pressure too low yields weak, droopy placement; too high increases rebound and dust. Also watch for questions on pre-wetting the surface, cleaning lines, and the need for a consistent, uninterrupted supply.
Worked example: if rebound increases sharply and the applied material looks dry and sandy, the likely causes are excessive nozzle distance, too much air, or insufficient water (dry-mix), not a mixture problem-check nozzle technique and air/water settings first.