What is Sprayed Concrete? Sprayed concrete (also known as shotcrete) is a construction technique where concrete is pneumatically projected at high velocity onto a surface using compressed air. Unlike traditional poured concrete, it is sprayed directly through a nozzle, allowing it to adhere tightly to complex or vertical surfaces without formwork. Developed in the early 20th century, this technique has become indispensable across various civil engineering and construction disciplines.
At its core, sprayed concrete consists of cement, aggregates (typically sand), water, and sometimes chemical admixtures or fibers to enhance properties such as setting time, adhesion, or tensile strength. The material is conveyed through a hose using compressed air, exiting the nozzle at high speed. Upon impact, the mix compacts densely against the target substrate, achieving excellent bond strength without the need for formwork in many cases. Two primary methods exist:
① Dry-mix process: The dry ingredients are pre-mixed, and water is added at the nozzle. suitable for remote sites but generates more dust.
② Wet-mix process: All ingredients, including water, are mixed before being pumped to the nozzle. offers lower rebound (waste) and less dust.
Each method has pros and cons regarding control of water content, rebound (waste material that bounces off the surface), and pumpability, but both deliver high-performance results when properly executed.
Primary Applications of Sprayed Concrete
Sprayed concrete is widely used in scenarios requiring rapid application, structural reinforcement, or adaptability to irregular shapes:
① Tunnel and Mine Support: Provides immediate stabilization of rock surfaces in underground excavations, preventing collapses.
② Slope Stabilization: Secures soil or rock on embankments and cuttings to prevent erosion or landslides.
③ Structural Repairs: Restores deteriorated bridges, buildings, or dams by adding a durable, bonded layer.
④ Swimming Pools & Water Structures: Forms seamless, waterproof linings for reservoirs, canals, and pools.
Sprayed concrete is a versatile, efficient solution for challenging construction and repair tasks. Its unique application method and performance in structural reinforcement make it indispensable in modern engineering, particularly where speed, adaptability, and durability are critical.