Shotcrete is a construction technique that involves spraying concrete or mortar through a hose and pneumatically projecting it at high velocity onto a surface. Shotcrete can be applied using either a wet-mix or dry-mix process. In the wet-mix process, all ingredients, including water, are mixed before introduction into the delivery hose, while in the dry-mix process, water is added to the mix at the nozzle. Shotcrete is usually used to refer to the wet-mix process, while gunite is used to refer to the dry-mix process in pool construction. However, in other contexts, the terms are interchangeable.

Shotcrete has the characteristics of high compressive strength, good durability, water tightness, and frost resistance. It can be sprayed onto any type or shape of surface, including vertical or overhead areas, and can be used to reinforce both temporary and permanent excavations. Shotcrete is commonly used in tunnel walls, mines, subways, and automobile tunnels. It is also used to stabilize excavations for underground parking structures or high-rise buildings during construction.

Shotcrete has several advantages over traditional cast-in-place concrete, including:

• Rapid or instant capabilities: Shotcrete can be applied quickly and can rapidly set, making it ideal for complex forms or shapes.
• Excellent bond: The nature of the placement process results in an excellent bond with most substrates.
• Less formwork: The shotcrete process requires less formwork and can be more economical than conventionally placed concrete.
• Suitable for curved and thin elements: Shotcrete is suitable for curved and thin elements.

However, there are also some drawbacks to using shotcrete, such as higher production costs for the shotcrete materials and concerns about dust and concrete wastage compared to more precise methods.

In summary, shotcrete is a construction technique that involves spraying concrete or mortar onto a surface at high velocity using a hose and can be applied using either a wet-mix or dry-mix process. It has several advantages over traditional cast-in-place concrete, including rapid or instant capabilities, excellent bond, less formwork, and suitability for curved and thin elements.