Shotcrete is pneumatically sprayed concrete used for soil stabilization, tunnel support, and architectural finishes. The process involves mixing concrete and pneumatically projecting it through a nozzle onto a surface at high velocity. The impact compacts the concrete and forces it into irregular surfaces and soil voids. There are two application methods: dry-mix (dry materials mixed with water at the nozzle) and wet-mix (concrete pre-mixed and then pressurized for spraying). Dry-mix is more common for soil stabilization; wet-mix is used for thicker applications. Surface preparation is important; loose soil and vegetation must be removed. For slopes, any weak areas must be excavated and backfilled. The compressed air supply is critical; adequate volume and pressure are required. Typical air pressure is 80-90 psi. Concrete mix design includes fiber reinforcement (polypropylene or steel fibers) in addition to Portland cement, sand, and water. The fibers provide tensile strength and crack control. Rebound (material bouncing off the surface) is typical and should be minimized through proper nozzle technique. Experienced nozzlemen produce less rebound. The crew includes a concrete pump operator and nozzleman, with spotters directing the spraying. Thickness control is important; multiple passes build thickness. In tunnel applications, shotcrete is sprayed in layers; first layer (initial support) may be 2-3 inches, followed by additional layers. Curing requirements are similar to conventional concrete. Strength development may be accelerated with admixtures. Shotcrete compacts better than placed concrete and often achieves higher strength due to the impact consolidation.